Cardiac Output is determined by

19c

Venous return, neural controls, hormonal controls

During rest, heart rate is maintained by ____________ via _____________

19c

Cardioinhibitory Center via parasympathetic vagus nerves

Stroke volume is controlled by
*During rest

19c

Venous return (EDV)

During Stress, cardioacceleratory center increases __________ and ________ via __________________

19c

increases HEART RATE and STROKE VOLUME via SYMPATHETIC STIMULATION

(During stress) Heart rate _______ via action on _________

19c

INCREASES via action on SA NODE

(During stress) Stroke Volume _______ via enhancement of __________

19c

INCREASES via enhancement of contractility

*ESV decrease (less blood in left ventricle)

What factor does exercise play in enhancing cardiac output

19c

-Increased activity of respiratory pumps (ventral body cavity pressure)
-Increased activity of muscular pump (skeletal muscle)
-Increased sympathetic venoconstriction
Then...
-Increased venous return
Then...
-Increased EDV
Then..
Increased stroke volume
Results in...
-Increased Cardiac output

What factor does the following play a role in enhancing cardiac output

Decreased BP activates cardiac centers in medulla

19c

A)
-Increased sympathetic activity
Then...
-Increased epinephrine in blood
Then..
-Increased contractility of cardiac muscle
Then...
-Decreased ESV
Then..
-Increased Stroke volume
Results in...
-Increased Cardiac output

B)
-Decreased parasympathetic activity
Then...
-Increased heart rate
Results in...
-Increased Cardiac output

What are the 2 processing in Blood pressure regulation

19c

1) Short-term Regulation
2) Long-term Regulation

Short-term Regulation has 2 controls...

19c

1) Neural (nervous) control
2) Hormonal (endocrine) controls

Short-term regulation counteracts fluctuations in blood pressure by:

19c

-Changing peripheral resistance
-Changing cardiac output

Name the control that is involved in long-term regulation

19c

-Renal control

Long-term regulation counteracts fluctuations in blood pressure by

19c

-Changing blood volume

Neural controls alter _________ and ___________ .

19c

Cardiac Output and Peripheral Resistance

In what two ways do neural controls alter cardiac output and peripheral resistance

19c

1) Alter blood vessel diameter
-If blood volume is low, all vessels constrict
-Except those to heart and brain
2) Alter blood distribution to organs
-In response to specific demands
-Blood is shunted from digestive tract to skeletal muscles during exercise

Neural Controls operate via ______
(short term)

19c

Reflex arcs that involve...
-Baroreceptors (stretch receptors)
-Cardiovascular center of medulla oblongata (vasomotor center)
-Autonomic vasomotor fibers to heart and vascular smooth muscle
-Sometime input from chemoreceptors and higher brain centers

There are clusters of ___________ in the medulla oblongata
(short term)

19c

Sympathetic neuron
*Causes changes in CO and blood vessel diameter

The clusters of sympathetic neurons in medulla oblongata consists of...
(short term)

19c

-Cardiac Centers
.Cardioacceleratory (sympathetic)
--> SA node, AV node, myocardium
--> Increases heart rate and force of contraction
.Cardioinhibitory (parasympathetic)
--> Vagus nerve --> SA node, AV node
--> Decreases heart rate
-Vasomotor Center
--> Regulates diameter of blood vessels

Cardiovascular center receives inputs from

19c

Baroreceptors
Chemoreceptors
Higher brain centers

Baroreceptors

19c

(pressure-sensistive mechanoreceptors)
-Respond to changes in arterial pressure and stretch

Chemoreceptors respond to changes in

19c

Blood levels of carbon dioxide, H+, and oxygen

Higher brain centers include the following and respond to ...

19c

Include - Cerebral cortex, limbic system, hypothalamus
respond to exercise, stress, emotions, body temperature

Locations of baroreceptors:

19c

- Carotid Sinuses (dilations in internal carotid arteries --> Major blood supply to brain)
- Aortic Arch
- Walls of large arteries of neck and torax

In what 3 ways do baroreceptor reflexes decrease BP

19c

1) Cause arterioles to dilate
.By inhibiting vasomotor center
.This decreases peripheral resistance
2) Cause veins to dilate
.By inhibiting vasomotor center
.This decreases venous return and cardiac output
3) decrease heart rate and contractile force
.By inhibiting sympathetic (cardioacceleratory) activity and stimulating parasympathetic (cardioinhibitory) activity
.This decreases cardiac output

Chemoreceptors in carotid and aortic bodies detect:
(short term)

19c

Increase in CO2
Decrease in pH
Decrease in O2 (sudden drop)

Chemoreceptor reflexes (short term) increase blood pressure by stimulating

19c

-Cardioacceleratory center
-->Causes increased cardiac output

-Vasomotor center
-->Causes vasoconstriction (sympathetic

Reflexes regulating BP involve
(influence of higher brain centers)

19c

Medulla oblongata

What can modify arterial pressure?
(influence of higher brain centers)

19c

Hypothalamus
Cerebral cortex
Limbic system
-->Via relays to medulla oblongata

Does the hypothalamus increase OR decrease BP during stress?
(influence of higher brain centers)

19c

Increase

Hypothalamus mediates redistribution of _____________ during _________ and what changes?
(influence of higher brain centers)

19c

Mediates redistribution of blood flow during exercise and body temperature changes

What are hormones that cause increased blood pressure?
(hormonal controls of BP - short term)

19c

-Epinephrine/norepinephrine
-Angiotensin II
-Antidiuretic Hormone

How does epinephrine/norepinephrine cause an increase in BP?

19c

Increase CO & vasoconstriction
Released from adrenal medulla during stress

How does angiotensin II cause an increase in BP?

19c

Vasoconstriction
Low BP
Kidneys release renin

How does antidiuretic hormone (ADH) cause an increase in BP?

19c

Kidneys conserve more water causing vasoconstriction when BP falls to dangerously low levels (hemorrhage)
*Released from hypothalamus/posterior pituitary

Hormones causing decreased blood pressure
(hormonal controls of BP - short term)

19c

Atrial Natriuretic Peptide (ANP)

How does Atrial Natriuretic Peptide (ANP) decrease blood pressure
(hormonal controls of BP - short term)

19c

It is released from the heart
Antagonizes aldosterone --> causes kidneys to excrete more sodium and water --> decreases blood volume and BP
*Also causes generalized vasodilation

Kidneys maintain blood pressure by
(Renal Regulation of BP - Long Term)

19c

Regulating blood volume

What are the two methods of renal control?
(Renal Regulation of BP - Long Term)

19c

1. Direct renal mechanism

2. Indirect renal mechanism
---> (Renin-angiotensin-aldosterone mechanism)

Direct Renal mechanism alters blood volume without...

19c

Hormones

Increased BP or blood volume causes...
(Direct Renal Mechanism - Long Term)

19c

Elimination of more urine due to increased filtration --> Decreases blood volume and BP

Decreased BP or blood volume causes...
(Direct Renal Mechanism - Long Term)

19c

Kidneys to conserve water --> increases blood volume and BP

Indirect Renal Mechanism is also known as ...
(Renal Regulation of BP - Long Term)

19c

Renin-angiotensin-aldosterone mechanism

Decreased arterial blood pressure ...
(Indirect Renal Mechanism - Long Term)

19c

--> Release of renin (enzyme) from kidneys

--> Renin causes production of angiotensin II
.Angiotensinogen (plasma protein)
-Renin
.Angiotensin I
-Angiotensin converting Enzyme (ACE)
.Angiotensin II

Angiotensin II increases blood volume (and thus increases BP) by stimulating...
(Indirect Renal Mechanism - Long Term)

19c

-Adrenal cortex to secrete aldosterone
.Increases reabsorption of sodium/water by kidneys

-Stimulates posterior pituitary to release ADH
.Increases water reabsorption by kidneys

-Stimulates hypothalamic thirst center
.Increases water consumption

Angiotensin II increases blood pressure directly and causes
(Indirect Renal Mechanism - Long Term)

19c

vasoconstriction
--> Increases peripheral resistance

Autoregulation is controlled intrinsically by

19c

Modifying diameter of arterioles feeding capillaries

Organs regulate their own blood flow by

19c

varying resistance of own arterioles

What are the 2 types of auto regulation

19c

1) Metabolic (chemical) controls
-Responds to changing levels of chemicals
2) Myogenic (physical) controls
-Respond to stretch

All info on metabolic (chemical) controls

19c

– Respond to changing levels of chemicals
– Vasodilation of arterioles and relaxation of precapillary sphincters caused by:
• Decreased tissue O2
• Increased H+, CO2, lactic acid, K+, adenosine, prostaglandins
• Inflammatory chemicals (histamine, kinins, prostaglandins)
• Nitric oxide (NO) – major controller of vasodilation
– Released by vascular endothelium (can override sympathetic)

– Vasoconstriction is caused by:
• Endothelins released from endothelium (to prevent blood loss in injury)

All info on myogenic (physical) controls

19c

Keep tissue perfusion constant despite changes in systemic pressure
• Increased intravascular pressure promotes vasoconstriction
– Decreases blood flow to the tissue
• Decreased intravascular pressure promotes vasodilation
– Increases blood flow to the tissue

Long-term auto regulation occurs with

19c

Occurs when short-term autoregulation cannot meet tissue nutrient requirements

Long-term auto regulation develops over

19c

Develops over weeks or months

Angiogenesis
(Long-term auto regulation)

19c

– Number of vessels to region increases
– Existing vessels enlarge
– Common in
• Heart when coronary vessel partially occluded
• Throughout body in people in high-altitude areas

Blood flow to skeletal muscles increases in response to

19c

greater metabolic activity -->

– Increased metabolic activity causes decreased O2 and increased metabolic wastes
– Metabolic controls cause relaxation and dilation
of skeletal muscle arterioles to supply more O2 and nutrients to muscles

Blood flow to digestive and urinary tracts decreases to

19c

divert blood to skeletal muscles
– Sympathetic activity increases with exercise
--> vasoconstriction of digestive/urinary tracts

Circulatory shock is any condition is which

19c

– Blood vessels are inadequately filled
– Blood cannot circulate normally
• Results in inadequate blood flow to meet tissue needs --> cells die

-Hypovolemic shock
-Vascular shock
-Cardiogenic shock

Hypovolemic shock results from

19c

large-scale blood or fluid loss
– Hemorrhage, burns, severe vomiting or diarrhea

Vascular shock results from

19c

extreme vasodilation and decreased peripheral resistance
– Anaphylaxis, septicemia

Cardiogenic shock results when

19c

an inefficient heart cannot sustain adequate circulation
– Myocardial damage

The lymphatic system returns

20

Returns excess interstitial fluid and leaked plasma proteins
back to circulatory system (~3 L per day)

What are the 3 parts of the lymphatic system?

20

• Lymphatic vessels (lymphatics)
• Lymph – fluid in vessels
• Lymph nodes – cleanse lymph as passes

What are the lymphoid organs and tissues?

20

Spleen, thymus, tonsils, Peyer's patches, appendix, and lymphoid tissues

House phagocytic cells and lymphocytes

What do the lymphoid organs and tissues provide

20

Structural basis of immune system

Lymph vessels (lymphatics) include:

20

Lymphatic capillaries
Collecting lymphatic vessels
Lymphatic trunks
Lymphatic ducts

The lymphatic system is a one-way system - meaning...

20

Lymph flows toward the heart

Info on Lymphatic capillaries

20

• Weave between tissue cells and capillaries
• Absent from bones, teeth, bone marrow, and CNS
• Similar to blood capillaries, except:
– Blind-ended
– Very permeable
• Proteins, cell debris, pathogens, cancer cells enter lymphatics

What makes lymphatic vessels so permeable?

20

– Endothelial cells overlap loosely
• Form one-way, flaplike minivalves
– Collagen filaments anchor endothelial cells to surrounding structures
• Prevent collapse of capillaries
• Open minivalves when interstitial fluid volume/pressure increases

Pathogens can travel throughout the body via

20

Lymphatics
--> Lymph nodes serve to "cleanse" and "examine"

What are lacteals?

20

– Specialized lymph capillaries present in
small intestinal villi
– Absorb digested fat and deliver fatty lymph (chyle) to the blood

Lymphatic collecting vessels are similar to veins, except...

– Have thinner walls
– Have more internal valves
– Anastomose more frequently

Collecting vessels in skin travel with

superficial veins

Deep vessels travel with

arteries

Distribution of lymphatic vessels varies between

individuals

Lymphatic trunks are formed by...

Uniion of largest collecting vessels

Lymphatic trunks drain

large areas of the body

Name the "paired lymphatic" trunks

– Lumbar
– Bronchomediastinal
– Subclavian
– Jugular trunks

Name the "single" lymphatic trunk

Intestinal trunk

How many lymphatic ducts are there?

2
Right Lymphatic duct
Thoracic duct
*Lymph is delivered into either of the ducts

The right lymphatic duct drains

Right arm and right side of head and thorax

Thoracic duct drains

rest of body
-Superiorly, it drains left thorax, left arm, and left side of head

The thoracic duct arises as

Cisterna chyli
– Enlarged sac anterior to first two lumbar vertebra
– Collects lymph from legs and digestive organs

Each duct empties lymph into

Venous circulation
– At junction of internal jugular and subclavian veins
– On its own side of body

Lymph is propelled by

– Milking action of skeletal muscle
– Pressure changes in thorax during breathing
– Valves that prevent backflow
– Pulsations of nearby arteries
– Contractions of smooth muscle in walls of lymphatic vessels

Lymphoid cells are aka

lymphocytes

Lymphocytes are...

The main warriors of the immune system
-Arise in red bone marrow

Lymphocytes mature into one of two main varieties

– T cells (T lymphocytes)
– B cells (B lymphocytes)

Lymphoid cells protect against

antigens
– Anything the body perceives as foreign and that provokes an immune response
• Bacteria, bacterial toxins, viruses, cancer cells,
mismatched RBCs

T cells...

– Manage immune response
– Attack and destroy infected cells

B Cells

– Produce plasma cells
• Which secrete antibodies

Macrophages

– Phagocytize foreign substances
– Help activate T cells

Dendritic cells

– Capture antigens
– Deliver them to lymph nodes

Reticular cells (fibroblast-like cells)

– Produce reticular fiber stroma
• Network supporting other cells in lymphoid organs

Lymphoid tissue houses and provides

proliferation site for lymphocytes

lymphoid tissue is a surveillance vantage point for

lymphocutes/macrophages

Lymphoid tissue is composed mainly of what type of tissue?

Reticular connective
– Macrophages live on fibers
– Lymphocytes squeeze through postcapillary venules, rest in lymphoid spaces, then return to blood
• Movement allows lymphocytes to reach infected or damaged tissues

What are the 2 main types of lymphoid tissue

1. Diffuse lymphoid tissue
2. Lymphoid follicles

Info on diffuse lymphoid tissue

– Scattered lymphoid cells and reticular fibers
• In ~ every body organ
– Larger collections in lamina propria of mucous membranes (digestive tract)

Info on lymphoid follicles (nodules)

– Solid, spherical bodies
• Of tightly packed lymphoid cells and reticular fibers
– Germinal centers of proliferating B cells
• Plasma cells --> antibodies
– May form part of larger lymphoid organs or nodes
– Isolated aggregations in intestinal wall (Peyer's patches) and in appendix

What are the principal lymphoid organs of the body

Lymph nodes

Lymph nodes are embedded in

connective tissue

Lymph nodes are clustered along

lymphatic vessels

3 regions of lymph nodes

Inguinal region
Axillary region
Cervical region

Functions of lymph nodes

Filtration
– Filter lymph as it is transported
– Macrophages destroy microorganisms and debris so they don’t enter bloodstream

Immune system activation
– Lymphocytes become activated and mount
attack against antigens

Structure of lymph node

• Bean shaped
• External fibrous capsule
• Trabeculae (connective tissue strands)
extend inward
– Divide node into compartments
• Two histologically distinct regions
– Cortex
– Medulla

The cortex contains

- Lymphoid follicles with germinal centers (with dividing B cells)
- Dendritic cells surround follicles
– Rest of cortex is primarily T cells in transit
• T cells circulate continuously among blood, lymph nodes, and lymph

Medullary cords extend inward from the

Cortex

The medulla contains what kind of cells

B Cells
T Cells
Plasma Cells

Lymph sinuses in the medulla contain

macrophages

Lymph enter via

afferent lymphatic vessels

Lymph travels through

large subcapsular sinus and smaller sinuses to medullary sinuses

Lymph extis at hilum via

efferent lymphatic vessels

What does having fewer efferent vessels do

Stagnates flow which allows lymphocytes and macrophages time to function

Which lymphoid organ is not composed of reticular connective tissue?

Thymus

The spleen, thymus, tonsils, peyer's patches and appendix help with what?

They help protect the body but do not filter lymph
-Have efferent lymphatics
-No afferent lymphatics

Info on spleen

• Largest lymphoid organ
• Structure
– Fibrous capsule and trabeculae
– White pulp - contains lymphocytes
– Red pulp – contains macrophages, many old erythrocytes
• Served by splenic artery and vein (enter/exit at its hilum)

Functions of spleen

– Site for lymphocyte proliferation
– Immune surveillance and response
– Cleanses blood of:
• Aged/defective blood cells and platelets
• Debris and foreign matter
– Removed by macrophages

Additional functions of the spleen

• Stores breakdown products of RBCs
– For later reuse
– Iron to make more hemoglobin
• Stores blood platelets and monocytes
– For release into blood when needed
• May be site of fetal erythrocyte production (normally ceases before birth)

The thymus is important during

early in life
– T lymphocyte presursors mature into immunocompetent lymphocytes

Thymus is found in

inferior of neck
– Extends into mediastinum
– Partially overlies heart

The thymus is prominent in

Newborns
– Increases in size during first year
– Most active during childhood
– Gradually atrophies after puberty
• Becomes fibrous and fatty tissue
– Still produces immunocompetent cells, though slowly

Other info on thymus

• Bilobed
• Thymic lobules - outer cortex, inner medulla
• Most thymic cells are lymphocytes
• Cortex contains rapidly dividing lymphocytes and scattered macrophages
• Medulla contains fewer lymphocytes and
thymic corpuscles
– Concentric whorls of keratinized epithelial cells
– Involved in development of regulatory T cells (prevent autoimmunity)

How does the thymus differ from other lymphoid organs

• Has no follicles because it lacks B cells
• Does not directly fight antigens
– Functions only in T lymphocyte maturation
• Blood thymus barrier
• Keeps bloodborne antigens out of thymus to prevent premature activation of lymphocytes

• Stroma made of epithelial cells
(not reticular fibers)

What does MALT stand for

Mucosa-Associated Lymphoid Tissue

Info on MALT

• Lymphoid tissues in mucous membranes
• Protects from pathogens trying to enter body
• Largest collections of MALT in
– Tonsils
– Peyer's patches – Appendix
• Also in mucosa of respiratory and genitourinary organs and rest of digestive tract

What is the simplest lymphoid organs

tonsils

Tonsils from a ring of what type of tissue around pharynx

lymphatic

Location of palatine tonsils

At posterior end of oral cavity

Location of lingual tonsils

At base of tongue

Location of pharyngeal tonsils

in posterior wall of nasopharynx
• “Adenoids”

Location of tubal tonsils

surround openings of auditory tubes into pharynx

What are the tonsils role with pathogens

They gather and remove pathogens in food or air

Other info on tonsils

• Follicles with germinal centers
• Not fully encapsulated
• Overlying epithelium invaginates forming tonsillar crypts
– Trap and destroy bacteria and particulate matter
– Immune cells build memory for pathogens
• Fighting pathogens in childhood leads to increased immunity later in life

Where are groups of lymphoid follicles

Peyers patches and appendix

Where are groups of lymphoid follicles in the peyer's patches

-In wall of distal small intestine (ileum)

Where are groups of lymphoid follicles in the appendix

– Tubular appendage at beginning of large
intestine

What do peyer's patches and the appendix do with the aggregates of lymphoid follicles

– Destroy bacteria, preventing them from breaching intestinal wall
– Generate "memory" lymphocytes

What is the function of the the Lymphatic System

To return excess interstitial fluid and leaked plasma proteins back to circulatory system and allow the tissue fluid to be filtered by the lymph nodes

What is contained in lymph

Fluid

List the major components of the lymphatic system and some accessory lymphoid organs.

Provide structural basis of immune system
House phagocytic cells and lymphocytes
Include spleen, thymus, tonsils, and other lymphoid tissues

How does flow in the lymphatic system differ from flow in the circulatory system?

One-way system – lymph flows to the heart

Why are lymphatic capillaries so permeable?

Endothelial cells overlap loosely → form one-way, flaplike minivalves
Collagen filaments anchor endothelial cells

What molecules can pass through lymphatic capillaries but not through blood capillaries?

Pathogens

Name four tissues where lymphatic capillaries are absent.

Bones, teeth, bone marrow and CNS

Define lacteals. What is their function?

Specialized lymph capillaries present in small intestinal villi
They absorb digested fat and deliver fatty lymph (chyle) to the blood

Lymphatic collecting vessels are similar to what blood vessel? Compare them.

Similar to veins, except:
-Have thinner walls
-Have more internal valves
-Anastomose more frequently
Collecting vessels in skin travel with superficial veins
Deep vessels travel with arteries
Distribution of lymphatic vessels varies between individuals

Name the lymphatic trunks that are paired

Lumbar
Bronchomedialstinal
Subclavian
Jugular Trunks

Name the single lymphatic trunks

Intestinal Trunk

Name the lymphatic ducts and state which body regions are drained by each duct.

Right lymphatic duct
Drains right arm and right side of head and thorax
Thoracic duct
Drains rest of body

Where do T lymphocytes and B lymphocytes mature?

Thymus

Describe the histologic composition of lymphoid tissue.
What are the functions of lymphoid tissue?

Houses and provides proliferation site for lymphocytes
Surveillance vantage point for lymphocytes/macrophages
Composed mainly of reticular connective tissue
Two main types:
Diffuse lymphoid tissue
Lymphoid follicles

Differentiate between diffuse lymphoid tissue and lymphoid follicles (nodules).
What type cell predominates in follicles?

- Diffuse lymphoid tissue:
Scattered lymphoid cells and reticular fibers
In apporoximately every body organ
Larger collections in lamina propria of mucous membranes

- Lymphoid Follicles (nodules)
Solid, spherical bodies of tightly packed lymphoid cells and reticular fibers
May form part of larger lymphoid organs or nodes

What are the principle lymphoid organs of the body? Where are they located?

Spleen, thymus, tonsils

Name three areas where clusters of lymph nodes can be palpated near the body surface.

Inguinal region
Axillary Region
Cervical Region

Describe the functions of lymph nodes.

Filtration
Immune system activation

Describe the gross and histological structure of lymph nodes.

Bean shaped
External fibrous capsule
Two histologically distinct regions:
Cortex
Medulla

What is the benefit of having fewer efferent than afferent lymphatic vessels in lymph nodes?

Allows lymphocytes and macrophages time to function

Which lymphoid organ is the only one that filters and cleanses lymph?

Lymph Nodes

What is the largest lymphoid organ? Describe its structure and cells.

Spleen
Structure:
Fibrous capsule and trabeculae
White pulp – contains lymphocytes
Red pulp – contains macrophages, may old erythrocytes
Served by by splenic artery and vein (enter/exit at its hilum)

List the functions of the spleen.

Removes old and damaged RBCs
Site for lymphocyte proliferation
Immune surveillance and response

What is the only function of the thymus?

Development of T cells

What is the main cell found in the thymus?

Lymphocytes

Compare the histological structure of the thymus to other lymphoid organs

Thymus has no follicles because it lacks B cells
Does not directly fight antigens
Stroma made of epithelial cells

Define MALT. What is its function? Where are the largest collections of MALT found in the human body?

Mucosa-Associated Lymphoid Tissues
Lymphoid tissues in mucous membranes
Protects from pathogens trying to enter body
Largest collections of MALT:
Tonsils
Peyer’s Patches
Appendix

Name the four tonsils.

Palatine Tonsils – At posterior end of oral cavity
Lingual Tonsils – At base of tongue
Pharyngeal Tonsils – in posterior wall of nasopharnyx (adenoids)
Tubal Tonsils – Surrond opening of auditory tissues into pharynx

What are tonsillar crypts and what are their functions?

- Trap and destroy bacteria and particulate matter
- Immune cells build memory for pathogens (fighting pathogens in childhood leads to increased immunity later in life)

How do the tonsils help to strengthen immunity later in life?

- Trap and destroy bacteria and particulate matter
- Immune cells build memory for pathogens (fighting pathogens in childhood leads to increased immunity later in life)

Where are Peyer’s Patches located?

In wall of distal small intestine (ileum)

Where is the appendix?

Tubular appendage at beginning of large intestine

List the functions of Peyer’s Patches and the appendix.

- Destroy bacteria, preventing them from breaching intestinal wall
- Genterate “memory” lymphocytes

What 2 organs does the digestive system consist of?

Alimentary Canal - Gastroentestinal (GI) tract
Accessory Digestive Organs

What are the accessory digestive organs?

Teeth
Tongue
Gallbladder
Digestive glands
-Salivary Glands
-Liver
-Pancreas

Describe the Alimentary Canal

– Muscular tube from mouth to anus
– Digests food and absorbs nutrients
– Mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus

What are the 6 essential activities of the digestive processes

1. Ingestion
2. Propulsion
3. Mechanical Breakdown
4. Digestion
5. Absorption
6. Defecation

Describe ingestion

taking food into digestive tract via the mouth

Describe propulsion

movement of food through GI tract

Describe mechanical breakdown

reduction of food to smaller pieces to increase surface area for digestion

Describe digestion

chemical breakdown of food by enzymes

Describe absorption

active or passive transport of nutrients, vitamins, minerals, and water from GI tract lumen into blood or lymph

Describe defecation

elimination of indigestible substances from the body via the anus in the form of feces

Peristalsis

Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally. Major means of propulsion.

Segmentation

Nonadjacentsegments of alimentary tract organs alternately contract and relax, moving food forward then backward. Food mixing and
slow food propulsion occurs

GI Tract Regulatory Mechanisms

Mechanoreceptors and Chemoreceptors
Intrinsic and extrinsic controls

Where are mechanoreceptors and chemoreceptors located

In the walls of GI tract

Mechanoreceptors and chemoreceptors respond to

Stretch
Changes in osmolarity and pH
Presence of substrate and end products of digestion

Mechanoreceptors and chemoreceptors initiate reflexes that

• Activate or inhibit digestive glands
• Stimulate smooth muscle to mix and move contents

Describe intrinsic and extrinsic controls

– Nerve plexuses (“gut brain”) respond to stimuli in GI tract to regulate GI tract activity via short reflexes

– CNS centers and autonomic nerves respond to stimuli inside or outside GI tract via long reflexes

– Stomach and small intestine release hormones
that stimulate target cells in same or different organs, causing them to secrete or contract

describe the peritoneum

– Serous membrane of abdominal cavity
– Visceral peritoneum covers external surfaces of most digestive organs
– Parietal peritoneum lines body wall

Describe Peritoneal cavity

– Narrow space between the two peritoneums
– Serous fluid lubricates organs

Describe the mesentery

- double layer of peritoneum
– Extends from body wall to digestive organs
– Routes for blood vessels, lymphatics, and nerves
– Holds organs in place
– Stores fat

Describe the Retroperitoneal organs

- partially surrounded
– Lie against posterior abdominal wall
– Pancreas, duodenum, part of large intestine

Describe the Intraperitoneal (peritoneal) organs

– Completely surrounded by peritoneum

Some organs...

lose their mesentery and move,
becoming retroperitoneal, during development.

What are the parts of the mesentery

Greater Omentum
Lesser Omentum
Falciform ligament
Mesentery Proper
Mesocolon

Describe the greater omentum

“fatty apron”
– Extends from greater curvature of stomach
– Covers most abdominal organs

Describe the lesser omentum

– Connects lesser curvature of stomach and proximal duodenum to liver

Describe the falcofrom ligament

- Attaches the lier to the anterior abdominal wall

Describe the mesentery proper

– Fan-shaped peritoneum that suspends jejunum and ileum from posterior abdominal wall

Describe the mesocolon

– Attaches large intestine to posterior abdominal wall

Blood supply - The splanchnic circulation

• Arteries
– Hepatic, splenic, left gastric arteries
• Branches of celiac trunk
• Supply corresponding organ
– Inferior mesenteric artery
• Supplies small intestine
– Superior mesenteric artery
• Supplies large intestine

• Hepatic portal circulation
– Drains nutrient-rich blood from digestive organs
– Delivers it to the liver for processing

Four basic layers (tunics) of the alimentary canal

– Mucosa
– Submucosa
– Muscularis externa
– Serosa

Describe the mucosa

• Innermost layer that lines the lumen
• Functions
– Secretes mucus, digestive enzymes, hormones
– Absorbs end products of digestion
– Protects against infectious disease

What are the 3 sub layers of the mucosa

-Epithelium
-Lamina Propria
-Muscularis mucosae

Describe the Epithelial layer of the mucosa

– Simple columnar epithelium with mucus-secreting cells
– Exception – stratified squamous in mouth, esophagus, anus
– Mucus protects from enzymes and eases food passage
– May synthesize and secrete enzymes and hormones
• Stomach and small intestine

Describe the lamina propria layer of the mucosa

– Loose areolar connective tissue
– Capillaries for nourishment and absorption of nutrients
– Lymphoid follicles (part of MALT) defend against pathogens

Describe the muscularis mucosae of the mucosa

– Thin layer of smooth muscle

Describe the submucosa

• Areolar connective tissue
• Rich supply of:
– Blood vessels
– Lymphatic vessels
– Lymphoid follicles
– Nerve fibers
– Elastic fibers (in stomach for stretching)

Describe the muscularis extern (muscularis)

• Composed of two layers of smooth muscle
– Inner circular
• Thickens in some areas to form sphincters
– Outer longitudinal layer
• Responsible for segmentation and peristalsis

Describe the serosa

• Visceral peritoneum
• Areolar connective tissue
– Covered with mesothelium in most organs
• Simple squamous epithelium
• Replaced by adventitia in esophagus
– Fibrous connective tissue

The enteric nervous system of the alimentary canal

• Intrinsic nerve supply of alimentary canal regulates digestive system activity - enteric neurons
• Linked to CNS via afferent visceral fibers
• Long ANS fibers synapse with enteric plexuses
– Sympathetic impulses inhibit digestive activities
– Parasympathetic impulses stimulate digestive activities

Submucosal nerve plexus

– In submucosa
– Regulates glands and smooth muscle in mucosa

Myenteric nerve plexus

– Between circular and longitudinal layers of muscularis
– Controls GI tract motility

info on mouth = oral (buccal) cavity

• Bounded by lips, cheeks, palate, tongue
• Oral orifice is anterior opening
• Lined with stratified squamous epithelium
– Produces defensins – antimicrobial peptides

Lips (labia) and checks

– Orbicularis oris (lips) and buccinator (cheeks) muscles
– Vestibule - recess bounded externally by lips and cheeks, internally by teeth and gums (gingiva)
– Labial frenulum – median fold that attaches lip to gum

The oral cavity proper lies within

teeth and gums

Palets from the .....

Roof of the mouth

Hard palate – anterior part

– Formed by palatine bones and palatine processes of maxillae
– Midline ridge - raphe
– Mucosa is slightly corrugated to create friction against tongue during chewing

Soft palate - posterior part

– Fold formed mostly of skeletal muscle
– Rises and closes nasopharynx during swallowing
– Uvula projects downward from its free edge

The tongue is composed of

Skeletal muscle

Functions tongue

– Positioning of food between teeth
– Mixing of food with saliva
– Formation of bolus (compact mass of food) – Initiation of swallowing
– Speech production
– Taste

What is lingual frenulum

– Attaches tongue to floor of mouth and limits posterior movements

Structure of the tongue and list the 4 types of papillae

Surface bears papillae (peglike projections of underlying mucosa)
-Filiform papillae
-Fungiform papillae
-Circumvallate (vallate) papillae
-Foliate Papillae

Describe the filiform papillae

– smallest and most numerous
– Contain keratin – stiffens and makes tongue whitish
– Roughens tongue surface/provides friction to manipulate foods
– Do not contain taste buds

Describe fungiform papillae

- reddish, mushroom shaped
– Scattered over tongue
– Contain taste buds

Describe circumvallate (vallate) papillae

– ten to twelve
– V-shaped row at back of tongue
– Contain taste buds

Describe Foliate papillae

– pleatlike, on lateral aspect of posterior tongue
– Contain taste buds that function only in infants and children

Where is the terminal sulcus

on the tongue

Describe the terminal sulcus

– Just posterior to vallate papillae
– Groove that marks division between
• Body - anterior 2/3 tongue in oral cavity
• Root - posterior third of tongue in oropharynx
– Mucosa covering root of tongue lacks papillae
• Bumpy due to lingual tonsil deep to mucosa

Describe lingual lipase

– Secreted by serous cells beneath foliate and vallate papillae
– Fat-digesting enzyme that becomes functional in acid of stomach

Major or extrinsic salivary glands lie outside the

Oral cavity

Major or extrinsic salivary glands empty secretions into the oral cavity via

ducts

These salivary glands produce the most saliva

- Parotid
- Submandibular
- Sublingual

Minor or intrinsic salivary glands are ______ throughout ___________________.

Are scattered though out oral cavity mucosa

Minor or intrinsic salivary glands augment

salivary output

Functions of saliva

– Cleanses the mouth
– Dissolves food chemicals for taste
– Moistens food
– Compacts food into bolus
– Begins chemical breakdown of starch

Controls of salivation

– Parasympathetic nervous system
• Stimulates secretion of saliva
– Sympathetic nervous system
• Inhibits secretion of saliva

Info on parotid gland

– Anterior to ear and external to masseter muscle
– Parotid duct parallels zygomatic arch
• Duct opens into vestibule next to second upper molar
– Facial nerve branches run through parotid gland
• Parotid surgery may cause facial paralysis
– Mumps virus causes inflammation of parotid glands

Info on submandibular glands

– Medial to body of mandible
– Duct opens at base of lingual frenulum

Info on sublingual gland

– Anterior to submandibular gland under tongue
– Opens via 10–12 ducts into floor of mouth

Composition of saliva

• Mostly water and slightly acidic
– Electrolytes (Na+, K+, Cl–, PO4 2–, HCO3–) – Salivary amylase
– Lingual lipase
– Mucin – forms mucus in water
• Lubricates oral cavity and hydrates food
– Metabolic wastes (urea and uric acid)
– Lysozyme – bacteriocidal enzyme
• Inhibits bacterial growth and prevents tooth decay
– IgA antibodies
– Defensins

Teeth _______ and ________ food for ______

Teeth TEAR and GRIND food for digestion

Primary and permanent dentitions are formed by age

21

Teeth are served by branches of

maxillary artery and trigeminal nerve (cranial nerve V)

what are incisors

– Chisel shaped for cutting

What are canines

(cuspids or eye-teeth) – Fanglike teeth that tear or pierce

What are premolars (bicuspids)

– Broad crowns, rounded cusps – grind/crush

What are molars

– Broad crowns, rounded cusps – best grinders

Structure of crown

- exposed part above gum (gingiva)
– Covered by enamel—hardest substance in body
– Calcium salts and hydroxyapatite crystals

Structure of root

- portion embedded in jawbone
– Connected to crown by neck (constricted region)

Structure of cement

- calcified connective tissue
– Covers root
– Attaches tooth to periodontal ligament

Structure of periodontal ligament

– Forms fibrous joint called gomphosis
– Anchors tooth in bony socket (alveolus)

Structure of gingival sulcus

- groove where gingiva borders tooth

Structure of dentin

- bonelike material under enamel
– Maintained by odontoblasts of pulp cavity
• Produced throughout life

Structure of pulp cavity

- Surrounded by dentin

Structure of pulp

-connective tissue, blood vessels, nerves

Structure of root canal

– extension of pulp cavity into root

Structure of apical foramen

- at proximal end of root
– Entry for blood vessels and nerves

How many roots do the canine, incisor and premolars have

One root
-First upper premolar often has two

How many roots do the first two upper molars have

Three roots

How many roots do the first two lower molars have

Two roots

How many roots do the third molars have

It varies
-Usually single fused root

Describe Dental Cavities

Demineralization of enamel and dentin from bacterial action
– Dental plaque adheres to teeth
• Film of sugar, bacteria, and debris
– Bacterial metabolism produces acids that dissolve calcium salts
– Bacterial enzymes digest organic matter
– Prevention - daily flossing and brushing

Describe gingivitis

- red, swollen, sore, bleeding gums
– Plaque calcifies to form calculus (tartar)
• Disrupts seal between gingivae and teeth
– Anaerobic bacteria infect gums
– Infection reversible if calculus removed

Describe periodontitis (periodontal disease)

neglected gingivitis
– Immune cells attack intruders and body tissues
• Destroy periodontal ligament
• Activate osteoclasts

How does food pass from the mouth

Mouth --> Oropharynx --> Laryngopharynx

The pharynx is a common passageway for

Food, fluids, and air

What cells are in the pharynx

• Stratified squamous epithelium (inner lining)
– Mucus-producing glands

What skeletal muscle layers are involved in the pharynx

– Inner longitudinal
– Outer pharyngeal constrictors
• Contractions propel food into esophagus

Describe the esophagus

• Flat muscular tube
• From laryngopharynx to stomach
• Pierces diaphragm at esophageal hiatus • Joins stomach at cardial orifice
• Gastroesophageal (cardiac) sphincter
– Surrounds cardial orifice
– Reinforced by presence of diaphragm

What happens during heartburn

– Stomach acid regurgitates into esophagus
– Excess food/drink, extreme obesity, pregnancy, running

– Hiatal hernia - structural abnormality
• Part of stomach protrudes above diaphragm
–Weakened gastroesophageal sphincter
• May lead to esophagitis, esophageal ulcers, esophageal cancer

What type of cells is the mucosa made of

- stratified squamous epithelium
– Changes to simple columnar at stomach

What type of cells is the submucosa - esophageal glands

– Secrete mucus to aid in bolus movement
Areolar connective tissue

What type of cells is the muscularis externa

– Skeletal muscle in superior 1/3
– Mixture of skeletal and smooth in middle
– Smooth muscle in last 1/3
-Has a circular layer and longitudinal layer

what type of cells is the adventitia

fibrous connective tissue– Instead of serosa

Digestive process - Mouth to esophagus

• Mouth
– Ingestion
– Mechanical digestion (breakdown)
• Chewing (mastication)
– Propulsion
• Swallowing (deglutition)
– Chemical digestion
• Salivary amylase - begins digestion of carbohydrates
• Lingual lipase (activated by stomach acid)
– No absorption occurs in mouth (except for few drugs)
• Pharynx and esophagus
– Sole function is propulsion of food
• Transport of food from mouth to stomach

Deglutition

=Swallowing
Involves 22 muscles

Describe the buccal phase during deglutition

- Voluntary
- Occurs in mouth
- Tongue contracts to force bolus into oropharynx

During the buccal phase, the upper esophageal sphincter is contracted.
The tongue presses against the hard palate and contracts, forcing the food bolus into the oropharynx.

Describe the Pharyngeal-esophageal phase during deglutition

– Involuntary – begins when tactile receptors in posterior pharynx are stimulated by bolus
– Controlled by medulla and pons
– Vagus nerve transmits motor impulses from swallowing center to muscles of pharynx and esophagus

The pharyngeal-esophageal phase begins as the uvula and larynx rise and the epiglottis bends to prevent food from entering respiratory passageways. The tongue blocks off the mouth. Upper esophageal sphincter relaxes, allowing food to enter the esophagus.

The constrictor muscles of the pharynx contract, forcing food into the

the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters.

Peristalsis moves food through the

esophagus to the stomach

The gastroesophageal sphincter surrounding the

cardial oriface opens, and food enters the stomach

Describe the locations and functions of the stomach

• Located in upper left quadrant

• Functions:
– Food storage
– Begins digestion of proteins – Converts food into chyme

What does the cardinal part of the stomach surround

Cardial orifice

The cardinal orifice of the stomach is the entry from the

esophagus

The fundus of the stomach is a ___________________ beneath the

Dome-shaped region beneath the diaphram

Describe the body of the stomach

midportion

Describe the pyloric part of the stomach

– funnel-shaped region near duodenum
– Pyloric antrum (superior portion) --> pyloric canal --> pylorus
– Pyloric sphincter - controls stomach emptying

Describe the greater curvature of the stomach

- Convex lateral surface

Describe the lesser curvature of the stomach

- Concave medial surface

Describe the arterial supply of the stomach

Branches of celiac trunk

The veins of the stomach empty into what vein

hepatic portal vein

What is Rugae in the stomach

Folds of lining seen when stomach is empty

Mesenteries associated with the stomach

-Lesser omentum
– From liver to lesser curvature

-Greater momentum
– From greater curvature
--> drapes anteriorly over small intestine
--> wraps spleen & transverse colon
--> blends with mesocolon
- Contains fat deposits & lymph nodes

Four tunics of the stomach

mucosa, submucosa, muscularis, serosa
-Muscularis and mucosa modified

Describe the muscularis externa of the stomach

– Three layers of smooth muscle (instead of two)
– Inner oblique layer allows stomach to churn, mix, move, and physically break down food

Describe the mucosa of the stomach

– Simple columnar epithelium
• Composed of mucous (goblet) cells
– Dotted with gastric pits --> gastric glands
• Gastric glands produce gastric juice

Describe the 2 types of chief cells in the stomach

– Pepsinogen - activated to pepsin by HCl & by pepsin itself (a positive feedback mechanism)
– Lipases - digest lipids

Mucosal barrier protects the stomach from _____ and ______

acids and enzymes

The mucosal layer protects the stomach from acids and enzymes by

• Thick layer of bicarbonate-rich mucus
• Tight junctions between epithelial cells
– Prevent juice seeping underneath tissue
• Damaged epithelial cells are quickly replaced by division of stem cells
– Surface cells replaced every 3–6 days

Describe gastritis

– Inflammation of stomach wall caused by anything that breaches mucosal barrier

Describe peptic ulcers

– Erosions of stomach wall
• Can perforate --> peritonitis and hemorrhage
– Most caused by Helicobacter pylori bacteria

Digestive processes in the stomach

• Physical digestion
• Denaturation of proteins by HCl
• Enzymatic digestion of proteins by pepsin
– Protein digestion begins in the stomach
• Lingual lipase becomes activated and digests some triglycerides before it is digested
• Delivers chyme to small intestine
– Chyme – partially digested food and gastric juice

Regulation of gastric secretion

• Neural and hormonal mechanisms
• Vagus nerve stimulation-->secretion increases
• Sympathetic stimulation --> ecretion decreases
• Hormonal control is mainly gastrin
– Stimulates enzyme and HCl secretion
– Stimulates most small intestine secretions - gastrin antagonists

What are the 3 phases of gastric secretion

1. Cephallic (reflex) phase
2. Gastric Phase
3. Intestinal phase

Describe Cephallic (reflex) phase

*before food enters stomach
– Conditioned reflex triggered by sight, smell, taste, or thought of food
– Sensory receptors --> hypothalamus --> medulla oblongata --> vagus nerve --> enteric neurons --> stimulates glands

Describe the gastric phase

– lasts 3–4 hours (2/3 gastric juice released)
– Stimulated by distension, peptides, low acidity (high pH), gastrin (major stimulus)
– Caffeine, peptides, rising pH (from ingested proteins) stimulate enteroendocrine G cells to release gastrin
– Gastrin stimulates parietal cells to release HCL
– HCL digests proteins

What are the 2 components of the intestinal phase

-Stimulatory component
-Inhibitory component

Describe the Stimulatory component of the intestinal phase

• Partially digested food enters duodenum
• Duodenum releases intestinal (enteric) gastrin
– To blood --> stomach
– Stimulates gastric glands to continue secretions

Describe the Inhibitory component (enterogastric reflex) of the intestinal phase

• Intestine distends with chyme
– Chyme contains H+, fats, peptides, irritating substances
• Distension of intestine
– Inhibits gastric activity
» To protect small intestine from excessive acidity
– Causes pyloric sphincter to tighten
» To prevent further food entry

Three chemicals are necessary for maximum HCl secretion:

– Acetylcholine (ACh)
• Released by parasympathetic nerve fibers
– Gastrin
• Secreted by G cells in stomach
– Histamine
• Released by enteroendocrine cells of glands
–In response to gastrin
• Antihistamines block histamine receptors of parietal cells --> decrease HCl --> decrease ulcers

Peristalsis begins near what?

gastroesophageal sphincter
--> gentle rippling

Peristaltic waves ______ and move toward ______ at a rate of __ per _______

Peristaltic waves STRENGTHEN and move toward PYLORUS at rate of 3 per MINUTE

How is the contractile rhythm set during peristaltic waves?

Contractile rhythm set by enteric pacemaker cells located in longitudinal smooth muscle layer

What are pacemaker cells linked by?

Gap junctions --> entire muscularis contracts

Distension of stomach and gastrin secretion increase

force of contractions

Chyme is delivered in

3 ml spurts to duodenum

List the 3 steps during peristaltic waves in the stomach

1) Propulsion: Peristaltic waves move from the fundus toward the pylorus.

2) Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus.

3) Retropulsion: The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach.

Describe the regulation of gastric emptying

• As chyme enters duodenum
– Receptors respond to stretch and chemical signals
– Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling
• Enterogastrones = secretin, cholecystokinin, vasoactive intestinal peptide

• Stomach usually empties completely within four hours after a meal
• Carbohydrate-rich chyme moves quickly through duodenum
• Fatty chyme remains in stomach 6 hours or more

What is the major organ of digestion and absorption

The small intestine

What supplies blood to the small intestine

superior mesenteric artery

Describe venous drainage of the small intestine

Veins --> superior mesenteric vein --> hepatic portal vein --> liver -->
inferior vena cava --> heart

What are the subdivisions of the small intestine

– Duodenum (retroperitoneal)
– Jejunum (attached posteriorly by mesentery)
– Ileum (attached posteriorly by mesentery)
• Joins large intestine at ileocecal valve

Describe the duodenum

• Shortest part – 25 cm (10 inches)
• Curves around head of pancreas
• Bile duct (from liver) and pancreatic duct (from pancreas)
– Join at hepatopancreatic ampulla
– Enter duodenum at major duodenal papilla
– Hepatopancreatic sphincter controls entry of bile and pancreatic juice (Sphincter of Odi)

Describe the anatomy of the small intestine

• Highly adapted for absorbing nutrients
• Wall has three structural modifications to increase surface area for absorption (primarily in proximal part)
– Circular folds (plicae circulares)
– Villi
– Microvilli

Describe circular folds

Circumferential --> force chyme to slowly spiral through lumen (speed bumps)

Describe Villi

– Fingerlike projections (~1 mm high) of mucosa
– Capillary bed and lacteal in center of each villus

Describe Microvilli (brush border)

– Extensions of plasma membrane of columnar epithelial cells lining small intestine
– Contain brush border enzymes that complete digestion of carbohydrates and proteins

Describe the mucosa in the small intestine (microscopic)

– Simple columnar epithelium
• Absorptive cells = enterocytes
• Goblet cells secrete mucus
• Studded with pits between villi
-->tubular glands called intestinal crypts
– Lamina propria
• Capillary and lacteal extend into each villus
– Muscularis mucosa
• Thin layer of smooth muscle

Describe Peyer's patches

MALT
– Located in lamina propria of mucosa
• May protrude into submucosa
– Prominent in ileum
– Protect against bacteria entering bloodstream

Describe Duodenal (Brunner's) glands

– In submucosa of duodenum
– Secrete alkaline (bicarbonate-rich) mucus to neutralize acidic chyme

Describe intestinal Juice

• Secreted by epithelial cells of intestinal crypts
– In response to distension or irritation of mucosa
• Slightly alkaline (7.4-7.8)
– Isotonic with blood plasma
• Mainly water with some mucus from mucosa goblet cells and duodenal Brunner’s glands
– Enzyme-poor
(enzymes of small intestine only in brush border)
• Facilitates transport & absorption of nutrients

Describe the liver

• Largest gland in body (weighs 3 lbs)
• Four lobes—right, left, caudate, quadrate
• Many metabolic functions
– Important – processes nutrient-laden venous blood from digestive organs
• Only digestive function is bile production
– Bile – fat emulsifier
• Breaks down fats to smaller particles that are more readily digestible

Describe the falciform ligament of the liver

– Separates larger right and smaller left lobes
– Suspends liver from diaphragm and anterior abdominal wall

Describe the round ligament (ligamentum teres) of the liver

– Remnant of fetal umbilical vein
– Along inferior edge of falciform ligament

The liver is enclosed by the

visceral peritoneum
- Except bare area which touches diaphragm

Bile ducts of the liver

– Common hepatic duct leaves liver
– Cystic duct leaves gallbladder
– Bile duct formed by union of common hepatic and cystic ducts

Hypatocyte functions

• Produce bile (900 ml per day)
• Process bloodborne nutrients
– Store glucose as glycogen
– Use amino acids to make plasma proteins
• Store fat-soluble vitamins
• Perform detoxification
• Participate in Vitamin D synthesis

Describe Bile

• Yellow-green, alkaline solution containing
– Bile salts - cholesterol derivatives that function in fat emulsification and absorption
– Bilirubin - pigment formed from heme
• Bacteria in small intestine break down to stercobilin --> brown color of feces

– Cholesterol
– Triglycerides
– Phospholipids
– Electrolytes

Some substances secreted in bile leave body in feces but ______ ______ do not

Bile salts

Describe enterohepatic circulation

– Recycles bile salts (3-5 times per meal)
– Bile salts --> duodenum --> reabsorbed from ileum --> hepatic portal blood --> liver secreted into newly formed bile

Describe the Gallbladder

• Thin-walled muscular sac on ventral surface of liver
• Stores and concentrates bile by absorbing water and ions
• Releases bile into cystic duct, which flows into bile duct

Bile in the gallbladder

• Bile is major means of cholesterol excretion from body
• Bile salts keep cholesterol dissolved in bile
• High cholesterol or too few bile salts
--> cholesterol crystalizes
--> gallstones (biliary calculi)
• Gallbladder contracts against crystals --> pain
• Gallstones obstruct bile flow
--> may cause obstructive jaundice

Describe the location of the pancreas

• Mostly retroperitoneal
• Deep to greater curvature of stomach

Describe the regions of the pancreas

• Head - encircled by duodenum
• Tail - touches the spleen
• Body – mid portion of gland
• Uncinate process – folded posteriorly

Importance of the pancreas

Produces enzymes that break down all food categories

What is the endocrine function of the pancreas

– Pancreatic islets = Islets of Langerhans
• Secrete insulin and glucagon

What is the exocrine function of the pancreas

– Acini secrete pancreatic juice
• Acini - clusters of secretory acinar cells
• Zymogen granules of acini cells contain inactive digestive enzymes (proenzymes)

– Pancreatic juice empties into the duodenum via main pancreatic duct

Pancreatic juice is secreted by

acinar cells

Info on pancreatic juice

• Watery alkaline solution (pH 8)
– Neutralizes acidic chyme that enters duodenum
– Optimal environment for intestinal & pancreatic enzymes
• Electrolytes (primarily HCO3– , --> raises pH)
• Enzymes
– Secreted in active form
• Amylase – digests starch
• Lipase – digests fats
• Nuclease - digests nucleic acids
– Secreted in inactive form and activated in duodenum
• Proteases - digest proteins
– Trypsinogen --> trypsin -->
» Chymotrypsinogen --> chymotrypsin
» Procarboxypeptidase --> carboxypeptidase

During active digestion (after a meal) the most important stimulus for bile secretion is

increased bile salts* in enterohepatic circulation
• Causes liver to produce more bile

The liver also produces more bile in response to

• Secretin released from intestinal cells (duodenum)
–Exposed to acidic fatty chyme

Other functions of secretin:

• Stimulates pancreatic release of HCO3 rich juice
• Inhibits gastric secretions and motility

Hepatopancreatic sphincter is closed unless

digestion is active

The liver produces and releases bile

continuously

Bile backs up to _________ when sphincter is ______

Bile backs up to GALLBLADDER when sphincter CLOSED
--> bile stored in gallbladder

Bile is released to small intestine only when

gallbladder contracts

Gallbladder contraction is stimulated by

Cholecystokinin (cck)***
• Released from intestinal cells in response to acidic, fatty chyme entering duodenum
– Parasympathetic vagal stimulation (minor)

Other functions of cholecystokinin

– Stimulates secretion of enzyme-rich pancreatic juice
– Relaxes hepatopancreatic sphincter
• Allows bile & pancreatic juice to enter duodenum
– Inhibits gastric secretion and motility

Steps of the mechanisms promoting secretion and release of bile and pancreatic juice

1. Chyme entering duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin.

2. CCK (red dots) and secretin (yellow dots) enter the bloodstream.

3. CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3− -rich pancreatic juice.

4. Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly.

5. CCK (via blood stream) causes gallbladder to contract and hepatopancreatic sphincter to
relax. Bile enters duodenum.

Chyme from stomach contains

– Partially digested carbohydrates and proteins
– Undigested fats

• 3–6 hours in small intestine
– Most water and virtually all nutrients absorbed

Digestion Requires

• Digestion requires:
– Slow delivery of acidic, hypertonic chyme
– Delivery of bile, enzymes, and bicarbonate ions from liver, gallbladder, and pancreas
– Mixing

What influence does the small intestine have one digestion

• Most substances needed for SI digestion originate outside the SI & are delivered to the SI
– Bile
– Digestive enzymes (most)
– Bicarbonate ions
• Brush border enzymes of SI microvilli complete digestion of carbohydrates, proteins, & nucleic acids

* Anything that impairs liver, gallbladder, or pancreatic function or delivery of their substances hinders digestion

Describe the motility of the small intestine

• Smooth muscle activity in small intestinal wall has three primary functions:
– Mixes chyme with accessory gland secretions
– Brings chyme in contact with brush border
of mucosa
– Propels contents toward large intestine
• Accomplished by segmentation & peristalsis

Describe segmentation of the small intestine

– Most common motion of small intestine*
– Initiated by intrinsic pacemaker cells
– Mixes chyme with digestive secretions
– Helps bring chyme in contact with mucosa
– Moves contents toward ileocecal valve
– Intensity altered by long & short reflexes and by hormones
• Parasympathetic increases ; Sympathetic decreases
– Wanes in late intestinal (fasting) phase

Describe peristalsis of the small intestine

– Initiated by rise in motilin hormone
• Released by duodenal mucosa
• In late intestinal phase (after most nutrients absorbed)
• Starts in proximal duodenum every 90–120 minutes
– Each successive wave starts distal to previous
• Migrating motor complex (MMC)
– Propels meal remnants, bacteria, and debris to large intestine
• “Housekeeping function” --> sweeps to LI
– From duodenum to ileum ~ 2 hours

The ileocecal sphincter is usually

constriced

What 2 mechanism cause the sphincter to relax and admit chyme into cecum

– Gastroileal reflex (triggered by stomach activity) increases force of segmentation in ileum
– Gastrin (released by stomach) increases motility of ileum

Ileocecal valve flaps _____ when chyme exerts __________ _________

Ileocecal valve flaps CLOSE when chyme exerts BACKWARD PRESSURE
– Prevents regurgitation into ileum

What are the functions of the large intestine

• Absorbs water (not absorbed by SI)
• Absorbs vitamins produced by bacterial flora
• Absorbs electrolytes (mainly Na+ and Cl-)
• Temporarily stores digestive residues
• Eliminates indigestible material from body as feces
• The colon is not essential for life

List some of the unique features of the large intestine

• Teniae coli
– Three bands of longitudinal smooth muscle in
muscularis (act like elastic)

• Haustra
– Pocketlike sacs caused by tone of teniae coli

• Epiploic appendages
– Fat-filled pouches of visceral peritoneum that
hang from surface (unknown significance)

What are the subdivisions of the large intestine

Cecum
Appendix
Colon
Rectum
Anal Canal

Describe the cecum

(“blind pouch”) – first part of LI – Ileocecal valve

Describe the appendix

– fingerlike projection attached to posteromedial surface of cecum
– Contains masses of lymphoid tissue
• Part of MALT of immune system
– Bacterial storehouse
--> recolonizes gut when necessary
– Structure allows enteric bacteria to accumulate and multiply --> appendicitis

Describe the colon

– Ascending colon (right side)
- Right colic (hepatic) flexure
– Transverse colon
- Left colic (splenic) flexure
– Descending colon (left side)
– Sigmoid colon (S-shaped in pelvis)
– Ascending colon and descending colon are retroperitoneal
– Transverse and sigmoid colon are intraperitoneal and anchored to posterior abdominal wall by mesocolons

Describe the rectum

– Joins sigmoid colon at level of third sacral vertebra
– Three rectal valves stop feces from being passed with gas (flatus)

Describe the anal canal

- last segment of large intestine
– Lies external to abdominopelvic cavity
– Opens to body exterior at anus
– Two sphincters
• Internal anal sphincter - smooth muscle, involuntary
• External anal sphincter - skeletal muscle, voluntary

What type of tissue is in the large intestine

Simple columnar epithelium
– Except in anal canal (stratified squamous – abrasion)

Randomness about LI

• No circular folds or villi
• No cells that secrete digestive enzymes
– Because food is digested and absorbed before reaching large intestine

• Abundant deep crypts with GOBLET CELLS***
– Mucus eases passage of feces and protects mucosa
from irritating bacterial acids and gases
• Superficial venous plexuses (hemorrhoidal veins) of anal canal form hemorrhoids if inflamed

Describe bacterial flora of the large intestine

• Most bacteria are killed before enter LI
• Enter from small intestine or anus
– Colonize colon
– Synthesize B complex vitamins and vitamin K
– Ferment indigestible carbohydrates (cellulose)
– Release irritating acids and gases (flatus)
• Prevented from breaching mucosal barrier by IgA response of MALT

What is inflammatory Bowel Disease (IBD)

• Periodic inflammation of intestinal wall
• Abnormal immune response to normal bacterial antigens
• Linked to newly discovered helper T cell and deficits of
lysozymes, defensins etc secreted by gut mucosa
• Symptoms – cramping, diarrhea, weight loss, bleeding
• Two subtypes:
– Ulcerative colitis – shallow inflammation, mainly rectum
– Crohn’s disease – more serious, with deep ulcers and fissures in entire intestine, but mostly terminal ileum

What is the treatment for IBD

diet, antibiotics, anti-inflammatory drugs, immunosuppressant drugs, stress reduction

Describe defecation

Mass movements force feces toward rectum
Muscles of rectum contract to expel feces
Assisted by Valsalva's maneuver

Describe chemical digestion

• Digestion
– Catabolic process that breaks down large molecules to monomers small enough to be absorbed

• Uses enzymes secreted by intrinsic and accessory glands
• Enzymatic breakdown occurs by hydrolysis – Water is added to break bonds

***Most digestion and absorption occurs in the small intestine

Describe carbohydrate digestion

• Carbohydrates must be broken down to monosaccharides to be absorbed
– Glucose, fructose, galactose
• Begins in mouth
– Salivary amylase
• Continues in small intestine
– Pancreatic amylase
– Brush border enzymes of small intestine

Describe protein digestion

• Proteins digested include
– Dietary proteins, enzymes, and mucosal cells
• Begins in stomach
– Pepsinogen secreted by chief cells of stomach is activated to pepsin (by HCl and pepsin itself)
• Inactivated by high pH of duodenum
• Continues in small intestine
– Pancreatic enzymes
• Trypsin, chymotrypsin, carboxypeptidase
– Brush border enzymes

Describe lipid digestion

• Very small amount (10%) of fat is digested by lingual lipase after it is activated in stomach
**Small intestine is primary site of lipid digestion**
– Pancreatic lipase
• Fats must be emulsified for efficient digestion
– Broken down in duodenum to smaller fat droplets by bile salts contained in bile from liver

Emulsification and absorption of fats

• Does not break chemical bonds
• Reduces attraction between fat molecules
• Disperses fat molecules
• Increases exposure to pancreatic lipases
• Fatty acids and monoglycerides associate with bile salts
to form micelles

Nucleic Acid Digestion

• Occurs in small intestine
• Pancreaticnucleases
– Ribonuclease & deoxyribonuclease
– Hydrolyze to nucleotide monomers
• Intestinal brush border enzymes
– Nucleosidases and phosphatases
• Break nucleotides apart to release
–Nitrogenous bases
–Pentose sugars
–Phosphate ions

Describe absorption

***Almost all food, 80% electrolytes, and 95% water are absorbed in small intestine
***Most absorption complete before chyme reaches ileum
• All that remains at end of ileum is
– Small amount of water
– Indigestible food materials (cellulose)
– Bacteria!!!
***Ileum’s major absorptive role is to reclaim bile salts
to be recycled back to liver
– Enterohepatic circulation

Absorption of nutrients

• Most nutrients are absorbed by active transport
– Enter villus capillaries
– Transported by hepatic portal vein to liver (processed)
– Empties into inferior vena cava

• Exception – lipids
– Absorbed by passive diffusion
– Enter lacteals in villi of small intestine
– Enters blood at junction of left internal jugular vein and subclavian vein

Malabsortion of Nutrients

• Gluten-sensitive enteropathy (celiac disease)
– Immune reaction to gluten
• Protein in all grains except corn and rice
– Gluten complexes with immune system molecules
• Immune complexes attack intestinal lining
–Damage intestinal villi and brush border
– Bloating, diarrhea, pain, malnutrition
– Treated by eliminating gluten from diet

Absorption of Vitamins

• Most dietary vitamins absorbed by small intestine
• Large intestine absorbs some of Vitamin K and B vitamins made by its enteric bacteria
• Fat-soluble vitamins (A, D, E, K) dissolve in dietary fats and are absorbed by passive diffusion
– Enter lacteals
– Thus must eat fatty food to absorb these vitamins
• Vitamin B12 absorption requires intrinsic factor produced by the stomach