Human A&P II exam 4

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1

The Digestive System and Body Metabolism

Digestion

  • breakdown of ingested food

Absorption

  • Passage of nutrients into the blood

Metabolism

  • Production of cellular energy (ATP)
2

6 Major Processes of Digestive System

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Digestive System

  • Two groups of organs
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  1. Alimentary canal (gastrointestinal or GI tract)
  • Mouth to anus
  • Digests food and absorbs fragments
  • Mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
4

Digestive System

  • Two groups of organs
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2. Accessory digestive organs

  • Teeth, tongue, gallbladder
  • Digestive glands

–Salivary glands

–Liver

–Pancreas

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Peritoneum and peritoneal cavity

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Peritoneum and Peritoneal Cavity

  • Peritoneum -serous membrane of abdominal cavity

visceral peritoneum on external surface of most digestive organs

Parietal peritoneum lines body wall

  • Peritoneal cavity

–Between two peritoneums

–Fluid lubricates mobile organs

7

Figure 23.5a The peritoneum and the peritoneal cavity

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8

Peritoneum and Peritoneal Cavity

  • Mesentery - double layer of peritoneum

–Routes for blood vessels, lymphatics, and nerves

–Holds organs in place; stores fat

9

Organs of the Digestive System

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10

Mouth (Oral Cavity) Anatomy

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  • lips (labia) – protect
    the anterior opening
  • Cheeks – form the
    lateral walls
  • Hard palate – forms
    the anterior roof
  • Palatine bones and palatine processes of maxillae
  • soft palate – forms
    the posterior roof
  • Skeletal muscle
  • Uvula – fleshy
    projection of the
    soft palate
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Mouth (Oral Cavity) Anatomy

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  • Vestibule – space between lips externally and teeth and gums internally
  • labial frenulum - median attachment of each lip to gum
  • Oral cavity – area contained by the teeth
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Tongue

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  • Skeletal muscle
  • L ingual frenulum

–Fold of tissue anchoring tongue to floor of mouth

Functions include

–Repositioning and mixing food during chewing

–Formation of bolus (ball of food)

–Initiation of swallowing, speech, and taste

13

Salivary Glands

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  • Accessory digestive organs
  • Major salivary glands

–Produce saliva; outside oral cavity

Parotid

submandibular

Sublingual

  • minor salivary glands

–Scattered throughout oral cavity

14

Salivary Glands

  • Function of saliva

–cleanses mouth

–Dissolves food chemicals for taste

–Moistens food; compacts into bolus

–Begins breakdown of starch with enzymes

15

Saliva

  • Mixture of mucus (stringy, viscous) and serous (watery; digestive enzymes) fluids
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Processes of the Mouth

  • mastication (chewing) of food
  • Mixing masticated food with saliva
  • Initiation of swallowing by the tongue
  • Allowing for the sense of taste
17

Pharynx Function

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Passageway for air and food

Food is propelled to the esophagus by two muscle layers

  • Longitudinal layer
  • Circular outer layer

Peristalsis

  • Food movement --> alternating contractions of the muscle layers
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Esophagus

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  • From pharynx to stomach through the diaphragm
  • Conducts food by peristalsis
    (slow rhythmic squeezing)
  • Passageway for food only (respiratory system branches off after the pharynx)
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Layers of Alimentary Canal Organs

  • 4 layers
  • Esophagus to anus --> different functions along GI tract

1.Mucosa

  • Innermost layer
  • mouth to anus
  • Secrete, absorb, protect
  • moist membrane
  • Surface epithelium
  • Small amount of connective tissue
    (lamina propria)
  • Small smooth muscle layer
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Layers of Alimentary Canal Organs

2.Submucosa

  • Just external to mucosa
  • Soft connective tissue with blood vessels, nerve endings, and lymphatics
  • Supply GI tract wall
21

Layers of Alimentary Canal Organs

3.Muscularis externa

Surrounds submucoso

  • Segmentation (food mixing) and peristalsis (moves food)

Smooth muscle

  • Inner circular layer
  • Outer longitudinal layer

4. Serosa

  • Outermost layer – visceral peritoneum
  • Layer of serous fluid-producing cells
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Layers of Alimentary Canal Organs

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23

6 Major Processes of Digestive System

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24
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Stomach Anatomy

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  • Located on the left side of the abdominal cavity
  • Food leaves esophagus and enters stomach at the gastroesophageal sphincter
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Stomach Anatomy

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Regions of the stomach

  • cardiac region – near the heart
  • Fundus
  • Body
  • Phylorus – funnel-shaped terminal end

Food empties into the small intestine at the pyloric sphincter

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Stomach Anatomy

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Rugae – internal folds of the mucosa

External regions

  • lesser curvature
  • greater curvature
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Stomach Anatomy

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Muscularis externa

3 layers

  • Longitudinal
  • Circular
  • oblique

Different from other regions of GI tract

  • For churning
  • Others have 2 layers of smooth muscle
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Stomach Anatomy

  • Layers of peritoneum attached to the stomach
  • Lesser omentum _– attaches the liver to the lesser curvature
  • gr eater omentum – attaches the greater curvature to the posterior body wall
  • Contains fat to insulate, cushion, and protect abdominal organs
29

Stomach Functions

  • Acts as a storage tank for food
  • Site of food breakdown
  • Chemical breakdown of protein begins
  • Very acidic
  • Delivers chyme (processed food) to the small intestine
30

Specialized Mucosa of the Stomach

Gastric pits formed by folded mucosa

Simple columnar epithelium

  • Mucous neck cells – produce a sticky mucus
  • gastric glands – secrete gastric juice
  • Chief cells – produce protein-digesting enzymes (pepsinogens)
  • Parietal cells – produce hydrochloric acid
  • Enteroendocrine cells – produce gastrin (hormone that regulates stomach secretions)
31
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Structure of the Stomach Mucosa

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32

Small Intestine

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  • Body’s major digestive organ
  • 2-4 meters long
  • Site of nutrient absorption into the blood
  • Muscular tube extending form the pyloric sphincter to the ileocecal valve
  • Suspended from the posterior abdominal wall by the mesentery
33

Subdivisions of the Small Intestine

Dogs Just Itch!”

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Duodenum

  • Attached to the stomach
  • Curves around the head of the pancreas

Jejunum

  • Attaches anteriorly to the duodenum
  • Ileum
  • Extends from jejunum to largeintestine
34

Chemical Digestion in the Small Intestine

Source of enzymes that are mixed with chyme

  • Intestinal cells
  • pancreas

Bile enters from the gall bladder (stores bile produced in liver)

  • Breaks down fats
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Chemical Digestion in the Small Intestine

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36

Villi of the Small Intestine

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  • Fingerlike structures formed by the mucosa
  • Give the small intestine more surface area
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Structures Involved in Absorption of Nutrients

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  • Absorptive cells
  • Blood capilalries
  • Lacteals (specialized lymphatic capillaries)
  • Absorb dietary fats
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Microvilli of the Small Intestine

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  • Also called brush border
  • Small projections of the plasma membrane
  • Found on absorptive cells of small intestine
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Folds of the Small Intestine

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  • Circular folds or plicae circulares
  • Deep folds of the mucosa and submucosa
  • Do not disappear when filled with food
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Digestion in the Small Intestine

enzymes from the brush border (microvilli)

  • Break double sugars into simple sugars
  • Complete some protein digestion

pancreatic enzymes play the major digestive function

  • Help complete digestion of starch (pancreatic amylase)
  • Carry out about half of all protein digestion (trypsin, etc.)
41

Digestion in the Small Intestine

Pancreatic enzymes play the major digestive function (continued)

  • Responsible for fatdigestion (lipase)
  • Digest nucleic acids (nucleases)
  • Alkaline content neutralizes acidic chyme
42

Absorption in the Small Intestine

water absorbed along the length of the small intestine

End products of digestion

  • Most substances absorbed by active transport through cell membranes
  • Lipids absorbed by diffusion

Substances are transported to the liver by the hepatic portal vein or lymph

43

Propulsion in the Small Intestine

peristalsis is the major means of moving food

Segmental movements

  • Mix chyme with digestive juices
  • Aid in propelling food
44

Large Intestine

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  • Larger in diameter, but shorter than the small intestine
  • frames the internal abdomen
45

Functions of the Large Intestine

  • Absorption of water
  • Digestion of remaining food by bacteria
  • Eliminates indigestible food from the body as feces
  • Goblet cells produce mucus to act as a lubricant
46

Large Intestine

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  • Cecum

–Appendix

  • Colon
  • Rectum
  • Anus
47

Structures of the Large Intestine

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Cecum – saclike first part of the large intestine

Appendix

  • Accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)
  • Hangs from the cecum
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Structures of the Large Intestine

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Colon

  • Ascending
  • Transverse
  • Descending
  • Sigmoid (S-shaped)

Rectum

Anus – external body opening

49

Food Breakdown and Absorption in the Large Intestine

No digestive enzymes are produced

Resident bacteria digest remaining nutrients

  • Produce some vitamin K and B
  • Release gases

Water and vitamins K and B are absorbed

Remaining materials are eliminated via feces

50

Propulsion in the Large Intestine

sluggish peristalsis

Mass movements

  • Slow, powerful movements
  • Occur three to four times per day

Presence of feces in the rectum causes a defecation reflex

  • Internal anal sphincter is relaxed
  • Defecation occurs with relaxation of the voluntary (external) anal sphincter
51

Accessory Digestive Organs

  • Salivary glands
  • Teeth
  • Pancreas
  • Liver
  • Gall bladder
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Pancreas

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Produces wide spectrum of digestive enzymes

  • Break down all categories of food
  • Enzymes are secreted into the duodenum (small intestine)
  • Alkaline fluid introduced with enzymes neutralizes acidic chyme

endocrine products of pancreas

  • Insulin; Glucagons
53
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Liver

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  • largest gland in the body
  • Right side of the body under the diaphragm
  • Four lobes suspended from the diaphragm and abdominal wall by the falciform ligament
  • Connected to the gall bladder via the common hepatic duct
  • Comprised of hepatocytes (liver cells)
54

Bile

Produced by cells in the liver

Breaks down fats

Composition

  • Bile salts (acids, break down fats)
  • Bile pigment (mostly bilirubin, a waste product from the breakdown of hemoglobin)
  • Cholesterol
  • Phospholipids
  • Electrolytes
55

Role of the Liver

Primary role in digestion

  • Produces bile (breaks down fats)

Role in metabolism

  • Process nutrient rich venous blood from digestive organs (from hepatic portal vein)
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Gall Bladder

  • Sac found in hollow fossa of liver
  • stores bile from the liver
  • Bile is introduced into the duodenum in the presence of fatty food
  • Gallstones can cause blockages
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Processes of the Digestive System

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  • Ingestion – getting food into the mouth
  • Propulsion – moving foods from one region of the digestive system to another
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Processes of the Digestive System

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Propulsion

  • Peristalsis – alternating waves of contracation
  • Segmentation – moving materials back and forth to aid in mixing (mostly in small intestine)
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Processes of the Digestive System

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  • Mechanical digestion
  • Mixing of food in the mouth by the tongue
  • Churning of food in the stomach
  • Segmentation in the small intestine
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Processes of the Digestive System

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  • Chemical Digestion
  • enzymes break down food molecules into their building blocks
  • Each major food group uses different enzymes
  • Carbohydrates are broken to simple sugars
  • proteins are broken to amino acids
  • Fats are broken to fatty acids and alcohols
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Processes of the Digestive System

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  • Absorption
  • End products of digestion are absorbed in the blood or lymph
  • Nutrients must enter mucosal cells and then into blood or lymph capillaries
  • Defecation
  • Elimination of indigestible substances as feces (stool)