Vertebrate Histology Exam 4

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1

Respiratory System

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Respiratory System

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Lungs and air passages

Functions:

  • Air conduction
  • Air filtration and conditioning
  • Gas exchange (external respiration)
  • Speech (larynx)
  • Smell (nasal cavity)
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Conducting Portion of Respiratory System

  • Nasal cavities, pharynx, larynx, trachea, bronchi, and large bronchioles
  • Lined with pseudostratified ciliated columnar epithelium with numerous mucus-secreting goblet cells
  • As passage branches, tubes become smaller (diameter) and height of epithelium decreases (width of blue)
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Respiratory Portion of Respiratory System

  • Where external respiration occurs
  • Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli
  • Respiratory bronchioles are transition between conducting and respiratory portions of respiratory system
  • Alveoli are lined with a thin simple squamous epithelium (no goblet cells)
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Nasal Cavity

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Paired chambers separated by septum of cartilage and bone

Pseudostratified columnar epithelium lines most of nasal cavity (similar to rest of respiratory tract)

  • Lamina propria attached to seputm

Stiff hairs (vibrissae) trap large particulate matter in anterior portion of cavity

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Pseudostratified Columnar Epithelium (Respiratory Epithelium) Cell Types

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  • Ciliated cells: tall with cilia projecting into mucus that covers surface of the epithelium
  • Goblet cells: synthesize and secrete mucus
  • Basal cells: stem cells for other cell types
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Olfactory Epithelium

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Part of dome (roof) of each nasal cavity

Lined with olfactory mucosa

  • Olfactory epithelium (pseudostratified columnar, but no goblet cells)
  • Olfactory (Bowman’s) glands

Lamina propria: blood and lymphatic vessels, unmyelinated olfactory nerves, myelinated nerves, and olfactory glands

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Respiratory and olfactory epithelium of nasal cavity

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Olfactory epithelium is much larger in rodents vs. humans.

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Olfactory Epithelium Cell Types

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  • Olfactory cells/bipolar neurons (sensory cells): cilia on apical dendrite where odors bind; quickly replaced
  • Supporting/sustentacular cells: columnar with microvilli, provide mechanical and metabolic support for olfactory cells
  • Basal cells: stem cells
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Olfactory Glands (Bowman’s Glands)

Within mucosa

Branched, tubuloalveolar serous glands

Secretion traps and acts as a solvent for odor molecules

  • Thinner than mucus secreted by goblet cells throughout the rest of the nasal cavity
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Olfactory Epithelium

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Larynx

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  • Passageway for air between pharynx and trachea
  • Irregularly shaped plates of hyaline and elastic cartilage
  • Vocal folds (cords): two folds of mucosa that project into lumen (speech)
  • Luminal surface of vocal folds and epiglottis covered with stratified squamous epithelium
  • Rest of larynx covered with ciliated pseudostratified columnar epithelium
  • CT contains mixed mucus/serous glands
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Trachea

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  • Short, flexible tube from larynx to mid thorax (divides into main bronchi)
  • Lumen remains open due to cartilaginous rings
  • Runs parallel to esophagus
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Trachea: Wall Layers

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Mucosa

  • Ciliated, pseudostratified columnar epithelium in elastic fiber-rich lamina propria
  • Goblet cells and mucosal folds

Submucosa

  • Slightly denser CT (but still classified as loose) than in lamina propria
  • Seromucus tracheal glands

Cartilaginous layer

  • C-shaped hyaline cartilage (holds tube open)

Adventitia

  • CT that binds trachea to adjacent structures
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Trachea:
Wall Layers

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1.Mucosa

2.Submucosa

3.Cartilaginous Layer

4.Adventitia

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Bronchi

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  • Trachea divides into 2 main/primary bronchi
  • Before entrance to lungs, bronchi are same histologically as trachea
  • In lungs, cartilage rings replaced by irregular plates that decrease in size with branching of bronchi and they have a circumferential layer of smooth muscle
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Bronchus wall layers

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Mucosa

  • Pseudostratified epithelium with lamina propria

Muscularis

  • Continuous layer of smooth muscle in larger bronchi; attenuated and loose in smaller bronchi

Submucosa

  • Loose CT, glands in larger bronchi, and adipose tissue in larger bronchi

Cartilage layer

  • Discontinuous cartilage plates

Adventitia

  • Dense CT
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Respiratory Portion: Gas Exchange

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Bronchioles

  • Terminal bronchiole
  • Respiratory bronchiole

Alveolar ducts

Alveolar sacs

Alveoli

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Majority of lung tissue:

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Majority of lung tissue volume is dedicated to alveoli for maximum gas exchange. Cross-sections of blood vessels and airways (bronchus and bronchioles) are also visible. Lymphatic nodules are sporadically placed within the lung tissue.

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Bronchiolar structure

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≤1 mm diameter

Larger bronchioles have ciliated, pseudostratified columnar epithelium which transforms into simple ciliated, columnar epithelium

  • No goblet cells in terminal bronchioles
  • No glands or cartilage plates
  • Thick layer of smooth muscle

Small bronchioles

  • Simple cuboidal epithelium
  • Smooth muscle
  • Thin CT
  • Clara non-ciliated cells (club cells): secrete surfactant to hold lumen open
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Surfactant: product of clara/club cells

  • Decreases surface tension of alveoli
  • Clears foreign materials
  • Modulates immune responses
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Terminal bronchiole with mucosal folds

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Alveoli

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  • Alveolar ducts: elongated airways with only alveoli as peripheral boundary
  • Alveolar sacs: spaces surrounded by clusters of alveoli
  • Alveoli are surrounded by thin CT layer that has capillaries (alveolar septum or septal wall)
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Respiratory bronchiole, alveolar duct, and alveoli

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Small Bronchiole vs. Artery

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Bronchiole:

  • Clear lumen
  • Prominent mucosa folds (epithelium + lamina propria)
  • Pseudostratified ciliated columnar epithelium
  • Thin layer of smooth muscle

Artery:

  • Erythrocytes in lumen
  • Simple squamous epithelium
  • Thick layer of smooth muscle
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Alveoli

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  • Increase surface area for gas exchange
  • Site of exchange between air and blood
  • Each alveolus is surrounded by network of capillaries
  • Alveoli attach to alveolar sac
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Alveolar epithelium

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Type I cells (pneumocytes)

  • Thin, squamous cells (gas exchange)
  • Line 95% alveolar surface
  • Joined by occluding junctions (barrier)
  • No cell division

Type II cells (pneumocytes)

  • Secretory cells, dispersed among type I cells
  • Cuboidal
  • Congregate at septal junctions
  • Secrete lamellar bodies (surfactant)
  • Stem cells

Alveolar macrophages (dust cells)

  • Scavenge air spaces to remove inhaled particulates, microorganisms, and red blood cells
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Alveoli

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Emphysema

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Emphysema: disease caused from destruction of walls of alveoli

  • Alveoli enlarged sacs
  • Decreased elasticity of lungs—less able to recoil during expiration

Dust cells produce enzyme that destroys elastic fibers—normal lungs protected by endogenous inhibitor

  • Inhibitor destroyed by cigarette smoke and other substances

Panacinar emphysema (image): uniform damage to respiratory bronchiole, alveolar ducts, alveolar sacs, and alveoli

  • Alveolar septa almost entirely destroyed
  • Lung has lacy appearance (“cotton candy lung”)
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Pneumonia

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Potentially lethal infection of alveoli and connective tissue of lungs

20-35% of those infected succumb to disease

  • Immunocompromised and those with chronic illnesses most succeptible

Numerous types based on pathogen: bacterial, viral, fungal

  • Inhaled or introduced in blood to lungs

Symptoms: productive coughs, fever, shollow breathing, rasping sounds, white foci on lung x-rays

Increased leukocytes and fluid within infected lungs

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summary table of respiratory system

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Digestive System I

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The digestive system (Chapters 13-15)

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Components of digestive tract

  • Oral cavity (13)
  • Esophagus (14)
  • Stomach (14)
  • Small intestine (14)
  • Large intestine (14)
  • Rectum (14)
  • Anal canal (14)

Accessory Organs

  • Salivary glands (15)
  • Liver (15)
  • Gallbladder (15)
  • Pancreas (15)
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Oral cavity

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First site of food entry to digestive tract

  • Ingestion
  • Mastication (chewing)
  • Lubrication with saliva (tasting, swallowing)

Lined with non-keratinized stratified squamous epithelium & connective tissue (lamina propria)

  • Protection
  • Called mucosa
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Lips

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Inner lining identical to rest of oral cavity (non-keratinized stratified squamous epithelium)

  • Labial mucus glands (moisten inside of lips)

Outer lining is very thin skin

  • Keratinized stratified squamous epithelium
  • Skin derivatives (hair, glands, etc.)

Orbicularis oris (skeletal muscle)

  • Movement of lips
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Tongue

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Skeletal muscle arranged in bundles running in 4 planes

  • Flexibility and precision of movement

Adipose tissue and dense irregular CT among muscle fiber groups

Mucosa: epithelium and underlying CT called lamina propria

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Papillae of tongue mucosa

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Dorsal surface of tongue is rough due to projections called papillae (ventral surface is smooth—no papillae)

  • Filiform (no taste buds)
  • Fungiform (taste buds)
  • Circumvallate (taste buds)
  • Foliate (taste buds)

All papillae covered with partially keratinized stratified squamous epithelium with underlying lamina propria

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Filiform papillae

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  • Smallest
  • Most numerous
  • Narrow, conical, elongated projections of CT
  • Cover entire dorsal surface of tongue
  • No taste buds
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Fungiform papillae

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  • Mushroom-shaped projections larger than filiform
  • More numerous at the tip of the tongue
  • Core of lamina propria CT
  • Taste buds at dorsal surface of papillae within the stratified squamous epithelium
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Fungiform papillae zoomed in

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Circumvallate papillae

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  • Largest papillae
  • Dome-shaped structures that reside toward rear of tongue
  • 8-12 papillae per tongue
  • Each surrounded by moat-like invagination (furrow) lined with stratified squamous epithelium
  • Numerous taste buds in furrow
  • Ducts of von Ebner’s serous glands empty into furrow
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Foliate papillae

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  • Well developed in rodents
  • Poorly developed in humans
  • Parallel low ridges on lateral edge of tongue separated by deep mucosal clefts
  • Numerous taste buds in clefts and furrows
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Taste buds

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  • Barrel-shaped structures in dorsal epithelium of foliate and fungiform papillae and lateral epithelium of circumvallate papillae, soft palate, pharynx, and epiglottis
  • Taste pore at free surface allows chemicals dissolved in saliva access to cells in taste bud
  • Taste buds span entire thickness of stratified squamous epithelium
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Taste bud cell types

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Neuroepithelial taste cells (sensory receptor)

  • Most numerous
  • Elongated with microvilli at apical surface with taste receptors
  • Cell junctions near apical surface
  • Synapse with sensory afferent neurons
  • Turnover every 10 days

Sustentacular cells (support)

  • Less numerous
  • Elongated, microvilli
  • No synapse
  • Turnover every 10 days

Basal cells

  • Basal portion of taste bud
  • Stem cell
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Tonsils

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Aggregates of diffuse lymphoid tissue and lymphatic nodules located in oral pharynx and tongue

  • Palatine tonsils (“the tonsils”)
  • Pharyngeal tonsil (“adenoid”)
  • Lingual tonsils
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Palatine tonsils

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  • Located on lateral walls of oral pharynx
  • Lined with non-keratinized stratified squamous epithelium, like oral cavity mucosa
  • Connective tissue capsule separates the tonsils from underlying tissue
  • Contain numerous tonsilar crypts lined with lymphatic nodules
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Palatine tonsil

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Pharyngeal tonsil

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Single structure in superior, posterior pharynx

Covered with pseudostratified ciliated columnar epithelium

  • Rests on fewer lymphatic nodules compared to palatine tonsils
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Lingual tonsils

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  • Located on dorsal surface of posterior third of tongue
  • Several masses of lymphoid aggregations
  • Lined with non-keratinized stratified squamous epithelium
  • Numerous tonsilar crypts with muscosal ridges lined with lymphatic nodules
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summary of the Oral Mucosa

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Digestive System II

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Layers of the digestive tract wall

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Layers of the digestive tract wall—general plan

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1.Mucosa: lining epithelium, underlying loose CT (lamina propria), muscularis mucosae (smooth muscle), glands (some locations)

2.Submucosa: dense irregular CT, glands (some locations)

3.Muscularis externa: 2 layers of smooth muscle

4.Serosa: serous membrane of simple squamous epithelium (mesothelium) and small amount of underlying loose CT; Adventitia of CT is found instead of serosa where attachments to other structures occurs

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Mucosa organized to perform functions

Protection

  • Epithelial lining is barrier to external environment (pathogens and noxious substances)
  • Esophagus has stratified squamous epithelium to protect against physical abrasion
  • GI tract has simple columnar epithelium that acts as selective permeability layer
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Mucosa organized to perform functions

Absorption

Projections of mucosa and submucosa increase surface area for absorption of nutrients

  • Plicae circulares: circumferentially arranged folds of submucosa along small intestine
  • Villi: mucosal projections of small intestine
  • Microvilli: tightly packed apical projection of intestinal absorptive cells (simple columnar)

Glycocalyx: has enzymes from absorptive cells essential for final digestion of proteins and sugars

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Mucosa organized to perform functions

Secretion

  • Carried out by glands distributed down length of canal
  • Mucus: protective lubrication, buffer
  • Substances that assist in digestion: enzymes, HCl, peptide hormones, water

Gland types

Intrinsic glands: lie within wall layers of digestive tract

  • Mucosal glands that extend into lamina propria (esophagus, stomach, small intestine, large intestine)
  • Submucosal glands deliver secretions to lumen of mucosal glands or to surface of canal itself (esophagus, small intestine)

Extrinsic glands: lie outside GI tract and deliver secretions to digestive system via ducts (liver, pancreas, gallbladder, salivary glands)

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Mucosa: lamina propria

Contains mucus secreting glands to protect from chemical and mechanical injury

Where absorption occurs through numerous blood and lymphatic vessels

Lymphatic tissues act as immunologic barrier

Gut-associated lymphatic tissue (GALT)

  • Diffuse lymphatic tissue
  • Lymphatic nodules (numerous in ileum: Peyer’s patches)
  • Eosinophils, macrophages, and neutrophils in addition to lymphocytes located in two areas above
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Mucosa: muscularis mucosae

  • Smooth muscle
  • Move mucosa layer creating ridges and valleys to facilitate absorption and secretion
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Submucosa

Dense irregular CT

Large blood vessels and lymphatic vessels

Meissner’s nerve plexus

  • Part of enteric nervous system
  • Controls smooth muscle of alimentary canal

Occasional glands

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Muscularis externa

2 concentric, thick layers of smooth muscle

  • Inner circular layer: mixes and compresses contents by constricting lumen
  • Outer longitudinal layer: propels contents by shortening of tube (peristalsis)

Thin layer of CT between muscle layers

  • Myenteric plexus (Auerbach’s): controls smooth muscle
  • Blood and lymphatic vessels

Variations of this layer occur along digestive tract

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Muscularis externa: differences along tract

  • Esophagus and anus have skeletal muscle that form sphincters
  • Esophagus contains skeletal and/or smooth muscle depending on segment
  • Stomach has a third oblique layer of smooth muscle that is deep to circular layer
  • Large intestine has thickened parts of longitudinal muscle layer that from 3 equally spaced bands called teniae coli
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Serosa and adventitia

Mesothelium and small amount of underlying CT

Continuous with mesentery and lining of abdominal cavity

Large blood and lymph vessels and nerve trunks

Large amounts of adipose tissue can develop here

Parts of tract without serosa (adventitia)

  • Thoracic part of esophagus
  • Portions fixed to cavity wall or neighboring organs
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Esophagus

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Mucosal layer with non-keratinized stratified squamous epithelium.

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Esophagus

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~25 cm long

Lumen normally in collapsed state

Mucosa of nonkeratinized stratified squamous epithelium

  • Diffuse lymphatic tissue and lymphatic nodules throughout lamina propria
  • Deep layer has muscularis mucosae with longitudinally arranged smooth muscle

Submucosa like described for GI tract in general; glands may be present

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Esophagus

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Muscularis externa: 2 muscle layers like most of canal

  • Upper 1/3 made of skeletal muscle
  • Middle 1/3 mix of skeletal and smooth muscle
  • Distal 1/3 made of smooth muscle

Adventitia comprises most of outer layer

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Esophageal glands proper

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  • Secrete slightly acidic mucus—stains pink to pale white
  • Protects mucosa
  • Aids in food passage
  • Located in submucosa
  • More located in upper ½ of esophagus
  • Small, compound glands
  • Excretory duct of stratified squamous epithelium
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Esophageal cardiac glands

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Located within lamina propria of mucosa

Mostly in terminal portion of esophagus

Secrete a neutral mucus (appears clear or white)

  • Protects mucosa
  • Aids in food passage

Resemble glands in cardiac portion of stomach

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Wall of upper esophagus

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skeletal muscle

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Lower esophagus

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  • Muscularis externa is entirely smooth muscle.
  • Serosa with mesothelium instead of adventitia.
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Stomach

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  • Cardiac region (cardia): part near esophageal orifice and contains cardiac glands
  • Fundic region (fundus) and body region: largest part of stomach, between cardia and pylorus, contains fundic/gastric glands; rugae are longitudinal folds to allow for distension
  • Pyloric region (pylorus): part proximal to pyloric sphincter and contains pyloric glands
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Esophageal-stomach junction: Cardiac portion of stomach

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  • Esophagus- Stratified squamous epithelium
  • stomach- Simple columnar epithelium
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Esophageal-stomach junction

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Stomach

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Stomach

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Gastric mucosa

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  • Inner surface has longitudinal folds called rugae
  • Gastric pits form openings with gastric glands emptying into bottom of pits
  • Simple columnar cells at surface secreting mucus (glandular sheet of cells)
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Fundic glands of gastric mucosa

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  • Simple, branched, tubular glands extending from bottom of gastric pits to muscularis mucosae
  • Several glands open into a single pit
  • Produce 2L/day of gastric juice (water, electrolytes, HCl, pepsin, mucus, intrinsic factor)
  • Produce gastrin and other hormones
  • Cell types: mucus neck cells, chief cells, parietal cells, enteroendocrine cells, and undifferentiated cells
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Fundic glands: mucus neck cells

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  • Produce soluble mucus
  • Located in neck of gland along side parietal cells
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Fundic gland: chief cells

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  • Produce pepsin (begin protein digestion)
  • Basophilc base (nucleus, rER, etc.)
  • Eosinophilic apical region (secretory granules)
  • Cuboidal cells in lower region of gland
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Fundic gland: parietal cells

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  • Large polygonal cells located in neck of fundic glands
  • Secrete HCl and intrinsic factor (vitamin B12 absorption)
  • Can be binucleate
  • Large cells with intracellular canalicular and tubulovesicular systems
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Fundic gland: enteroendocrine (DNES) cells

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  • More prevalent in base of gland
  • Rest on basal lamina but may not reach lumen
  • Clear cytoplasm with H&E stain
  • Produce peptide hormones
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Stomach: fundus and body

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Cardiac glands of gastric mucosa

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  • Only around esophageal orifice
  • Protects esophagus against gastric reflux
  • Mucus secreting cells with a few enteroendocrine cells
  • Flattened basal nucleus with apical cytoplasm filled with mucin granules
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Pyloric glands of gastric mucosa

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  • In pyloric antrum near junction with small intestine
  • Branched, coiled, tubular glands
  • Wide lumen
  • Secrete mucus and lysozyme
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Stomach: other layers

Mucosa: areas in addition to lining epithelium

  • Lamina propria
  • Sparse, only around gastric pits and glands
  • Reticular fibers with fibroblasts, smooth muscle cells, and immune cells
  • Occasional lymphatic nodules
  • Muscularis mucosae is same as rest of canal

Submucosa like the rest of the canal

Muscularis externa: 3 layers of muscle (inner oblique, middle circular, & outer longitudinal)

Serosa like the rest of the canal

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Pyloric-duodenal junction

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Small intestine

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Long, convoluted tube with 3 segments

Duodenum

  • ~25cm long
  • First, shortest, widest part of small intestine

Jejunum

  • ~2.5m long
  • Upper 2/5 small intestine after duodenum

Ileum

  • ~3.5m long
  • Lower 3/5 of small intestine
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Small intestine

  • Principal site of digestion and absorption
  • Duodenum receives chyme from stomach, enzymes from pancreas, and bile from liver/gallbladder
  • Enzymes are also located in the glycocalyx of microvilli of enterocytes (intestinal absorptive cells)—breakdown sugar and protein
  • Absorption of water and electrolytes in addition to sugar and protein
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Small intestine: modifications of submucosa and mucosa to increase surface area for absorption

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Plicae circulares

  • Permanent spiral folds that contain core of submucosa
  • Extend half to two-thirds around lumen
  • Decreased frequency in ileum

Villi

  • Fingerlike projections of mucosa into lumen
  • Completely cover surface of small intestine
  • Decrease in height toward ileum

Microvilli (brush border) with glycocalyx

  • Apical surface of enterocytes (mucosa)
  • Biggest increase in surface area for absorption
  • 1000s/cell
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Villi and intestinal glands

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  • Villi contain core of loose CT (extension of lamina propria).
  • Intestinal glands extend from muscularis mucosae to base of villi.
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Lamina propria of small intestine: GALT and Peyer’s patches (lymphatic nodules)

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Direct exposure to external environment. Therefore, a large percentage of lymphatic tissue found here.

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Cell types of intestinal mucosal epithelium (glands and villi)

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  • Stem cells: origin of all cell types at base of intestinal glands
  • Enterocytes (absorptive cells): absorption—most common
  • Goblet cells: unicellular mucus secreting glands
  • Paneth cells: secrete antimicrobial substances; base of glands
  • Enteroendocrine (DNES) cells: secrete paracrine and endocrine hormones
  • M cells: cover enlarged lymphatic nodules, antigen presenting cells
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Enterocytes

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  • Tall columnar cells with basally positioned nucleus
  • Microvilli on apical surface
  • Junctional complexes between cells
  • Membrane transporters for absorption
  • Secrete glycoprotein enzymes (glycocalyx), water, and electrolytes
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Goblet cells

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  • Produce mucus
  • Increase in number towards ileum
  • Apical cytoplasm appears empty in specimens
  • Distorts shape of neighboring cells with apical mucus cup
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Paneth cells

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  • Found in bases of intestinal glands
  • Basophilic basal cytoplasm
  • Large, intensely eosinophilic apical secretory granules
  • Lysozyme and defensins in granules (control bacteria)
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Enteroendocrine and M cells

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Enteroendocrine (DNES) cells

  • At all levels of intestinal gland and villi (most in lower portion)
  • Secrete peptide hormones that regulate secretion and absorption

M cells

  • Antigen transporting cells to underlying lymphatic nodules
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Small intestine: submucosa, muscularis externa, and serosa

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Submucosa

  • Localized aggregates of adipose tissue in the dense CT
  • Duodenum has submucosal glands (Brunner’s glands)

Muscularis externa and serosa have same features of general digestive tract

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Duodenum

Shortest segment

Broad, tall, and numerous villi

Fewer goblet cells

Brunner’s glands present in submucosa

  • Mucus and bicarbonate ions protect mucosa from acidic chyme entering from stomach
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Duodenum

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Brunner’s glands in submucosa are distinctive feature of this segment.

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Jejunum

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  • Villi are shorter, narrower, and less numerous
  • Increased number of goblet cells
  • NO Brunner’s glands
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Jejunum

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Plica circulares and villi are distinctive features of this segment.

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Ileum

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Fewest number of villi

  • Short and narrow

Most goblet cells

Peyer’s patches

  • Aggregations of large lymphatic nodules
  • Covered by M cells
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Ileum

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Peyer’s patches and short villi are distinctive features of this segment.

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Large intestine

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Cecum (with appendix), colon, rectum, and anal canal

Distinctive features

  • Muscularis externa has outer longitudinal layer arranged into 3 thickened bands (taeniae coli)
  • Bulges/sacks called haustra between taeniae
  • Mucosa is smooth (no plicae circulares or villi)
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Mucosa

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  • Numerous, straight, tubular glands throughout full thickness of mucosa (mucus)
  • Simple columnar epithelium
  • Reabsorb water and electrolytes
  • No paneth cells but all other types in small intestine also here
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Lamina propria

Same basic components as rest of canal

Distinctive features

  • Well-developed GALT: large lymphatic nodules that distort mucosal surface and extend into submucosa
  • No lymphatic vessels in lamina propria core
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Wall of large intestine

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Colon

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Presence of taeniae coli and lack of villi are distinctive features of this segment.

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Cecum and appendix

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Cecum is blind pouch distal to ileocecal valve connects to small intestine

Appendix is a fingerlike extension of cecum

  • Uniform layer of longitudinal muscle in muscularis externa
  • Large number of lymphatic nodules
  • Less glands than colon
  • In adults may just be fibrous scar tissue
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Appendix

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Rectum

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  • No taenia coli
  • Covered with adventitia
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Anorectal junction

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Rectum lined with simple columnar epithelium

Anus lined with stratified squamous epithelium

  • No submucosa, just lamina propria

Skeletal muscle present in anus (voluntary sphincter)

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Anorectal junction

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Anorectal junction

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Digestive System III

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Accessory organs that lie outside main digestive tract.

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Accessory organs of the digestive system

  • Liver
  • Gallbladder
  • Pancreas
  • Salivary glands
  • The liver, gallbladder, and pancreas deliver their secretory products to the small intestine via excretory ducts, while the salivary glands deliver their secretory products to the oral cavity via excretory ducts.
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Liver

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The liver is divided into hexagon-shaped lobules

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Liver

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  • Largest gland and internal organ
  • 4 lobes that are further divided into lobules, which are separated by CT septa
  • Lobules are repeating hexagonal units
  • Hepatocytes (liver cells) arranged into cords (plates) radiating outward from a central vein (cords are 1 cell in width)
  • Sinusoids fill spaces between cords of hepatocytes
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Liver functions

  • Receives all liquids and nutrients absorbed from intestines
  • Produces plasma proteins
  • Storage and conversion of vitamins (A, D, K)
  • Storage, metabolism, and homeostasis of iron
  • Degradation of drugs, toxins, and foreign proteins (via oxidation and conjugation)
  • Glucose metabolism (glycogen formation)
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Liver functions

  • Lipid metabolism (oxidation of fatty acids)
  • Synthesis and uptake of cholesterol
  • Converts ammonium ions to urea
  • Synthesis and conversion of nonessential amino acids
  • Produces bile
  • Modifies structure and function of hormones (vitamin D, thyroxine, growth hormone, insulin, and glucagon)
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Hepatocytes

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  • Large, polygonal cells
  • Nuclei are large, spherical, and in center of cell
  • Acidophilic cytoplasm (stain with eosin—pink)
  • Capable of regeneration
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Blood supply to liver from portal triad

Venous (portal) supply via the hepatic portal vein

  • 75% of blood supply to liver
  • Comes from intestines, pancreas, and spleen
  • Depleted of oxygen
  • Liver first organ to receive metabolic substrates and nutrients—filtration

Arterial supply via the hepatic artery

  • 25% of blood supply to liver
  • Oxygenated blood

Blood distributed to hepatocytes via sinusoids flowing toward central vein in lobule

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Classic liver lobule

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  • Repeating hexagonal unit: based on distribution of branches of portal vein and hepatic artery
  • Portal triads within portal canals form corners of hexagon
  • Sheets of hepatocytes separated by sinusoids
  • Blood flows from portal triad toward central vein
  • Bile flows from hepatocytes at central vein out toward portal triad
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Plates/cords vs. sinusoids

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Reticular fibers organize hepatocytes into plates/cords

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Kupffer cells (sinusoidal macrophages)

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Kupffer cells line sinusoids. They destroy erythrocytes, recycle iron, and get rid of foreign substances.

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Bile

Adult secretes about 1L/day

  • Water
  • Phospholipids and cholesterol
  • Bile salts: emulsifying agents
  • Bile pigments: detoxify bilirubin
  • Electrolytes

Secretion controlled by nervous system and hormones

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Gallbladder

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Pear-shaped sac that holds about 50 mL bile

  • Storage
  • Concentrates

Attached to visceral surface of liver

Contractions releases bile into common bile duct and delivered to duodenum

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Gallbladder

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  • Deep folds in mucosa in empty gallbladder
  • Mucosal surface of simple columnar epithelium with short microvilli
  • Lamina propria rich in fenestrated capillaries and small venules with lymphocytes and plasma cells
  • No muscularis mucosae or submucosa
  • Thick serosa/adventitia outside of muscularis externa
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Gallbladder: NO muscularis mucosae or submucosa

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Mucosa

  • Simple columnar epithelium (Ep)
  • Lamina propria of loose connective tissue (CT)

Smooth muscle (SM) of muscularis externa

Connective tissue of serosa/adventitia

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Gallbladder concentrates bile

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1.Epithelial cells of gallbladder actively transport Na, Cl, and HCO3 ions from the cytoplasm to intercellular space across lateral plasma membrane

2.Water moves from lumen of gallbladder to dilute high concentration of ions in interstitial space, concentrating bile solution remaining in lumen

3.Excess fluid and ions within interstitial spaces are taken up by fenestrated capillaries underneath epithelium

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Pancreas

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  • Elongated gland behind stomach
  • Main pancreatic duct extends through length of gland and empties into duodenum
  • Thin layer of loose CT forms capsule around gland and septa that divide gland into lobules
  • Exocrine and endocrine components
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Exocrine pancreas

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Serous gland with numerous acini

  • Acidophilic granules in apical cytoplasm

Produce digestive enzyme precursors

  • Endo- and exopeptidases, amylolytic enzymes, lipases, and nucleolytic enzymes
  • Activated in small intestine by enzymes in glycocalyx of enterocytes
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Endocrine pancreas

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  • Islets of Langerhans’ are groups of endocrine cells found throughout pancreas
  • Polygonal cells within a network of fenestrated capillaries
  • With H&E, the cells are pale surrounded by the more intensely staining exocrine acini
  • 3 types of cells (A, B, D) secrete hormones
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Pancreatic hormones: regulate metabolic functions

Insulin (B cells)

  • Decrease blood glucose levels
  • Increase uptake, storage, and use of glucose (liver, skeletal muscle, and adipose)
  • Stimulates glycerol synthesis
  • Inhibits lipase activity

Glucagon (A cells)

  • Increases blood glucose levels
  • Increases proteolysis
  • Increases mobilization of fatty acids

Somatostatin (D cells)

  • Inhibits insulin and glucagon secretion
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Pancreas: islets vs. acini

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The islets of the pancreas are generally lighter stained when compared to the acini. The islet cells are smaller and integrated among capillaries. The acini are connected to excretory ducts.

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Pancreas: islets (IL) vs. acini (Ac)

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Salivary glands

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  • In tissue surrounding oral cavity, excretory ducts transport secretions into oral cavity
  • Parotid glands
  • Submandibular glands
  • Sublingual glands
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Secretory gland acini and ducts

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  • Acinus: blind sac of secretory cells (serous, mucus, or both) & myoepithelial cells
  • Intercalated ducts
  • Striated ducts
  • Excretory ducts
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Acinar cells

Serous cells (secretory)

  • Pyramidal shaped
  • Round nuclei near basal portion of cell
  • Numerous spherical secretory granules (protein secretion) in apical cytoplasm (eosin)

Mucus cells (secretory)

  • Mucus secretion stored in granules filling cells
  • Flattened nuclei at basal surface of cell

Myoepithelial cells

  • Contractile cells with numerous processes between secretory cells and basal lamina
  • Move secretory products toward excretory duct
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Salivary ducts

  • Increase in size as leave acini
  • Intercalated duct: leads directly from acinus lined with simple cuboidal epithelium (small lumen)
  • Striated duct: merger of intercalated ducts, has basal infoldings of plasma membrane of simple columnar epithelial cells
  • Excretory intralobular duct: simple to stratified cuboidal epithelium and surrounded by CT
  • Interlobular and interlobar ducts: empty into oral cavity, lined with stratified cuboidal epithelium (largest)
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Salivary ducts modify secretions

Intercalated ducts

  • Secrete bicarbonate ions
  • Absorb chloride ions

Striated ducts

-Basal infoldings allow for:

  • Reabsorption of sodium ions
  • Secretion of potassium and bicarbonate ions
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Salivary gland structure

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Parotid gland

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  • Largest
  • Paired
  • Compound tubuloacinar gland
  • Serous gland (stains with eosin)
  • Located below and in front of ear
  • Large amounts of adipose tissue within gland
  • CT capsule creates septa forming lobules
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Parotid gland

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The lack of islets distinguishes the parotid gland from the pancreas.

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Submandibular gland

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  • Paired
  • Compound tubuloacinar gland
  • Mixed gland (mostly serous)
  • Mixed acini push serous cells to outside of acinus forming crescent (serous demilune)
  • Floor of mouth near mandible
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Submandibular
gland

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  • Individual serous (majority) or mucus (few) acini.
  • Mixed acini with serous secretory cells (demilunes) surrounding mucus secretory cells.
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Sublingual gland

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  • Smallest
  • Aggregates of small glands
  • Mixed glands (mostly mucus) with serous demilunes
  • Compound tubuloacinar gland
  • Floor of mouth anterior to submandibular gland
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sublingual gland

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Mostly mucus acini, but some are mixed with serous demilunes.

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Saliva

  • Combined secretions of all salivary glands
  • 1 L/day
  • Calcium and phosphate ions for tooth development and maintenance
  • Antibodies and other antibacterial agents to slow down tooth decay
  • Water (majority), proteins, glycoproteins, and electrolytes
  • High potassium and bicarbonate and low sodium concentrations
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Functions of saliva

  • Moistening of oral mucosa
  • Moistening of dry foods for swallowing
  • Solvent to dissolve foods to stimulate taste buds
  • Buffer contents of oral cavity
  • Contains amylase to digest carbohydrates
  • Contains lysozyme to kill certain bacteria in oral cavity
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Urinary System

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Urinary system

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Kidney functions

Maintain homeostasis!

  • Conserve water, electrolytes, and metabolites
  • Remove waste products of metabolism (urine)
  • Maintain composition and volume of extracellular fluid
  • Maintain acid-base balance (secretion of H+ or HCO3-)

Endocrine organ

  • Erythropoietin: erythrocyte production
  • Renin: blood pressure and volume regulation
  • Hydroxylation of Vitamin D3: Ca+2 regulation
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Structure of kidney

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  • Hilum: where blood vessels, nerves, and ureters enter kidney
  • Capsule made of dense irregular CT
  • Renal pelvis collects urine from collecting ducts and funnels them into ureter
  • Cortex and medulla
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Cortex vs. medulla

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  • Cortex: renal corpuscles, convoluted and straight tubules, collecting tubules and ducts, vascular supply
  • Medulla: straight tubules, collecting ducts, and vasa recta
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Cortex vs. medulla

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Nephron: renal corpuscle (cortex) and renal tubules (cortex & medulla)

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  • Structural and functional unit of kidney
  • Each kidney contains about 2 million nephrons
  • Produces urine from ultrafiltrate of blood by secretion and reabsorption along tubules
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Kidney tubule function

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  • Filtration: All substances except proteins & cells
  • Reabsorption: water, Na+, bicarbonate, and glucose
  • Secretion: creatinine & organic acids/bases
  • Excretion: filtered substances not reabsorbed + secreted substances
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Nephron Cortex Structures: Renal Corpuscle With Glomerulus & Renal Tubules

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Nephron Medulla Structures: Renal Ducts and Tubules

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Pathway Through Nephron Tubules

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Proximal convoluted tubule

  • Where most reabsorption takes place due to specializations of tubule cells (microvilli & basal infoldings)

Loop of Henle

  • Concentrates urine

Distal convoluted tubule

  • Reabsorb Na+ and excrete H+ and K+

Collecting duct

  • Water reabsorption (regulated by aldosterone and antidiuretic hormone (ADH))
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Types of nephrons: based on corpuscle location

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  • Cortical: corpuscles in outer part of cortex with short Loops of Henle
  • Juxtamedullary: corpuscles near medulla with long Loops of Henle (concentrate urine)
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Filtration apparatus

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  • Endothelium of glomerular capillaries
  • Glomerular basement membrane (endothelium and podocytes)
  • Podocyte foot processes and filtration slits
  • Limits substances filtered by size
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Mesangial cells

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Form juxtaglomerular apparatus and some found in glomerulus

Phagocytosis

Structural support

Secretion

  • Synthesize ECM
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Juxtaglomerular apparatus

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  • Regulates blood volume & blood pressure by monitoring filtrate volume & Na+ concentration
  • Macula densa of distal tubule near glomerulus (regulates filtration rate and renin release)
  • Juxtaglomerular cells near afferent and efferent arterioles (sensor of blood volume)
  • Extraglomerular mesangial cells
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Blood supply with portal system

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Urine collection and excretion

Ureter: tube from kidney to bladder

Urinary bladder: reservoir for urine

Urethra: tube exiting body

Walls have 3 layers (Digestive system had 4 layers)

  • Mucosa (with transitional epithelium and lamina propria)
  • Muscularis (2-3 layers of smooth muscle cells mixed with CT)—inner layer is longitudinal vs. circular in the digestive tract
  • Adventitia (often adipose tissue; blood vessels and nerves travel here)
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Transitional epithelium of ureters, bladder, and urethra

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Ureter

Mucosa folded when ureter is undistended

  • Transitional epithelium
  • Thick lamina propria

Muscularis: 2-3 layers of smooth muscle

Adventitia: loose to dense irregular connective tissue

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Ureter wall

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Mucosa folded when ureter is undistended

  • Transitional epithelium
  • Thick lamina propria

Muscularis: 2-3 layers of smooth muscle

Adventitia: loose to dense irregular connective tissue

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Urinary bladder

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Mucosa folded when bladder is undistended

  • Transitional epithelium
  • Thick lamina propria

Muscularis: 3 layers of smooth muscle

Adventitia or Serosa: loose to dense irregular connective tissue

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Relaxed Bladder

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stretched bladder

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