Gastrointestinal tract and glands Flashcards
Development of the GI tract
- 4th week: gut tube with three Segments from endoderm
Endoderm just gives rise to epithelium
1- foregut
2- midgut
3- hindgut
Four laysers of GI tract
Mucosa
Submucosa
Muscularis Propria
Adventitia/Serosa
Mucosa
- Epithelium
- lamina propria
- muscularis mucosae
Basic mucosal types in GI tract
- Protective (oral, esophagus, anal canal, stomach, colon) –> stratified suquamous
- Absorptiv (small intestine, colon) –> simple cplumnar
- Secretory (stomach, small intestine, colon) –> tubular Glands and crypts
- Mixed:absorptive/protective in colon; secretory/protective in stomach
Submucosa
- loose CT with nerves, vessels, ganglia
+ Glands in esophagus and Duodenum
+ lymph nodules in Ileum and appendix
Muscularis propria
Inner circular layer
Outer longitudinal layer
layers are separated by loose CT
Adventitia or serosa
Adventitia: loose CT, everyhting that is not covered by peritoneum
Serosa: loose CT and Mesothelium, ecerything that is covered by Peritoneum)
Nerve Plexus and ganglia
Submucosal (Meissner’s Plexus): contraction of muscularis mucosae and secretory activity of Glands
Myenteric (auerbach’s) plxus: contraction of muscularis propria
Esophagus
Mucosa:
- stratified suqamuos non-keratinized
- lamina propria mucosae with cardiac Glands in lower part
- muscularis mucosae
Submucosa:. loose CT with Glands
Muscularis propria:
inner circular
outer longitudinal
Adventitia (and Serosa below diaphragm)
Stomach
function: to produce chime
Mucosa:
- simple columnar with pits and Glands
- lamina propria with glands
- lamina muscularis
Submucosa
Muscularis propria:
inner oblique
middle circular
outer longitudinal
Serosa
3 types of Glands in stomach
- cardiac Glands
- gastric Glands
- Pylroic glands
Cardiac Glands in stomach
- tubular, sometimes branched
- in lamina propria and open into pits
- mostly mucous cells
look at picture
Gastric glands
- tubular
- several Glands open into one pit
- cells:
>Stem cells (in neck)
>Mucous neck cells
>Parietal cells (have micorvilli, secrete HCl and intrinsic factor)
>Chief cells: in lower portions, secretes pepsinogen
>Enteroendocrine cells (belong to DNES, in base, secrete Hormones)
Diffuse neuroendocrine system
- throughout GI tract
- cells secrete into blood vessels of CT not into the lumen
- derived from neural crest
Hormones:
- Gastrin
- Somatostatin
. Vasoactive intestinal pepitde
Pyloric glands
- tubular and branched
- Deep and Broad pits
- mucous and enteroendocrine cells
Small intestine
Mucosa:
- simple columnar
- lamina propria
- lamina muscularis
Submucosa:
- loose CT
+ Glands in Duodenum
+ lymphoid nodules in Ileum
Muscularis externa:
inner circular
outer longitudial
Serosa or Adventitia
Structures of mucosa in small intesine
plicae
villi
crypts
microvilli
Villus
- fingerlike projections
- core of lamina propria
- enterocytes with microvilli –> striated border
Crypts in small intestine
- simple clumnar Epithelium invaginations
. crypts are Shorter than villi
Small intesine epithelial cell types
Enterocytes: columnar with microvilli, glycocalyx, membrane Digestion and absorption
Goblet cells: produce mucus
Enteroendocrine cells: produce hormones
paneth cells: at base of crypts, secrete lysozyme and defensins
Stem cells: base of crypts
M cells: above lymph nodes in Ileum, pressent Antigen to lymphoid cells
Regional differences in mucosa in small intestine
Duodenum: Brunners Gland in submucosa
Jejunum: no Glands, no nodules
Ileum: Peyer’s pathces –> Aggregates of lymphoid nodules in submucosa
Large intesine
Parts: cecum, colon, rectum
Mucosa:
- simple columnar with crypts
- lamina propria
- lamina muscularis mucosae
Submucosa:
Muscularis propria:
thick inner circular
3 separate longitudianl bands –> taniae coli
Advdentitia or serosa
Epithelial cells in large intestine
Goblet cells
Enterocytes
Stem cells
Enteroendocrine cells
Appendix
colonic mucosa
lymphoid nodules in submucosa
Rectoanal jucntion
from simple columnar to stratified squamous
Muscularis mucosa disappears!!
Circular muscular layer gives the internal anal sphincter
Functions of saliva (7)
- Lubrication
- Taste
- Initiates Digestion
- Controls bacterial flora
- Defense
- Buffers Content
- Source of Ca and Ph
Organization of Major salivary gland
Capsule –> dense irregular CT
Septa –> loose CT, divide Glands in lobes and lobules
Stroma and Parenchyma of lobule
Stroma: loose CT from Mesenchyme
Parenchyma: epiheltial tissue from primitive mouth ectoderm
Major salivary Glands are…
branches and compound
Types of secretory units
serous
mucous
mixed
Serous cells
- stain basohilic
- round nucleus, in lower part of cell
- secretory granules in apical part
- watery secretion rich in Enzymes, proteins, ions
Mucous cell
- stain pale
- nucleus pressed to the base
- cytoplasm full of mucigen granules
Forms of secretory units
Acinar: each acinus is composed mostly of serous cells
Tubular: each tubule is composed mostly of mucous cells, serous cells could be at end
Duct System of Major salivary glands
Intercalated duct (within lobule) Striated duct (within lobule) Excretory duct (interlobular, interlobar, common excretory duct, oral cavity)
Intercalated duct
- small Diameter
- suquamous or low cuboidal Epithelium
- Functions: they secrete HCO3, absorb Cl-
Straited duct
- large Diameter
- columnar Epithelium
- basal striations (Plasma membrane infoldings)
- secrete HCO3, K+, absorb Na, Cl
Excretory ducts
as Diameter enlarges:
pseudostratified –> stratified columnar –> stratified suqamous
Myoepithelial cells
- between epithelial cells and b.m.
- ectodermal origin
- flattened, Long processes
- during contraction, force secretion from secretory unit into duct system
Parotid gland
- largest Gland
- makes only 25% of saliva
- acini with serous cells
- Long intercalated ducts
- large striated ducts
- much adipose tissue
Submandibular gland
- makes 65%
- acinar or tubular, serous or mixed
- more serous cells than mucus
- some serour cells form serous demilunes
- good developed branched striated ducts
Sublingual gland
- tubular or acina, serous or mixed
- mucous cells predominate over serous
- poorly developed intercalated and striated ducts
Pancreas
- Capsule: dense irregular CT with Septa (loose CT)
- Stroma: loose CT
- Parenchyma: epithelial tissue
- exocrine and endocrine part
- Epithelium from endoderm and CT from mesenchyme
Types of acini in exocrine pancreas
simple
compound
simple acinus
regular round shape
serous cells
into intercalated duct
Acinar cell
- central nucleus
- basophilic basal part
- apical part full of granules
Compound acinus
- irregular shape
- composed of acinus and centroacinar cells
- when intercalated duct invaginates into lumen of simple acinus
- in exocrine part of pancreas
Centroacinar cells
- invaginated cells of intercalated ducts
- more pale nuclei in Center of acinus
System of pancreatic ducts
intercalated ducts –> interlobular ducts –> principal and accessory duct –> Duodenum
- from simple cuboidal Epithelium to simple columnar
Endocrine part of pancreas
- islet of Langerhans
- islets are scattered throughout the organ in cell Groups of varying size
Endocrine cells of pancreas
- polygonal cells invested by capillaries
- 3 main cell types:
> Beta cells: most abundant, centrally, Insulin
>Alpha cells: peripheral, glucagon
>Gamma: peripheral, Somatostatin
other cells secrete pancreatic polypeptide
Liver functions (6)
- Haemopoiesis (in fetal period)
- Metabolism
- Synthesis and secretion of bile
- Detoxification
- Storage of glycogen, Lipids, Vitamins…
- storage of blood
Classic lobule in liver
Central vein in Center
Portal triad in apices of lobue
look at drawing for other types of lobules!!!
Stroma and parenchyma of liver
- Stroma: reticular CT
- Parenchyma: epitheliual cells (hepatocytes)
Hepatocytes
- large
- polygonal
- 1 to 2 nuclei
- rich in organelles and inclusions
- arranged in hepatic plates
Hepatic plate
- 1 to 2 cells thick
- radiate towards central vein
- separated by vascular sinusoids
Vascular sinusoids
- Sinusoidal capillaries between hepatic plates
- large Diameter
- mixed blood in lumen
Wall of sinusoids in liver
- discontinuous epithelial cells with pores
- Discontinuous b.m.
- Kupffer cells between endothelial cells
Kupffer cells
- stellar macrophages
- phagocytosis of spent erythrocytes and other debris
- from monocytes and belong to MPS
Space of Disse
- between each hepatic plate and sinusoid
- filled with blood Plasma
- allows Absorption of nutirents into blood
- in fetal liver: contains Islands of blood-forming cells
- Postnatal period: contains few CT fibers and Ito cells
Ito cells
- fat storing
- stellate cells –> are modified pericytes
- accumulate Vitamin A
- when Liver is damaged, differentiate into myofibroblasts
Bile canaliculi
- small Diameter
- between hepatocytes
- wall is formed by incurvation of Plasma membrane
- Transport bile produced by hepatocytes
- drain bile into canals of Hering
Canals of Hering / bile collecting ducts
- near Portal triads but still within lobule
- hepatocytes and cholangiocytes (simple cuboidal)
- drain into interlobular bile ducts
Portal triad
- interlobular artery (branch of hepatic artery)
- Interlobular vein (branch of hepatic Portal vein)
- Interlobular bile duct (simple cuboidal)
- lymphatic vessel
Portal lobule
- axis: interlobular bile duct
- outer margins are imaginary lines drawn between 3 central veins
- blood flows from Center to the periphery, bile from periphery to the center
look at drawing!!
Portal acinus
- rhomb-shaped
- short axis of acinus is between 2 Portal triads
- Long axis between 2 central veins
- 3 zones:
>Central(closest to short axis and blood supply)
>Intermediate
>Peripheral (closest to central vein and receives least Oxygen)
Gallbladder
- stores and concentrated bile
Mucosa:
- simple columnar Epithelium with convoluted folds
- Lamina propria with occasional mucous Glands
- no lamina muscularis mucosae
Submucosa is absent or loose!!!
Muscularis externa:
- interlacing myocytes (longitudinal, trnasverse, oblique)
Serosa in lower Surface
Adventitia in upper Surface)
