Microanatomy Flashcards
what are the normal functions of the GI system
- absorption of nutrients from ingested food
2. protection against ingested pathogens
what are the 4 phases of nutrient abospriton
fragmentation
digestion
absorption
elimination
describe fragmentation
- this starts in the oral cavity
- it is aided by saliva
- continues in the stomach and small intestine
describe digestion
- starts int he mount
- continues in the stomach and small intestine
- aided by salivary, gastric and pancreatic secretions, enzymes associated with the brush border of enterocytes and bile salts
describe absorption
- occurs in the jejunum and ileum and is facilitated by the large surface area of these regions and microvilli on enterocytes
- capillaries and lacteals transport absorbed nutrients away from the mucosa
describe elimination
- by defacation of solid faeces occurs after absorption of water in the large intestine
what is the basic structure of the alimentary tract
- basically is an muscular tube with the same basic structure though the length
what are the 4 basic layers in the alimentary tract
- mucosa
- submucosa
- muscularis propria
- adventtia or serosa
what is the mucosa compromised of
- epithelium
- lamina propria
- muscularis mucosa
it varies between regions and changes abruptly at several places for example at the oesophageal gastric junction
describe the submucosa
- loose connective tissue that carries blood and lymphatic vessels and nerves
- ganglion cells found in clusters here form the submucosal (meissner’s) plexus of the enteric nervous system and supply parasympathetic innervation to control the muscularis mucosa, glandular secretion and local blood flow
describe the muscualris propria (externa)
- compromised of an inner circular layer and an outer longitudinal smooth muscle layer
- intrinsicu muscle contractions are responsible for peristalsis
- ganglion cells of the myeternic (Auerbach’s) plexus are found between the muscle layers and modulate muscle activity
describe the adventitia or serosa
- when the alimentary tract is located int he peritoneal cavity it is covered by a mesothelium which is supported by a thin loose connective tissue (serosaa)
- in other areas an outer connective tissue layer called the adventitia connects it to underlying tissues, major vessels and nerves travel in this layer
where are vili only found
- only found in the small intestines only
what does the lamina propria do
- supports the epithelium
describe the lamina propria
- very cellular
- has fibroblasts that make the supportive fibrocollagenous extracellular matrix
- has defence cells such as lymphocytes and plasma cells
- it is part of MALT (mucosa associated lymphoid tissue)
- smooth muscle comes up into the villus from the underlying muscularis mucosa, this smooth muscle moves the villus and increases its contact with the watery digesting food in order to aid further digestion and absorption
where does nutrient abospriton occur
small intestine
what happens to the absorbed nutrients
- ## they are carried away in capillaries and lymphatic vessels called lacteals, these carry materials away
what does the smooth muscle do in the lamina propria
- smooth muscle comes up into the villus from the underlying muscularis mucosa, this smooth muscle moves the villus and increases its contact with the watery digesting food (watery digestive food is called chyme) in order to aid further digestion and absorption
what does the oesophagus do
- it conveys food from the oropharynx to the stomach
describe the structure of the oesophagus
- it is lined by stratified squamous epithelium in order to resist abrasion
- has slightly more collagen in its lamina propria and a thicker muscularis mucosa
- glands are found along the length of the oesophagus to secrete mucus to help keep it lubricated
describe the muscles of the oesophagus
- imitation of swallowing is voluntary
- involves the skeletal muscle of the oropharynx
- upper 1/3 of the oesophageal muscularis externally is also comprised of skeletal muscle
- the lower 1/3 of the muscularis external is comprised of only smooth muscle
- in the middle part the oesophagus, skeletal muscle mixes with the smooth muscle
what happens when the oesophagus is relaxed
- deeply folded
- can accomodualte a bolus of food passing down it
what does the outermost loose connective tissue do to the oesophagus
- supports and protects it by anchoring to other structures in the mediastinum
what colour is the normal oesophageal mucosa
white due to the thick stratified squamous epithelium
describe the mucosa of the stomach
- the mucosa of the stomach is glandular
- has tubular glands that extend downwards from the surface
- in both the cardia and pylorus they secrete protective mucus
- fundus and body glands secrete acid and pepsin in addition to the mucus
what is the glandular make up of the cardia
secretion - mainly mucus
cell type - mucus neck cells
what is the glandular make up of the fundus
secretion
- mucus
- HCL pH 1 and intrinsic factor, pepsin
- gut hormones
cell type
- mucous neck cells
- parietal cells
- chief cells
- endocrine cells
what is the glandular make up of the pylorus
secretion
- mainly mucus
- gut hormones including gastrin
cell type
- mucous neck cells
- endocrine including G cells
the gastric pit is the..
opening of the gland and it is lined by surface mucous cells
- in the bases there are mainly pepsinogen secreting chief cells
what is the oesophageal gastric junction
- this is the place where the oesophagus enters the stomach
describe the structure of the small intestine
- same structure as the rest
- in order to continue digestion and absorb nutrients from the digested food it posses several adaptations to increase its surface area
- these include fingerlike villli and larger folds called place circulates v
- the enterocytes also have microvilli that act to increase each cells digestive absorptive surface
what are intestinal cells called
enterocytes
how long is the small intestine
4-6m
enterocytes make up….
the majority of the simple columnar epithelial cells
what do the enterocytes do
- they continuous digestion of food by having enzymes incorporated into their apical plasma membranes
- absorb nutrients and water from digestive food
what do goblet cells do
- lubricate the passage of good
- mucus protects the small intestines like it does in the stomach from auto digestion
what does peridocia cid ship stain
- stains carbohydrates red
- labels the goblet cell mucin which is highly glycosylated and the enterocyte microvilli which have a glycocalyx, a coating of glycoproteins and polysaccharides that protects against auto digestion and binds to digestive enzymes to the enterocyte surface enabling the final stages of digestion of carbohydrates and proteins
what are the major cells of the lining epithelium of the small intestine
the enterocyte and goblet cell
What are the small intestine glands that extend deeper into the lamina propria from the bases of the vili
crypt of LieberKuhn
where is the enterocyte located and what is its function
Located
- lining villus
- in crypt
function
- lining villus - digestion using brush border enzymes, absorption
- in crypt - secretion of watery intestinal juice, mainly water and enteropeptidase that activates pancreatic trypsin
where is the goblet cell located and what is its function
located
- scattered along villus between enterocytes, increased numbers distally
function - mucus secretion for protection/lubrication
where is the endocrine cell located and what is its function
located
- crypt
function - regulation of gut function
where is the stem cell located and what is its function
located
- crypt
function - regeneration of the epithelium
where is the paneth cell located and what is its function
located
- crypt
function - antimicrobial agent's, defensives, lysozyme, these regulate the bacterial content of the intestine
what do crypt cells include
- include stem cells that divide and form daughter cells that move up the villus and differentiate to replace the villus epithelium
what is the lifespan of enterocytes and goblet cells
3-5 days
what do enteroendocrine cells do
- release hormones including secretin and cholecystokinin and are found in crypts
describe what happens in coeliac disease
- this is when the immune system reacts to gliadin, which is present in wheat
- antibodies in the blood can confirm this
- the immune reaction acts to destroy the mucosa of the small intestine which causes the loss of enterocytes and the entire vili
- the stem cells in the crypts try to replace the damaged cells resulting in elongation of the glands
- there are increased intrapeithelial lymphocytes
- increase lymphocytes and plasma cells in the lamina propria
describe the structure of the large intestine
- along most of the large intestine except the rectum and appendix, the longitudinal smooth muscle of the msucarulis external is collected in three bands called Tania coli
- intestinal glands and crypts make up some of the mucosa
- there are no vili
- glands are longer than the small intestine
- glands contain both enterocytes for absorption of mainly water and goblet cells to provide protective mucus
