Digestion 3: pancreas to anus Flashcards
What is the exocrine function of the pancreas
The pancreas makes precursors of digestive enzymes (that digest proteins, carbs, lipids and nucleic acids) in secretes them in an alkaline juice which goes to the duodenum through a duct system
What is the endocrine function of the pancreas
Has islets of langerhans which secrete insulin and glucagon for glucose homeostasis
Is the spleen part of the digestive system
no
describe the path of the pancreatic juice from point of secretion to the main pancreatic duct
It originates from serous type secretory cells arranged in a unit called Acinus (leaf) opening to an intercalated duct (twig). These join interlobular ducts (small branches) which lead to the trunk (main pancreatic duct).
What is the order of things added to the duodenum for digestion and where do they come from
- Chyme from the stomach connects directly through pyloric sphincter
- Bile from the liver is either released into the common bile duct from the gall bladder where it has been concentrated or just straight from the liver
- Prancreatic juice containing precursors go through the main pancreatic duct
Describe the 3 regions of the small intestine describe the main function of the small intestine
- Duodenum
2.Jejunum - Ileum
Main function is the most digestion and absorption. Its upper end (duodenum) also receives secretions from the liver, pancreas as well as the chyme from stomach
What are the differences in the gut tunics for the small intestine
- Mucosa: is specialised to greatly increase surface are available for secretion
- Submucosa just downstream of the pyloric sphincter contains Glands of Brunner which secrete HCO3 rich mucous which neutralises acidic chyme and buffers to optimise pH for pancreatic enzymes.
What are the modifications done to increase surface area in the small intestine (big to small)
- Gross convolutions
- Plicae (circular folds that are permanent wrinkles. Each plica has a core of submucosa covered in mucosa
- Villi (made of lamina propria covered by epithelium
- Microvilli (extensions of cell membrane making the brush border on individual absorptive cells).
What are the epithelial cells in the villus of the small intestine and what do they do
- Columnar absorpative cells (enterocytes) which absorb the molecules from digestion
- Goblet cells: that secrete mucus
What are the epithelial cells in the intestinal glands mucosa of the small intestine and what do they do
- Undifferentiated cells (for generating new epithelium)
- Enteroendocrine cells: secrete hormone secretin into the capillaries of the lamina propria
- Paneth cells: secrete bacteriocidal enzyme lysozome and phagocytose
Where are the digested carbohydrates, proteins, water and electrolytes transported compared to lipids
They go to venules in the submucosa which are tributaries of the hepatic portal veins.
The lipids are transported by the lymphatic vessel (also goes to the submucosa) in each villi which eventually drain into the venous system
How are the epithelial cells on the villus of the small intestine replaced
Cell division occurs deep in the intestinal glands then the entire sheet (except Paneth cells) moves slowly up the gland walls and up the sides of the villi because old cells are shed from the tip.
What stimulates the release of secretin from what cell and what does it do
Secretin release from enterendocrine cells is stimulated by arrival of acid chyme. It stimulates the release of pancreatic juice. Cholecystokinin from the same cells is released in response to amino acids and also stimulates pancreatic juice + bile release.
What is special about the lymph vessel in villus of the small intestine
They are lacteal- meaning that Lymph is milked by contraction of the smooth muscle which shorten the villus. These smooth muscle fibres are in the lamina propria and arise from the muscularis mucosae
List the 7 regions of the large intestine
Cecum, Ascending colon, transverse colon, descending colon, Sigmoidal colon, rectum, anus
What are the main functions of the large intestine
- Absorption of salts and water (but still less than small intestine)
- Conversion of chyme into feces with remaining carbs fermented by bacteria
- Production of some vitamins B&K which are absorbed
- Secretion of mucus to lubricate feces
- Defecation
What controls the flow of chyme from the ileum into the cecum
ileocecal valve
What is the cecum structure and function
Dilated pouch containing Bacteria (not enzymes) for digestion. Humans have none for digestion of cellulose
What is the structure and function of the appendix
Vestigal worm like appendage of the cecum which contains lymphatic tissues
What is the final composition of feces
- Bacteria 30%
- Undigested dietary fibre 30%
- Cells shed from the intestinal lining and mucus
What is the colour of the feces from
the bacterial decomposition of bilirubin
What are the special features about the Mucosa of the large intestine
- No villi but many intestinal glands
- surface epithelial cells that are enterocytes (absorpative
- intestinal glands containing mostly goblet cells but not paneth (no more digestion)
- Many clusters of lymphocytes in the lamina propria
- cell renewal like small intestine- replaced every 5 days
What are the special features about the Muscularis externa of large intestine
The outer longitudinal muscle is thickened in three strips. The strips called tenae coli contract to pull the intestinal tube into sac like pockets called haustra coli. Haustra change shape and position
Describe the cells found in the mucosa of the colon intestinal glands (lumen to deep)
- Columnar absorpative cells (enterocytes) which are absorping water
- Goblet cell: secreting mucus to lubricate the passage of the faeces and increase in frequency as you approach the anus
- Undifferentiated cells: stem cells to form new epithelium
- White blood cells in the lamina propria - lymphocytes that provide defense against invading bacteria from the colon lumen
What are the main causes of diarrhoea and therefore reverse is constipation
- Too much intestinal motility : too much peristalsis so transmission time is reduced and not able to reabsorb
- Enterocytes not functioning : unable to reabsorb water
- Cholera toxin: locks G protein in active phase and results in excess up regulation of Cl- ion channels
- Colon cancer causing removal of parts of the colon
What is between the rectum and anus
2cm of anal canal that is closed by 2 sphincters. The inner collar is smooth muscle and outer is skeletal muscle
What causes defecation
Stretching of the rectal wall intiates a reflex contraction of the teniae coli in the descending colon and rectum.
Shortening of this part of the gut tube increases pressure on the rectum and causes the internal sphincter to relax (open). The outer voluntary muscle will then be relaxed voluntarily or if cant defecate then it will stay in contracted state and the defecation reflex subsides
What epithelium is in the anus
It changes from glandular epithelium to stratified squamous which is sacrificial
