Digestion 3: pancreas to anus

Question 1

What is the exocrine function of the pancreas

Answer 1

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

Question 2

What is the endocrine function of the pancreas

Answer 2

Has islets of langerhans which secrete insulin and glucagon for glucose homeostasis

Question 3

Is the spleen part of the digestive system

Answer 3

no

Question 4

describe the path of the pancreatic juice from point of secretion to the main pancreatic duct

Answer 4

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).

Question 5

What is the order of things added to the duodenum for digestion and where do they come from

Answer 5

1. Chyme from the stomach connects directly through pyloric sphincter
2. 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
3. Prancreatic juice containing precursors go through the main pancreatic duct

Question 6

Describe the 3 regions of the small intestine describe the main function of the small intestine

Answer 6

1. Duodenum
   2.Jejunum
2. 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

Question 7

What are the differences in the gut tunics for the small intestine

Answer 7

1. Mucosa: is specialised to greatly increase surface are available for secretion
2. 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.

Question 8

What are the modifications done to increase surface area in the small intestine (big to small)

Answer 8

1. Gross convolutions
2. Plicae (circular folds that are permanent wrinkles. Each plica has a core of submucosa covered in mucosa
3. Villi (made of lamina propria covered by epithelium
4. Microvilli (extensions of cell membrane making the brush border on individual absorptive cells).

Question 9

What are the epithelial cells in the villus of the small intestine and what do they do

Answer 9

1. Columnar absorpative cells (enterocytes) which absorb the molecules from digestion
2. Goblet cells: that secrete mucus

Question 10

What are the epithelial cells in the intestinal glands mucosa of the small intestine and what do they do

Answer 10

1. Undifferentiated cells (for generating new epithelium)
2. Enteroendocrine cells: secrete hormone secretin into the capillaries of the lamina propria
3. Paneth cells: secrete bacteriocidal enzyme lysozome and phagocytose

Question 11

Where are the digested carbohydrates, proteins, water and electrolytes transported compared to lipids

Answer 11

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

Question 12

How are the epithelial cells on the villus of the small intestine replaced

Answer 12

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.

Question 13

What stimulates the release of secretin from what cell and what does it do

Answer 13

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.

Question 14

What is special about the lymph vessel in villus of the small intestine

Answer 14

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

Question 15

List the 7 regions of the large intestine

Answer 15

Cecum, Ascending colon, transverse colon, descending colon, Sigmoidal colon, rectum, anus

Question 16

What are the main functions of the large intestine

Answer 16

1. Absorption of salts and water (but still less than small intestine)
2. Conversion of chyme into feces with remaining carbs fermented by bacteria
3. Production of some vitamins B&K which are absorbed
4. Secretion of mucus to lubricate feces
5. Defecation

Question 17

What controls the flow of chyme from the ileum into the cecum

Answer 17

ileocecal valve

Question 18

What is the cecum structure and function

Answer 18

Dilated pouch containing Bacteria (not enzymes) for digestion. Humans have none for digestion of cellulose

Question 19

What is the structure and function of the appendix

Answer 19

Vestigal worm like appendage of the cecum which contains lymphatic tissues

Question 20

What is the final composition of feces

Answer 20

1. Bacteria 30%
2. Undigested dietary fibre 30%
3. Cells shed from the intestinal lining and mucus

Question 21

What is the colour of the feces from

Answer 21

the bacterial decomposition of bilirubin

Question 22

What are the special features about the Mucosa of the large intestine

Answer 22

1. No villi but many intestinal glands
2. surface epithelial cells that are enterocytes (absorpative
3. intestinal glands containing mostly goblet cells but not paneth (no more digestion)
4. Many clusters of lymphocytes in the lamina propria
5. cell renewal like small intestine- replaced every 5 days

Question 23

What are the special features about the Muscularis externa of large intestine

Answer 23

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

Question 24

Describe the cells found in the mucosa of the colon intestinal glands (lumen to deep)

Answer 24

1. Columnar absorpative cells (enterocytes) which are absorping water
2. Goblet cell: secreting mucus to lubricate the passage of the faeces and increase in frequency as you approach the anus
3. Undifferentiated cells: stem cells to form new epithelium
4. White blood cells in the lamina propria - lymphocytes that provide defense against invading bacteria from the colon lumen

Question 25

What are the main causes of diarrhoea and therefore reverse is constipation

Answer 25

1. Too much intestinal motility : too much peristalsis so transmission time is reduced and not able to reabsorb
2. Enterocytes not functioning : unable to reabsorb water
3. Cholera toxin: locks G protein in active phase and results in excess up regulation of Cl- ion channels
4. Colon cancer causing removal of parts of the colon

Question 26

What is between the rectum and anus

Answer 26

2cm of anal canal that is closed by 2 sphincters. The inner collar is smooth muscle and outer is skeletal muscle

Question 27

What causes defecation

Answer 27

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

Question 28

What epithelium is in the anus

Answer 28

It changes from glandular epithelium to stratified squamous which is sacrificial