Lecture 23 - Gut endocrinology

Question 1

which vehicle is the length of a digestive tract?

Answer 1

standard car length if alive
ford ranger (4-5m) in between
Dumper truck if dead (7m) dead

Question 2

where are the endocrine areas in the GI tract?

Answer 2

there is more than 20 distinct enteroendocrine cells with scattered distribution

Question 3

what percentage of cells in the GI tract are endocrine cells?

Answer 3

1 percent

Question 4

what is an example of an endocrine cell which is histologically distinct, and why

Answer 4

enterochromaffin (EC) cells
they take up the chromium salts in the dye and appear darker

Question 5

what do enterochomaffin cells do?

Answer 5

secrete serotonin and contributes to gut motility

Question 6

what are the regions of the stomach?

Answer 6

fundus, body, antrum, through pylorus

Question 7

what are the accessory organs of the gut?

Answer 7

pancreas, liver, gall bladder etc

Question 8

pancreatic juices drain into the _________ via the _________ ____

Answer 8

duodenum, pancreatic duct

Question 9

what do pancreatic secretions consist of?

Answer 9

water, ions, digestive enzyme precursors and bicarbonate

Question 10

true or false, the bile duct converges with the pancreatic duct and enters the duodenum

Answer 10

true

Question 11

what does bile consist of?

Answer 11

bile salts and bilirubin (breakdown of RBCs)

Question 12

what is the function of bile?

Answer 12

aids absorption of fats, lipids and come vitamins (hydrophobic)

Question 13

what are the three capillary beds supplying the gut?

Answer 13

each capillary bed supplies one of:
- foregut
- midgut
- hindgut

Question 14

describe the venous return of the gut

Answer 14

all via the hepatic portal system into the liver
- one single capillary bed for gut leading to the liver’s own capillary bed

Question 15

what are the 2 separate lymphatic systems of the gut mucosa, and where do they drain?

Answer 15

lacteals drain the villi layer
another drains the muscle layer
- both drain into common collecting ducts

Question 16

describe the structue of lymph nodes

Answer 16

Lymph nodules (dense in lymphocytes and macrophages) and sinus tissue

Question 17

what is the role of the lymphatic system?

Answer 17

• immune
• fluid pressure
• nutrient absorption (lipids)

Question 18

describe the sympathetic innervation of the gut

Answer 18

comes from T and L regions of spinal cord and predominantly controls motor input

Question 19

describe the parasympathetic innervation of the gut

Answer 19

vagus nerve controls foregut and midgut
pelvic splanchnic nerve for hindgut
mostly sensory (80%) and 20% motor

Question 20

decibe the vagus enrve

Answer 20

90% of the vagus nerve fibers are afferent (to brain) to tell brain im hungry, im sick etc
10% is efferent, which controls secretion of gastric acid and enzymes

Question 21

what are the two layers of the intestinal wall of the enteric nervous system

Answer 21

• submucosal plexus - in contact with mucosa and detects blood flow and responds by secreting hormones
• myenteric - involved in contraction and relaxation of gut wall

Question 22

true or false, ENS is large and complex and can act independently of the CNS

Answer 22

true

Question 23

what is the gut brain axis

Answer 23

brain and autonomic nervous system interacting with the enteric nervous system, neuro-hormonal system and microbiome

Question 24

true or false, most gut pits will have more or less the same composition of cells and functions

Answer 24

false, they are different and contain different cell types

Question 25

what kinds of glands will we see in the corpus vs pylorus vs the antrum of the stomach?

Answer 25

- corpus contains more acid secreting parietal glands - antrum contain more gastrin secreting glands (hormones) - pylorus will contain more G cells

Question 26

describe neuronal and endocrine control of gastric function

Answer 26

- ENS senses distension of the stomach - vagus nerve innervates cells to secrete acid and hormones, and inhibits D cells in the corpus and antrum and reduces somatostatin release

Question 27

what does the vagus nerve innervate via the ENS after eating?

Answer 27

G cells secrete gastin to stimulate ECL cells, which secrete histamine to activate parietal cells, which secrete HCL - signal amplification

Question 28

what happens when pH gets below 2?

Answer 28

stimulation of D cells to release somatostatin, which inhibits parietal and ECL cells

Question 29

what happens when chyme enters the duodenum?

Answer 29

pH lowers and stimulates S cells to secrete secretin, which stimulates D cells and also stimulates pancreas to release bicarbonate - to bring pH back up and counteract HCl

Question 30

where are G cells found?

Answer 30

stomach

Question 31

what three cell types does G cell activity stimulate/effect?

Answer 31

chief cells to secrete pepsinogen parietal cells ECL cells

Question 32

what are the two hormones secreted in the upper intestine (duodenum)?

Answer 32

Secretin (S cells) Cholecystokinin (CCK, I cells)

Question 33

what does cholecystokinin cells do?

Answer 33

stimulates pancreatic acinar cells to secrete enzymes and stimulates gall bladder to release bile

Question 34

which hormone is found throughout the GI tract?

Answer 34

somatostatin (SST, D cells)

Question 35

what are the main three cells which signal to the pancreas, liver and intestine?

Answer 35

L cells K cells P/D1 cells

Question 36

what four hormones do L cells secrete?

Answer 36

GLP-1 GLP-2 Oxyntomodulin PYY

Question 37

what does GLP-1 do?

Answer 37

many actions - slow gastric emptying, maintains blood glucose level

Question 38

what does GLP-2 do?

Answer 38

increases nutrient transport and possibly enhances gut surface area

Question 39

what does oxyntomodulin do?

Answer 39

suppresses appetite

Question 40

what does PYY do?

Answer 40

lowers enzyme, bicarbonate and bile secretion and slows gastric empyting

Question 41

what do K cells secrete and what effect does that have

Answer 41

GIP (gastric inhibitory peptide) acts on pancreas to enhance insulin secretion and decrease glucagon secretion

Question 42

what do P/D1 cells secrete?

Answer 42

ghrelin stimulates hunger, gastric motility and emptying

Question 43

true or false, the microbiome is responsive

Answer 43

true

Question 44

how does our microbiome contribute to our endocrine control?

Answer 44

microorganisms produce chemicals which interact with neurons and hormone producing cells. - e.g microbes generate short chain fatty acids which triggers PYY and serotonin release

Question 45

what is FMT?

Answer 45

fecal microbial transplant (study more closer to exam)

Question 46

what is the suspected function of the appendix?

Answer 46

repopulation of gut microbiome

Question 47

what is interesting about the tissue of the appendix?

Answer 47

contains a lot of lymphoid tissue, suspected to prevent immune responses against good microorganisms and vice versa