Overview and Control of the GI System

Question 1

Sphincters under voluntary control (muscle type)

Answer 1

Upper esophageal sphincter, external anal sphincter
skeletal

Question 2

Sphincters under involuntary control (muscle type)

Answer 2

Lower esophageal sphincter, pylorus, sphincter of oddi, ileocecal valve, internal anal sphincter
smooth muscle

Question 3

Mucosa layers from lumen to outside

Answer 3

Epithelium -> laminate propria -> muscular is mucosae -> submucosa

Question 4

Lamina propria

Answer 4

Blood and lymphatic vessels absorbs

Question 5

Submucosa

Answer 5

Connective tissue layer with larger blood vessels and an externsive lymphatic system.

Question 6

Muscular mucosae

Answer 6

Thin muscle layer generating local movements, folds that increase surface area

Question 7

Sphincters are formed from the ________ muscle layer

Answer 7

Circular

Question 8

Layers of the enteric nervous system

Answer 8

Submucosal plexus, myenteric plexus.

Question 9

Serosa

Answer 9

Covers the muscle layer

Question 10

Neural control of the GI

Answer 10

ANS (PsNS and SNS)
- intrinsic control by ENS that processes sensation and motor output.

Question 11

Chemical control of the GI

Answer 11

Endocrine - EECs secrete peptides that travel via the blood to target organs.
Paracrine - EECs secrete local peptides.

Question 12

Parasympathetic cholinergic effects

Answer 12

Stimulates ENS neurons, increasing motility and secretion
Through the vagus nerves and pelvic nerves.

Question 13

Sympathetic cholinergic effects

Answer 13

Inhibits ENS neurons, decreasing motility and secretion, and lowering blood flow to the gut.
Through superior cervical ganglion

Question 14

Parasympathetic innervation nerves

Answer 14

Vagus, pelvic nerves.
ACh, synapse on nicotinic close to target organs.
ACh, synapse on muscarinic in smooth muscles and glands.

Question 15

Sympathetic innervation nerves

Answer 15

Superior cervical ganglion and thoracolumbar region.
ACh, on nicotinic receptors in the sympathetic ganglia (chain).
NE, on adrenergic cells in the ENS, smooth muscle.

Question 16

All GI hormones are _____ released by ________ cells.

Answer 16

Peptides; enteroendocrine.

Question 17

Enteroendocrine cells

Answer 17

Electrically excitable cells that can detect sensory stimuli, releasing peptides that. may be endocrine, paracrine, or acting as neurosciences to influence enteric sensory neurons.

Question 18

Gastrin release

Answer 18

Secreted upon sight, thought, smell of food, and distension of the stomach.
Secreted in presence of nutrients.
Secreted upon vagal stimulation (including subsequent release of Ghrelin-releasing peptide).
Inhibited by somatostatin secretion as stomach acidity increases.

Question 19

Gastrin acts on parietal cells and ECLs

Answer 19

Enhances gastric motility, acid secretion
Increases histamine release from ECLs
Growth of gastric mucosa.

Question 20

Cholecystokinin (CCK) release

Answer 20

By I-cells in the duodenum and jejunum.
Occurs upon the arrival of nutrients such as fatty acids, peptides, etc, to. the small intestine.

Question 21

CCK binds

Answer 21

CCK1 and CCK2/gastrin receptors.

Question 22

CCK effects

Answer 22

Towards aiding digestion.
Increases pancreatic enzyme/fluid secretion, stimulates bile secretion, D-cell somatostatin release.
Inhibits gastric emptying.
Sphincter of oddi relaxation.

Question 23

CCK1 receptors

Answer 23

Binds only CCK and mediates typical CCK actions

Question 24

CCK2/Gastrin receptors

Answer 24

Bind both peptides.
Found in parietal and eco cells.
More often bound to gastrin (5-10 x greater concentration)

Question 25

Secretin secretion

Answer 25

Secreted by S-cells of the small intestine (duodenum) in response to the arrival of chyme and the increased acidity)

Question 26

Secretin functions

Answer 26

Neutralises contents of small intestine. Stimulates pancreatic and hepatic HCO3- release, stimulates pancreatic growth, and inhibits gastric acid secretion.

Question 27

Incretins

Answer 27

GIP - Glucose dependent insulinotropic peptide GLP-1 - Glucagon-like peptide-1

Question 28

GIP release

Answer 28

Secreted by K cells in the duodenum and jejenum.

Question 29

GIP and GLP-1 both;

Answer 29

stimulate pancreatic β-cells to increase insulin secretions and tissue glucose uptake.

Question 30

GLP-1 secretion

Answer 30

L-cells in the jejunum, ileum, and colon. Colonic secretion occurs when secondary metabolites appear (hours after ingestion).

Question 31

Only GLP-1 acts to;

Answer 31

Inhibits pancreatic α-cells, decreasing glucagon secretion, and decreasing glucose uptake by the liver. Signals the CNS (satiety). Slows gastric emptying.

Question 32

Insulin and GLP-1

Answer 32

Impaired secretion Treat with GLP-1 agonists, such as ozempic.

Question 33

Peptides in the control of food intake

Answer 33

Grehlin, CCK, GLP-1, PYY, PP, amylin Plus signals from higher brain areas involved in rewards and addictive behaviours.

Question 34

Function of ghrelin

Answer 34

Stimulates neuroleptics Y and AgRP release from the arcuate nucleus, increasing appetite.

Question 35

CCK, GLP-1, PYY, PP, amylin function

Answer 35

Stimulates POMC and CART release from the arcuate nucleus, signalling satiety.

Question 36

Plasma levels of ghrelin are highest;

Answer 36

Just before each daily meal.

Question 37

Motilin (M-cells) on the GI tract, CNS, pancreas, and gallbladder

Answer 37

Secreted during inter digestive period GI - Stimulates migrating myoelectric complex, emptying, motility, and inhibits gastric accomodation. CNS - increase hunger GB - contraction and emptying P - insulin secretion

Question 38

Somatostatin Stimulus, secretor, receptor, and function

Answer 38

Acidity of GI tract D-cells Many GPCRs Inhibits gastric acid secretion

Question 39

Histamine Stimulus, secretor, receptor, and function

Answer 39

Food in stomach ECL-cells H2 GPCRs in parietal cells Stimulates gastric acid secretion

Question 40

5-HT (serotonin) Stimulus, secretor, receptor, and function

Answer 40

Nutrients in GI, distension EC-cells Many receptor types Regulates GI motility, secretion, nausea.