lecture 2- stomach

Question 1

Stomach functions

Answer 1

Store food (release into S.I), secrete HCI & enzymes (begins protein digestion), create chyme (from mixing food with secretions)

Question 2

Gastric filling- Receptive relaxation

Answer 2

of the stomach as it receives food- folds get smaller and flatten out (allows stomach to increase in size)

Question 3

Gastric mixing

Answer 3

ICC’s create electrical rhythm, slow wave potentials sweep from fundus to pyloric sphincter via gap junctions. If SWP reaches threshold in smooth muscle cells, action potentials are triggered (contraction/peristalsis= mixing)

Question 4

Gastric emptying

Answer 4

Direction of peristaltic wave pushes food forward gradually from body into antrum, towards pyloric sphincter

Question 5

Duodenum affects gastric motility via neural responses-

Answer 5

intrinsic nerve plexuses and autonomic nerves (short and long reflexes)

Question 6

Duodenum affects gastric motility via hormonal responses-

Answer 6

Hormones secretin and cholecystokinin (CCK) inhibit antral contractions

Question 7

External factors influencing motility

Answer 7

Increased sympathetic activity can alter motility (e.g. fear and pain decrease motility)

Question 8

Gastric secretions

Answer 8

secretory cells are located in mucosal infoldings (may be exocrine, paracrine or endocrine secretions)

Question 9

Gastric juices=

Answer 9

collective exocrine secretions

Question 10

2 areas of gastric mucosa

Answer 10

pyloric gland area (antrum) and oxyntic mucosa (funds and body)

Question 11

Hydrochloric acid-

Answer 11

aids digestion, activates pepsinogen enzyme, breaks down connective tissue and muscle fibres

Question 12

Pepsinogen

Answer 12

major digestive component- synthesised and packaged by ER and Golgi complex in chief cells

Question 13

Pyloric glad area- G cell

Answer 13

secretes gastrin, stimulates acid secretion by ACh and acts on ECL and parietal cells, release peptide hormone, chief cells secrete pepsinogen

Question 14

Oxyntic area- ECL cell

Answer 14

secretes histamine (amplifies gastrin signal and ACh, stimulates acid secretion by acting on parietal cells

Question 15

Pyloric glad area- D cell

Answer 15

secretes somatostatin, inhibits gastrin and acid secretion, acts as a “turning off” signal

Question 16

3 phases of Gastric secretion

Answer 16

Cephalic, Gastric, Intestinal Phase

Question 17

Cephalic phase

Answer 17

increased secretion of HCI and pepsinogen in response to thinking about eating food (vagal stimulation of the intrinsic plexuses sends signal to medulla oblongata

Question 18

Gastric phase

Answer 18

Food reaches the stomach and proteins increase gastric secretions via both vagal and direct stimulation of the intrinsic nerve plexuses (enteric nervous system)

Question 19

Intestinal phase

Answer 19

Encompasses inhibitory factors originating from the S.I. This stops the flow of gastric juices and gastric motility as chyme is processed in the S.I

Question 20

How can the gastric mucosa withstand strong acid and proteolytic enzymes without damage?

Answer 20

Epithelial cells impermeable to HCI, tight junctions prevent acid diffusing between cells, mucus stops acid from physically penetrating, Bicarbonate secreted into mucus neutralises acid and inactivate pepsin

Question 21

Stomach body digestion

Answer 21

the semi-solid mass of food is not well mixed with gastric secretions (due to thinness of muscle), salivary amylase digestions of carbs can continue in centre of food mass.

Question 22

Stomach Antrum digestion

Answer 22

Digestion by gastric juice as food mass mixed with HCI and pepsin (protein digestion)

Question 23

HCI

Answer 23

hydrochloric acid (protein)

Question 24

Absorption

Answer 24

no food or water absorbed, small amount of lipid soluble compounds can diffuse across cell membranes

Question 25

why is alcohol absorption slowed when consumed with a meal?

Answer 25

Fat entering slows activating in the stomach, alcohol sits much longer in stomach due to food. S.I is much more efficient at absorption

Question 26

Myenteric plexus

Answer 26

between circular and longitudinal layers of muscularis externa, controls motility;

Question 27

Submucosal plexus

Answer 27

submucosa, controls blood flow and secretions

Question 28

Briefly describe the 3 functions of hydrochloric acid as a component of gastric secretion

Answer 28

hydrochloric acid acts by activating pepsinogen to pepsin, denaturing proteins, breaking down connective tissue, killing microorganisms. It is not an enzyme, but helps with protein digestion.