Stomach

Question 1

What cells in the stomach secrete hormones / histamine

Answer 1

15+ cells in the mucosa of GI tract that secrete hormones
 Enteroendocrine cells
 Generally identified by letters
 G,S,D

Cells that secrete histamine
 Enterochromafin (like cells) -ECL cells

Question 2

How do hormones travel

Answer 2

Hormones
 Peptides released from endocrine cells
 Into portal circulation
 Pass through liver
 Enter systemic circulation
 End up pretty close to where they were
All viscera in GI tract drai through liver -> IVC -> heart

Question 3

Define paracrine

Answer 3

 Peptides released by endocrine cells
 Act in local environment
 Diffuse short distances

Question 4

Define neurocrine

Answer 4

 Peptides released by neurones in the GI tract
 Released after action potential
 Example Gastrin releasing peptide (GRP)
 Increases release of Gastrin from G cells

Question 5

What are the 2 families of GI hormones

Answer 5

Gastric family and secretin family

Question 6

Describe the gastric family

Answer 6

 Gastrin family
 Gastrin
 G cells in antrum of. stomach
 Increases gastric acid secretion
 Will talk much more about this later

 cholecystokinin (CCK)
 I cells in duodenum and jejunum
 Increases pancreatic/gallbladder secretions
 Stimulated by fat and protein in duodenum
 Gall bladder contracts
 Pancreas stimulated

Question 7

Describe the secretin family

Answer 7

 Secretin family
 Secretin
 S cells in the duodenum 
 Stimulated by H+ and fatty acids
 Increases HCO3 from pancreas/gallbladder
 Decreases gastric acid secretion

 Gastric inhibitory polypeptide (GIP)
 Cells in the duodenum and jejunum
 Stimulated by sugars, amino acids and fatty acids
 Increases insulin
 Decreased gastric acid secretion
They can detect how much coming in - they can delay the stomach from releasing contents into the duodenum

Question 8

What are the basic fucntions of the stomach

Answer 8

Receive food
 Short term storage facility
Food arrives relatively unchanged

Disrupt food
 Vigorous contractions of the smooth muscle

Continue/commence digestion
 Mainly proteins

Disinfect

Question 9

Describe the location of the stomach an surrounding structures

Answer 9

Lies quite a lot underneath left lobe of liver . Small window between liver and stomach - this is where lesser ommentum is - behind this lies blood supply to stomach - celiac trunk off aorta

Question 10

Describe the joining of the oesophagus to stomach

Answer 10

Oesophagus comes through diaphragm - right crus - loops around oesopphgus. Closes liek a drawstring when coughing to prevent reflux of contents. Also oesophagus joins at an angle to protect from flux.

Question 11

Describe the basic structure of the domach

Answer 11

Fund us, body, annum. Thicker walled distally, thinner prodigally. “Line” between body and antrum is the angularis of the lesser curvature there is pyrosis (sphincter) at end of stomach.. Lesser ommentum attaches to first part f duodenum.. then duodenum becomes retroperitoneal

Question 12

Descrbe the structure of the surface of the stomach

Answer 12

From lower oesophagus to stomach
 Abrupt transition of stratified squamous to columnar
 This is about secretion

Mucosa/submucosa thrown into folds
 Rugae - these open out and become flat when stomach is full

View surface of the stomach with a magnifying glass
 Lots of little holes
 Gastric pits

Question 13

What are the cells covering the surface of th stomach

Answer 13

Epithelial cells
 Cover surface and extend into pits/glands
 Mucous cells
 Parietal cells
 Chief cells
 G cells

Question 14

Describe the stomach smooth muscle

Answer 14

Inner circular outer longitudinal - standard. But stomach has an extra layer

Extra oblique layer of muscle Contractions
 Mix/grind contents
 Move contents along
Upper stomach
 has sustained contractions - waves of peristalsis to clear it out even when not eating
 Creates basal tone - doesnt completely relax

Question 15

Describe how food is moved through the stomach

Answer 15

Lower stomach
 Strong peristalsis mixes stomach contents
 Coordinated movements
 Contractions every 20 seconds (or so)
 Proximal to distal

Shape of stomach
 Larger (proximal) to smaller (distal)
 Contents accelerates
 bigger Lumps left behind (separates contents) - smaller ones proceed forwards so they can go faster
 Liquid chyme ejected into duodenum 3 times a minute

Question 16

Give an overview of the blood supply to the stomach

Answer 16

Foregut trunk. Pierces diaphragm, comes through i.
Celiac trunk has 3 main branches”
Splenic artery (wavy)
Left gastric - goes down lesser rude of stomach to supply this
Common Hepatic artery

Question 17

Describe the venous drainage of the gut

Answer 17

Portal vein has a lot of tributaries - git drains into this. Goes to liver.
(Hepatic veins drain the liver)
Major branches coming into partial vein come from foregut midgut and hindgut. Aka entire gut.
Gastric vein from foregut
SMV from midgut
IMV from hindgut

Spleen drains along with gut. Has its blood supply with the foregut

Question 18

Describe how food is received

Answer 18

From oesophagus We consume food faster than we can digest
 Need to store
 Receptive relaxation - mediated by distal oesophagus contractions
 Vagally mediated relaxation of orad stomach
 Allows food to enter stomach without raising intra-gastric pressure too much
 Prevents reflux of stomach contents during swallow
 Gastric mucosal folds (rugae) allow distension

Question 19

Describe the acidic conditions fo the stomach

Answer 19

Acidic conditions
◦ Helps unravel proteins - increases SA for digestive enzymes
◦ Activates proteases
◦ Pepsinogen to Pepsin
◦ Disinfect stomach contents
Mucus and bicarbonate protects epithelia of stomach from acid. Pproteases oly activated in the zone where they will not affect the stomach itself.

Question 20

What does the stomach secrete

Answer 20

 HCL
Intrinsic factor - helps vit b12 be absorbed
Mucus/HCO3-
Pepsinogen (pepsin)

Question 21

What. Are some important cells in the stomach and what do they secret e and state their location

Answer 21

See slide, Parietal cell
G cell
Chief cell
D cells
HCL & Intrinsic factor
Product
Gastrin
Histamine
Pepsinogen
Somatostatin
Enterochromaffin like cell (ECL)
Mucous cells (surface & neck)
Mucus

Question 22

Decsribe the disctibiton of different cells / secretions in the stomach

Answer 22

See slide 
Cardia
 Predominantly mucus secretion
Fundus/body
 Mucus, HCL, pepsinogen
Pylorus
 Gastrin, somatostatin
However, lots of crossover

Question 23

What are inputs into the parietal cels

Answer 23

Parietal cell (stimulated by)
◦ Gastrin released by G cells, binds to parietal cells 
◦ Histamine - released from ECL cells
◦ Ach
See slide

Question 24

Describe the control of gastric secretion

Answer 24

G cells located in Antrum G cell (stimulated by)
◦ Peptides/amino acids in stomach lumen - need acids to unravel proteins
◦ Vagal stimulation - preempt the arrival of food. Can activate g cells
Also stretch of walls of stomach can swish this on
◦ Acetylcholine
◦ Gastrin-releasing peptide (GRP)

To switch on acid production, neED TO SWITCH ON G CELL

Question 25

HOW IS HCL PRODUCTION INHIBITED

Answer 25

``` Essentially an inhibition of G cells ◦ When food leaves stomach pH drops ◦ Food is a buffer ◦ Low pH activates D cells ◦ D cells release somatostatin ◦ Somatostatin inhibits G cells (and ECL cells) ◦ Stomach distension reduces ◦ Reduced vagal activity ``` Turns off g cues and ECl cells If histamine receptors blocked, fine tuning Down graded. Histamine plays a role in fine tuning acid control

Question 26

How s acid secreted and what is the alkaline tide

Answer 26

Acid produced - H+ ions - combine with Cl- ions. H+ ions get pumped by H+/K+ ATPase into lumen of stomach H2) combines with CO2 to give HCO3- in stomach It’s of acid in lumen, bicarbonate go into venous blood Alkaline tide - corresponding to acid going into stomach

Question 27

What are the 3 phases of digestion

Answer 27

Cephalic Gastric Intestinal

Question 28

What is the cephalon phase

Answer 28

Cephalic (30% of total HCL) ◦ Parasympathetic stimuli ◦ Smelling, tasting, chewing, swallowing ◦ Direct stimulation of parietal cell by vagus nerve ◦ Stimulation of G cells by vagus (GRP released) ‘Anticipating food’ ◦ Also increases gastric motility (slightly)

Question 29

What is the gastric phase

Answer 29

Gastric (60% of total HCL) ◦ Distension of stomach stimulates vagus ◦ Which then stimulates Parietal cells and G cells ◦ Presence of amino acids and small peptides ◦ Stimulate G cells ◦ Food acts as a buffer in stomach ◦ Removes inhibition on Gastrin production Enteric NS and Gastrin ◦ Cause strong smooth muscle contractions

Question 30

What is the intestinal phase

Answer 30

Intestinal (10% of HCL production) ◦ Chyme initially stimulates Gastrin secretion ◦ Partially digested proteins detected in duodenum ◦ Short phase ◦ Soon overtaken by inhibition of G cells ◦ Presence of lipids activate enterogastric reflex ◦ Reduces vagal stimulation ◦ Chyme stimulates CCK and secretin (help suppress secretion)

Question 31

What are stomach defences from digestion

Answer 31

``` Stomach designed to digest biological material ◦ Therefore it can digest itself ◦ Needs to protect itself ◦ Mucus ◦ HCO3- release ``` ``` Mucus/HCO3- ◦ Released by ◦ surface mucus cells ◦ Neck cells in gastric glands ◦ Forms thick alkaline viscous layer that adheres to epithelium ◦ Epithelial surface kept at higher pH ``` High turnover of epithelial cells ◦ Helps keep epithelia intact Prostaglandins ◦ Maintain mucosal blood flow ◦ Supplying epithelium with nutrients

Question 32

What can breach stomach defences

Answer 32

Alcohol ◦ Dissolves mucus layer Helicobacter pylori ◦ Chronic active gastritis NSAIDS ◦ Inhibits prostaglandin