Stomach Flashcards
What cells in the stomach secrete hormones / histamine
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
How do hormones travel
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
Define paracrine
Peptides released by endocrine cells
Act in local environment
Diffuse short distances
Define neurocrine
Peptides released by neurones in the GI tract
Released after action potential
Example Gastrin releasing peptide (GRP)
Increases release of Gastrin from G cells
What are the 2 families of GI hormones
Gastric family and secretin family
Describe the gastric family
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
Describe the secretin family
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
What are the basic fucntions of the stomach
Receive food
Short term storage facility
Food arrives relatively unchanged
Disrupt food
Vigorous contractions of the smooth muscle
Continue/commence digestion
Mainly proteins
Disinfect
Describe the location of the stomach an surrounding structures
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
Describe the joining of the oesophagus to stomach
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.
Describe the basic structure of the domach
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
Descrbe the structure of the surface of the stomach
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
What are the cells covering the surface of th stomach
Epithelial cells Cover surface and extend into pits/glands Mucous cells Parietal cells Chief cells G cells
Describe the stomach smooth muscle
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
Describe how food is moved through the stomach
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
Give an overview of the blood supply to the stomach
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
Describe the venous drainage of the gut
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
Describe how food is received
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
Describe the acidic conditions fo the stomach
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.
What does the stomach secrete
HCL
Intrinsic factor - helps vit b12 be absorbed
Mucus/HCO3-
Pepsinogen (pepsin)
What. Are some important cells in the stomach and what do they secret e and state their location
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
Decsribe the disctibiton of different cells / secretions in the stomach
See slide Cardia Predominantly mucus secretion Fundus/body Mucus, HCL, pepsinogen Pylorus Gastrin, somatostatin However, lots of crossover
What are inputs into the parietal cels
Parietal cell (stimulated by) ◦ Gastrin released by G cells, binds to parietal cells ◦ Histamine - released from ECL cells ◦ Ach See slide
Describe the control of gastric secretion
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
HOW IS HCL PRODUCTION INHIBITED
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
How s acid secreted and what is the alkaline tide
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
What are the 3 phases of digestion
Cephalic
Gastric
Intestinal
What is the cephalon phase
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)
What is the gastric phase
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
What is the intestinal phase
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)
What are stomach defences from digestion
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
What can breach stomach defences
Alcohol
◦ Dissolves mucus layer Helicobacter pylori
◦ Chronic active gastritis NSAIDS
◦ Inhibits prostaglandin
