|G-I hormones||Site of production||Actions||Control of release|
|Gastrin||Gastric antrum, duodenum and jejunum to lesser extent (G cells)||+ gastric acid & pepsin secretion
+ growth of the mucosa of
the stomach and small and large intestines
+ glucagon secretion
+ gastric motility
|Stimuli – luminal distension, peptides, amino acids, increased vagal tone, blood borne Ca or adrenaline
Inhibitors – luminal acid or somatostatin, blood borne secretin, GIP, VIP, glucagon, calcitonin
|CCK||Duodenum and Jejunum, ileum to lesser extent (I cells)||+ pancreatic enzyme secretion
+ Gall bladder contraction
Relaxation of sphincter of Oddi
Augments action of secretin
+ glucagon secretion
|Stimulated by luminal peptides and amino acids, fatty acids–> positive feed back but this is terminated when the products move down the GI tract.|
|Secretin||Duodenum and Jejunum, ileum to lesser extent (S cells)||+ bicarbonate secretion by pancreas
Inhibits gastric acid secretion
? Cause contraction of pyloric sphincter
|Stimulated by protein products and acid|
|VIP||Nerves of GIT||+ intestinal secretion of electrolytes & water.
Relaxation of intestinal
smooth muscle, including sphincters; dilation of peripheral
blood vessels; and inhibition of gastric acid secretion.
|GIP(gastric inhibitory peptide)||Duodenum and Jejunum, (K cells)||+Insulin secretion
Inhibit gastric acid secretion and motility
|Stim by luminal glucose and fat|
|Somatostatin||Hypothalamus, D cells in pancreatic islets||Inhibit GH
Inhibit secretion of gastrin, secretin, VIP, GIP
Inhibit pancreatic exocrine secretion
Inhibit gall bladder contraction
Inhibit gastric acid secretion
Inhibit absorption of glucose, AA and TGs.
|Stim by acidic contents in lumen,|
- Amylase – initiates starch digestion
- Lingual lipase – start fat digestion
- Mucus – lubricant
- Proteins and enzymes eg lysozyme
- Electrolyte solution to moisten food – Hypotonic and alkaline
- NaCl extracted and K and bicarb added to saliva
- 1000-1500mL of saliva per day
- Control of secretion almost all neural – parasympathetic stimulation of the glands (otic and submandibular ganglions)
- Other stimuli – chewing, thinking about/smelling food, nausea
- Inhibited by fear and during sleep
- Food made into bolus and pushed to back of mouth actively
- Swallowing is an unconscious reflex
Regulation of gastric acid secretion and motility
- Gastric acid secretion
- Promoter – gastrin, Ach, Histamine
- Inhibitor – secretin, VIP, GIP, somatostatin
- Gastric motility
- Promoter – gastrin
- Inhibitor – VIP, GIP
Functions of the stomach.
- Gastric acid production
- Control of secretion and motility
- Mixing of food
- Digestion of starches
- Absorption of water, nutrients, B12
- EtOH break down
- Retroperitoneal organ
- Secretes 2-2.5L per day
- Phospholipase A
- Conversion of proenzymes requires conversion of trypsinogen to trypsin by duodenal enteropeptidase.
- Enzymes released in active form
Functions of the liver.
- Nutrient uptake from portal circulation –> glycogen synthesis, protein synthesis, fat synthesis, cholesterol synthesis
- Gluconeogenesis, glycogenolysis, lipolysis in starvation
- Metabolism – phase 1 and phase 2 to modify toxins, proteins, drugs
- Synthesis of coagulation factors
- Synthesis of bile
- Synthesis of IGF-1
- Synthesis angiotensinogen
- Fetal RBC production
- Break down of insulin, hormones, ammonia to urea.
- Storage of ADEK vitamins, copper, iron, blood reservoir
- Immune role – Kuppfer cells
Composition of bile
- Water 97%
- Bile acid 0.7%
- Pigment 0.2%
- Fatty acid 0.15%
- Cholesterol 0.06%
- Phosphatidylcholine 0.2%
- Alkaline electrolyte solution
Bilirubin metabolism / excretion
- RBC break down –> haem–> unconjugated bilirubin –> bound to albumin in plasma –> hepatic uptake –> glucuronidation/conjugation –> water soluble conjugated bilirubin –> excreted in bile –> colon and out or metabolisedby gut bacteria –> urobilinogen–> reabsorbed in bowel –> excreted renally.
- Cholesterol stones
- Black pigment stones
- Mixed stones
- Tell me about gastric acid secretion.
- Tell me about the control of gastric secretion.
- What are the functions of the stomach ?
- What are the functions of the liver ?
- Tell me about bilirubin metabolism.
- Tell me about the function and composition of bile