Physiology 1 Flashcards
Which of the 6 sphincters in the GI tract are made of skeletal muscle?
Upper oesophageal sphincter (UOS)
External anal sphincter
Which of the 6 sphincters in the GI tract are made of smooth muscle?
Lower oesophageal sphincter (LOS)
Pyloric sphincter
Ileocaecal valve
Internal anal sphincter
Where does carbohydrate begin and with what?
Mouth
Salivary amylase
Where does protein digestion begin and with what?
Stomach
Pepsin and HCl (hydrochloric acid)
How does the duodenum delay gastric emptying until it is ready to receive chyme?
Neuronal response –> enterogastric reflex
Hormonal response –> cholecystokinin (CCK)
Which factors within the duodenum prompt a delay in gastric emptying?
- Fat: delay required for digestion and absorption
- Acid: time required for neutralisation of gastric acid by bicarbonate secreted from pancreas
- Hypertonicity of carbohydrate and protein breakdown products
- Distension
Which factors are released from the fundus and body of the stomach?
HCl Pepsinogen Intrinsic factor Gastroferrin Histamine Mucus
Which factors are released from the pylorus and antrum area of the stomach?
Gastrin
Somatostatin
Mucus
Where are gastrin and somatostatin released from and where do they go?
Gastrin released from G cells
Somatostatin released from D cells
–> into the blood
What is the function of gastrin?
Stimulates HCl secretion
What is the function of somatostatin?
Inhibits HCl secretion
Where is pepsinogen released from?
Chief cell
What is pepsinogen?
Inactive precursor of pepsin (a peptidase)
–> activated by HCl
Which factors are released from gastric parietal cells?
HCl
Intrinsic factor
Gastroferrin
What is the role of HCl?
- activates pepsinogen to pepsin
- denatures protein
- kills most (not all) micro-organisms ingested with food
What is the role of intrinsic factor?
Binds vitamin B12, facilitating subsequent absorption
What is the role of gastroferrin?
Binds Fe2+, facilitating subsequent absorption
Where is histamine secreted from and what is its role?
Secreted from enterochromaffin-like cells
Acts on parietal cells to stimulate HCl secretion
Which 3 factors induce acid secretion from the parietal cells?
ACh
gastrin
histamine
Which 2 factors inhibit acid secretion?
Somatostatin
Prostaglandins
What are the three phases of gastric acid secretion and inhibition?
Cephalic phase - in the head
Gastric phase
Intestinal phase
How does the cephalic phase work?
Prepares stomach to receive food
- -> driven by CNS and vagus nerve
- -> causes release of gastric acid inducing factors
How does the gastric phase work?
When food in stomach, distension activates reflexes that –> acid secretion
How does the intestinal phase work?
Chyme entering upper small intestine –> stimulation of acid secretion
Where does the majority of digestion and absorption occur?
Small intestine
What are the three parts of the small intestine?
Duodenum
Jejunum
Ilium
How does pancreatic juice and bile enter the small intestine?
Via the sphincter of Oddi
How is the surface area of the small intestine increased?
Circular folds
Villi
Microvilli (the brush border)
What is segmentation?
The mixing of chyme with digestive juices
Due to alternating contraction and relaxation of circular muscle
What is the gastroileal reflex?
Segmentation in the empty ileum is triggered by gastrin from the stomach
What is the migrating motor complex?
Strong peristaltic contraction slowly passing the length of the small intestine between meals to ‘clear’ it
Triggered by motilin
Why do macrolide antibiotics e.g. erythromycin cause GI disturbance?
They mimic the effect of motilin
Which hormones does the small intestine secrete into the blood and where from?
Gastrin - G cells of gastric antrum (mainly) and duodenum
Secretin - S cells of duodenum
Cholecystokinin (CCK) - I cells of duodenum and jejunum
Gastric inhibitory peptide (GIP) - K cells of duodenum and jejunum
Glucagon-like peptide-1 (GLP-1) - L cells of small intestine
Motilin - M cells of duodenum and jejunum
Ghrelin - Gr cells
What is the function of secretin?
Released in response to H+ and fatty acids in lumen
Promotes secretion of pancreatic and biliary HCO3
What is the function of CCK?
Released in response to monoglycerides, free fatty acids, amino acids and small peptides in the lumen
- inhibits gastric emptying
- causes secretion of pancreatic enzymes
- relaxation of sphincter of Oddi + contraction of gall bladder
- potentiates secretin
What is the function of GIP?
Stimulates release of insulin from pancreatic beta-cells in response to glucose in lumen
What is the function of GLP-1?
- stimulates insulin secretion
- inhibits glucagon secretion from pancreatic alpha-cells
- decreases gastric emptying and appetite
What is the function of motilin?
Secreted during fasting state
Initiates the migrating motor complex
What is the function of ghrelin?
Stimulates appetite (hunger)
What does small intestine secretion (juice) contain?
Mucus
Aqueous salt
What are the endocrine pancreatic secretions?
Insulin
Glucagon
–> secreted into blood
What are the exocrine pancreatic secretions?
Digestive enzymes –> acinar cells
Aqueous NaHCO3 solution –> duct dells
–> secreted into duodenum as ‘pancreatic juice’
What is the function of the aqueous NaHCO3 solution?
Alkaline solution neutralises acidic chyme entering duodenum
- provides optimum pH for pancreatic enzymes
- protects mucosa from erosion by acid
Which enzymes are released from acinar cells in the pancreas?
Active: - pancreatic amylase - pancreatic lipase Inactive: - trypsinogen - chymotrypsinogen - procarboxypeptidase A and B
How are the inactive pancreatic enzymes activated?
Enterokinase in the duodenum
