6 - Digestive system II

Question 1

Pancreas

Answer 1

• About 20 cm long, weighs ~100g
• Digestive enzymes made by acinar cells (exocrine cells) released into duodenum via secretory duct
• Chymotrypsin, trypsin, carboxypeptidase, elastase made as zymogens
• Also pancreatic amylase (digests starch), lipase (digests fat), proteases, DNase, RNase
• Acinar cells also make bicarbonate
• Islets of Langerhans (endocrine cells) make hormones which are secreted into the blood

Question 2

Histology of the pancreas

Answer 2

Acinar cells (A): Make digestive enzymes and bicarbonate
Islets of Langerhans (I):
- β-cells make insulin - stimulates glucose glycogen
- α-cells make glucagon - stimulates glycogen glucose
- d-cells make somatostatin - regulates digestion, absorption & release of other hormones

Question 3

Insulin

Answer 3

Proinsulin has 86 amino acids
To make insulin, 4 amino acids are removed leaving the A and B chains, plus the C-peptide
Forms a 31AA chain, 21AA a chain and 30AA B chain.

Question 4

Type 1 diabetes

Answer 4

an autoimmune disease caused by loss of insulin secretion from the islets of Langerhans
• Treated with insulin administration

Question 5

Type 2 diabetes

Answer 5

associated with obesity, sedentary lifestyle, and is due initially to loss of responsiveness to insulin, followed by reduced insulin secretion
• At ‘pre-diabetes’ or ‘metabolic disorder’ stage, type 2 diabetes can be avoided through diet and exercise, may require insulin in advanced stages

Question 6

Absorption

Answer 6

• Occurs mainly in the small intestine (duodenum and jejunum)
• Monosaccarides and amino acids are transported into blood capillaries of
villi, then to the liver (via the hepatic portal vein)
• Fats are emulsified into fat droplets by the action of bile salts, they are then susceptible to digestion by pancreatic lipase
• Resulting long chain fatty acids and monoglycerides are converted into
chylomicrons (small particles) which enter the lymphatic system (drains into blood in left subclavian vein in the neck)
• Some small short-chain fatty acids are absorbed straight to the blood instead of the lymph

Question 7

Formation of chylomicrons

Answer 7

• Fatty acids and monoglycerides from fat digestion are absorbed and synthesised into triglycerides, which are then packed into chylomicrons
• After exocytosis, chylomicrons enter the lacteals and into the lymphatic system

Question 8

Microbiota

Answer 8

• Ecological communities of commensal, symbiotic and pathogenic organisms
• most in colon
• diet influences type and amount of bacteria
• influence digestion, production, nutrient absorbance.
• Vitamin K, thiamine, folate, bioth
• FIAF: fasting induced adipocyte facto

Question 9

Lymphatic system

Answer 9

• The thoracic duct drains into the left subclavian vein
• It carries lymph (water and solutes) from the lymphatic system, as well as chylomicrons from intestinal absorption of dietary fat and lipids
• Helps to return surplus plasma filtered by capillaries back into the blood vessels – water balance
• Important component of the immune system

Question 10

Transport to liver

Answer 10

• Monosaccharides, amino acids, electrolytes, water, absorbed from the intestines travel to the liver via mesenteric veins and the hepatic portal vein
• They can then enter the general circulation via the hepatic vein
• Drugs given orally must survive ‘first pass’ through the liver