The Peripheral Endocrine Glands Lecture 8 - hormones secreted by pancreas

Question 1

Question 2

Beta cells

Answer 2

• 60%
• site of insulin synthesis and secretion
• located centrally in islets

Question 3

Alpha cells

Answer 3

• 25%
• produce glucagon

Question 4

delta cells

Answer 4

• 10%
• pancreatic site of somatostatin synthesis

Question 5

F cells

Answer 5

• 1%
• least common islet cells
• secrete pancreatic polypeptide (PP)
• reduce appetite and food intake

Question 6

Connective tissue, blood vessels and nerves

Answer 6

• 4%

Question 7

Epsilon cells:

Answer 7

secrete Ghrelin

Question 8

Somatostatin is produced by

Answer 8

• delta-cells in pancreas
• hypothalamus (aka GHIH) – inhibits secretion of GH

Question 9

Somatostatin
Stimulus for secretion:

Answer 9

increased blood sugar and blood amino acids during absorption of a meal

Question 10

Somatostatin functions:

Answer 10

decrease digestion and absorption of nutrients
Prevents excessive plasma levels of nutrients
Presence of somatostatin - decrease secretion of insulin, glucagon, and somatostatin itself

Question 11

Insulin:

Answer 11

Decreases blood glucose, fatty acids & amino acids – promotes their storage

Question 12

During absorptive state:

Answer 12

(just after a meal)
- Most NB time for insulin
- insulin promotes cellular uptake of blood glucose, fatty acids & amino acids and their conversion into glycogen, triglycerides and protein

Question 13

Insulin exerts its effects through:

Answer 13

• increased activity of glycogen synthase (glucose –> glycogen)
  = glycogenesis
• decreased activity of hormone sensitive lipase
  (triglycerides –> free fatty acids and glycerol)

Question 14

Question 15

Circulating glucose concentrations are determined by:

Answer 15

Question 16

Action of insulin on blood glucose levels and storage of carbohydrates

Answer 16

insulin:
- Facilitates glucose transport into most cells
- increases glycogenesis (glucose –> glycogen) in skeletal muscle and liver

decrease glycogenolysis (glycogen –> glucose)
decrease hepatic glucose output by decreasing gluconeogenesis (amino acids –> glucose)

Question 17

Glucose transport into cells

Answer 17

• Transport between blood and cells – plasma membrane carrier, glucose transporter (GLUT)
• 14 forms
• Passive facilitated diffusion across plasma membrane
• Inside cell glucose is P to glucose-6-phosphate –> glucose is trapped inside the cell, also keeps [ ] of plain glucose inside cell low – gradient favouring facilitated diffusion of glucose into cell
• Family members of GLUT family performs different functions

Question 18

GLUT-1:

Answer 18

transport glucose across blood-brain barrier

Question 19

GLUT-2:

Answer 19

transfer glucose that has entered the kidney and intestinal cells into adjacent bloodstream by means of sodium and glucose co-transporter.

Question 20

GLUT-3:

Answer 20

transport glucose into neurons

Question 21

GLUT-4:

Answer 21

abundant in tissues that account for the bulk of glucose uptake in the absorptive state – skeletal muscle & adipose tissue

Question 22

GLUT-4 is the only glucose transporter that responds to insulin
- Why?

Answer 22

• these organs are responsible for highest uptake of glucose for storage, thus must respond to insulin
• No insulin, no GLUT-4 in plasma membrane
• Intracellular vesicles contain GLUT-4
• When insulin binds to receptor (phosphorylated tyrosine kinase) on surface membrane of target cell, vesicles moves to plasma membrane, fuse with it and inserting GLUT-4 on membrane
• Decrease in insulin – glucose transporters are retrieved from membrane by endocytosis, returned to intracellular pool

Question 23

Brain, working muscles and liver _______ depend on insulin for glucose uptake

Answer 23

DO NOT

Question 24

Brain, working muscles and liver DO NOT depend on insulin for glucose uptake
Brain:

Answer 24

requires constant supply of glucose – freely permeable to glucose at all times – GLUT-1 & GLUT-3

Question 25

Brain, working muscles and liver DO NOT depend on insulin for glucose uptake Skeletal muscle

Answer 25

depend on insulin ONLY at rest for glucose uptake Muscle contraction triggers insertion of GLUT-4 on plasma membrane

Question 26

Brain, working muscles and liver DO NOT depend on insulin for glucose uptake Liver

Answer 26

does not depend on insulin for glucose uptake; does not use GLUT-4 Insulin enhance the metabolism of glucose by liver through P glucose to glucose-6-phosphate

Question 27

Action of insulin on FAT

Answer 27

- increase fatty acids into adipose tissue - increase glucose into adipose tissue through GLUT-4 recruitment - Promotes chemical reactions that use glucose and fatty acids derivates for triglyceride synthesis - decreases lipolysis (fat breakdown) THUS: favouring removal of fatty acids and glucose from blood, promotes their storage as triglycerides

Question 28

Actions of insulin on PROTEIN

Answer 28

- increase active transport of amino acids from blood into muscle and other tissue – provides building blocks for protein synthesis - increase rate of amino acid incorporation into protein – stimulating cell’s protein-synthesizing machinery - Inhibits protein degradation THUS: protein anabolic effect – essential for normal growth (permissive to GH).

Question 29

Glucose stimulates insulin secretion through excitation-secretion coupling process NB

Answer 29

Must be able to draw and explain! - high levels of glucose are detected by the beta cells of the pancreas - these beta cells then take up the glucose via the GLUT-2 transporter - this will increase the intracellular glucose levels - this glucose is then phosphorylated to form G6P - it will then be oxidised and ATP will be formed - ATP responsible for closure of ATP sensitive potassium channels - this results in an increase in intracellular potassium levels, which causes depolarization of the membrane of the cell - this then opens up the voltage-gated calcium channels and calcium will enter the cells - high levels of calcium in the cells will be responsible for the exocytosis of the vesicles which are filled with insulin

Question 30

inputs for insulin secretion:

Answer 30

- high blood glucose levels - increase in blood amino acid level - induces insulin secretion in the same way as glucose - by generating ATP, which leads to excitation-excretion coupling - gastrointestinal hormones (incretins) incretins - consist of GIP (Glucose-dependent insulinotropic peptide) and GLP (glucose-like peptide) the secretion of these hormones will notify the Beta cells (stimulated by food intake)

Question 31

Question 32

Most common of all endocrine disorders

Answer 32

Diabetes Mellitus

Question 33

Diabetes Mellitus Prominent features:

Answer 33

elevated blood glucose levels Urine acquires sweetness from excess blood glucose that spills into urine

Question 34

Type I diabetes

Answer 34

Characterized by lack of insulin secretion

Question 35

Type II diabetes

Answer 35

Characterized by normal or even increased insulin secretion but reduced sensitivity of insulin’s target cells

Question 36

Question 37

https://www.youtube.com/watch?v=JAjZv41iUJU

Question 38

3 P’s of Diabetes

Answer 38

- polydipsia: extreme thirst - polyuria: frequent urination - polyphagia: hunger

Question 39

NB diagram!!

Question 40

Diabetic person can lose consciousness and die from:

Answer 40

diabetic ketoacidotic coma due to insulin deficiency (deep laboured breathing and fruity breath) acute hypoglycemia caused by insulin shock

Question 41

Insulin excess hypoglycemia is caused by:

Answer 41

In diabetic patient when too much insulin is injected – insulin shock Consequences: - More glucose than necessary is driven into insulin-dependent cells > decrease blood glucose, brain starves, depressed brain function, unconsciousness, death. Treatment: Immediately eat or drink something sugary

Question 42

Insulin excess: hypoglycemia

Answer 42

Reactive hypoglycemia is caused by: B-cell tumours: secreting increased insulin B-cells: over-responsive to glucose Consequences: tremor, fatique, sleepiness, inability to concentrate (non-specific) Treatment: limit sugar and carbohydrate intake

Question 43

Question 44

Question 45

What will be the metabolic effects in a diabetic persons under stress conditions?

Answer 45

- look at metabolic effect of cortisol and epinephrine (stress hormones) - both these hormones increase blood glucose levels - diabetic person already has elevated blood glucose levels, which is now further aggravated by these stress hormones - must inject a little bit higher level of insulin to regulate blood glucose levels

Question 46

NB: Study this summary of the metabolic effects of the different hormones and the control of secretion

Answer 46