Endocrine Pathways

Question 1

Renin-angiotensin pathway

Answer 1

1. Decrease in BP and/or Na+ conc stimulate secretion of renin enzyme from kidneys
2. Renin enzyme acts on angiotensinogen (inactive) from liver to make angiotensin 1 (inactive)
3. Angiotensin 1 is converted to angiotensin 2 (active) in the lung epithelium by ACE (angiotensin converting enzyme)
4. Angiotensin 2 is a vasoconstrictor (which increases BP), and it also stimulates adrenal cortex cells of the Z. Glomerulosa to secrete aldosterone
5. Aldosterone acts on the kidney to conserve Na+ and water, which increases BP through increase in blood volume
6. Aldosterone also promotes secretion of K+ and H+ through urine
7. Blood pressure returns to normal, renin secretion inhibited

Question 2

Blood Ca2+/Vit D pathway

Answer 2

1. Ingest cholesterol and cholecalciferol from foods
2. Sunlight converts cholesterol into cholecalciferol
3. Liver adds -OH to make calcidiol
4. Kidney adds -OH to make calcitriol (active Vit D), and is released into blood
5. Hypocalcemia stimulates PTH release
6. PTH and calcitriol work synergistically at kidney decreasing Ca2+ loss in urine
7. Calcitriol increases absorption of Ca2+ in small intestine
8. PTH and calcitriol act synergistically increasing osteoclasts activity, resorption of bone matrix, resulting in Ca2+ release from bone
9. Increase in blood Ca2+ inhibits PTH

Question 3

Growth Hormone pathway

Answer 3

1. Hypothalamus stimulated by age, time of day, nutrient levels in blood, stress, exercise
2. Hypothalamus releases GHRH to ant pit
3. Ant pit releases GH
4. GH acts on liver to make IGF1
5. Both GH and IGF1 act on effector cells/organs
6. Liver increases glycogenolysis and gluconeogenesis, decreases glycogenesis
7. Adipose tissue increases lipolysis and decreases lip-genesis
8. Bone, cartilage, muscle, and all other cells use glucose and amino acids to grow, differentiate, divide
9. Net effect is increased protein synthesis, cell division, cell differentiation
10. Increase GH in blood neg feedback on ant pit
11. Increase GH and IGF1 neg feedback on hypothalamus

Question 4

Thyroid hormone pathway

Answer 4

1. Hypothalamus stimulated by decrease in TH (T3/T4 ), cold weather, pregnancy, high altitude, hypoglycemia
2. Hypothalamus releases TRH (thyrotropin releasing hormone)
3. Ant pit releases TSH
4. Thyroid releases TH (T3/T4)
5. TH (T3/T4) bound by carrier protein in blood
6. T4 most abundant in blood, converted to more potent T3 at target cells
7. Adipose tissue increases lipolysis and decreases lipogenesis
8. Liver increases glycogenolysis and gluconeogenesis, decreases glycogenesis
9. All cells, esp neurons, take up glucose and amino acids, increased metabolic rate
10. Lung and heart increase rates to meet increased demand for O2 for aerobic metabolism
11. Net effect: increased metabolic rate occurs, which is supported by increased release of stored nutrients, and increased deliver of O2
12. TH levels in blood increase, inhibiting release of TRH and TSH

Question 5

Cortisol pathway

Answer 5

1. Hypothalamus stimulated by time of day and stress
2. Hypothalamus releases CRH (corticotropin releasing hormone)
3. Ant pit releases ACTH (adrenocorticotropic hormone)
4. ACTH stimulates adrenal cortex to release glucocorticoids (e.g. cortisol) from the Z. Fasciculata into the blood
5. cortisol bound by carrier proteins in blood
6. Stimulates liver to increase glycogenolysis and gluconeogenesis, and decrease glycogenesis
7. Adipose cells increase lipolysis and decrease lipogenesis
8. All cells have stimulation of protein catabolism (breakdown), and decreased glucose uptake
9. High cortisol increases retention of Na+ and H2O, decrease inflammation, suppresses immune system, and inhibits connective tissue repair
10. Net effect: increase of all nutrients in blood (think stress for fight/flight)
11. Increase levels of cortisol inhibits CRH and ACTH release

Question 6

Insulin pathway

Answer 6

1. Pancreas stimulated by increase in BGL (blood glucose level)
2. Pancreatic Beta cells release insulin into blood, travels to target cells (effectors)
3. Liver uses glucose for glycogenesis, decreased glycogenolysis and gluconeogenesis
4. Adipose cells take in fatty acids to increase lipogenesis and decrease lipolysis
5. All cells (esp muscle) take in amino acids, which stimulates protein anabolism (growth)
6. Most cells take in glucose
7. Net effect: decreased BGL, fatty acids, and amino acids in blood
8. Insulin release inhibited as BGL drops

Question 7

Glucagon pathway

Answer 7

1. Pancreas stimulated by decrease in BGL
2. Pancreatic alpha cells release glucagon
3. Glucagon travels in blood to effector organs/cells for stimulation
4. Adipose cells increase lipolysis and decrease lipogenesis
5. Liver increases glycogenolysis and gluconeogenesis, decreases glycogenesis
6. Net effect: increase in BGL and fatty acid levels in blood to be used by cells for energy
7. Rise in BGL inhibits glucagon release