Hormones and Mineral Homeostasis

Question 1

Functions of aldosterone

Answer 1

Regulates sodium and potassium in the extracellular fluid by increasing the renal uptake of sodium and excretion of potassium through urine
Because of this:
- A decrease in K inhibits the secretion of aldosterone
- A decrease in Na causes the release of aldosterone

Question 2

Functions of Calcitonin

Answer 2

• Decreases the entry of calcium form bone to plasma
• Inhibits bone osteoclast activity and bone resorption
• Enhances bone mineralization
• Causes varying degrees of hypophosphatemia

**Overall net decrease in calcium in circulation. Calcitonin reduces calcium when calcium levels are high in circulation

Question 3

What are calcitonin antagonistic to?

Answer 3

Antagonistic to the effects of PTH (counter regulation) and vice versa

Question 4

Functions of parathyroid hormone

Answer 4

• Elevates blood concentration of calcium
• Decreases blood levels of phosphorus
• Increases urinary excretion of phosphorus
• Decreases kidney tubular reabsorption of phosphorus
• Increases kidney tubular reabsorption of calcium
• Increases rate of skeletal remodeling
• Increases rate of bone resorption
• Increases the number of bone osteoclasts
• Increases the rate of osteolysis
• Accelerates the formation of active form of vitamin D

OVERALL, causes a net increases in calcium in circulation, and a net decrease in phosphorus. PTH mobilizes calcium when calcium levels are low

Question 5

Functions of Vitamin D/cholecalciferol (CC)

Answer 5

• Increases the absorption of calcium and phosphorus form the intestine
• Ensures the sufficient availability of minerals for bone mineralization
• Necessary for osteoclastic resorption and calcium mobilization from the bone

Question 5

Vitamin D deficiency

Answer 5

• Rickets
• Causes deformities of bones in the axial and abaxial skeleton

Question 6

Excess of Vitamin D

Answer 6

Results in hypercalcemia and hyperphosphatemia in cattle and horses

• High intake of vitamin D from plants can cause enhanced intestinal absorption of calcium and phosphorus. Results in high mineralization of cardiovascular tissues, kidneys, lungs, and other soft tissues

Question 7

Are receptors always located on target sites?

Answer 7

No, not all target cells will have receptors for the specific hormone. Therefore the targets will have intermediary actions from the receptor elsewhere that will eventually pass on the information

PTH acts on osteoblasts where receptors are located. Acts on RANK-L which causes signalling cascade which passes on to osteoclasts

Question 8

Maintenance of calcium and phosphorus in ECF

Answer 8

Gut
- Increase in parathyroid hormone and vitamin D increases Calcium intake from diet

Kidney
- Parathyroid hormone and vitamin D help reabsorption of calcium from glomerular filtrate
- Parathyroid hormone and calcitonin help remove phosphate

Bone
- Calcitonin acts on osteoclasts at calcitonin receptors and decreases calcium release
- Parathyroid hormone increases osteoclast calcium release

Question 9

Distribution of adenylate cyclase-linked hormone receptors in the nephron

Answer 9

Glomerulus and kidney tubules
1. Proximal convoluted tubule
- Parathyroid hormone binding here will increase phosphate
2. Distal convoluted tubule
- Parathyroid binding here will remove calcium from kidney, increasing it in the body
- Calcitonin binding here will do the opposite
3. Collecting tubule
- ADH helps with reabsorption of water

Question 10

Receptor locations in the kidney

Answer 10

• Proximal convoluted tubule- parathyroid receptors
• Loop of henle- calcitonin receptors
• Distal convoluted tubule- parathyroid receptors and calcitonin receptors

Question 11

Renin-Angiotensin- Aldosterone (RAAS) pathway/system

Answer 11

• Integration of different organ systems and hormones (kidneys, liver, lungs, adrenal gland)

Steps:
1. Dehydration, sodium deficiency, or hemorrhage
2. Decrease in blood volume
3. Decrease in blood pressure
4. Juxtaglomerular cells of kidneys sense decrease of blood pressure and will release increased amounts of renin
5. Liver will be releasing angiotensinogen at the same time. Angiotensinogen will be converted by renin into angiotensin I
6. The lungs will convert angiotensin I to angiotensin II by angiotensin converting enzyme
7. Increased Angiotensin II will cause vasoconstriction of arterioles and increased blood pressure AND adrenal cortex to increase aldosterone causing the kidneys to increase Na and water reabsorption and increase secretion of K and H into urine
8. Results in increased blood volume and an increase in blood pressure