Parathyroid Glands

Question 1

How does PTH is regulated?

Answer 1

1. decrease of blood Ca
2. release of PTH
3. target organs response :
   - intestine Ca absorption
   - bone resorption
   - kidney Ca reabsorption
4. increase blood Ca
5. negative feedback on PTH release

Question 2

How does calcitonin is regulated?

Answer 2

1. rise in blood Ca
2. release of calcitonin
3. target organ response
   - bone Ca deposition
   - secretion of Ca by kidneys
4. decrease in blood Ca

Question 3

What is calcitonin?

Answer 3

the only hormone that decreases endogenous blood Ca
first discovered in fish
however human gene sequence not identical to fish so role in humans not clear

Question 4

I am the cells that secrete PTH. Who am I?

Answer 4

chief cells or oxyphil cells

Question 5

I am the cells that secrete calcitonin. Who am I?

Answer 5

parafollicular cells (c-cells)

Question 6

what are the roles of calcium?

Answer 6

• main structural component of the skeleton
• enzyme activity
• second messenger
• muscle contraction
• membrane excitability
• blood clotting

Question 7

where is the majority of the total body calcium?

Answer 7

in bones (99%)

Question 8

How tetany occurs?

Answer 8

1. hyperventilation = low pCO2 = low H+
2. proteins release their protons to compensate
3. Ca binds to proteins
4. lower blood Ca
5. release of Ca from sarcoplasmic reticulum
6. muscle contraction = spasm of skeletal muscle

Question 9

How is PTH secretion regulated when high blood Ca?

Answer 9

high blood Ca = binds to G coupled receptor
=> decrese cAMP and increase IP3
=> Gi activated to reduce cAMP
=> PLC to convert IP2 to IP3
=> inhibition of PTH exocytosis

Question 10

How is PTH regulated when low blood Ca?

Answer 10

increase in cAMP and a decrease in IP3

=> expression and exocytosis of PTH

Question 11

what are the two major proteins in bones?

Answer 11

• osteocalcin (from osteoblasts) binds to hydroxyapaptite (calcium salts)
• osteonectin (fibroblasts) binds collagen and hydroxyapaptite and may serve for calcification

Question 12

what can serve as an indicator for bone growth?

Answer 12

osteocalcin serum levels

Question 13

what factors can trigger bone remodeling?

Answer 13

• physical factors (fractures)
• hormonal factors (PTH)
• paracrine factors (IGF-II from osteoblasts)

Question 14

I am a protein that helps osteoblasts to attach to the bone surface. Who am I?

Answer 14

integrins

Question 15

How do osteoclasts dissolve hydroxyapaptite?

Answer 15

proton pump (H+ ATPase) move H+ out into the extracellular matrix => acid pH degrading bone

Question 16

What compound found in urine can indicate bone resorption?

Answer 16

pyridinoline => collagen breakdown product

Question 17

what are the steps of bone remodeling?

Answer 17

1. PTH with vit D stimulate osteoblasts to secrete OAF (osteoclasts activating factor)
2. osteoclasts are activated = bone resorption
3. macrophages phagocytose debris
4. osteoblasts fill the cavity
5. osteoid is mineralized

Question 18

What is the role of PTH related to phosphate?

Answer 18

inhibits reabsorption of phosphate by kidneys

Question 19

What is PTHrP?

Answer 19

PTH related protein => effects similar to PTH => binds to PTH receptors

Question 20

What protein is produced by the placenta and fetus and what is its role?

Answer 20

PTHrP

• placental transport of Ca
• dev of chondrocytes

Question 21

What are the receptors to PTH?

Answer 21

PTHR-1 = binds to PTH + PTHrP (bone + kidneys)
PTHR-2 = binds only PTH

Question 22

What are 3 diseases of the bone and their main characteristics?

Answer 22

1. osteoporosis = XS osteoclast function (decreases bone Ca) = frequent fractures
2. osteopetrosis = + calcification, decreased osteoclasts activity = brittle bone + prone to fractures
3. involutional osteoporosis = decrease BMD with age

Question 23

How does menopause affect bone remodeling?

Answer 23

At menopause, there is no more follicles that produce estrogen. Estrogen regulates osteoclasts activity by inhibiting cytokines that promote osteoclasts dev and stimulating cytokine TGFB that causes apoptosis of osteoclasts. So with lower estrogen levels, osteoclasts are stimulated and it leads to osteoporosis.

Question 24

What are the signs and symptoms of hyperthyroidism?

Answer 24

psychic moans
groans
stones
bones

Question 25

What can be the causes of hyperthyroidism?

Answer 25

• parathyroid adenoma
• enlargement of a single gland
• can be from gene mutation => loss of tumor gene suppressor

Question 26

What can cause hypothyroidism?

Answer 26

• failure to secrete PTH
• altered response to PTH
• vit D deficiency
• resistance to vit D

Question 27

What are the symptoms of hypothyroidism?

Answer 27

tetany

Question 28

How can hypothyroidism be treated?

Answer 28

vit D and Ca supp

Question 29

What calcitonin action on metabolsim?

Answer 29

acts through GPCR = neurotransmitter, and vasodilator

Question 30

What is calcitriol and why is it important?

Answer 30

vit D form

• acts on intestine cells for Ca absorption
• physiological aspects
• nuclear receptor promoting calbindin

Question 31

what is osteomalacia?

Answer 31

vit D deficiency in adults

Question 32

What are the consequences of vit D toxicity?

Answer 32

• weakness, lethargy, headaches, polyuria

- calcification in soft tissues

Question 33

how can vit D toxicity be treated?

Answer 33

decrease Ca and vit D, cortisol, rehydration. takes time to be cleared out

Question 34

What are the steps for Ca uptake by intestine cells?

Answer 34

1. Ca enters cell
2. transported by proteins (myosin and calmodulin) across villi
3. Ca accumulation into cytoplasm
4. excreted by exocytosis (vesicular transport or calbindin)

Question 35

where is vit D converted?

Answer 35

liver + kidneys to increase Ca absorption