Parathyroid Gland and hormones regulating Ca and Po

Question 1

What is the structural and regulatory role of plasma ca and Po?

Answer 1

S- hard tissues like bone and teeth

R- metabolic and signaling pathways

Question 2

what are the primary sources of plasma ca and Po

Answer 2

diet and skeleton

Question 3

What forms can Phosphate be in?

Answer 3

Free, ionised from

Protein bound form and complexed with cations

Question 4

What are the three tissues, cells and hormones involved in Calcium regulation?

Answer 4

Three tissues: bone, intestine and kindey

Three hormones: PTh, Calcitonin and vitiman D

Three cells: osteoblast, osteocytes and osteoclast

Question 5

What occurs when there is high oestoblasts activity?

What happens when there is high osteoclast activity?

Answer 5

More osteoblast activity = bone activity

More osteoclast activity= reabsorption

Question 6

What is the most important form of calcium and why?

Answer 6

ionised = MOST IMPORTANT as is diffusible and biologically active

Question 7

name some functions of calcium

Answer 7

SECOND MESSENGER

Structural integrity and metabolism of the bone,

Synaptic transmission

Coenzyme function

Control of excitability of nerve and muscle cells

Excitation (contraction coupling)

Stimulus (secretion coupling)

Regulation of transmembrane ion transport

Second messenger in the signal transduction pathways

Question 8

What does the regulation of ca encompass?

Answer 8

Intestinal absorption (vitamin D dependant) in the duodenum and proximal jejunum.

Renal tubular reabsorption and excretion (dietary)

Exchange of calcium between plasma and the bone (bone remodelling)

Question 9

what does the regulation of Ca depend on?

Answer 9

Hypocalcaemia effects of calcitonin

Hypercalcaemia effects of PTH and Vitiman D

Calcium intake

Question 10

Where is the parathyroid gland?

Answer 10

behind the thyroid gland

one behind each of the upper and lower lobes of the thyroid

Question 11

What cell is believed to secret the most PTH?

Answer 11

The Chief Cells

Question 12

what is the chemical nature of PTH?

Answer 12

84 amino acid polypeptide

Question 13

what are the actions of PTH on bone?

Answer 13

Liberates calcium from the bone

Bone resorptive effect

Transports calcium from bone to ECF

Question 14

What are the two phases that release Ca and Po from bone?

Answer 14

Rapid Phase

Slower phase

Question 15

How long is the rapid phase?

Answer 15

Begins in minutes

Increases progressively from several hours

Question 16

What occurs in the rapid phase?

Answer 16

Activates existing cells (osteocytes) to promote ca and po removal

Question 17

What occurs in the slower phase?

Answer 17

Proliferation of osteoclasts followed by increased osteoclastic resorption of the bone.

Question 18

how long is the slower phase?

Answer 18

several days or weeks

Question 19

What are some actions of PTH on GIT?

Answer 19

Uptake of Calcium

Increased absorption of phosphate

Indirect actions: using vitamin D – increase Ca absorption

Acts synergistically with Vit D to absorb Ca and Phosphate

Question 20

What are some actions of PTH on the kidney?

Answer 20

Increased reabsorption of ca (

Increased urinary excretion of phosphate

Question 21

What are the steps for Ca absoprtion?

Answer 21

Ca2+ enters the cell across the apical membrane through a channel

Inside the cell, Ca2+ binds to proteins, such as calbindin, and is taken up into intracellular organelles

The intestinal cell extrudes Ca2+ across the basolateral membrane through a Ca2+ pump and an Na-Ca exchanger

1,25 dihydroxyvitamin D stimulates all three steps of transcellular Ca2+ absorption

Question 22

What are the actions of PTH on the bone?

Answer 22

Liberates calcium from the bone

Bone resorptive effect

Transports calcium from bone to ECF

Bone remodelling: needs continuous removal or bone followed by synthesis of new bone matrix

Osteoblasts express surface receptors for PTH

PTH acts on osteoblasts to induce cytokines that increase the no. And activity of bone-resorbing osteoclasts.

Question 23

What are the effects of Calcitonin?

Answer 23

Opposite to PTH

Question 24

What is the origin of calcitonin?

Answer 24

parafollicular cells or C cells of thyroid gland

Question 25

How is calcitonin stored?

Answer 25

secretory vesicles in C cells

Question 26

What triggers and diminishes calcitonin?

Answer 26

Trigger: rise in extracellular Ca2+ Lowering: Extracellular Ca2+ diminished secretion

Question 27

What are some actions of Calcitonin?

Answer 27

Decrease the absorptive activities of the osteoclasts in the bone * Inhibit osteoclastic bone resorption – Within bone, the osteoclast—which lacks PTH receptors—is the principal target of calcitonin – Increased deposition of calcium in the bone – Decreased formation of new osteoclasts [prolonged effect] – In the kidneys – opposite to PTH [minor effect]

Question 28

What are the properties of Vitiman D?

Answer 28

Fat-soluble, water-insoluble

Question 29

What is the form of vitamin D in circulation?

Answer 29

either solubilised with chylomicrons or associated with a Vitamin-D-Binding protein (globulin)

Question 30

What is vitamin D similar to?

Answer 30

Similar to Steroid hormones= lipophilic, nuclear receptors

Question 31

What are the actions of Vitamin D?

Answer 31

Increases intestinal Ca absorption increases Po absorption acts synergetically with PTH to enhance Ca reabsorption increases both osteoblastic and osteoclastic differentiation

Question 32

What are the causes of primary hyperparathyrodisim?

Answer 32

Most Common: (functionally active) Tumour of the PT Gland, parathyroid adenomas or hyperplasia of Excess PTH secretion Increased Ca in ECF

Question 33

What are the consequences of Primary Hyperparathyroidism?

Answer 33

Extensive decalcification of bone (hypercalcemia and hypercalciuria) Large cystic areas (holes) in bone (osteitis fibrosa cystica) High Ca levels

Question 34

What are the consequences of high serum Ca levels

Answer 34

Decrease neuromuscular excitability – psychological disorders (depression, mental confusion, and fatigue), that are associated with hypercalcemia Cause a number of cardiovascular symptoms (palpitations, arrhythmias, and hypertension) Muscle weakness, decreased muscle tone and kidney stones

Question 35

What are the causes of secondary hyperparathyroidism?

Answer 35

Compensation for hypocalcaemia Increased parathyroid hormone Can occur as a complication of chronic renal failure (can't produce 1,25 DHCC)

Question 36

What is PseudoHypoparathyroidism

Answer 36

Rare familial disorder = tissue resistance to PTH Non-functioning PTH receptor

Question 37

What are the consequences of PseudoHypoparathyroidism

Answer 37

Decreased levels of guanine nucleotide-binding protein, Gs Increased PTH secretion and low serum calcium Congenital defects of skeleton including shortened metacarpal and metatarsal bones

Question 38

What does 'plasia' refer to?

Answer 38

number of cells

Question 39

What are the causes of hypoparathyroidism

Answer 39

No sufficient PTH from parathyroid glands

Question 40

what are the consequences of hypocalcaemia?

Answer 40

Increased neuromuscular excitability (tetany) Laryngeal stridor Cardiac effects (delayed repolarization is delayed = prolongation of GT interval) Dermatological effects (dry skin) Carpopedal spasm: tetany in the hand (spastic contraction). Occurs when ca blood conc. is less than normal range (6-10mg/dL) Chvostek's sign: twitching of facial muscles in response to contact

Question 41

What is Hypocalcaemia?

Answer 41

Low calcium in blood