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Endo > Parathyroid Gland and hormones regulating Ca and Po > Flashcards

Parathyroid Gland and hormones regulating Ca and Po Flashcards

Wk 7

1
Q

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

A

S- hard tissues like bone and teeth

R- metabolic and signaling pathways

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2
Q

what are the primary sources of plasma ca and Po

A

diet and skeleton

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3
Q

What forms can Phosphate be in?

A

Free, ionised from

Protein bound form and complexed with cations

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4
Q

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

A

Three tissues: bone, intestine and kindey

Three hormones: PTh, Calcitonin and vitiman D

Three cells: osteoblast, osteocytes and osteoclast

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5
Q

What occurs when there is high oestoblasts activity?

What happens when there is high osteoclast activity?

A

More osteoblast activity = bone activity

More osteoclast activity= reabsorption

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6
Q

What is the most important form of calcium and why?

A

ionised = MOST IMPORTANT as is diffusible and biologically active

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7
Q

name some functions of calcium

A

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

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8
Q

What does the regulation of ca encompass?

A

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)

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9
Q

what does the regulation of Ca depend on?

A

Hypocalcaemia effects of calcitonin

Hypercalcaemia effects of PTH and Vitiman D

Calcium intake

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10
Q

Where is the parathyroid gland?

A

behind the thyroid gland

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

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11
Q

What cell is believed to secret the most PTH?

A

The Chief Cells

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12
Q

what is the chemical nature of PTH?

A

84 amino acid polypeptide

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13
Q

what are the actions of PTH on bone?

A

Liberates calcium from the bone

Bone resorptive effect

Transports calcium from bone to ECF

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14
Q

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

A

Rapid Phase

Slower phase

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15
Q

How long is the rapid phase?

A

Begins in minutes

Increases progressively from several hours

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16
Q

What occurs in the rapid phase?

A

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

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17
Q

What occurs in the slower phase?

A

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

18
Q

how long is the slower phase?

A

several days or weeks

19
Q

What are some actions of PTH on GIT?

A

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

20
Q

What are some actions of PTH on the kidney?

A

Increased reabsorption of ca (

Increased urinary excretion of phosphate

21
Q

What are the steps for Ca absoprtion?

A

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

22
Q

What are the actions of PTH on the bone?

A

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.

23
Q

What are the effects of Calcitonin?

A

Opposite to PTH

24
Q

What is the origin of calcitonin?

A

parafollicular cells or C cells of thyroid gland

25
Q

How is calcitonin stored?

A

secretory vesicles in C cells

26
Q

What triggers and diminishes calcitonin?

A

Trigger: rise in extracellular Ca2+

Lowering: Extracellular Ca2+ diminished secretion

27
Q

What are some actions of Calcitonin?

A

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]

28
Q

What are the properties of Vitiman D?

A

Fat-soluble, water-insoluble

29
Q

What is the form of vitamin D in circulation?

A

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

30
Q

What is vitamin D similar to?

A

Similar to Steroid hormones= lipophilic, nuclear receptors

31
Q

What are the actions of Vitamin D?

A

Increases intestinal Ca absorption

increases Po absorption

acts synergetically with PTH to enhance Ca reabsorption

increases both osteoblastic and osteoclastic differentiation

32
Q

What are the causes of primary hyperparathyrodisim?

A

Most Common: (functionally active) Tumour of the PT Gland, parathyroid adenomas or hyperplasia of

Excess PTH secretion

Increased Ca in ECF

33
Q

What are the consequences of Primary Hyperparathyroidism?

A

Extensive decalcification of bone (hypercalcemia and hypercalciuria)

Large cystic areas (holes) in bone (osteitis fibrosa cystica)

High Ca levels

34
Q

What are the consequences of high serum Ca levels

A

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

35
Q

What are the causes of secondary hyperparathyroidism?

A

Compensation for hypocalcaemia

Increased parathyroid hormone

Can occur as a complication of chronic renal failure (can’t produce 1,25 DHCC)

36
Q

What is PseudoHypoparathyroidism

A

Rare familial disorder = tissue resistance to PTH

Non-functioning PTH receptor

37
Q

What are the consequences of PseudoHypoparathyroidism

A

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

38
Q

What does ‘plasia’ refer to?

A

number of cells

39
Q

What are the causes of hypoparathyroidism

A

No sufficient PTH from parathyroid glands

40
Q

what are the consequences of hypocalcaemia?

A

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

41
Q

What is Hypocalcaemia?

A

Low calcium in blood

42
Q
A

Endo (14 decks)

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