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Renal Module > Lecture 8 - Plasma Ca2+ And Vitamin D > Flashcards

Lecture 8 - Plasma Ca2+ And Vitamin D Flashcards

1
Q

What are ca2+ ions in the intracellular fluid essential for?

A

Muscle contraction, neurotransmitter release and enzyme activation

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2
Q

What is the extracellular function for ca2+?

A

Blood coagulation - it is a key cofactor in the clotting cascade

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3
Q

What can ca2+ also exist as?

A

Calcium salts in bone which provide the structural integrity of the skeleton

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4
Q

What happens when Extracellualr ca2+ falls below normal?

A

The nervous system becomes progressively more excitable because of increased permeability of neuronal membranes to Na+

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5
Q

What does hyperexcitability cause?

A

Tetanic contractions - because at the neuronal muscle junction it will cause uncontrolled muscle contractions which lead to a condition called hypocalcaemic tetany

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6
Q

What is hypocalacaemic tetany?

A

It occurs in the hand and it leads to very painful muscle spasms

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7
Q

What are the different types of extracellular ca2+?

A

Protein bound (albumin), anion complexed (bicarbonate) and ionised

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8
Q

What are the tissues involved in ca2+ homeostasis?

A

GI tract, Kidney and bone

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9
Q

How much ca2+ do we absorb every day?

A

1000mg

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10
Q

How much ca2+ is absorbed?

A

35% - therefore 35% needs to get rid,
15% through the GI tract
20% through the kidneys

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11
Q

What is the readily exchangeable pool?

A

It is the ca2+ ions on the surface of the bones but they don’t stay on the surface they move in one direction or the other.
- they might flow into the bone to be incorporated as a ca2+ salt in the bone
- or into the extracellular fluid

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12
Q

What are the main target organs or ca2+ homeostasis?

A

Intestine, kidney and bone

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13
Q

What organs have vitamin D metabolites?

A

Intestine and kidney

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14
Q

Where is 60% of the total plasma ca2+ filtered and then reabsorbed?

A

In the PCT of the kidney by active transport, 30% is in the TAL through passive diffusion, 30% is absorbed through active transport in the DT, 9% collecting duct

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15
Q

Where are the passive mechanisms of the kidney absorption found?

A

In the loop of henle of the nephron in the kidney, the ca2+ ions move between the cells by paracellular transport

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16
Q

What are the active mechanism for the reabsorption of ca2+ in the kidney?

A

PCT and DT - have a transcellular transport of ca2+,
Ca2+ ions are moved into the cell from the lumen and then moved out across the opposite membrane into the blood

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17
Q

What is trancellular transport driven by?

A

The concentration gradient of ca2+ in the lumen

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18
Q

What happens if the conc in the lumen is higher than 2.5mM (in the blood)?

A

Ca2+ moves down the conc gradient (paracelllar pathway_ there is no limiting step

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19
Q

Higher the conc gradient =

A

The more ca2+ will be transported

20
Q

What pump is involved in the active mechanism?

A

PMCA pump which pumps ca2+ out of the cell

21
Q

What is an advantage and disadvantage of the active pathway?

A

It never stops, but disadvantage = there is a rate limiting step

22
Q

What does the parathyroid hormone do?

A

Opens the ca2+ channel to get more ca2+ ions to enter the lumen for the paracellular pathway

23
Q

What are the 3 hormones that regulate the Extracellular ca2+?

A

Parathyroid hormone, 1,25 DHCC and calcitonin

24
Q

What form of vitamin D is found in human ?

A

Vitamin D3

25
Q

What cells are the principal site for the parathyroid hormone (PTH)?

A

Chief cells

26
Q

What is the main effect for PTH?

A

Increase plasma ca2+ - it is a hypercalcaemic hormone

27
Q

What is the stimulus for PTH?

A

A decrease in plasma ca2+

28
Q

What part of the nephron is stimulated by the PTH?

A

The distal tubule

29
Q

What else does the PTH stimulate?

A

The activity of 1-alpha-hydroxylase which catalyses the formation of 1,25-DHCC

30
Q

What is the 1,25 DHCC structure similar to?

A

A steroid hormone

31
Q

What 2 sources do humans acquire vitamin D from?

A

The diet and the skin by ultraviolet radiation

32
Q

What year did lots of people have vitamin D deficiency?

A

In 1929 - the Great Depression, as people couldn’t afford food. Started fortifying food to add vitamin D like a supplement (Kelloggs still do it)

33
Q

Is vitamin D3 inactive or active?

A

Inactive - therefore it must be converted to 1,25DHCC

34
Q

What does calcitonin do?

A

Acts to decrease plasma ca2+ levels - it is the only home one that causes a decrease in plasma ca2+

35
Q

What is hypocalcaemia caused by?

A

A deficiency in vitamin D activity

36
Q

What does hypocalcaemia result in?

A

It results in neuromuscular excitability

37
Q

What are the symptoms for neuromuscular excitability?

A

Numbness, tingling, hyperventilations and tetany. Also a prolonged Q-T interval

38
Q

What can hypocalcaemia result in?

A

A metabolic bone disease

39
Q

What are examples of a metabolic bone disease?

A

Osteomalacia and rickets

40
Q

What are the two phases of bone?

A

An organic matrix (osteroid) whic becomes mineralised to form hydroxyapatite

41
Q

What does too little collagen cause

A

Too little mineralisation - the organic matrix is lower than normal (bones bend outwards)

42
Q

How can you get a deficinency of vitamin D

A

Insufficient exposure to sunlight and in the diet,
Malabsorption of vitamin D in GI tract and inability to convert vitamin D to 1,25DHCC

43
Q

what happens if there is a mutation in the receptor for 1.25DHCC?

A

Can cause a disease called rickets type II

44
Q

What is rickets type II characterised by?

A

Impaired intestinal absorption

45
Q

What are the treatments for type II rickets?

A

Calcitriol, dietary ca2+, injections if malabsorption can not be ovecome by dietary supplements

Renal Module (10 decks)

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