Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

SFIV Test 2 > Calcium Homeostasis II > Flashcards

Calcium Homeostasis II Flashcards

1
Q

What is transcellular pathway of calcium absorption?

A

Calcium enters the apical membrane via calcium channels

Upon entering, calcium binds to calbindin-D9k

It is extruded across the basolateral membrane via a calcium ATPase - PMCA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does Vitamin D3 affect calcium reabsorption in the small intestine?

A

Increases absorption via the transcellular pathway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How is phosphate absorbed in the intestine?

A

Paracellularly at tight junctions

Active transport involving a Na-phosphate cotransporter

Expression increased by Vitamin D3 and when dietary phosphate is low

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does PTH affect calcium resabsoprtion in the kidney?

A

Stimulates TRPV5 activity in the PCT and TAL

Also stimulates reabsorption in the DCT

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does PTH affect phosphate reabsorption in the kidney?

A

Increases urinary phosphate excretion by inhibiting reabsorption in the proximal and distal tubules

Promotes removal of sodium-dependent phosphate cotransporters from the luminal membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the affect of PTH on 1a-renal hydroxylase?

A

Induces its synthesis in the PCT

Catalizes the formation of active vitamin D (1,25(OH)2D3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the active portion of PTH?

A

N-terminal region

Synthetic N-terminal fragments can induce all known actions of PTH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How do chief cells regulate the quantity of intact PTH getting released?

A

Utilize intraglandular degradation of stored hormone

Secretory vesicles contain proteases that degrade intact PTH to inactive C-terminal fragments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the secretion of PTH in hypercalcemic and hypocalcemic states?

A

Hypercalcemic - decrease in secretion of intact PTH and an increase in release of inactive C-terminal fragments

Hypocalcemia - cheif cells release mostly intact PTH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the principal physiological regulator of PTH secretion?

A

Plasma concentration of ionic calcium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the response of chief cells to a decline in serum Ca?

A

Respond immediately to an acute decline in Ca by release preformed PTH

Decrease in intraglandular degradation of PTH, causing the release of more intact PTH

If prolonged, PTH gene transcription and an increased rate of chief cell proliferation occurs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do chief cells respond to hypercalcemia?

A

Intraglandular PTH breakdown increases

However, PTH secretion is not totally suppressed due to the basal rate of PTH secretion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the calcium-sensing receptor (CaSR)?

A

G protein-coupled receptor that monitors minute-to-minute fluctuation in extracellular fluid Ca

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the effect of 1,25(OH)2D3 on PTH secretion?

A

Active Vitamin D3 inhibits PTH secretion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the principal targets of PTH?

A

Kidneys and Bone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the type 1 PTH receptor?

A

Binds both PTH and PTH releated protein (PTHrP)

Increases intracellular cAMP levels

17
Q

What is the affect of PTH on bone?

A

Mobilizes calcium from bone by promoting the expression of RANK-L

Also downregulates the expression of OPG

18
Q

What are the affects of PTH on the kidneys?

A

Increase Ca reabsorption by acting on Tubule cells

Promotes phosphate excretion

Induces 1a-renal hydroxylase expression

19
Q

What is the direct effect of PTH excess?

A

Bone lesions due to PTH-induced bone resorption

20
Q

What are the effects of PTH-induced hypercalcemia?

A

Fatigue

Vomiting, ab pain, constipation, pancreatitis

Neuro symptoms

Impaired kidney function due to kidney stones

Decreased membrane excitability

21
Q

What are the clinical features of PTH deficiency?

A

Tetany from the spontaneous discharge of the peripheral nerves

22
Q

What is Pseudohypoparathyroidism?

A

Rare familial disorder characterized by target tissue resistance to PTH

23
Q

What is the function of PTH related protein?

A

Activates the same receptor as PTH

But is produced locally and acts as a paracrine or autocrine regulator

Regulates calcium flux through the placenta

24
Q

What is humoral hypercalcemia of malignancy?

A

Syndrome associated with malignant tumors

PTHrP is the most common mediator of HHM

25
Q

What is Vitamin D3 and D2?

A

D3 - lipid soluble vitamin formed by a photolytic reaction

D2 - Formed from a platn sterol

Both are inactive until modification by kidney or liver enzymes

26
Q

How is Vitamin D activated?

A

First step: conversion of vitamin D to 25 hydroxyvitamin D, this step is essentially unregulated

Second Step: Hydroxylation of 25(OH)D, this process is highly regulated and occurs in the PCTs of the kidneys

27
Q

What is 25(OH)D?

A

Has very little activity

Long circulatory half-life and the most abundant form in the blood

This is what is measured when clincally assessing a patient’s Vitamin D status

28
Q

How is the activation of Vitamin D regulated?

A

Hypocalcemia and increased PTH have stimulatory affects on 1a-hydroxylase activity

Increased calcium and low PTH decrease 1a-hydroxylase activity

Active Vitamin D also has a negative feedback effect on the enzyme

29
Q

What is Vitamin D binding protein?

A

Principal carrier of vitamin D and vitamin D metabolites

30
Q

What are the principal targets of active Vitamin D?

A

Small intestine

Bone

Parathyroid glands

31
Q

What is the affect of active Vitamin D on the small intestine?

A

Enhances calcium absorption by inducing expression of epithelial calcium channels and calbindin-D9k

32
Q

What is the most apparent consequence of vitamin D deficiency?

A

Decreased bone mineralization

33
Q

What is the effect of active vitamin D on the parathyroid glands?

A

Negative feedback effect on PTH secretion by inhibiting the expression of the PTH gene

Induces the expression of the genes for the CaSR and the Vitamin D receptor

34
Q

What is the effect of active vitmain D on bone?

A

Promotes mineralization by ensuring calcium and phosphate availability via its actions in the small intestine

Promotes osteoclastogenesis by inducting RANK-L expression

Suppresses OPG

35
Q

What is the effect of active vitamin D on the kidney?

A

Modulates its own formation by inhibiting 1a-hydroxylase activity and stimulating 24-hydroxylase activity

36
Q

What is the mechanism of action for Vitamin D?

A

Binds to Vitamin D receptor which acts as a ligand activated transcription factor

Forms a heterodimer with an unliganded retinoid X receptor (RXR)

The complex binds to a vitamin D response element in the regulatory region of a target gene

37
Q

What results from vitamin D deficiency?

A

Rickets

Osteomalacia

38
Q

What is calcitonin?

A

Polypeptide hormone secreted by parafollicular cells in the thyroid

Lowers plasma calcium levels by supressing bone resorption by osteoclasts

39
Q

What stimulates the release of calcitonin?

A

High calcium levels

Gi hormones, particularly gastrin

SFIV Test 2 (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions