Calcium & Phosphorous
What role does Vit D have in the small intestine?
Ca2+ cannot cross cell membrane of epithelial cells without the mechanisms activated by 1,25-hydroxycholecalciferol
What inhibits osteoclastic activity in bones?
Calcitonin
What is bone absorption inhibited by?
Calcitonin
Is the action of PTH on intestines direct or indirect?
Indirect *via activation of vitamin D
What physiological processes involve calcium?
Muscular contraction Membrane permeability Endocrine and exocrine secretions Enzyme regulation Coagulation
What must happen to vitamin D to be an active metabolite?
Must be successfully hydroxylated
What three hormones are involved in calcium regulation?
PTH Calcitonin Vitamin D3
What two things combined become the second major regulatory hormone for Ca2+ and phosphate metabolism?
PTH & Vitamin D
What is the relationship b/w PTH and the small intestine?
PTH activates Vitamin D synthesis and indirectly stimulates intestinal Ca2+ absorption
What regulates blood calcium levels?
PTH and Calcitonin
How does PTH inhibit phosphate reabsorption?
PTH binds to receptor on the cell membrane of target tissue (kidney cell/ bone cell) --> PTH receptor via G protein to adenylyl cyclase --> cAMP--> cAMP activates a series of protein kinases which phosphorylate intracellular proteins leading to the inhibition of Na+ phosphate co-transport--> decreased phosphate reabsorption and phosphaturia
How does PTH activate vitamin D synthesis ?
PTH stimulates renal I a-hydroxylase
Where is 99% of calcium found?
bones and teeth
What is it called when bone fails to mineralize in adults?
osteomalacia
What deepens Vitamin D formation in the skin?
sun exposure (specifically UVB radiation)
Where is calcitonin secreted from?
thyroid gland
What is the role of PTH?
to regulate concentration of Ca2+ in ECF
Where are the parathyroid glands embedded?
In the posterior thyroid capsule
What increases I a-hydroxylase activity?
-Decreased plasma Ca2+ -Increased circulating levels of PTH -Decreased plasma phosphate concentration
What is the role of phosphate in the body?
-Formation of ATP -Phosphate can serve as biologic buffer -Phosphate can act as a modifier of proteins, thereby altering their functions
What happens when blood calcium concentration fails?
-PTH formation increases -Higher rate of formation of Vit D -Elevated Vit D stimulates formation of calcium-binding protein which increases the rate of absorption of calcium from the lumen of the gut
What are the roles of calcium in the body?
-Signal transduction (neurotransmitter release) -Second messenger -Structural component in bone matrix -Muscle contraction -Bone formation
What is the total Ca2+ concentration in blood?
10 mg/dL
The enzyme necessary for the conversion and activation of vitamin D is:
1a-hydroxylase
What is Vitamin D converted to in the liver?
25-hydroxycholecalciferol
How is Vitamin D activated in the kidney?
25-hydroxycholecalciferol undergoes hydroxylation --> 1,25-hydroxycholecalciferol
Which of the following best describes the effect of parathyroid hormone (PTH)? A. It increases plasma Ca 2+ concentration B. It decreases plasma Ca 2+ concentration C. It increases the rate of ATP formation D. It stimulates the thyroid gland to produce thyroxine
A. It increases plasma Ca 2+ concentration
Blood calcium levels are controlled by hormones from which structures? A. The parathyroid glands and the thyroid gland B. The anterior lobe of the pituitary gland and the thyroid gland C. The parathyroid glands and the anterior lobe of the pituitary gland D. The adrenal cortex and the hypothalamus.
A. Parathyroid glands and the thyroid gland
What does PTH cause on bone initially?
An increase in bone formation (short term effect)
Which of the following statements is CORRECT? A. Calcitonin acts to increase blood calcium levels B. Parathyroid hormone release is inhibited by increased calcium levels C. Parathyroid hormone stimulates bone-resorbing cells to take up calcium D. Calcitonin inhibits parathyroid hormone
B. Parathyroid hormone release is inhibited by increased calcium levels
Which of the following describes a function of calcitonin? A. accelerating Ca 2+ release from bone B. stimulating Ca 2+ excretion by the kidneys C. reducing Ca 2+ deposition in bone D. stimulating the formation of 1,25 (OH)2-vitamin D in the kidneys
B. stimulating Ca2+ excretion by the kidney
What three tissues involve calcium regulation?
Bone (and teeth) Intestine Kidneys
What form of calcium accounts for 40%?
Bound calcium
What hormone is produced by the parafollicular cells of the thyroid gland? A. Parathyroid hormone B. Calcitonin C. Thyroid hormone D. Thyroxine
C. Calcitonin
Which of the following statement about calcitonin is CORRECT? A. Calcitonin supports and amplifies the effects of PTH B. Calcitonin lowers blood calcium levels by suppressing osteoblast activity in the bones C. Calcitonin lowers blood calcium levels by increasing the amount of calcium excreted in the urine D. In the cortex of the kidney, the reaction that converts Vitamin D into an active form is stimulated and tightly controlled by calcitonin
C. Calcitonin lowers blood calcium levels by increasing the amount of calcium excreted in the urine
Which of the following is NOT a target for PTH? A. Bone B. Kidney C. Thyroid gland D. Small intestine
C. Thyroid gland
Which of the following increases the reabsorption of Ca ++ from the filtrate in the kidney tubule? A. calcitonin B. mineralocorticoids C. parathyroid hormone D. aldosterone
C. parathyroid hormone
What cells in the parathyroid synthesize and secrete PTH?
Chief cells
Acid-base abnormalities after the ionized Ca2+ concentration by changing the fraction of Ca2+ bound to plasma albumin. Which of the following statements in correct? A. If a patient's blood has low [H+], free calcium blood levels are increased B. In acidemia, more calcium ion is bound to albumin C. Free blood calcium levels increase in alkalemia D. Free ionized Ca2+ concentration is increased in a patient with diabetic ketoacidosis
D. Free ionized Ca2+ concentration is increased in a patient with diabetic ketoacidosis
Regarding PTH, which of the following statements is FALSE? A. PTH has actions on bone, kidney, and intestine B. PTH is synthesized and secreted by chief cells of the parathyroid glands C.PTH increases the activity of osteoclasts D. Hormones of the anterior pituitary gland regulate the secretion of PTH
D. Hormones of the anterior pituitary gland regulate the secretion of PTH
Complete the sentence correctly. Parathyroid hormone: A. is produced by the parafollicular cells of the thyroid gland B. decreases the concentration of Ca ++ in the blood C. releases Ca ++ from the sarcoplasmic reticulum D. increases the concentration of Ca ++ in the blood.
D. increases concentration of Ca++ in the blood
Post-menopausal women are at greater risk for osteoporosis. This is primarily d/t increasing estrogen levels. What protective effect does estrogen have on bone physiology?
Estrogen binds to osteoclasts and inhibits bone degradation
What is the only form of Ca2+ that is biologically active?
Free, ionized Ca2+
What can albumins negatively charged sites bind to?
H+ ions or Ca2+ ions
What does vitamin D do?
Helps the body absorb calcium
What enzyme hydroxylates 25-hydroxycholecalciferol in the kidney?
I alpha hydroxylase
What stimulates I alpha hydroxylase?
Increase in PTH
What does PTH cause on bone?
Increase in bone resorption
What actions does PTH have on the kidney?
Inhibits phosphate reabsorption Stimulates Ca2+ reabsorption
What happens to formation of Vitamin D when calcium concentration in the blood decreases?
It increases
How does PTH regulate calcium levels?
It promotes calcium release from bone tissue Stimulates kidney to conserve calcium *Resulting in increase in blood calcium levels
What does calcitonin do?
Lowers blood calcium levels
What do the cytokines released from osteoblasts do?
Mediate PTH on osteoclasts then increase the number and activity of bone-resorbing osteoclasts
What is the relationship between the kidneys and GIT?
Net excretion of Ca2+ by the kidney is = to net absorption from GIT
What is ultrafilterable calcium?
Not protein bound Complexed to anions Free, ionized Ca2+
Where are PTH receptors located in bone?
On osteoblasts
What three cell types are involved in calcium regulation?
Osteoblasts Osteocytes Osteoclasts
What happens if low levels of calcium concentration persist?
Parathyroid glands hypertrophy *occurs w/ pregnancy and ds such as rickets
What is bone resorption stimulated by?
Parathyroid hormone
What does vitamin D deficiency in children cause?
Ricketts
What 3 organs are involved with Vitamin D synthesis?
Skin Liver Kidney
What is bone absorption stimulated by?
Vitamin D (1,25-dihydroxcholecalciferol)
What does albumin carry?
a negative net charged on its surface
What is 25-hydroxycholecalciferol bound to?
a-globulin in plasma
calcium binding protein, calcium-stimulated ATPase, and alkaline phosphatase promote what?
absorption of calcium ions out of the lumen of the intestine
What is PTH coupled with in bone and kidney?
adenylyl cyclase via Gs protein
What is calcium normally bound do? (specific)
albumin
What is renal I a-hydroxylase?
an enzyme that converts 25-hydroxycholecalciferol to active form (1,25 hydroxycholecalciferol) Vitamin D
What happens in acidemia?
an excess of H+ in blood -> more H+ binds to albumin leaving fewer sites for Ca2+ Free ionized Ca2+ concentration increases
What mediates the PTH on bone and kidney?
cAMP
What does Vitamin D stimulate the formation of?
calcium binding protein calcium-stimulated ATPase alkaline phosphatase
What mediates PTH action on osteoclasts?
cytokines released from osteoblasts
What happens in alkalemia?
deficit of H+ in blood -> less H+ will be bound to albumin, leaving more sites for Ca2+ to bind Free ionized Ca2+ concentration decreases
Where is Vitamin D provided?
diet and is produced in the skin from cholesterol
Is PTH's action on the kidney and bone direct or indirect?
direct
What does PTH do?
increases blood calcium levels
What is phosphate reabsorption inhibition?
inhibiting Na+-phosphate co-transport in the convoluted tubule of the nephron
What secretes PTH?
parathyroid gland
1,25 Dihydroxycholecalciferol (Vitamin D) affects intestinal Ca2+ absorption through a mechanism that
stimulates formation of calcium binding protein
What is phosphaturia?
the phosphaturic action of PTH causes phosphate that was resorbed from bone to be excreted in the urine
What does excreting phosphate in urine "allow"?
the plasma ionized Ca2+ concentration to increase
60% of calcium is ______
ultrafilterable calcium
What has been shown to increase and maintain bone mass?
weight bearing exercises
