PHGY 210 Lecture Notes - Lecture 3: Mineralocorticoid, Glycogen, Carbohydrate Metabolism
Jan 9, 2017
Endocrine Control of Calcium Homeostasis
-calcium ion plays key role in many fundamental biological processes
-essential structural component of skeleton
-important in normal blood clotting
-helps maintain transmembrane potential of cells
-w/ Na+ and K+
-important in excitability of nervous tissue
-important in contraction of muscles
-important in release of hormones and neurotransmitters
-list not tested
-concentration in cellular and extracellular fluid
-~10mg/100ml
-in circulation 50% free, 50% bound to albumin
-about 99% of body’s calcium is in bone
-part of this calcium is quite loosely bound
-bone thus serves as calcium reservoir
-hormonal control
-maintenance of plasma calcium is achieved mainly by exchange b/w bone and plasma
under influence of hormones
-hormones also affect intestinal absorption of calcium and excretion of by kidneys
Three Hormones in Particular are of Importance
-parathyroid hormone (PTH)
-protein
-produced by parathyroid glands
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-increases circulating levels of Ca++
-calcitonin
-protein
-produced by parafollicular or “C” cells of thyroid gland
-lowers circulating levels of Ca++
-vitamin D
-increases circulating levels of Ca++
Calcium Cycle
-obtained in diet
-milk, cheese, eggs, butter, etc.
-absorbed from digestive tract primarily in duodenum and upper jejunum
-its absorption is increased by vitamin D and PTH
From plasma
-some of the calcium will be deposited in bone or cells of other tissues
-calcitonin increases calcium deposition in bone
-some will go through kidney and into urine
-calcitonin increases this loss
-when plasma concentration is below 10mg/100ml then PTH will stimulate reabsorption of
calcium from kidney and removal of calcium from bone (bone resorption)
-stable concentration in blood is achieved mainly by exchange of calcium b/w bone and plasma
under hormonal influence
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Parathyroid Hormone
-secreted from parathyroid chief cells embedded in surface of thyroid
-4 parathyroid glands
-located on back side of thyroid gland
-removal of parathyroids:
-severe drop in plasma calcium levels causing tetanic convulsions and death
-PTH structure:
-84 amino acid polypeptide
-only N-terminal 34 amino acids important for full activity
-synthesized as part of larger protein
-preproparathyroid hormone
-which undergoes proteolytic cleavage to produce PTH
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find more resources at oneclass.com
Document Summary
Calcium ion plays key role in many fundamental biological processes. In circulation 50% free, 50% bound to albumin. About 99% of body"s calcium is in bone. Part of this calcium is quite loosely bound. Maintenance of plasma calcium is achieved mainly by exchange b/w bone and plasma under influence of hormones. Hormones also affect intestinal absorption of calcium and excretion of by kidneys. Produced by parafollicular or c cells of thyroid gland. Absorbed from digestive tract primarily in duodenum and upper jejunum. Its absorption is increased by vitamin d and pth. Some of the calcium will be deposited in bone or cells of other tissues. Some will go through kidney and into urine. When plasma concentration is below 10mg/100ml then pth will stimulate reabsorption of calcium from kidney and removal of calcium from bone (bone resorption) Stable concentration in blood is achieved mainly by exchange of calcium b/w bone and plasma under hormonal influence.
