Endocrine System: Calcium + Phosphate Homeostasis
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- Created by: Bhickling
- Created on: 21-04-21 09:42
How is GH (Growth Hormone) secretion regulated?
2 hypothalamic - neuro hormones:
1. GHRH (most important)
2. GHIH (somatostatin)
- directly effects GH + stimulates of insulin growth factor-1 from the liver
- IGF-1 mediates the growth stimulating effect of GH
1. GHRH (most important)
2. GHIH (somatostatin)
- directly effects GH + stimulates of insulin growth factor-1 from the liver
- IGF-1 mediates the growth stimulating effect of GH
1 of 30
What increases GH secretion? (8)
- inputs from CNS
- strenuous physical activity
- starvation
- stress
- decreased plasma glucose + free fatty acids
- increased plasma amino acid concentration
- ghrelin from parietal cells + hypothalamus
- thyroid hormone, androgens, oestrogens
- strenuous physical activity
- starvation
- stress
- decreased plasma glucose + free fatty acids
- increased plasma amino acid concentration
- ghrelin from parietal cells + hypothalamus
- thyroid hormone, androgens, oestrogens
2 of 30
What does GH do?
- stimulates growth of body mass + elongation of bones
- bone + cartilage growth, soft tissue growth
- lactation
- anabolic (protein synthesis, lipolysis, inhibits tissue uptake + utilisation of glucose)
- bone + cartilage growth, soft tissue growth
- lactation
- anabolic (protein synthesis, lipolysis, inhibits tissue uptake + utilisation of glucose)
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Compare GH and IGF-1
GH:
- protein- 191 amino acids
- 50% protein bound
- tyrosine kinase receptor
- GH-synthesising cells = most abundant in anterior pituitary
- similar structure of prolactin
- little -ve feedback on GHRH
IGF-1:
- protein- 70 amino acids
- 95% protein bound
- protein- 191 amino acids
- 50% protein bound
- tyrosine kinase receptor
- GH-synthesising cells = most abundant in anterior pituitary
- similar structure of prolactin
- little -ve feedback on GHRH
IGF-1:
- protein- 70 amino acids
- 95% protein bound
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What is required for normal growth?
- GH
- thyroid hormones
- insulin
- sex hormones at puberty
- good diet, absence of chronic stressors/ disease
- thyroid hormones
- insulin
- sex hormones at puberty
- good diet, absence of chronic stressors/ disease
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Where would calcium pools be found in the body?
- 99% found in bone as hydroxyapatite
- Intracellular fluid = free + protein bound
- Extracellular fluid = free + protein bound- includes interstitial fluid, blood plasma, rapidly mobilisable soluble bone Ca2+
- Intracellular fluid = free + protein bound
- Extracellular fluid = free + protein bound- includes interstitial fluid, blood plasma, rapidly mobilisable soluble bone Ca2+
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Where do you find the greatest concentration of free Ca in the body?- why is this important?
Extracellular fluid (actively pumped out of cells)
- important bc Ca is a very important signalling molecule in a huge amount of bodily processes
- important bc Ca is a very important signalling molecule in a huge amount of bodily processes
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Describe calcium homeostasis?
- linked to the concentration of free Ca in plasma
- tight regulation- within 2% of limits
- total plasma concentration = 2.5mM/l (10% associated w/ anions, 40% protein bound)
- free Ca concentration = 1- 1.25mM/l
- tight regulation- within 2% of limits
- total plasma concentration = 2.5mM/l (10% associated w/ anions, 40% protein bound)
- free Ca concentration = 1- 1.25mM/l
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How does calcium homeostasis occur?
- intestinal absorption
- renal excretion
- release + uptake by bone
- renal excretion
- release + uptake by bone
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Compared how Vitamin D2 + Vitamin D3 are produced
Vitamin D2 = produced by plants
Vitamin D3 = produced by UV light activity
Vitamin D3 = produced by UV light activity
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What needs to occur for Vitamin D2/3 to become biologically active?- where does this happen?
needs to be hydroxylated
- 1st hydroxylation in liver (either circulates or stored in adipose tissue)
- 2nd hydroxylation in kidney
- 1st hydroxylation in liver (either circulates or stored in adipose tissue)
- 2nd hydroxylation in kidney
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What is the active form of Vitamin D called?
calcitriol
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What does calcitriol do?
Overall effect = increase conc. of Ca in blood plasma
- increases Ca2+ uptake by SI
- increases renal absorption
- increases mobilisation of Ca from bone
- increases Ca2+ uptake by SI
- increases renal absorption
- increases mobilisation of Ca from bone
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Where are the parathyroid glands located in the domestic animal (in general)?
2 pairs at the cranial + caudal poles of the thyroid lobes
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What does the parathyroid hormone produce and by what type of cell?
Chief cells of the parathyroid gland produce parathyroid hormone (PTH)
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What does Parathyroid Hormone (PTH) do?
- cells in the parathyroid gland directly detect very small decreases in free Ca concentration- causes PTH release
Overall effect= increase the concentration of Ca in blood plasma
- increases absorption of Ca from GI tract
- decreases mobilisation of Ca f
Overall effect= increase the concentration of Ca in blood plasma
- increases absorption of Ca from GI tract
- decreases mobilisation of Ca f
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What does PTHrP stand for?
Parathyroid Hormone related Protein
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What does PTHrP do?
- produced in most tissues in the body
- activates the same receptors as PTH
- same function as PTH
- produced by certain types of cancer + cancer producing cells- no -ve feedback mechanism so over production = hypercalcaemia
- activates the same receptors as PTH
- same function as PTH
- produced by certain types of cancer + cancer producing cells- no -ve feedback mechanism so over production = hypercalcaemia
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Where is calcitonin made?
C cells (parafollicular cells) of the thyroid gland
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What does calcitonin do?
- secreted in response to an increase in free Ca2+ concentration
- Overall effect = decrease Ca concentration in blood plasma by affecting transport mechanisms in bone
- Overall effect = decrease Ca concentration in blood plasma by affecting transport mechanisms in bone
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How does calcitonin decrease Ca blood plasma concentration?
-Affecting transport mechanisms in bone
- targets osteoclasts, making bone remodelling less active, flux of Ca2+ + PO4 from bone to plasma decreases
- targets osteoclasts, making bone remodelling less active, flux of Ca2+ + PO4 from bone to plasma decreases
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Describe the process of calcium regulation
1. Increase of Ca2+ in blood = parafollicular cells of thyroid release more CT
2. CT inhibits osteoclasts = decreases Ca2+ conc.
3. Decrease of Ca2+ in blood = chief cells of parathyroid gland release more PTH
4. PTH promotes release of Ca2+ from bone, sl
2. CT inhibits osteoclasts = decreases Ca2+ conc.
3. Decrease of Ca2+ in blood = chief cells of parathyroid gland release more PTH
4. PTH promotes release of Ca2+ from bone, sl
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Where can phosphate pools be found in the body?
- 85% in bone as hydroxyapatite
- majority of rest found within cells
- intracellular + extracellular fluid as inorganic phosphates + organic phosphates (nucleotides, phospholipids, ATP)
- majority of rest found within cells
- intracellular + extracellular fluid as inorganic phosphates + organic phosphates (nucleotides, phospholipids, ATP)
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How is phosphate concentration regulated?
- linked to conc. of free Ca2+ in plasma
- absorbed in intestines, filtered, reabsorbed
- excreted in urine
- stored in bone
- absorbed in intestines, filtered, reabsorbed
- excreted in urine
- stored in bone
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What is the role of PTH in phosphate regulation?
- increases urinary excretion
- increases calcitriol secretion (increases dietary uptake)
- decreases serum phosphate
- increases calcitriol secretion (increases dietary uptake)
- decreases serum phosphate
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How is regulation of phosphate different from regulation of calcium?
- regulation of Ca largely depends on differential absorption from SI
- regulation of PO4 largely depends on urinary excretion
- regulation of PO4 largely depends on urinary excretion
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How can disorders of phosphate homeostasis cause issues with the regulation of Ca2+?
- phosphate regulation is linked to the concentration of free Ca2+ in plasma
- hyperphosphataemia causes increased PTH secretion + inhibits activation of Vit. D
- hyperphosphataemia causes increased PTH secretion + inhibits activation of Vit. D
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Name 2 normal physiologically challenges to Calcium homeostasis
- late pregnancy + parturition
- laying hens
- laying hens
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How does late pregnancy + parturition challenge calcium homeostasis?
- mammary cells extract a large amount of Ca2+ from ECF
- mineralisation of foetal skeleton
- homeostatic mechanisms have to supply Ca demands
- mineralisation of foetal skeleton
- homeostatic mechanisms have to supply Ca demands
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How does laying hens challenge calcium homeostasis?
- 2 wks before laying oestrogen + progesterone stimulate extra bone to be deposited in bone marrow cavities
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Other cards in this set
Card 2
Front
What increases GH secretion? (8)
Back
- inputs from CNS
- strenuous physical activity
- starvation
- stress
- decreased plasma glucose + free fatty acids
- increased plasma amino acid concentration
- ghrelin from parietal cells + hypothalamus
- thyroid hormone, androgens, oestrogens
- strenuous physical activity
- starvation
- stress
- decreased plasma glucose + free fatty acids
- increased plasma amino acid concentration
- ghrelin from parietal cells + hypothalamus
- thyroid hormone, androgens, oestrogens
Card 3
Front
What does GH do?
Back
Card 4
Front
Compare GH and IGF-1
Back
Card 5
Front
What is required for normal growth?
Back
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