Download Calcium Homeostasis(1)

Calcium Homeostasis
By
Dr. Shereen Samir
Normal level of calcium
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Calcium is the most abundant essential mineral
in the human body.
In the average adult it range from1000gm.
99% is present in the bone and teeth.
1% is present in the extracellular fluid and
blood with a smaller amount inside the cells.
Functions and health benefit of
calcium
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Muscle contraction and nerve excitability.
Neurotransmitter and hormonal release.
Enzyme function.
Blood coagulation.
maintain healthy bone and strong teeth.
Membrane integrity and permeability.
Calcium regulation
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Calcium regulation involves three tissues:
Bone ,intestine and kidney.
Three hormones :
Parathyroid hormone, calcitonine, and
activated vitamin D.
Hormones regulating calcium
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Parathormone: it is hormone secreted from
parathyroid gland .
It increases calcium blood level
It acts on bone ,kidney and intestine.
It increases calcium reabsorption from kidney
and excretion of phosphate.
It increases Ca absorption from intestine
It helps mobilization of Ca from bone.
Calcitonin
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It is hormone secreted form thyroid gland.
It decreases blood calcium level.
It helps mobilization of calcium from blood to
bone.
It stimulates osteoblast cells and inhibit
osteoclast.
Hormonal control of calcium
Vitamin D
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It is lipid soluble vitamin.
vitamin D2 &vitamin D3 are the most common types.
It is found in fish, liver, oil ,egg yolk and animal fat.
Vitamin D either ingested or formed in skin is transported
to liver.
In the liver:
It is transformed to inactive form 25hydroxycholeciferol
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In the kidney:
It is converted1- 25 dihydroxycaciferol.(vitD)
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Normal calcium level
Normal Serum calcium =9-11 mg/dl
Hypocalcemia i.e decreased blood calcium level
causes tetany.
In children a disease called rickets and in adult
osteomalecia
Hypercalcemia increase calcium level.
Tetany
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Increased neuromuscular excitability due to
decreased calcium below normal level.(911mg%)
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It is a state of spastic contraction of skeletal
muscles.
Types of tetany
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Latent tetany:
Calcium level 7-9 mg%
The symptoms are absent during rest but
appears to emotional stress ,pregnancy
&lactation.
Manifest tetany:
Plasma calcium level drop below 7mg%.
Regulation of blood
glucose
Endocrine regulation of blood glucose
-The normal blood glucose level ranges between 80-120
mg/100 ml blood.
-This level is controlled by the following hormones:
1- Pancreatic h.
2- Adrenaline.
3- Glucocorticoids.
4-Thyroxine.
5-Growth h.
Importance of blood glucose regulation:
!!!
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Glucose is the only nutrient that normally
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can be used by the brain and retina.
Glucose is important source of energy for the
cells.
a) Pancreatic hormones
-The endocrine cells of the pancreas are
present in discrete groups called ‘islets of
Langerhan’s’, which are more numerous in
the tail than in the body
and comprise 1-2% of
its weight.
Four groups of cells are now identified in
the islets:
1.Alpha cells,( 25% of islet mass)  glucagon h.
2.Beta cells,(about 60%), located in the centre of
the islet.  insulin h.
3.Delta or D cells, (10% of the islet mass) 
somatostatin h.
4.F
cells,
(only
polypeptide h.
about
5%)
pancreatic
I. Insulin
1-Insulin  blood glucose level by:
a. Glycogenesis
b. Inhibition of glycogenolysis
c. glucose uptake by the tissues
d-gluconeogenesis
5.  transformation of glucose into fat.
2-Anabolic action
Insulin is an essential hormone for growth:
a)In muscle, insulin stimulates the uptake of certain
amino acids across the cell membrane.
b)Insulin also stimulates the rate of protein synthesis.
c) Anti-catabolic effects i.e. it inhibits proteolysis.
2.Insulin increases cellular uptake of potassium,
phosphate and magnesium.
3.It
increases
the
reabsorption
of
phosphate and sodium by renal tubules
potassium,
Regulation of secretion
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The major regulation is the plasma glucose level
(no insulin when glucose < 50 mg%).
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A half maximum insulin secretion occurs at a
plasma glucose level of about 150 mg% and a
maximum response at 300 to 500 mg%.
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GIP
(glucose
dependent
peptide), gastrin, secretin,
pancreatic glucagons
insulinotropic
Cholecystokinin,
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Oral protein, Triglycerides and fatty acids
II. Glucagon
-Glucagon is a hyperglycemic polypeptide from α
cells.
1.glucose:glycogenolysis andgluconeogenesis
2.lipolysis and hepatic cholesterol synthesis.
4.Natriuresis, by renal tubular Na+ reabsorption
5. myocardial contractility  COP.
6.A local CNS h. for regulation of appetite.
1. Glucagon release is stimulated by:
a) Hypoglycaemia  2-4 fold  in glucagon level.
b) Protein meal
c)  FFA.
d) Exercise.
e)Vagal stimulation or administration of acetylcholine.
f)Stress, including infection, toxaemia, burns and
major surgery.
g) Growth hormone.
2. Glucagon release is inhibited by
a)Hyperglycaemia:
50%.
b)  FFA.
c) Somatostatin.
glucagon
level
by
B) Other hormones which regulate blood
glucose level
1.Adrenaline:
-glycogenolytic on liver and muscles.
2.Glucocorticoids:
I-  gluconeogenesis.
II-  glucose uptake by the tissues.
3.Growth hormone:
- glucagon hormone.
-Inhibits glucose uptake by tissues.
4.Thyroxin:
- glucose absorption from intestine.
- glycogenolysis.
The net result is a rise in blood glucose level.
Danger of increased blood glucose:
(Diabetes Mellitus)
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2 forms of diabetes mellitus:
 Type I: insulin dependent diabetes
(IDDM).
 Type II: non-insulin dependent
diabetes (NIDDM).
Diabetes Mellitus
Diabetes mellitus
It results from deficiency of insulin action , which
leads to:
1.Hyperglycaemia:
- due to absence of effects of insulin.
2.Glucosuria: i.e loss of glucose in urine.
- when the blood glucose level becomes >
renal threshold (180 mg%).
3.Polyuria due to:
a)Excretion of glucose in urine.
b) osmotic pressure
of the blood drags water out of the cells
towards the blood.
-This causes dehydration of the tissue cells.
4.Polydepsia:intense thirst due to dehydration.
5.
Acidosis:
- Due to inhibition of carbohydrate metabolism.
-The body depends on the fat metabolism
which supplies most of the energy needed.
-Uncontrolled diabetes  accumulation of
acetoacetic acid and beta hydroxybuteric acid
 acidosis.
6.Loss of weight and asthenia:
-Due to mobilization of fat and proteins for
supply of energy.
7. cholesterol and TG in blood:
- early development of arteriosclerosis.