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Assist prof. of Medical Physiology. It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Dec 18, 2015

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Page 1: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Assist prof. of Medical Physiology

Page 2: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 3: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

It is not essential for life but essential for

growth and for physical and mental well-

being.

Site: • On both sides of the lower aspect of the

larynx and upper trachea.

Lobes: Thyroid gland is formed of 2 lobes

Page 6: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Histology:

• Thyroid follicle is functional

unit– A spherical structure lined

with cuboidal cells carrying microvilli (follicular cells)

– filled with ‘thyroid colloid’ containing protein called ‘thyroglobulin’.

• Parafollicular cells are present

between the follicles there are

Page 7: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Microscopic structure of the thyroid gland.

Page 8: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

ThyroglobulinThyroid folliclesParafollicular

C cells

Thyroid Follicles

Page 9: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Thyroid gland secrete:

1. Thyroid hormones: • Thyroxin or tetraiodothyronine (T4) • Triiodothyronine (T3) • Both secreted by thyroid follicular cells

2. Calcitonin is synthesized by the Para

follicular cells• Decrease blood Ca++ level.

Page 10: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 11: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

1. Thyroxin or T4 • Discovered first• About 90% of the thyroid output

2. T3 (Triiodothyronine) • Secreted in smaller amount

• Have shorter half life than T4

• Most active at the cellular level (3 - 5

times more active than T4)

Page 13: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Blood Follicular Cell Lumen

TG

TG

TG

I-

Na+

I-

Na+

I-

I2 +

TGT3

T4

T3

T4

10 times of plasma

Active transport

Oxidation(Peroxidase)

Iodination(Peroxidase)

Coupling(Peroxidase)

Endocytosis

Proteolysis Diffusion

Page 14: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

• Steps :• a) Active uptake of inorganic iodide

(I-)

– by an active pump. – I- is concentrated in follicular cells (> 10

times plasma level).

•Stimulated by the TSH and • inhibited by thiocyanate and perchlorate

(competitive inhibition).

Page 15: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Steps :

• b) Oxidation of I- to organic iodine

(I2) – By thyroid peroxidase enzyme.

• c) Iodination of tyrosine – to produce mono- and di-iodotyrosine.

Page 16: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 17: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

d) Oxidative coupling

• Thyroxin (T4): by union of 2 diiodotyrosine

molecules.

• Triiodothyronine (T3): by union of

monoiodotyrosine with diiodotyrosine molecule.

Page 18: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 19: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

1. Oxidation of I-, to iodine2. Iodination of tyrosine & 3. Oxidative coupling, • All require thyroid peroxidase enzyme.

• Blocked by ‘thiocarbamides’ • As thiouracil or carbimazole,

decrease T3 & T4 synthesis. • Used in treatment of

hyperthyroidism.

Page 20: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 21: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

• Thyroid hormones present in peptide linkage with thyroglobulin protein in the colloid.

• On stimulation by TSH

– Thyroglobulin is broken by a protease

enzyme to release T3 and T4.

Page 22: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 25: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

• In blood most of the thyroid hormones are bound to plasma proteins.

• Normal plasma level:

– T4 level is 8 mcg/dl,

• of which 99.98% is bound and only 0.02% is free.

– T3 level is 0.15 mcg%

• and 99.8% of it is bound while 0.2% is free.

– T3 has a shorter plasma half-life (less bound)

Page 26: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Transport proteins are:

• a) Thyroxin Binding Globulin’ or TBG (α globulin):

– Carry about 50% of the hormones.

• b) Pre albumin (migrating ahead of albumins in

electrophoresis)

– called ‘Thyroxin Binding Prealbumin’ TBPA, or

Transthyretin.

– transports about 40%.

• c) Plasma albumin

– Carry the remaining 10%.

Page 27: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

A. Intracellular actions (mechanism of action)B. On the whole body produce:• 1) Growth and development• 2) Energy metabolism• 3) GIT.• 4) CVS.• 5) Respiratory system.• 6) Gonads and other endocrine systems. • 7) Skeletal muscles. • 8) Vitamins and drugs.• 9) Carbohydrate metabolism.• 10) Protein metabolism.• 11) Fat metabolism. • 12) Haemopoietic system.

Page 28: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

• T3 and T4 enter the cell by diffusion:

– a) Bind to a specific nuclear receptor

protein.

– HRC direct transcription of specific mRNA &

specific protein synthesis.

Page 30: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

• T3 and T4 Increase:

b) number and size of mitochondria & rate of

cell respiration.

c) activity and number of cell membrane

Na+-K+ Pump.

d) amino acid transport across the cell

membrane & protein synthesis.

e) Activate proteolytic and lysosomal

enzymes especially in muscles.

Page 31: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

•1) Growth and development: – Thyroid hormones stimulate physical,

mental and sexual growth. – Act with GH to achieve proper growth

of the body.

Page 32: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

• a) Physical growth:

– Has a synergistic effect on GH &

potentiate the effect of somatomedins.

– development & Eruption of teeth.

– Closure of fontanels.

Page 33: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

• b) Mental growth:

– Growth, development & function of CNS

during fetal life & 1st few years.

– Myelination of nerve fibers & development of

synapses.

• c) Sexual growth:

– Essential for maturation & fertility.

– Help milk secretion during lactation.

Page 34: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

2) Energy metabolism:

– Stimulate

•BMR, & O2 consumption,

•heat production, and glucose uptake by cells.

– Increase Heat production by accelerating

the catabolic metabolism of cells.

– 1 mg of thyroxin increase heat

production by about 1000 calories.

Page 39: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

7) Gonads and other endocrine systems: – Normal hyroid hormones level required for

proper sexual functions. – Both hyper and hypothyroidism lead to infertility

in males and females.

– Decrease the metabolic clearance of oestogen and testosterone as they Increase the synthesis of SHBG.

– Increase metabolic clearance of glucocorticoids by the liver and increase ACTH release from the ant pituitary.

– Potentiate the action of most of other hormones.

Page 40: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

8) Vitamins and drugs:

– Increase the synthesis of vitamin A from

carotenes in the liver.

– Stimulate the utilization and clearance of all

vitamins.

– Enhance the clearance of number of drugs

as digitalis. Vitamin A

Page 41: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

9) Carbohydrate metabolism. – In physiologic amounts,

•Potentiate the action of insulin &– promote glycogenesis and glucose

utilization.

– In large doses, induce hyperglycemia by:

– Increase •1) the glycogenolytic effect of epinephrine,

leading to glycogen depletion.•2) gluconeogenesis.•3) intestinal glucose absorption.

Page 42: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

10) Protein metabolism. – In physiologic amounts: have protein anabolic effect, – In large doses: increase protein catabolism.

11) Fat metabolism. – Stimulate all aspects of lipid metabolism:

• synthesis, mobilization and utilization.

– Decrease the blood level of:

• cholesterol, triglycerides, and phospholipids.

– Increase the plasma free fatty acids and glycerol.

Page 43: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

12) Haemopoietic system.

– Stimulate erythropoiesis through

stimulation of erythropoietin

production (increase O2 carrying

capacity of the blood).

– Increase the amount of 2,3 DPG

in the RBCs.

– So, facilitate the

dissociation of O2 from Hb.

Page 44: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

NB:

• There is (synergism) interaction between thyroid hormones and catecholamines.

• B adrenergic blockade, – is effective in decreasing cardiovascular

and CNS manifestations of hyperthyroidism.

Page 45: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 46: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Control of thyroid gland:

The thyroid gland activity is regulated by:

• 1. Plasma level of TSH. • 2. Thyroid stimulating immunoglobulin (TSI), • 3. Stress conditions: enhance thyroid activity • 4. Age: tends to be decrease activity with increasing age.

• 5. Pregnancy: • 6. Antithyroid agents (Goitrogens): • 7. Blood iodine level

Page 47: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Control of thyroid function:

1. Thyroid stimulating hormone (TSH).

• TSH has the following effects on the thyroid gland:

– a) Promote hyperplasia of the follicular cells.

– b) Increase iodide uptake of from the blood.

– c) Stimulates synthesis & release of T3 & T4.

Page 48: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 49: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 50: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Control of thyroid function:

1. Thyroid stimulating hormone (TSH).

• There is a negative feedback between thyroid hormones

and TSH secretion.

• Excess T3 and/or T4 suppresses the release of TSH:

– by acting on the thyrotrop cells, more than on the anterior

hypothalamus (site of release of TRH).

The feedback mechanism controlling thyroid gland activity

act mainly on the ant pituitary.

Page 51: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Hypothalamic control of thyroid gland.

Page 52: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Hypothalamus

Pituitary g.

Thyroid g.

TRH

TSH

T3 & T4

--

--

Negative feedback

Page 53: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 54: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

2. Thyroid stimulating immunoglobulin (TSI),

– known as ‘long acting thyroid stimulator’ (LATS).

• produced by lymphocytes in all cases of Grave’s disease

(autoimmune disorder leads to hyperthyroidism).

– TSI acts on the thyroid similar to TSH

– but

– there is no –ve feed back to increased T3 and T4.

Control of thyroid function:

Page 55: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

3. Stress conditions enhance thyroid activity:

• e.g.

– Exposure to cold

– Increase the thyroid activity:

• that increase BMR and heat production

– to

– counteract the effects of low temperature.

Control of thyroid function:

Page 56: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

3.All types of stress

e.g exposure to cold environment stimulates the

thyroid with consequent increase in metabolic

rate and heat production to counteract the effects

of low temperature.

Page 57: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

4. Age:

– Thyroid activity tends to decrease with increasing

age. But this effect is small.

5. Pregnancy:

– Thyroid activity increase during pregnancy.

– The placenta secretes HCG which is structurally

similar to TSH. (physiological goiter).

Control of thyroid function:

Page 58: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

4.Age:

Although its effect is small, but there tends to

be a decrease in activity with increasing age.

Page 59: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

5-Pregnancy

-Thyroid activity increases during pregnancy.

-The placenta secretes a hormone called ‘human

chorionic gonadotropin’ or hCG which is

structurally similar to TSH.

Page 60: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

6. Antithyroid agents (Goitrogens):

– Primary goitrogens include thiocyanates:

• found in cabbage that inhibit I- uptake.

• Interfere with T3 and T4 synthesis.

– T4 & T3 level leads to TSH level which results

in enlargement of the thyroid gland (goiter).

Control of thyroid function:

Page 61: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

7. Blood iodine level:

– a) Iodine deficiency: decreased T3 & T4 formation

TSH goiter.

– b) Excess iodine (Wolff– Chaikoff) results in:

• 1- Decrease in organic binding of iodine in the gland.

• 2- Inhibition of TSH effect on the gland by ↓ cAMP

response to it.

• 3- Decreased proteolysis of thyroglobulin.

Control of thyroid function:

Page 62: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Disorders of the thyroid gland

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Disorders of the thyroid gland

1. Hypofunction (Hypothyroidism)

• may be

– Primary (thyroid defect) or

– Secondary (defect in the pituitary gland).

Manifestations vary according to the age:

– 1. Cretinism: Hypothyroidism in human infants.

– 2. Myxoedema: Hypothyroidism of human adults.

Page 64: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

1. Cretinism

• Hypothyroidism in infants.

• May not recognized until 5-6 months after birth,

– Some thyroid hormones reach the infant through milk from his

mother.

Clinical features

a) Growth Retardation: physical , mental & sexual.

The cretin is dwarf.

b) Low BMR and O2 consumption.

Page 65: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 66: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Clinical features of Cretinism

c) The skin is:

– yellowish, scaly and

– scanty coarse hair, due to failure of formation of

vitamin A in the liver from carotins.

– The resulting carotinaemia gives the yellowish skin.

Page 67: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Clinical features of Cretinism

c) The skin: yellowish, scaly and scanty coarse hairs.

d) Facial features: – Dull, uninterested expression and puffy eye lids.

– Thick protruded tongue (macroglossia).

Page 68: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Infantile hypothyroidismInfantile hypothyroidism

Page 69: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Clinical features of Cretinisma) Growth Retardation.

b) Low BMR.

c) The skin: yellowish, scaly and scanty coarse hairs.

d) Facial features: Dull, puffy eye lids. macroglossia).

e) Abdomen is protuberant (potbelly) and

umbilical hernia.

Page 70: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Critinism: puffy eyelids, depressed nose, disproportionate dwarfism

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Treatment

• Should be started as early as possible

– by giving thyroid hormones,

– because mental retardation, once developed, is

irreversible.

Page 72: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

2. Myxoedema:• - Hypothyroidism in adults

Characterized by:

a) Retardation of all mental functions e.g. – lack of concentration, slow thinking, – long reflex time and sleepiness.

b) Low BMR & O2 consumption leads to:– - Weight gain.– - Increased sensitivity to cold weather.

c) Bradycardia & hypotension.

Page 73: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Myxoedema: puffy face, generalized fatigued appearance

Page 74: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.
Page 75: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

d) Skin changes:

– Thick doughy Skin: due to

• deposition of myxoedematus tissue in SC.

– Pale Skin due to: • iron deficiency anaemia and

• compression of cutaneous BV by the deposited SC myxoedematus tissue.

– Yellowish due to carotinaemia.

– Cold due to decreased BMR.

– Dry scaly & brittle hair (vitamin A deficiency).

2. Myxoedema:

Page 76: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

d) Skin changes

1- Thick Skin due to (myxoedematus tissue).

2-Skin looks pale due to iron deficiency anaemia.

Page 77: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

3- It looks yellowish due to carotinaemia.

4- It is cold due to decreased BMR.

5- dry scaly with brittle hair due to vitamin

A deficiency.

Page 78: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

f) Failure of sexual functions e.g.

– Impotence in the male and

– Menstrual disturbances in the female, mainly

oligomenorrhea.

e) Increased level of cholesterol & triglycerides.

Treatment by giving thyroid hormones.

2. Myxoedema:

Page 79: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Hyperthyroidism or

Thyrotoxicosis

Page 80: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

II. Hyperfunction of the thyroid gland

• Hyperthyroidism or thyrotoxicosis:

Due to

– thyroid tumour or

– over stimulation of the thyroid by TSH or

TSI.

Page 81: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Hyperthyroidism or thyrotoxicosis

Clinical features

a) Excessive nervousness and irritability with insomnia

and tremors of hands.

b) Loss of weight inspite of Increased appetite .

– Increased catabolism of tissue proteins and oxidation of the

stored fat

c) Warm moist skin, and Fine silky hair.

Page 82: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Hyperthyroidism or thyrotoxicosis

Clinical features

d) Low serum cholesterol level.

e) Increased BMR and O2 consumption

– Body temp is not raised as the extra heat is lost

by excess sweating.

– Hot intolerance and prefer cold weather.

Page 83: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Hyperthyroidism or thyrotoxicosis

f) Ocular signs include:

• Sympathetic overstimulation.

– 1) Characteristic stare look.

– 2) Infrequent blinking.

– 3) Lid lag phenomenon.

– 4) Failure of convergence.

• 5) Exophthalmos (protrusion of eye balls) as a result of :

– ‘exophthalmos producing factor’ a degradation product of

TSH.

– accumulation of fat, water and inflammatory cells in the

retroorbital tissue and extra ocular muscles.

Page 84: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Ocular signs include

1-Characteristic stare due to upward retraction of

upper eye lid.

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2-Lid lag phenomenon i.e a delay in the

downward movement of the upper eye lid

on following a falling object.

3-Failure of convergence.

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5- Infrequent blinking.

Exophthalmos

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Hyperthyroidism or thyrotoxicosis

g) Tachycardia, atrial arrythmias (as AF) and

– high systolic pressure.

– The diastolic pressure is not raised due to

peripheral VD.

– So There is high pulse pressure.

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Hyperthyroidism or thyrotoxicosis

h) Rapid muscular fatigue due to reduced ATP synthesis.

i) Sexual disturbances

– Impotence in males and

– Menstrual disturbances in the female.

• polymenorrhea or

• menorrhagia

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II. Manifestations of Hyperthyroidism

1) Nervousness and irritability, insomnia and tremors of hands.

2) Loss of weight inspite of Increased appetite.

3) Warm moist skin, and Fine silky hair.

4) Increased BMR and O2 consumption

5) Low serum cholesterol level.

6) Ocular signs include:– Staring look, & Infrequent blinking.– Lid lag phenomenon & Failure of convergence. – Exophthalmos

Page 92: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

II. Manifestations of Hyperthyroidism

7) Tachycardia, arrythmias (as AF) and Systolic HTN, high

pulse pressure.

8) Rapid muscular fatigue.

9) Sexual disturbances

– In males: impotence and

– In the female: Frequent menses (polymenorrhea) and

(menorrhagia).

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Goiter

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Goiter

Means: enlargement of the thyroid gland. – It is accompanied by either hypo, or hyperfunction.

Causes

1. Goitrogens: – Substances that block synthesis of thyroid hormones, – e.g. thiocyanates and thiocarbamides. – They lead to T3 & T4 TSH gland size.

2. Iodine deficiency– T3 & T4 TSH goiter. – Called colloid goiter, the acini distended with colloid.

Page 96: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Causes of Goiter

3. Grave’s disease:– due to TSI which binds to TSH receptors on thyroid

cells diffuse goiter.

4. Nodular goiter: – Irregular enlargement of the thyroid with varying

numbers of discrete nodules, – due to exposure to stresses.

5. Physiological goiter– Sometimes noticed in adolescence and during

pregnancy.

Page 97: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.

Goiter: (enlargement of the thyroid gland)

Page 98: Assist prof. of Medical Physiology.  It is not essential for life but essential for growth and for physical and mental well-being. Site: On both sides.