This is a summary of the whole Human Endocrine System chapter in the Life Sciences Mind Action Series Grade 12 IEB textbook.
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Summary Life Sciences, ISBN: 9781869214470 Life Sciences (Biology)
IEB Life Sciences: Human reproduction
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Summary by: Kaylin Teneal
Human Endocrine System
Enable animals to respond to external changes and to control conditions inside their bodies.
CHEMICAL CO-ORDINATION
DEFINITIONS:
Slow, prolonged process of communicating information throughout the body by
HORMONE – organic chemical substance
the way of chemicals called hormones. A variety of hormones are secreted by secreted by an endocrine gland and
special glands or tissues called endocrine glands. carried in the blood stream.
TARGET ORGAN – specific cells that
respond to a given hormone have
EXO- AND ENDOCRINE GLANDS receptor sites for that hormone, can
be a single gland or organ or scattered
Exocrine glands – secretions are carried in ducts to where they are needed.
throughout the body.
Endocrine glands – secretions are carried in the bloodstream, they don’t have
ducts. ENDOCRINE GLAND – vascular, ductless
gland that secretes hormones carried in
the bloodstream.
1. HYPOTHALAMUS
® Secretes the hormone ADH (anti-diuretic hormone)
VASCULAR – richly supplied with blood
vessels.
® Osmoreceptors in the blood vessels of hypothalamus detect an
increase in the osmolarity (low water levels) of the blood,
ADH is then secreted.
® ADH helps conserve water by causing more water to be
reabsorbed back into the blood.
2. PITUITARY GLAND
® ‘Master gland’ as it acts as the chemical coordinator.
® Attached to the hypothalamus at the base of the brain.
® Hormones secreted by it:
1. Thyroid stimulating hormone (TSH)
Stimulates the thyroid to secrete thyroxin
2. Follicle stimulating hormone (FSH)
Stimulates oogenesis in the ovary in females, stimulates spermatogenesis in the testis in males.
3. Luteinizing hormone (LH)
Stimulates ovulation from the ovary and formation of the corpus luteum.
4. Prolactin
Stimulates milk production in female mammary glands after the birth of a baby.
5. Adrenocorticotropic hormone (ACTH)
Stimulates the adrenal cortex to secrete the hormones, cortisone, and aldosterone.
6. Interstitial cell stimulating hormone (ICSH)
, Summary by: Kaylin Teneal
Stimulates the testes to secrete testosterone.
7. Growth Hormone (GH)
Promotes skeletal and muscular growth, stimulates the synthesis of proteins.
® GROWTH DISORDERS:
In children:
1. Hypersecretion (over secretion of GH) resulting in gigantism, usually caused by a tumour in the
pituitary gland.
2. Hyposecretion (under secretion of GH) resulting in dwarfism, they often are sexually immature.
Can be treated by injections of synthetic growth hormone (STH).
In adults:
1. Over-secretion of GH leads to a condition called acromegaly where the bones of the face, hands
and feet are enlarged.
3. THYROID GLAND
® Secretes thyroxin
® Functions of thyroxin:
1. Increases the basal metabolic rate in all body cells
2. Promotes the normal functioning of the heart
3. Promotes the normal functioning of the nervous system by increasing nervous activity and
sharpening alertness and reflexes.
® HYPOTHYROIDISM DISORDER:
Producing too little thyroxin and causes a low metabolic rate. Can be treated with iodine supplements.
Developmental and mental abnormalities cannot be reversed.
In children:
1. Results in cretinism, a condition where a child doesn’t grow physically, has immature sexual
development and is mentally retarded.
In adults:
1. Results in myxoedema, a condition of mental and physical sluggishness, with low blood pressure, a
slow heart and respiratory rate.
® HYPERTHYROIDISM DISORDER:
Producing too much thyroxin and causes a high metabolic rate
1. Body temperature is high and sweating increases.
2. Heart and respiratory rate and blood pressure increases.
3. Are muscular tremors and nervousness.
4. Swollen thyroid gland
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