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Human Endocrine System Grade 12 Life Sciences
Human Endocrine System. Detailed. Images Included
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Human endocrine system: Enable animals to respond to external changes and to control conditions inside their bodies.
Chemical co-ordination:
Slow, prolonged process of communicating information throughout the body by the way of
chemicals called hormones.
Hormones are secreted by special glands or tissues called endocrine glands.
Hormone?
A hormone is an organic chemical substance, usually protein but sometimes a steroid,
secreted by an endocrine gland and carried in the bloodstream to its target organ/s where
it regulates metabolic reactions.
Broken down by enzymes (do not last long)
Target organ?
A target organ are specific cells that hormones affect and then respond to, as they have
receptor sites for that hormone.
Endocrine gland?
A vascular, ductless gland that secretes hormones which are carried in the bloodstream
to their target organs.
Vascular – richly supplied with blood vessels.
Exocrine glands?
Do not have ducts and their secretions are carried in the bloodstream to their target
organs.
Endocrine glands?
Carried in ducts to where they are needed
E.g. salivary glands, liver, pancreas.
Endocrine gland
Exocrine gland (has
(Ductless) e.g. Adrenal
ducts) e.g. salivary gland
gland
, Endocrine glands in the body.
1. Hypothalamus:
Part of the brain situated above the
pituitary gland.
Secretes ADH (anti-diuretic hormone)
What is the role of ADH?
Osmoreceptors in the blood vessels of
hypothalamus detect an increase in the
osmolarity (low water levels) of the
blood. Hypothalamus then responds
and releases ADH.
Helps to conserve water if body is
dehydrated: causes more water to be
absorbed. Gonads –
reproductive organs
2. Pituitary Gland:
Hypophysis
Chemical coordinator of most endocrine glans (master gland).
Attached to hypothalamus at the base of the brain by a short stalk.
Situated in small bone cavity in floor of cranium called ‘Turkish Saddle’
What hormones are secreted by pituitary gland?
Name Description
Thyroid stimulating hormone Which stimulates thyroid gland to secrete its hormone,
(TSH) thyroxin.
More thyroxin which is produced and released, the more
thyroxin. Less TSH=less thyroxin
Follicle stimulating hormone Females = FSH stimulates oogenesis in ovary. i.e. formation of
(FSH) eggs (ova)
Males = FSH stimulates spermatogenesis. i.e. sperm formation
Luteinizing hormone (LH) Stimulates ovulation (release of an egg) from the ovary and
the formation of the corpus luteum.
Prolactin Stimulates production of milk in female mammary glands after
the birth of the baby.
This will continue for as long as the baby suckles.
Prolactin is also responsible for much of the maternal instinct.
Growth hormone (GH) or STH Promotes skeletal and muscular growth
(somatotrophic hormone) Does this by stimulating the synthesis of proteins.
Oxytocin (Love hormone) Stored in the posterior love of pituitary gland
Released during labour when the foetus stimulates the cervix
and vagina, it enhances the contraction of the uterine smooth
muscles to facilitate birth.
Stimulating milk ejection to facilitate breast feeding
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