2.1 Human Endocrine System:
The nervous and endocrine system enables animals to respond to external changes
and to control internal body conditions.
Chemical coordination:
● Slow, prolonged process of communication info throughout the body by
chemicals called hormones
● Variety of hormones are secreted by special glands or tissues called endocrine
glands (glands work with the nervous system)
Hormone:
● Organic chemical substance, usually a protein (sometimes a steroid) secreted by
endocrine gland
● Carried in blood to target organ/s where it regulates metabolic rates
● Dont last long in body as enzymes break them down
Target organ:
● Hormones are carried through blood but only affect certain cells
● The specific cells have receptor sites to respond to a given hormone
● These cells are called target tissue/organ
● Can be single gland or organ scattered through body
Endocrine gland:
● Vascular (lots of blood vessels) ductless glands that secrete hormones that are
carried in bloodstream to target organs
Exo- vs endocrine glands:
● Exocrine glands secrete through ducts to where they are needed
○ Poured into cavity
○ Produce enzyme juice/biological catalyst
○ Secreted in large amounts
○ Slight change causes no disorders
○ E.g. Salivary glands, liver, pancreas
, ● Endocrine glands do NOT have ducts and secretions carried IN bloodstream to
target organs
○ Directly into blood
○ Secrete hormones
○ Secretions released in small amounts
○ Slight change can cause a disorder
Endocrine glands in the body:
1. HYPOTHALAMUS
Is a part of the brain, situated above the pituitary gland and secretes and produces
hormones such as ADH (antidiuretic hormone)
● ADH
○ Osmoreceptors in the blood vessels of the hypothalamus detects an
increase in osmolarity (lower water levels) of blood = hypothalamus
responds by releasing ADH
○ ADH helps conserves water if body dehydrated
○ Causes body to reabsorb into blood from collecting ducts of the kidney so
less water isn’t in urine
, 2. PITUITARY GLAND (connected to hypothalamus @ base of brain by short stalk)
Gland acts as the chemical co-ordinator of most other endocrine glands (master gland)
● Hormones secreted by pituitary:
○ Thyroid stimulating hormones (TSH)
Stimulates the thyroid gland to secrete thyroxin
○ Follicle stimulating hormone (FSH)
a) In females = stimulates oogenesis in ovary
Formation of eggs (ova)
b) In males = stimulates spermatogenesis in testes
Formation of sperms
○ Luteinizing hormone (LH)
Stimulates ovulation (release of egg) from ovary and formation of the
corpus luteum
○ Prolactin
Stimulates the production of milk in female mammary glands after birth,
will continue for as long as baby suckles
Responsible for maternal instinct
○ Adrenocorticotropic hormone (ACTH)
Stimulates adrenal cortex to secrete hormones, cortisone and aldosterone
○ Interstitial cell stimulating hormone (ISSH)
Stimulates testes to secrete testosterone
○ Growth hormone (GH)/ Somatotrophic hormone (STH)
Promotes skeletal and muscle growth by stimulating protein synthesis
★ Growth Disorders: In prepubertal (before growth stops) children
● Hypersecretion (over secretion) of growth hormones results in OVERGROWTH
of the skeleton, aka gigantism. Usually caused by a tumor in pituitary gland
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