This is an in-depth summary of The Human Endocrine System from the Mind Action Series Life Sciences Grade 12 Textbook. Written by a student who achieved a distinction in life sciences in 2022, these well-organized notes are packed with clear explanations and helpful illustrations that make complex ...
Human Endocrine System
Chemical coordination: Process of communicating info throughout body by way of chemicals (hormones)
Hormones are secreted by glands/tissue know as endocrine glands
Endocrine system works together with the Nervous System
Hormone
• A chemical substance, usually a protein but can sometimes be a steroid, secreted by an endocrine glad & carried in the
blood stream to its target organ.
Target organ
• Speci c cells that respond to given hormones
• Have receptor sites for hormone to attach
Endocrine gland
• Vascular ductless gland that secretes hormones which are carried in blood stream to target organs
Exocrine & endocrine glands
• Exocrine - secretions carried in ducts
• Endocrine - Don't have ducts - secretions are carried in blood stream
Hypothalamus
• Part of brain - located above pituitary gland
• Secretes ADH (anti-diuretic hormone)
Role of ADH
• Osmoreceptors in hypothalamus detect increase in osmolarity (low water levels)
• Responds by releasing ADH
• ADH helps to conserve water if body is dehydrated
• Cause more water to be reabsorbed back into blood from collecting ducts of kidney
• Less water lost in urine
Pituitary gland
• Attached to hypothalamus at base of brain
• Master gland - acts as a chemical coordinator of most of the other endocrine glands
, • Growth hormone (GH /STH) - stimulates synthesis of protein & promotes skeletal & muscular growth
Disorders
• Arises from too much / too little of growth hormone
• Hyper-secretion - over secretion of hormone
• Hypo-secretion - under secretion of hormone
In Prepubertal children
Hyper-secretion: Giantism - overdevelopment of skeleton
- often caused by tumor in pituitary gland
Hypo-secretion: Pituitary dwar sm - underdevelopment of skeleton
- reduced height but normal body proportions
- not mentally retarded
- treated by injections of synthetic growth hormone - produced by
genetically engineered bacteria
In Adults
Hyper-secretion: Acromegaly - bones of face, hands + feet are enlarged
- thickening of soft tissue leads to enlarged facial-features & enlarged tongue
Thyroid gland
• Located on either side of trachea below larynx
Thyroxin (hormone)
• Needs Iodine for production which comes from sea food & salts
Functions
• Promotes normal functioning of heart
• Increases basal metabolic rate (& therefore production of body heat) - controlling the rate of
cellular respiration
• Promotes normal functioning of nervous system - increases nervous activity & sharpens alertness & re exes
Disorders
Hypothyroidism
• Producing too little thyroxin - causes low metabolic rate
• Treated by iodine supplements or synthetic iodine
• Once developmental + mental abnormalities have occurred in children it can't be reversed
• Children: Cretinism- child doesn't grow physically + immature sexual development + mentally retarded
• Adults: Myxoedema - condition of mental & physical sluggishness
- low BP, slow heart rate & respiratory rate & low body temp
Hyperthyroidism
• Producing too much thyroxin - causes high metabolic rate
• High body temp + sweating increases
• Heart + respiratory rate increases , BP increases
• Muscular tremors + nervousness
• Swollen thyroid glad - exophthalmic goiter
Keeping thyroxin in blood constant
• Control mechanism - negative feedback
• Pituitary gland detects decreased thyroxin in blood - secretes more TSH
• TSH stimulates thyroid to secrete more thyroxin retuning its level to normal
• Higher level if thyroxin inhibits further secretion of TSH
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