HUMAN ENDOCRINE SYSTEM
Enables animals to respond to external changes and control conditions inside their bodies
Chemical co-ordination Slow process of communicating information
throughout the body by hormones
Hormone Organic chemical substance secreted by endocrine
gland and carried in blood to target organ to regulate
metabolic reactions (broken down by enzymes)
Target organ Specific cells that respond to a given hormone with
receptor sites for that hormone (single gland/ organ/
scattered)
Endocrine gland Vascular ductless gland that secretes hormones
carried in bloodstream to target organs
● Exocrine glands → secretions carried in ducts to necessary areas
● Endocrine gland → secretions carried in bloodstream to target organs (no ducts)
Hypothalamus
- Part of the brain situated above pituitary gland
- Secretes ADH (anti-diuretic hormone)
Role of ADH:
● Osmoreceptors in blood vessels of hypothalamus detect increase in osmolarity of blood (low water
levels)
● Hypothalamus responds and secretes ADH
● ADH = conserves water if body is dehydrated
● Causes more water to reabsorb into blood from kidney collecting ducts = less water lost in urine
Pituitary gland
- Chemical co-ordinator of most endocrine glands
- ‘Master gland’
- Attached to hypothalamus by short stalk at base of brain
Growth disorders:
- Too much/ too little growth hormone
- Hypersecretion → over secretion
- Hyposecretion → under secretion
In prepubertal children:
Hypersecretion
● Overdevelopment of the skeleton (gigantism)
● Caused by tumor in pituitary gland
● Very rare
Hyposecretion
● Underdevelopment of the skeleton (pituitary dwarfism)
● 91-122 cm with normal proportions
● Sexually immature
● Treatment = STH injections (genetically engineered bacteria)
In adults
Hypersecretion
● Enlargement of bones in face, hands and feet (acromegaly)
● Thickened soft tissue = enlarged features/ tongue
Thyroid gland
- 2 butterfly shaped lobes
- On either side of trachea below larynx
- Secretes thyroxine
Thyroxin:
- Iodine necessary
Functions:
1. Increases basal metabolic rate in cells → controls rate of cellular respiration
2. Functioning of heart
3. Functioning of nervous system → increases nervous activity and sharpening alertness/ reflexes
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