Human Bio - Endocrine System

• Hypothalamus:

  • Regulates basic homeostatic functions
  • such as body temperature, water balance, + heart rate
• Pituitary Gland:

  • Controlled by hypothalamus
  • Consists of anterior + posterior lobes that regulate other endocrine glands
  • Infundibulum connects it to the hypothalamus
• Pineal Gland:

  • Deep inside brain (in children about the size of a pea)
  • After puberty = gradual decrease in size
  • Secretes melatonin -regulate sleep patterns
  • Production of melatonin - stimulated by darkness + inhibited by light
• Thyroid Gland:

  • Thyroxine (T4) and T3: increases metabolic rate = raised oxygen consumption + increased heat production
  • Calcitonin: decreases calcium + phosphate levels in blood
• Parathyroid Glands

  embedded in posterior surface of thyroid 

  secrete parathyroid hormone in response to hypocalcaemia (low Ca levels)

  PTH raises blood Ca levels
• Thymus Gland

  Secretes thymosin = necessary for T lymphocytes' development + production
• Adrenal Cortex

  Cortisol: secreted in response to adrenocorticotrophic hormone

  Promotes normal metabolism + repair of damaged cells (helps body adapt to stress)

  Aldosterone: stimulates kidneys to retain sodium + excrete potassium
• Adrenal Medulla

  Adrenaline + Noradrenaline: prepares body for fight-or-flight response
• Pancreas

  Secreted from Islets of Langerhan (cluster of cells)

  Alpha cells: secrete glucagon (increase blood glucose levels - stimulate breakdown of glycogen to glucose)

  Beta cells: secrete insulin (decrease blood glucose levels - stimulate uptake of glucose)

  Together regulate blood sugar
• Gonads

  Testes – male gonads:

  testosterone = stimulate sperm production, development of sex characteristics

  Ovaries – female gonads:

  oestrogen = development of sex characteristics + regulate menstrual cycle

  progesterone = regulate menstrual cycle + prepare mammary glands for milk secretion
• Amine (water-soluble):

  1. travel in blood to target cell
  2. hormone leaves blood + binds to specific receptor on target cell
  3. hormone + receptor = allow for secondary messenger to enter cell
  4. secondary messenger activates specific enzyme

  cannot diffuse across target cell membranes

  act via secondary messenger mechanism

  cause quick response but w/ short-lasting effects

  all pituitary hormones are amine
• Steroid (lipid soluble):

  1. hormone diffuses through cell membrane
  2. attaches to receptor inside cell to become a hormone-receptor complex
  3. receptors in internal organelles – mitochondria or nucleus
  4. hormone-receptor complex activates specific genes to produce proteins

  directly enter target cell membrane to initiate response

  act via direct messenger mechanism
• Anterior Pituitary:

  connected to hypothalamus via BVs in infundibulum

  hypothalamus releases releasing or inhibiting factors that travel down infundibulum - stimulates AP to produce or not

  FSH: stimulate sperm production; growth of follicle

  LH: stimulate testosterone production; bring about ovulation, formation of corpus luteum

  GH: increase rate of protein synthesis

  TSH: stimulate thyroid to produce + release hormones

  ADCH: stimulate adrenal cortex to produce + release hormones

  PRL: mammary gland milk production
• Posterior Pituitary:

  anatomically joined to hypothalamus via nerve cells

  hormones produced by nerve cells in hypothalamus

  travel down infundibulum through cell extensions + stored

  release when triggered by nerve impulses from hypothalamus

  hormones:

  oxytocin - uterus contractions, mammary gland release of milk

  antidiuretic hormone - reabsorption of water in kidneys
• Homeostasis: ability of body to maintain relatively constant internal environment, regardless of environmental changes

  · concentration of oxygen + carbon dioxide

  · pH of 7

  · concentration of nutrients + waste

  · concentration of slats + electrolytes

  · volume + pressure of extracellular fluid

  · volume + pressure of intercellular fluid

  · stable body temp