Endocrine system Flashcards
What is the endocrine system?
- Influence activity of cells by releasing chemical messengers (hormones).
- Manages homeostasis (constant internal environment).
Exocrine glands
- Secrete into a duct that carries secretion to bodies surface or to a body cavity.
- E.g. Sweat, Mucous, Salivary and Alimentary glands.
Endocrine (ductless) gland
- Secrete hormones into extracellular fluid of surrounding cells.
- Secretion passes into capillaries and transported by blood.
Hormones
- A secretion from an endocrine gland.
- Can be proteins, amines or steroids.
- Transported in blood to cell/groups of cells called target cells or target organs.
- Specific – target cells must have correct receptors. Saturation can also occur (when all receptors are used).
- Once hormone has produced desired effect it must be ‘turned off’ by breaking down hormone molecules.
- Can be done in target cells, but mostly in liver and kidneys. Degraded hormones are then excreted in bile or urine.
Hormones may…
- Activate certain genes so a particular enzyme/protein is produced.
- Hormone triggers cascading effect – Enzyme Amplification. • Change structure of enzymes.
- Change rate of production of enzyme/protein by changing rate of transcription/translation.
Protein, Amine hormones
- Attach/bind to receptors on surface of cell membrane of target cell.
- Combination of hormone and receptor (hormone – receptor complex) causes a secondary messenger to diffuse through cell and activate particular enzymes in cytoplasm.
- Faster acting hormones (seconds/minutes).
Steroid hormones
- Enter target cells and combine with receptor protein on nucleus inside cytoplasm of cell.
- Lipid soluble, easily diffuse through cell membrane.
- Hormone receptor complex forms inside cytoplasm/on nucleus.
- Activates genes controlling formation of particular proteins.
- Regulates gene expression. Slower acting hormones (hours/days).
Thyroid
Thyroxine: Most body cells - Increases metabolic rate, oxygen consumption and heat production.
Calcitonin: Bones, Kidney - Decrease calcium and phosphate levels in blood.
Parathyroid
Parathyroid hormone: Bones, Kidneys - Increases level of calcium in blood.
Thymus
Thymosins: T-lymphocytes - Stimulates maturation of T lymphocytes.
Adrenal cortex
Aldosterone: Kidneys - Increases reabsorption of Na+ and excretion of K+.
Cortisol: Most body cells - Promotes metabolism; helps body deal with stress; promotes repair of damaged tissues.
Adrenal medulla
Adrenaline and Noradrenaline: Most body tissues - Prepares body for fight or flight responses; reinforce effects of sympathetic nervous system.
Pancreas
Insulin: Most body cells - Lowers blood glucose level; Increase glucose in cell.
Glucagon: Liver and fat storage tissues - Increase blood glucose level; stimulates breakdown of glycogen and fat.
Testes
Androgens - Testosterone: Testes, Bones, Brain - Stimulates sperm production; male sexual characteristics.
Ovaries
Oestrogen: Many tissues - Stimulate development of female sexual characteristics; regulates menstrual cycle.
Progesterone: Uterus and mammary glands - Prepares mammary glands for milk secretion.
