endocrine system (chapter 2)

• endocrine glands • exocrine glands

• secrete substances into a duct that carries secretions to the body surface or to one of body cavities • e.g. sweat glands, mucous glands, salivary glands

• secrete hormones into the extracellular fluid that surrounds cells that make up the gland • secretions passes into the capillaries to be transported by the blood • sometimes called ductless glands • e.g. hypothalamus, pituitary gland, pineal gland

• are chemicals, secreted by endocrine glands, transported around the body via the blood • change the functioning of cells by changing the type, activities or quantities of proteins produced. • aren’t enzymes, but can exert their influence over changing activity of enzymes by: - activating certain genes in nucleus (to produce particular enzyme/protein - change structure of enzyme or protein = on or off - changes rate of translation/transcription • can effect either all cells of body, target cells or organs

• once released into blood, they bind to transport proteins to travel through bloodstream • once reaching target cells, steroid hormones separate from protein and diffuse across the cell membrane. • once inside cells, combine with receptor proteins in cytoplasm or nucleus • the hormone-receptor complex activates genes controlling the formation of particular proteins • by binding to promotor section of certain gene stimulating or inhibiting transcription (protein synthesis) • are lipid soluble (cannot dissolve in water, but through cell membrane) • are slow to effect but are long lasting

• they work by attaching to receptor proteins in the membrane of a target cell • combination of hormone and receptor causes a secondary messenger substance to diffuse through the cell and activate particular enzymes. • are water soluble (cannot diffuse through cell membrane) • are quick to effect but are short lasting

• are specific, one binding to one specific molecule • lock and key (lock = receptor protein, key = binding molecule) • there are a limited number of receptor proteins in the membrane of each cell • when each receptor is bound to a molecule there can be no further increase in the rate of the cell’s activities = saturation (the addition of more hormones does not produce a greater effect • different cells have different types and number of receptor proteins (causing varied sensitivities of cells to hormones) • e.g. an increase of insulin when each insulin receptor of a cell is being used causes no further glucose uptake

• one hormone molecule causes the manufacture or activation of thousands of molecules of enzymes • this is achieved through the process enzyme amplification • a very small stimulus can cause a very large effect

• once a hormone has produced the required effect, it must be turned off • this is done by breaking down the hormone molecules • either in target cells, or in the liver and kidneys (excreted via bile or urine).

• plays a role in both endocrine and nervous systems • it regulates many of the basic functions of the body (e.g. body temperature, water balance, heart rate and increasing/decreasing release of other hormones) • many functions are carried out through the pituitary gland • it secretes releasing or inhibiting factors which stimulate or lessen the secretion of a hormone (which travel through blood vessels to APG and PPG) • other hormones are produced by hypothalamus and pass along the nerve fibres to PPG where they are released

melatonin (amine): - targets many tissues - it is involved in the regulation of circadian rhythm, induces sleep, immune system support and protection of nervous system

oxytocin (protein): - targets the uterus and mammary glands - it stimulates contraction of the muscles of the uterus (released in large quantities during labour) - stimulating contraction of cells in mammary glands (releases milk during breastfeeding) antidiuretic hormone/vasopressin (protein): - targets nephrons in the kidneys - it increases re-absorption of water from the kidneys during the formation of urine - at higher concentrations it can cause constriction of the arterioles

follicle stimulating hormone (protein): - targets gonads - it stimulates the development of follicles (in females) and the production and maturation of sperm (in males) luteinising hormone (protein): - targets gonads - it works with FSH to bring about ovulation and in the formation of of the corpus luteum (females) - stimulates the interstitial cells of the testes to secrete testosterone (males) growth hormone (protein): - targets all cells - it stimulates growth of body, skeleton, the increase in the rate at which amino acids are taken up by cells to form proteins and once maturing is reached helps maintain size of organs thyroid stimulating hormone (protein): - targets thyroid gland - stimulates the production and release of hormones from thyroid adrenocorticotropic hormone (protein): - targets the adrenal cortex - it controls the production and release of some of the hormones from the adrenal cortex prolactin/lactogenic (protein): - targets mammary glands - works with other hormones to initiate and maintain milk production

thyroxine (T4) and triiodothyronine (T3) (amines): - targets most body cells - it increases metabolic rate and therefore oxygen consumption and heat production calcitonin (amine): - targets bone and cells of the kidneys - it decreases calcium and phosphate levels in the blood by inhibiting bone reabsorption/degeneration - increase calcium deposits in bones.

parathormone (protein): - targets cells of kidneys, intestines and bones - it increases calcium levels in the blood by stimulating bone reabsorption, increased calcium absorption in the intestines and increased reabsorption of calcium in the kidneys

thymosin (protein): - targets t-lymphocytes (bone marrow) cells - it stimulates the development and maturation of disease fighting t-lymphocytes

insulin (protein): - targets most body cells - stimulates uptake of glucose - reduces blood glucose levels via the conversion of glucose to glycogen and fat glucagon (protein): - targets the liver’s fat storage tissue - it stimulates breakdown of glycogen and fat into glucose - increasing blood glucose levels

aldosterone (steroid): - targets most body cells - it increases reabsorption of sodium ions and excretion of potassium ions via urine cortisol (steroid): - targets kidneys - it promotes normal metabolism, helps the body to withstand stress and repair damaged tissue and increases blood glucose levels

adrenaline (amine): - targets most body cells - it helps prepare body for flight or fight response - reinforces the effects of the sympathetic division of the autonomic nervous system x noradrenaline (amine): - targets cardiac muscles cells - it increases rate and forces of heartbeat

erythropoietin (protein): - targets bone marrow - it stimulates production of red blood cells

oestrogen (steroid): - targets many tissues - it stimulates development of female sexual characteristics and regulates menstrual cycle progesterone (steroid): - it targets uterus and mammary glands - it maintains endometrium, ‘let down’ reflex prepares mammary glands for milk secretions

testosterone/androgens (steroid): - targets many tissues - it stimulates sperm production, growth of skeleton and muscles and development of male sexual characteristics

• it is controlled by hypothalamus, controls the functioning of many of the other glands and the hormones it secretes