EXCRETION
Excretion-process whereby metabolic waste products removed from body of an organism
Metabolic waste products-CO₂ (respiration), urea (deamination), etc. harmful if accumulates in body > must be expelled or converted into harmless substances. Collected > carried to organs by circulatory system excreted from the body

Egestion-(defecation)removal of undigested matter from alimentary canal in the form of faeces through anus
(formation of faeces not a metabolic reaction)

secretion-production of useful chemical substances by living cells which have definite functions

Human Excretory System
Mammalian Urinary System
-consists of a pair of kidneys, a pair of ureters, a urinary bladder and urethra
kidneys-bean-shaped organs embedded in a mass of fat in abdominal cavity, near back of abdomen, behind intestines
hilus-depression at centre of concave surface where renal artery & vein, nerves + ureter (connects to urinary bladder) are connected
made up of 2 main parts; outer dark-red region-cortex + inner thicker pale red region-medulla
medulla consists of 12-16 conical structures (pyramids) which project into funnel-like structure-renal pelvis
Each kidney made up of about 1 million coiled tubes-uniferous tubules/ renal tubules/ nephrons

Nephrons
-begin in cortex as cup-like, Bowman's capsule which contains a group of fine blood vessels-glomerulus. Together called Malpighian corpuscle
-proximal convoluted tubule (90% reabsorbed here, glucose) leads out of the Bowman's capsule into the medulla, making a U-shaped Loop of Henle which passes back into the cortex to from the distal convoluted tubule, which opens up into a collecting duct which runs through the medulla and opens at the apex of the pyramid into the renal pelvis. Blood capillaries surround the convoluted tubules for reabsorption

Production of Urine
Kidney's main function-produce urine in nephrons
afferent artery > glomerulus > efferent artery
due to differences in size (efferent > smaller) > blood pressure increases in glomeruli
process of urine production involves 2 steps; ultra-filtration (Bowman's capsule) + selective reabsorption (loop of Henle + convoluted tubules)

Ultra-filtration: due to high pressure in afferent arteriole substance < 68000 RMM (Relative Molecular Mass) filtered out (H₂O, urea, amino acids, salts) Glomerular filtrate-solution forced out of blood capillaries into Bowman's capsule (blood corpuscle + large molecules e.g. proteins + fats not filtered off > remain in capillaries)

Selective Reabsorption: as glomerular filtrate passes through tubules > selective absorption of useful substances. Most H₂O reabsorbed by osmosis. Normal individual-some mineral salts (depends on plasma conc.), all glucose + amino acids reabsorbed through walls of tubules into surrounding blood capillaries. Requires energy-active transport. Excess H₂O, mineral slats + nitrogenous waste (urea, uric acid) pass along tubule into collecting duct then renal pelvis as urine [sometimes on a heavy intake of sugar, beyond kidney's capacity to reabsorb all glucose >glucose in urine]

Normal Constituents of Urine (g/100cm3)
H₂O=96gUrea=2gMineral Salts (mainly NaCl)=1.8gOther Nitrogenous Substances=0.2g

Diabetes Mellitus-sugar diabetes-glucose in urine-body unable to store excess glucose as glycogen-lack of secretion of insulin by Islets of Langerhans (beta cells, alpha cells-glucagon) in pancreas > more glucose filtered > beyond kidney's capacity to reabsorb all > a lot of glucose in urine

Functions of Kidneys
-filters blood to remove excess salts, nitrogenous waste, water, glucose, urea + other unwanted substances less then 68000 RMM, by ultra-filtration and excretes them in urine
-selectively reabsorbs substances needed by body (low on amino acids> reabsorb amino acids)
-regulate water: salt balance in body, osmoregulation (hot day>sweat production increases >more water reabsorbed)

Regulation of Salt: Water Balance (Osmoregulation)
Water-essential-from drinks, food, metabolic water. Water reabsorption-controlled by Anti-Diuretic Hormone ADH, secreted by pituitary gland in cranium when water levels-low. Makes tubules' walls more permeable to water. Enough water reabsorbed, ADH production stops
Hot day>sweat prod. high (dilation of skin blood vessels > lose more heat)>ADH sec. high>water reabsorption high > urine conc. high, volume low
Salt balance; body needs more salt > ADH sec. low > more water excreted > salt conc. in body fluids increase
Regulation of water: salt balance stimulated by changes in osmotic pressure detected by osmo receptors in brain which send msgs to pituitary glands to start/stop ADH sec.
Low salt/excess H₂O: osmotic pressure in blood falls > osmo-receptor cells in hypothalamus of brain detect fall, send msg. to pituitary gland > ADH prod. less > less H₂O reabsorbed, large volume of diluted urine excreted > salt balance increases

Artificial Kidney (Dialysis Machine)
-Kidney failure due to accident, disease, drop in blood pressure, high tension, diabetes. Possible to live w/ 1 kidney, but if both fail > patient's blood composition has to be regulated
-In principle, it consists of a long cellulose, semi-permeable coiled tube (dialysis tubing-cellulose acetate) placed in a water bath (dialyser). Patient's blood drawn into tube from radial artery by a pump. Pores in dialysis tube allow small molecules (salts, glucose, urea) to leak out into water bath (blood cells and protein molecules too big). Events that occur are similar to ultra-filtration in glomerulus.
-Bathing fluid :-contains sugar + other substances in correct composition to prevent loss of glucose and essential salts
   -at body temp. 37°C for normal temp. for blood for optimum diffusion
   -constantly changed: prevent accumulation of unwanted substances
-Blood returned to radial vein after passed through a bubble and clot trapper to trap bubbles and clots
-Better solution-kidney transplant, but difficult to find suitable donor of healthy kidney to prevent rejection when body produces lymphocytes which attack organ > rejection. Prevent rejection; 1choose right donor, tissues are similar to patients & 2take immunosuppressive drugs
-Peritoneal (body cavity) dialysis-hole made in abdomen, fluid pumped in and left for 5-6 hours

Homeostasis
The Eye
Nervous System
Chemical Control of Plant Growth
The Use and Abuse of Drugs
Diversity of Organisms
Nutrient cycles and Ecology
Parasitism
The Human Impact on the Environment
Reproduction in plants
Sexual reproduction in animals
Genetics
Cell Structure and Organisation
Enzymes
Nutrition
Transport in Plants
Support, Movement and Locomotion
Transport system in man-circulatory system
Respiration

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