excretion and osmoregulation

Question 1

what is excretion

Answer 1

• removal of metabolic waste (mainly urea) from the body
• animals do not store amino acids, excess amino acids are reanimated to form ammonia (extremely toxic) in the liver, ammonia is promptly converted to a less toxic nitrogenous compound, urea, in the liver
• urea is transported in blood from liver to kidneys and excreted by kidneys

plasma:

• consists of 90% water and soluble proteins
• mineral salts, dissolved food substances, waste products and hormones

red blood cell
- transport oxygen molecules from the lungs to body cells
features:
- filled with red pigment–> haemoglobin for binding oxygen
- absence of nucleus to provide more space for haemoglobin to carry more oxygen
- biconcave shape to increase surface area to volume ratio to increase uptake of oxygen
- elastic to enable cells to squeeze through blood capillaries
- produced in bone marrow and destroyed in the lier

white blood cell
- protect body against pathogens
features:
- colourless as they do not contain haemoglobin
- irregular in shape and contains a nucleus
- motile as they are able to move, change their shape and squeeze through the walls to thin blood capillaries
lymphocyte: produce antibodies that protect hje body from diseases
phagocytes: ingest pathogens

platelets

• bring about blood clotting of blood
• feature: membrane-bound fragments of white blood cell

Question 2

function of a kidney

Answer 2

• regulates concentration of inorganic ions (e.g. sodium and chloride)
• removes waste products of metabolism such as urea from the blood in urine
• maintains a constant water potential

Question 3

formation of urine

Answer 3

1. ultrafiltration in the bowman’s capsule to form glomeruli filtrate
   - in the glomerulus, water and relatively small molecules of the blood plasma (ions, mineral salts, urea, glucose, and amino aids) pass out of the capillaries into the lumen of the capsule (filtrate is the glomerular filtrate)
   - red blood cells, white blood cells, platelets and proteins are retained in the glomerulus – too large to pass out
   - process is powered by high pressure of the blood
2. selective reabsorption in the proximal convoluted tubule
   - longest section of the nephron
   - large part of glomerular filtrate (most of the mineral salts, all of the glucose and amino acids) is reabsorbed into the capillary network via facilitated diffusion and active transport
   - reabsorption is highly selective:only substances required by body are reabsorbed
   - most of the water in the glomerular filtrate is reabsorbed by osmosis
3. blood pH and ion concentration regulation in the distal convoluted tubule
   - cells of the tubule walls adjust the composition of the blood (the pH by the controlled secretion of H+ and reabsorption of HOO3-)
   - pH of blood remains in the range of ph 7.35-7.45
   - concentration of useful ions is regulated
   - concentration of K+ is regulated by secretion any excess in the plasma into the filtrate
   - concentration of sodium and chlorine ions in the body is regulated by varying the quantity of any sodium and chloride ions reabsorbed from the filtrate
4. further water reabsorption in the collecting ducts by osmosis and the fluid left in the collecting duct become urine
   when we have drunk a lot of water:
   - hypothalamus detects this and stops the posterior pituitary gland secreting ADH
   -ADH absent
   - collecting duct walls less permeable to water
   - a lot of dilute urine formed

when we have taken in too little water/sweated excessively/eaten salty food

• hypothalamus detects this and directs the posterior pituitary gland to secret ADH
• ADH present
• collecting duct permeable to water
• small quantity of urine formed