Chapter 11: Excretion

• %%Catabolic activities%% are chemical processes which cause the breakdown of complex substances into simpler ones. For example, tissue respiration and deamination of proteins and amino acids to form urea.
• %%Anabolic activities%% are chemical processes in which the simpler substances are built up into more complex substances. For example, the formation of new protoplasm from amino acids (proteins) and process of photosynthesis.
• The sum of all chemical activities within the body is %%metabolism.%%
• %%Excretion%% is the process by which metabolic waste products and toxic materials are removed from the body of an organism.

  ## Excretory Products:

• Carbon dioxide - lungs - gas is expired
• Nitrogenous waste products - kidneys - urine
• Excess Water
  • kidneys - urine
  • skin - sweat
  • lungs - expired air
• Bile pigments - liver - intestines

Mammalian Urinary System:

• Consists of a pair of kidneys, pair of ureter, a urinary bladder and urethra.
• ^^kidneys^^:
  • Bean shaped.
  • Attached to dorsal body wall.
  • Lie above waistline.
  • Renal artery & renal vein connected.
• Urine from each kidney passes through the ureter to the __Urinary Bladder.__
• __Urinary bladder:__
  • elastic muscular bag.
  • ventral to the rectum.
  • stores urine.
  • when the bladder is full the sphincter muscle relaxes to allow the urine flow into urethra and pass out of the body.

Longitudinal section of kidney:

• Two regions:
  • ^^Cortex^^
  • outer region.
  • ^^Medulla^^
  • inner region.
  • projects into a funnel shape space __renal pelvis__.
  • nephrons.
    • contains __glomeruli__; where blood is filtered and glucose, urea and salts are removed.
    • contains tubule; where water and some mineral salts are reabsorbed (after filtration in glomerulus). This prevents loss of too much water. (urea is not reabsorbed leading to a high concentration in urine).

Formation of Urine:

• the $glomerulus$ filters water and other substances from the bloodstream.
• the $filtration membrane$ keeps blood cells and large proteins in the bloodstream.
• reabsorption moves nutrients and water back into the bloodstream.
• waste ions and hydrogen ions secreted from the blood complete the formation of urine.

Kidney as Osmoregulators:

• %%Osmoregulation%% is the control of water and solute levels in the blood to maintain a constant water potential in the body.

Function of Kidneys:

• excretory organs.
• help regulate salt and water balance of the body fluid.

KIdney Failure:

• two solutions:
  • dialysis

  %%Dialysis fluid%% contains essential salts for the body - if the blood lacks essential salts dialysis fluid will diffuse its salts to it through membrane.