Chapter 7 Excretory system

• some by-products can be used, while others are

  wastes
• most wastes are 


  toxic and would be harmful to ones health if allowed to accumulate
• every cell produces 


  waste products
• removing wastes before they reach 


  harmful concentration is extremely important
• excretion 


  removal of wastes of metabolism from the body
• organs involved in processing or excretion of wastes

  lungs, liver, sweat glands, alimentary canal, kidneys
• urea


  produced in liver from breakdown of amino acids
• liver and skin play important role in 


  processing and excreting waste materials
• liver has host of different functions including

  preparation of materials for excretion
• proteins


  make up structural materials of cells
• as long as body has sufficient supply of carbs and fats/stored fats 


  then little protein is used in energy-releasing reactions
• excess protein from diet cannot be 


  stored in cells

  processes are required to remove it from body
• some protein broken down in body all the time although most 


  breakdown is incomplete
• worn out cells are source of protein and are 


  broken down into constituent amino acids
• very small amount of amino acid is list from body via 


  urine, skin, hair and fingernails
• proteins become primary constituents of cell 


  structures, enzymes, antibodies and many glandular secretions
• if other energy sources have been used, the body is able to

  metabolise large amounts go proteins breaking them down to produce energy
• to make proteins as energy (deamination) 


  amino group (NH4) must first be removed from amino acids
• deamination occurs 


  in liver with aid of enzymes
• one amino group has been removed 


  it id converted by the liver cells to ammonia (NH3) and then finally urea
• urea is eliminated from body 


  in urine
• remaining part of amino acid (carbon and hydrogen) is converted 


  into a carbohydrate
• carbohydrate can be readily broken down by


  cells to release energy, carbon dioxide and water
• deamination equation 


  amino acid + oxygen -----enzymes----> carbohydrate + ammonia
• ammonia 


  extremely soluble in water

  highly toxic to cells
• cell in liver rapidly convert ammonia 


  to less toxic molecule urea
• urea easily extracted by

  kidneys

  eliminated from body in urine

  also lost in sweat from sweat glands
• process of conversion to urea

  energy + carbon dioxide + ammonia ----> urea + water
• the liver also 


  detoxifies alcohol and many other drugs (antibiotics)

  deactivates many hormones and converts them into form that can be excreted

  breaks down haemoglobin from dead red blood cells to produce bile pigments
• skin main function 


  provide protective covering over surface of body

  regulate body temperature
• even when there is no visible perspiration on skin 


  sweat glands secrete about 500ml of water per day
• dissolved in water is

  sodium chloride, lactic acid, urea, some drugs, being excreted from body
• sweat glands located 


  lower layers of skin
• duct carries sweat to 


  hair follicle or skin surface where it opens at a pore
• cells surrounding glands are able to

  contract and squeeze sweat to skin surface
• urinary system 


  kidneys, bladder and their associated ducts
• kidneys enclosed by 


  renal capsule
• under renal capsule is 


  outer renal cortex, inner renal medulla nd then renal pelvis sits in concave side of kidney
• renal hilum lies on 


  concave surface of kidney and is where vessels enter and leave
• medulla consist of number of 


  renal pyramids, separated by renal columns, where blood vessels lie