Excretion in humans Flashcards iGCSE Biology

[q] Dialysis Machine Process

[a]

• Dialysis membrane is partially permeable;
• Minerals / salts / ions / urea move by diffusion down a concentration gradient;
• Water moves by osmosis down the water potential gradient across membrane;
• Proteins / blood cells too large to move across membrane;
• Glucose is not removed by dialysate (same concentration);
• Fresh dialysate maintains a concentration gradient;

[q] Function of Nephrons (Kidney/Renal Tubules)

[a]

1. Ultrafiltration
   • Ultrafiltration is the process by which the fluid is filtered out of the blood by the glomerulus.
   • Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (the glomerulus) sitting inside the cup-shaped Bowman’s/Renal capsule 
   • The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them (which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta) 
   • The blood pressure in a glomerulus causes part of the blood plasma to leak through the capillary walls.
   • The red blood cells and the plasma proteins are too big to pass out of the capillary, so the fluid that does filter through is plasma without the protein, i.e. similar to tissue fluid. 
   • The fluid thus consists of:
     • mainly of water 
     • with dissolved salts, 
     • glucose,
     • urea and
     • Hormones

[q] What are the Functions of Kidneys?

[a]

1. Regulate water content of the blood (a.k.a Osmoregulation)
2. Remove/filter toxic waste products of metabolism (e.g: urea) and substances in excess of requirements (e.g: salts) from the blood to be excreted from the body as urine.

[q] How Urea is made?

[a]

1. Protein in food is taken into the alimentary canal.
2. Protein molecules are broken down to amino acids during digestion.
3. The amino acids are absorbed into the blood and taken to the liver by the hepatic portal vein.
4. Amino acids that are needed are released into circulation.
5. Excess amino acids that are not needed are deaminated into carbohydrates and ammonia.
6. The carbohydrate is converted into a polysaccharide called glycogen.
7. The ammonia is converted into urea
   • nitrogen-containing amino group is removed from ammonia
8. Urea dissolves in the blood and is taken to the kidney to be excreted. The solution is now known as urine.

• Deamination;
• (part of excess) amino acids converted to urea;
• (part of) amino acid converted to ammonia;
• ammonia converted to urea;
• ammonia is harmful;
• (rest of) amino acid molecule, releases energy / converted to glucose / glycogen / respired;
• (some amino acids) used to make proteins e.g. fibrinogen;
• AVP ; e.g. transamination.

[q] Name the Green Stars

[a]

[q] Name the Yellow Stars

[a]

[q] Name the Yellow Stars

[a]

[q] Name the Yellow Stars

[a]

[q] Nephrons (Kidney/Renal Tubules)

[a] 2) Selective Reabsorption

[q] Renal Capsule Function

[a]

[q] The liver and its role in producing proteins:

[a]

• • As well as being an excretory organ, the liver plays a very important role in assimilating amino acids.
  • Amino acids in the liver undergoes deamination
    • Part of excess amino acids converted to urea;
    • Part of amino acid converted to ammonia;
    • ammonia converted to urea;
      • ammonia is harmful;
  • Rest of amino acid molecule converted to glucose;
  • Some amino acids used to make proteins e.g. fibrinogen;

[q] The Renal System:

[a]

• Blood enters the kidney through the renal artery and exits through the renal vein. 

• Cortex –
  • The dark, outer region of the kidney
  • Contains nephrons.
  • Blood is filtered

• Medulla –
  • The lighter, inner region of the kidney.
  • Contains nephrons.

• Nephron –  (a.k.a Kidney/Renal tubules)
  • Located within the cortex and medulla of each kidney.
  • The nephron is the functional unit of the kidney. 
  • It contains the glomerulus, which is where the blood is filtered and glucose, urea, water and salts are removed.

[q] Ureter

[a]

• Long narrow tubes with expanded upper end (renal pelvis).
  • Function is to carry the urine produced from the kidneys, to the urinary bladder.

[q] Urinary bladder

[a]

• Elastic muscular organ, capable of great expansion.
  • Function is to store the urine until it is released.

[q] Urethra

[a]

• Function is to carry the urine from the bladder to the outside of the body.

[q] Waste products in Humans

[a]

[q] Water balance and osmoregulation

[a]

• The volume and concentration of urine produced is affected by water intake, temperature and exercise:
  • E.g: Dilute urine is likely when:
    • High water intake
      • Less water is reabsorbed into kidney, leaving more to enter the bladder
    • Low temperature
      • Water is not lost through sweating
    • Less Exercise
      • Water is not lost through sweating

[q] What are the advantages of Kidney Transplants?

[a]

• Patients do not need to return to clinic for dialysis / AW;
• Can eat normally / do not need to eat a restricted diet / AW;
• Periods of feeling unwell / tired / nausea reduced;
• No needles / no fistula, permanently in arm;

[q] What are the disadvantages of Kidney Transplants?

[a]

• Finding compatible donor;
• The operation is very expensive;
• Risk of rejection of the donated kidney;
  • Immunosuppressive drugs have to be used for the rest of their lives – these can have long term side effects and leave the patient vulnerable to infections;
• Risk of death during the operation;