Biology Practicals - Maintaining a Balance


Perform a firsthand investigation of the structure of the mammalian kidney by dissection, use of model or visual resource and identify the regions involved in the excretion of waste products


  • The kidney has a nephron where blood from the aorta (maximum pressure) is fed into the Bowmans capsule where everything (bar cells and proteins) is forced out of the blood

  • The filtrate passes through a long tubule surrounded by capillaries and along this tube useful substances like glucose and vitamins are reabsorbed (energy is required)

  • Water diffuses passively in the descending loop of Henle until at the bottom of the loop, it is hypertonic (Having a higher osmotic pressure in a fluid relative to another fluid) compared to surrounding tissue

  • Active transport: A kind of transport wherein ions or molecules move against a concentration gradient, which means movement in the direction opposite that of diffusion – or – movement from an area of lower concentration to an area of higher concentration. Hence, this process will require expenditure of energy, and the assistance of a type of protein called a carrier protein

  • Passive transport: A kind of transport by which ions or molecules move along a concentration gradient, which means movement from an area of higher concentration to an area of lower concentration.

  • In the ascending tubule salt is reabsorbed

  • Re-absorption of water is passive transport by osmosis

  • The re-absorption of glucose, sodium salts and amino acids is active transport

  • Some substances like potassium ions are actively secreted in the kidney tubules

Aim: to identify the parts of a mammalian kidney and to identify the regions involved in the excretion of waste products


  1. Work in pairs and lay the kidney on the dissecting tray

  2. Examine the external structure of the kidney, notice its surrounding fat (adipose tissue) before removing it. Remove fat and leave vessels and hilum intact

  3. Compare the size of the kidney that you have for dissection with the dimensions given for an average human kidney

  4. Identify the vessels, distinguishing between the renal artery, vein and ureter. Locate the adrenal gland (in the fat)

  5. Detach the renal capsule

  6. Draw a life size diagram to show the external structure of kidney

  7. Cut the kidney in longitudinal section; make incision on side opposite to hilum. Note opening to ureter. Insert probe through hole and see where it exits

  8. Identify regions of kidney, outer cortex, the medulla and the renal pelvis. Compare colour and appearance of medulla and cortex

  9. Insert probe between renal pyramids, slip the lower blade of the scissors into the gap and slit through each pyramid to follow the path of calyces. Urine from the collecting tubules drains into these calyces, which carry the urine to the renal pelvis, ureters and bladders

  10. Draw diagram showing internal structure

  11. Use toothpicks with coloured flags to identify regions