Kidney

• What do the kidneys excrete?

  urea in the form of urine
• The outer region of a kidney is called the cortex
• What is the main role of the kidney?

  Excretion
• The inner region of a kidney is called the medulla
• The centre of a kidney is called the pelvis
• Label this longitudinal section.

  1. Cortex
  2. Medulla
  3. Pelvis
  4. Ureter

  
• The pelvis leads into the ureter
• The outermost layer of the kidneys is called the capsule
• Define Nephrons:

  The functional unit of the kidney in the form of tiny tubules
• Each kidney contains approx. one million nephrons which starts in the cortex at a cup-shaped structure called the Bowman's capsule
• The renal artery splits to form lots of arterioles arranged in a knot of capillaries called the glomerulus
• Blood enters the glomerulus through...

  afferent arteriole
• Blood leaves the glomerulus through the...

  efferent arteriole
• Each glomerulus is surrounded by the Bowman's capsule
• Label this diagram:

  1. afferent arteriole
  2. lumen of Bowman's capsule
  3. podocytes
  4. cells of proximal convoluted tubule
  5. epithelium of Bowman's capsule
  6. efferent arteriole

  
• In the Bowman's capsule, what are the pores between the endothelial cells called?

  Fenestrations
• What does the basement membrane consist of?

  • collagen fibres
  • glycoproteins
• What is the role of the basement membrane in the Bowman's capsule?

  to act as a filter preventing large molecules from passing through
• Define Ultrafiltration:

  The filtration of the blood at a molecular level under pressure
• Blood plasma containing dissolved substances is pushed under high hydrostatic pressure from the capillary of the glomerulus into the lumen of the Bowman's capsule.
• Blood plasma contains:

  • water
  • amino acids
  • glucose
  • urea
  • inorganic mineral ions
• Name three examples of inorganic mineral ions in blood plasma.

  • sodium
  • chloride
  • potassium
• The Loop of Henle consists of the...

  • descending limb
  • ascending limb
• The arrangement of the loop of Henle is known as what?

  A hairpin countercurrent multipier system
• The Bowman's Capsule leads into the rest of the tubule which has three parts:

  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
• Suggest why the proximal and distal tubules are convoluted

  • it makes the tubules longer so there is a larger total surface area for selective reabsorption
• Explain why reabsorption from the nephron must be selective.

  • all useful substances must be removed from the fluid in the nephron
  • all metabolic wastes should remain in the fluid so that they can be excreted as urine
• Why is it essential that most of the water is reabsorbed from urine?

  • A large volume of blood passes through the kidney
  • If the water in it is all lost in urine, the body will dehydrate very quickly
  • A terrestrial animal cannot find and drink enough water to replace all the water that passes through the kidney
• Is glucose normally found in urine?

  NO
• Are mineral ions normally found in urine?

  YES
• Blood has a very low water potential
• Most minerals and some water of the fluid is reabsorbed in the proximal convoluted tubule
• Why is most of the fluid reabsorbed in the proximal convoluted tubule?

  • it has a highly folded surface
  • increasing the surface area
• What causes the water potential to decrease at the descending limb?

  • water diffuse out via osmosis
  • mineral ions diffuse in
• Where does ultrafiltration occur?

  The Bowman's capsule
• Where is glucose reabsorbed?

  the proximal convoluted tubule
• What is the role of heparin in haemodialysis?

  to prevent blood clotting
• Name the two types of renal dialysis:

  • Haemodialysis
  • Peritoneal dialysis
• What property of the hormone hCG allows it to be detected in urine?

  • it has a relative molecular mass of less than 69 000
  • so it can pass out of the capillaries
• Outline what happens when the hypothalamus secretes antidiuretic hormone (ADH) into the blood?

  • ADH bind to their receptors on the collecting duct
  • more vesicles containing aquaporins are inserted into the cell surface membranes of the collecting duct
  • allows more water to be reabsorbed
  • a smaller volume of urine will be produced
  • the urine has a lower water potential (less dilute)