Excretion

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  • Created by: Harry
  • Created on: 17-05-14 14:15

Homeostatis

  • The keeping of constant conditions in the body => e.g water intake being equal to exhaled air, sweat and cell respiration
  • Is important because cells will only function properly if they are bathed in tissue fluid => provides them with their optimum conditions
  • Factors that affect tissue fluid: pH (affects activity of cell's enzymes), body temp. (37 degrees), being too dilute (causes swelling of water)
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The urinary system diagram

(http://www.ivy-rose.co.uk/HumanBody-Images/Urinary/UrinarySystem_cIvyRose.jpg)

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The urinary system

  • Each kidney is supplied with blood via a short renal artery => leads straight from body's main artery (aorta) => suggests that is at high pressure
  • Inside kidneys = blood is filtered + cleaned blood passes out via each renal vein
  • Urine passes out of kidney via two tuves => ureters (stored in a muscular bag called the bladder)
  • Bladder has a tube leading to the outside = urethra
  • Wall of urethra contains two ring-like muscles => sphincters
  • Sphincters can contract to close urethra and hold back urine
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The kidneys diagram

(http://www.ivy-rose.co.uk/HumanBody-Images/Urinary/Kidney_cIvyRose.png)

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The kidneys

  • Darker outer region = cortex
  • Filtering units = nephrons
  • Nephrons run down the middle layer of the kidney = medulla
  • Medulla has bulges called pyramids that consist of tubules that eventually lead to the tips of these pyramids and empty urine into a space called the pelvis
  • Pelvis is connected with the ureter in which carries the urine to the bladder
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Nephrons

(http://click4biology.info/c4b/11/11.3/nephron.gif)

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The Nephron (part 1)

  • At the start of the nephron = hollow cup => Bowman's capsule
  • Bowman's capsule surounds a ball of blood capillaries known as the Glomerulus
  • It is here that blood is filtered => blood enter the kidney via the renal artery, which divides into smaller and smaller arteries
  • Smallest arteries (arterioles) supply the capillaries of the glomerulus
  • A blood vessel with a smaller diameter carries blood away from the glomerulus => capillary networks which surround other parts of the nephron
  • Because of resistance to flow caused by glomerulus, pressure of the blood in the arteriole leading to the glomerulus is very high
  • This pressure forces fluid from blood through walls of the capillaries + bowman's capsule and into the space of the bowman's capsule
  • Blood and glomerulus and space in capsule are separated by two layers of cells => act like a filter, allowing water, ions and small molecules to pass through whilst holding back blood cells and large molecules 
  • Fluid that enturs the capsule space is called the GLOMERULAR FILTRATE 
  • This process that separates different sized molecules under pressure is called ULTRAFILTRATION
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The Nephron (part 2)

  • There are two coiled regions of the tubule (aka. cortex) that are separated by a U shaped loop that runs down into the medula => Loop of Henle
  • After the second coiled tubule, several nephrons join up to form a collecting duct where the final urine passes out into the pelvis
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