🏥 Chapter 8 - Excretion in Humans

• Excretion

  • removal of metabolic waste products, toxic substances and excess substances
• Metabolic Substances

  • Carbon Dioxide
  • Urea
  • Excess Mineral salts/ions
  • Excess water
• Carbon Dioxide

  If there is an abnormally high CO2 concentration in the blood, then hypercarbia occurs, → headache, rapid breathing, premature heartbeat and confusion
• Urea

  Abnormally high urea concentration →abdominal pain, nausea, irregular heartbeat and muscle cramps
• Excess Mineral salts/ions

  Decreases water potential in blood plasma, causing water to diffuse out of tissue cells into blood via osmosis, dehydrating cells
• Excess water

  Increases water potential in blood plasma, causing water to diffuse out of blood plasma into tissue cells via osmosis, and this may cause cells to swell and burst
• Human Urinary System

  1. Kidneys

  - bean-shaped organs, 10 to 13 cm long and about 5 to 7 cm wide. main function of the kidneys is to excrete urea and excess salt and water as urine.

  2. Ureter

  - narrow tube connecting kidneys & urinary bladder. urine pass through this to reach bladder

  3. Urinary bladder

  - muscular, elastic bag that stores urine

  4. Urethra

  - duct in which urine passes from the urinary bladder to outside of the body

  
• Structure of Kidneys

  Renal Artery = unfiltered blood

  Renal Vein = filtered blood

  
• Nephrons

  Nephrons have:

  1. Bowman's Capsule
  2. Glomerulus (the "filter")
  3. Proximal convoluted tubule (PST)
  4. Loop of Henle
  5. Distal convoluted tubule (DST)
  6. Collecting Duct (not part of nephron)

  
• Functions of Kidney in Excretion


  • nephrons are surrounded by blood capillaries that are connected to renal artery and renal vein
  • blood enters the kidney via the renal artery, and branches to form afferent aterioles, which brings blood to the glomerulus
  • each arteriole branches further into a mass of blood capillaries in the Bowman's capsule known as the glomerulus
  • efferent arterioles transport blood away from the glomerulus
  • blood leaving blood capillaries unites, leading into a branch of the renal vein
• Ultrafiltration : Urine Production (I)

  • there is high blood pressure in the glomerulus (width of afferent arterioles > width of efferent arterioles)
  • blood plasma is forced out of glomerular blood capillaries into the Bowmans capsule
  • filtered blood (ie. glomerular filtrate) contains small soluble molecules such as salts, water, glucose, amino acids and other waste products such as urea
• Ultrafiltration : Urine Production (II)

  • glomerulus is a knot of blood capillaries which provides a large surface area for filtration to occur
  • blood capillaries have a one-cell thick wall and tiny pores in them
  • blood capillaries are covered by a thin partially-permeable membrane which only allows small molecules to pass through such as water, salts , glucose ,amino acids, waste products etc
  • impermeable to blood cells platelets, and large molecules such as proteins

  
• Selective Reabsorption : Urine Production (I)

  • after ultrafiltration occurs, selective reabsorption takes place in order not to lose too much water and useful substances
  • as glomerular filtrate (from ultrafiltration) passes along the nephron, useful substances are reabsorbed into the surrounding blood capillaries.
• Selective Reabsorption : Urine Production (II)

  In Proximal Convoluted Tubule:

  1. most of the water is reabsorbed via osmosis
  2. all glucose and amino acids are reabsorbed via active transport( conc. in nephron < conc in blood capillaries)
  3. most mineral salts are reabsorbed via diffusion and active transport

  In Distal Convoluted Tubule and Loop of Henle:

  1. some water is reabsorbed via osmosis
  2. some mineral salts are reabsorbed via active transport.

  In Collecting Duct:

  1. some water reabsorbed via osmosis

  
• Kidney Dialysis (I)

  • man cannot live without kidneys as they are excretors, which remove metabolic waste products in the form of urine, and they are also osmoregulators (out of syllabus)
• Kidney Dialysis (II)

  • kidneys fail because of:

  1. high blood pressure
  2. diabetes
  3. alcohol
  4. severe accidents that physically damage the kidney
  5. complications from surgergy
• Kidney Dialysis (III)

  Haemodialysis:

  1. blood is drawn from the veins in the patients arm and is pumped through the tubing in the dialysis machine (ie. dialysis tubing)
  2. the tubing is bathed in a specially controlled dialysis fluid, and the walls of the dialysis tubing are partially permeable
  3. small molecules such as urea and other metabolic waste products diffuse out of the tubing and into the dialysis fluid.
  4. blood cells, platelets and large molecules such as protein remain in the tubing

  
• Kidney Dialysis (IV)

  1. The dialysis fluid contains the same concentration of essential substances as healthy blood, ensuring these substances do not diffuse out of the blood into the dialysis fluid. Furthermore, if the patient's blood lacks these essential substances, these substances will diffuse from the dialysis fluid into the blood.
  2. tubing is narrow long and coiled to increase surface area-to-volume ratio for faster rate of exchange of substances between blood and dialysis fluid

  
• Kidney Dialysis (V)

  3. Direction of blood flow is opposite of direction of dialysis fluid to maintain the concentration gradient for removal of waste products

  4. dialysis fluid does not contain metabolic waste products to provide a steep diffusion gradient for urea, excess water and salts to diffuse out of blood into dialysis fluid
• how opposing directions maintain conc. gradient

  yeah

  
• yt video on chapter

  https://www.youtube.com/watch?v=q5qaGHfdmYM