Excretion

• What is excretion

  • Process whereby metabolic waste products and toxic materials are removed from the body

  What is urea

  • Waste product made from the deamination of excess amino acids in the liver
• Structure and function of mammalian excretory system

  Structure

  1. Posterior vena cava
  2. Renal artery and renal veins
  3. Aorta
  4. Ureter
  5. Urinary Bladder
  6. Urethra

  Functions

  • Supplied with blood by renal artery and drained by renal vein
  • Urea leaves the kidney via the ureters
  • Both ureters drain urea into urinary bladder

  
• Kidney structure

  1. Renal medulla
  2. Renal cortex
  3. Renal pelvis
  4. Cortex
  5. Ureter
  6. Renal vein
  7. Renal artery

  
• Nephron structure

  1. Efferent arteriole
  2. Afferent arteriole
  3. Bowman's capsule
  4. Glomerulas
  5. Proximal convoluted tubule
  6. Distal convoluted tubule
  7. Loop of Henle
  8. Collecting duct

  
• How blood enters the kidney tubule

  1. Blood enters the kidney via the renal artery
  2. Renal artery branches into many arterioles
  3. Arterioles further divide to form a mass of blood capillaries
  4. Blood leaves the renal corpuscle, which consists of the glomerulas and bowman's capsule, and enters the tubule
  5. Capillaries unite to form venules
  6. Venules join together to form renal vein
  7. Blood leaves the kidney via the renal vein
• Urine formation - (Glomerular filtration)

  1. Water and small molecules forced out of blood into bowman's capsule
  2. Renal artery branches into numerous arterioles, each entering a nephron
  3. Arterioles split to form numerous capillaries which form a knot called glomerulas
  4. Surrounded by bowman's capsule
  5. Afferent arteriole is wider than efferent arteriole
  6. Causes there to be high blood pressure in capillaries in glomerulas
• Urine formation - (Ultra filtration)

  1. High blood pressure forces plasma out of blood
  2. Only blood cells, platelets and large plasma proteins/fat molecules with plasma remains in blood
  3. Basement membrane wraps around capillaries in glomerulas
  4. Has small pores to allow water and small molecules to pass through
  5. Filtrate collected in bowman's capsule of renal corpuscle
• Urine formation - (Selective reabsorption)

  1. Starts at proximal convoluted tubule
  2. 80% of filtrate is selectively absorbed back into blood
  3. Ensures that useful substances returns to blood
  4. All glucose and amino acids + 85% of mineral ions reabsorbed by active transport
  5. Small proteins also reabsorbed
  6. 80% of water absorbed into blood by osmosis
• Urine formation - (Selective reabsorption)

  1. Proximal convoluted tubule cells have
  2. Many mitochondria to provide ATP for active transport
  3. Many microvilli to increase surface area
  4. Some water is reabsorbed in distal convoluted tubule, loop of Henle, and collecting duct
  5. Some salts also reabsorbed into distal convoluted tubule
  6. Water, salts, and metabolic waste products passes through collecting duct into renal pelvis to be passes out as urine
• Urine formation - (Urine and blood)

  1. Glucose - 0.009 and 90
  2. Proteins - 0.000 and 7500
  3. Urea - 1800 and 305
  4. Ammonia - 60 and 0.2
• What does this graph show

  • Shows that all glucose that is filtered gets reabsorbed till 400. After that, reabsorption stops and excess glucose is excreted

  
• Renal handling of glucose as a function of plasma glucose concentration (what happens with glucose when someone has untreated diabetes)

  • In healthy people, 100% of glucose is reabsorbed by active transport
  • However, there is a maximum rate at which active transport can reabsorb glucose
  • Maximum rate is exceeded for person with untreated diabetes
  • Active transport cannot keep up with reabsorbing glucose and excess glucose is excreted as urine
• Chemical composition of urine

  • 95% water + 5% solutes
  • nitrogenous waste includes urea, uric acid, and creatine
  • Solutes include sodium, potassium, magnesium, bicarbonate ions, calcium, phosphate, and sulfate
  • Abnormally high concentrations of any urinary constituents may cause disease.
• Osmoregulation – (Mechanism)

  1. Amount of water reabsorbed by kidney controlled by ADH
  2. ADH secretion by pituitary gland depends on instructions from hypothalamus
  3. Hypothalamus has receptors that detect changes in blood water potential
• Osmoregulation - (Dehydration)

  1. Loss of water through sweating
  2. Water potential of plasma decreases
  3. Hypothalamus makes pituitary gland secrete more ADH
  4. More ADH causes kidneys to reabsorb more water
  5. Water potential returns back to normal
• Osmoregulation - (Excess water)

  1. Large intake of water
  2. Water potential of plasma increases
  3. Hypothalamus makes pituitary gland secrete less ADH
  4. Less ADH causes kidneys to reabsorb less water
  5. Water potential returns back to normal
• How is blood cleaned in a dialysis machine - (DKDDCB)

  • Dialysis membrane
  • Partially permeable membrane
  • Diffusion of small molecules
  • Prevents large molecules from getting loss
  • Long narrow coiled tube
  • Increases surface area
  • Diffusion of waste products
  • Kidney dialysis
  • Process of removing excess fluid and toxins from blood
  • Continual shunting of patient's blood through dialysis machine for filtration
  • Dialysis machine is a system of partially permeable membrane tubings surrounded by dialysis fluid
  • Clean blood returned to patient's bloodstream
• How is blood cleaned in a dialysis machine - (DKDDCB)

  • Dialysis fluid
  • Essential salt and glucose solution
  • Prevents diffusion of salts and glucose from blood to fluid
  • No loss of salts from blood
  • No urea, uric acid and creatine
  • Increase concentration gradient for faster diffusion of waste products
  • Direction of dialysis fluid opposite to direction of blood
  • Maintain concentration gradient for removal of waste products
• How is blood cleaned in a dialysis machine - (DKDDCB)

  • Constant temperature bath
  • Ensures that temperature of blood returning to body is 36.9 degrees
  • Blood pump
  • Moves blood through dialysis machine
• Dialysis machine diagram

  1. Artery
  2. Vein
  3. Dialysis tubing
  4. Pump
  5. Dialysis fluid
  6. Dialysis machine
  7. New dialysis fluid
  8. Filtered blood

  
• Old way of cleaning blood in dialysis machine

  1. Blood drawn from artery in patient's arm
  2. Blood pumped through dialysis tubing into dialysis membrane
  3. Tubing surrounded by dialysis fluid and tubing which are partially permeable
  4. Diffusion of small molecules and metabolic waste product out of tubing
  5. Large molecules remain in tubing
  6. Filtered blood returned to a vein in patient's arm
• New way of cleaning blood in dialysis membrane

  1. Fistula inserted into forearm via minor surgery
  2. Forms direct connection between artery and vein
  3. Blood drawn from vein and filtered blood returned to vein
• Region of nephron + molecules that are reabsorbed

  1. Proximal convoluted tube
  2. All glucose and amino acids + most water + most mineral salts
  3. Loop of Henle
  4. Some water and some mineral salts
  5. Distal convoluted tube
  6. Some water and mineral salts
  7. Collecting duct
  8. Some water