Chapter 8

• Chemical activities or metabolic activities occur all the time in the body
• Metabolic waste products that are not needed by the body can become toxic when accumulated and will need to be removed
• Metabolic waste products


  • Carbon dioxide
  • Urea
  • Mineral salts/ions
  • Water
• Carbon dioxide (CO2)


  Waste product of aerobic respiration, removed at the lungs during breathing
• Abnormally high level of CO2 in the blood may lead to hypercarbia with symptoms such as headaches, confusion and rapid breathing
• Urea


  Excess produced from proteins in food and excreted via the kidneys
• Abnormally high level of urea in blood may cause conditions such as nausea and vomiting
• Mineral salts or ions


  Excess in food used by the body and excreted by the kidneys
• High level of salts in the blood


  Water potential of blood will be lowered, causing water to exit tissue cells via osmosis
• Water (H2O)


  Produced as a waste product of aerobic respiration, excess excreted
• Excretion is the process of removing metabolic waste products, toxic substances and excess substances from the body
• Excretion is important so that harmful substances will not build up in the body to cause harm
• Main excretory products


  • Urea
  • Water
  • Mineral salts/ions
  • Carbon dioxide
• The Human Urinary System


  • A pair of kidneys
  • A pair of ureters
  • Urinary bladder
  • Urethra
• Kidney structure


  • Bean-shaped
  • Visible dark outer region (cortex)
  • Pale inner region (medulla)
  • Receives blood through the renal artery
  • Returns blood through the renal vein
  • Basic functional unit is the nephron
• Structure of a nephron

  • Bowman’s capsule
  • Proximal convoluted tubule
  • Loop of Henlé
  • Distal convoluted tubule
• Blood capillaries around the nephron

  • Afferent arteriole
  • Glomerulus
  • Efferent arteriole
  • Blood capillaries surrounding the nephron
• Ultrafiltration


  The first stage of urine formation, process by which small molecules are filtered out of the blood by the glomerulus into the Bowman’s capsule
• High hydrostatic blood pressure in the glomerulus is caused by the difference in the diameter of the afferent and efferent arterioles
• How urine is formed

  • Ultrafiltration
  • Selective reabsorption
• Glomerular filtrate


  Filtered blood plasma containing only small, soluble molecules (e.g. glucose, urea, ions, amino acids)
• Glomerulus structure


  • Knot of blood capillaries
  • Large surface area for ultrafiltration
  • One-cell thick capillary wall with pores to aid in filtration
  • Thin partially permeable membrane wraps around blood capillary
• Selective absorption


  The second stage of urine formation, process in which useful substances that the body needs are reabsorbed into the blood capillaries
• Proximal convoluted tubule


  • Most water reabsorbed by osmosis
  • Most mineral salts reabsorbed by diffusion and active transport
  • All glucose and amino acids reabsorbed by active transport
• Loop of Henle


  • Some water reabsorbed by osmosis
  • Some mineral salts reabsorbed by active transport
• Distal convoluted tubule


  • Some water reabsorbed by osmosis
  • Some mineral salts reabsorbed by active transport
• Collecting duct


  • Some water reabsorbed by osmosis
• Some urea is still reabsorbed into the proximal convoluted tubule by diffusion down a concentration gradient
• The remaining urea that is not reabsorbed along the nephron or collecting duct will be excreted in the urine
• Diuretic


  Causing frequent passing of urine
• Osmoregulation


  The maintenance of a constant body water potential by controlling the water potential and solute concentration in the blood
• The water potential in the blood is dependent on the amount of water and mineral salts in the blood plasma
• Antidiuretic hormone (ADH)


  Produced in the hypothalamus, released by the pituitary gland, increases water reabsorption in the nephrons
• The kidneys excrete metabolic waste products such as urea, excess water and mineral salts