excretion in humans

• Excretion is the removal of metabolic waste products, toxic substances, and substances in excess of the body's requirements
• Carbon dioxide is a product of expired air excreted via the lungs
• Hypercarbia occurs due to high levels of CO2 in the blood
• Symptoms of hypercarbia include headache, confusion, rapid breathing, and premature heartbeats
• Urea is a waste product formed from the breakdown of proteins
• Urea is excreted as a constituent of urine and in traces in sweat via the kidney and skin
• High concentration of urea in blood leads to symptoms such as abdominal pain, nausea, vomiting, irregular heartbeat, and muscle cramps
• Mineral salts are excreted as a constituent of urine and sweat via the kidneys and skin
• Urea is produced by transporting excess amino acids in the blood to the liver where they are deaminated
• During deamination, part of the amino acid molecule is removed and converted to urea
• Water is excreted as a constituent of urine and sweat via the kidneys and skin
• Excess water will increase the water potential in the blood plasma, causing cells to swell and burst
• Ultrafiltration:

  • Afferent arteriole wider than efferent arteriole creates high blood pressure in the glomerulus
  • Blood plasma forced out of glomerular blood capillaries into Bowman's capsule
  • Glomerular filtrate contains small, soluble molecules forced out into Bowman's capsule
• Selective reabsorption:

  • Glomerular filtrate passes along the nephron, useful substances are reabsorbed into surrounding blood capillaries
  • Most water reabsorbed by osmosis
  • Some salts reabsorbed by active transport
  • All glucose and amino acids reabsorbed by active transport
  • Waste products such as urea, excess water, and mineral salts passed out of the nephron as urine
• Selective reabsorption is needed to prevent the body from losing too much water and other useful substances, causing dehydration
• Osmoregulation is the control of water potential and solute concentration level in the blood to maintain a constant water potential in the body
• ADH controls the amount of water in the blood plasma
• ADH increases water reabsorption at the nephron
• If water potential increases above normal levels and isn't regulated, cells may swell and burst
• If water potential decreases below normal levels and isn't regulated, cells will become dehydrated and shrink
• The kidneys play an important role in excreting metabolic waste products, regulating solute concentration and water potential in blood to maintain a constant water potential in the body
• Causes of kidney failure include high blood pressure, diabetes, alcohol abuse, severe accidents, and complications from major surgery
• A dialysis machine mimics the functions of a kidney
• Blood is drawn from a vein in the patient's arm and pumped through tubing in the dialysis machine
• The dialysis fluid in the machine allows small molecules like urea to diffuse out while blood cells and large molecules remain in the tubing
• Features of a successful dialysis machine include:

  • Dialysis fluid containing the same concentration of essential substances as healthy blood
  • Preventing essential substances from diffusing out of the blood
  • Setting up a concentration gradient for waste products to diffuse out
  • Narrow, long, and coiled tubing to increase surface area for exchange
  • Opposite direction of blood flow to dialysis fluid to maintain concentration gradient