Homeostasis Capillary Exchange Capillaries exchange compounds such as wastes, oxygen, and carbon dioxide across the blood vessel wall. A pressure gradient exists moving from the arterial end of the capillary to the venous end. The pressure causing oxygen and glucose to move from the blood to tissue is higher at the arterial end and decreases towards the venous end. The pressure for carbon dioxide and waste materials is higher closer to the venous end. For more information, refer to page 134 of your lab manual. The Lungs The lungs are located in the thoracic cavity on either side of the heart. Alveoli, irregularly shaped air spaces within the lungs, are responsible for exchanging oxygen and carbon dioxide to and from the bloodstream. Oxygen and carbon dioxide move across a concentration gradient, from higher to lower pressure. Because the pH of blood is related to the concentration of dissolved carbon dioxide, the lungs are important for regulating the acidity of the blood. For more information, refer to pages 135, 136 and 137 in your lab manual. The Liver Location - upper right quadrant of the abdominal cavity. Contribution to homeostasis – the liver produces urea, the primary waste product of humans. The liver also controls blood composition (ex. glucose/glycogen). The Kidneys Location – Dorsal wall of the abdominal cavity Structure – The primary unit of the kidney is the nephron, which is responsible for blood filtration and urine production. Contribution to homeostasis – Maintains blood pH, monitors blood glucose levels, removes waste and controls blood volume. Urine ProductionGlomerular filtration – Blood pressure forces filtrate into the glomerular capsule from the arteries including glucose, amino acids, salts, urea and water. Tubular reabsorption – Compounds from the proximal convoluted tubule are forced back into the blood, including water and salts to maintain blood volume and pH. Tubular secretion – Blood secretes hydrogen and ammonia into the tubule to maintain blood equilibrium. Urine Constituents In Blood of Glomerulus – Protein, Glucose, Urea, Water In Filtrate – Glucose, Urea, Water In Urine – Urea, Water For more information, refer to pages 142 - 146 in your lab