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Blood Pressure Regulation

• When blood volume and blood pressure fall too low, the juxtaglomerular apparatus responds by secreting renin, an enzyme that leads to the secretion of aldosterone by the adrenal glands.
• Renin secretion can contribute to high blood pressure by reabsorbing excess salt and water.

Hormones and Blood Pressure Regulation

• Antidiuretic hormone (ADH) is produced by the hypothalamus and secreted by the posterior pituitary according to the osmolarity of the blood.
• ADH promotes water reabsorption from the distal convoluted tubule and collecting duct into the blood when water intake is low.
• Atrial natriuretic hormone (ANH) is secreted by the atria of the heart when cardiac cells are stretched due to increased blood volume.
• ANH inhibits the secretion of renin and aldosterone, promoting the excretion of sodium ions (natriuresis).

Diuretics

• Diuretics are chemicals that increase urine flow, such as alcohol, which inhibits ADH secretion, leading to dehydration.
• Caffeine is a diuretic because it increases the glomerular filtration rate and decreases the tubular reabsorption of sodium ions.
• Diuretic drugs developed to counteract high blood pressure decrease the tubular reabsorption of sodium ions, leading to a decrease in water reabsorption and blood volume and pressure.

Acid-Base Balance of Body Fluids

• A basic solution has a lower hydrogen ion concentration than the neutral pH of 7.0, while an acidic solution has a greater concentration.
• The normal pH for body fluids is between 7.35 and 7.45, which is the pH at which proteins, such as cellular enzymes, function properly.
• Alkalosis occurs when the blood pH rises above 7.45, and acidosis occurs when the blood pH decreases below 7.35.
• The pH of body fluids is maintained at around 7.4 via acid-base buffer systems, the respiratory center, and the kidneys.
• Foods and metabolism can add basic or acidic substances to the blood, affecting the pH of body fluids.