Water Balance • In a general sense: • increased water intake = increase urine output • exercise or decreased water = reduce urine output • These adjustments involve the interaction of the body’s two communication systems: • the nervous system • the endocrine system
Regulating ADH Antidiuretic Hormone (ADH) • Helps regulate the osmotic pressure of body fluids by causing the kidneys to increase water reabsorption • Results in a more concentrated urine, therefore conserving body water • ADH is produced by specialized nerve cells in the hypothalamus • Stored and released by the pituitary gland
Regulating ADH • Specialized nerve receptors in the hypothalamus detect changes in water (osmotic) pressure. • osmoreceptors • When our water level decreases, blood becomes more concentrated (more solutes, less water) • The osmotic pressure of the blood increases • Water then moves into the bloodstream, • causes the cells of the hypothalamus to shrink • When the hypothalamus shrinks, a nerve message is sent to the pituitary, • signals the release of ADH, travels through blood vessels to the kidneys • Kidneys respond be reabsorbing more water
Regulating ADH • The shrinking of the cells of the hypothalamus also initiates a behavioural response • Thirst! Opposite Response to Increased water levels: • If more water is taken in, it is absorbed by the blood and the concentration of solutes in the blood decreases. • as the volume of water consumed increases, osmotic pressure decreases • As the blood becomes more dilute, fluids move from the blood into the hypothalamus. • The cells of the hypothalamus swell, and nerve messages to the pituitary stop. • Less ADH is released, and less water is reabsorbed from the nephrons.
ADH and the Nephron • Approximately 85% of the water filtered into the nephron is reabsorbed in the proximal tubule. • The proximal tubule is very permeable to water • BUT most of the rest of the nephron is NOT • Without ADH, the remaining 15% of the H2O filtered into the nephron will be lost • ADH makes the upper part of the distal tubule and collecting duct permeable to water • Water is drawn from these areas due to the high concentration of NaCl • As more water is drawn out, the remaining filtrate(urine) in the nephron becomes more concentrate
Alcohol and ADH • Alcohol impedes the release of ADH • How does this explain some of the symptoms related to excessive alcohol consumption • Dehydration • Frequent Urination • Headaches • Dizziness
Alcohol and ADH • …because I know you are probably falling asleep Class Activity: • Design a short 3-5 minute skit that demonstrates your understanding of ADH, water balance, and how alcohol interferes with the regular function of ADH • Must involve some moving around!
Kidneys and Blood Pressure • The kidneysalso playsa role in the regulation of blood pressure • By adjusting for blood volume • Aldosterone = A hormone calledthatacts on the nephrons to increase Na+ reabsorption (salt) • The hormone is produced in the adrenal glands • Located above the kidneys. • As NaCl reabsorption increases, theconcentration gradient increases • Therefore more water moves out of the nephron by osmosis.
Kidneys and Blood Pressure • Conditions that lead to increased fluid loss can decrease blood pressure • Reducesthe delivery of oxygen and nutrients to tissues • What are some examples of such conditions? • Low Blood Pressure is detected by the nephron, and the enzyme angiotensin is released. • Angiotensin has two important functions • Causes constriction of blood vessels. • Stimulates the release of aldosterone from the adrenal gland. • Aldosterone acts onthe nephronto increase Na+transport.