WATER BALANCE

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 H 2 O 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 kidneys also plays a role in the regulation of blood pressure  By adjusting for blood volume  Aldosterone = A hormone called that acts on the nephrons to increase Na + reabsorption (salt)  The hormone is produced in the adrenal glands  Located above the kidneys.  As NaCl reabsorption increases, the concentration 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  Reduces the 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 1. Causes constriction of blood vessels. 2. Stimulates the release of aldosterone from the adrenal gland.  Aldosterone acts on the nephron to increase Na+ transport.