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 ADHAntidiuretic 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 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.