https://www.iitutor.com In this video: Salt and water balance in the bloodstream, Osmoreceptors, Anti-diuretic Hormone, and Aldosterone Hormone. To maintain the water concentration in our blood, you must drink 2.0 L of water a day or obtain these fluids from our food. For example foods high in water include: Watermelon, Zucchini Cucumber, Most fruits and Vegetables. We lose 2 L of water per day through perspiration, urine, exhaled air and exercise. A drop in fluid intake will cause thirst. A drop in fluid beyond 10% of body mass can cause death. A decrease in the concentration of sodium ions in the bloodstream leads to a decrease in blood volume. This can cause many symptoms including fatigue, nausea, thirst and feeling faint. When you eat salty foods such as chips, what do you feel like doing after? Often people feel thirsty and want to drink water. This is to even out the salt and water balance. Water is drawn to salt. Water is a really good solvent which means it likes to dissolve substances, like salt. Water is attracted to salt. So when there is a high salt concentration in the body, from foods, you will also experience more water retention. When there are more salts present in the bloodstream, there will also be a higher amount of water retention. This is why on some diets, a tactic is to cut the salt out completely – the weight you may lose is water. This is not a healthy way to lose weight as water is needed in the body – and also salt in moderation. An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most endothermic organisms that detect changes in osmotic pressure. Osmoreceptors detect changes in the blood water and salt concentrations in body cells and tissues. The hypothalamus detects in the blood a decreased amount of water by an increase in blood concentration (thicker blood). When we become dehydrated, by decreasing water intake or increasing water loss, water is lost from our bloodstream. This increases it is osmotic pressure and the cells become hypertonic. Water levels are unbalanced when cells are hypertonic. More water (and potentially salt – if levels are low) is needed to balance the cells. If salt is inside the cell, water will follow. We aim for our cells to have an isotonic balance. An equal amount of water on each side so cells are nourished, but not overfull. If you consume too much water it can be detrimental to your body as it puts the cells under stress with too much water. When under this amount of pressure cells can burst (and therefore die). When we become dehydrated (by sweating for example), it causes the blood to be more concentrated (thicker) which pulls water into the blood from the cells as the osmotic pressure has increased. The cells of the hypothalamus shrink. This is when the hypothalamus sends a message to the pituitary gland to release more Antidiuretic Hormone into the blood. The hypothalamus also sends a message to make you feel thirsty. Drinking water is a behavioural response that decreases osmotic pressure. Adjustments to the concentration of water and salts within the urine takes place mainly in the distal parts of the kidney tubules and the collecting tubules, by alterations to the permeability of the membranes of cells lining the nephron walls. These changes in permeability are brought about by two main hormones: Aldosterone brings about retention (conservation) of salts within the body. ADH (anti-diuretic hormone) brings about water reabsorption (conservation) within the body. When a mammal begins to dehydrate, blood volume drops and this is detected in the hypothalamus of the brain. It stimulates the pituitary gland to release the hormone ADH, which acts on the nephrons of the kidneys to increase the reabsorption of water. The Antidiuretic Hormone works by making the kidneys more permeable to water. This means the kidneys allow more water to be reabsorbed in the body. When water levels are restored, there is less ADH produced, meaning less water is reabsorbed by the kidneys. Aldosterone (SALT regulation) is a steroid hormone secreted by the cortex of the adrenal gland. Its function is to regulate the transfer of sodium and potassium ions in the kidney. A decrease in the concentration of sodium ions in the bloodstream leads to a decrease in blood volume and this stimulates cells in the cortex of the adrenal gland (above the kidney) to secrete the hormone aldosterone. If sodium ions (salt) are in lower than normal concentration in the blood, less sodium is excreted in the urine as these ions are moved from the nephron into the surrounding capillaries by active transport. As water is attracted to sodium it also moves as a result. This increases the blood volume and so maintains blood pressure, as well as the sodium ion levels of the body fluids.

• published: 26 Dec 2015
• views: 3317