Control Of Water And Ion Content Of The Body
Visão Geral
Drink a large glass of water and your bladder will remind you about it within the hour. Spend that same hour running about in the sun and it stays quiet. Nothing you did consciously produced either result. Two organs roughly the size of your clenched fist took the decision for you, sampling the blood that poured through them and adjusting, minute by minute, how much water they were willing to let go.
This lesson follows water, dissolved ions and waste nitrogen through the body. You will sort the routes that lose water without asking permission from the single route that is genuinely controlled, watch the liver convert a poison it has just made into something safe enough to carry in the blood, take a healthy kidney apart into its two jobs of filtering and reabsorbing, and finish with the hormone that decides whether the urine you produce today is pale and plentiful or dark and scarce.
Objetivos
- Water leaves the body via the lungs when we breathe out and the skin when we sweat. Excess water is removed via the kidneys in the urine.
- Urea and ions are lost via the skin when we sweat. Excess ions are removed via the kidneys in the urine.
- In the liver: excess amino acids are deaminated to form ammonia, which is converted into urea for excretion; poisonous substances are detoxified, and the breakdown products are excreted in the urine via the kidneys; old blood cells are broken down and the iron is stored.
- In a healthy kidney: the blood is filtered; all the glucose is reabsorbed; the dissolved ions needed by the body are reabsorbed; as much water as the body needs is reabsorbed; urea, excess ions and excess water are released as urine.
- If the water content of the blood is too low, the pituitary gland releases a hormone called ADH into the blood. This causes the kidneys to reabsorb more water and results in a more concentrated urine.
- If the water content of the blood is too high, less ADH is released into the blood. Less water is reabsorbed in the kidneys, resulting in a more dilute urine.
- The production of ADH is controlled by a negative feedback mechanism.
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- Which substance is filtered out of the blood in a healthy kidney but is absent from the urine that reaches the bladder? A. Water B. Urea C. Glucose D. Sodium ions Answer: C
- In which organ is ammonia converted into urea? A. The kidney B. The liver C. The bladder D. The pituitary gland Answer: B
- Which gland releases ADH into the blood? A. The pancreas B. The thyroid gland C. The pituitary gland D. The adrenal gland Answer: C
- The water content of a person's blood rises above its normal level. What happens next? A. More ADH is released and the urine becomes more concentrated B. Less ADH is released and the urine becomes more dilute C. More ADH is released and the urine becomes more dilute D. Less ADH is released and the urine becomes more concentrated Answer: B
- What happens during deamination? A. Glucose is converted into glycogen for storage B. The nitrogen-bearing group is removed from an amino acid the body cannot use C. Water is reabsorbed from the kidney tubule into the blood D. Old red blood cells are broken down and their iron is stored Answer: B
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