A hormone released by the posterior lobe of the pituitary gland.

This hormone serves to help conserve body water. it acts on the kidneys and causes them to concentrate urine by reabsorbing more water from the distal or collecting tubules. the hypothalamus detects changes in osmolality of the blood and adjusts the level of ADH appropriately.

Also increases blood pressure by causing arteriole constriction.

This hormone is also known as antidiuretic hormone.

Insufficient ADH production leads to the disorder known as diabetes insipidous

Vasopressin is a hormone secreted by the pituitary gland. In the human body, vasopressin serves both as a neurotransmitter and as a regulatory hormone for the kidneys.

When a person is water deprived, vasopressin secretion will be stimulated, and the kidneys will excrete less water, reducing the deprivation by enabling the body to use water that would have been lost by urination.

In the brain, vasopressin seems to play an important role in male sexual behavior. When male rats were given a subtance that prevented vasopressin from working, they no longer performed sexual behaviors. Also, castration is associated with both a decline in sexual performance and a decrease in vasopressin production. When drugs are administered to enhance vasopressin production, sexual behavior returns.

My old biology teacher once told me a story about a friend of his in order to help me remember just what the effectn of Antidiuretic hormone are. At the time, both were at university. His friend had drunk away most of his money, and so signed up for some experiments at the local medical school (This was London - there are several of the things about). In this instance, they were investigating the degree to which water retention was increased when ADH was administered in distinctly non-physiological concentrations.

So, they injected him with a large quantity of ADH and then gave him several litres of water to drink. After a few hours, he still hadn't urinated. Apparantly deeming the experiment a success, the researchers (probably a jumped-up bunch of medical students who enjoyed inflicting pain on others - it seems pretty standard practice (1)) gave him his money and kicked him out.

The scene now shifts to an Underground station. Those of you who have visited London will probably be aware that public toilets were not a priority when the Underground was built. It is approximately midnight. The ADH decides to take the opportunity to drop back within the realms of normal levels. Our hero was suddenly left with several litres of excess water in his bloodstream and kidneys that were working overtime to remove it. Faced with a five minute wait until the next train and having no chance of making it back above ground, he ran to the end of the platform and relieved himself at quite some length. By some miracle he managed to avoid being electrocuted, but as he gasped in relief, he was tapped on the shoulder by a member of the Transport Police and spent the night in a cell with a toilet in the corner.

And that's how I manage to remember that antidiuretic hormone causes increased water retention.

(1) Yes, I have been a medical student. Can't you tell?

A hormone that can lead to fainting and long hospital stays. I speak of my poor girlfriend's scary experience.

After getting sick from eating something and vomiting a bit, she tried to sleep. The next day, when she tried to get up, she was still vomiting and couldn't keep down water. She was walking out of the bathroom and fainted. She hit her head and had a nice welt. Well, we took her to a walk-in clinic and they said since she passed out, she should go to the emergency room. I am sure everyone knows how quick those can be. To keep this brief and to leave out the sob stories of poor service in hospitals, I will try to explain the diagnosis. (What i remember.)

The doctor said that her brain releases too much ADH. This in turn keeps her electrolytes out of equilibrium, kind of similar to a state of dehydration, with respect to the low level of electrolytes in her. It is not a major concern, she is kind of like a camel, cause she hardly ever drinks. They did suggest that she drink Gatorade or one of those other sport-drinks, instead of water. She also tends to eat foods higher in sodium to make sure there is enough in her system, but she was like that to start with.

Which makes me wonder about that thing people say where if you crave a food, it usually is because your body knows it is deficient in some part of that food. Of course, we could exclude chocolate. I don't think endorphins can be deficient.

Also known as vasopressin, this hormone is vital in the regulation of plasma volume. This same hormone was given two names because it was originally associated with what were thought to be separate mechanisms, but in actuality are pretty much indistinguishable. This hormone is indeed secreted from the posterior pituitary, but like all hormones secreted from that particular part of the gland is actually formed in the hypothalamus, from whence it travels down the axons of neurons, and is released into the capillary bed within the posterior pituitary. The release is stimulated by a change in plasma osmolality. If plasma osmolality increases above the desired level, ANP is released.

It travels through the bloodstream, eventually reaching the kidneys, where it causes insertion of aquaporin proteins in the apical membrane of the distal tubule. This allows water from the distal tubule to reenter the hypertonic renal medulla, via facilitated diffusion. This leads to a decrease in plasma osmolality, and decreases dehydration.

While baroreceptors can also have an effect on ANP secretion, the osmoreceptors are by far the dominant stimulus.

Finally, should water diuresis be desired, a low level of vasopressin wil do the trick, causing aquaporins to be removed from the apical membrane.

These are my interpretation of my lecture notes, but I may have used some references from Hole's Anatomy and Physiology (Shier, Butler, Lewis) and Human Physiology (Vander, Sherman, Luciano)

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