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A hormone produced in the brain

How water balance is regulated by ADH

ADH is a hormone produced in the brain by the pituitary gland to control the water concentration of the blood. When we sweat during exercise then the concentration of water in the blood is reduced.

After drinking water the blood water concentration increases. The brain detects this change and less ADH is produced. Then the kidney takes an action by reabsorbing less water and therefore more water goes in the urine. This indicates that more volume of dilute urine is produced.

Both the brain and kidneys control the volume of water which has been excreted by the body. If the volume of the blood is low then the concentration of solutes in the blood is high. The brain takes an action to this state by stimulating the pituitary gland to release (ADH) hormone, which indicate the kidneys to reabsorb and circulate the water again. When we need more water, the kidneys will excrete less and reabsorb some.

The pituitary gland which is near the brain checks for the concentration water in the blood and releases the ADH if the blood is short of water. Then the ADH would be flowing in the blood and will not take effect until it gets to the kidneys. If there the ADH is in the blood then the kidneys will go into water by reabsorbing most of the water which is in the tubules and so a smaller volume of urine will be produced. As it still needs to get rid of the water substances, it means that the urine is more concentrated

If there's no ADH our kidneys would just let the water go and high volume of dilute urine will be produced until the water levels turn back down to normal.

Explanation of how the kidney uses a counter current mechanism

Inside the renal medulla, capillaries are formed around the tubules. Some of these blood capillaries are thin walled, straight and loop which are the vasa rectae. The blood flows in the opposite directions in the limbs of the vasa rectae. Blood that enters the renal medulla in the descending limb it comes close to the outgoing blood in the ascending limb.

When the blood is flowing to the renal medulla, Na+ and Cl- diffuse in the blood. However, as the blood flows to the renal cortex Na+ and Cl- diffuse into the interstitial fluid. This checks the loss of Na+ and Cl- from the renal medulla and then it regulates a high concentration of these in the interstitial fluid.

When the filtrate passes through the ascending limb of the loop of Henle, NaCl is lost to the interstitial fluid in the renal medulla by the process of diffusion. The increase in the concentration of the solutes that is in the interstitial fluid draws out water by the process of osmosis from the narrow region of the descending limb as well as the collecting duct, both are permeable to water. The water that is drawn quickly enters the vasa recta and is carried away. This regulates a high concentration of the solutes in the interstitial fluid and helps turn the isotonic glomerular filtrate into hypertonic urine. There is no water reabsorption in the ascending limb this is because its walls are impermeable to water.

Since a large volume of Na+ is lost because of the active transport, the filtrate again becomes isotonic. Then mainly the water reabsorption occurs through the wall of the collecting tubules, the permeability is controlled by ADH hormone of the pituitary gland. The secretion of ADH is controlled by the osmotic pressure of the blood. So counter current mechanism is that process which changes isotonic filtrate to hypertonic urine. The urine is approximately 4 times as concentrated as the blood plasma in humans.

How the PH is controlled by the kidney

The secretion of further substances which are not needed by the body may take place in the distal convoluted tubule, e.g. hydrogen and hydro carbonate ions. This is very important in the control of plasma Ph, which has to be maintained at 7.4. If the pH plasma falls, hydrogen ions are excreted by the kidney; if the plasma pH increases hydrogen carbonate ions secreted.

Active Transport

Active transport is the energy-demanding transport of a substance across a cell membrane against its concentration gradient, i.e., from lower concentration to higher concentration.

Special proteins within the cell membrane function as specific protein 'carriers'. The energy for active transport comes from ATP generated by respiration in the mitochondria.

Major examples of Active Transport such as:

  • Re-absorption of glucose,
  • Amino acids
  • Salts by the proximal convoluted tubule of the nephron in the kidney.

A mechanism of active transport moves potassium ions into and sodium ions out of a cell along with protein channel. It is found in all human cells, but is particularly important in nerve and muscle cells. The sodium-potassium pump uses active transport, with energy that is supplied by the ATP molecules, so that it moves 3 sodium ions to the outside of the cell for each 2 potassium ions that it moves in. One third of the body's energy outgoings is used in this process.

Buffer system

Both of the kidneys and the lungs cooperate to maintain a blood pH of 7.4 by affecting the mechanism of the buffers in the blood. Acid-base buffers present resistance to a change in the pH of a solution when hydrogen ions or hydroxide ions are added or removed. An acid-base buffer typically consists of a weak acid, and its base. Buffers starts its function because the concentrations of the weak acid and its salt are large compared to the amount of protons or hydroxide ions which are added or removed.

As protons added to the solution from an exterior source, some of the base component of the buffer is then converted to the weak-acid component and when hydroxide ions are added to the solution protons are dissociated from some of the weak-acid molecules of the buffer, converting them to the base of the buffer.

But, the change in acid and base concentrations is small relative to the amounts of these species present in solution and so the ratio of acid to base slightly changes. Therefore, the effect on the pH of the solution is small, in some limits on the amount of H+ or OH- added or removed.

Other buffers function as a minor role than the carbonic-acid-bicarbonate buffer in maintaining the pH of the blood. The phosphate buffer consists of phosphoric acid in equilibrium with dihydrogen phosphate ion and H+. The pK for the phosphate buffer is 6.8, which allows this buffer to work within its best buffering range at physiological pH.

The phosphate buffer only functions as a minor role in the blood, however, because phosphoric acid and phosphate ions are found in very low concentration in the blood. Haemoglobin is also acting as a pH buffer in the blood. Protein can reversibly combine either H+ or O2 to the protein, but when one of these substances is bound, the other is released.

As we exercise, the haemoglobin assists to control the pH of the blood by combining some of the excess protons which are generated in the muscles and the molecular oxygen is released for use by the muscles.

Kidney failure

The main function of the kidneys is to get rid of the waste products which result from the body's metabolism. One of the main by-products of the metabolism of the protein is urea. The kidneys will get rid of the waste products by taking them out from the blood and send them along the ureter into the bladder.

If there is a failure in the function of the kidney then the by products builds up in the blood and the body. Very mild levels of azotaemia may give little symptoms, however if the kidney failure continues then the symptoms will occur.

There are two types of kidney failure; one of them is acute renal failure and the other type is: Chronic renal failure.

Acute renal failure

The acute renal failure may appear with any serious illness or operation, mostly those complicated by severe infection. When the blood supply into the kidneys is reduced too much from blood loss, then there will be a fall in blood pressure, severe dehydration or lack of salt, which then the kidneys may be damaged. If this problem lasts long enough there can be permanent damage to the kidney tissue.

Unexpected blockage to the drainage of urine from the kidney can cause damage. Also a kidney stone is a possible cause of this. Acute kidney damage can occur as a unusual side effect of some medications and other uncommon conditions.

Symptoms of Acute renal failure

Here the symptoms are largely those of the condition causing the kidney failure, such as:

  • Blood loss, causing a drop in blood pressure.
  • Vomiting and diarrhoea, causing dehydration.
  • Crush injuries. If large amounts of muscle are damaged there is a release of toxic protein substances that are harmful to the kidneys.
  • Sudden blockage of urine drainage.

Chronic renal failure

Chronic kidney disease, also called as chronic kidney failure, is a permanent condition which is caused by damages to the kidneys. Chronic kidney disease is a serious condition because our kidneys carry out some important functions within the body, such as filtering by products from the blood and regulating blood flow. The major common cause of this chronic kidney disease is damage caused by other chronic conditions, such as diabetes and high blood pressure.

Symptoms are uncommon unless kidney failure is far advanced, when any of the following may be present:

The symptoms of Chronic renal failure

  • Tiredness
  • Itching
  • Loss of appetite
  • Nausea and vomiting
  • Breathlessness
  • Fluid retention, shown as ankle swelling
  • Weakness.

The importance to the body to maintain acid base levels

All the cells which make up our body are slightly alkaline and this alkalinity should be maintained in so that it can function properly and remain healthy. However, their cellular activity makes acid and this acid gives the cell energy and function. Since each of the alkaline cell complete its task of respiration, it secrets metabolic wastes and these products of cellular metabolism are acid in nature.

An important property of blood is its amount of acidity or alkalinity. The acidity which is in our body increases when the level of acidic compounds in the body increases or when the level of basic (alkaline) compounds in the body falls. Body alkalinity increases with the reverse of these processes.

The acidity or alkalinity of any solution, including blood, is indicating on the pH scale. The blood's acid-base balance is accurately controlled, because even if there's a minor difference from the normal range it can severely affect many organs. The body uses different mechanisms to maintain the acid base balance in the blood.

When our body becomes more acidic the body begins to set up resistance mechanisms to prevent the damaging acid from entering our organs. However, if the acid does come to contact with an organ the acid has a possibility to make holes in the tissue which may cause the cell to change in a chromosome or a gene.

The level of oxygen falls in this acidic environment and calcium starts to be at a low level. So as a protection mechanism, our body may actually make fat to protect us from our overly-acidic self. These fat cells may actually be packing up the acid and trying to maintain it a safe distance from our organs to protect them from damage.

Role of the Lungs:

One of the main mechanisms which the body uses to control pH of the blood involves the release of carbon dioxide from the lungs. Carbon dioxide, which is slightly acidic, is a by product of the metabolism of oxygen and is continuously produced by cells. All the waste products, carbon dioxide get excreted into the blood.

The blood carries carbon dioxide to the lungs, where it is breathed out. As the carbon dioxide builds up in the blood, the pH of the blood decreases. The brain controls the amount of carbon dioxide which is breathed out by controlling the speed and depth of breathing. The amount of carbon dioxide breathed out and as a result the pH of the blood, increases as breathing becomes faster and deeper. By changing the speed and depth of breathing, the brain and lungs are able to control the blood pH.

Role of the Kidneys:

The kidneys are can also affect blood pH by excreting excess acids or bases. The kidneys can also change the amount of acid or base that is excreted, but because the kidneys make these alterations more slowly than the lungs do, this process generally takes several days.

Buffer Systems:

There is another mechanism to control the blood pH involves the use of buffer systems, which functions against sudden shifts in acidity and alkalinity. The pH buffer systems are groupings of the body's own naturally occurring weak acids and weak bases.

These weak acids and bases exist in balance under normal pH conditions. The pH buffer systems work chemically to reduce the changes in the pH of a solution by changing the amount of acid and base. The most important pH buffer system in the blood involves carbonic acid which is a weak acid formed from the carbon dioxide which dissolved in blood as well as bicarbonate ions.

Acidosis and Alkalosis:

There are two abnormalities of acid-base balance.

Acidosis: This is when the blood has too much acid which results in a decrease in the blood pH.

Alkalosis: This when the blood has too much base or little acid which results in an increase in blood pH.

Acidosis and alkalosis are not diseases but they are actually the result of various disorders. The presence of acidosis or alkalosis gives an important hint to doctors that there is a serious problem exists.

Acidosis and alkalosis are known as metabolic or respiratory, depending on their primary cause. Metabolic acidosis and metabolic alkalosis are caused by the imbalance in producing the acids or bases and their excretion by the kidneys. Respiratory acidosis and respiratory alkalosis are often caused by the changes in carbon dioxide breathed out because of lung or breathing disorders.

Lactic acid in anaerobic respiration

Lactic acid is commonly used by athletes to describe the severe pain which is felt during extensive exercise, especially in events like the 400 metres and 800 metres. When energy is required to perform exercise, it is supplied from the breakdown ATP. The body has a partial store of about 85 grams of ATP and would use it up very quickly if we did not have ways of resynthesising it.

The lactic acid system is capable of releasing energy to resynthesise ATP without the involving oxygen which is known as anaerobic glycolysis. Glycolysis causes the formation of pyruvic acid and hydrogen ions (H+). The pyruvic acid molecules go through oxidation in the mitochondrion and the Krebs cycle begins.

A build up of H+ will make the muscle cells acidic and interfere with their operation so a carrier molecule, which is NAD+, remove the H+. The NAD+ is reduced to NADH that deposit the H+ at the electron transport gate in the mitrochondria to be joined with oxygen to form water.

If there is inadequate oxygen then NADH cannot release the H+ and they build up in the cell. To avoid the rise in acidity pyruvic acid accepts H+ forming lactic acid which is then dissociates into lactate and H+. Some of the lactate diffuses into the blood stream and takes some H+ with it as a way of dropping the H+ concentration in the muscle cell. The normal pH of the muscle cell is 7.1 but if the build up of H+ continues and pH is decreased to around 6.5 then the muscle contraction could be impair and the low pH will stimulate the free nerve in the muscle which results in the perception of pain.

The process of the removal lactic acid takes about one hour, but this can go faster by undertaking the suitable cool down which ensures a quick and continuous supply of oxygen to the muscles.

Dehydration and Performance

Many athletes get dehydration during competitions, especially long ones, even when it's not particularly hot. They can't depend on feeling thirsty as a reminder to replace fluid lost through sweating. Dehydration impairs both physical and mental performance in all types and levels of sport, and it can be minimised by appropriate drinking plan.

Exercise causes body fluid losses from moisture when breathing out air as well as from sweating. Although the rate sweat are highest under conditions of high-intensity exercise in heat and high humidity. If fluid losses are not replaced by drinks, sweating causes progressive reduction of circulating blood volume, causing dehydration and a thickening of blood.

This causes a strain on the cardiovascular system, with an increase in heart rate in order to control adequate blood flow to exercising muscles and essential organs. When blood volumes reduce, blood flow to the skin is reduced. As a result, sweating decreases causing body core temperature to rise, potentially leading to heat stress.

During intensity exercise, sweat rate rises and is increased by a hot or humid environment and heavy clothing both of which interfere with sweat evaporation.

Prediction of fluid and sodium losses in sweat is slightly complex, since sweat rates and sweat Na concentrations differs widely between individuals exercising under the same conditions.

Concentration of urine

Urine becomes more acidic as the volume of excess acid retained by the body rises. Alkaline urine, more often contains bicarbonate-carbonic acid buffer, is often excreted when there is an excess of a base or alkali in the body. The secretion of acid and alkaline urine by the kidneys is one of the main mechanisms which the body uses to keep a stable body pH. When we exercise, the ph of the urine becomes more acidic because the acidosis condition has occurred and which is as a result from a build-up of carbon dioxide in the blood, as well as dehydration.

Therefore, exercisers should aim to be well hydrated before they start their training sessions or competitions. The pale yellow urine would indicate a well-hydrated body, but dark yellow urine is a positive sign of dehydration. This is a very visual way of managing the right fluid volume. Checking the colour of urine is much easier than trying to find out the quality of urine.

When the body loses water, the blood becomes more concentrated with sodium and other electrolytes. This activates the thirst mechanism telling the body to enhance fluid intake to regain proper concentrations. However, this mechanism is often unreliable or misread. Older adults also tend to be less sensitive to signals of thirst. Amazingly, most exercisers only replace about 2/3 of the losses from perspiration.

Sources used

  • http://www.brianmac.co.uk/lactic.htm
  • http://www.pponline.co.uk/encyc/0824.htm
  • http://girlfriendsintraining.com/Publications/Hydration%20and%20Exercise.pdf
  • http://cnserver0.nkf.med.ualberta.ca/cn/Schrier/Volume1/chap6/ADK1_06_1-3.pdf

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