Changes

===Regulation===

===Regulation===

The total body content of sodium is regulated rather than the actual plasma concentration.  It would be impossible to regulate actual plasma concentration for 3 reasons:

The total body content of sodium is regulated rather than the actual plasma concentration.  It would be impossible to regulate actual plasma concentration for 3 reasons:

* When sodium is reabsorbed water follows it so the volume of the plasma is altered rather than the concentration of sodium changing

* When sodium is reabsorbed water follows it so the volume of the plasma is altered rather than the concentration of sodium changing

* [[Renin Angiotensin Aldosterone System#Effects of Angiotensin 2 On Sodium|Angiotensin 2]] and [[Aldosterone|Aldosterone]] affect sodium but they also affect ECF volume so only quantity affected not concentration

* [[Renin Angiotensin Aldosterone System#Effects of Angiotensin 2 On Sodium|Angiotensin 2]] and [[Aldosterone|Aldosterone]] affect sodium but they also affect ECF volume so only quantity affected not concentration

* [[Pituitary Gland - Anatomy & Physiology #Posterior Pituitary Gland | ADH]] and thirst response also work together to dilute the ECF if concentrations of sodium are high so although there is more NaCl the actual concentration is not really changed.

* [[Pituitary Gland - Anatomy & Physiology #Posterior Pituitary Gland | ADH]] and thirst response also work together to dilute the ECF if concentrations of sodium are high so although there is more NaCl the actual concentration is not really changed.

The kidneys are the most important regulatory organs of sodium in the body.  They adjust their excretion to match the amount taken in through the digestive tract taking into account the amount lost through sweat.  The handling of sodium by the kidneys is also essential to allow the reabsorption of many other important nutrients which would otherwise be lost in the urine.  These nutrients include glucose, amino acids, chloride, bicarbonate and phosphate.  It is also exchanged for the likes of potassium and hydrogen ions to aid in their secretion.  As a result sodium transport accounts for over 80% of the energy metabolism in the kidneys

The kidneys are the most important regulatory organs of sodium in the body.  They adjust their excretion to match the amount taken in through the digestive tract taking into account the amount lost through sweat.  The handling of sodium by the kidneys is also essential to allow the reabsorption of many other important nutrients which would otherwise be lost in the urine.  These nutrients include glucose, amino acids, chloride, bicarbonate and phosphate.  It is also exchanged for the likes of potassium and hydrogen ions to aid in their secretion.  As a result sodium transport accounts for over 80% of the energy metabolism in the kidneys

===Salt Hunger===

===Salt Hunger===

The diet of a herbivore contains little sodium and as such an important aspect of their sodium homeostasis is the physiological salt appetite where the animal actually craves salt if it is deficient.  This is especially apparent in sheep.  By contrast carnivores have a very poorly developed physiological salt appetite probably because their salt intake tends to outstrip their requirement.

The diet of a herbivore contains little sodium and as such an important aspect of their sodium homeostasis is the physiological salt appetite where the animal actually craves salt if it is deficient.  This is especially apparent in sheep.  By contrast carnivores have a very poorly developed physiological salt appetite probably because their salt intake tends to outstrip their requirement.

===Cellular Translocation===

===Cellular Translocation===

* Vital for rapid control of potassium loads

* Vital for rapid control of potassium loads

* Helps control plasma concentration

* Helps control plasma concentration

==Acid / Base==

==Acid / Base==

It is essential that 50-100meq of acid is excreted by the kidneys every day.  This is achieved by secretion of H⁺ in two regions of the nephron, the proximal tubule and the collecting ducts, and is essential for maintaining the acid base ratio, within the body, at the correct levels. If there is a net gain or loss of H⁺ within the body then the kidneys will compensate for it.  The H⁺ ions cannot be secreted as free ions, however virtually all filtered HCO₃^- must be reabsorbed.  The result is that the H⁺ ions bind to other filtered buffers which are not fully reabsorbed such as ammonia or phosphate.  Extracellular pH is th main physiological regulator affecting how much acid is secreted.  In pathological states circulating volume, aldosterone and plasma potassium affect it.

It is essential that 50-100meq of acid is excreted by the kidneys every day.  This is achieved by secretion of H⁺ in two regions of the nephron, the proximal tubule and the collecting ducts, and is essential for maintaining the acid base ratio, within the body, at the correct levels. If there is a net gain or loss of H⁺ within the body then the kidneys will compensate for it.  The H⁺ ions cannot be secreted as free ions, however virtually all filtered HCO₃^- must be reabsorbed.  The result is that the H⁺ ions bind to other filtered buffers which are not fully reabsorbed such as ammonia or phosphate.  Extracellular pH is th main physiological regulator affecting how much acid is secreted.  In pathological states circulating volume, aldosterone and plasma potassium affect it.

=====Alkalosis=====

=====Alkalosis=====

In a situation of alkalosis the kidneys allow more HCO₃^- to be excreted.  This results in an increase in an increase of un-buffered H⁺ and thus returns the pH towards normal.

In a situation of alkalosis the kidneys allow more HCO₃^- to be excreted.  This results in an increase in an increase of un-buffered H⁺ and thus returns the pH towards normal.

=====Acidosis=====

=====Acidosis=====

In a situation of increased H⁺ levels the body is said to be in a state of acidosis and the kidneys stop excreting HCO₃^- and the tubular cells produce more bicarbonate.  This results in more H⁺ being buffered and the pH increases back to normal

In a situation of increased H⁺ levels the body is said to be in a state of acidosis and the kidneys stop excreting HCO₃^- and the tubular cells produce more bicarbonate.  This results in more H⁺ being buffered and the pH increases back to normal

===The Effect of The Buffers on Body pH===

===The Effect of The Buffers on Body pH===

* When H⁺ is binding to buffers other than bicarbonate it is excreted.  This means that the reabsorption of bicarbonate represents a net gain of bicarbonate not just a replacement of what was filtered.  This results in an increase in plasma pH.  

* When H⁺ is binding to buffers other than bicarbonate it is excreted.  This means that the reabsorption of bicarbonate represents a net gain of bicarbonate not just a replacement of what was filtered.  This results in an increase in plasma pH.  

* Bicarbonate is also produced as part of the secretion of ammonium in the proximal tubule

* Bicarbonate is also produced as part of the secretion of ammonium in the proximal tubule

==Calcium==

==Calcium==

[[Calcium Homeostasis - Anatomy & Physiology|Calcium Homeostasis]] has three aspects:

[[Calcium Homeostasis - Anatomy & Physiology|Calcium Homeostasis]] has three aspects:

* Renal reabsorption - dealt with here

* Renal reabsorption - dealt with here

* Intestinal absorption

* Intestinal absorption

==Urea==

==Urea==

===Urea and Foregut Fermenters===

===Urea and Foregut Fermenters===

If species such as cows are fed a low nitrogen diet then a smaller portion of the filtered urea is excreted.  Indicating that it is being transported to the fore stomach for processing into microbial protein.  This allows the animal to survive longer on low protein diets

If species such as cows are fed a low nitrogen diet then a smaller portion of the filtered urea is excreted.  Indicating that it is being transported to the fore stomach for processing into microbial protein.  This allows the animal to survive longer on low protein diets

===Protein in Feed and Urine Concentration===

===Protein in Feed and Urine Concentration===

* If feed is high in protein then lots of urea is produced and the urine is more concentrated

* If feed is high in protein then lots of urea is produced and the urine is more concentrated

* If feed is low in protein then less urea is produced and the urine is less concentrated

* If feed is low in protein then less urea is produced and the urine is less concentrated

==Revision==

==Revision==

Use the [[Essential Ion and Compound Balance and Homeostasis - Renal Flash Cards - Anatomy & Physiology|flash card revision resource]] for this section to test yourself.

Use the [[Essential Ion and Compound Balance and Homeostasis - Renal Flash Cards - Anatomy & Physiology|flash card revision resource]] for this section to test yourself.