Changes

Peptide hormones and small amounts of albumin make it through the [[Glomerulus and Bowmans Capsule - Anatomy & Physiology#Function of Renal Corpuscle|glomerular filtration barrier]] and these need to be reabsorbed.  The reabsorption occurs via '''endocytosis''' in the [[Proximal Tubule - Anatomy & Physiology| proximal tubules]].  They are then broken down to amino acids in the epithelial cell cytoplasm and move via facilitated diffusion into the interstial fluid.  The reabsorption of protein is usually complete though it is normal to detect small quantities of protein in the urine of some mammals e.g. the dog

Peptide hormones and small amounts of albumin make it through the [[Glomerulus and Bowmans Capsule - Anatomy & Physiology#Function of Renal Corpuscle|glomerular filtration barrier]] and these need to be reabsorbed.  The reabsorption occurs via '''endocytosis''' in the [[Proximal Tubule - Anatomy & Physiology| proximal tubules]].  They are then broken down to amino acids in the epithelial cell cytoplasm and move via facilitated diffusion into the interstial fluid.  The reabsorption of protein is usually complete though it is normal to detect small quantities of protein in the urine of some mammals e.g. the dog

===Primary Active Secretion - Organic Acids and Bases===

 

 

====Primary Active Secretion - Organic Acids and Bases====

The secretion of these compounds occurs '''only in the proximal tubules'''.  These molecules are mainly bound to plasma proteins with a small amount free in an active ionised form.  It is only the free ions which are able to be transported.  As the ionised molecules are transported into the blood more molecules are released from the plasma proteins to take their place.  These can then be secreted etc etc.  This allows a large amount of the substance to be secreted at one time.  The mechanisms are not very selective and so many different substances are secreted at the same time.  Secretion mechanisms are responsible for the secretion of drugs, hormones and things like food additives.  Many unwanted or toxic organic molecules which enter the body are unionized.  They therefore cannot be secreted so it falls to the liver to alter them into ionized forms to allow them to be disposed of.

The secretion of these compounds occurs '''only in the proximal tubules'''.  These molecules are mainly bound to plasma proteins with a small amount free in an active ionised form.  It is only the free ions which are able to be transported.  As the ionised molecules are transported into the blood more molecules are released from the plasma proteins to take their place.  These can then be secreted etc etc.  This allows a large amount of the substance to be secreted at one time.  The mechanisms are not very selective and so many different substances are secreted at the same time.  Secretion mechanisms are responsible for the secretion of drugs, hormones and things like food additives.  Many unwanted or toxic organic molecules which enter the body are unionized.  They therefore cannot be secreted so it falls to the liver to alter them into ionized forms to allow them to be disposed of.

===[[Acid Base Balance By The Kidney - Anatomy & Physiology#Secretion of H+ and the Reabsorption of HCO3- in the Proximal Tubule|H⁺ and HCO₃^-]]===

===[[Acid Base Balance By The Kidney - Anatomy & Physiology#Secretion of H+ and the Reabsorption of HCO3- in the Proximal Tubule|H⁺ and HCO₃^-]]===