Study urine formation

1. PHYSIOLOGY

2. It is composed of water, certain
electrolytes, and various waste products
that are filtered out of the blood system
The kidneys accomplish their excretory
function by formation of urine

3.  Urine is formed by filtering the blood at renal
corpuscle and reabsorption of necessary
substances in renal tubule
 Formation of urine involves three basic
processes;
 GLOMERULAR FILTRATION
 TUBULAR REABSORPTION
 TUBULAR SECRETION

5. Glomerular filtration is the first step in
urine formation.
It is the process that your kidneys use
to filter excess fluid and waste products
out of the blood into the urine collecting
tubules of the kidney, so they may be
eliminated from your body.

6. The resulting filtrate contains waste ,but
also other substances the body needs ;
essential ions , glucose ,amino acids, and
smaller proteins.
When the filtrate exits the glomerulus , it
flows into the bowman’s capsule
The product formed is collectively
known as glomerular filtrate.

8.  It is the amount of filtrate formed in all the
nephrons of both kidneys in one minute.
 The normal rate is 125ml/min or 180L/day
 The number of functioning nephrons decreases
as the age advances and , hence the GFR
decreases in old age

9.  Net filtration pressure (NFP)
it is the total pressure that promotes filtration
10-20 mm is ideal for glomerular filtration
 Renal blood flow- GFR is directly propotional
to renal blood flow
 Permiability of glomerular membrane
 Surface area of filtering membrane

10. As filtered fluid flows through the
renal tubules,the tubules reabsorb 99% of
water and solutes.This is called tubular
reabsorption.
It is known as selective reabsorption
because the tubular cells reabsorb only
the substance necessary for the body.

11.  Reabsorption is achieved by active transport,
passive transport, osmosis.
 Reabsorption begins in the pct and continues in
the loop of henle, dct and collecting duct
 Substance reabsorbed are water, glucose and
other nutrients and sodium and other ions.
 Nutrient glucose is entirely reabsorbed back
into the blood from the pct.
 Sodium ions and other ions are only partially
reabsorbed from the renal tubules back into the
blood.
 increase Na+ intake = decrease Na reabsorption in the blood

13.  Parathyroid hormone & calcitonin
-Regulates reabsorption of calcium and
phosphate
 ADH (antidiuretic hormone)
-increase permiability of DCT,increase water
reabsorption
 Aldosterone
-increase reabsorption of sodium and excretion
of potassium
 ANP (atrial natriuretic peptide)
-inhibit NaCl reabsorption

14.  PCT - 65%
 Loop of Henle - 15%
 DCT -5%
 Collecting duct -14%

15. OBLIGATORY WATER REABSORPTION
It is a type of water reabsorption in
proximal convoluted tubule,which is
secondary to sodium reabsorption.
When sodium is reabsorbed from the
tubule,the osmotic pressure decreases.
it causes osmosis of water from the renal
tubule.

16. FACULTATIVE WATER REABSORPTION
It is a type of water reabsorption in
distal convoluted tubule and collecting duct that
occure by the activity of ADH.
Normally, DCT and collecting duct are not
permeable to water. But in presence of ADH ,it
become permeable to water and so it is
reabsorbed.

17.  This is the process of removing chemicals from
the blood and secreting them into the tubular
fluid
 This helps to remove wastes and plays a core
role in acid-base balance.
 Tubular secretion occurs throughout
the different parts of the nephron; from the
PCT and DCT