Physiology of Urine Formation

1. Presented by-
Shruti Richa
Assistant Professor
Central Institute of Pharmacy
PHYSIOLOGY OF URINE
FORMATION

2. INTRODUCTION
 The process of urine formation is also called as
uropoeisis.
 It occurs in renal pyramid region where basically
nephrons are found (renal cortex + renal medulla) in
kidney.
 It involves the following steps:
Glomerular filtration/
Ultrafiltration
Tubular reabsorption
Urine formation
Tubular secretion

4. Ultrafiltration
 For ultrafiltration, we need to know few facts &
few terms:
Fact: The affarent arteriole has much diameter
(thicker) than efferent arteriole.
Terms: Structures found near/ in bowman’s
capsule:
Fenestration
Basement membrane
Podocytes
Pedicles
Filtration slits

5.  Fenestration: The enothelial cells/ glomerules have
small pores (50–100 nm in diameter), they are called
as fenestrations. It cannot pass the blood cells.
 Basement membrane: The base where glomerules
lie. They are made up of extracellular materials like:
fibrils. They restricts the entry of proteins & large
molecules.
 Podocytes: Bowman’s capsule is made up of two
layers. The inner layer is made up of highly modified
squamous epithelial cells. These are called as
podocytes.
 Pedicles: Thousands of foot like structures, extend
from each podocyte is called as pedicles.
 Filtration slits: These are the spaces between the
pedicles. These acts as slits to filter the material 7
generally they filters medium size particles:

7.  Pressures exerted:
Glomerular blood hydrostatic pressure
(55mmhg)
Pressure Hydrostatic Pressure exerted by liquids
present in capsule
(15mmhg)
Osmotic pressure exerted by colloids
(30mmhg)
Net Filtration Pressure (NFP/ GFP)= 55- (15+30)
= 55- 45

9. TUBULAR REABSORPTION
 This step is also called as selective reabsorption
because the substances get selectively reabsorbed
from the tubule since they are essential for our body,
thus, they should not be eliminated.
 In tubular reabsorption, all the tubules contributed
their role.
1. PCT:
 It generally follows active transport.
 Firstly, it starts in PCT, which has microvilli & brush
border enzymes.
 Basic substances which get reabsorbed in PCT are:

10.  Glucose – 100%
 Amino Acids – 100%
 Na+ – 70%
 K+ – 75%
 Cl - – 50%
 Urea – 50%
 Water – 65%
 HCO3
- – 10%

11. 2. Loop of Henle:
o Descending Loop of Henle: It is selectively permeable
only
for water
o Ascending Loop of Henle: It is impermeable only
for water but is
permeable for
Na+
K+
Cl –

12. 3. DCT: DCT help in reabsorption of:
• Urea
• Na+
• K+
• Cl –
• HCO3
-
4. Collecting duct: It reabsorbs water

13. TUBULAR SECRETION
 Tubular secretion means secretion of waste from the blood
into formed urine so that these wastes can be eliminated.
H+
NH3+
PCT Creatinine
Hippuric Acid
Drugs
Secretion (Glandular cells)
HCO3
-
NH4+
DCT K+
H+
These wastes are to taken up by the
glandular cells of PCT & DCT from the peritubular

14.  The waste materials come from peritubular
capillaries & gets mixed into the nephric filtrate in
PCT. The peritubular capillary is the capillary arises
from the outer side of the efferent arteriole which
surrounds the tubules of the nephron.

16. Normal Urine CHARATERISTIC
S. No. Parameter Characteristic
1. Colour Pale yellow
2. Odour Specific Bad aromatic, later on
ammonia like
3. pH Acidic, 6.0
4. Specific gravity 1.003- 1.030
5. Volume 1- 2 Lt/DAY
6. Tonicity Hypertonic

17. COMPOSITION OF URINE
S. No. Chemical Composition %
1. Total solid content 30-70 gm/Lt
2. Main constituent Water – 95-96%
3. Organic constituents •Urea – 2%
•Creatinine
•Uric acid
4. Inrganic constituents •Na+
•K+
•Cl -
•SO4
2-
•Mg2+
•NH4+
•Ca2+
5. Other things Hippuric acid
Oxalates

18. FACTS & DATA
 Filtration rate of blood= 1100-1200 blood/
min/day.
 GFR= 125ml/ min
OR
 GFR= 180 Lt/day
 Urine Output= 1.5 Lt
 The entire volume of the blood is filtered through
the kidneys about 300 times per day.