Physiology of Urine Formation

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

3. 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

4. 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:

5. 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 = 10 mmhg

6. 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. 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:

7. Glucose – 100% Amino Acids – 100% Na + – 70% K + – 75% Cl - – 50% Urea – 50 %   Water – 65% HCO 3 - – 10 %

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

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

10. 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) HCO 3 - NH 4 + DCT K + H + These wastes are to taken up by the glandular cells of PCT & DCT from the peritubular capillaries.

11. 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 .

12. 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

13. 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 - SO 4 2- Mg 2+ NH 4+ Ca 2+ 5. Other things Hippuric acid Oxalates

14. 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.