Renal Physiology And Excretion Question And Answers

Draw and label the parts of a nephron. Explain the formation of urine. (or) Draw an eat labelled diagram of nephron.
Answer:

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Formation of urine:

• The urine formation takes place in three steps.
  1. Glomerular filtration:
     • It occurs in the glomerulus.
     • It is the initial step in urine formation, the plasma that transverses the glomerular capillaries is filtered by the highly permeable glomerular membrane and the resultant fluid the glomerular filtrate, is passed into Bowman’s capsule.
     • Glomerular filtrate is a proteinfree filtrate of plasma.
     • All the substances of plasma are filtered except the plasma proteins.
     • During the filtration, the substances pass through a filtering membrane.
     • This filtration depends upon.
       1. Glomerular hydrostatic pressure (HP)
          • It provides driving force for the filtration.
       2. Colloidal osmotic pressure (OP).
          • Oppose the process of filtration.
       3. Intracapsular pressure (ICP).
          • Oppose the process of filtration.
          • The resultant of these factors is termed as the effective filtration pressure (EFP).
            EFP = HP (OP+ICP).
          • Glomerular filtration rate is the rate at which the filtrate is formed.
  2. Tubular reasborsption:
     • When the glomerular filtrate flows through the tubular portion of nehpron, both quantitative and qualitative changes occur.
     • Large quantity of water, electrolytes and other substances are reabsorbed by the tubular epithelial cells.
     • The reabsorbed substances move into the interstitial fluid of renal medulla.
     • From here, the substances move into the blood in peritubular capillaries.

Mechanism:

1. Active reabsorption:

• It is the movement of molecules against the electrochemical gradient.
• It needs liberation of energy.
• Sodium, calcium, potassium, phosphates, sulphates bicarbonates, glucose, amino acids, ascorbic acid uric acid and ketone bodies are actively reabsorbed.

2. Passive reabsorption:

• It is movement of molecules along the electrochemical gradient without energy.
• Chloride, urea and water are passively reabsorbed.

3. Tubular secretion:

• In addition to reabsorption from renal tubules some substances are also secreted into the lumen from the pertibular capillaries through the tubular epithelial cells.
• Substances secreted in different segments of renal tubules are: