Micturition, Other Organs of Excretion and Kidney Disorders: Quick Revision

A brief note on Micturition, Other Organs of Excretion and Kidney Disorders. Read it before a test. Try each question at the end before you open its answer.

Micturition and urine

• Micturition: release of urine. Stretch receptors send signals to the CNS. The bladder muscle contracts, and the urethral sphincter relaxes. The neural mechanism is the micturition reflex.
• Urine: 1 to 1.5 L a day, light yellow, slightly acidic (pH about 6.0), 25 to 30 g of urea a day.
• Glycosuria and ketonuria: point to diabetes mellitus.

Other organs

• Lungs: CO$_2$ (about 200 mL a minute) and water.
• Liver: bile with bilirubin, biliverdin, cholesterol, degraded steroids, vitamins, drugs. They pass out with the digestive wastes.
• Sweat glands: water, NaCl, a little urea, lactic acid. The main work is cooling.
• Sebaceous glands: sterols, hydrocarbons, waxes in the sebum.
• Saliva: small amounts of nitrogenous wastes.

Disorders

• Uraemia: urea in the blood, may lead to renal failure.
• Haemodialysis: blood from an artery, heparin, a coiled cellophane tube in a dialysing fluid of plasma composition without nitrogenous wastes, diffusion, anti-heparin, return through a vein.
• Transplant: a functioning kidney, preferably from a close relative (not in the NEET syllabus text).
• Renal calculi: stones of crystallised salts such as oxalates. Glomerulonephritis: inflamed glomeruli.

A worked example

A person forms 1.2 L of urine in a day. How much urine forms in an hour, at an even rate?

1. 1.2 L is 1200 mL.
2. In an hour: $\dfrac{1200}{24} = 50$ mL.

Practice with new numbers

A program to try

The program finds the hourly rate and the time to collect 300 mL.

Mistakes to avoid

• Saying that the urethral sphincter contracts in micturition. It relaxes.
• Saying that the primary function of sweat is excretion. It is cooling.
• Giving the heparin after the dialysing unit. Heparin comes before. Anti-heparin comes after.
• Mixing up uraemia and glycosuria. Uraemia is urea in the blood.

Check yourself

1. What is the pH of urine?

2. Which gland removes sterols, hydrocarbons and waxes?

3. Which anticoagulant is used in haemodialysis?

4. What are renal calculi?

Sources

• NCERT (2023). Biology, Textbook for Class XI, chapter 16.
• Hall J. E. and Hall M. E. (2021). Guyton and Hall Textbook of Medical Physiology, 14th edition, Elsevier.