Question

(a) Why is bile juice considered to be very important for digestion, even though it doesn't contain any digestive enzymes?
(b) Name some substances present in initial filtrate and subsequently selectively reabsorbed in the tubules of nephron.

Hint:

Bile emulsifies fats (no enzymes needed). PCT reabsorbs essential nutrients (glucose, amino acids, ions, water). DCT and collecting duct fine-tune reabsorption under hormonal control.

Answer 1

(a) Importance of Bile Juice in Digestion:

Bile juice is considered very important for digestion even though it does not contain any digestive enzymes because it plays a crucial supportive role in the digestion and absorption of fats.

Bile is produced by the liver and stored in the gallbladder. It is released into the small intestine (duodenum) during digestion.

Reasons for its importance:

1. Emulsification of Fats:
Bile contains bile salts which break large fat globules into smaller droplets. This process is called emulsification. It increases the surface area of fats, making it easier for the enzyme lipase to act on them.

2. Provides Alkaline Medium:
The food coming from the stomach is acidic due to hydrochloric acid. Bile juice is alkaline in nature and helps neutralize this acidity, creating a suitable medium for pancreatic enzymes to function properly.

3. Helps in Absorption of Fats and Fat-Soluble Vitamins:
Bile aids in the absorption of fatty acids, glycerol, and fat-soluble vitamins such as A, D, E, and K.

Thus, even without digestive enzymes, bile juice plays an essential role in the proper digestion and absorption of fats.

(b) Substances Present in Initial Filtrate and Selectively Reabsorbed in Nephron Tubules:

The initial filtrate (glomerular filtrate) is formed in the Bowman’s capsule during the process of ultrafiltration in the kidneys. It contains water and many small dissolved substances.

Substances present in the initial filtrate:
– Water
– Glucose
– Amino acids
– Salts (ions such as sodium and chloride)
– Urea

During the process of selective reabsorption in the renal tubules, useful substances are reabsorbed back into the blood.

Substances selectively reabsorbed:
– Glucose
– Amino acids
– Most of the water
– Useful salts (such as sodium ions)

Urea and excess salts are not completely reabsorbed and are excreted in urine.

Conclusion:
(a) Bile juice is essential for digestion because it emulsifies fats and provides an alkaline medium, even though it contains no enzymes.
(b) The initial filtrate contains water, glucose, amino acids, salts, and urea, and useful substances like glucose, amino acids, water, and salts are selectively reabsorbed in the nephron tubules.