Question

During mastitic infection, chloride influx in milk increases to compensate for the reduced biosynthesis of lactose for maintaining the

• A. Density of milk
• B. Osmotic pressure of milk
• C. Viscosity of milk
• D. Electrical neutrality of milk

Hint:

Mastitic Milk Chemistry: Lactose DECREASES $\implies$ Sodium ($\text{Na}^+$) & Chloride ($\text{Cl}^-$) INCREASE to maintain CONSTANT OSMOTIC PRESSURE of milk.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Mammary gland physiological pathophysiology in bovine mastitis: inflammation damages tight junctions, reducing lactose synthesis; compensatory paracellular influx of sodium and chloride ions from blood maintains constant milk osmotic pressure ($300 ext{ mOsm/kg}$).
Key Formula or Approach:
\[ \text{Mastitis: Lactose Biosynthesis} \downarrow \implies \mathbf{\text{Chloride (Cl}^-) \uparrow + \text{ Sodium (Na}^+) \uparrow} \implies \mathbf{Maintains \text{ } Constant \text{ } Osmotic \text{ } Pressure} \]

Step 2: Detailed Explanation:
In mammary physiology, milk secretion kinetics, and mastitis pathophysiology:
- Bovine milk must remain strictly isosmotic with blood plasma at all times (osmotic pressure $\approx 6.7\text{ atmospheres} \approx 300\text{ mOsm/kg}$).
- In healthy milk, Lactose contributes $> 50\%$ of this total osmotic pressure.
- During Bovine Mastitis:
1. Bacterial inflammation and cytotoxic damage to mammary alveolar epithelial cells suppress lactose synthase, drastically reducing lactose biosynthesis (dropping lactose from $4.8\%$ down to $3.0\%$).
2. Increased permeability of leaky intercellular tight junctions allows blood serum electrolytes—predominantly Chloride ($\text{Cl}^-$) and Sodium ($\text{Na}^+$)—to pour into the alveolar lumen.
3. This rapid chloride influx directly compensates for the loss of lactose, strictly maintaining the Osmotic Pressure of Milk (B) (and resulting in an elevated electrical conductivity and high Koestler number).

Step 3: Final Answer:
Therefore, chloride influx maintains the Osmotic pressure of milk, corresponding to option (B).