(a) Define and classify diuretics. Write about the mechanism of action of high efficiency diuretics. (20 marks) (b) Describe and…

(a) Diuretics: definition, classification and mechanism of high-efficiency diuretics

Diuretics are drugs that increase urine volume and sodium excretion by reducing tubular reabsorption of sodium and water.

Classification:

• High efficiency (high ceiling, loop) diuretics: furosemide, bumetanide, torsemide and ethacrynic acid, acting on the thick ascending limb of the loop of Henle.
• Medium efficiency: thiazides and related drugs (hydrochlorothiazide, chlorthalidone), acting on the distal convoluted tubule.
• Low efficiency: potassium-sparing diuretics (spironolactone, eplerenone, triamterene, amiloride) acting on the late distal tubule and collecting duct; carbonic anhydrase inhibitors (acetazolamide) acting on the proximal tubule; and osmotic diuretics (mannitol).

Mechanism of loop diuretics: furosemide is secreted into the tubular fluid by the organic anion transporter of the proximal tubule and acts from the lumen. It binds the chloride site of the Na⁺–K⁺–2Cl⁻ cotransporter (NKCC2) in the thick ascending limb and blocks it. About 25% of filtered sodium is normally reabsorbed here, so sodium, potassium and chloride are retained in the lumen. Loss of the lumen-positive potential also reduces paracellular reabsorption of calcium and magnesium. Since this segment builds the medullary gradient, urine cannot be concentrated and large volumes of dilute urine result. Furosemide also raises renal prostaglandin synthesis, which increases renal blood flow, and dilates veins, relieving pulmonary oedema before diuresis begins.

Uses and adverse effects: pulmonary oedema and congestive heart failure, udder oedema and ascites, acute renal failure, and reduction of exercise-induced pulmonary haemorrhage in racehorses. Adverse effects are hypokalaemia, hyponatraemia, hypomagnesaemia, dehydration, metabolic alkalosis and ototoxicity.

(b) Housing requirements of pregnant and milking cows

Pregnant cows: the dry cow and close-up cow (last three weeks) need a separate, quiet, clean and well-bedded area away from the milking herd. Covered space is about 3.5–4 m² per cow, with open paddock about 7–8 m², and a calving pen of about 10–12 m² for each cow near calving. Flooring is non-slip, dry and soft, which reduces injuries and abortion. Ventilation is good and draught-free, and shade and water are provided.

Milking cows: housing is designed for milk yield, comfort and hygiene, in a loose-housing or tie-stall system. A tie-stall standing space of about 1.7 m × 1.1 m per cow, with a manger, is usual for Indian cattle. The floor is about 1–2% sloped towards a gutter so it stays dry and clean, and feed-bunk space is about 60–70 cm per cow. Heat stress is reduced by roof insulation, fans, sprinklers and shade, and the milking area is kept clean to prevent mastitis.

Differences: pregnant cows stress isolation, extra space, soft footing and calving facilities, whereas milking cows stress hygiene, feed and water access, cooling and ease of milking.

(c) Role of birds in the transmission of zoonotic diseases

Birds act as reservoirs, amplifiers and carriers of zoonotic pathogens.

• Avian influenza: wild waterfowl are the natural reservoir, and domestic poultry amplify it. H5N1 is highly pathogenic in poultry, while H9N2 and H7N9 are usually low pathogenic in birds, though they can infect humans.
• Psittacosis (Chlamydia psittaci): parrots, pigeons and poultry spread it by dried faeces and aerosol.
• Salmonellosis and campylobacteriosis: by faecal contamination of food, eggs and water.
• Arboviruses: West Nile virus and Japanese encephalitis, in which wild birds, particularly herons, are amplifying hosts and mosquitoes transmit.
• Newcastle disease (conjunctivitis) and cryptococcosis and histoplasmosis from droppings are also zoonotic.

Transmission is by faecal–oral spread, aerosol or droplets, direct contact and handling, and vectors. Backyard poultry and live-bird markets increase human exposure in India.

Control follows One Health: biosecurity, surveillance and testing at ICAR-NIHSAD, Bhopal, under the national action plan for avian influenza, vaccination where permitted, culling, and protective equipment for handlers.