(a) Classify diuretics with examples on the basis of efficacy and also write down their mechanism of action. (20 marks) (b)…

(a) Classification and Mechanism of Diuretics Diuretics increase urine output by reducing tubular sodium (and water) reabsorption. They are classified by efficacy, the fraction of filtered sodium excreted.

High-ceiling (loop) diuretics, up to 15–25% of filtered sodium: furosemide, bumetanide, torsemide. They inhibit the Na⁺-K⁺-2Cl⁻ cotransporter (NKCC2) in the thick ascending limb of the loop of Henle, abolishing the medullary gradient, so urine cannot be concentrated; K⁺, Ca²⁺ and Mg²⁺ excretion rise. Used in pulmonary oedema, heart failure and exercise-induced pulmonary haemorrhage in horses.

Medium-ceiling diuretics, about 5–10%: thiazides (hydrochlorothiazide, chlorothiazide) block the Na⁺-Cl⁻ cotransporter in the distal convoluted tubule, raising K⁺ loss but reducing Ca²⁺ excretion. Used in mild oedema and in hypertension.

Low-ceiling diuretics, 2% or less:

• Potassium-sparing: spironolactone and eplerenone block aldosterone receptors in the collecting duct; amiloride and triamterene block the epithelial sodium channel (ENaC); K⁺ is retained.
• Carbonic anhydrase inhibitors (acetazolamide) act in the proximal tubule, reducing bicarbonate and sodium reabsorption.
• Osmotic diuretics (mannitol) are filtered but not reabsorbed, holding water in the tubule; used for cerebral oedema and acute renal failure.

Potassium-sparing drugs are often combined with loop diuretics to prevent hypokalaemia in dogs with heart failure.

(b) Processing of Butter and Defects in Stored Butter Butter is a water-in-oil emulsion with at least 80% milk fat and not more than 16% moisture. The flow diagram below runs through these steps:

1. Receiving and cooling of milk, then separation of cream (30–40% fat); neutralise acidity if cream is sour.
2. Pasteurisation at a high temperature (about 85–95°C) for short time to destroy lipase and microbes; vacuum deodorisation if flavours are present.
3. Cooling and ageing at 4–7°C for 12–16 hours, so fat crystallises.
4. Churning at about 8–12°C, until butter grains the size of peas form and buttermilk is drained.
5. Washing of grains with chilled water.
6. Salting (1–2.5%) and working, which expels water and distributes moisture in fine droplets.
7. Packing in parchment, foil or cartons and cold storage (0 to 5°C for short term, minus 18°C or below for long term).

Defects in stored butter:

• Flavour: rancid (hydrolytic, from lipase, with butyric acid), oxidised or tallowy (from light, air and copper, iron), fishy (trimethylamine), cheesy and yeasty (from microbial growth), and metallic or feed flavours.
• Body and texture: crumbly (too cold or low moisture), sticky or leaky (excess moisture, poor working), greasy and weak, and gritty from salt.
• Colour: mottled or streaky from uneven salting or working, and surface fading or darkening.
• Microbial: mould (white, green, black spots), yeasts, souring, and putrid or surface taint. Prevention: good quality cream, adequate pasteurisation, correct working, airtight packaging and cold storage.

(c) Antimicrobial Components and Microbial Spoilage of Shell Eggs Defences:

• Cuticle (bloom) seals the pores; shell and shell membranes form a physical barrier.
• Albumen: alkaline pH (9 or more after storage), viscosity, lysozyme (breaks peptidoglycan), ovotransferrin (binds iron), avidin (binds biotin), ovomucoid and ovoinhibitor (protease inhibitors), and cystatin.
• Yolk: vitelline membrane and IgY antibodies from the hen.
• Eggs also hold little free iron or nutrients.

Spoilage: if the cuticle is damaged or eggs are washed, stored warm, humid or sweating, bacteria enter through pores, with penetration helped by moisture. Common rots:

• Green rot (Pseudomonas fluorescens): fluorescent green albumen.
• Colourless rot (Pseudomonas, Acinetobacter, Alcaligenes): watery albumen and yolk.
• Black rot (Proteus, Aeromonas): H₂S gives a dark blackened yolk and foul smell.
• Pink rot (Pseudomonas) and red rot (Serratia): pink or red discolouration.
• Custard rot (Proteus): yolk thickened and custard-like.
• Fungal spoilage (Penicillium, Cladosporium, Mucor, Aspergillus): pin-point colonies on shell and membranes in damp storage. Salmonella may be present without spoilage, so cold storage and unwashed, clean eggs are advised.