JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Pharmacy I Year HUMAN ANATOMY AND PHYSIOLOGY-I Previous Question Paper (October-2020 - R17)

The plasma membrane is a semi-permeable, dynamic structure described by the Fluid Mosaic Model. Its composition includes:

• Phospholipid Bilayer: The structural foundation consisting of two layers of phospholipids. Each molecule has a hydrophilic phosphate head facing the aqueous environment and two hydrophobic fatty acid tails facing inward, creating a barrier.
• Proteins: Integral proteins span the entire membrane (transmembrane), acting as channels or transporters, while peripheral proteins are attached to the inner or outer surfaces, serving as enzymes or structural anchors.
• Cholesterol: Interspersed among phospholipids, cholesterol molecules regulate membrane fluidity, preventing it from becoming too rigid in cold temperatures or too fluid in heat.
• Carbohydrates: Found on the outer surface, these form glycoproteins and glycolipids, which function in cell-to-cell recognition and immune system signaling.

A negative feedback mechanism is a homeostatic control system where the body detects a deviation from a set point and triggers a response that reverses the change, bringing the variable back to its normal range.

The mechanism functions through three main components:

• Sensor (Receptor): Monitors the environment and detects changes (stimuli) in a specific variable, such as body temperature or blood glucose levels.
• Control Center: Receives input from the sensor, compares it against the set point, and determines the appropriate response.
• Effector: Receives instructions from the control center and produces an effect that opposes the initial stimulus.

For example, in thermoregulation, if body temperature rises above the set point, sensors in the skin and hypothalamus detect the increase. The hypothalamus (control center) activates effectors like sweat glands and blood vessel dilation (vasodilation) to release heat, thereby lowering the temperature back to the set point. This continuous loop ensures internal stability despite external fluctuations.