Explain How Does The Body Maintain Homeostasis

1. Briefly explain how does the body maintain homeostasis?
Homeostasis is a existence and maintenance of a relatively constant internal environment. Homeostasis is maintain by negative and positive feedback mechanism. Most homeostatic control mechanisms are negative feedback mechanisms. In these system, the output shut off the original stimulus or reduce its intensity. These mechanisms cause the variable to change in a direction opposite to that of the initial change, returning it to its “ideal” value, thus the name “negative” feedback mechanism. In positive feedback mechanisms, the result or response enhances the original stimulus so that the response is accelerated. This feedback mechanisms is ”positive” because the change that results proceed in the same direction as the initial change, causing the variable to deviate further and further from its original value or range.
2. EXPLAIN the functions of plasma membrane components:
a) Phospholipids
Two general features of phospholipid bilayers are critical to membrane function.
First, the structure of phospholipids is responsible for the basic function of membranes as barriers between two aqueous compartments. Because the interior of the phospholipid bilayer is occupied by hydrophobic fatty acid chains, the membrane is impermeable to water-soluble molecules, including ions and most biological molecules. Second, bilayers of the naturally occurring phospholipids are viscous fluids, not solids. The fatty acids of most natural phospholipids have one or more double bonds, which introduce kinks into the hydrocarbon chains and make them difficult to pack together. The long hydrocarbon chains of the fatty acids therefore move freely in the interior of the membrane, so the membrane itself is soft and flexible. In addition, both phospholipids and proteins are free to diffuse laterally within the membrane—a property that is critical for many membrane
functions.
b) Glycoprotein
Glycoproteins play a crucial part in cell-cell recognition, and have important roles in protection and the immune response, reproduction, structural integrity and cell adhesion.

c) membrane protein
The membrane protein provide structural / mechanical support. It is also transport molecules across the membrane. Enzymatic control of chemical reactions at cellular surface. The other functions are, receptors for hormones, regulatory molecules that arrive at outer surface of the membrane and serve as ‘markers’ (antigens),that identify blood & tissue type of an individual.

d) Cholesterol
Cholesterol gives the mechanical stability and strength. Cholesterol also makes the membrane flexible, permeable and reduces leakage of small polar molecules.
3. DESCRIBE the functional mechanism of facilitated transports
a) Symport
A symporter is an integral membrane protein that is involved in movement of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in the same direction. Transport of the two solutes is obligatorily coupled. A gradient of one substrate, usually an ion, may drive uphill (against the gradient) transport of a co-substrate. It is sometimes referred to as secondary active transport. Examples include the glucose-Na+ symport found in plasma membranes of some epithelial cells and the bacterial lactose permease, a H+ symport carrier.

b) Antiport
A cotransporter and integral membrane protein involved in transporting of two or more different molecules or ions across a phospholipid in opposite directions. One species of solute moves along its electrochemical gradient, allowing a different species to move against its own electrochemical gradient. For example, the Na+/Ca2+ exchanger which involve the exchanges one calcium ion for three sodium ions.

4. EXPLAIN:
a. the pain pathway
Pain receptors or Nociceptors are found on the free nerve endings of primary sensory fibers that detect unpleasant stimuli and pass the information to CNS to be interpreted as pain. They are distributed all over the body (skin, muscles, joints, internal organs but not brain). When tissue gets damaged by certain (mechanical, thermal or chemical) stimuli, it releases inflammatory mediators (eg bradykinin, serotonin, prostaglandin, cytokinase and H+) which can activate primary nociceptors. When these neurons reach the spinal cord, they pass the pain to secondary sensory fibers located around the spinal cord where key NT substance P. The secondary sensory fibers transmits information to brain where it is interpreted as pain.
b. Analgesic mechanism
Activation of peripheral nociceptive fibers causes release of substance P and other pain-signaling neurotransmitters from nerve terminals in the dorsal horn of the spinal cord.
Release of pain-signaling neurotransmitters is regulated by endogenous endorphins or by exogenous opioid agonists by acting presynaptically to inhibit substance P release, causing analgesia.
Two components: spinal and supraspinal inhibits the release of excitatory transmitters from primary afferent in the Substantia gelatinosa of dorsal horn. Exerted through interneurones for gating of the pain. At supraspinal level in cortex, midbrain and medulla oblongata alter processing and interpretation and send inhibitory impulses through descending pathway.