Question

1). Describe in as much detail as you can the Homeostatic Feedback Loop for the regulation of blood calcium levels (Calcium homeostasis). (This is an Endocrine (Hormonal) reflex).

2. Describe the structure and function of cardiac and smooth muscle physiology. Compare and contrast the physiology of skeletal, cardiac, and smooth muscle contraction. Include in your discussion the regulatory and contractile proteins involved in contraction as well as the source of calcium for contraction in all 3 muscle types

Answer 1

1. Blood calcium levels are regulated by parathyroid hormone,which is produced by the parathyroid glands. PTH is released in response to low blood calcium levels.it increases calcium levels by targeting the skeleton, the kidneys, and the intestine. Parathyroid hormone in maintaining blood calcium homeostasis.It increases blood calcium levels when they drop too low. Conversely,calcitonin,which is released from the thyroid gland,decreases blood calcium levels when they become too high.

2. cardiac muscle pumps blood through the body and is under voluntary control. The attachment junctions hold adjacent cells together across the dynamic pressures changes of the cardiac cycle.smooth muscle tissue responsible for involuntary movements in the internal organs.cardiac muscle tissue is a specialized,organised type of tissue that only exists in the heart.It is responsible for keeping the heart pumping and   blood circulating around the body. cardiac muscle tissue or myocardium,contains cells that expand and contract in response to electrical impulses from the nervous system. COMPARE AND CONTRAST: CARDIAC MUSCLE TISSUE: a.cardiac muscle tissue is found in the heart wall. b.Its fibers are arranged similarly to skeletal muscle fibers.cardiac muscle fibers connect to adjacent fibers by intercalated disc which contain desmosomes and gap junctions. cardiac muscle contractions last longer than the skeletal muscle twitch due to the prolonged delivery of calcium ions from the sacroplasmic reticulum and the extracellular fluid.cardiac muscle fibers contract when stimulated by their own autorythymic fibers.this continuous ,rhythmic activity is a major physiological difference between cardiac and skeletal muscle tissue. SMOOTH MUSCLE: Smooth muscle tissue is nonstriated and involuntary and is classified into two types:a visceral smooth muscle and b. multiunit smooth muscle. Visceral smooth muscle is found in the walls of hollow viscera and small blood vessels.the fibers are arranged in a network. Multiunit smooth muscle is found in large blood vessels,large airways,arrector pili muscles,and the iris of the eye.the fibers operate singly rather than as a unit. In smooth muscle,the regulator protein that binds calcium ions in the cytosol is calmodulin(in place of the role of troponin in striated muscle).calmodulin activates the enzyme myosin light chain kinase,which facilitates myosin actin binding and allows contraction to occur relatively slow rate.the delivery of calcium ions from the extracellula fluid. The prolonged presence of calcium ions in the cytosol of smooth muscle fibers provides for smooth muscle tone,a state of continued partial contraction. Smooth musclefibers can stretch considerably without developing tension;this phenomenon is termed the stress-relaxation response. PHYSIOLOGY OF THE SMOOTH MUSCLE: -contraction starts slowly and lasts longer - no transverse tubules and very little SR -Ca+2 must flows in from outside -calmodulin replaces troponin - Ca+2 binds calmodulin turning on an enzyme that phosphorylates the myosin head so that contraction can occur, - enzyme works,slowly,slowing contraction. skeletal muscle delivery of calcium ions from the sacroplasmic reticulum. SKELETAL MUSCLE: Skeletal muscle fibers cannot divide and have limited powers of regeneration.the number of new skeletal fibers from satellite cells is minimal.extensive repair results in fibrosis,the placement of muscle fibers by scar tissue.