i) What are the functions of liver, skeletal muscle, adipose tissue and heart mu
ID: 78313 • Letter: I
Question
i) What are the functions of liver, skeletal muscle, adipose tissue and heart muscle? Don’t forget the endocrine functions of some of these tissues.
ii) Relate the functions of liver, skeletal muscle, adipose tissue and heart muscle to the dominant metabolic pathways in these tissues. NOTE! , not all pathways take place in all tissues.
iii) What hormones have effects on these tissues and what receptors do they bind to in liver, skeletal muscle, adipose tissue and heart muscle? Also what are the effects of these hormones on these tissues? Include specifics about pathways and specific enzymes of pathways that are affected .
iv) What metabolic pathways are most active and what are the preferred fuels of these tissues in the fed (high blood glucose) state, under mild fasted (low blood glucose) and under starvation conditions (very low and prolonged low blood glucose concentrations) of liver, skeletal muscle, adipose tissue and heart muscle?
Explanation / Answer
1. The main function of the liver is metabolism of nutrients and xenobiotics as well as detoxification. It can renew its cells and regenerate 2/3rd of mass after partial hepatectomy. In addition, it has specialized endocrine functions as it is responsible for secretion of 4 hormone or its precursors such as insulin-like growth factor, angiotensinogen, thrombopoietin, and hepcidin.
The skeletal muscles help in the support and movement of the body. Skeletal muscles contractions pull on tendons, which are attached to bones. The contraction of skeletal muscles cause the muscle to shorten, the bone and thus the body part will move. The major physiological function of myokines is to protect the functionality and to enhance the exercise capacity of skeletal muscle. Myokines control adaptive processes in skeletal muscle by acting as paracrine regulators of fuel oxidation, hypertrophy, angiogenesis and regulation of extracellular matrix.
The adipose tissue acts as an insulating layer helping to reduce heat loss through the skin. It has a protective function, providing mechanical protection and support around some of the major organs. Adipose tissue also means of energy storage. Adipose tissue produces and secretes several hormones involved in lipid metabolism and storage. One important example is leptin, a protein manufactured by adipose cells circulates in amounts directly proportional to levels of body fat.
The heart is a pump which moves the blood. The arteries and veins are the pipes through which the blood flows. The lungs provide a place to exchange carbon dioxide for oxygen. In response, specialized cells in the wall of the atria produce and secrete the peptide hormone atrial natriuretic peptide. ANP signals the kidneys to reduce sodium reabsorption, thereby decreasing the amount of water reabsorbed from the urine filtrate and reducing blood volume.
2. Most fructose is metabolized in the liver, which explains some of fructose and glucose. The dominant metabolic pathway proceeds via fructose-1-phosphate and joins the glycolysis pathway at the level of trioses glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
Resting muscle uses fatty acids as its major fuel source. By contrast, exercising muscle initially uses its glycogen stores as an energy. During intense exercise, glucose 6-phosphate derived from glycogen is converted to lactate by anaerobic glycolysis. As these glycogen reserves are depleted, free fatty acids provided by the mobilization of triacylglycerol from adipose tissue become the dominant energy source.
In fasting, lipoprotein lipase activity of adipose tissue is low. Consequently, circulating triacylglycerol of lipoproteins is not available for triacylglycerol synthesis in adipose tissue.
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