Homeostasis and Regulation of Blood Sugar - Essay Example

Homeostasis Homeostasis Introduction Homeostasis is the process in which the body maintains a constant internal environment of the body to ensure optimum functioning. These optimal conditions include; temperature, electrolyte concentrations, pH of body fluids, oxygen level and carbohydrate concentration. In order to maintain cellular constituents they must be continuously resynthesized so that the constant internal state is maintained. Many cells aggregate to form various tissues and organs. All the cells contribute towards maintenance of homeostasis. Nutrients are supplied in the cells through extracellular fluid. Homeostasis includes control of the blood water balance, blood sugar level, body temperature and the urea level in the blood. All these mechanisms have a specific sensor that is able to detect the value of the factor being monitored (Ratan, 1993). Homeostasis is achieved through a variety of automatic mechanisms that compensate for internal bodily changes and external changes. Any deviation from the norm whether a rise or a fall is referred to as a positive feedback. The negative feedback is a control mechanism in which when a change causes a response, the mechanism is corrected. The corrective mechanism action would cause an opposite effect resulting to the factor falling back to the norm value. Stressors are changes in the internal or external environment that affect normal conditions within the body. Sensors that detected changes in the internal conditions and the effectors work to correct these changes. For example, the skin has nerve cell endings that predict changes in temperature and send the signals to the brain through nerves (Chiras, 2003). Homeostasis controls the system variable within a narrow range about a set point. Sensors detect these values and compares with the set point. Controls commence on bidirectional processes to correct these changes. Humans have physiological and behavioural ways of controlling temperature. Regulation of blood sugar Glucose is transported in the body through the blood at a norm of approximately 80mg per 100cm3. Glucose regulation is by both the liver and the pancreas. The Islets of Langerhans are cells that secrete insulin and glucagon. In case of elevated sugar levels in the blood, the cells produce more insulin. Thermoregulation Any significant variation in the internal temperature could damage the body’s enzymes. Human beings are endotherms, that is, they maintain a constant internal temperature of about 37oC. The skin is important in regulation of temperature. Sweating, flattening of hairs on the skin and vasodilation are ways in which temperatures can be lowered (Givens & Reiss, 2002). Defects in homeostasis mechanism may lead to many diseases such as cancer, diabetes and hypertension. Damaged homeostatic mechanism can result to autoimmune diseases in which the immune system attacks the body’s own tissue. A sustainable system requires combination of both positive and negative feedback. Due to divergence from homeostatic condition, positive feedback is recognised. The negative feedback corrects the conditions creating an equal stability. Homeostatic systems are stable therefore are capable of testing the variables that can be adjusted. The systems contribute to the maintenance of balance. Osmoregulation is the process in which the right amount of water and proper ionic balance is maintained. This is achieved though excretion in which metabolic waste products are removed through the lungs, skin and kidneys. In the kidneys, osmoregulation ensures water and solute content of body fluids. Nitrogenous wastes come from protein metabolism. Proteins are ingested through the mouth, digested in the intestinal lumen to generate smaller sizes that can be assimilated in the blood. The main nitrogenous substance is called urea. Other nitrogenous wastes include ammonia and uric acid. Proteins are made up of chains of amino acid residues which are held together by peptide bonds. The short amino acid chains are often referred to as peptides. Peptide bonds are stable and can only be broken through specific enzymes or heating in strong acid. Excess proteins are converted to nitrogenous wastes through deamination. These wastes are carried to the kidneys from the liver by the blood to be eliminated. These nitrogenous wastes are toxic especially in high concentrations differ in their toxicity and solubility. Ammonia is toxic all cells particularly to the brain cells and causes disorientation and a diminished level of consciousness. Therefore ammonia is added to glutamate to form glutamine which is a non-toxic neutral amino acid. The excretion of nitrogenous wastes is determined by availability of water and capability of the organism. Structure and function of the urinary system The urinary system is made up of the kidneys. The kidneys are two reddish-brown bean shaped organs on either side of the vertebral column. The right kidney is positioned slightly lower than the left kidney. On the inner concave side of the kidney is the hilum. The outer layer is referred to as the cortex. The inner layer is filled with pyramids and is called the medulla. These pyramids point towards the pelvis, a funnel shaped cavity found at the anterior part of each ureter in the kidney. The pelvis leads to a long narrow tube called the ureter which empties itself in the urinary bladder. The ureter arises from within the renal sinus of the kidneys at the hilum. The urinary balder acts as a muscular reservoir for urine and lies in the pelvic cavity of the abdomen. The neck of the urinary bladder is surrounded by sphincters which remain closed until urination. Structure and function of the kidney nephron The kidney is made up of more than one million nephrons. The nephron is the functional unit of the kidney. Each nephron consists of a malpighian capsule, a nephritic tubule and a collecting tubule. The malpighian capsule has the Bowman’s capsule and a glomerulus. The Bowman’s capsule forms the dilated blind end of the nephron. It is a double-walled cup shaped structure lined by a thin semi-permeable squamous epithelium. The glomerulus is the outer concavity of Bowman’s cup contains a knot-like mass of blood capillaries. The glomerulus has an afferent arteriole enters in Bowman’s capsule and divides into a collection of capillaries. These capillaries reunite to form efferent arteriole Ultrafiltration occurs on the walls of glomerular and Bowman’s capsule are thin and semipermeable therefore act as ultra-filters. Due to high filtration pressure in the blood of glomerulus, a part of water and dissolved constituents of blood such as nitrogenous wastes, glucose, amino acids and mineral ions are filtered out in the Bowman’s capsule therefore forming the glomerular filtrate. The nephritic tubule is divided into the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule. The proximal convoluted tubule is the initial convoluted region of the nephritic tubule. It is highly coiled to increase the surface area of re-absorption. Water is reabsorbed by osmosis. Selective reabsorption of glucose, amino acids and salts also takes place. The Loop of Henle is U-shaped and has a thin descending limb and a thick ascending limb. The distal convoluted tubule is found at cortex region and opens into the collecting tubule. The collecting ducts are large tubules which receive and collect from several nephrons. The collecting ducts drain the urine collected from the nephrons (Rowland, 1992). Hormonal control of osmoregulation Antidiuretic Hormone (ADH) also known as vasopressin is synthesised in the supraoptic and paraventricular nuclei in the hypothalamus. ADH passes along neurosecretory cells to the posterior pituitary gland where it is secreted into the capillaries. Antidiuretic hormone passes in the blood to the kidney where it increases the permeability to water of the cell surface membrane of the cells that make up the walls of the distal convoluted tubule and the collecting duct. The receptors on the cell surface membrane pick up the ADH molecules therefore activating an enzyme within the cell. The activation of this enzyme causes vesicles within the membrane to move to and fuse with its cell surface membrane. These vesicles contain pieces of membrane that have many water channels and when they fuse with the membrane, the number of water channels is increased making the cell surface membrane more permeable to water. In addition, ADH increases the permeability of the collecting duct to urea which therefore passes out decreasing the water potential of the fluid around the duct. The combined effect is that more water leaves the collecting duct by osmosis and re-enters the blood. Reabsorption does not increase the water potential of the blood but prevents it from getting worse. This leads to the osmoreceptors to stimulate thirst, in order to encourage the individual to take more water. The osmoreceptors in the hypothalamus detect the rise in water potential and stop sending impulses to the pituitary gland. The pituitary glands reduces the release of ADH and the permeability of the collecting ducts to water and urea is therefore reduced to its former state (Toole & Toole, 2004). Aldosterone stimulates Na+ reabsorption in the connecting segment of the distal tubule of the nephron. Aldosterone promotes K+ secretion as a secondary effect of its action on Na+ reabsorption. In the distal nephron, the linked Na+ reabsorption-K+ secretion is referred to as the distal Na+ - K+ exchange process (Bullock, et al., 2001). Conclusion Osmoregulation maintains a desirable balance of water and ions therefore important in homeostasis. Osmoregulation is important because changes in the amount of water in the blood and tissue fluid can have great effects on body cells. This regulation of water content is vital to ensure normal metabolism of cells. Maintenance of water content and also the concentration of Na+, Cl-, Ca2+, and K+ ions in its cells to lead a healthy lifestyle. In case of defects in osmoregulation, certain diseases such as diabetes insipidus and diuresis. Diabetes insipidus is caused by hormonal imbalance involving the production of ADH by the hypothalamus which makes the kidneys overactive. In case of kidney failure several approaches must be taken. These include haemodialysis or kidney transplant (Wright, 2000). References Bullock, J., Boyle, J. & Wang, M. B., 2001. Physiology. 4th ed. Philadelphia: Lippincott Williams & Wilkins. Chiras, D. D., 2003. Human body systems : structure, function, and environment. Sudbury, Mass: Jones and Bartlett. Givens, P. & Reiss, M. J., 2002. Human biology and health studies. 2nd ed. Cheltenham: Nelson Thornes. Ratan, V., 1993. Handbook of human physiology. 7th ed. New Delhi: Jaypee Bros. Medical Publishers. Rowland, M., 1992. Biology. Walton-on-Thames, Surrey: Nelson. Toole, G. & Toole, S., 2004. Essential A2 biology for OCR. Cheltenham: Nelson Thomes. Wright, D. B., 2000. Human physiology and health. Oxford: Heinemann. Read More