Issues of Cardiovascular System - Essay Example

Essay, Biology Number Cardiovascular System - Heart The atrial systole occurs when the atria contracts and the ventricles relax. Lasting about 0.1 seconds, the atrial systole has a blood volume of 260ml (130ml pumped into each ventricle). The contraction of the atria causes increased pressure within these chambers which forces blood into the ventricles through the AV valves. The ventricular systole on the other hand lasts 0.3 seconds and occurs when the ventricles contract while the atria relax causing a steep rise in pressure in the left and right ventricles. For a person typically at rest, each ventricle ejects 70ml of blood (stroke volume) during the ventricular systole. The SL valves for the left ventricle opens when the ventricular pressure passes the aortic pressure (80mmHg) while the SL valve for the right ventricle opens when the ventricular pressure passes the pressure in the pulmonary trunk, that is, 20mmHg. The relaxation period lasts about 0.4 seconds but shortens when the heart beats faster. It occurs when blood flows towards the heart from the aorta and pulmonary trunk as the SL valves close at a pressure of about 100mmHg due to backflow to prevent blood from re-entering the ventricles (Tortora & Derrickson, 2009). Heart sounds can be heard due to the turbulent flow of blood after the heart valves close. Although there are four heart sounds, only S1 and S2 are loud enough to be heard from a healthy heart. S1 (lub) results from the closure of the AV valves when the ventricular systole begins while S2 (dup) results from the closure of SL valves at the start of ventricular diastole. S1 and S2 are best detected from chest locations slightly away from the valves because the sound waves are carried by blood flow through the arteries. S3 and S4 are not loud enough to be heard by the naked ear and so a stethoscope comes in handy. S3 is due to blood turbulence during ventricular filling while S4 is a result of blood turbulence during atrial systole (Tortora & Derrickson, 2009). Cardiovascular System – Blood Pressure and Hemodynamic Systematic vascular resistance (SVR) refers to the sum total of the vascular resistances of all systemic blood vessels. Vascular resistance, the opposition of blood flow due to friction between the blood and the tunica interna of the walls of the blood vessels, is controlled by three main factors namely; lumen diameter, blood viscosity and blood vessel length. The smaller the lumen diameter, the greater the resistance to blood flow (vasodilation widens the lumen while vasoconstriction narrows it). Resistance to blood flow increases with blood viscosity. Blood viscosity is itself dependent (directly proportional) on concentration of red blood cells (RBCs) and proteins in the blood plasma. Blood vessel length is also directly proportional to the resistance to blood flow, that is, the larger the blood vessel, the greater the vascular resistance (Tortora & Derrickson, 2009). The skeletal muscles and respiratory pumps help propel blood from the lower body to the heart (during venous return to the right atrium). The veins in the legs have distal and proximal pairs of one-way valves which open and close to facilitate blood flow to the right atrium and prevent backflow into extremities such as the lungs. The respiratory pump enables the alternating compression and decompression of veins. The diaphragm moves downwards during inhalation to increase pressure in the abdominal cavity and decrease pressure in the thoracic cavity where the heart is located. The abdominal veins are therefore compressed to propel blood into the decompressed thoracic veins and into the right atrium. Valves prevent backflow of blood from thoracic veins into abdominal veins during exhalation when the pressure differential reverses (Tortora & Derrickson, 2009). Respiratory System Gaseous exchange has three main components – pulmonary ventilation, external respiration and internal respiration. Pulmonary respiration, commonly referred to as breathing, entails the inhalation and exhalation of air. In pulmonary ventilation, air is exchanged between the atmosphere and the alveoli of lungs. External respiration on the other hand is the exchange of gases between the alveoli and the pulmonary capillaries, and in the process, pulmonary blood acquires oxygen and releases Carbon IV Oxide. The third component, internal respiration is the exchange of gases between the blood in the systemic capillaries and interstitial fluid and cells. During internal respiration, systemic blood loses oxygen and gains Carbon IV Oxide (Tortora & Derrickson, 2009). Lung compliance is a measure of the amount of physical effort required to stretch the lungs. High compliance means that the lungs can expand readily while low compliance on the other hand means that the lungs resist expansion. Lung compliance is controlled by two main factors. One of these factors is the elasticity of fibers of the lungs. Elasticity of fibers is directly proportional to lung compliance, that is, high elasticity increases compliance (as fibers can be easily stretched) and vice-versa. Another factor that affects lung compliance is the presence/ amount of suffocant. Suffocants increase lung compliance since they reduce surface tension in the alveoli, therefore making lungs highly stretchable with very little application of force (Tortora & Derrickson, 2009). Renal System The efferent arterioles branch to form the peritubular capillaries that surround the tubular portions of the nephrons in the renal cortex. Long, loop-shaped capillaries known as the vasa recta extend from the efferent arterioles. They supply the tubular portions of the nephrons in the renal medulla. The peritubular capillaries join to form the peritubular veins and then the interlobular veins. The interlobuar veins also receive blood from the vasa recta. Return blood flows through the arcuate veins into the interlobar veins between the renal pyramids. Blood leaves each kidney through a renal vein that carries it into the inferior vena cava. The fraction of blood plasma in the afferent arterioles that becomes glomerular filtrate is known as the filtration fraction. The fraction normally ranges between 16 and 20 percent, although it can vary considerably in health and disease. The average daily volume of glomerular filtrate is 150 liters in females and 180 liters in males. More than 99 percent of the glomerular filtrate returns to the blood via the process of tubular reabsorption—1 to 2 liters are excreted as urine. Glomerular blood pressure is high because the efferent arteriole is smaller in diameter than the afferent arteriole, which increases blood flow resistance. Dilation of the afferent arterioles increases GFR by increasing blood flow into the glomerular capillaries where blood is filtered. Constriction of the afferent arterioles decreases GFR by decreas-ing blood flow. Constriction of the efferent arterioles increases glomerular blood hydrostatic pressure, which increases the net filtration pressure (Tortora & Derrickson, 2009). Anti-diuretic hormone (ADH) is secreted by the posterior pituitary gland and functions to regulate water re-absorption in the kidneys. The hormone does this by increasing the permeability of the collecting ducts and distal convoluted tubules. When the osmolarity of blood plasma and interstitial fluid increases due to water loss by even as little as 1%, osmoreceptors in the hypothalamus detect the change and more anti-diuretic hormone is secreted to act upon the kidneys to conserve water. The atrial natriuretic peptide (ANP) is produced from the atria of the heart. Its function is to inhibit re-absorption of sodium ions and water in the kidneys, increase secretion of sodium ions in urine and increase urine output while also inhibiting the release of anti-diuretic and aldosterone hormones. The release of atrial natriuretic peptide is stimulated by an increase in blood pressure and its secretion serves to decrease blood volume and blood pressure as a result of the above mentioned functions (Tortora & Derrickson, 2009). Digestive System The salivary gland secretes fluid called saliva. Salivation is the secretion of saliva and is controlled by the autonomic nervous system. Parasympathetic activity produces continuous secretion of moderate amounts of saliva whereas sympathetic activity is responsible for decreasing salivary secretion resulting in a dry mouth, for example during anxiety and fear. Saliva is composed of water, solutes in ionic form, mucus, urea, uric acid, immunoglobulin A, bacterial enzymes and salivary amylase. Water dissolves the food and breaks it down further while also facilitating tasting of the food. Solutes perform specific functions such as activation of salivary amylase by chloride ions and buffering of acidic foods by bicarbonate and phosphate ions. Immunoglobulin A prevents microbial penetration of the mucous membrane while the enzyme lysozyme helps destroy certain bacteria in food. Mucus lubricates the food for easy manipulation in the mouth (formation of a bolus) and swallowing (Tortora & Derrickson, 2009). Most digestion and absorption of food occurs in the small intestine and so it’s fairly lengthy (3meters) to provide a large surface area for these purposes. The surface is greatly increased by millions of circular folds, villi and microvilli. The intestinal glands contain the paneth cells (secretes lysozyme that breaks down and destroys bacteria) and enteroendocrine cells – S cells, CCK cells and K cells (secrete hormones). The duodenal glands secrete alkaline mucus which neutralizes gastric acid in chyme. Pancreatic juice and intestinal juice provide a liquid medium to help in absorption of nutrients. The brush border enzymes of the villi aid in chemical digestion. In addition, segmentations and migrating motility complex produced by the myenteric plexus in the small intestines aid in further mechanical digestion. The large intestines function to complete absorption, production of some vitamins, formation and elimination of feces from the body. It is about 1.5 meters long consisting of caecum, colon, rectum and anal canal. The primary function of the absorptive cells in the large intestines is the absorption of water from the lumen. Absorption of ions also occurs in the large intestines. Goblet cells secret mucus that lubricates the passage of the colonic contents. The large intestines lack the villi but instead have microvilli which handle the small amounts of absorption. There is also some forms of mechanical digestion in the large intestines through the gastroileal reflex and ileocecal sphincter which facilitate peristalsis and haustral churning. Mucus performs most of the chemical digestion in the small intestines as no enzymes are secreted here. Finally, the large intestines form feces from the unabsorbed/ undigested food material which is then passed via the anus to the outside of the body (Tortora & Derrickson, 2009). References Tortora, G. J., & Derrickson, B. (2009). Principles of anatomy and physiology (12th ed.). 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