Transport and Homeostasis
Theheart is a muscular organ that serves to pump blood via the bloodcirculatory system through the contraction and relaxation of itsmuscles. The figure 1.0 below shows the structure of the heart.
Figure1.0:The structure of the human heart. Adoptedfrom (https://parallelevision.wordpress.com,accessed on 20thJune)
Inthe heart, there are two types of circulation, pulmonary circulationand systemic circulation. Pulmonary circulation refers to themovement of blood to the lungs from the heart so as to be oxygenated.This circle continues on and on. In the pulmonary circulation, bloodmoves through capillaries on the alveoli as it flows through thelungs which enable the blood to be oxygenated while the systemiccirculation basically refers to the circuit that blood followsthrough the rest of the body to deliver the oxygenated blood to theother parts of the body as it makes a circle that completes in thelungs.
Bloodfrom the rest of the body enters the heart through the vena cava onthe right side of the heart, the blood then moves into the rightatrium, which contracts forcing blood into the right ventricle viathe tricuspid valve. When the right ventricle is filled, it shuts thetricuspid valve and blood leaves the right ventricle into thepulmonary artery to the lungs for purification. Oxygenated blood fromthe lungs flows back into the heart through the pulmonary vein intothe left atrium, which contracts releasing blood into the leftventricle. When the left ventricle is filled, it contracts lettingblood out through the aorta, which then supplies the oxygenated bloodto the rest of the body.
Thecirculatory system performs several functions in the human body(Altman, 1971, 59). The circulatory system undertakes respiration inthe body by delivering oxygen to the body tissues and carrying carbon(IV) oxide away from the body tissues. It also facilitatestemperature regulation in the body through the transportation of heator coldness to all the body parts. The circulatory system providesbody immunity since it is composed of white blood cells (leukocytes)which prevent the body from various disease attacks. It does alsoundertake the removal of waste products from the body through itsmechanisms, which enable the disposal of wastes and toxic materialsfrom the body. In aiding cellular communication, the circulatorysystem facilitates this function since it undertakes the transport ofhormones across the body. Additionally, the circulatory systemultimately undertakes nutrition by transporting digested foodmaterials and minerals to the body tissues.
Bloodis made up of four components namely, plasma, red blood cells, whiteblood cells and platelets which all serve different but very criticaltasks. Plasma is the liquid part of blood, which composes more thanhalf of the blood level. It consists of water, proteins and mineralsalts (electrolytes). The blood plasma provides a medium in which allthe other blood components (white blood cells, red blood cells andplatelets) are suspended and transported. The plasma acts as areservoir for checking the level of water in the body tissues. Tothis end, it can either add water to tissues with levels belowthreshold or rather sip out from those that have excess water.Moreover, the proteins contained in the plasma perform a variety offunctions. For instance, immunoglobulin protects the body fromdisease causing agents such as bacteria and fungi.
Thered blood cells (RBC) comprise approximately 40% of the bloodcapacity (Dacie & Lewis, 2002, 52). The red blood cells containhemoglobin, which is the medium that facilitates the transport ofoxygen and carbon dioxide by the blood. The oxygen so transported isutilized by the body tissues to generate energy. The red blood cellsalso facilitate waste removal by carrying carbon (IV) oxide to thelungs for removal as it is sucked into the alveoli. The shape of thered blood cells are shaped in a manner that suits them to transportoxygen in the body. In some instances, the red blood cells becomerigid and deformed in shape, a condition referred to as sickle-cellanaemia. The red blood cells affected become characteristically stiffand do not move smoothly in the blood vessels. The affected cells(sickle-shaped) are then likely to pile up in some sections of bloodvessels in the process inhibiting transport in the circulatorysystem. The white blood cells (WBC) undertake the protection of thebody against disease causing micro-organisms such as bacteria andfungi. The white blood cells are majorly of five main types namelyEosinophil, Basophils, Monocytes, Lymphocytes and Neutrophils. TheEosinophil is responsible for destroying the parasites and cancerouscells. Basophils are responsible for neutralizing the effects ofallergic reactions in the body. The monocytes are responsible for‘swallowing’ of dead body tissues. Neutrophils are responsiblefor killing and ‘swallowing’ disease-causing bacteria and fungithat might gain access into the human body. Finally, Lymphocytes takecare of infections caused by viruses and is also responsible fordestroying cancerous body tissues. Additionally, lymphocytes generateantibodies. The fourth blood component is platelets, which are alsopopularly known as thrombocytes. Platelets aid in the formation ofplugs, which serve to block blood vessels (at the affected part)during bleeding. Platelets form this plug by first attachingthemselves to substances outside the affected endothelium andsecretin chemical messengers which connect to each other to form anetwork (plug) which seals the wound and stops bleeding (Fuentes etal, 2013).
Thecirculatory system comprises three main vessels namely, thecapillaries, veins and arteries in the order of sizes. Thecapillaries are the smallest vessels and aorta is the largest arteryand vessel for that matter. In their structure, capillaries areenjoined with the smallest of the arteries while the capillaries aresubsequently enjoined with an array of small veins to complete thecapillary-vein-artery nexus. The largest of the blood vessels,arteries, are comprised of thick, elastic walls that are designed towithstand the high pressure usually caused by blood pumped from theheart. The artery is made up of four layers namely, the outerprotective layer, the muscle layer, the elastic layer and the innerlining. The structure of the artery is shown in figure 1.0 below.
Figure1.0:Structure of the artery. Adoptedfrom Aviva (http://www.aviva.co.uk/,accessed on 20thJune 2015)
Veins,on the other hand, have relatively thin walls as compared to those ofarteries these thin walls enable veins to open up outwards so as toprovide additional capacity required for holding big volumes of bloodwhen the body is in as state of rest. Unlike the arteries, thestructure of the vein is composed of valves along the lengths of thevessel, which are meant to ensure a unidirectional flow of blood. Thebasic structure of a vein is shown in figure 1.2 below.
Figure1.2:Structure of the vein. .Adoptedfrom Aviva (http://www.aviva.co.uk/,accessed on 20thJune 2015)
Capillariesare the smallest blood vessels. They are made up of cells, which areonly one cell thick. Figure 1.3 below shows the structure of thecapillaries.
Figure1.3:Structure of the capillaries. Adoptedfrom Aviva (http://www.aviva.co.uk/,accessed on 20thJune 2015)
Thereare several blood disorders, which are varied depending on thecomponents of blood that are affected. Two common diseases of bloodare haemophilia and anaemia. Haemophilia is a blood disorder, whichoccurs when the platelets are impaired such that the body’scapability to stop bleeding through the clotting of blood is greatlyreduced. The disorder has been found to have a very high probabilityto occur in males than in females since males only have one Xchromosome as compared to females who have two X-chromosome and assuch, a defective chromosome is guaranteed in any male carrier (Dacie& Lewis, 2002, 56). The symptoms of the disease haemophilia varydepending on the degree of severity and individual immunity.Individuals with a high degree of severity usually experience moresevere and more frequent bleeds. The other common blood disorder isiron anaemia. Anaemia is caused by an acute reduction in the numberand health of red blood cells in an individual’s blood. A specifictype of anaemia that is most prevalent is the iron deficiencyanaemia, which is caused by a significant reduction in the number ofred blood cells (RBC) in the blood due to inadequate or completelylack of iron. Additionally, it can be caused by intestinal bleeding,heavy monthly periods in women and during the stages of pregnancy. Affected individuals usually manifest symptoms like lethargy (generalbody weakness) and paleness in complexion. Other than this, there aredisorders that affect the blood vessels which impair theirfunctioning. Aneurysm and phlebitis are common examples. Aneurysm isa condition that results when the walls of the arteries are damagedand can rupture in extreme circumstances. The disease can lead todeath if not detected early enough. The two most common types ofaneurysm are cerebral aneurysm and aortic aneurysm. Phlebitis ischaracterized by the swelling of vein walls especially in the legs.It is mostly caused by an intravenous catheter inserted in the bloodvessel. Phlebitis is detrimental to the circulatory system since itcauses blood clot to break immaturely.
Thereare as much a variety of heart diseases as there are blood diseases.The two most common heart diseases are heart failure and coronaryartery disease (Maron et al, 2006, 1812). Heart failure is the mostcommon heart disease today. It is commonly referred to as the chronicheart failure. This heart disease results when the heart does notpump blood in the required frequency to sustain blood flow in thewhole body. Patients suffering from this disorder usually exhibitlethargy, shallow breath and to some extent swelling of legs (Kannelet al, 1974, 32). Heart failure is mostly caused by the coronaryartery infection, high blood pressure and excessive consumption ofalcohol. These mechanisms result in heart failure either by alteringthe heart’s characteristic structure or rather altering itsfunctioning. The severity of the condition is usually correlated withthe extent in which an individual undertakes physical practice(Mosterd,2007, 1139).Patients suffering from heart failure usually experience symptomssimilar to those of anaemia and kidney failure. As for coronaryartery disease, which is commonly referred to as ischemic heartdisease, it occurs due to disorders in the cardiovascular structures(Kannel et al, 1974, 34). It is usually characterized by chest painand shallow breadth. This heart disease leads to other physiologicaldisorders like heart failure. The disease is majorly caused by heavysmoking, diabetes, physical inactivity, excessive alcohol consumptionand high blood pressure (McMurray, 2000, 598). There is need forconsuming a healthy balanced diet, avoid drugs (especially alcoholand cigarettes) if the disease is to be kept at bay (Yu et al, 2003,58).
Thelymphatic system is yet another important coordination of processesin the body. It is made up of a dense network of lymphatic vessels,the lymph fluid and the lymphatic organs. In its structure, thelymphoid tissue, which has less of lymph, undertakes to facilitateimmunity if only it is confronted with antibodies that lea toinflammation. This is achieved by importing the lymph debris fromblood and the lymph. It is also composed of the bone marrow andthalamus, which together forms the fundamental lymphoid organsresponsible for generating T-cells and the subsequent advancement ofdeveloping the B-cells. The underlying mechanism of how this systemworks begins in the bone marrow where the B-cells are located. Thesecells leave the bone marrow and are transported to the thalamus foradvancement in maturity and ultimately travel to the organs of thelymphatic system so as to find disease-causing pathogens.Additionally, the fundamental lymphatic organs produce lymphocytesusing budding progenitor cells (Mathews et al, 1985, 414). Thestructure of the lymphatic system is as presented in figure 1.4below.
Figure1.4:The structure of the lymphatic system.
Thelymphatic system performs a lot of functions in the human body. It isthe system that is responsible for the transportation of fatty acidsto the rest of the body from the digestive system. The lymphaticsystem also carries the leukocytes from the nodes of the lymphaticsystem to the bone marrow and back as it strives to facilitate theattack on disease-causing pathogens. The antigen-presenting cells(APCs) are also carried by the lymphatic system to the nodes of thelymphatic system so as to initiate an immune system from the lymphnodes. Additionally, the lymphatic system undertakes to free the bodyorgans from the toxic interstitial fluid (Butcher & Picker, 1996,62).
Thelymphatic fluid forms at the joints between the capillaries and thearteries. The formation at this point is usually due to the highpressure between the high pressures of blood that enters thecapillaries relative to that which leaves the capillaries through theveins.Theprocess of lymph formation begins when nutrients are carried by bloodto body tissues and in return, waste products from the tissues areremoved through the same medium (blood). In the process, blood formsa fluid referred to as tissue fluid, which then fills the spacesbetween the body organs and the medium that blood is. The compositionof the tissue fluid changes as the blood continues its activities oftransporting digested food to the body tissues and carrying away theresulting waste materials way from the body organs (Tsien et al,1982, 329). The composition of the tissue fluid changes since waterand salts diffuse across the walls of capillaries to form anon-static equilibrium between the tissue fluid and blood (Mathews etal, 1985, 414). Finally, the tissue fluid enters the smallest vesselsof the lymphatic system (lymph capillaries) as lymph. The lymph flowsthrough the entire lymphatic system in the process accumulatingtraces of blood and protein to resume its characteristic composition.The mechanisms through which lymph forms can however lead to a typeof cancer referred to as Non-Hodgkin’s lymphoma which isfundamentally a type of cancer that results from the human lymphaticsystem during the formation of lymphatic fluid. It results whentumors are generated from a variety of lymphocytes. A common type ofthis cancer is follicular lymphoma.
Therelationship between the blood circulatory system and the lymphaticsystem is anchored on their respective functions of transport andbody waste removal (Spector & Johansson, 2007, 431). The twosystems fundamentally form an important system that complements thecardiovascular system in the functioning of the body. The circulatorysystem and the lymphatic system are related since they both serve totransport substances in the human body. More directly, the lymphaticsystem relies on the blood in the circulatory system for theformation of its medium of transport, lymph. Similarly, the lymph soformed removes dead cells of the blood from the body in performingits excretion role. Both the circulatory system and the lymphaticsystem function in a similar manner in the sense that they all makeuse of liquid state compositions (blood and lymph) as their mediumsof transport.
Homeostasisrefers to the regulation of internal body processes so as to maintaina stable internal equilibrium. An example of a homeostatic process inthe human body includes the temperature regulation and blood sugarregulation. Homeostasis fundamentally involves the processes andmechanisms through which the internal conditions are maintained atequilibriumand any deviations from this equilibrium are respondedto by the body. The adjustment process requires a sensor to perceivethe deviations from the equilibrium, an effector channel to execute acondition and a (negative) feedback condition that relates the twotenets of the process. In the homeostasis process, the functionmechanisms are triggered when the receptor perceives a component thatregulates variations in the internal processes. The receptortransmits the perceived information to the nerve center whichascertains the respective response and communicates to the effectorwhich institutes the changes through a negative feedback mechanism.
Homeostasisplays a very critical role in the blood sugar regulation,thermoregulation and regulating the breathing and heart rates(Bailey, 1964, 1222). Homeostasis facilitates the blood sugarregulation through the negative feedback mechanism in which the levelof glucose level in the blood is restored to normal if it does riseabove the equilibrium. When the level of blood glucose is high, thesensor perceives these levels and sends signals to the control centerwhich responds by stimulating the pancreas to release insulin. Theinsulin converts conversion of glucose to the inactive glycogenthereby reducing the level of glucose in blood. When the glucoselevel falls below the normal level, the same mechanisms are used butthis time glucagon is released which increases glucose level in theblood to normal level thereby maintaining a stable internalcondition. If however, the level of blood sugar rises persistentlywithout any intervention, a disorder hypoglycemia results.Homeostasis is also involved in the regulation of the breathing rate. When the breathing rate increases, muscles are fatigued and thelevel of oxygen in the blood falls below the normal level. This lowlevel of oxygen is perceived by the sensor which initializes thehomeostatic processes. The control center responds through a negativefeedback mechanism by increasing the heart rate through muscularcontractions and relaxations which serves to increase the oxygensupply in the body thereby restoring the initial equilibrium.In thermoregulation, homeostasis regulates internal body temperaturethrough the negative feedback mechanism. When the body temperaturerises over and above the normal body temperature, the sensorperceives these high levels and sends a message to the controlcenter. The control center responds by stimulating sweating andoccasioning vasodilation both of which serve to enhance heat loss bythe body. The processes are sustained until the normal bodytemperature is restored to normal. Similarly, if the body temperaturedeeps too low, the sensor sends messages to the control center whichresponds through the effectors (muscles) leading to vasoconstrictionand closure of sweat pores to prevent further heat loss. Internalheat generation processes are usually instigated through homeostaticmechanisms, which result in shivering (King & Farner, 1961, 218).The processes persist until the internal body temperature is restoredto normal. However, should the body temperature increase persistentlywithout homeostatic interventions, a condition known as hypothermiaresults, which can lead to death.
Theurinary system is another critical system in the functioning of thehuman body. The urinary system fundamentally implies the organs thatproduce and facilitate the movement of urine in its removal from thebody. The system is usually made up of two kidneys. Urine is howeverproduced in organs referred to as nephrons, which are located in thekidney. The urine then travels in tubules referred to as urine ducts.The urine is then transported to the ureter and ultimately to thebladder where it awaits removal from the body. Figure 1.5 below showsthe basic structure of the human urinary system.
Figure1.5: The Urinary System. Adoptedfrom Ivyrose Hollistic(http://www.ivyroses.com/HumanBody/Urinary/Urinary_System.php,accessed on 22ndJune 2015)
Theurinary system performs several functions in the human body. Theurinary system is responsible for balancing the levels of calcium andsodium salts in the body. It undertakes the removal of uric acid andurea from the body and facilitates the regulation of blood pressure.
Generally,excretion is the process through which living organisms get rid ofthe waste products of metabolism. In higher animals, the process isfacilitated by special body organs such as kidneys, skin and lungs.The process is a vital phenomenon in every living organism (Goodarziet al, 2011, 408). In lower organisms, like amoeba, the process ismuch simpler since the waste products of metabolism are removedacross the surface of the organisms’ body. In plants, the wasteproducts usually excreted include water and oxygen. In animals, thewaste products include carbon (IV) oxide, salts, guanine andcreatine. Excretion is important since it enables removal of wasteproducts from the body and regulates the salt level while ensuringcontinuity of body processes.
Osmoregulationrefers to the processes through which the levels of concentration ofbody fluids are checked to ensure a homeostatic balance. The processfundamentally involves balancing the concentration of the body fluidssuch that they are not too concentrated or diluted thus osmoticpressure control (Robertson & Aycinena, 1982, 349).Osmoregulation is important to the body since it aids in maintainingthe salt and water balance in the body and thus keeps dehydration atbay.
Anotherimportant excretory organ is the skin. The human skin is basicallymade up of three layers namely, the epidermis, dermis and thesubcutaneous layer. The epidermis is the outer interface, whichprotects the inner sections of the organ. It also protects the bodyfrom entry of pathogens while facilitating temperature regulation inthe body. This layer usually does not contain blood vessels. Thedermis is the inner layer of the skin on which skin appendages areattached. The subcutaneous layer is the inner most and is a liningof fats below the skin. The structure of the skin is shown in figure1.6 below.
Figure1.6:Structure of the human skin. Adopted from abpl(http://www.abpischools.org.uk/page/modules/homeostasis,accessedon 22ndJune 2015)
Incontrolling the body temperature, the blood vessels in the skinbecome critical (Schneider, 2012, 25). When body temperature is low,blood vessels constrict to minimize the loss of heat from the body.When body temperature is high, blood vessels widen to increase heatloss and at the same time, sweat is secreted from the sweat glandsonto the surface of the skin. The sweat evaporates due to the heatfrom the body thereby creating a cooling effect on the skin, whichreduces body temperature. Erector Pilli muscles usually relax toflatten hair on the skin so as to increase heat loss in the body(Denda, 2002, 128: Blanpain & Fuchs, 2009, 210). This isnecessary since if the body is too hot, proteins I the body will bedestroyed leading to several disorders.
Themuscles of the heart and the valves are structurally designed toenable a smooth and uninterrupted flow of blood through the heart.Blood from the rest of the body enters the heart through the venacava on the right side of the heart the blood then moves into theright atrium, which contracts courtesy of its muscles forcing bloodinto the right ventricle via the tricuspid valve. When the rightventricle is filled, it shuts the tricuspid valve and blood leavesthe right ventricle into the pulmonary artery to the lungs forpurification. In this respect, the tricuspid valve is structurallydesigned such that it enables the flow of blood into the rightventricle but closes automatically when full to create a closedchamber at the bottom with the only outlet through the pulmonaryartery. Oxygenated blood from the lungs flows back into the heartthrough the pulmonary vein into the left atrium, which contractsreleasing blood into the left ventricle. In the process, the musclesand chambers of the heart are at times faced by complications. Anexample of such a complication is the atrial and ventricularfibrillations which result when blood doesn’t empty completely intothe respective atrium or ventricle thereby resulting in anaccumulation of blood in some chambers of the heart and bloodvessels. The effects of these complications become real when thepooled blood clots thereby inhibiting the blood flow in the heart.This can lead to death.
Congestiveheart failure, which results when the heart in not able to pumpenough blood (Kannel et al, 1974, 30) to sustain the blood flowthrough the body and therefore body demand of oxygen and nutrients,results in a reduction in oxygen levels since the amount suppliedfalls below the required levels. This is so because blood is themedium through which oxygen is transported to body tissues and carbon(IV) oxide is transported away from the tissues.
Whenthe homeostatic mechanisms for controlling blood sugar fail, therebyresulting to diabetes mellitus, an individual experiences severaldisorders due to the high levels of glucose in blood. This resultsif the secretion of glucagon and insulin are impaired. The individualexperiences persistent hunger, increased frequency of urination,lethargy and thirst. If the condition persists, the individual has ahigh probability of suffering from chronic kidney failure (CKF) andcardiovascular disease.
Finally,on the role of white blood cells in protecting the body, theleukocytes achieve this role through three different ways. First, thewhite blood cells can generate antitoxins to counter the poisonoussubstances of bacteria and other disease-causing pathogens. Second,they can also produce antibodies, which destroy a specific type ofpathogen thus enabling the phagocyte to ingest it. Finally, thephagocyte can engulf and subsequently ingest the pathogen.
Figure1.7:Detailed diagram of the heart showing pulmonary and systemiccirculation.
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