Theheart is a well-built organ in human beings as well as in otheranimals. The heart pumps blood through the blood vessels. Figure abelow shows the structure of the heart.

Structureof the Heart (retrieved from


Thereare two types of circulation, which are pulmonary circulation andsystemic circulation. Pulmonary circulation is the part of thecirculatory system, which transports deoxygenated blood from theright part of the heart to the lungs and returns oxygenated blood tothe left part of the heart. On the other hand, systemic circulationdescribes the part of the cardiovascular system that carriesoxygenated blood away from the heart to the body and returnsdeoxygenated blood back to the heart (Bittihn,2015. Pp. 4).Therefore, systemic circulation refers to the circulatory system inwhich the blood leaves the heart to the body cells and re-enters theheart.

Flowof Blood through the Heart

Bloodenters the right part of the heart through the inferior vena cava andsuperior vena cava. The inferior vena cava gathers blood from thelower half part of the body, while the superior vena cava gathersblood from the upper half of the body. Blood from the inferior venacava and superior vena cava enters the right atrium. The right atriumcontracts making blood to flow through the tricuspid valve into theright ventricle. The right ventricle contracts and blood becomespumped through the pulmonary valve into the pulmonary artery and intothe lungs, where it is oxygenated (Katz,2011. Pp. 4).Oxygenated blood flows into the heart through the pulmonary veinsinto the left atrium. The contraction of the left atrium forces bloodinto the left ventricle through the mitral valve. The left ventriclepumps blood into the aorta through the aortic valve. The aortadistributes blood to the rest parts of the body. The left ventriclecomprises of a thicker muscle compared to any part of the heart,which helps it in pumping blood to the body parts. On the other hand,the valves in the heart help in preventing blood from flowing back.

Functionsof the Circulatory System

Thecirculatory system comprises of four major components, which includethe heart, arteries, veins, and blood. The circulatory system isinvolved in different functions one of the functions entailsrespiration. The circulatory system helps in delivering oxygen tobody cells as well as removing carbon dioxide from the body cells.Another function of the circulatory system is providing the body withimmunity (Mehler,2001. Pp. 7).The white blood cells help in providing immunity to the body.Thermoregulation is another critical function of the circulatorysystem the circulatory system helps in transporting heat. Inaddition, the circulatory system is also involved in transportingdigested food substances to the body cells as well as transportinghormones. Furthermore, circulatory system aids in removing wasteproducts as well as poisons, which would harm the body in case theybecome accumulated.

Componentsof the Blood and Their Function

Theblood has different components, but the four main and most importantones include plasma, red blood cells, white blood cells, andplatelets. These components carry out different and vital functionsin the body. The red blood cells constitute 40-50% of the bloodvolume. They have the role of transporting oxygen from the lungs todifferent living tissues of the body, as well as carrying away carbondioxide. The red blood cells are also referred as the erythrocytes.The white blood cells, also known as the leucocytes, exist in typesand variable numbers. The white blood cells make up a very meagrepart of the blood’s volume. The white blood cells are not limitedto blood, but also occur elsewhere in the body such as in the liver,spleen, and lymph glands. The white blood cells have a generalfunction of providing the body with immunity against infections andforeign particles. White blood cells work through producingantitoxins, producing antibodies, or ingesting pathogens. Platelets,which are also known as thrombocytes, work with blood clottingchemicals at wound site. They carry out this function by adhering tothe blood vessels walls (Michelson,2012. Pp. 469).Platelets can also release coagulating chemicals that cause clots todevelop in the blood, which can plug up narrow blood vessels.Besides, recent research has indicated that platelets also aid infighting infections by releasing proteins, which kill invadingbacteria as well as other microorganisms. On the other hand, plasmacarries the white cells, red cells and platelets. Plasma providesnourishment to cells and removes waste products of metabolism.

Structureand Functions of the Blood Vessels

Thereare three kinds of blood vessels, which include veins, capillaries,and arteries. These blood vessels have different structures andfunctions. The following paragraphs discuss the structure andfunctions played by the blood vessels.


Thestructure of the arteries is such that the outer walls contain smoothmuscle fibre, which relaxes and contracts under the instructionsprovided by the sympathetic nervous system. The walls of arteries arethick and muscular, which make them resist a wave of high pressurewith every pump of blood. Figure b that follows depicts the structureof an artery.


Thefunction of arteries is to transport blood away from the heart. Allarteries, except pulmonary artery, transport oxygenated blood.


Capillariesare usually tiny and have a diameter of approximately 5-20micro-meters. The walls of capillaries have the thickness of only onecell, which allow the exchange of materials amid the surroundingtissue and contents of the capillary. They are capable of exchangingmaterials across cells because of their thin structure. The structureof a capillary is as shown in figure c below.


Capillarieshave the role of supplying body tissues with components of blood andremove waste from the surrounding cells. Capillaries also facilitatethe exchange of carbon dioxide, oxygen, salts, and water among othersubstances amid the blood and surrounding body tissues (Abramson&amp Dobrin, 1984. Pp. 64).


Thestructure of veins comprises of three tissue layers, which arethinner and less elastic to the layers of arteries. The thin walls ofveins help them to expand and hold vast volumes of blood the momentbody is at rest. Veins also have valves that help in preventing theflow of blood in the opposite direction. Figure d below shows thestructure of a vein


Thefunction of veins is transporting of blood towards the heart. Allveins, with an exception to the pulmonary vein, carry deoxygenatedblood.

Diseasesof the Heart and Diseases of the Blood

Thereare different diseases of the heart as well as diseases of the blood.Diseases of the heart include rheumatic heart disease, aneurysm,phlebitisand atherosclerosis. The rheumatic heart disease is usually caused byone or more rheumatic fevers, which result to the damaging of theheart especially the heart valves. In most cases, rheumatic feveroccurs in childhood and may follow a streptococcal infection. Attimes, the infection can affect the heart resulting in scarring ofthe valves, damaging the heart sac, or weakening the heart muscle. Inthe case of atherosclerosis, walls of the arteries become thick andstiff due to the build up of fatty deposits. Because of the fattydeposits build up, blood flow becomes restricted (Maciejko,2004. Pp. 4).Ananeurysm describes an abnormal protuberance in the wall of an artery.Aneurysm may form in any blood vessel, but it occurs most commonly inthe aorta. There are different causes of aneurysm, which includehypertension, weakness in the artery wall, age at menopause,syphilis, and arteriosclerosis. Aneurysmmay lead to severe haemorrhage as well as other complication that mayinclude sudden death. Phlebitisis a blood clot, which develops in a vein near the surface of theskin. Some of the causes of phlebitisinclude local injury to the vein, insertion of intravenous catheters,prolonged inactivity, and period after surgery among others.Phlebitiscan affect the functioning of veins, but local treatment can aid inmitigating the effects of phlebitis.On the other hand, diseases of the blood include haemophilia andanaemia. Haemophilia is a condition where the blood lacks some of theclotting factors this implies that a person suffering fromhaemophilia usually bleeds for a longer period than normal sinceblood lacks some clotting factors. Anaemia is a situation where aperson has less than usual quantity of haemoglobin in the blood. Inthe case of sickle cell anaemia, haemoglobin (which is a moleculethat delivers oxygen to cells in the body) is affected. Sickle cellanaemia affects transport of oxygen in the body since it may lead tovaso-occlusive crisis and splenic sequestration crisis (Bloom,1995. Pp. 39).

Structureand Functions of the Lymphatic System

Thelymphatic system comprises of organs and lymphatic tissues thesystem includes organs such as thymus and spleen while lymphatictissues include lymphatic vessels, nodes and capillaries (Scanlon&amp Sanders, 2015. Pp. 358). These components assist in achieving the functions of the lymphaticsystem. The lymphatic capillaries are blind end tubes, which arelarger than blood capillaries. The lymphatic capillaries have aspecial one-way structure that permits interstitial fluids in but notout. The role of the lymphatic capillaries is absorbing interstitialfluid built up in the tissue in the process, they also pick brokencells, viruses and bacteria. The structure of lymph capillary isshown in figure e that follows


Thelymph nodes are bean-shaped. They have a length of between 1-25 mmlong. These are usually found in groups (Scanlon&amp Sanders, 2015. Pp. 358).Lymph nodes are usually named depending with where they are, theorgan they receive lymph from, or depending on what they surround. Astructure of lymph node is as shown in figure f below


Thespleen entails a dark red, highly vascular organ that isapproximately 12 cm long. It is perceived as the largest lymphatictissue in the body. It is usually filled with red and white pulp thewhite pulp is the lymph tissue while the red pulp is blood and cordsof phagocyte cells. In the lymph system, the spleen has a function ofdestroying worn out red blood cells, platelets and bacteria throughphagocytosis. On the other hand, a thymus is a gland, which is madeup of lymphoid tissue. Unique lymphocytes are produced in the thymusand these attacks and destroy antigens.

Thelymphatic system has three chief functions. One of the functionsentails draining of interstitial fluid. The second function of thelymph system is fighting infection capillaries of the lymph pick upbacteria and viruses, which are later destroyed once they reach thelymph nodes. This helps in fighting infections. In addition, thelymph system also has the function of transporting lipids(Karunamuni,2013. Pp. 74).

Formationof Lymphatic Fluid

Lymphaticfluid becomes formed when the interstitial fluid forms a contact withthe blood. Initially, the lymphatic fluid is a watery liquid havingsimilar constituents as interstitial fluid however, the lymphaticfluid becomes thicker as it accumulates extra materials such aslymphocytes and proteins from blood (Gerard&amp Bryan, 2006. Pp 85).The lymphatic fluid becomes formed when the interstitial fluidbecomes collected through lymph capillaries. After collecting throughthe lymph capillaries, it is transported to the lymph nodes throughthe lymph vessels before being emptied into the left or rightsubclavian vein, where it mixes with blood. When this fluid itcombines with some constituents of the blood such as lymphocytes andproteins, it becomes lymphatic fluid.

TheInterrelationship of the Circulatory and Lymphatic Systems

Thereis an interrelationship between the lymphatic and circulatory system.One of the interrelationships between the two systems is that blood,which is the transport fluid in the circulatory system, contributesmajorly in the formation of lymph. Blood plasma becomes a substancereferred to as interstitial fluid the moment it comes into contactwith the body tissues. Part of this fluid enters the lymphaticvessels, where it becomes transformed into lymph. Besides, a person’scirculatory system and lymphatic system work together in providingthe body with lymph. The lymph fluid is initially carried by thelymph vessels, but later it is emptied into the subclavian veins inthe circulatory system. Another interrelationship between the twosystems is that the circulatory system uses lymphatic system as ameans of disposal. The lymphatic system usually functions as a wasteremoval system in the body. The lymph picks up any unneeded materialsabsorbed by muscles and transports them to the lymph nodes, wherethese materials become ingested. Unusable and old red blood cells areusually eliminated in this manner, which makes circulatory system beseen to use the lymphatic system for disposal. Despite these positiveinterrelationships between the two systems, there is a negative roleof the two systems in the spread of cancer. Because lymph andlymphatic vessels are very prevalent in all areas of the body, thelymph will often carry cancer cells into the blood, which wouldtransport the cells into new bodily parts. This process is referredto as metastasis. Furthermore, in case the lymphatic system becomesdamaged, it may supply the blood with depleted or excess amounts oflymph such an effect may result to the development of diseases likelymphedema.

Homeostasisin the Human body

Homeostasisplays a very vital role in the blood sugar regulation,thermoregulation and the regulation of the breathing and heart rates.Homeostasis helps in blood sugar regulation by a negative feedbackmechanism in which the level of glucose level in the blood isrestored to normal levels. Homeostasisdescribes the capacity of an organism or environment to maintain astate of stability despite the availability of changes in theenvironment (Chiras,2012. Pp. 6).In spite of fluctuating environmental conditions, the human body iscapable of maintaining different physiological conditions. Forinstance, the body is capable of maintaining temperature balance,glucose concentration balance, acid-base balance, and fluid volumeamong other internal conditions. All these entails the homeostasisprocesses in the human body. When the body or body tissues are not inproper working condition, the maintenance of some internalphysiological processes may be difficult. For instance, in the caseof a heart disease, medications are required in order to restoreheart rates to a balance. In case a person has Atrial Fibrillation,the heart rates are abnormal and may also make the breathing rate toincrease (Camm&amp Waktare, 1999. Pp 48).The abnormal heart rates may make an individual to experiencedizziness, palpitations, chest discomfort, shortness of breath, andfainting. In order to restore the heart rate and breathing rate tonormal, medications that slow the heart rate to a normal range haveto be administered. Non-Hodgkinlymphoma is a cancer, which starts in lymphocytes that are part ofthe immune system. When the lymphocytes become affected, the immunesystem of the body also becomes affected.

TheHomeostatic Control Mechanisms for the Heart Rate, the BreathingRate, Temperature and Blood Sugar Regulation in the Human Body

Thebrain is critical in the control of different body physiologicalprocesses. It is the brain that sends and receives messages in theform of chemicals from the nerves that ensures that the bodyprocesses are maintained. In the case of the heart rate, the medullahelps in maintaining a stable heart rate. The medulla receivesmessages from the nerves, organs, and other body parts regularly.Homeostasis steadily monitors messages from the nervous system thatcorresponds between body’s joints and muscles. Through theinterventions of the medulla, hormones that increase or lower heartrates can be produced these help in maintain a normal range of heartrate. In the case of breathing rate, the medulla and Pons help inmaintaining the right range of breathing rate. The medulla detectsthe carbon dioxide and oxygen levels and signals the lungs, diaphragmand muscles in the heart to decrease or increase the breathing. Onthe other hand, Pons controls the speed of exhalation or inhalationdepending with the body’s need. The same case applies to themaintaining of a normal temperature range however, hypothalamus isresponsible for the regulation of temperature. Changes in the normalrange of temperature makes the hypothalamus send nerve impulses tothe blood vessels, sweat glands, and muscles in order to lower orraise temperature. On the other hand, in maintaining the right bloodglucose level in the body, the beta cells of the pancreatic isletsincreases the release of insulin or glucagon in order to maintain thecorrect range of blood sugar level (Kent,2000. Pp. 138).

Failureof HomeostaticControl Mechanisms

Afailure of homoeostasis implies a disaster to an organism. Failure ofmaintaining the right body temperature can result to heatstroke orhypothermia (Hopkins,1996. Pp. 64).Alternatively, failure to maintain the appropriate blood sugar levelcan result in diabetes and obesity (Evans&amp Tippins, 2008. Pp. 24).On the other hand, failure of maintaining appropriate breathing ratecan result in hypoxia. Furthermore, failure of homeostasis inmaintaining the right heart rate can result in congestive heartfailure as well as inflammation. Congestive heart failure affectsevery organ system that is involved with oxygen transport. Theventilator response to exercise in patients having congestive heartfailure is enhanced despite normal arterial oxygen saturation.

TheStructure and Functions of the Urinary System

Theurinary system comprises of the urethra, bladder, ureters, andkidneys (Joneset al., 1998. Pp. 35).These system components have different structures and functions thatenable the urinary system to carry out its work efficiently.


Thisorgan is bean-shaped and is approximately 11 cm in length. In thehuman body, there are two kidneys that are at the middle of the back.The kidney comprises of two distinct parts the medulla on the insideand cortex on the outside (Rosdahl&amp Kowalski, 2008. Pp. 278).The medulla leads into pelvis. The kidney has a concave centre, wherenerves, ureter, blood vessels, and lymphatic vessels enter the organ.The structure of the kidney is shown in figure g that follows


Thefunction of kidney is filtering the blood. Besides, it has thefunction of reabsorbing useful materials that are required by thebody and form urine.


Theseare tubes, which join the kidneys to the bladder. They have thefunction of taking urine from kidneys to the bladder.


Thisentails a sac-like organ, which is in pelvic cavity. The function ofthe bladder is acting a reservoir for urine. The bladder comprises ofan internal sphincter muscle that relaxes when the walls contract(Rosdahl&amp Kowalski, 2008. Pp. 278).This aids in opening and emptying of urine into the urethra.


Thisis a narrow tube that passes from the bladder to the outside of thebody. It comprises of an external sphincter that is voluntarilycontrolled by the Central Nervous System. The function of the urethrais taking urine from the bladder to the outside of the body.

Urethra,Bladder, and Ureters

TheProcesses of Excretion and Why It Is Important In the Body

Excretiondescribes the process by which humans eliminate waste products ofmetabolism as well as other non-useful materials (Alters,2000. Pp. 245).In the human body, there are four key excretory organs. One of themis the kidney, which excretes urine. Urine comprises of mineral saltsand nitrogenous wastes, excess water, uric acid and urea. The lungsconstitute the other excretory organ in the human body, which excretewater vapour and carbon dioxide. The skin is the third excretoryorgan in the human body, which excretes sweat and foreign substances.In addition, the liver is the other key excretory organ in the humanbody, which helps in detoxifying poisonous substances (Alters,2000. Pp. 246).The excretion process is important in the human body because it helpsan organism to control osmotic pressure, thus maintaining anacid-base balance. Hence, excretion helps in promoting homeostasis.

Osmoregulationand Why It Is Important In the Human Body

Osmoregulationentails the process of actively regulating the osmotic pressure ofthe body fluids in order to maintain the homeostasis of the body’swater content (Stretch,2002. Pp. 137).The tissues and organs of the body function in a fluid that has aconstant temperature, solute concentration and PH. This helps incontributing to the maintenance of body’s homeostasis. The solutesin the body fluids are chiefly sugars and mineral salts.Osmoregulation is important because it helps in keeping these solutesat an ideal concentration (Bradley,2009. Pp. 168).Therefore, osmoregulation ensures that body fluids exist at the rightconcentrations, despite external influences such as diet andtemperature.

TheStructure and Functions of the Skin

Theskin comprises of three chief layers, which include the dermis,epidermis, and subcutaneous layer (Wright,2000. Pp. 111).These layers are discussed in the paragraphs that follow.


Thisis an elastic outer layer, which is continually regenerated. Thislayer has keratinocytes, corneocytes, and melanocytes. Keratinocytesare the main epidermis cells formed through cell division at its base(Montagna&amp Parakkal, 2012. Pp. 94).Corneocytes are dead keratinocytes that make up the very outer layerof the epidermis known as the horny layer. On the other hand,melanocytes produce melanin, which gives skin its colour and protectsagainst ultraviolet radiation (Scott,2014. Pp. 66).


Thisis an inner layer that comprises of sweat glands, hair follicles, andsebaceous glands. Sweat glands play a role of regulating temperature.Hair follicles entail pits where hairs grow. The hairs play asignificant role in regulation of temperature (MarshallCavendish,2003. Pp. 2087).The sebaceous glands produce sebum that helps in keeping hairs freefrom bacteria and dust.


Thisis a layer that lies below the dermis. This layer is made up of fatand connective tissue. Because of the fat making up the layer, thislayer has he role of acting as an insulator (Rosdahl&amp Kowalski, 2008. Pp. 144).

Structureof the Skin

Theskin has different functions, which usually emanate from itsstructure. The skin offers a protective barrier against thermal,physical and mechanical damage and hazardous substances. The skinalso reduces harmful effects of ultraviolent radiation and preventsloss of moisture. Besides, the skin aids in the regulation oftemperature and as a sensory organ. In addition, the skin has a rolein the synthesis vitamin D (Rosdahl&amp Kowalski, 2008. Pp. 145).

Howthe Skin Controls Temperature in the Human Body

Theskin has a significant role in regulating the temperature of thehuman body. When it is too cold, the skin triggers shivering which inturn results in the contraction of the blood vessels. The contractionof the blood vessels makes the hairs on the skin to stand. Whenstanding, these hairs trap more warmth, which helps in keeping thebody warm. On the other hand, when it is too cold, the skin triggersthe blood vessels to relax (MarshallCavendish,2003. Pp. 2088).The relaxation of the blood vessels makes the hair on the skin tofall, which helps in heat reduction. Besides, the glands in the skinsecrete sweat, which increase heat loss through evaporation(Jablonski,2013. Pp. 52).The secretion of sweat slows as the body temperature returns tonormal.

Overheatingand Overcooling of Human Body

Mostof the body tissues and organs function at a given range oftemperature. This implies that maintenance of body temperature withina given range is significant to humans. When the human bodyoverheats, the most vulnerable tissues to the heat strain are thenerve cells. When the nerve cells become incapacitated in theirfunction, it implies that the nerve cells cannot be in a position tosend or receive impulses. This eventually leads to heatstroke, whichcan make an individual to be dehydrated (Wright,2000. Pp. 110).The excessive dehydration may result in death if not corrected sinceit can cause much strain to the heart. On the other hand, overcoolingof the body temperature may also have adverse effects. Overcooling ofthe body temperature makes the blood circulation to suffer when thebody temperature overcools, it is makes blood flow difficult. Thiscan result in swelling of face and limbs, as well as fatigue.


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