РефератыИностранный языкCiCirculatory Systerm Essay Research Paper The circulatory

Circulatory Systerm Essay Research Paper The circulatory

Circulatory Systerm Essay, Research Paper


The circulatory system, which


functions in the rapid internal transport of substances


to and from cells.


Your body’s differentiated cells, which perform


specialized tasks, cannot fend for themselves. Different


types must interact in coordinated ways to maintain the


composition, volume, and temperature of a tissue fluid


surrounding them, the interstitial fluid. A circulating


connective tissue-blood-interacts with tissue fluid,


making continual deliveries and pickups that help keep


conditions tolerable for enzymes and other molecules


that carry out cell activities.


A muscular punip, the


heart, generates pressure that keeps blood flowing. Like


many anirnals, you have a closed circulatory system-


blood is confined within the continuously connected


walls of the heart and blood vessels.


The required slowdown proceeds a


capillary beds. At such beds, the flow fans out through


vast numbers of senall-diameter blood vessels called


capillaries.


In birds and mamntals, the


heart’s right half pumps oxygen-poor blood to the


lungs, where blood picks up oxygen and gives up car-


bon dioxide. The freshly oxygenated blood then flows


to the heart’s left half. This is the pulmonary circuit. By


contrast, in a systemic circuit, the Itft half of the heart


pumps oxygenated blood to all tissues where oxygen is


used and carbon dioxide forms.


an elaborate network of drainage vessels picks up


excess interstitial fluid and reclaimable solutes, then


returns them to the circulatory system. This network is


part of the lymphatic system.


27.2


Blood, a connective tissue, has multiple functions. It


transports oxygen, nutrients, and other solutes to cells.


The volume of blood depends on body size


average-size adult humans is about 6 to 8 percent


of the


body weight. That amounts to about four or five quarts.


Plasma,


red blood cells, vehite blood cells, and platelets are its


componentl


Plasma normally


accounts for 50 to 60 percent of the total blood volume.


Plasena Plasma, which is mostly water, functions as a


transport medium for blood cells and platelets. It also


serves as a solvent for ions and molecules, including


hundreds of different kinds of plasma proteins. Some of


the plasma proteins transport lipids and fat-soluble


vitamins through the body.


Erythrocytes, or red blood ceils, are


biconcave disks, like doughnixts with a squashed-in


center instead of a hole. A cell


count is the number of cells of a given type in a micro-


I liter of blood. The average number of red blood cells is


5.4 million in males and 4.8 million in females.


Leakocytes, or white brood cells,


( arise from stem cetls in bone marrow.


Each platelet only lasts five to nine days, but


hundreds of thousands are always circulating in blood.


27.4


if the volume of blood were to decrease by more than


30 percent, then circulatory shock would follow


and could lead to death. In a


defensive response called agglutination, proteins called


antibodies that are circulating in plasma act against the


foreign cells and cause them to clump.


Molecular variations in one kind of self marker on red


blood cells are analyzed in ABO blood typing.


27.5


In the human cardiovas-


cular system, a heart pumps blood into large-diameter


arteries. From there, blood flows into small, muscular


arterioies, which branch into the even smaller diameter


capillaries introduced earlier. Blood llows contintrously


from capiliaries into sma!! venules, then into large-


diameter veins that return blood to the heart.


The pulmonary circuit, a short loop, rapidly


oxygenates blood. It leads from the heart’s right half to


capillary beds in both lungs, then returns to the heart’s


left half. The systemic circuit is a longer loop. It starts at


the heart’s left half and the aorta (the main artery carry-


ing oxygenated blood away from the heart), branches to


all organs and tissues with metabolicaily active cells,


then converges into major veins that deliver oxygen-


poor blood to the heart’s right half.


27.6


the human heart beats about


2.5 billion times during a seventy-year life span, and


you know it must be a truly durable pump.


Each half of the heart has two chambers-an atriun


(plural, atria) and a ventricle.


The sequence of contraction and relaxation is a cardiac


cycle. .


About 1 percent of the cardiac muscle


cells don’t contract. Instead, they function as a cardiac


conduction system. These specialized cells initiate and


Propagate waves of excitation abottl seventy-five times


a minute.


The wave passes through the wall to


another eell body cluster, the AV node. This is the only


electrical bridge between atria and ventricies (which


connective tissue insuiates everys.vhere else). After the


AV node, conducting cells are arranged as a bundle i=


the partition between the heart’s two halves. The cells


then branch, and the branches detiver the excitatory


wave up the ventricle walls. The ventricles contract in


response with a forvisting movement, upward from the


heart’s apex, that ejects blood into the great arteries.


The SA node fires action potentials faster than the


rest of the system and serves as the cardiac pacemaker.


27.7


Blood pressure, the fluid pressure generated by heart


contractions, is highest in contracting ventricles. During


the time it takes for a given volume of blood to leave


and reenter the heart, pressure is still high in arteries,


then drops along the cirettit, and is lowest tn the relaxed


atria


the average restinn value stars fairly constant o-


few weeks, even months about 120/80 mm Hg. ‘


is vasodilation,


an increase in blood vessel diameter. If the resting value


falls, the brain makes the heart beat faster and contract


more forcefully. And it makes rings of arteriole muscles


contract. The result is vasoconstriction, a decrease in


blood vessel diameter.


Capillaries thread through nearly every tissue, and


at least one of thern is as ciose as 0.001 centimeter to


every living cell.


27.8


Cardiovascular disorders are the leading cause of death in


the United States. They affect at least 40 million people and


kill about a mmillion each year. The most common disorders


are called hypertension (sustained high blood pressure) and


atherosclerosis (progressive thickening of the arterial wall


and narrowing of the arteriai lumen).


Extensive research indicates the following


risk factors have roles in cardiovascular disorders:


1. Smoking


2. Genetic predisposition to heart failure


3. High level of cholesterol in the blood


4. High blood pressure


5. Obesity


6. Lack of regular exercise


7. Diabetes mellitus


8. Age (the oider you get, the greater the risk)


9- Gender (until age fifty, males are at much greater


risk than females)


Hypertension is called the “silentt killer”‘ because affected


persons may have no outavard symptoms. `


With arteriosclerosis, arteries thicken


and lose elasticity. 1


When


circulating in blood, cholesterol is bound to proteins as


low-density lipoproteins (LDLs). These bind to receptors on


celis throughout the body.


338


holt

Сохранить в соц. сетях:
Обсуждение:
comments powered by Disqus

Название реферата: Circulatory Systerm Essay Research Paper The circulatory

Слов:1274
Символов:9213
Размер:17.99 Кб.