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.

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