biology of the heart and blood vessels borga manual 2

8/6/2019 Biology of the Heart and Blood Vessels Borga Manual 2

1/8


2/8

Borgastatin

M.Hanafy

-Some veins, particularly veins in the legs, have valves in them, to prevent blood

from flowing backward.

- When these valves leak, the backflow of blood can cause the veins to stretch

and become elongated and convoluted (tortuous). Stretched, tortuous veins nearthe body's surface are called varicose veins .

Blood Vessels: Circulating the Blood

y Blood travels from the heart in arteries, which branch into

smaller and smaller vessels, eventually becoming arterioles.

y Arterioles connect with even smaller blood vessels called

capillaries. Through the thin walls of the capillaries, oxygen andnutrients pass from blood into tissues, and waste products pass

from tissues into blood.

y From the capillaries, blood passes into venules, then into veins

to return to the heart.


3/8

Borgastatin

M.Hanafy

y Arteries and arterioles have relatively thick muscular walls

because blood pressure in them is high and because they must

adjust their diameter to maintain blood pressure and to control

blood flow.

y Veins and venules have much thinner, less muscular walls than

arteries and arterioles, largely because the pressure in veins

and venules is much lower; veins may dilate to accommodate

increased blood volume.

Effects ofAging-As people age, the heart tends to enlarge slightly, developing thicker walls and

slightly larger chambers.

-The increase in size is mainly due to an increase in the size of individual heartmuscle cells.

-During rest, the older heart functions in almost the same way as a younger heart

except the heart rate is slightly lower.

-However, during exercise, the older heart cannot increase the amount of blood

pumped out as much as a younger heart can.

-The walls of the arteries and arterioles become thicker, and the space within the

arteries expands slightly.

- Elastic tissue within the walls of the arteries and arterioles is lost. Together,

these changes make the vessels stiffer and less resilient.

-Because arteries and arterioles become less elastic as people age, they cannot

relax as quickly during the rhythmic pumping of the heart.

- As a result, blood pressure increases more when the heart contracts (during

systole)sometimes above normalthan it does in younger people.

-Abnormally high blood pressure during systole with normal blood pressure

during diastole is very common among older people; this disorder is called

isolated systolic hypertension


4/8

Borgastatin

M.Hanafy

-Many of the effects of aging on the heart and blood vessels can be reduced by

regular exercise.

-Exercise helps people maintain cardiovascular fitness as well as muscular

fitness as they age. Exercise is beneficial regardless of the age at which it isstarted.

Heart-The heart, a hollow muscular organ, is located in the center of the chest.

-The right and left sides of the heart each have an upper chamber (atrium),

which collects blood and pumps it into a lower chamber (ventricle), which pumps

blood out.

-To ensure that blood flows in only one direction, each ventricle has an "in" (inlet)

valve and an "out" (outlet) valve. In the left ventricle, the inlet valve is the mitral

valve, and the outlet valve is the aortic valve.

-In the right ventricle, the inlet valve is the tricuspid valve, and the outlet valve is

the pulmonary (pulmonic) valve.

-Each valve consists of flaps (cusps or leaflets), which open and close like one-

way swinging doors.

-The mitral valve has two cusps; the others (tricuspid, aortic, and pulmonary)

have three.

- The large inlet valves (mitral and tricuspid) have tethersconsisting of the

papillary muscles and cords of tissuewhich prevent the valves from swinging

backward into the atria.

- If a papillary muscle is damaged (for example, by a heart attack), the valve may

then swing backwards and start leaking.

- If a valve opening is narrowed, blood flow through the valve is reduced.

-A valve may have both problems.

-The heartbeats are evidence that the heart is pumping.


5/8

Borgastatin

M.Hanafy

-The first sound(the lub of lub-dub) is the sound of the mitral and tricuspid valves

closing.

-The second sound(the dub) is the sound of the aortic and pulmonary valves

closing.

Each heartbeat has two parts:diastole and systole.

y During diastole, the ventricles relax and fill with blood; then the atria

contract, forcing more blood into the ventricles.

y During systole, the ventricles contract and pump blood, and the atria relax

and begin filling with blood again.

FUNCTIONOFTHEHEARTy The heart's only function is to pump blood.

y The right side of the heart pumps blood to the lungs, where oxygen is

added to the blood and carbon dioxide is removed from it.

y The left side pumps blood to the rest of the body, where oxygen and

nutrients are delivered to tissues and waste products (such as carbon

dioxide) are transferred to the blood for removal by other organs (such as

the lungs and kidneys)

A Look Into the Heart


6/8

Borgastatin

M.Hanafy

Blood travels the following circuit:

y Blood from the body, which is depleted of oxygen and laden with carbon

dioxide, flows through the two largest veins (the venae cavae) into the

right atrium.

y When the right ventricle relaxes, blood in the right atrium pours through

the tricuspid valve into the right ventricle.

y When the right ventricle is nearly full, the right atrium contracts, propelling

additional blood into the right ventricle, which then contracts.

y This contraction propels blood through the pulmonary valve into the

pulmonary arteries, which supply the lungs.

y In the lungs, blood flows through the tiny capillaries that surround the air

sacs. Here, the blood absorbs oxygen and gives up carbon dioxide, which

is then exhaled.

y Blood from the lungs, which is now oxygen-rich, flows through the

pulmonary veins into the left atrium. When the left ventricle relaxes, the

blood in the left atrium pours through the mitral valve into the left ventricle.

y When the left ventricle is nearly full, the left atrium contracts, propelling

additional blood into the left ventricle, which then contracts.

(In older people, the left ventricle does not fill as well before the left atrium

contracts, making this contraction of the left atrium especially important.)

y The contraction of the left ventricle propels blood through the aortic valve

into the aorta, the largest artery in the body.

y This blood carries oxygen to all of the body except to the lungs.

y The circuit between the right side of the heart, the lungs, and the left

atrium is called the pulmonary circulation.

y The circuit between the left side of the heart, most of the body, and the

right atrium is called the systemic circulation.


7/8

Borgastatin

M.Hanafy

BLOOD SUPPLYOFTHEHEART

-Like all organs, the heart needs a constant supply of oxygen-rich blood.

- A system of arteries and veins called the coronary circulation supplies the heart

muscle (myocardium) with oxygen-rich blood and then returns oxygen-depleted

blood to the right atrium.

-The right coronary artery and the left coronary artery branch off the aorta (just

after it leaves the heart) to deliver oxygen-rich blood to the heart muscle.

-These two arteries branch into other arteries, including the circumflex artery, that

also supply blood to the heart.

-The cardiac veins collect blood from the heart muscle and empty it into a large

vein on the back surface of the heart called the coronary sinus, which returns the

blood to the right atrium.

-Because of the great pressure exerted in the heart as it contracts, most blood

flows through the coronary circulation only while the heart is relaxing between

beats (during diastole).

Supplying the Heart With Blood


8/8

Borgastatin

M.Hanafy

REGULATIONOFTHEHEART

-The contraction of the muscle fibers in the heart is very organized and highly

controlled.

-Rhythmic electrical impulses (discharges) flow through the heart in a precise

manner along distinct pathways and at a controlled speed.

- The impulses originate in the heart's pacemaker (the sinus or sinoatrial nodea

small mass of tissue in the wall of the right atrium), which generates a tiny

electrical current.

-The rate at which the pacemaker sends out its impulses (and thus governs the

heart rate) is determined by two opposing systemsone to speed the heart rateup (the sympathetic division of the nervous system) and one to slow it down (the

parasympathetic division

-The sympathetic division works through a network of nerves called the

sympathetic plexus and through the hormones epinephrine (adrenaline) and

norepinephrine (noradrenaline), which are released by the adrenal glands and

the nerve endings.

-The parasympathetic division works through a single nervethe vagus nerve

which releases the neurotransmitter acetylcholine.

biology of the heart and blood vessels borga manual 2

Documents