CHAPTER 37 – THE CIRCULATORY AND RESPIRATORY SYSTEMS



CHAPTER 37 – THE CIRCULATORY AND RESPIRATORY SYSTEMS

THE CIRCULATORY SYSTEM

All organisms move substances internally from one place to another. Some organisms rely on diffusion for this movement; humans cannot because we are too large & complex. We require a circulatory system for the movement of substances (O2, CO2, nutrients, & wastes) through the body. Humans have a closed circulatory system, which means blood is enclosed in vessels. The human circulatory system has three components: the heart, the blood vessels, and the blood.

I. THE HEART

The function of the heart is to keep the blood moving constantly in the body.

The heart is a large organ made of cardiac muscle cells that have a high

number of mitochondria. Humans (plus other mammals and birds) have a 4-

chambered heart. The heart is divided into a right and left side with two

chambers making up each side. The two sides are divided by a septum.

[pic]

A. Structure

1. Membranes – There are 3 layers of tissue that surround the heart.

a. Pericardium – Outermost layer; membrane composed of

connective tissue that surrounds and protects the heart.

[pic][pic]

b. Myocardium – Middle layer; muscle tissue that forms the four

chambers of the heart. Cardiac muscle cells are striated and

interconnected to produce strong, powerful contractions.

[pic][pic]

c. Endocardium – Innermost membrane that lines the chambers,

covers the valves, and continues into the vessels. Composed of

smooth, epithelial tissue to prevent blood clotting.

[pic]

2. Chambers

a. Atria (atrium =singular) Upper chambers of the heart that receive

blood. Walls are thinner and less elastic than ventricles.

b. Ventricles – Lower chambers of the heart that pump blood to the

lungs and body. Have thick, elastic walls, especially the left

ventricle because it pumps blood out to the body.

3. Valves – Flaps of epithelial tissue reinforced with connective tissue

that keep blood flowing in one direction and increase the pumping

efficiency of the heart.

[pic]

a. Atrio-Ventricular Valves: between the atria & ventricles; attached by chordae tendineae to papillary muscles; these valves prevent the backflow of blood into the atria when the ventricles are pumping the blood away from the heart (systole).

• Tricuspid Valve – between the RA & RV

• Bicuspid (Mitral) Valve – between the LA & LV

[pic]

b. Semi-Lunar Valves: between the ventricles and the vessels that

lead away from the heart (aorta & pulmonary arteries); prevent the

reflux of blood into the ventricles when the ventricles are relaxing

and the atria are contracting (diastole).

• Pulmonary Valve – between the RV and the pulmonary artery

[pic]

[pic]

• Aortic Valve – between the LV and the aorta

[pic]

B. Types of Circulation

1. Systemic – The flow of blood from the left side of the heart to the body

and back to the heart. The main artery involved is the aorta; main veins

involved are the superior and inferior vena cava.

[pic]

2. Pulmonary – The flow of blood from the right side of the heart to the

lungs and back to the heart. Pulmonary arteries carry O2 poor blood

from the heart to the lungs; pulmonary veins carry O2 rich blood from

the lungs to the heart.

[pic]

[pic]

3. Coronary – since the heart is a major organ, it needs its own supply of O2

rich blood. This is referred to as coronary circulation. The coronary

arteries are the first two branches of the aorta. These arteries branch

into capillaries that circulate oxygenated blood to the myocardium for the

heart to use, then the coronary veins return the deoxygenated blood to the

right atrium.

[pic]

THE HEART

[pic]

C. The Heartbeat

1. Contraction

Although the rate and force of contraction can be changed by the medulla

oblongata, the heart generates and maintains its own beat. The

heartbeat is divided into systole, which is when the ventricles are

contracting to push blood away from the heart; and diastole, which is

when the ventricles are relaxed & the atria are contracting to push

blood from the atria into the ventricles.

• The beat originates in the Sinoatrial Node (SA node or pacemaker). The SA node is a cluster of cardiac muscle cells located in the top part of the right atrium that do not contain sarcomeres. These cells are responsible for initiating an electrical impulse that triggers the contraction of cardiac muscle cells of the right and left atria. (Remember : contraction means depolarization of the cells, followed by the release of Ca+ ions from the ER, & then the formation of cross-bridges between myosin and actin)

[pic]

2. The Pulse

The powerful contraction in the left ventricle causes a surge of blood to

leave through the aorta. From there it travels to the arteries leading to the

rest of the body. This is known as a pulse.

[pic]

II. THE BLOOD VESSELS

Blood vessels are composed of connective tissue for strength, smooth muscle

tissue to facilitate blood flow, and they are lined with epithelial tissue for

smoothness.

A. Types – There are three types of blood vessels:

1. Arteries – Carry blood Away from the heart. Arteries have thick, elastic

walls to withstand the pressure of spurts of blood from contraction of the

heart. Arteries are deeply buried in skin to protect them from injury; it is

hard to staunch blood flow due to pressure of blood leaving left ventricle.

Arteries branch into arterioles and then to capillaries. Arteries carry blood

that is high in oxygen and low in carbon dioxide, except for the

pulmonary artery.

[pic][pic]

2. Veins – Carry blood to the heart. Veins have thinner, less elastic walls.

They contain valves to keep blood flowing in one direction. Valves are

especially important in the legs because blood flows against gravity.

Veins branch into venules which lead to the other side of the capillary

bed. Veins carry blood low in oxygen and high in carbondioxide

except for the pulmonary vein. [pic]

[pic]

3. Capillaries – Network in which O2 , glucose, & other nutrients are

exchanged with CO2 and other wastes. Capillaries are only one-cell

thick, so red blood cells must flow through one-by-one. This allows time

for diffusion to occur.

CAPILLARY NETWORK [pic]

[pic]

B. Blood Pressure – Measurement of pressure exerted on the walls of

arteries. Systolic pressure is the pressure on the artery walls when the

ventricles contract and diastolic pressure is the pressure when the

ventricles relax (atria contract). Written as a fraction (systolic

pressure / diastolic pressure. Average Range = 100 – 140 / 60 – 90.

[pic][pic]

III. THE BLOOD

Blood is classified as connective tissue with a matrix of plasma. Plasma is

the liquid that makes up approximately 55% of blood. Plasma is 90% water,

the other 10% is made up of proteins, ions, vitamin K, lipids, hormones, etc.

[pic]

A. Erythrocytes (RBC’s)

Function is to deliver O2 to all body cells. Most numerous cells in blood,

they are doughnut-shaped cells that lose their nuclei as they mature in the

red marrow. This adaptation allows them to squeeze through tiny

capillaries and provides more area for oxygen transport. Red blood cells

contain hemoglobin, an iron- containing protein that binds oxygen.

Erythrocytes circulate every 120 days & are destroyed in the spleen.

[pic][pic]

B. Leukocytes (WBC’s)

Larger and fewer in number than RBC’s. Their primary function is to fight

infection by engulfing pathogens or marking them for destruction. Some

WBC’s are able to leave the blood vessels.

[pic][pic]

C. Thrombocytes (platelets)

Cell fragments that break off from large cells produced in the red marrow.

Like RBC’s, they lack a nucleus, but platelets are smaller than red blood

cells. Platelets begin the clotting process by sticking together to form a plug

when they come in contact with a rough surface. The platelets that make up

the plug release a series of proteins called fibrinogens (clotting factors) which

trigger a series of chemical reactions to produce a clot. Thrombocytes live

about 10 days.

[pic][pic]

D. Blood Types – There are ID tags on the surface of RBC’s that are composed

of carbohydrates and proteins called antigens. The two antigens that

determine human blood types are A and B. The presence or absence of

these antigens is an inherited trait that has 3 alleles and shows co-

dominance. The A & B antigens on RBC’s are very important because an

individual is also born with antibodies dissolved in the plasma to any foreign

antigen(s). An antibody attaches to a foreign particle and marks it for

destruction.

[pic]

III. DISEASES OF THE CIRCULATORY SYSTEM

A. Atherosclerosis – Plaques of cholesterol build up on the wall of arteries

(most commonly, coronary arteries). Restricts blood flow and creates a

rough surface that may trigger clot formation. [pic][pic]

B. Arteriosclerosis – Also known as “hardening of the arteries”. Artery walls

lose their elasticity, become weakened and more susceptible to rupture.

C. Heart Attack (Myocardial Infarction)– Caused by blockage of coronary

artery which cuts off blood flow to the myocardium of the heart. Cells die

due to lack of O2.

[pic]

D. Anemia – Caused by either a deficiency of red blood cells or hemoglobin

in RBC’s. Both result in less O2 available for cells and a lack of energy due to

decreased ATP production.

[pic]

E. Hypertension – High blood pressure. Called the “silent killer” because it may

be fatal before noticeable symptoms appear. Risk of hypertension is

increased by smoking, obesity, high salt intake, lack of exercise.

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