The Circulatory System

Introduction

The circulatory system comprises of three parts: the Heart, blood vessels

and blood. Circulation is the transport of blood throughout the body. The

heart pumps blood throughout the body via the pipes called blood vessels.

There are two completely separate routes leading to and from the heart

known as the pulmonary and systemic circuits. The pulmonary circuit

carries oxygen-poor blood to the lungs where oxygen is added to the blood.

The systemic circuit takes oxygen-rich blood from the heart and delivers it

to the rest of the body.

Blood vessels consist of arteries veins and capillaries. Generally, arteries

carry oxygen-rich blood away from the heart and veins carry oxygen-poor

blood to the heart. In each circuit, arteries send blood to arterioles which

then deliver blood to capillaries. Exchange of nutrients, gases and waste

occur across the capillary walls. Venules merge into veins which drain

blood void of oxygen back to the heart.

Pattern of blood flow occurs:

Heart-arteries-arterioles-capillaries-venules-veins-heart

Objectives:

You should be able to:

1. identify the parts of blood on a slide

2. locate and identify the chambers of the heart

3. locate and identify the vessels connected to the heart

4. name and locate the valves of the heart

5. trace the path of blood through the heart

6. determine heartbeat by taking the pulse

7. distinguish among artery, capillary, and vein

The Blood

The blood is composed of two parts, cells and plasma. Plasma is the fluid

part of the cell composed mainly of water and some dissolved substances

like ions, hormones, enzymes and antibodies. There are three types of cells:

Red Blood cells, white blood cells, and platelets. Red Blood cells transport

oxygen, white blood cells fight infection and platelets are involved in blood

clotting.

a. erythrocytes

b. neutrophil

c. eosinophil

d. lymphocyte

Observation of a human blood slide

Observe a prepared blood smear slide. Red blood cells also known as

erythrocytes are more numerous. Erythrocytes are concave disks and do not

have a nucleus. They are pink in color.

Scattered among the red blood cells are the white blood cells also known as

leukocytes. Leukocytes are larger than red blood cells and contain a

nucleus. They are stained purple. There are five types of white blood cells.

Observe the figure below of the five different types.

The five types are:

1. neutrophils: leave the blood early in an inflammation to become

phagocytes, cells that eat bacteria.

2. eosinophils: phagocytes that are elevated during allergic reactions.

3. basophils: contain histamine which makes blood vessels leaky. It also

contains heparin that dilutes blood.

4. lymphocytes: cells that perform central functions for the immune

system

5. monocytes: leave the blood to form large phagocytes.

Try to locate atleast three out of the five leukocytes: neutrophils,

lymphocytes and eosinophils.

Platelets (thrombocytes)

Platelets are involved in blood clotting. Move the human blood slide slowly

and look for fragments of cells between the erythrocytes and leukocytes.

These are usually small purple-stained granules and are usually clumped

together.

BloodVessels:

Obtain a prepared slide of a cross section of an artery and vein

Arteries have thick walls compared to other blood vessels.

Make a drawing of the artery

Veins have valves to prevent backflow of blood away from the heart. Find

and examine the cross section of a vein. The vein has thinner walls than

arteries.

Draw the vein

Observe the differences in the structure of the artery and vein.

List the differences that you observe between the two.

The Heart

Normally, the heart beats over 100,000 times a day, pumping the blood

around the circulatory system of the body. Obtain a sheep heart and prepare

for dissection of the heart to observe the following parts. Proceed step by

step in the dissection and make sure to compare the parts to the heart figure

and heart model.

The outer covering of the heart is a tough, double-walled membrane called

the pericardium. This is a tough, protective covering of the heart. Carefully

remove the pericardium using scizzors of your dissecting kit.

The heart is divided into four chambers in mammals: two ventricles (bottom

half of heart) and two atria (top half of heart). The atria receive blood and

the ventricles pump it out of the heart.

Observe the following structures of the heart:

1. The right atrium: receives blood from the systemic circuit by the

superior and inferior vena cava

2. The right ventricle: blood enters from the right atrium

3. left atrium: receives blood from the pulmonary circuit by the

pulmonary veins.

4. left ventricle: receives blood from the left atrium. This is the harder

part of the heart. Also, it is part of the apex or pointed part of the

heart.

5. Aorta: largest artery that directs oxygenated blood throughout the

body

6. superior vena cava receives deoxygenated blood from the upper body

7. inferior vena cava receives deoxygenated blood from the lower body

8. pulmonary vein sends oxygenated blood to the left atrium

9. pulmonary artery sends deoxygenated blood from the right ventricle

Make a long incision through the right atrium in line with the superior vena

cava and continue throughout the heart so to separate it into two. Observe

the superior and inferior vena cava and notice how they enter the right

atrium. Observe the thick wall that separates the heart into two halves. This

wall is called the septum.

Observe the three rounded flaps of membranous tissue suspended into the

ventricle and held in place by tendinous cords. These flaps are called the

tricuspid valve which prevents backflow of blood into the right atrium.

Observe the left atrium and left ventricle. Using a probe follow the flow of

blood into the aorta. There are two tendinous cords that link the left atrium

and left ventricle called the bicuspid valve.

The mammalian heart is a double pump. It comprises of two circuits that do

not mix. The circuit from the heart to the lungs and back is the pulmonary

circuit. The circuit from the heart to the body tissues and back is the

systemic circuit. These circuits act concurrently and interdependently in that

no more blood can be sent through the pulmonary circuit than is delivered to

it by the systemic circuit.

Heartbeat

During a heartbeat, the atria contract and then the ventricles contract.

Usually there are two heart sounds with each heartbeat known as lub-dub.

Heartbeat at rest.

You will employ one method to determine the heartbeat at rest, by obtaining

a pulse rate. Position the fingers of one hand over the large artery near the

outer thumb side of your arm so the little finger is slightly beyond the wrist.

Count the pulse rate for 15 seconds and then multiply by 4. This is your

resting heartbeat per minute.

Record your heartbeat per minute __________________

Heartbeat after exercise

Run in place for 30 sec. Now record your heartbeat per minute using the

same procedure as above.

Record your heartbeat per minute after exercise _______________

Why is it advantageous for the heartbeat to increase during

exercise?_________________________________________________

Questions:

Suppose you are an erythrocyte in the right atrium of the heart. Describe

one trip through the human circulatory system, ending back where you

started.

Compare the structure and function of an artery, vein and capillary

Under what conditions in every day life would you expect the heartbeat to

increase?

Label the parts of the heart.

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