Circulatory system

Premedical 26

The circulatory system carries blood and dissolved substances to and from different places in the body.

The heart has the job of pumping these things around the body.

The heart pumps blood and substances around

the body in tubes called blood vessels.

How does this system work?

lungs

head & arms

liver

digestive system

kidneys

legs

pulmonary artery

aorta

pulmonary vein

main vein

Left Right

Lungs

Body cells

double circulatory systemlymphatic system

the right side of the

system

deals with

deoxygenated

blood.

the left side of the

system

deals with

oxygenated

blood.

The Heart

These are arteries. They carry blood away from the heart.

This is a vein. It brings blood from the body, except the lungs.

Coronary arteries, the hearts own blood supply

The heart has four chambers

2 atria

2 ventricles

Thoracic cavity

between the lungs and is contained in the

pericardial sac

• Epicardium – outer layer of heart wall

• Endocardium – inner layer that consists of

endothelial cells, which line the heart, covers the

heart valves, and lines the blood vessels.

• Myocardium – middle layer composed of cardiac

muscle.

The Heart

left ventricle

left atriumright atrium

right ventricle

valve

Artery from lungs

artery to head and bodyvein to lungs

vein from head and body

valve

The AV valve on the right side of the heart is called the

tricuspid valve because it has three leaflets (cusps).

The AV valve on the left side of the heart is called the

bicuspid valve (or mitral valve) because it has two

leaflets.

the pulmonary valve

the aortic valve

How does the heart work?

blood from the body

blood from the lungs

The heart beat begins when the

heart muscles relax and blood

flows into the atria.

STEP ONE

The atria then contract and

the valves open to allow blood

into the ventricles.

How does the heart work?

STEP TWO

How does the heart work?

The valves close to stop blood

flowing backwards.

The ventricles contract forcing

the blood to leave the heart.

At the same time, the atria are

relaxing and once again filling with

blood.

The cycle then repeats itself.

STEP THREE

Blood pressure

is a force exerted by circulating blood on the walls of blood

vessels.

During each heartbeat, BP varies between a maximum

(systolic) and a minimum (diastolic) pressure.

Systole is a phase where the myocardium is contracting in a

coordinated manner in response to an endogenous electrical

stimulus

Diastole is the period of time when the heart fills with blood

after systole.

Classification of blood pressure for adults

Category systolic, mmHg diastolic, mmHg

Hypotension < 90 < 60   

Normal  90 – 120 and 60 – 80   

Prehypertension 121 – 139 or 81 – 89  

Stage 1 Hypertension 140 – 159 or 90 – 99  

Stage 2 Hypertension ≥ 160 or ≥ 100  

There are 3 types of blood vessels

a. ARTERY

b. VEIN

c. CAPILLARY

The ARTERY

thick muscle and

elastic fibres

the elastic fibres allow

the artery to stretch

under pressure

the thick muscle can

contract to push the

blood along.

The VEIN

thin muscle and elastic fibres

veins have valves which act to stop the blood from going in the wrong direction.

body muscles surround the veins so that when they contract to move the body, they also squeeze the veins and push the blood along the vessel.

The CAPILLARY

the wall of a capillaryis only one cell thick

they exchange materials between the blood and other body cells.

The exchange of materials between the blood and the body can only occur through capillaries.

artery vein

capillariesbody cell

The CAPILLARYA collection of capillaries is known as a capillary bedcapillary bed.

The semi-permeable membrane

of capillary walls allows

nutrients, oxygen, and water

to diffuse from the blood to the tissues.

Waste products, like

carbon dioxide, diffuse from the tissues

into the blood.

• Veins have valves

prevent the blood from reversing flow

the return flow of blood to the heart when blood

pressure is low

• the aorta, the largest artery in the body

• blood from the stomach, pancreas, small

intestine, and spleen goes through the liver for

filtration

This portion of the systemic system is known as the

hepatic portal system.

The gastric vein (stomach), splenic vein (spleen),

pancreatic vein (pancreas), and mesenteric veins

(small intestines) empty into the portal vein that

carries the blood to the liver.

the hepatic vein

carries blood to the inferior (caudal) vena cava

The lymphatic system is part of the immune system and acts as a

secondary (accessory) circulatory system.

• remove excess fluids from body tissues,

• absorb fatty acid and transport fat to circulatory

system, and

• produce immune cells (lymphocytes, monocytes,

and plasma cells).

Flow of Blood & Lymph Within Tissue

As the collecting lymph vessel accumulates lymph from

more and more lymph capillaries in its course, it becomes

larger and is called the afferent lymph vessel as

it enters a lymph node. Here the lymph percolates through

the lymph node tissue and is removed by the efferent

lymph vessel. An efferent lymph vessel may directly

drain into one of the (right or thoracic) lymph ducts

Both

the lymph ducts

return the lymph to

the blood stream

by emptying into

the subclavian

veins

lymphoid tissue:

spleen, thymus,

bone marrow and the

lymphoid tissue

associated with the

digestive system.

Lymph nodes filter

foreign substances, such

as bacteria and cancer

cells, before it is re-

entered into the blood

system through the larger

veins.

Lymph nodes act as the

body’s first defense

against infection.

Photo from U. S. Federal Government courtesy of Wikipedia.

lymph node has a fibrous outer covering (capsule), a cortex, and a medulla

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