CirculationVCE BIOLOGY – UNIT 1

The HeartThe biological pump

UNoxygenated blood enters the

atrium on the right side of the heart.

Unoxygenated blood comes in from the

top of the body through the

superior vena cava.

Unoxygenated blood comes in from the lower body though

the inferior vena cava.

While the unoxygenated blood is in the

right atrium, the tricuspid valve is closed to keep the blood from

flowing down to the ventricle.

The atrium

contracts and the tricuspid

valve opens,

forcing the blood

down into the

ventricle.

The tricuspid valve closes again so that blood cannot move back up

into the atrium.

The ventricle contracts. This

forces the unoxygenated blood through the pulmonary valve and into the pulmonary

arteries.

The right pulmonary artery takes the

unoxygenated blood to the right lung.

The left pulmonary artery takes the

unoxygenated blood to the left lung.

THE PULMONARY ARTERIES ARE THE

ONLY ARTERIES THAT CARRY

UNOXYGENEATED BLOOD.

http://www.webmd.com/hw/health_guide_atoz/tp10237.asp

In the lungs, the carbon

dioxide in the blood diffuses

into the alveoli.

The oxygen in the lungs

diffuses into the blood.

This is called gas exchange.

Oxygenated blood from the lungs

enters the heart through the left

atrium.

The mitral valve is closed to keep the blood from going into the ventricle.

Oxygenated blood from the right lung returns to the heart

through the right pulmonary vein.

Oxygenated blood from the left lung

returns to the heart through the left pulmonary vein.

THE PULMONARY VEINS ARE THE ONLY VEINS THAT CARRY

OXYGENATED BLOOD.

The left atrium contracts. This

forces the oxygenated

blood through the mitral valve

into the right ventricle.

The mitral valve closes again. This keeps the

oxygenated blood from

moving back up into the

atrium.

Oxygenated blood is forced into the aorta

to be carried to the rest of the

body.

Oxygenated blood is carried to all

body cells where oxygen diffuses

into the cells and carbon dioxide

diffuses into the blood.

Blood carrying carbon dioxide

then returns to the heart.

And the cycle begins

again.

Blood Flow: Summary

Blood Vessels

Blood Vessels: Arteries, Veins, and CapillariesArteries and arterioles have a layer of smooth muscle tissue which allows them to contract (vasoconstrict) and expand (vasodilate), altering their diameter and thus blood flow.

Walls of arteries and arterioles have many elastic fibers enabling them to withstand high pressures.

Artery and Vein

Artery

VeinNote the much thinner walls in

veins.

Components of Blood

Haemoglobin

Chemical – protein

Binds to oxygen to carry oxygen around the body. When oxygen is bound to it, it is called oxyhaemoglobin.

Types of Circulatory System

Circulatory Systems

• Two types of circulatory system are found:Open Circulatory Systems Closed Circulatory Systems

For larger or more active animals, some form of more efficient circulatory system is necessary for internal transport.

Open Circulatory System

• Hemolymph leaves the heart in short, branched arteries that open up into large spaces called sinuses.

• Hemolymph percolates around organs, directly bathing the cells.

• Hemolymph then returns to the heart directly or through short veins.

Open Circulatory System• Advantage - Exchange of materials is direct

between the hemolymph and tissues. There is no diffusion barrier.

• Disadvantage - Little fine control over distribution of the hemolymph to body regions. No mechanism for reducing flow to a specific part of an organ.

Open Circulatory System

• Open circulatory systems tend to be found in more inactive animals.

• Most molluscs have an open system, but the highly active cephalopods (squid and octopus) have evolved a closed system.

• Insects have circumvented limitation of their open system by their tracheal system for oxygen supply.

Closed Circulatory System• The blood is contained

within a completely closed system of vessels.

• Vessels form a closed loop, usually with some sort of pumping organ like a heart or contractile vessels.

• Vessels branch into smaller and smaller tubes that penetrate among the cells of tissues.

Closed Circulatory System

• Fine-scale control over the distribution of blood to different body regions is possible.

• Muscular walls of vessels can constrict and dilate to vary the amount of flow through specific vessels.

• Blood pressures are fairly high and the circulation can be vigorous.

Advantages:

Human Circulatory SystemA Closed Circulatory System

lungs

head & arms

liver

digestive system

kidneys

legs

pulmonary artery

aorta

pulmonary vein

main vein

Left Right

How does this system work?

Circulatory System

Lungs

Body cells

Our circulatory system is a double circulatory system.

This means it has two parts parts.

the right side of

the system

deals with

deoxygenated

blood.

the left side of

the system

deals with

oxygenated

blood.