Circulatory System

Circulatory system consists of:

• Heart• Blood Vessels• Blood

Closed System in Humans

Arteries, Arterioles, Capillaries, Venules, Veins

Heart

Artery

ArterioleCapillaryVenule

Vein

Portal Vein

Has capillaries at both ends

E.g. hepatic portal vein

Carries:

• glucose• amino acids• minerals

from intestine to liver

Structure of Arteries, Veins and Capillaries

ARTERY VEIN CAPILLARY

Small lumen

Large lumen

Thick muscular

wall

Thinwall Very thin

wall

Veins have Valves

Artery Vein CapillaryLumen Small lumen Large lumen Very tiny vessel

Walls Thick muscular walls Thin muscular walls Walls only one cell thick

Valves Does not contain valves

Contains valves to prevent backflow of blood

Does not contain valves

Direction of blood flow

Carries blood away from heart

Carries blood into heart

Carries blood from arterioles to venules

Pressure High blood pressure Low blood pressure Medium pressure

Oxygen Usually carries blood rich in oxygen, apart from pulmonary artery

Usually carries blood low in oxygen, apart from pulmonary vein

Oxygen passes out of capillary into body cells

Double Circulatory

System

Heart StructureAorta

Pulmonary veinLeft Atrium

Left ventricle

Semilunar valve

Right ventricle

SeptumCardiac Muscle

Tricuspid valve

Right Atrium

Vena cava

Pulmonary artery

Valves

Human Circulatory System

Structure of Human

CirculatorySystem

Heart

• Located in thoracic cavity: area inside rib cage

• Contains strong double pump

• Made of a special muscle which does not tire

• Coronary artery supplies heart itself with blood

Cardiac Cycle

Systole and Diastole• Diastole: the filling phase of the heart with

blood (the heart is relaxed)

• Systole: the emptying phase when the heart muscles contract

Pacemakers

Pacemakers• Heartbeat can occur independently of the brain• Controlled by a small bundle of specialised

tissue called pacemakers (SA and AV nodes) in the right atrium

• Sinoatrial (SA) node sends out regular electrical impulses causing the atria to contract

• It also stimulates the atrio-ventricular (AV) node• The AV node then stimulates the ventricles to

contract

What affects the pacemakers?

• The pacemaker itself controls the heartbeat

• Average rate = 75 beats per minute

• But signals from the brain (via nerves) and hormones can change the rate at which it operates

Factors that can increase the heart rate include:

• Exercise• Temperature• Emotions and shock

Factors that decrease the heart rate include:

• Relaxation• Sleep• Alcohol

Pulse

What causes a pulse?

The expansion of an artery due to the pumping of the heart

What is blood pressure?• Recall : Pressure = Force/area

• Blood pressure is the force exerted by blood on the wall of a blood vessel

Effects of External Factors on Heart Rate

To maintain a healthy heart• Don’t smoke• Eat less fat• Eat less salt• Exercise regularly• Avoid excess stress