Respiratory and Circulatory Systems

Chapter 30

THE HEART AND CIRCULATION 30.3

Key Concept

• The heart is a muscular pump that moves the blood through two pathways

Heart Structure

• Made of cardiac tissue

• Efficient pump

• Works continuously without tiring

NORMAL HUMAN HEART

Heart Structure

• Four chambers: – 2 atria – 2 ventricles

• Valves prevent the backflow of blood

• Muscles squeeze the chambers in a powerful pumping action

Heart Beat

• Consists of 2 contractions: – SA node, or

pacemaker, stimulates atria to contract

– AV node stimulates ventricles to contract

Blood Flow

• Blood flows through the heart in a specific pathway

Blood Flow

• Oxygen-poor blood enters right atrium, then right ventricle

• Right ventricle pumps blood to lungs

• Oxygen-rich blood from lungs enters left atrium, then left ventricle

• Left ventricle pumps blood to body

Pulmonary Circulation

• Occurs between the heart and lungs – oxygen-poor blood

enters lungs – excess carbon dioxide

and water expelled

– blood picks up oxygen – oxygen-rich blood

returns to heart

Systemic Circulation

• Occurs between the heart and the rest of the body – oxygen-rich blood goes to

organs, extremities

– oxygen-poor blood returns to heart

• The two pathways help maintain a stable body temperature

BLOOD VESSELS AND TRANSPORT 30.4

Key Concept

• The circulatory system transports materials throughout the body

Blood Vessels

• Arteries carry blood away from the heart – blood under great

pressure

– thicker, more muscular walls

Blood Vessels

• Veins carry blood back to the heart – blood under less pressure

– thinner walls, larger diameter

– valves prevent backflow

Blood Vessels

• Capillaries move blood between veins, arteries, and cells.

Blood Pressure

• A measure of the force of blood pushing against artery walls – systolic pressure: left ventricle contracts

– diastolic pressure: left ventricle relaxes

• High blood pressure can precede a heart attack or stroke

Blood Pressure

Circulatory Disease

• Some choices lead to an increased risk of circulatory diseases. – smoking – long-term stress – excessive weight – lack of exercise – diet low in fruits

and vegetables, high in saturated fats

Circulatory Disease

• Affects mainly the heart and arteries – artery walls become thick and inflexible

– plaque blocks blood flow in arteries