Blood Vessels and the Mammalian Heart

Types of Blood Vessels• Arteries – carry blood away from the

heart• Capillaries – smallest blood vessels

– Site of exchange between blood and tissues

• Veins – carry blood toward the heart

Blood Vessel Structure• Artery: strong walls to withstand

high pressure. Middle layers made of muscle fibres and connective tissue

• Arteriole: middle layers made of elastic fibres and smooth muscle

• Capillary: composed of a single layer of cells

• Venule: walls of smooth muscle• Vein: thinner middle layers with

one-way valves

Structure of Blood Vessels

Structure of Blood Vessels

Mechanisms to Counteract Low Venous Pressure

• There are valves in some veins to stop backflow

• Skeletal muscle pump– Muscles press against

thin-walled veins

Atherosclerosis• Video

The Pulmonary and Systemic Circuits

Figure 18.1

The Mammalian Heart

• Pulmonary circuit: carries blood to and from the lungs

• Systemic circuit: carries blood to and from the body

Heart Chambers

Figure 18.5b

The Mammalian Heart• The four chambered heart contains two

upper chambers called atria, and two lower chambers called ventricles

• The atria pump blood into the ventricles, then from there is pumped out to the body

• The chamber alternately contract (pumping blood) and relax (filling with blood) in a rhythmic cycle called the cardiac cycle.

Heart Chambers

Figure 18.5e

Blood Flow Through the Heart

Interior Valves• Four valves in the heart prevent backflow of the

blood• Atrioventricular (AV) Valves: located between

each atrium and ventricle are forced closed during ventricle contraction (also known as tricuspid valves)

• Semilunar valves: located at the top of the aorta (exit of left ventricle) and pulmonary artery (exit of right ventricle) are forced open during ventricle contraction and close during relaxation of ventricles (also known as bicuspid valves)