Blood vessels

11.3

Arteries

• The blood from the heart is carried through the body by a complex network of blood vessels

• Arteries take blood away from the heart • The main artery is the aorta• Aorta branches into other major arteries,

which take blood to different limbs and organs

Arteries

• Carotid artery takes blood to the brain • Brachial arteries take blood to the arms • Thoracic artery take blood to the thorax and

then into the hepatic, renal and gastric arteries for the liver, kidneys and stomach respectively

• Iliac artery takes blood to the lower limbs

Layers of the arteries

• The arteries have three layers of tissues:– An outer layer of connective tissues (stretches to

support blood flow)– A middle layer of smooth muscles (regulate blood

flow by altering vascular resistance by constriction and dilation)

– A smooth inner single layer of epithelial cells called the endothelium

Pulse

• When blood is forced through the artery by the contraction of the heart, the artery expands

• The expansion can be felt as the pulse • The artery has to be large, close to the skin

and in front of a bone • Do mini investigation page 488

Arterioles

• The major arteries diverge into minor arteries, and then into smaller vessels called arterioles

• Arterioles reach more deeply into the muscles and organs of the body

• Arterioles have smooth muscle in their wall, thus they can be controlled by the nervous system

Arterioles

• Signals from the nerves can regulate the diameter of the arterioles and control the blood flow to certain parts of the body– Vasodilation: an increase in the diameter of

arterioles that increases the blood flow to tissues – Vasoconstriction: a decrease in the diameter of

the arterioles that decreases the blood flow to tissues

Arterioles

• Vasoconstriction is an important feature of the circulatory system. Without it your body will need 200 L of blood to fill all the blood vessels

• The ability to control blood flow ensure that the 5 L of blood we have is distributed where it is needed

Capillaries • Arterioles diverge into capillary beds • Capillary beds contain 10 to 100 capillaries

that branch among the cells and tissues of the body

• https://www.youtube.com/watch?v=Q530H1WxtOw

Capillaries

• Capillaries are narrow diameter tubes • Can fit blood cells in a single-file lines • Supply oxygen and nutrients to every cell

throughout the body tissues • Carbon dioxide and other waste produced

during aerobic cellular respiration diffuse into the tissue fluid and then into the capillaries

Fluid exchange

• High fluid concentration on the arterial side cause water to diffuse from the blood to the tissue fluid

• On the venous side, high concentration of water in the tissue fluid causes water to move from the tissue fluid to the blood

• This maintains a balance between the fluids in the circulatory system and the tissues

Controlling blood flow

Page 489https://www.youtube.com/watch?v=yeX0uDpPBj4

Venules and veins

• The capillaries connect the arteries to the veins

• On one side we have the arteries and arterioles carrying oxygenated blood and nutrients to the tissues

• On the other side the capillaries merge into small vessels called venules that merge to form large vessels called veins

Venules and veins

• Venules and veins carry deoxygenated blood containing carbon dioxide and other waste products from the tissues to the heart

• The middle layer of smooth muscle is not as thick as the arteries

• The walls in the veins are not as elastic as the arteries

• Blood pressure in veins are lower than in arteries

Venules and veins

• Veins have valves to prevent the backflow of blood

• Because veins have to work against gravity to get blood back to the heart,

• contraction of skeletal muscle assists with the flow of blood back to the heart

• https://www.youtube.com/watch?v=HNuPWdfjDoc

Blood pressure

• https://www.youtube.com/watch?v=qWti317qb_w