11.3 Blood Vessels

Question 1

3 Main Blood Vessels

Answer 1

Arteries
Veins
Capillaries

Question 2

Arteries

Answer 2

A blood vessels that carries blood away from the heart toward the body tissue
The main artery leaving the heart is called the aorta
The walls of arteries have three layers of tissue:
Outer layer of connective tissue
Middle layer of smooth muscle tissue
Smooth inner layer of epithelial cells
As blood pumps into the aorta, the diameter expands to account for extra pressure
When measuring blood pressure we feel a pulse when the diameter expands

Question 3

Arterioles

Answer 3

Arteries that branch off from the aorta further branch into small arteries called arterioles
Their size can be controlled by the nervous system
Vasodilation: an increase in diameter of arterioles, including blood flow to tissues, causing you to look flush or blush
Vasoconstriction: a decrease in diameter of arterioles that decrease the blood flow to tissues. This happens when you get cold.

Question 4

Capillaries

Answer 4

When the arterioles reach the tissues of the body, it branches into smaller blood vessels called capillaries
These are a network of blood vessels supplying oxygen and nutrients throughout the body
Network then reaches the venules
The capillary wall is so thin it allows for diffusion of substances through it
Examples: oxygen, nutrients go out, carbon dioxide and waste go in
Fluid exchange and blood flow
Difference in pressure and water concentration are responsible for the exchange of fluids in the capillary networks
Higher fluid pressure in the capillary (closer to the artery) causes water to diffuse from the blood into the tissue
No smooth muscle in the wall of capillaries, the diameter of capillaries cannot be controlled.
There are pre-capillary sphincter muscles where the arteriole branches into capillary, controlling blood flow.
Blood flow in capillaries
Capillaries are so small that blood cells move through them in a single file
Since they make up such a large area, the rate of blood flow decreases

Question 5

Venules and veins

Answer 5

Capillaries are attached to arterioles to venules, eventually merging to form veins
They carry deoxygenated blood back to the heart, waste to be exchanged
Their structure is different from arteries
The smooth muscle layers is not as thick
Walls are not as elastic, causing diameter to be greater
If the heart pumps blood into the body, what drives the blood back to the heart?
Blood to the heart
Larger veins have valves to ensure blood flows in one direction back to the heart
Skeletal muscles contract, squeezing the veins
The increase in pressure caused by the squeeze forces blood back up to the heart
If these valves do not function properly, blood accumulates in the veins and permanently stretches them out, called varicose veins
Blood pressure
Since blood exerts a force against the network of tubes in the circulatory system, it puts pressure on the walls
We measure this and call it blood pressure
The more blood found in our system, the higher the blood pressure
There is a certain extent before this becomes unsafe
We can measure blood pressure with a sphygmomanometer