Structures of the Circulatory System
Main Functions:
1. Transportation of gases (respiratory), nutrient molecules
(digestive, waste (excretory)) materials and hormones (motor
system).
2. Regulates internal temperature.
3. Protection against blood loss from injury and against diseasecausing microbes or toxic substances introduced into the body.
Components of the Circulatory System
- The heart is about the size of a clenched fist.
- Located to the left of the chest.
o Pumps blood throughout the body.
o Keeps oxygen-rich blood separate from oxygen-poor
blood.
o Ensures one direction of blood flow.
- Cardiac muscle tissue are only found on the walls of the heart.
o The contractions are involuntary and rhythmical.
o Between contractions are slight relaxations that prevent
the heart from becoming tired.
- 4 chambers:
o Top 2 chambers are the atria.
o Bottom 2 chambers are the ventricles.
o Separated by the septum.
- 4 valves:
o Ensure blood flows in the correct direction.
o The atria and ventricles are separated from each other by
two atrioventricular valves.
o Tricuspid valve (3 flaps). Right side. (atrioventricular valve)
o Bicuspid valve (2 flaps). Left side. (atrioventricular valve)
o 2 semilunar valves (aortic and pulmonary)
Oxygen-poor blood
- Superior and Inferior vena cava (collects oxygen-poor blood)
open into the right atrium and flows into the right ventricle
and then out the pulmonary trunk before entering the right
and left pulmonary arteries (the only arteries in the circulatory
system that contain oxygen-poor blood).
- Blood now flows from the right and left pulmonary arteries
into the right and left lungs for gas exchange.
Oxygen-rich blood
- Flows from the pulmonary veins (the only veins in the
circulatory system that contain oxygenated blood) to the left
atrium which pumps blood into the left ventricle and leaves
the heart (to go to the body tissues) through the aorta.
Arteries (figure 8.4 page 271)
- Carry oxygen-rich blood away from the heart.
- Have elastic walls, which expands as blood comes through
during the contractions of the ventricles. They snap back
during relaxation of the ventricles.
Veins (figure 8.5 page 271)
- Carry oxygen-poor blood toward the heart.
- Are not as elastic as arteries. Have thinner walls.
- Cannot contract to help move the blood back to the heart.
Only muscle contractions keep the blood flowing to the heart.
- Have one way valves that prevents the blood from flowing
backwards - important when the blood is going against gravity.
Capillaries
- Connects the arteries and the
veins.
- Where gases, nutrients and other
materials are transferred to the
tissue cells and move into the
blood.
- Blood comes from the arteries and after the oxygen is used up,
leaves in the veins.
- Smallest blood vessels.
Assignment: p.269-272 #’s 1-8