circulatory system (incomplete)

Circulation in Animals

• Double circulation in mammals depends on the anatomy and pumping cycle of the mammal's heart
• Pulmonary and system circuit operate simultaneously
• - Two ventricles pump almost in unison
• - While a certain volume of blood travel to the pulmonary circuit and the rest of the blood flows in the systemic circuit

How the circulatory system works (general)

• The right ventricle pumps blood to the lungs via the pulmonary arteries
• Blood loads O2 and unloads CO2 as it flows through the capillary beds in the left and right lungs
• Oxygen rich blood blood returns from the lungs via the pulmonary veins to the left atrium of the heart
• Blood is pumped out of the heart via the aortic artery to delivers O2 to the rest of the tissues in the body

Slide 3

• Left ventricle pumps oxygen rich blood to the body tissues through the systemic circulation
• Blood leaves the left ventricle via the aorta, which conveys blood to arteries leading throughout the body
• The first branches from the aorta are the coronary arteries, which supply blood to the heart muscle.
• The next branches lead to capillary beds in the head and arms
• the aorta continues in a posterior direction, supplying oxygen rich blood to arteries leading to arterioles and capillary beds in the abdominal organs and legs

Slide 4

• Within the capillaries, the blood gives up much of it's O2 and picks up CO2 produced by cellular respiration.
• Venous return to the right side of the heart begins as capillaries rejoin to form venules and then veins.
• Oxygen poor blood from the head and neck and forelimbs is channeled into a large vein called the anterior (or superior) vena cava
• Another large vein called the posterior (or inferior) vena cava drains blood from the trunk and hind limbs
• the two vena cava empty their blood into the right atrium, from which the oxygen poor blood flows into the right ventricle.

Slide 5

• The mammalian heart is located beneath the breastbone (sternum) and consists mostly of cardiac muscle.
• These two atria have relatively thin walls and function as collection chambers for blood returning to the heart
• these ventricles have thicker walls and contract much more strongly than the atria
• A cardiac cycle is one complete sequence of pumping, as the heart contracts, and filling, as it relaxes and it's chambers fill with blood
• the contraction phase is called systole
• the relaxation phase is called diastole
• For a human at rest with a pulse of about 75 BPM, one complete cardiac cycle takes about 0.8 seconds
• Cardiac output depends on two factors; the rate of contraction or heart rate ( number of BPS) and stroke volume, the amount of blood pumped by the left ventricle in each contraction.

Order of blood flow through the heart

• 1. Oxygen poor blood enters the heart through the superior and inferior vena cava, the blood remains in the right atrium
• - large veins that bring oxygen poor blood back from the top and bottom of the body.
• 2. Blood enters right ventricle by passing through the tricuspid valve.
• 3. Blood is pushed out to the pulmonary artery and passess through the pulmonary semilunar valve

Slide 7

• 4. Blood is directed into the lungs
• - where blood gets rid of carbon dioxide and picks up oxygen
• 5. Oxygen rich blood is carried through the pulmonary vein and back to the left atrium of the heart.
• - left ventricle is a room with even stronger, thicker, and more muscular walls than the right ventricle.
• 6. Going through the bicuspid valve, oxygen rich blood enters the left ventricle
• 7. Oxygen rich blood passess through the aortic valve down to the aorta to the rest of the body.

Slide 8