Major Organs and Systemic Circulation

All the organs of the body are supplied with blood. This is necessary so that the cells can obtain oxygen, which is required for cellular respiration, as well as essential nutrients. Each organ has an artery that supplies it with blood from the heart. Metabolic wastes, including carbon dioxide, need to be removed from cells and returned to the heart. These move into the capillaries which enter into veins that eventually enters either the superior or inferior vena cava which then enters the right atrium.

Arteries and veins have been named according to the organ to which they supply blood. The liver receives oxygenated blood from the heart via the hepatic artery. This artery runs alongside the hepatic portal vein. The hepatic portal vein contains nutrients that have been absorbed by the digestive system. This nutrient-rich blood must first pass through the liver, so that the nutrient composition of the blood can be controlled. Blood passes from the liver to the heart through the hepatic vein. Metabolic waste is circulated in the blood, and if allowed to accumulate, would eventually reach toxic levels. The kidneys are supplied with blood (which contain waste) via the renal arteries. The kidneys filter metabolic waste from the blood, passing it to urine to be excreted safely. Blood leaves the kidney via the renal vein.

The brain is supplied with blood via the carotid arteries and the vertebral arteries. The blood from the brain is drained via the jugular veins. The brain is supplied with \(\text{15}\%\) of the total amount of blood pumped by the heart. The heart is also a muscle (myocardium) that requires blood flow to work. Blood is supplied to the heart via two coronary arteries, and leaves the heart via four cardiac veins.

Optional Class Investigation: Dissecting a Mammalian Heart

Aim

To dissect a mammalian heart (sheep or ox heart).

Apparatus

your teacher will give each group a heart to dissect
a scalpel handle with a blade or a sharp non-serrated knife
a sharp pair of scissors
a pair of forceps
gloves
paper towel
pictures of the external and internal views of the heart

Method

Work in groups of four.
Place the heart on the dissecting board with the atria at the top and the ventricles facing downwards.
Carefully examine the external view of the heart. Try identify the vertical and horizontal groves on the heart. This is the position of the internal walls between the chambers of the heart.
Examine and note the difference in the walls of the ventricles and atria. Also note the difference in appearance between the walls of the ventricles and atria.
With the scalpel or sharp knife carefully cut the heart open across the left atrium.
Compare the thickness and the size of the right ventricle and atrium.
Identify the valves and examine the tendinous cords which are attached to the valves.
Identify the semi-lunar valves at the bottom of the pulmonary artery.
Now cut through the left side of the heart in the same way as you did the right side of the heart.
Carefully cut through the septum of the heart so that you have two halves.

Questions

What is the smooth outer layer of the heart called?
Did you notice any fat around the heart?
Did you notice a difference between the atria and ventricles externally?
Name the blood vessels visible on the outside of the heart.
Compare the thickness of the walls of the atria and ventricles. Explain why they are different.
Explain the difference between the left and right ventricular walls.

Answers

Pericardium
Yes - fat should be present in some places, especially in the grooves.
Yes – the atria are much smaller than the ventricles, they have thinner muscle walls and are at the top of the heart, whereas ventricles are at the bottom.
Coronary arteries and veins
Atria have thin, flexible walls and ventricles have much thicker, stronger walls. This is because atria only have to pump blood down to the ventricles (short distance), so they do not have to be as strong as ventricles, that pump blood much further (to the lungs or the entire body).
The wall of the left ventricle is much thicker than that of the right ventricle, since it needs to exert greater force / be stronger. The left ventricle pumps blood to the entire body, which requires much more force than simply pumping blood from the right ventricle to the lungs, which are also in the thoracic cavity.

Major Organs and Systemic Circulation