Chapter 5.
Circulatory System (Cardiovascular, Lymphatic, Immune)
The life of every tissue and organ in the body depends on the receipts of nourishment, such as glucose, and oxygen, and on the removal of waste products that result from cellular activity. The blood is pumped by the heart through the arteries to the capillaries and is returned to the heart via the venules and veins.
The capillaries form a dense network throughout the body. There are microscopic channels that receive blood from the arterioles (small arteries), and deliver it into the venules (small veins). These canals consist of a single layer of cells.
Arteries are thick walled with elastic tissue. The veins have thinner walls than the arteries, and in the lower limbs have valves that help push the blood upwards, back to the heart.
The heart is a hollow, muscular organ, about the size of a clenched fist that lies in the thoracic cavity behind the sternum. The heart is separated into right and left sides by a septal wall. The heart is further divided into upper and lower chambers; the upper chambers are called at atria, and the lower chambers are called the ventricles.
The largest compartment is the left ventricle, which pumps freshly oxygenated blood (coming from the lungs) through the aorta, to all parts of the body. The blood returns to the heart by entering the right atrium through the superior vena cava and inferior vena cava.
From the right atrium, the blood goes into the right ventricle and is pumped into the lungs to get oxygenated, then flows back into the heart (left atrium) via pulmonary veins. It continues to flow into the left ventricle, to all parts of the body.
Blood is a body fluid that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. It is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume), and contains proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and blood cells themselves.
The blood cells are mainly red blood cells (also called RBCs or erythrocytes), white blood cells (also called WBCs or leukocytes) and platelets (also called thrombocytes).
Please watch the following videos:
- Meet the heart! | Circulatory system physiology | NCLEX-RN | Khan Academy (about 10 minutes)
- Arteries, arterioles, venules, and veins | Health & Medicine | Khan Academy (about 8 minutes)
- Introduction to the Lymphatic system (video by Osmosis, about 11 minutes)
- The Immune System Overview, Animation – Alila Medical Media (about 6 minutes)
Back to Introduction Ch. 4 – Muscular System Ch. 6 – Respiratory System