Human Circulatory and Lymphatic Systems

Blood Components

Platelets

Platelets are tiny specialized cells that are activated whenever there is blood clotting or repair is needed. They are colorless and deform easily.

Blood Plasma Composition

Blood Plasma: Fluid formed by amino acids, carbohydrates, proteins, salts, lipids, hormones, antibodies, enzymes, and dissolved gases. Its two main components are water and proteins (albumin, globulin, and fibrinogen).

The Heart: Structure and Blood Flow

Heart Wall Layers

The endocardium consists of epithelial tissue lining that is continuous with the endothelium of blood vessels. The myocardium is the most voluminous layer, being composed of a special type of muscle tissue called cardiac muscle tissue. The pericardium forms the wall that surrounds the heart completely.

Heart Chambers and Circulation

The right pump always contains oxygen-poor blood, coming from the superior vena cava and inferior vena cava. The left heart pump always has oxygen-rich blood coming from the pulmonary veins.

Heart Valves Regulating Flow

Control of blood flow is carried out by four valves:

• The tricuspid and mitral valves, also called atrioventricular valves.
• The tricuspid valve controls blood flow between the right atrium and right ventricle.
• The mitral valve allows oxygen-rich blood from the lungs to pass from the left atrium to the left ventricle.
• The pulmonary valve, which controls blood flow from the right ventricle to the pulmonary arteries, which carry blood to the lungs for oxygen.
• The aortic valve allows oxygen-rich blood to pass from the left ventricle to the aorta (the body's largest artery, which carries blood throughout the body).

Major Veins: Vena Cava

Superior Vena Cava: Collects blood from the head and arms, being the result of the confluence of four veins (two subclavian and two jugular).

Inferior Vena Cava: Collects blood from the rest of the body. It is parallel to the aorta, receiving blood from the legs (iliac and femoral veins) and kidneys (renal veins).

The Lymphatic System

Lymphatic System Functions

Functions:

• Maintain osmolar balance.
• Returns fluid and active blood.
• Forms the main pathway of the immune system.
• Collects the chyle.

Lymph Fluid

Lymph: It is a body fluid that runs through the lymphatic vessels. It occurs after the excess fluid that leaves the blood capillaries into the interstitial space is collected by draining lymphatic capillaries. These drain into lymph vessels, which converge into thicker tubes that empty into the subclavian veins. Lymph travels through the lymphatic system via weak muscle contractions. If a vessel undergoes an obstruction, fluid accumulates in the affected area, resulting in edema.