Human Blood: Composition, Functions, Cardiac Cycle & Edema

Blood: Functions and Composition

Blood is a type of connective tissue. It is a thick red liquid made up of specialized cells suspended in a watery solution of molecules and ions. Blood transports nutrients and oxygen to the cells and carries waste residues to where they can be eliminated. Besides that, it regulates body temperature, pH and water volume, transports hormones, and defends our body from infections or from excessive blood loss when we get wounded. Blood is the only liquid tissue in our body because the matrix in which blood cells are immersed is liquid. The liquid component of blood is called plasma and it represents about 55% of blood volume.

Plasma: Composition and Role

Plasma is a pale yellow liquid. About 90% of it is water. The rest is dissolved proteins (antibodies, transporting proteins, clotting proteins, albumins…), hormones, amino acids, sugars, lipids and lipoproteins, vitamins, mineral ions, dissolved gases and waste products.

Cells of Blood: Erythrocytes, Buffy Coat, Platelets

Cells of blood — Erythrocytes: Red blood cells carry oxygen and carbon dioxide, and they make up about 45% of total blood volume.

Buffy coat: Leukocytes (white blood cells) defend your body from toxins and foreign microbes.

Platelets: Help with blood clotting and make up less than 1% of blood volume.

Cardiac Cycle: Heartbeat Phases

Cardiac cycle: The heart collects blood from the veins and then pumps it out into the arteries. This pumping movement, the heartbeat, occurs through three phases: atrial systole, ventricular systole and diastole. In healthy adults, there are two normal heart sounds (often described as a "lub" and a "dub") that occur in sequence with each heartbeat. These sounds correspond to valves closing.

Pulse: Arterial Wave

During ventricular systole the aorta dilates and a wave passes through its walls. This wave then travels through all the arteries in the body. It is called a pulse.

Edema: Symptoms and Causes

Edema refers to the abnormal accumulation of excess fluid in a tissue.

Symptoms: swelling and enlarged internal organs.

Causes:

• Increased filtration (for example, because of increased blood pressure or increased capillary permeability).
• Decreased reabsorption (for example, because of the lack of blood albumin).
• Obstruction of the lymphatic drainage.