1.1 - Overview Blood Composition and Functions

Cardiovascular system

The body system made up of blood, heart, and vessels; blood is the medium of transport in this system

Blood

A fluid connective tissue made up of cellular elements (formed elements) and a fluid extracellular matrix (plasma)

Formed elements

The cellular elements of blood, including erythrocytes, leukocytes, and thrombocytes

Erythrocytes

Red blood cells (RBCs); the most abundant blood cells, essential for the transport of oxygen in the blood

Leukocytes

White blood cells (WBCs); play a role in the body's defense mechanisms; there are five classes, each with slightly different functions

Thrombocytes

Platelets; small, membrane-bound cell fragments that contain enzymes and other substances important for clotting

Plasma

The fluid extracellular matrix of blood, mostly water, that makes blood unique among connective tissues because it is fluid; perpetually suspends the formed elements

Blood color

Blood that has just taken up oxygen in the lungs is bright red, while blood that has released oxygen in the tissues is a darker red, due to hemoglobin changing color depending on oxygen saturation

Viscosity

A measure of a fluid's thickness or resistance to flow; blood has a viscosity approximately five times greater than water, influenced by plasma proteins and formed elements

Blood temperature

The normal temperature of blood is about 100.4°F, slightly higher than normal body temperature (98.6°F), due to friction and resistance as blood flows through vessels

Blood pH

Averages about 7.4, ranging from 7.35 to 7.45 in a healthy person; blood is slightly more alkaline (basic) than pure water (pH 7.0) and contains numerous buffers to help regulate pH

Blood volume

Constitutes approximately 8 percent of adult body weight; adult males average about 5-6 liters, while females average 4-5 liters

Transportation function of blood

Blood carries nutrients from the digestive tract to the liver and body cells, oxygen from the lungs to the body, hormones from endocrine glands to target cells, and wastes such as carbon dioxide to the lungs and other wastes to the kidneys and liver for excretion

Defense function of blood

Leukocytes protect the body from external threats like disease-causing bacteria and internal threats like cancerous or virus-infected cells; platelets and plasma proteins interact to block ruptured blood vessels and prevent further blood loss

Maintenance of homeostasis (blood function)

Blood helps regulate body temperature by shifting blood flow between the core and periphery, helps maintain chemical/pH balance via proteins and compounds acting as buffers, and helps regulate water content and fluid distribution in the body

Megakaryocytes

Cells that fragment to form platelets (thrombocytes)