The Circulatory System: An Overview
Blood
Blood is a specialized body fluid. It has four main components: plasma, red blood cells, white blood cells, and platelets. Blood has many different functions, including:
- transporting oxygen and nutrients to the lungs and tissues
Interstitial Fluid
Interstitial fluid consists of a water solvent containing sugars, salts, fatty acids, amino acids, coenzymes, hormones, neurotransmitters, white blood cells, and cell waste-products.
Red Blood Cells
The main job of red blood cells, or erythrocytes, is to carry oxygen from the lungs to the body tissues and carbon dioxide, as a waste product, away from the tissues and back to the lungs. Hemoglobin (Hgb) is an important protein in the red blood cells that carries oxygen from the lungs to all parts of our body.
Plasma Cells
Plasma cells can only produce a single kind of antibody in a single class of immunoglobulin. In other words, every B cell is specific to a single antigen, but each cell can produce several thousand matching antibodies per second.
White Blood Cells
White blood cells protect the body against infection. If an infection develops, white blood cells attack and destroy the bacteria, virus, or other organism causing it.
Blood Viscosity
Viscosity is a measure of a fluid’s resistance to flow. It describes the internal friction of a moving fluid. Blood has greater internal friction towards resisting motion as a fluid because of its greater and more complex molecular structure compared to the lower internal friction towards resisting motion of water as a fluid, which has a smaller and simpler molecular structure.
Blood Production
Blood is made in vertebrates. The various cells of blood are made in the bone marrow in a process called hematopoiesis, which includes erythropoiesis, the production of red blood cells; and myelopoiesis, the production of white blood cells and platelets.
Red marrow is found mainly in the flat bones, such as the hip bone, breast bone, skull, ribs, vertebrae, and shoulder blades, and in the cancellous (“spongy”) material at the proximal ends of the long bones, the femur and humerus.
Hemolytic Disease of the Newborn
Hemolytic disease of the newborn (HDN) – also called erythroblastosis fetalis – is a blood disorder that occurs when the blood types of a mother and baby are incompatible.
Circulatory Systems
Pulmonary Circulation
Pulmonary circulation moves blood between the heart and the lungs. It transports deoxygenated blood to the lungs to absorb oxygen and release carbon dioxide. The oxygenated blood then flows back to the heart.
Systemic Circulation
Systemic circulation moves blood between the heart and the rest of the body.
Fetal Circulation
Ductus arteriosus – protects lungs against circulatory overload, allows the right ventricle to strengthen.
Ductus venosus – fetal blood vessel connecting the umbilical vein to the IVC.
Foramen ovale – shunts highly oxygenated blood from the right atrium to the left atrium.
Heart Chambers
The right atrium receives blood from the veins and pumps it to the right ventricle.
The right ventricle receives blood from the right atrium and pumps it to the lungs, where it is loaded with oxygen.
The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.
The left ventricle (the strongest chamber) pumps oxygen-rich blood to the rest of the body. The left ventricle’s vigorous contractions create our blood pressure.
Heart Structure and Location
The heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone (sternum). A double-layered membrane called the pericardium surrounds your heart like a sac.
The valves prevent the backward flow of blood. These valves are actual flaps that are located on each end of the two ventricles (lower chambers of the heart). They act as one-way inlets of blood on one side of a ventricle and one-way outlets of blood on the other side of a ventricle.
The right side of the heart collects oxygen-poor blood from the body and pumps it to the lungs. The left side of the heart collects oxygen-rich blood from the lungs and pumps it to the body.
Cardiac Muscle
Cardiac and skeletal muscle are both striated in appearance, while smooth muscle is not. Both cardiac and smooth muscle are involuntary, while skeletal muscle is voluntary.
While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles, called intercalated discs.
Cardiac muscle tissue works to keep your heart pumping through involuntary movements.
Heart Attack vs. Stroke
A heart attack occurs when blood flow to a part of the heart is blocked, usually by a blood clot. Without oxygenated blood, the heart muscle begins to die. A stroke is a brain attack, cutting off vital blood flow and oxygen to the brain.
Heart Innervation
The heart is innervated by vagal and sympathetic fibers. The right vagus nerve primarily innervates the SA node, whereas the left vagus nerve innervates the AV node; however, there can be significant overlap in the anatomical distribution.