The Circulatory System

Human circulatory system Closed system-blood moves through a series of vessels Consists of the heart, a series of blood vessels, and the blood

Heart Hollow organ, composed mostly of muscle, the size of your clenched fist Enclosed in protective covering called pericardium Heart walls have two layers of epithelial and connective tissues that form around the muscle called myocardium Contractions of myocardium pump blood through the system

Heart Contracts 72 times per minute and pumps 70 ml of blood with each contraction Septum divides the right side from the left side and prevents mixing of oxygen-rich and oxygen-poor blood Upper chambers, atria (atrium), receive blood Lower chambers, ventricles, pump blood away from the heart

Circulation through the body Right side of heart pumps blood from heart to lungs in pulmonary circulation to exchange carbon dioxide and oxygen Oxygen-rich blood returns to the left side of the heart to be pumped to the body in systemic circulation Systemic circulation carries oxygen to all cells and picks up carbon dioxide before returning to the right side of the heart

Circulation through the heart Blood enters heart through right and left atria When heart contracts blood moves from atria to ventricles (and out of ventricles to body or lungs) Valves between atria and ventricles prevent blood from flowing backwards Valves also prevent blood from flowing back into the ventricles when it leaves the heart Valves keep blood moving in one direction and increases pumping efficiency

Blood vessels Blood moves through 3 types of vessels Arteries Capillaries Veins

Arteries Large vessels that carry blood from heart to tissues All carry oxygen-rich blood (except for the pulmonary artery that carries oxygen-poor blood from heart to lungs) Blood leaving heart to go to body tissues must first pass through the aorta (large artery)

Capillaries Smallest blood vessels Walls only 1 cell thick Bring oxygen and nutrients to tissues and absorb carbon dioxide and other wastes

Veins Return blood to heart after passing through capillaries Walls contain connective tissue and smooth muscle Large veins also contain valves to prevent back flow Many located between or within skeletal muscles whose contractions help force blood toward the heart

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Blood pressure Produced when heart contracts and forces a wave of fluid through the arteries Force of blood on arterial walls is blood pressure Without pressure, blood would stop flow

Regulation of blood pressure Sensory receptors in body detect level of blood pressure and sends impulses to medulla oblongata If pressure is too high, neurotransmitters are released by autonomic nervous sys. Causing vessel walls to relax and lower pressure If pressure is too low, neurotransmitters can elevate pressure by causing vessel walls to contract

Regulation of blood pressure Kidneys also help control blood pressure Hormones from heart and other organs cause kidneys to remove water from blood when pressure is too high This reduces blood volume and lowers blood pressure

Blood plasma 55% of blood is fluid called plasma Plasma is 90% water and 10% dissolved gases, salts, nutrients, enzymes, hormones, wastes, and plasma proteins (albumins, globulins, fibrinogen) Albumins and globulins transport fatty acids, hormones, and vitamins Albumins regulate osmotic pressure and blood volume Globulins fight viral and bacterial infections Fibrinogens are proteins that help blood to clot

Red blood cells Most numerous cells in blood (also called erythrocytes) Used to transport oxygen Color comes from hemoglobin (iron-containing protein that binds oxygen for transport) Produced from red marrow Do NOT have nuclei Circulate for 120 days and are then destroyed by the spleen

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White blood cells Also called leukocytes Do NOT have hemoglobin Produced in bone marrow and have nuclei Live for days, months, or years Guard against infection, fight parasites, and attack bacteria

Types of white blood cells Phagocytes-engulf and digest bacteria and other disease-causing microorganisms; some release histamines that produce redness and swelling (allergies) Lymphocytes-produce antibodies (proteins) that destroy pathogens; essential to fighting infection and produce immunity to diseases

Importance of white blood cells First lines of defense in fighting infection Part of immune system

Platelets Made of plasma proteins and cell fragments Produced in bone marrow Platelets come in contact with broken blood vessel, they become “sticky” and gather at the wound Platelets release clotting factor (thromboplastin) that converts prothrombin to thrombin (changes fibrinogen to mesh of fibrin filaments) to stop bleeding

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