Biology: The Circulatory System and Heart

The Circulatory System

• Some small animals use diffusion and active transport to supply cells with oxygen and nutrients, but larger animals like humans need a circulatory system to transport oxygen, nutrients, and waste products.
• The heart pumps blood through the body, contracting about 72 times a minute and pumping 70 milliliters of blood with each contraction.

The Heart

• The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle.
• The septum separates the right and left sides of the heart, preventing oxygen-poor and oxygen-rich blood from mixing.
• Valves between the atria and ventricles and between the ventricles and vessels prevent blood from flowing backward.
• The aorta carries oxygen-rich blood from the left ventricle to the body.
• The superior vena cava and inferior vena cava bring oxygen-poor blood from the upper and lower body to the right atrium.
• The right pulmonary veins bring oxygen-rich blood from the right lung to the left atrium.
• The pulmonary arteries carry oxygen-poor blood to the lungs.
• The left atrium and left ventricle pump oxygen-rich blood to the body.

Circulation

• The heart functions as two pumps: one pumps oxygen-poor blood to the lungs, and the other pumps oxygen-rich blood to the rest of the body.
• The right side of the heart pumps oxygen-poor blood to the lungs through the pulmonary circulation.
• In the lungs, carbon dioxide diffuses from the blood, and oxygen is absorbed into the blood.
• Oxygen-rich blood then flows to the left side of the heart, which pumps it to the rest of the body through the systemic circulation.
• Cells absorb oxygen and load the blood with carbon dioxide, which returns to the heart.

Blood Vessels

• There are three types of blood vessels: arteries, capillaries, and veins.
• Arteries carry blood away from the heart and have thick elastic walls to withstand blood pressure.
• Capillaries are tiny blood vessels that allow oxygen and nutrients to diffuse from the blood into the tissues, and allow carbon dioxide and other waste products to move from the tissues into the blood.
• Veins carry blood back to the heart and have valves to prevent backflow.

Blood Vessel Structure

• Arteries have three layers: endothelium, smooth muscle, and connective tissue.
• Capillaries have very thin walls to allow the transfer of materials between the blood and the tissues.
• Veins have endothelium, smooth muscle, and connective tissue, and also have valves to prevent backflow.

Exercise and Heart Rate

• Exercise affects heart rate, which is the number of times per minute that the heart contracts.
• Heart rate increases during exercise to maintain homeostasis.

Blood Clotting

• Platelets help blood to clot and seal wounds by releasing thromboplastin, which triggers a series of reactions that form a clot.
• The clot is composed of fibrin filaments that trap blood cells.

Blood

• Blood is composed of 55% plasma, which is about 90% water and 10% dissolved gases, salts, nutrients, enzymes, and other compounds.
• Plasma proteins consist of albumin, globulins, and fibrinogen, which have various functions such as transporting substances, fighting infections, and clotting.
• Red blood cells, or erythrocytes, transport oxygen and are produced in the bone marrow.
• White blood cells, or leukocytes, guard against infection and fight parasites.
• Platelets are formed in the bone marrow and help blood to clot.

The Lymphatic System

• The lymphatic system is a network of vessels, nodes, and organs that recycles fluids from tissues, plays a role in nutrient absorption, and aids in immunity.
• The lymphatic system has three main roles: circulation, immunity, and nutrient absorption.
• The lymphatic system collects fluids that leak from blood vessels, returns it to the circulatory system, and aids in the absorption of fats and fat-soluble vitamins.
• Lymph nodes filter lymph and trap microorganisms, stray cancer cells, and debris.

Learn about the circulatory system, how it works, and its importance in larger animals like humans. This quiz covers the heart's structure and function, including its chambers and pumping action.