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Circulation

The movement of blood through the body, delivering oxygen and nutrients to cells and removing waste products.

Gas Exchange

The process by which oxygen is taken in and carbon dioxide is expelled from the body.

Plasma Membrane

The outer membrane of a cell that controls the movement of substances in and out of the cell.

Specialized Systems

Systems in multicellular organisms that are specifically adapted for certain functions.

Gills

Organs in aquatic animals that are used for gas exchange.

Diffusion

The movement of molecules from an area of high concentration to an area of low concentration.

Exchange Surfaces

Surfaces in organisms where exchange of substances occurs.

Circulatory Systems

Systems in animals that transport materials throughout the body.

Open Circulatory System

A circulatory system in which the circulatory fluid is not confined to vessels.

Closed Circulatory System

A circulatory system in which the circulatory fluid is confined to vessels.

Hemolymph

The circulatory fluid in open circulatory systems.

Blood

The circulatory fluid in closed circulatory systems.

Cardiovascular System

The closed circulatory system in humans and other vertebrates.

Arteries

Blood vessels that carry blood away from the heart.

Veins

Blood vessels that carry blood back to the heart.

Capillaries

Small blood vessels where exchange of substances occurs between the blood and interstitial fluid.

Atria

The chambers of the heart that receive blood.

Ventricles

The chambers of the heart that pump blood out.

Single Circulation

A type of circulation in which blood passes through two capillary beds before returning to the heart.

Double Circulation

A type of circulation in which oxygen-poor and oxygen-rich blood is pumped separately from the heart.

Pulmocutaneous Circuit

The circuit in amphibians where blood flows to the lungs and skin for gas exchange.

Systemic Circuit

The circuit in amphibians where oxygenated blood is pumped to the rest of the body.

Septum

A partition that separates the ventricle in certain animals with double circulation.

Endotherms

Animals that generate their own body heat and maintain a constant internal temperature.

Ectotherms

Animals that rely on external sources of heat to maintain their body temperature.

Cardiac Cycle

One complete sequence of heart contraction and relaxation.

Systole

The contraction phase of the cardiac cycle.

Diastole

The relaxation phase of the cardiac cycle.

Cardiac Output

The amount of blood pumped by the heart in one minute.

Stroke Volume

The amount of blood pumped by a ventricle in one contraction.

Valves

Structures in the heart that prevent backflow of blood.

Atrioventricular (AV) Valves

Valves that separate each atrium and ventricle.

Semilunar Valves

Valves that control blood flow to the aorta and pulmonary artery.

Heart Murmur

Abnormal sounds caused by backflow of blood through a defective valve.

Autorhythmic

Cells that can contract without any signal from the nervous system.

Sinoatrial (SA) Node

The pacemaker of the heart that sets the rate and timing of heart contractions.

Electrocardiogram (ECG or EKG)

A recording of the electrical impulses produced by the heart.

Pacemaker

A specialized group of cells in the heart that controls the rhythm and rate of heartbeat.

Hormones

Chemical messengers produced by the body that can influence the pacemaker and heart tempo.

Temperature

A factor that can also influence the pacemaker and heart tempo.

Blood vessels

Tubes that carry blood throughout the body.

Structure and function

The arrangement and characteristics of blood vessels that determine patterns of blood pressure and flow.

Central lumen

The cavity or space within a blood vessel.

Endothelium

The epithelial layer that lines the blood vessels and minimizes resistance to blood flow.

Capillaries

Blood vessels with thin walls that facilitate the exchange of substances.

Arteries

Blood vessels that carry blood away from the heart and have thicker walls to accommodate high blood pressure.

Veins

Blood vessels that carry blood back to the heart and have thinner walls than arteries.

Blood flow velocity

The speed at which blood flows through blood vessels, influenced by the diameter of the blood vessel.

Blood pressure

The force exerted by blood against the walls of blood vessels.

Systole

The phase of the cardiac cycle when the heart contracts and arterial blood pressure is highest.

Diastole

The phase of the cardiac cycle when the heart relaxes and arterial blood pressure decreases.

Vasoconstriction

Contraction of smooth muscle in arteriole walls, which increases blood pressure.

Vasodilation

Relaxation of smooth muscles in the arterioles, which causes blood pressure to fall.

Fainting

A condition caused by inadequate blood flow to the head.

Gravity

A consideration for blood flow in veins, particularly in the legs.

One-way valves

Valves in veins that prevent backflow of blood.

Lymphatic system

A network of vessels that returns leaked fluid, called lymph, back to the circulatory system.

Lymph

Fluid that leaks out from the capillary beds and has a similar composition to interstitial fluid.

Lymph nodes

Organs that filter lymph and play a role in the body's defense.

Edema

Swelling caused by disruptions in the flow of lymph.

Blood components

The different types of cells and plasma that make up blood.

Plasma

The liquid matrix of blood that contains various solutes, including inorganic salts and plasma proteins.

Red blood cells

Cells that transport oxygen and contain hemoglobin.

Hemoglobin

An iron-containing protein in red blood cells that binds to oxygen.

White blood cells

Cells that function in defense against foreign substances and bacteria.

Platelets

Fragments of cells involved in blood clotting.

Coagulation

The formation of a solid clot from liquid blood.

Atherosclerosis

The hardening of arteries due to the accumulation of fatty deposits.

Cholesterol

A key player in the development of atherosclerosis.

Low-density lipoprotein (LDL)

A type of lipoprotein that delivers cholesterol to cells.

High-density lipoprotein (HDL)

A type of lipoprotein that scavenges excess cholesterol for return to the liver.

Heart attack

The death of cardiac muscle tissue resulting from blockage of one or more coronary arteries.

Stroke

The death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head.

Hypertension

High blood pressure, which contributes to the risk of heart attack and stroke.

Statins

Drugs that reduce LDL levels and the risk of heart attacks.

Inflammation

The body's reaction to injury, which plays a role in atherosclerosis and thrombus formation.

Gas exchange

The uptake of molecular O2 from the environment and the discharge of CO2 to the environment.

Partial pressure

The pressure exerted by a particular gas in a mixture of gases.

Equilibrium

A state in which the partial pressure of each gas is the same in a liquid and the air.

Respiratory surfaces

Large, thin, and moist surfaces across which gas exchange occurs by diffusion.

Gills

Outfoldings of the body that create a large surface area for gas exchange in aquatic animals.

Countercurrent exchange system

A mechanism in fish gills where blood flows in the opposite direction to water passing over the gills, allowing for efficient gas exchange.

Tracheal system

A network of air tubes in insects that transport O2 and CO2 without the participation of the circulatory system.

Lungs

Infoldings of the body divided into numerous pockets that are used for gas exchange in vertebrates.

Ventilation

The movement of the respiratory medium over the respiratory surface to maintain necessary partial pressure gradients of O2 and CO2.

Negative pressure breathing

A mechanism used by mammals to pull air into the lungs by increasing lung volume through contraction of rib muscles and diaphragm.

Tidal volume

The volume of air inhaled with each breath.

Alveoli

Air sacs at the tips of bronchioles where gas exchange takes place in mammalian lungs.

Surfactants

Secretions that coat the surface of alveoli and help reduce surface tension, preventing the collapse of alveoli.

Positive pressure breathing

A mechanism used by amphibians, such as frogs, to force air down the trachea into the lungs.

Respiratory pigments

Specialized carrier proteins, such as hemoglobin, that bind and transport gases in the blood or hemolymph.

Hemoglobin

The respiratory pigment found in almost all vertebrates and many invertebrates that can carry four molecules of O2.

Cooperativity

The phenomenon where the binding of O2 to one subunit of hemoglobin increases the affinity of the other subunits for oxygen.

Bohr shift

The decrease in the affinity of hemoglobin for O2 due to the decrease in blood pH caused by the production of CO2 during cellular respiration.

Carbon Dioxide Transport

The process by which CO2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to hemoglobin or as bicarbonate ions (HCO3 –).

Hemoglobin

A protein in the blood that binds to oxygen and carbon dioxide for transport.

Oxygen Transport

The process by which oxygen is transported from the lungs to the blood and then to the tissues.

Interstitial Fluid

The fluid that surrounds and bathes the cells in the tissues.

Capillary

Small blood vessels that connect arteries and veins, allowing for exchange of gases and nutrients with the tissues.