Circulatory System: Blood, Heart, and Vessels

Functions of Circulatory System

Transports oxygen, nutrients, hormones, wastes, carbon dioxide, and heat throughout the body.

Open Circulatory System

Circulating fluid leaves vessels and bathes organs; found in insects and many arthropods.

Closed Circulatory System

Blood remains inside vessels; found in humans and other vertebrates.

Fish Heart

2 chambers; one atrium and one ventricle; single circulation.

Amphibian Heart

Usually 3 chambers; two atria and one ventricle; some blood mixing.

Reptile Heart

Most have 3 chambers with partial separation; crocodilians have 4 chambers.

Bird and Mammal Hearts

4 chambers; oxygen-rich and oxygen-poor blood remain separated.

Plasma

Liquid portion of blood; carries nutrients, hormones, and wastes.

Red Blood Cells (RBCs)

Contain hemoglobin and transport oxygen.

White Blood Cells (WBCs)

Defend body against infections and pathogens.

Platelets

Cell fragments that help form blood clots and stop bleeding.

Blood Type

Determined by antigens on red blood cells; includes ABO and Rh systems.

Antigens

Markers on red blood cells that the immune system can recognize.

Antibodies

Proteins that recognize specific antigens.

Agglutination

Red blood cells clump when incompatible antibodies bind their antigens; dangerous during transfusions.

Blood Clotting

Platelets form a plug and fibrin strengthens it into a clot to stop bleeding.

Arteries

Carry blood away from heart; thick muscular walls; usually high pressure.

Veins

Carry blood toward heart; often have valves to prevent backflow.

Capillaries

Tiny, thin-walled blood vessels where oxygen, nutrients, and wastes are exchanged.

Blood Flow Through Heart

Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body.

Right Side of Heart

Receives oxygen-poor blood and pumps it to the lungs.

Left Side of Heart

Receives oxygen-rich blood and pumps it to the body.

Atria

Upper chambers of heart that receive blood.

Ventricles

Lower chambers of heart that pump blood out.

Heart Valves

Prevent blood from flowing backward.

Myocardium

Muscular tissue of heart responsible for pumping.

Cardiac Cycle

One complete heartbeat, including filling and contraction.

SA Node

Heart's natural pacemaker; starts the electrical signal for each heartbeat.

AV Node

Briefly delays electrical signal before sending it toward ventricles.

Cardiac Output

Amount of blood one ventricle pumps per minute; heart rate × stroke volume.

ECG/EKG

Records electrical activity of heart.

Systole

Ventricles contract and pump blood; represented by top blood-pressure number.

Diastole

Ventricles relax and fill; represented by bottom blood-pressure number.

Blood Pressure

Force of blood pushing against blood vessel walls; often measured as 120/80 mmHg.

Vasoconstriction

Vessels narrow, raising resistance and tending to increase blood pressure.

Vasodilation

Vessels widen, lowering resistance and tending to decrease blood pressure.

Pulmonary Circulation

Blood travels between heart and lungs for gas exchange.

Systemic Circulation

Blood travels between heart and rest of body.

Lymph

Fluid traveling through lymphatic vessels.

Lymphatic Vessels

Return excess tissue fluid to blood.

Lymph Nodes

Filter lymph and help detect pathogens.

Lymphocytes

White blood cells that help defend against infections.