Animal Circulatory Systems (7)

Gastrovascular Cavity

A central digestive compartment in simple animals (like jellies) that also functions in distribution of substances via diffusion.

Open Circulatory System

A system where circulatory fluid (hemolymph) bathes the organs directly and is not always confined to vessels.

Hemolymph

The combined fluid of blood and interstitial fluid found in animals with open circulatory systems, like insects.

Closed Circulatory System

A system where blood is confined to vessels and is distinct from the interstitial fluid; found in annelids and vertebrates.

Atrium

A chamber of the heart that receives blood returning from the body or lungs.

Ventricle

A muscular chamber of the heart responsible for pumping blood out to the body or respiratory surfaces.

Single Circulation

A circulatory arrangement in fish where blood passes through the heart once in a complete circuit.

Double Circulation

A system in amphibians, reptiles, and mammals where blood is pumped separately to pulmonary and systemic circuits.

Pulmonary Circuit

The flow of blood from the heart to the gas exchange tissues and back to the heart.

Systemic Circuit

The flow of blood from the heart to the rest of the body’s organs and tissues and back.

Arteries

Thick-walled vessels that carry blood away from the heart at high pressure.

Capillaries

Microscopic vessels with thin walls (one cell thick) where the exchange of nutrients and gases occurs via diffusion.

Veins

Thin-walled vessels with valves that return blood to the heart at lower pressure.

Endothelium

The smooth, simple squamous epithelial layer that lines the lumen of all blood vessels.

Systole

The contraction phase of the cardiac cycle when the heart pumps blood out.

Diastole

The relaxation phase of the cardiac cycle when the heart chambers fill with blood.

Atrioventricular (AV) Valves

Valves located between the atria and ventricles that prevent backflow when the ventricles contract.

Semilunar Valves

Valves located at the exits of the heart (pulmonary artery and aorta) that prevent backflow into the ventricles.

Cardiac Output

The volume of blood each ventricle pumps per minute, determined by heart rate and stroke volume.

Sinoatrial (SA) Node

The "pacemaker" of the heart; a cluster of cells in the right atrium that sets the rate and timing of cardiac contraction.

Atrioventricular (AV) Node

A point in the heart's conduction system that delays the electrical impulse to allow atria to empty completely.

Electrocardiogram (ECG/EKG)

A record of the electrical impulses that travel through the heart muscle during the cardiac cycle.

Systolic Pressure

The highest arterial blood pressure reached during ventricular contraction.

Diastolic Pressure

The lowest arterial blood pressure occurring when the ventricles are relaxed.

Vasoconstriction

The narrowing of arteriole walls caused by smooth muscle contraction, which increases blood pressure.

Vasodilation

The widening of arteriole walls caused by smooth muscle relaxation, which decreases blood pressure.

Precapillary Sphincters

Rings of smooth muscle that regulate the flow of blood into specific capillary beds.

Lymphatic System

A network of vessels that returns leaked fluid (lymph) and proteins from the interstitial space back to the blood.

Plasma

The liquid matrix of blood, consisting of water, ions, proteins, and transported substances.

Platelets

Cell fragments involved in the blood clotting process (hemostasis).