Circulatory and respiratory systems

Arteries

Blood vessels that carry blood away from the heart toward capillaries.

Arterioles

Small branches of arteries that lead to capillary beds and regulate blood flow.

Capillaries

Microscopic blood vessels where exchange of gases, nutrients, and wastes occurs between blood and tissues.

Veins

Blood vessels that carry blood toward the heart from capillaries.

Venules

Small vessels that gather blood from capillaries into veins.

Atria

The heart's upper chambers that receive blood returning to the heart.

Ventricles

The heart's lower chambers that pump blood out to the body or lungs.

Pulmonary circuit

Carries blood between the heart and lungs for gas exchange.

Systemic circuit

Carries blood between the heart and the rest of the body.

Systole

Contraction phase of the cardiac cycle, when blood is pumped out.

Diastole

Relaxation phase of the cardiac cycle, when the heart fills with blood.

Sinoatrial (SA) node

Pacemaker cells in the right atrium that set the heart's rhythm.

Atrioventricular (AV) node

Relays signals from the SA node to the ventricles, causing them to contract.

Low-density lipoprotein (LDL)

"Bad" cholesterol; delivers cholesterol to cells and can form plaques in arteries.

High-density lipoprotein (HDL)

"Good" cholesterol; removes excess cholesterol and returns it to the liver.

Ventilation

The process of moving air or water over a respiratory surface.

Countercurrent exchange

Opposite flow of fluids (e.g., blood and water in fish gills) that maximizes diffusion efficiency.

Larynx

Voice box; part of the airway containing the vocal cords.

Trachea

Windpipe; conducts air from the larynx into the bronchi.

Bronchi

Two main branches leading from the trachea into each lung.

Bronchioles

Smaller branching tubes within the lungs that lead to alveoli.

Alveoli

Tiny air sacs at the end of bronchioles; primary sites of gas exchange in mammals.

Diaphragm

Sheet of muscle at the base of the lungs that drives inhalation and exhalation.

Hemoglobin

Iron-containing protein in red blood cells that binds oxygen and facilitates gas transport.

Bohr shift

The effect of lowered pH (from CO₂ accumulation) decreasing hemoglobin's affinity for O₂, enhancing oxygen delivery to tissues.

Hemolymph

Circulatory fluid in animals with open circulatory systems (combines blood and interstitial fluid).

Tracheal system

Network of air tubes in insects that directly deliver oxygen to tissues.

Circulatory fluid

e.g., blood or hemolymph

Set of interconnecting vessels

Network of tubes that transport circulatory fluid

Muscular pump

Heart that moves the circulatory fluid

Open circulatory system

Circulatory fluid (hemolymph) bathes organs directly; found in arthropods and mollusks.

Closed circulatory system

Blood is confined to vessels, distinct from interstitial fluid; found in annelids, cephalopods, and vertebrates.

Single circulation

Blood passes through the heart once per circuit; characteristic of fish.

Double circulation

Blood passes through the heart twice (once for lungs, once for body); seen in amphibians, reptiles, and mammals.

4-chambered heart

Heart structure in mammals that separates oxygenated and deoxygenated blood completely.

Blood flow pathway in mammals

Right atrium → right ventricle → pulmonary arteries → lungs → pulmonary veins → left atrium → left ventricle → aorta → body tissues → vena cavae → right atrium

SA node

Initiates heartbeat and causes atria to contract.

AV node

Delays signal briefly before it travels down bundle branches and Purkinje fibers to cause ventricles to contract.

Velocity in capillaries

Slowest in capillaries for exchange.

Pressure in circulatory system

Highest in arteries, lowest in veins.

Plasma

Fluid matrix with nutrients, ions, proteins.

Erythrocytes (RBCs)

Transport O₂ via hemoglobin.

Leukocytes (WBCs)

Provide immune defense.

Platelets

Involved in blood clotting.

Atherosclerosis

Plaque buildup (LDL cholesterol) that narrows arteries.

Hypertension

High blood pressure that damages vessels.

Risk factors for cardiovascular disease

High LDL, low HDL, smoking, inactivity, poor diet, genetics.

Respiratory surfaces in animals

Skin (earthworms, amphibians), gills (fish, aquatic invertebrates), tracheal systems (insects), lungs (terrestrial vertebrates).

Positive pressure breathing

Air is pushed into lungs by muscular contraction; characteristic of amphibians.

Negative pressure breathing

Air is pulled in as diaphragm expands thoracic cavity; characteristic of mammals.

Hemocyanin

Copper-based pigment that carries O₂ in arthropods/mollusks; increases oxygen transport efficiency in the blood.