Human Circulatory System: Blood Vessels, Heart Function, and Cardiac Cycle

Arteries

Blood vessels that carry blood away from the heart to the body tissues. They have thick elastic walls that help them withstand the high pressure of blood pumped by the heart.

Capillaries

Where nutrient and gas exchange happens.

Veins

Blood vessels that carry blood toward the heart. They have thinner walls than arteries and often contain valves that prevent backflow of blood.

Pulmonary Circuit

Blood pumped from the heart to the lungs and back to the heart.

Systemic Circuit

Blood pumped from the heart to the rest of the body.

Pressure (mm Hg)

The force exerted by a fluid on its container.

Hydrostatic Pressure

The pressure exerted by a fluid that is not moving. Force is exerted equally in all directions.

Driving Pressure

The difference in pressure between two locations that causes something (such as blood, air, or fluid) to move. The heart creates higher pressure when it contracts.

Resistance

The tendency to oppose flow.

Vasoconstriction

Decrease in vessel diameter.

Vasodilation

Increase in vessel diameter.

Radius

The distance from the center of a blood vessel to its inner wall (half of the vessel's diameter).

Length

The distance blood must travel through a blood vessel from one end to the other.

Viscosity

Flow of fluid is related to the viscosity, the pressure gradient along the tube, and the length and diameter of the tube.

Flow Rate

Volume of blood passing a given point per unit of time.

Velocity of Flow

Distance a fixed volume of blood travels per unit time.

Right Atrium

The upper right chamber of the heart that receives oxygen-poor blood from the body.

Left Atrium

The upper left chamber of the heart that receives oxygen-rich blood returning from the lungs.

Right Ventricle

The lower right chamber of the heart that pumps oxygen-poor blood to the lungs through the pulmonary arteries.

Left Ventricle

The lower left chamber of the heart that pumps oxygen-rich blood to the rest of the body through the aorta.

Semilunar Valve

Located between the ventricles and arteries leaving the heart. They prevent blood from flowing backward into the ventricles after it has been pumped out.

AV Valve

Located between the atria and ventricles and prevent blood from flowing backward into the atria when the ventricles contract.

Contractile Myocardial Cells

Heart muscle cells that contract and generate force to pump blood out of the heart.

Autorhythmic Myocardial Cells

They are pacemakers. They can generate action potentials spontaneously.

Gap Junctions

Allow waves of depolarization to easily transfer from one cell to another.

Intercalated Disks

Specialized connections between cardiac muscle cells that hold the cells together and allow electrical signals to pass quickly from one cell to the next.

Pacemaker Potential

Unstable membrane potential. It starts at about -60 mV and slowly drifts toward about -40 mV.

If Channels

"Funny Channels." They are permeable to Na+ and K+.

SA Node

The heart's natural pacemaker that generates electrical impulses and starts each heartbeat.

AV Node

Receives the electrical signal from the SA node and briefly delays it before sending it to the ventricles.

AV Bundle (Bundle of His)

Group of specialized fibers that carry electrical signals from the AV node into the ventricles.

Right/Left Bundle Branches

Pathways that carry the electrical signal down the right and left sides of the interventricular septum toward the apex of the heart.

Purkinje Fibers

Specialized fibers that rapidly distribute the electrical signal throughout the ventricles, causing them to contract.

ECG/EKG

Surface recording of the electrical activity of the heart.

P Wave

Atrial depolarization. The SA node depolarizes and spreads through the atria.

QRS Complex

Atrial repolarization and ventricular depolarization.

T Wave

Ventricular repolarization.

Cardiac Cycle

One cycle of contraction and relaxation.

Systole

Contraction phase.

Diastole

Relaxation phase.

End-Diastolic Volume

Volume of blood in one ventricle at the end of diastole (average 135 mL).

End-Systolic Volume

Volume of blood in one ventricle at the end of systole (average 65 mL).

Stroke Volume

Volume of blood pumped by one ventricle during contraction (average 70 mL).

Cardiac Output

Volume of blood pumped by one ventricle in one minute.

Preload

Length of the muscle fibers at the beginning of contraction. It is determined by how much blood is in the heart.

Venous Return

How much blood is coming back to the heart.

Skeletal Muscle Pump

Skeletal muscle contractions that compress veins and push blood toward the heart.

Respiratory Pump

Expansion of the thoracic cavity creates lower pressure in the inferior vena cava and greater pressure in the abdominal veins.

Contractility

Intrinsic ability of cardiac muscle to contract.

Inotropic Agents

Any chemical that affects contractility.

Blood

Fluid connective tissue consisting of cellular elements suspended in plasma.

Plasma

The liquid portion of the blood that carries blood cells, nutrients, hormones, proteins, and waste products throughout the body.

Erythrocytes

Red blood cells. They transport CO2 and O2 in the blood.

Leukocytes

White blood cells. They play a key role in the body's immune system.

Platelets

Cell fragments that help with blood clotting and stop bleeding.

Bone Marrow

Soft tissue inside bones where blood cells are produced.

Hematopoiesis

The process of forming new blood cells in the bone marrow.

Hematocrit

The percentage of blood volume made up of red blood cells.

Hemoglobin

The protein in red blood cells that carries oxygen throughout the body.

Heme Group

The iron-containing portion of hemoglobin that binds oxygen.

Bilirubin

Waste metabolite excreted in bile and urine.

Jaundice

A condition when the skin and eyes appear yellow due to the buildup of bilirubin in the blood.

Megakaryocytes

Large cells in the bone marrow that produce platelets by breaking off small pieces of their cytoplasm.

Thrombopoietin

A hormone produced in the liver that stimulates the production of megakaryocytes and platelets.

Hemostasis

The process of keeping blood within the blood vessels (blood clotting).

Fibrin

A mesh created to temporarily seal a hole in a vessel during blood clotting.

Respiration

The exchange of gases between the atmosphere and blood.

Ventilation

Movement of air into and out of the lungs.

Inspiration

Movement of air into the lungs.

Expiration

Movement of air out of the lungs.

Type I Cells

They make up the walls of the alveoli. Their main function is gas exchange.

Type II Cells

Cells in the alveoli that produce surfactant.

Surfactant

Decreases the surface tension of fluid found in the alveoli.

Dalton's Law

The total pressure exerted by a mixture of gases is the sum of the pressures exerted by individual gases.

Boyle's Law

If the volume of a gas is reduced, its pressure increases.

Diaphragm

The primary muscle of respiration that contracts and flattens during inhalation.

External Intercostals

Located between the ribs and assist inhalation by elevating the ribs and expanding the chest cavity.

Scalenes

Accessory muscles of inspiration that help elevate the first and second ribs during deep or labored breathing.

Internal Intercostals

Located between the ribs and assist with forced exhalation.

Active Expiration

Uses internal intercostal and abdominal muscles to further reduce thorax volume.

Bronchoconstriction

The bronchioles become narrower.

Bronchodilation

Allows more air in and out of the lungs.

Tidal Volume

Amount of air moving in or out of the lungs per breath.

Inspiratory Reserve Volume

Amount of air that can be forcibly inspired beyond tidal volume.

Expiratory Reserve Volume

Amount of air that can be forcibly expired after tidal expiration.

Residual Volume

Amount of air in the lungs after forceful expiration.

Vital Capacity

Total amount of exchangeable air.

Total Lung Capacity

Maximum amount of air in the lungs.

Hypoxia

Low oxygen levels.

Hypercapnia

High CO2 levels.

Hypocapnia

An abnormally low level of carbon dioxide in the blood.

Respiratory Acidosis

Too much CO2 in the body causes pH to decrease.

Respiratory Alkalosis

Low CO2 levels cause pH to increase.

Hypoventilation

Low levels of ventilation causing oxygen levels to decrease and CO2 levels to increase.

Hyperventilation

Ventilation that is faster or deeper than necessary.

Emphysema

A lung disease where the walls of alveoli are damaged, reducing surface area for gas exchange.

Pulmonary Edema

Increases fluid in the lungs, creating a barrier between the alveolus and capillary.

Perfusion

The flow of blood through pulmonary capillaries surrounding alveoli.

Oxyhemoglobin

Oxygen bound to hemoglobin.

Carbonic Anhydrase

An enzyme found in red blood cells that rapidly converts carbon dioxide and water into carbonic acid.