The Circulatory System

Main function of the circulatory system

To transport necessary materials to cells and remove waste materials from them.

Major components of a circulatory system

Blood (transport medium), heart (pump), and blood vessels (in closed systems).

Open circulatory system

A system where hemolymph is pumped into the body cavity (hemocoel) and directly bathes organs.

Organisms with open circulatory systems

Most invertebrates.

Disadvantages of open circulatory systems

Blood is not delivered directly to metabolically active areas and blood flow is inefficient.

Closed circulatory system

A system where blood is pumped through vessels by a heart.

Advantages of a closed circulatory system

Matches organ demands, grows with the organism, and can repair itself when injured.

Organisms with closed circulatory systems

Earthworms, cephalopods (squid, octopi), and vertebrates.

Single circulatory system

Blood passes through the heart once; seen in fish with a 2-chambered heart.

Double circulatory system

Blood passes through the heart twice, using two circuits: pulmonary and systemic.

Organisms with double circulation

Crocodiles, birds, and mammals.

Function of the right side of the heart

Pumps deoxygenated blood to the lungs (pulmonary circulation).

Function of the left side of the heart

Pumps oxygenated blood to the body (systemic circulation).

Major components of blood

Plasma, leukocytes, erythrocytes, and thrombocytes.

Plasma

The liquid portion of blood, composed mostly of water and dissolved substances.

Leukocytes

White blood cells involved in immunity.

Erythrocytes

Red blood cells that carry oxygen.

Pigment giving red blood cells their color

Hemoglobin.

Composition of hemoglobin

A globin protein and a heme molecule with a central iron atom.

Percentage of oxygen carried by hemoglobin

99%.

Thrombocytes

Platelets involved in clot formation.

Three main steps in clot formation

Vascular spasm, platelet plug formation, and coagulation.

Myogenic heart

A heart that contracts due to signals from within the heart itself.

Atria

The upper chambers of the heart that receive blood.

Ventricles

The lower, muscular chambers that pump blood out of the heart.

Veins returning blood to the right atrium

Superior vena cava, inferior vena cava, coronary sinus.

Veins carrying oxygenated blood to the left atrium

Pulmonary veins.

Function of heart valves

To prevent backflow and ensure one-way blood flow.

AV valves

Tricuspid (right side) and bicuspid/mitral (left side) valves between atria and ventricles.

Chordae tendinae

Fibrous cords that anchor the AV valves to the heart muscle.

Chordae tendineae

Cordlike structures that anchor AV valve flaps to papillary muscles.

Semilunar valves

Pulmonary and aortic valves located between ventricles and arteries.

Circulation patterns

Pulmonary, systemic, and coronary circulation.

Pulmonary circulation

Blood travels from the right heart to lungs and back to the left heart.

Systemic circulation

Blood is pumped from the left heart to the body and back to the right heart.

Coronary circulation

Blood supply to the heart muscle (myocardium) itself.

Myocardial infarction

A heart attack caused by blocked blood supply to the heart tissue.

Heart attack treatments

Streptokinase (clot-dissolving) or surgery.

Brain region regulating heart activity

Medulla oblongata (via cardiovascular and cardioaccelerating centers).

Cardiac cycle

One complete heartbeat, including contraction and relaxation of atria and ventricles.

Systole

Contraction and emptying of heart chambers.

Diastole

Relaxation and filling of heart chambers.

Heart sounds

"Lubb" (AV valves closing during ventricular systole) and "Dubb" (SL valves closing).

P wave

Atrial depolarization and contraction.

QRS complex

Ventricular depolarization and contraction.

T wave

Ventricular repolarization and relaxation.

Blood flow order

Arteries -> Arterioles -> Capillaries -> Venules -> Veins -> Heart.

Arteries

Carry blood away from the heart (usually oxygenated).

Layers of an artery

Tunica interna, tunica media (smooth muscle), tunica externa (connective tissue).

Capillaries

Microscopic vessels where exchange of gases and nutrients occurs.

Veins

Vessels that return deoxygenated blood to the heart.

Vein valves

To prevent the backflow of blood, especially in limbs.

Oxygen content exception

Pulmonary artery (deoxygenated) and pulmonary vein (oxygenated).

Blood flow

The volume of blood flowing per minute; equivalent to cardiac output.

Blood pressure (BP)

The force exerted by blood against vessel walls, measured in mmHg.

Resistance in circulation

Opposition to blood flow due to friction.

Blood viscosity

The thickness of blood.

Systolic pressure

Pressure during ventricular contraction (approx. 120 mmHg).

Diastolic pressure

Pressure during ventricular relaxation (approx. 60-80 mmHg).

Blood pressure notation

As systolic/diastolic (e.g., 120/80).

Hypertension

High blood pressure (>140/95), caused by conditions like atherosclerosis or kidney disease.

Blood pressure controls

Vasomotor center (in medulla) and baroreceptors (in large arteries).