Circulatory Systems

albumin

A binding globulin (carrier protein) that is one of the primary proteins of vertebrate plasma and makes a major contribution to blood osmotic pressure.

anastomosis

A convergence of two or more branches of a tubular structure; e.g., a direct connection between two arteries in the circulatory system.

angiogenesis

Synthesis of new blood vessels, often in response to local hypoxia.

angiotensin II

A peptide hormone that controls blood pressure. Its precursor is angiotensinogen, which is cleaved by renin to form angiotensin I. This decapeptide is cleaved to the final form, angiotensin II, an octapeptide.

aorta

The major artery exiting the heart.

aortic body

sensory structure located in the vertebrate aorta that contains baroreceptors and chemoreceptors.

aortic semilunar valve

The valve between the left ventricle and the aorta of the mammalian cardiovascular system.

apex

The bottom of the heart in mammals.

arterial blood pressure

See mean arterial pressure.

arteriole

A small branch of the arterial network immediately preceding a capillary bed (see venule).

artery

A large blood vessel carrying blood away from the heart.

atrioventricular node (AV node)

Part of the conducting pathways of the mammalian heart; delays conduction of the electrical signal between the atrium and ventricles.

atrioventricular (AV) valves

Valves located between the atrium and the ventricle of vertebrate hearts.

atrium (plural: atria)

One of the chambers of a heart. Blood moves from the atrium to the ventricle.

autoregulation

Regulation of an organ by intrinsic mechanisms (within the same organ). For example, regulation of the force of cardiac contraction by the pressure exerted by the blood within the heart (see Frank-Starling effect).

baroreceptor

A receptor that senses pressure (by sensing the resulting stretch on the cell membrane).

baroreceptor reflex

A homeostatic feedback loop that regulates blood pressure. Pressure sensors in the heart and arterial system detect changes in blood pressure and send sensory feedback to the central nervous system that causes physiological responses that return blood pressure back to the normal range.

bicuspid valve

The valve between the left atrium and the left ventricle of the mammalian heart (also called the mitral valve).

blood

The circulatory fluid in animals with closed circulatory systems. Generally contains proteins, ions, organic molecules, and various cell types.

blood vessels

Tubes that carry blood through an animal's body.

bradycardia

A heart rate that is slower than normal.

bulbus arteriosus

The outflow tract of the heart in bony fishes; nonmuscular and elastic (see also conus arteriosus).

bulk flow

The movement of a fluid as a result of a pressure or temperature gradient.

bundle of His

One of the conducting pathways of the mammalian heart.

capillary

The smallest of the blood vessels in a closed circulatory system; the site of exchange of materials with the tissues.

capillary beds

A collection of capillaries.

cardiac cycle

The complete sequence of events from one heartbeat to the next (see systole and diastole).

cardiac output

The volume of blood pumped by the heart per unit time; the product of heart rate and stroke volume.

cardiomyocyte

A muscle cell found in the heart.

cardiovascular control center

A region of the brain within the medulla oblongata that is involved in regulating heart rate and blood pressure.

carotid body

A structure located in the carotid artery leading to the head of vertebrates; contains baroreceptors and chemoreceptors.

chordae tendineae

Chordlike tendons that connect the atrioventricular valves of the mammalian heart to the papillary muscles and prevent the valve from opening backwards.

closed circulatory system

A circulatory system in which the blood remains within a series of enclosed blood vessels throughout the circulation.

compact myocardium

One of the two types of heart muscle (see also spongy myocardium), consisting of tightly packed cells arranged in a regular pattern; the predominant form of muscle in the mammalian heart.

continuous capillaries

The most common type of capillary, found in organs such as skin and muscle; these capillaries have low permeability because they are surrounded by a complete basement membrane and most of the intercellular contacts are sealed by tight junctions, although this seal is not complete, allowing fluids and small molecules to pass from the blood to the interstitial fluid.

contractility

A measure of cardiac performance related to the ability of the heart muscle to contract.

conus arteriosus

The outflow tract of the heart ventricle in elasmobranchs, lungfish, and amphibians; muscular and valved (see also bulbus arteriosus).

coronary artery

Artery that supplies blood to the heart in vertebrates.

coronary circulation

The blood vessels that supply oxygenated blood to the heart of vertebrates.

diastole

The portion of the cardiac cycle in which the heart is relaxing.

diastolic pressure

The arterial blood pressure during cardiac diastole.

edema

Excess accumulation of fluid in a tissue.

elastic recoil

Movement as a result of the release of elastic storage energy.

electrocardiogram (ECG

EKG),A recording of the electrical activity of the heart.

electrocardiograph

An instrument that measures electrical potentials on the body surface as an indication of the electrical activity of the heart (see electrocardiogram).

end-diastolic volume (EDV)

The volume of blood in the heart at the end of diastole; the maximum volume reached during the cardiac cycle.

end-systolic volume (ESV)

The volume of blood in the heart at the end of systole; the minimum volume reached during the cardiac cycle.

endocardium

The internal layer of the heart.

endothelium

The innermost layer of blood vessels.

epicardium

the outer layer of the heart in vertebrates.

erythrocyte

A type of vertebrate blood cell that contains hemoglobin (red blood cell).

fenestrated capillaries

Capillaries with relatively high permeability because of the presence of perforations (fenestrae) through the cells of the capillary wall; found in tissues such as parts of the kidney, the endocrine organs, and the intestine.

flame cells

The flagellated cells within a protonephridium that generate movements that bring fluids into the structure.

gastrovascular cavity

A space that performs the functions of digestion and circulation; found in organisms such as cnidarians.

globulins

A type of protein found in blood. Alpha and beta globulins are transport proteins; gamma globulins are involved in the immune system.

Heart

A muscular pumping structure.

heart rate

The number of times the heart beats in a given period of time; typically measured as beats per minute.

hematocrit

The proportion of whole blood that is occupied by red blood cells.

hemocoel

Collective name for the sinuses in the open circulatory systems of many invertebrates.

hemocytes

Generalized term for blood cells. Most commonly used for the blood cells of invertebrates.

hemolymph

The circulatory fluid of arthropods.

hydrostatic pressure

Pressure exerted by a fluid at rest.

hypertension

A condition in which arterial blood pressure is elevated above the normal level.

interstitial fluid

The component of the extracellular fluid that exists between cells.

isovolumetric contraction (or isovolumic contraction)

A phase during the cardiac cycle in which the heart contracts, but does not eject blood because the valves are closed, and thus does not change in volume.

isovolumetric relaxation

A phase of the cardiac cycle when the ventricle relaxes without a change in volume.

law of bulk flow

Physical principle that states that fluids flow down pressure gradients, and that this flow is opposed by the resistance of the system; flow = pressure gradient/resistance.

lumen

The internal cavity of a multicellular unit, such as a kidney tubule or gastrointestinal tract.

lymph

A fluid consisting of an ultrafiltrate of blood and immune cells that travels through the lymphatic system of vertebrates.

lymph hearts

The pumping structures of the lymphatic system, present only in some vertebrates (including fish, amphibians, and reptiles).

lymph nodes

Small bean-shaped organs found in various locations in the lymphatic system of tetrapods; they filter lymphatic fluid and produce lymphocytes.

lymphatic system

In the vertebrates, a network of vessels or sinuses (depending upon the species) that carries lymph back to the primary circulatory system. In many species it also performs an immune function.

lymphocytes

Leukocytes that are involved in adaptive immunity in vertebrates.

mean arterial pressure (MAP)

The weighted average of the systolic and diastolic pressures, taking into account the relative length of each of these phases of the cardiac cycle.

medullary cardiovascular control center

The region within the medulla that regulates cardiac function.

myocardium

The muscle of the heart.

myogenic

Refers to something originating in the muscle, as in myogenic autoregulation of blood flow or myogenic muscle, which triggers its own activation.

myogenic autoregulation

Regulation of blood flow via contraction of vascular smooth muscle that is regulated by processes intrinsic to the muscle.

neurogenic

A contraction that occurs in response to a nervous stimulus.

oncotic pressure

The osmotic pressure of blood that is due to the concentration of large macromolecules, primarily protein.

open circulatory system

A circulatory system in which the blood passes through one or more unbounded spaces called sinuses.

ostia (singular: ostium)

An anatomical term for a small opening.

pacemaker cell

An excitable cell that spontaneously fires action potentials in a rhythmic pattern.

pacemaker potentials

Spontaneous depolarizations of the resting membrane potential that ultimately trigger action potentials within pacemaker cells.

papillary muscles

Muscles connected to the chordae tendineae of the mammalian heart that help to anchor the atrioventricular valves.

paracellular pathway

The pathway via which paracellular transport occurs.

pericardium

The sac surrounding a heart.

pericyte cell

Contractile cells that wrap around capillaries.

peristalsis

The rhythmic contractions of intestinal smooth muscle; involved in propelling a bolus of food along the gastrointestinal tract and in moving blood through the circulatory systems of some animals.

plasma

The liquid fraction of vertebrate blood.

plateau phase

The phase of a cardiac action potential characterized by a sustained depolarization as a result of calcium influx.

Poiseuille's equation

An equation describing the relationship between the flow, pressure, and resistance of a fluid moving through a rigid tube, including the factors influencing resistance (length, cross-sectional area, and viscosity).

pulmonary artery

Blood vessel leading from the heart to the lungs of mammals that carries deoxygenated blood.

pulmonary circuit

The part of the tetrapod circulatory system that carries blood from the heart to and from the lungs.

pulmonary semilunar valve

The valve between the right ventricle and the pulmonary artery of the mammalian cardiovascular system.

pulmonary vein

Blood vessel leading from the lungs to the heart of mammals that carries oxygenated blood.

Purkinje fibers

The terminal branches of the conducting fibers of the mammalian heart.

P wave

One of the waveforms of an electrocardiogram; represents the depolarization of the atria.

QRS complex

One of the waveforms of an electrocardiogram; represents the depolarization of the ventricles.

respiratory pigments

Metalloproteins that act as oxygen transport and storage molecules (e.g., hemoglobin).