Atrium (heart)

right atriumatrialeft atriumatriumatrialleft atrial appendageauricleauriclesright atrial appendageleft
The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the ventricles of the heart.wikipedia
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Ventricle (heart)

ventricleleft ventricleright ventricle
The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the ventricles of the heart.
A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs.

Vein

veinsvenousvenous system
There are two atria in the human heart – the left atrium receives blood from the pulmonary (lung) circulation, and the right atrium receives blood from the venae cavae (venous circulation).
These are two large veins which enter the right atrium of the heart from above and below.

Diastole

diastolicdiastolic pressurerelaxation
The atria receive blood while relaxed (diastole), then contract (systole) to move blood to the ventricles.
Ventricular diastole is the period during which the two ventricles are relaxing from the contortions/wringing of contraction, then dilating and filling; atrial diastole is the period during which the two atria likewise are relaxing under suction, dilating, and filling.

Inferior vena cava

inferiorIVCposterior vena cava
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
The inferior vena cava (or IVC) is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart.

Anterior cardiac veins

anterior cardiac
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
The anterior cardiac veins (or anterior veins of right ventricle) comprise a variable number of small vessels, usually between two and five, which collect blood from the front of the right ventricle and open into the right atrium; the right marginal vein frequently opens into the right atrium, and is therefore sometimes regarded as belonging to this group.

Superior vena cava

superioranterior vena cavaSVC
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
The superior vena cava (SVC) is the superior of the two venae cavae, the great venous trunks that return deoxygenated blood from the systemic circulation to the right atrium of the heart.

Tricuspid valve

tricuspidtricuspid valvesheart
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
The function of the valve is to prevent back flow (regurgitation) of blood from the right ventricle into the right atrium during right ventricular contraction: systole.

Coronary sinus

cardiac vein
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
It delivers less-oxygenated blood to the right atrium, as do the superior and inferior venae cavae.

Mitral valve

mitralbicuspid valvemitral annulus
The left atrium receives the oxygenated blood from the left and right pulmonary veins, which it pumps to the left ventricle (through the mitral valve) for pumping out through the aorta for systemic circulation.
The mitral valve, also known as the bicuspid valve or left atrioventricular valve, is a valve with two flaps in the heart, that lies between the left atrium and the left ventricle.

Smallest cardiac veins

foramina venarum minimarumThebesian veinPericardial veins
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
The thebesian veins are most abundant in the right atrium and least in the left ventricle.

Pulmonary circulation

pulmonary vesselspulmonary circuitpulmonary
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
This blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle.

Mollusca

molluskmolluscmolluscs
The atrium was formerly called the "auricle"; that term is still used to describe this chamber in some other animals, such as the Mollusca.
The heart consists of one or more pairs of atria (auricles), which receive oxygenated blood from the gills and pump it to the ventricle, which pumps it into the aorta (main artery), which is fairly short and opens into the hemocoel.

Sinus venosus

sinus venarumVenosus
Internally, there are the rough pectinate muscles and crista terminalis of His, which act as a boundary inside the atrium and the smooth-walled part of the right atrium, the sinus venarum, which are derived from the sinus venosus.
The sinus venosus is a large quadrangular cavity which precedes the atrium on the venous side of the chordate heart.

Pulmonary vein

pulmonary veinspulmonaryPulmonary venous
The left atrium receives the oxygenated blood from the left and right pulmonary veins, which it pumps to the left ventricle (through the mitral valve) for pumping out through the aorta for systemic circulation.
The largest pulmonary veins are the four main pulmonary veins, two from each lung that drain into the left atrium of the heart.

Interatrial septum

atrial septumatrial septainteratrial
The interatrial septum separates the right atrium from the left atrium; this is marked by a depression in the right atrium – the fossa ovalis. The interatrial septum has an opening in the right atrium, the foramen ovale, which provides access to the left atrium; this connects the two chambers, which is essential for fetal blood circulation.
The interatrial septum is the wall of tissue that separates the right and left atria of the heart.

Fossa ovalis (heart)

fossa ovalisLimbus of fossa ovalislimbus fossae ovalis
The interatrial septum separates the right atrium from the left atrium; this is marked by a depression in the right atrium – the fossa ovalis.
The fossa ovalis is a depression in the right atrium of the heart, at the level of the interatrial septum, the wall between right and left atrium.

Pectinate muscles

pectinate muscleMusculi pectinati
Internally, there are the rough pectinate muscles and crista terminalis of His, which act as a boundary inside the atrium and the smooth-walled part of the right atrium, the sinus venarum, which are derived from the sinus venosus.
The pectinate muscles (musculi pectinati) are parallel ridges in the walls of the atria of the heart.

Sinoatrial node

sinus nodeSA nodesinoatrial
The sinoatrial (SA) node is located in the posterior aspect of the right atrium, next to the superior vena cava.
The sinoatrial node (also known as the SA node or the sinus node) is a group of cells located in the wall of the right atrium of the heart.

Jugular venous pressure

jugular venous distensionjugular venous distentionbulging neck veins
The atria do not have valves at their inlets, and as a result, a venous pulsation is normal and can be detected in the jugular vein as the jugular venous pressure.
Pulses in the JVP are rather hard to observe, but trained cardiologists do try to discern these as signs of the state of the right atrium.

Atrial septal defect

patent foramen ovaleatrialhole in the heart
This is known as a patent foramen ovale, an atrial septal defect.
Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart.

Foramen ovale (heart)

foramen ovalePatent foramen ovaleatrial septal
The interatrial septum has an opening in the right atrium, the foramen ovale, which provides access to the left atrium; this connects the two chambers, which is essential for fetal blood circulation.
In the fetal heart, the foramen ovale, also foramen Botalli, or the ostium secundum of Born, allows blood to enter the left atrium from the right atrium.

Crista terminalis

Internally, there are the rough pectinate muscles and crista terminalis of His, which act as a boundary inside the atrium and the smooth-walled part of the right atrium, the sinus venarum, which are derived from the sinus venosus.
In the development of the human heart, the right horn and transverse portion of the sinus venosus ultimately become incorporated with and forms a part of the adult right atrium where it is known as the sinus venarum.

Oblique vein of the left atrium

Oblique vein of left atriumoblique cardiac veinoblique vein
The oblique vein of the left atrium is partly responsible for venous drainage; it derives from the embryonic left superior vena cava.
The oblique vein of the left atrium (oblique vein of Marshall) is a small vessel which descends obliquely on the back of the left atrium and ends in the coronary sinus near its left extremity; it is continuous above with the ligament of the left vena cava (lig.

Systole

systolicsystolic pressureventricular systole
The atria receive blood while relaxed (diastole), then contract (systole) to move blood to the ventricles.
The mammalian heart has four chambers: the left atrium above the left ventricle (lighter pink, see graphic), which two are connected through the mitral (or bicuspid) valve; and the right atrium above the right ventricle (lighter blue), connected through the tricuspid valve.

Pulmonary artery

pulmonary arteriespulmonary trunkpulmonary artery pressure
The right atrium receives and holds deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins and smallest cardiac veins and the coronary sinus, which it then sends down to the right ventricle (through the tricuspid valve), which in turn sends it to the pulmonary artery for pulmonary circulation.
The mean pressure is typically 9 - 18 mmHg, and the wedge pressure measured in the left atrium may be 6-12mmHg.