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Heart Anatomy & Function · Acedra
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Heart Anatomy & Function
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0:03
the heart is a muscular organ just slightly bigger than a person's Loosely clenched fist it's located in the thorax more specifically between the two lungs in a space called the media stum the heart is covered by a tough membrane called the pericardium that separates the heart from the other structures in the media stum this position allows the heart to do its job which is to pump oxygen-rich blood to the entire body and to send poorly oxygenated blood to the lungs where gas exchange can take
0:37
place the heart is made up of four chambers and as a whole can be functionally divided into the right heart made up of the right atrium and the right ventricle and a left heart made up of the left atrium and left ventricle both Atria have pouchlike protrusions called oracles which can increase the capacity when needed
1:02
okay now poorly oxygenated blood from our bodies and other tissues enters the right atrium through the superior vnea and inferior vnea from there blood passes into the right ventricle which pumps into the pulmonary trunk on a voyage towards the lungs and is considered part of the pulmonary circulation on the other hand after gas exchange takes place in the lungs oxygenated blood returns from the lungs through four pulmon AR veins which drain into the left atrium then oxygenated
1:34
blood goes in the left ventricle and from there it's pumped into the aorta so that it reaches the whole body and is considered part of the systemic circulation so looking at it in three dimensions the heart looks like an upside down tipped over pyramid with four sides a base that's mostly posterior and an apex or tip that points anteriorly and slightly to the left on an anterior or posterior view in two Dimensions the heart is shaped like a trapezoid so it has a superior and
2:07
inferior as well as a right and left border it's important to understand what comprises the borders of the heart because the heart is rotated to the left on its longitudinal axis within the medyum so the Apex is directed more posterior laterally the superior border is formed by the right and left Atria along the superior border from right to left there's a superior vnea which enters the right atrium then there's ascending aorta which emerges from the left ventricle and then curves
2:41
posteriorly to form an arch called the aortic Arch finally there's a pulmonary trunk and its two branches the right and left pulmonary artery with the right pulmonary artery going under the aortic Arch the inferior border is almost horizontal and is made up mainly by the right ventricle and part of the left ventricle the right border is made up by the right atrium and it's between the superior and inferior vnea and finally the left border is mainly made up by the
3:12
left ventricle and part of the left Oracle now pay a bit of attention here because the end of the inferior border along with the lower part of the left border make up the apex of the heart which represents the tip of the left ventricle some of these features can also be identified on a PO Z anterior chest x-ray the heart silhouette is between the lungs and the right border made up by the right atrium as well as the left border made up by the left ventricle and part of the left Oracle
3:41
can be clearly seen above the left Oracle we can identify the pulmonary artery and the aortic Arch the superior and inferior borders of the heart aren't as easy to see as the right and left borders now let's identify the structures in an anterior and poster ior view on an anterior view we can identify several structures starting with the four chambers and ending with the great vessels from right to left there's most of the right atrium located superiorly and inferiorly to it the right
4:16
ventricle they're separated by the coronary sulcus also called the atrio ventricular groove or AV Groove for short then there's the Oracle of the left atrium and the left ventricle which are also separated by the coronary sulcus the right ventricle and left ventricle are separated by the anterior interventricular sulcus moving on you can actually see parts of the great vessels on an anterior view so from right to left there's part of the superior vena which
4:49
opens in the Superior part of the right atrium then there's part of the inferior vnea which also opens in the right atrium but the opening can only be seen on a posterior view then there's the ascending aorta which emerges from the left ventricle and then arches toward the back to form the aortic Arch the branches of the aortic Arch can also be seen and from right to left they are the brachio falic trunk which branches into the right subclavian artery and right common cored
5:19
artery the left common caded and the left subclavian artery finally medial to the left Oracle there's the pulmonary trunk which emerges from the right ventricle and branches into the left and right pulmonary arteries with the right pulmonary artery going under theoric Arch interestingly enough the superior portion of the proximal left pulmonary artery is connected to the inferior surface of the aortic Arch by the ligamentum arteriosum even though this fancy termed
5:51
element is just a fibrous band now fact during embryological development it used to connect the aortic Arch and the pulmonary trunk as an adaptation of fetal circulation to intrauterine
6:06
life now on a posterior view we can see the left atrium and the left Oracle most of the left ventricle as well as the right atrium and right ventricle as before the Atria and ventricles are separated by the coronary sulcus but now the right and left ventricle are separated by the posterior intraventricular sulcus in the upper portion above the coronary sulcus there are the great vessels the left and right pulmonary veins which bring oxygenated blood into the left atrium and the left and right
6:39
pulmonary arteries which emerge from the pulmonary trunk and bring deoxygenated blood to the lungs above them the aortic Arch and the superior and inferior vnea it's also important to visualize that the most anterior portion of the heart is the right ventricle and the most posterior part of the heart is a left atrium which lies directly anterior to the esophagus and time for a pop quiz what are the borders of the heart and what structures form
7:15
them very well let's get back at it now let's have a look at each chamber of the heart starting with the right atrium this is the right anterior lateral view of the heart where we dissected the right atrium in order to see its contents the right atrium has a smooth thin walled posterior part called the sinus vum were both Superior and inferior vnea as well as a coronary sinus open then there's a rough muscular anterior part formed by the pectinate muscles externally the smooth and rough
7:50
parts of the atrium are separated by a vertical shallow Groove called the sulcus terminalis internally these structures are separated by a vertical Ridge called the Christa terminalis inferiorly you can also see the right AV orifice also known as a tricuspid orifice which is where the blood from the atrium goes into the ventricle now the superior venina CA enters through the Superior part of the right atrium which is roughly at the level of the third costal cartilage the inferior vnea opens
8:24
inferiorly almost parallel to the superior vnea roughly at the level of the the fifth costal cartilage finally the coronary sinus opens between the tricuspid orifice and the inferior vena orifice now the right and left atrium are separated by the intraatrial septum which has a depression called The Oval fosa or fosa ovalis which is a remnant of the oval Forin or Forin ovali that connected the Atria during embryological development in fetal life oxygen-rich
8:57
and nutrient-rich blood travels directly into the left atrium from the right atrium via the foreno valley to bypass the pulmonary circulation let's stay on the right track and move into the right ventricle just like before we're going to look at an anterior view of the heart where we dissected the right ventricle the right ventricle has an inflow part where blood gets inside The ventricle and the outflow part through which blood leaves the right ventricle the inflow part has
9:27
muscular elevations called the dular carne and the outflow of heart is formed by an infundibulum called the conus arteriosis located superiorly and leads to the pulmonary trunk so far so good now the right ventricle receives blood from the right atrium through the tricuspid orifice which is posterior to the body of the sternum at the level of the fourth and fifth intercostal space the tricuspid orifice is surrounded by a fibrous ring that's part of a fibrous skeleton of the heart
9:57
keeping its shape constant and in order for blood to flow from the right atrium to the right ventricle at exactly the right time during each heartbeat there's a tricuspid valve attached to the tricuspid orifice it's called the tricuspid valve because it has three cusps or leaflets that open and close during syy and diast an anterior one a posterior one and a sepal one the base of each cusp is attached to a fiberous ring while the free edges of the cusps are attached to
10:29
tendonous cords called the cordate tendon these cordate tendon anchor the leaflets to the papillary muscles which are projections of the right ventricle the anterior papillary muscle is the largest one and arises from the anterior wall of the right ventricle its cord tendon attached to the anterior and posterior cusps of the valve then there's a posterior papillary muscle that arises from the inferior wall of the right ventricle it's cord tendon attached to the posterior and
11:01
sepal cusps and finally there's a sepal papillary muscle which arises from the intraventricular septum and cordate tendon attached to the interior in sepal cusps this smart and complicated mechanism is mainly meant to block the back flow of blood from the right ventricle to the right atrium during syy which is when the heart contracts to pump blood out of the ventricles okay we're not done with the right ventricle hang in there the inter ventricular septum or IBS separates the
11:32
two ventricles and forms a part of the wall of each ventricle it's made up of muscular and membranous parts now the muscular part of the IVs is mostly part of the left ventricle so it's two to three times thicker than the rest of the right ventricle the membranous part is a thin membrane that's part of the fibros skeleton of the heart and it's located superiorly and posteriorly on the right side of the IVs the seple cusp of the trius ID valve attaches to the middle of the membranous
12:02
part finally in the right ventricle there's also a muscular bundle that crosses from the inferior part of the IVs to the base of the anterior papillary muscle this is called the moderator band or septomarginal tracula and it helps the right ventricle contract properly by making the anterior papillary muscle contract at the same time as the other two papillary muscles so to put all these structures into perspective let's briefly talk about blood flow the right atrium
12:33
contracts when the right ventricle is empty and relaxed so blood from the right atrium passes through the tricuspid valve and enters the right ventricle finally blood then leaves the right ventricle through the pulmonary valve which is located at the level of the third costal cartilage and enters the pulmonary trunk where blood is sent to the lungs for
12:56
oxygenation okay now let's pause for a heart beat and see if you can identify the structures that make up the right atrium and
13:07
ventricle okay if you didn't get them all right no worries we can go left now starting with the left atrium the left atrium is slightly thicker than the right atrium and along with the left Oracle and the pectinate muscles within it forms a large part of the base of the heart the rest of the left atrium is smooth the four pulmonary veins namely the left Superior left inferior right Superior and right inferior pulmonary veins enter the smooth part of the left atrium
13:41
posteriorly unlike other structures of the heart the pulmonary veins don't have any Valves and blood flows through them and into the left atrium freely now on the intraatrial septum there's a semi lunar depression indicating the floor of the oval faasa with a surrounding Ridge being the valve of the oval faasa which as we mentioned before used to represent a communication between the Atria during embryonic development finally inferiorly there's a left AV orifice or mital orifice through
14:13
which blood flows from the left atrium into the left ventricle finally let's look at the left ventricle which forms the apex of the heart since the pressure inside the left ventricle is higher its walls are two to three times as thick as those of the right ventricle the left ventricular walls have more but finer tabula carne than the right ventricle it also has a smooth walled non-muscular part which is called the aortic vestibule which leads to the aortic orifice and aortic valve the aortic
14:46
valve is located posterior to the left of the sternum at the level of the third intercostal space the mitro orus is surrounded by the mital valve which is located posterior to the sternum at the level of the fourth cost cartilage the mitro valve is also referred to as a bicuspid valve as it only has two cusps anterior and posterior compared to the three cusps of the tricuspid valve each of the cusps are attached to the papillary muscles through cord tendon which allow the cusps to resist
15:17
the high pressure during heart contraction now that we're done with the heart chamers we'll now take a look at the pulmonary trunk and aorta blood flows from the right ventricle to the pulmonary trunk via the pulmonary semi lunar valve while blood flows from the left ventricle to the ascending aorta via the aortic semi lunar valve these valves each have three cusps called the semi lunar cusps the pulmonary valve has an anterior a right and left cusp while the aortic valve has
15:51
a posterior right and left cusp unlike the tricuspid and mitro valves the sem lunar valves are smaller and don't have cord tendon to support them instead during ventricular relaxation blood is forced backwards into the heart where the cusps catch its reverse blood flow and snap close like an umbrella caught in the wind the cusps edge come together to close the semi lunar Valves and support each other as their edges meet to prevent backf flow the edge of each cusp
16:25
is thickened where they meet forming the lunal and at the AP apex of the angulated free Edge they form the nodule during ventricular contraction the semi lunar valves open as they are pressed towards the walls of the pulmonary trunk and aorta Superior to each semi linar cusp the walls of the origins of the pulmonary trunk and the aorta are a bit dilated forming a sinus where blood gets in to prevent the cusp from sticking to the wall of the vessel when they open and it also helps them close back
16:57
up the sinus formed above the right aortic cusp is the origin of the right coronary artery and the sinus formed about the left aortic cusp is the origin of the left coronary artery both of which nourish the heart muscle during ventricular relaxation when the semi lunar valves are closing the back flow of blood towards the heart fills these sinuses and the force of this back flow is what allows left and right coronary arteries to fill now before going any any further
17:29
let's take a look at the conducting system of the heart which consists of nodal tissue that automatically generates and transmits impulses that produce coordinated contractions of the heart muscle effectively turning the heart into a pump one special noal tissue is a sinoatrial or SA node located anterior laterally at the junction of the superior vnea and right atrium near the superior end of the sulcus terminalis the SA node is is the pacemaker of the heart and it establishes the basic heart
18:03
rhythm then there's the atrio ventricular or AV node which is a smaller bit of nodal tissue located in the posterior inferior region of the intraatrial septum near the opening of the coronary sinus the way it goes is that the SA node initiates an Impulse that's conducted in the Atria making them contract the impulse then spreads to the AV node and afterwards the AV node spreads the impulse to the ventricles to the AV bundle finally at the junction of the membranous and muscular part of the IVs
18:37
the AV bundle spreads into a right and left branch that further stimulates the IVs and then the respective ventricles through smaller branches called the pingi fibers this way the ventricles can contract effectively and that's the basic electrophysiology of how the heart coordinates its contractions so blood can leave the heart and reach every organ in the body in addition to the conducting system of the heart the heart is supplied by the cardiac plexus which is
19:07
most commonly found on the anterior surface of the bifurcation of the trachea posterior to the ascending aorta and the bifurcation of the pulmonary trunk the cardiac plexus has both sympathetic and parasympathetic fibers as well as visceral aphant fibers for the reflexive and nocioceptive or pain sensing fibers of the heart heart the fibers of the cardiac plexus run along the coronary vessels and conducting
19:37
system sympathetic innervation is from pre synaptic fibers with cell bodies found in the superior 5 to six thoracic segments of the spinal cord and post synaptic sympathetic fibers with cell bodies in the cervical and Superior thoracic par vertebral ganglia of the sympathetic trunks post synaptic fibers travel across cardiopulmonary splenic nerves and the cardiac plexus ending in the sa and AV nodes and they also have connections with the terminations of parasympathetic fibers on the coronary
20:10
arteries sympathetic innervation is needed to increase heart rate the force of heart contractions and increased flow through the coronary vessels to support the increased activity these actions are crucial if you're caught in the wrong neighborhood and are running from a pack of kittens
20:30
parasympathetic innervation which slows the heart rate and kicks in after you've escaped all those kittens derives from PR synaptic fibers of the vagus nerves post synaptic parasympathetic cell bodies are located in the atrial wall and the intraatrial septum near the sa and AV nodes and along the coronary arteries all right as a quick recap the heart is a muscular organ located in the medyum OR thorax between two lungs the heart has four chambers two Atria separated by the intraatrial septum and
21:01
two ventricles separated by the intraventricular septum the right atrium receives deoxygenated blood from the superior and inferior vnea and it sends it to the right ventricle through the tricuspid valve which has three cusps that attach to the papillary muscles via cord tendon then the blood passes to the pulmonary Sumer lunar valve and reaches the lungs via the pulmonary trunk and its two main branches the left and right pulmonary arteries the left atrium receives oxygenated
21:31
blood from the four pulmonary veins and then sends it to the left ventricle through the mitro valve also attached to papillary muscles via cord tendon from the left ventricle blood is pumped into the aorta through the aortic semilunar valve reaching the rest of the body the heart has a conducting system made up of the SA node located interior laterally at the junction of the superior vnea and right atrium the AV node located in the posterior inferior region of the interatrial
22:05
septum now on an anterior view you can see the following structures the coronary sulcus the anterior intraventricular sulcus the superior and inferior vnea the ascending aorta and the pulmonary trunk as well as the ligamentum arteriosum on a posterior view you can see the posterior in intraventricular sulcus left and right pulmonary veins left and right pulmonary arteries the aortic Arch and the superior and inferior
22:44
vinaa The Heart Is inated by sympathetic and parasympathetic nerve fibers from the cardiac plexus which is most commonly found on the anterior surface of the bifurcation of the trachea
22:59
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