Gross Anatomy Module 3: Pericardium and the Heart (internal and external features)

Mediastinum is the

Central compartment of thoracic cavity, extending from superior thoracic aperture to diaphragm inferiorly and from sternum and costal cartilages anteriorly to thoracic vertebrae posteriorly. It is occupied by mass of tissue between the two pulmonary cavities.

Mediastinum is covered

on each side by the mediastinal surface of the parietal pleura

Mediastinum contains

all thoracic viscera except the lungs, and it's highly mobile owing to containing hollow (air- or liquid-filled) visceral structures united by loose connective tissue

Mediastinum parts

-Superior mediastinum

-Inferior mediastinum

-Anterior mediastinum

-Middle mediastinum

-Posterior mediastinum

Superior mediastinum:

extends inferiorly from the superior thoracic aperture to the horizontal plane (transverse thoracic plane: sternal angle → IV disk of T4 - T5)

Inferior mediastinum:

between transverse thoracic plane and diaphragm, further divided by pericardium

Middle mediastinum:

contains the heart, roots of great vessels, and pericardium

Pericardium

A fibroserous membrane that comprises the middle mediastinum and covers the heart and the roots of its great vessels (ascending aorta, pulmonary trunk, and SVC)

Pericardium layers

fibrous and serous (parietal and visceral)

fibrous pericardium

tough, white fibrous connective tissue that is the outer layer of the pericardium. contains Sternopericardial ligament

Fibrous pericardium stabilizes

the heart and protects it against sudden overfilling

Fibrous pericardium is continuous superiorly with...

the great vessels entering and leaving the heart, and with the pretracheal layer of deep cervical fascia

Fibrous pericardium is continuous inferiorly with...

the central tendon of the diaphragm as the pericardiacophrenic ligament

Sternopericardial ligament:

attaches fibrous pericardium anteriorly to the posterior surface of sternum

fibrous pericardium bound posteriorly to

structures of the posterior mediastinum by loose connective tissue

serous pericardium

the inner layer of pericardium, which IS a serous tissue and made of two layers (parietal layer and the visceral layer)

Serous pericardium parietal layer

lines internal surface of the fibrous pericardium and it reflects onto heart at the great vessels

Serous pericardium visceral layer

lines external surface of the heart, forms epicardium (outermost layer of the heart wall)

pericardial sac

potential space between parietal and visceral layers of serous pericardium

transverse pericardial sinus

runs transversely within the pericardial cavity between the aorta and pulmonary trunk & the superior vena cava

Oblique pericardial sinus

pocket-like recess in the pericardial cavity formed by the L atrium. It is a blind sac

Pericardium Arteries-Pericardiacophrenic artery:

branch of the internal thoracic artery that accompanies the phrenic nerve to the diaphragm

Pericardium veins-Pericardiacophrenic vein:

tributary of the brachiocephalic (or internal thoracic) veins

Pericardium nerves

Phrenic nerve (C3 - C5)

Sympathetic trunk

Vagus nerve

Pericardium phrenic nerve

sensory (pain is referred to the skin of dermatomes C3 - C5, area where we more commonly receive sensation)

Pericardium sympathetic trunk

vasomotor

Pericardium Vagus nerve

function uncertain

Heart's external feature

-4 chambers: 2 atria & 2 ventricles

-Coronary sulcus (atrioventricular groove)

-Anterior and Posterior interventricular sulci

-Apex

-Base

Coronary sulcus (atrioventricular groove):

demarcate atria from ventricles

Anterior and Posterior interventricular sulci:

demarcate the R & L ventricles

apex of the heart

-Inferolateral part of L ventricle

-Posterior to left 5th intercostal space

-Remains motionless during the cardiac cycle

-Sound of mitral valve closure is maximal

Base of the heart

-Opposite the apex, facing posteriorly toward the body of thoracic vertebrae (T6 - T9)

-Formed primarily by L atrium, and lesser contribution by R atrium

-Receives pulmonary vv. and SVC and IVC

Cardiac cycle

synchronous pumping action of the atrioventricular chambers

-Diastole

-Systole

Heart Sounds

snap shut of the oneway valves of the heart

1st sound (lub)

closure of the tricuspid and mitral valves, after emptying of atria

2nd sound (dub)

closure of the semilunar (aortic and pulmonary) valves, after emptying of ventricles

The wall of the heart consists of three layers

the epicardium (external layer), the myocardium (middle layer) and the endocardium (inner layer).

epicardium

thin external layer (most superficial) formed by the visceral layer of serous pericardium

Myocardium

muscular, middle layer of the heart. cardiac muscle

endocardium

inner layer of the heart; lines the heart chambers and valves

heart skeleton (fibrous skeleton)

Is made up of four rings of thick connective tissue which surround the base of the heart and large vessels. Framework formed of dense cartilaginous rings that surround the orifice of the valves

The heart skeleton, a fibrous skeleton, keeps orifices of the valves

patent and prevent their over-distention, and provide attachments for the valves

the heart skeleton, a fibrous skeleton, provides

Provides attachment for the myocardium

the heart skeleton, a fibrous skeleton, forms

an electric insulator for impulses of the atria and the ventricles

Heart Surfaces

- anterior (sternocostal) surface

- inferior (diaphragmatic) surface

- left pulmonary surface

- right pulmonary surface

anterior (sternocostal) surface of the heart

This heart surface is formed mainly by the right ventricle

Inferior (diaphragmatic) surface of the heart

-primarily the left ventricle

-lesser contribution by right ventricle

Right pulmonary surface

formed mainly by the right atrium

Left pulmonary surface

formed mainly by the left ventricle

heart borders

trapezoid in shape

Superior, right, left, inferior

Right border of the heart is formed by

the right atrium and extends between the superior vena cava and the inferior vena cava

Inferior border of the heart is formed by

Right ventricle and lesser contribution by Left ventricle

Left border of the heart is formed by

Left ventricle and left auricle

Superior border of the heart is formed by

right and left atria and auricles of the atria

The heart's big vessels have

entrances and exits to and from the heart

Heart Entrances

Right atrium and left atrium

Right atrium

Superior Vena Cava (SVC), Inferior Vena Cava (IVC), and coronary sinus. Receives deoxygenated blood from the body.

Left atrium connects to the

right and left pulmonary veins

Heart exits

right ventricle and left ventricle

Blood exits the right ventricle from the

pulmonary trunk

left ventricle pumps

oxygen-rich blood into the aorta (the largest artery in the body)

Heart chambers: right atrium

-Forms R. border of the heart

-Receives blood from the SVC, IVC, and coronary sinus

-Auricle

Auricle:

conical muscular pouch projecting from the R. atrium, and increasing its capacity

Right atrium (location)

upper right chamber of the heart and overlaps the ascending aorta

The interior of the right atrium

- Sinus Venarum

- Pectinate muscles

- Right AV orifice

Sinus venarum

smooth, thin-walled, posterior part; where SVC, IVC, and coronary sinus open

Pectinate muscles:

rough, muscular anterior wall

Right atrioventricular orifice:

R. atrium discharges the low-oxygen blood into R. ventricle

Sulcus terminalis

external vertical groove separating the smooth and rough parts of the R. atrium

Crista terminalis:

internal vertical ridge separating the smooth and rough parts of the R. atrium

superior vena cava

opens into superior part of R. atrium, at the level of the 3rd costal cartilage

inferior vena cava

opens into the inferior part of R. atrium, at the level of 5th costal cartilage

Opening of the coronary sinus:

short trunk receiving most cardiac veins, between the right Atrioventricular. orifice and the Inferior vena cava orifice

Interatrial septum:

separate atria

Oval fossa

oval depression on right side of interatrial septum, and it is the remnant of the foramen ovale in the fetus

right ventricle

-Forms the largest part of anterior surface of the heart, a small part of the diaphragmatic, and almost entire inferior border

-Outflow into the pulmonary trunk leaves superiorly and to the left, with the blood having a U-shape (140˚) trajectory inside the R. ventricle

interior of right ventricle

- Conus arteriosus

- Trabeculae carneae

- Supraventricular crest

- Right AV orifice

conus arteriosus of the right ventricle

smooth muscle wall, forming a superior narrowing of the ventricle, which leads into the pulmonary trunk

tabeculae carneae of the right ventricle

internal irregular muscular elevations

Supraventricular crest:

thick muscular ridge, separating the ridged muscular wall from the smooth wall of the conus arteriosus

Right AV orifice

receives low-oxygen from the R. atrium, at the level of the 4th - 5th intercostal spaces

Triscupid valve:

guards the right AV. orifice, attached to the fibrous ring around the right AV. orifice

Tendinous cords:

attach to free edges and ventricular surface of the anterior, posterior, and septal cusps, and to the apices of the papillary muscles

Papillary muscles:

conical muscular projections, with base on the ventricular wall

-Anterior: largest and most prominent, arises from anterior wall and attaches to anterior and posterior cusps

-Posterior: arises from inferior wall and attaches to posterior and septal cusps

-Septal: arises from interventricular septum and attaches to anterior and septal cusps

anterior papillary muscle of right ventricle

largest and most prominent, arises from anterior wall and attaches to anterior and posterior cusps

Posterior papillary muscle of right ventricle

arises from inferior wall and attaches to posterior and septal cusps

Septal muscle of right ventricle

arises from interventricular septum and attaches to anterior and septal cusps

Interventricular septum:

muscular and membranous parts located between the R. and L. ventricles

Septomarginal trabecula (moderator band):

curved muscular bundle running from inferior part of interventricular septum to base of anterior papillary muscle. Carries part of the right branch of the AV bundle and prevents overdistension

Pulmonary valve:

at the apex of the conus arteriosus and at the level of the 3rd costal cartilage, separates the right ventricle from the pulmonary trunk during filling of the ventricle.

left atrium

-Forms most of base of heart

-Receives the pairs R. & L. pulmonary veins in its smooth muscle wall

-Auricle

-Left AV. orifice: L. atrium discharges into the L. ventricle high-oxygen blood

left atrium (auricle)

trabeculated wall with pectinate muscles, and extends the L. atrium, overlapping the root of the pulmonary trunk

left ventricle functions

-Forms apex of heart, almost all of the pulmonary surface and border, and most diaphragmatic surface

-Performs more work than R. ventricle because of higher arterial pressure

-Outflow into the aorta leaves superiorly and to the right, with the blood having a U-shape (180˚) trajectory inside the L. ventricle

interior of left ventricle

- Walls 2-3 times thicker than right ventricle

- Covered with mesh of trabeculae (finer and more numerous)

- Larger conical cavity than right ventricle

- Anterior and posterior papillary muscles: more developed than in right ventricle

- Tendinous cords and papillary muscles attach to the anterior and posterior cusps

-Aortic vestibule

-Mitral valve

-Aortic orifice

-Aortic valve

Aortic Vestibule (Left Ventricle):

smooth-walled, leading to the aortic orifice and aortic valve

Mitral valve (left ventricle):

guards the right AV. orifice. Located posterior to sternum at the level of the 4th costal cartilage, with anterior and posterior cusps only

Aortic orifice

lies in the right posterosuperior part

Aortic valve

between L. ventricle and ascending aorta at the level of the 3rd intercostal posterior to left side of stern

Heart Vasculature

-Formed by coronary arteries and cardiac veins

-Blood exchange of the myocardium

-Run across the surface of the heart just deep to the epicardium (visceral layer of serous pericardium)

-Anastomoses

-Regulated by sympathetic and parasympathetic systems

anastomoses

the potential exists between the arteries -> potential collateral circulation in the heart, but the coronary arteries are terminal end arteries