PERICARDIUM AND HEART
I. PERICARDIUM
A. Double-walled fibroserous sac which surrounds and covers the heart and roots of great vessels
1. Serous pericardium - serous, lining layer
a. Parietal lamina - lines inside of fibrous pericardium
b. Visceral lamina - covers outside of heart = epicardium
2. Fibrous pericardium - C T layer outside of the parietal serous layer - forms bulk of the gross pericardial sac - fused to adjacent C T planes - pericardiacophrenic & sternopericardial lig.
3. Parietal pericardium - fibrous plus serous layers - separated from heart by a space
4. Visceral pericardium (epicardium) composed of serous pericardium covering heart and base of great vessels
5. Pericardial space - potential space between parietal and visceral layers - contains only a moistening layer of fluid
6. Serous pericardium = parietal and visceral layers
B. Pericardial sinuses - formed during folding of heart tube development
1. Transverse pericardial sinus: a space within the pericardial space
a. formed by reflections of serous pericardium from great vessels to heart
b. located posterior to great arteries (aorta and pulmonary a.) and anterior and superior to great veins (superior vena cava, pulmonary vv.)
2. Oblique pericardial sinus: a portion of the pericardial sac that forms a blind pouch where the pericardium is reflected from the pulmonary veins to the heart
C. Pericardial extent
1. Superiorly: fuses with adventitia of great vessels at level of the sternal angle
2. Inferiorly: rests on the diaphragm - fuses with fascia of the diaphragm
3. Laterally: fuses with mediastinal pleura
4. Posteriorly: fuses with adventitia of esophagus
D. Blood supply -
1. pericardiacophrenic - from internal thoracic
2. musculophrenic-terminal of I.T.
3. internal thoracic
4. esophageal aa. - from aorta
5. bronchial aa. - from aorta
6. pericardial – directly from aorta
E. Innervation
1. Phrenic n.(C3-5) - Sensory
2. Vagus n. (Parasympathetic) - Also contains GVA
3. sympathetic trunk - Contains nociceptive fibers and vasomotor fibers
II. HEART
A. Layers
1. Epicardium - visceral layer of the pericardium - external covering of heart
a. subepicardium - between epicardium and muscles - contains fat and major vessels to the heart
2. Myocardium - middle muscular layer – oblique fibers – torsion of chambers
3. Endocardium - inner lining layer - composed of endothelium backed by thin C T
a. subendocardium - just outside the endocardium - contains tissues of the conducting system
B. Surfaces
1. Base: faces posteriorly (T6-9), mostly left atrium - toward rt. shoulder
2. Apex: inferior, left corner of heart - formed by left ventricle - ICS5 - 10 cm left of midline
3. Diaphragmatic surface: inferior, rests on diaphragm - formed by both ventricles - mainly left ventricle
4. Sternocostal surface: anterior portion of heart - formed by both ventricles and right atrium - mostly right ventricle
5. Pulmonary - mainly LV - cardiac impression
C. Surface projection of the anterior thoracic wall - situated obliquely 2/3 to left and 1/3 to right
1. Superior border: inferior margin of 2nd left costal cartilage to superior border of 3rd right costal cartilage - extends 2-3 cm either side of sternum - RA, LA, aorta, PT
2. Right border: 3rd right costal cartilage to 6th right costal cartilage - 2 cm from median plane - RA
3. Inferior border: from inferior right border to 5th intercostal space near midclavicular line - RV, LV
4. Left border: connects superior and inferior borders - LV
5. Apex projection: can be palpated - 5th left interspace just medial to midclavicular line
(supine position) - erect posture, drops one interspace
D. Sulci
1. Coronary (atrioventricular) sulcus: encircles heart between atrium and ventricles
2. Anterior interventricular sulcus: between ventricles on sternocostal surface
3. Posterior interventricular sulcus: between ventricles on diaphragmatic surface
4. Sulci externally delineate the 4 chambers
E. Right atrium
1. Receives
a. Superior vena cava (SVC)
b. Inferior vena cava (IVC)
c. Anterior cardiac veins
d. Coronary sinus
2. Sulcus terminalis - slight groove running between the two venae cava near the right margin of the atrium
3. Auricle - anterior appendage, heavily muscled, may be site of embolism
4. Internal anatomy
a. Crista terminalis: ridge internally matching sulcus terminalis - separates smooth-walled sinus venosus (venarum) (where most veins enter) from more muscular anterior portion-embryonic origins are different
b. Pectinate muscles: ridge-like muscular bands in anterior portion
c. Fossa ovalis: depression along interatrial septum. Represents remnant of embryological foramen ovale – may be patent - septum secundum and septum primum
d. Orifice and valve of the coronary sinus, near septal cusp of a-v valve
e. Orifice and valve of inferior vena cava
f. Orifice of superior vena cava
g. Tricuspid valve – right A-V valve
F. Left atrium
1. Thin, smooth-walled chamber
2. Auricle - anterior appendage
3. Bicuspid valve - (A-V valve)
4. Orifices of the four pulmonary veins (2 superior- 2 inferior)
G. Right ventricle
1. Ends superiorly as conus arteriosus (infundibulum) - leads into PT
2. Muscular wall 1/3 as thick as left ventricle
3. Trabeculae carnae - raised ridges of muscular tissue
4. Papillary muscles: cone-shaped - connect internal walls to a-v valve cusps via chordae tendinae - 3 groups
a. anterior - from sternocostal wall - to A & P cusps
b. posterior - from diaphragmatic wall - to P & septal
c. septal - from i-v septum - to A & septal
d. attach to adjacent sides of 2 cusps
5. Septomarginal trabeculae (moderator band) - strip of muscle (mostly conducting tissue) connecting i-v septum with anterior papillary mm. - part of right bundle branch of A-V bundle
6. Infundibulum – smooth-walled – ends in pulmonary valve
7. Chorda Tendinae-attach to two different valve cusps (leaflet)-avascular
H. Left ventricle - forms apex
1. Ends superiorly as smooth-walled aortic vestibule
2. Muscular wall thick (3x that of Rt.)
3. Trabeculae carnae - finer and more numerous than rt. side
4. Papillary muscles
a. anterior - sternocostal wall
b. posterior - diaphragmatic wall
I. Interventricular septum
1. Muscular portion - lower portion
2. Membranous portion - upper corner, thin, little or no musculature - between i-v and right atrium common site of ventricular septal defect (VSD)
J. Arteries of the heart
1. Right coronary artery (RCA)
a. Arises from right aortic sinus
b. Courses in coronary sulcus from the aorta to region of the posterior interventricular sulcus
c. Branches
i. Right and Left marginal artery-toward apex and Rt. Ventricle
ii. Posterior interventricular artery - right dominant
iii. Sinuatrial (sinoatrial) branch - from rt. coronary (55%)
iv. Atrioventricular branch - from rt. coronary (85%) - at crux
v. Vasa vasorum
vi. Anastomosis w/ circumflex & ant. interventricular br.
2. Left coronary artery(LCA)
a. from left aortic sinus
b. from aorta to anterior interventricular sulcus where it divides
c. branches
i. Anterior interventricular (descending) artery (LAD)
ii. Circumflex coronary artery - w/ marginal artery
iii. Posterior interventricular artery - anastomosis with LAD
iv. Sinuatrial nodal br.
v. Left ventricular br. - marginal
3. Collateral circulation of the heart
a. Anastomotic connections variable - most are end arteries
b. React to sudden blockage as end arteries
4. Many variations in branching
K. Veins of the heart
1. Coronary sinus - posterior coronary sulcus - drains to rt. Atrium directly
2. Great cardiac vein- to coronary sinus
a. at left end
b. drains area supplied by left coronary a.(LAD primarily)
3. Middle cardiac vein - to coronary sinus - drains area of rt. coronary a.(most RIA) - post. IV septum
4. Small cardiac vein - to coronary sinus - drains area of rt. coronary a.(mostly ACA)
5. Anterior cardiac veins - to rt. atrium directly
6. Smallest cardiac vein - to chamber involved-drain myocardium
7. Oblique vein - lt. atrium - remnant of embryonic common cardinal vein
M. Heart valves
1. "Skeleton" of the heart -fibrous connective tissue to which valves and muscle of heart are attached - deep to coronary sulcus - support and rigidity, insulation-extend into the valve histologically - keeps orifices patent - attachment for valves & muscle insulator
a. Aortic fibrous ring (cuff) - origin of aorta
b. Pulmonary fibrous ring - origin of pulmonary trunk
c. Left and right a-v rings - surrounds a-v valves
d. Membranous portion of i-v septum - extension of aortic ring and rt. a-v ring
e. Right fibrous trigone - muscle attachments
f. Left fibrous trigone
2. Atrioventricular valves
a. Fibrous rings outline each valve
b. Each cusp has C T center with endocardium on each surface
c. Chordae tendinae attach each cusp to more than one papillary muscle
d. Bicuspid (mitral, left a-v) valve - anterior and posterior cusps
e. Tricuspid (rt. a-v) valve - anterior, posterior, septal cusps
3. Semilunar valves
a. Fibrous cuffs outline each valve
b. Each cusp has C T center with endothelium on both surfaces
c. Both valves have 3 cusps - no tendinous attachments
d. Edge of cusps subdivided in lunula and nodule – adds strength to cusp
e. Aortic semilunar valve - right, left and posterior cusps
i. 3 aortic sinuses superior to 3 cusps
ii. coronary arteries originate from right and left coronary sinuses
f. Pulmonary Semilunar valves (s)-R,L,Anterior
4. Surface projections of valves
a. Pulmonary - 3 - level of 3rd rib near left border of sternum
b. Aortic - 3 1/2 - level of ICS 3 near left border of sternum
c. Mitral - 4 - level of 4th rib near left border of sternum
d. Tricuspid - 4 1/2 - near ICS 4 near midsternum
5. Surface projections of valve sounds - projection of blood flow
a. Pulmonary - ICS 2 left of sternum - LUSB = L. upper sup. border
b. Aortic - ICS 2 right of sternum - RUSB
c. Mitral - apex of heart (ICS 5 near midclavicular line)
d. Tricuspid - near rib 6 right of sternum
N. Cardiac conduction system - composed of specialized cardiac muscle cells - coordinate cardiac cycle
1. Sinuatrial node (SA node) = pacemaker - specialized myocytes
a. located along upper end of sulcus terminalis - near SVC
b. initiates heart beat
c. supplied by both sympathetic (+) and parasympathetic nerves (-) - cardiac
plexus - myogenic conduction
d. blood supply via RCA
2. Atrioventricular node(AV) - located in interatrial septum adjacent to ostium (opening) of coronary sinus
3. Atrioventricular bundle (of His) - extends from a-v node along the i-v septum - Purkinje fibers
4. A-V bundle divides into right and left bundle branches in the septum (near junction of membranous and muscular part of septum) - R->Mod. band->R Papillary muscle; L->6 tracts->A&P Papillary muscle
5. Nodal arteries-from RCA and LCA (80% RCA)
O. Nerve supply to the heart - cardiac plexus (see diagram on next page)
1. Sympathetic innervation - SA & AV nodes - Increased heart rate & force; dilates coronary aa.
a. from cervical sympathetic trunk (cervical cardiac sympathetic nn.)
b. from direct branches of thoracic trunk (thoracic cardiac sympathetic nn)
c. preganglionic level: T1-5 - most ascend to synapse
d. GVA associated with ischemic pain and sensations reach CNS via sympathetic routes
2. Parasympathetic innervation - SA & AV nodes- Decreased heart rate & force; constricts coronary aa.
a. from vagus as cervical branches (superior and inferior)
b. from vagus as direct branches in thorax (thoracic)
c. GVA associated with visceral reflex activity reach CNS via vagal route
i. aortic bodies – in wall of ascending aorta – monitor(s) PCO2/PO2
ii. changes respiration rate
3. Cardiac plexus - both sympathetic and parasympathetic contributions - Sy (adrenergic)->atria & ventricles; Psy (cholinergic)->atria
a. Superficial plexus - located near aortic arch - input from:
i. Left inferior cervical br. of CN X
ii. Superior cervical sympathetic branches
b. Deep plexus - near tracheal bifurcation - all rest of inputs
i. Sympathetic = superior, middle and inferior (right), middle, and inferior (left)
ii. Parasympathetic = CN X
4. Functions - important influence on heart rate, contraction intensity, respiration rate, sensory (both Sy & Psy)
P. Referred pain - usually due to ischemia
1. Pain over midsternum, upper thorax and medial border of arm (ulnar radiation)
2. Related to dermatomes T1-2 (see dermatome maps below)
3. Impulses ascend via cardiac branches to sympathetic trunk at levels T1-5
4. Pain most noticeable in dermatomes T1-2
5. Visceral afferents run in sympathetic axons
a. middle cervical br. (C5-6)
b. inferior cervical br. (C7-T1)
c. thoracic cardiac br.
d. enter spinal cord T1-4