11. The fibrous skeleton and chambers of the heart. The histology of the red bone marrow. Formation of red blood cells (erythropoesis).

1. The fibrous skeleton and chambers of the heart. The histology of the red bone marrow. Formation of red blood cells (erythropoesis).

Anatomy: The fibrous skeleton and chambers of the heart.

Heart – Fibrous skeleton & Chambers

Fibrous skeleton of Heart = anulus fibrosus
made of 4 rings, 2 trigones, 1 ligament

Function:

• separates atria from ventricles
• provides attachment of cusps of valves & myocardium (all musc originate and insert into it)
• keep AV and semilunar valves open, but inhibits over distension
• forms an electrical “insulator”, by separating the electric impulses of atria and ventricle, so they contract independently, and by surrounding and making a passage way through which AV bundles travel

Position of it can be shown on the external side of the heart as coronary groove (sulcus)

1. L fibrous ring – around bicuspid valve
2. R fibrous ring – around tricuspid valve
3. Pulmonary ring – pulmonary valve
4. Aortic ring – around aortic valve
5. R fibrous trigone – R fibrous ring + aortic ring
6. L fibrous trigone – L fibrous ring + aortic ring

Chambers of Heart: Will be doing this in order of blood flow

R atrium – receives de-O2 blood from systemic circulation via SVC, IVC
remember that 3 things enter the R atrium – SVC, IVC, coronary sinus
Structure to mention/identify:

1. R auricle = sup/ant part of atrium, covers origin of R coronary a, has the pectinate m, which are ridges of myocardium that push up into endocardium
2. Sinus venarum cavarum – smooth area where SVC, IVC enter the R atrium, as well as coronary sinus, and ant cardiac v.
3. Crista terminalis – crest like line b/w rough part of atria (where pectinate m are), and smooth area – shown externally as sulcus terminalis
4. Opening of coronary sinus –  a vein that receives most of v of heart itself, covered by Thebesian valve
5. SA node – show this by crista terminalis as superior most point of sinus venarum cavarum, where SVC enters – is primary pacemaker of heart
6. AV node – secondary pacemaker of heart, show this by pointing to the area b/w opening of coronary sinus and R AV valve
7. Fossa ovalis – show this on intra-atrial wall,
   
   • to find it – put thumb in R atrium, and forefinger in L atrium and pinch the intra-atrial wall
     
   • the thinnest part of this wall is fossa ovalis.
     
   • Or hold it up to the light, and this is where light shines thru the intra-atrial wall.
   • Remnant of foramen ovalis, an opening b/w 2 atria that existed in embryonic life
8. Tricuspid valve – leading to R ventricle

R ventricle – receives blood from R atria, and pumps blood into pulmomary trunk –> lungs to be re-O2’d, major portion of ant surface of heart
Structures to identify/mention:

1. Inflow limb – area that leads from R atria directly, where blood flows down, desc part of V in longitudinal section
2. Outflow limb = infundibulum = conus arteriosus – asc part of V in longitudinal section – sends blood into pulmonary trunk
3. Papillary m – show all 3; ant, post, septal – cone shaped m that attach to cordae tendinae, valves open when these contract
4. Chordae tendinae – dense reg CT cords that run from papillary m –> each cusp of tricuspid,
   • NOTE – b/c action of valve opening is active, when m. not contracted, valve closes passively –> prevents blood from returning to R atrium
5. Trabeculae carnae – ridges of myocardium that projects into endocardium
6. Supraventricular crest – a ridge that separates inflow and outflow limb and also lifts septal cusp of tricuspid – remnant of ridge b/w bulbus cordis and primary ventricle
7. Septomarginal traveculae- has moderator band – which carries Purkinje fibers to ant pap m, and interventricular septa from R limb of Bundle of His to sternocostal wall of ventricle,
8. Moderator band – musc bundle that runs from inf part of IV septa to base of ant papillary musc. Look for it and show if you can.
9. Interventricular septum – has both muscular/membranous part, wall b/w R & L ventricle, show membranous part just below pulmonary/ aortic valve.
   
   • To find membranous part of septum, again, put thumb in R ventricle and forefinger in L ventricle, and feel up to sup most part of interventricular septum.
     
   • The wall should feel thinner here – membranous part.
     
   • Like fossa ovale, this part will also have light shine through it.
     
   • This membranous part was where the ventricles were closed of by downgrowth of endocardial cushions in embryonic life
10. Bundle of His = AV bundle = Tawara = located in lower part of IV septa, tertiary pacemaker
11. Pulmonary valve – leads from outflow limb –> pulmonary trunk, show all three cusps; right, left, ant

L atrium – receives O2 blood from lungs via 4 pulmonary v (Remember from lung, that R lung has 3 pulmonary v, and L has 2, but R sup/mid pulmonary v combine, so only 4 pulmonary v enter heart)

• pulmonary v have no valves
• very capable of strong contraction
• most posterior of the 4 chambers, makes most of diaphragmatic surface of heart
• just anterior to esophagus

Structures to mention/identify:

1. L auricle – sup/ant part of atrium, also has pectinate m, but less than R atrium, musc are active in atrial systole, covers origin of L coronary a
2. Fossa ovale – can also be shown here, but shown better in R atria
3. Smooth area of L atria – where 4 pul v enter
4. Bicuspid valve – leading to L ventricle

L ventricle – receives O2 blood from L atria –> sends it to aorta

• wall much THICKER than R, b/c has to pump blood out to entire system = 15 mm thick
• divided into L ventricle proper & aortic vestibule (upper/ant portion of ventricle — leads to aorta)
• longer, narrower and thicker than R ventricle

Structures to mention/identify:

1. Papillary musc – only 2 here, one for each cusp of bicuspid valve cone shaped, m. that attach to cordae tendinae, valves open when these contract, also larger than R ventricle
2. Chordae tendinae – dense reg CT cords that run from papillary m –> each cusp of bicuspid
3. Trabeculae carnae – ridges of myocardium that projects into endocardium, many more than in R ventricle
4. Aortic ventricle – sometimes called outflow part of L ventricle, area leading to aortic valve.
5. Interventricular septum – has both muscular/membranous part, wall b/w R & L ventricle,
   • show membranous part just below pulmonary/ aortic valve.
   • To find membranous part of septum, again, put thumb in R ventricle and forefinger in L ventricle
   • and feel up to sup most part of interventricular septum.
     
   • The wall should feel thinner here =  membranous part.
     
   • Like fossa ovale, this part will also have light shine through it.
     
   • This membranous part was where the ventricles were closed of by downgrowth of endocardial cushions in embryonic life.

Histology: The histology of the red bone marrow.

Embryology: Formation of red blood cells (erythropoesis).

Erythropoiesis is the development of mature red blood cells (erythrocytes). Like all blood cells, erythroid cells begin as pluripotential stem cells. The first cell that is recognizable as specifically leading down the red cell pathway is the proerythroblast . As development progresses, the nucleus becomes somewhat smaller and the cytoplasm becomes more basophilic, due to the presence of ribosomes. In this stage the cell is called a basophilic erythroblast . The cell will continue to become smaller throughout development. As the cell begins to produce hemoglobin, the cytoplasm attracts both basic and eosin stains, and is called a polychromatophilic erythroblast . The cytoplasm eventually becomes more eosinophilic, and the cell is called an orthochromatic erythroblast . This orthochromatic erythroblast will then extrude its nucleus and enter the circulation as a reticulocyte . Reticulocytes are so named because these cells contain reticular networks of polyribosomes. As reticulocytes loose their polyribosomes they become mature red blood cells.