Circulatory system - Heart

Question 1

124. Heart (trichrome stain)

Answer 1

• plane section, parallel to cardiac axis
• proximal half: coronary sinus + RA + interatrial septum + coronary sulcus
• distal half: LV + bicuspid valve

Question 2

Cardiac skeleton

Answer 2

• 3 rings of dense fibrous tissue
• trigona fibrosa: CT wedges
• site of origin and insertion for cardiac muscles
• AV bundle passes through skeleton
• irregular, dense collagenous CT
• no elastic fibers
• fibrocyte nuclei

Question 3

Epicardium

Answer 3

• external surface: Mesothelial cells
• internal surface: loose areolar CT + blood vessels and nerves
• epicardial fatty tissue

Question 4

Myocardium

Answer 4

• myocytes, endothelial cells, capillary network, CT cells
• endomysium:
  
  • encloses network of fine reticular and elastic fibers
  • surrounds cardiac muscle cells
  • absent in sites of desmosomal contacts and gap junctions of intercalated disc
• perimysium:
  
  • thicker CT
  • clamps large bundles of cardiac muscle together
• atrial cardiac muscle:
  
  • fewer or no T-tubules
  • smaller sized myocytes
• lack of satellite cells

Question 5

Endocardium

Answer 5

• thinner than epicardium
• no large vessels or nerves
• inner wall: endothelial cells
• sub endothelial CT:
  
  • inner layer: elastic fibers + thin delicate CT
  • middle layer: smooth muscle
  • deep layer: rough collagen fibers
• endocardium is thinner in ventricle than atria

Question 6

Impulse-conducting cells

Answer 6

1. P-cells ⇒ d=5-8um
2. Transitional cells
3. Purkinje fibers
   - lighter stained bc fewer microfibrils + glycogen accumulation
   - cells of SA and AV nodes embedded in collagenous CT
   - next to nodes autonomous ganglia and nerves
   - Bundle of HIS:
   * arises from AV
   * pierces right fibrous trigone
   * divides into left and right branches
   - Purkinje fibers:
   * connected bu intercalated discs
   * larger than ordinary myocytes
   * separated from myocardium by CT

Question 7

Heart valves

Answer 7

• duplication of endocardium + central CT layer
• Fibrosa:
  
  • densly collagenous CT under endocardial surface
  • fibrosal fibers join fibers of cardiac skeleton
• Spongiosa:
  
  • loose collagenous and elastic fibrous CT under endocardial surface
  • serves as damper
• avascular structures
• chordae tendon are tendon-like cords of fibers covered by endothelium

Question 8

23. Heart- SA node (trichrome stain)

Answer 8

• pacemaker region in RA
• SA node:
  
  • elliptical structure
  • large sinuatrial nodal artery located in middle
  • nodal cells circularly around artery
  • embedded in dense collagenous tissue
  • P cells are slender small cells- few myofibrils
• over the node: epicardial adipose tissue
• many nerve fibers + autonomic ganglia close