Heart Histology

Question 1

Fibrous Pericardium

Answer 1

Fibrocollagenous and Elastic tissue.

Fused to the diaphragm and the tunica adventitia of great vessels

Question 2

Parietal Serous Pericardium

Answer 2

Mesothelium cells with underlying LCT

Question 3

Visceral Serous Pericardium

Answer 3

(also the Epicardium)
Simple Squamous epithelium with underlying Fibroelastic connective tissue
Adipose tissue
Coronary vessels

Question 4

Myocardium

Answer 4

Cardiac muscle cells
Surrounding connective tissue
Nuclei of Fibroblasts visible
Blood vessels

Question 5

Endocardium

Answer 5

Simple squamous endothelium (luminal surface)
Underlying LCT
Some Purkinje Fibers may be visible
Nerves, some smooth muscle cells

*Atrial endocardium is thicker than ventricle endocardium

Question 6

Longitudinal arrangement of Cardiac Cells

Answer 6

Branching structure
Joined by intercalated disks (contain gap junctions & desmosomes)
Single nucleus

Question 7

Cross-section of Cardiac Cells

Answer 7

Single centrally located nucleus
Can see surrounding connective tissue layers

(endomysium around each muscle cell, perimysium around each fascicle and epimysium surrounds entire muscle?)

Question 8

Cardiac Muscle Ultrastructure

Answer 8

Striated (not as regularly as skeletal m)
Many mitochondria
Glycogen droplets
Less organised SR (compared with skeletal m)
SR and t-tubles form Diads (compared to triads in skeletal muscle)
Diads present at Z discs (not A/I junction as in skeletal m)
Intercalated discs between cells: desmosones, gap junctions
~15um diameter, ~100um long

Question 9

Describe the contraction of cardiac cells

Answer 9

Electrical depolarisation of the t-tubule activates channels in the SR resulting in release of Ca++ into the cytoplasm, which then allows cross-bridge cycling

Question 10

Describe Intercalated Disks

Answer 10

Join adjacent cardiac cells
Wavy arrangement
desmosomes on section that runs perpendicular to long axis of the cell
Gap junctions of section that runs parallel to long axis of the cell

Question 11

Atrial Cardiocytes - how do they differ from Ventricular cardiocytes?

Answer 11

In cross-section, A cardiocytes are smaller
Have more developed Golgi and RER
Because they produce membrane-bound granules containing Atrial Natriuretic Factor (ANF) - stimulates natiuresis and diuresis to manage hypervolaemia and HTN

Question 12

Fibrous Skeleton of the Heart

Answer 12

Fibrous Connective Tissue

Structural support

Surrounds valves, separates A/V (insulation)
Acts as anchorage point for cardiac muscle

Allows only the AV bundle to reach the ventricles from the RA (in normal hearts)

Question 13

Describe the conduction system of the heart

Answer 13

Pace-maker cells in SA node are specialised cardiac cells that determine rate of contractions of the heart: resting membrane potential is ~ -70mV. Usually 60-100bpm

Once depolarised, signal propagates throughout atrium and reaches AV node

AV node slows signal by 0.12 seconds to allow co-ordinated contraction of A and Vs

Signal propagates down rapidly conducting pathways: Bundle of His (specialised cardiac conduction cells)

Then the RBB and LBB

Which spreads signals to Purkinje systems in the L & R ventricles

Question 14

Characteristics of Purkinje Fibres

Answer 14

Specialised cardiac cells
Slightly enlarged
Roughly striated
High number of glycogen droplets puch myofibrils to the periphery
High concentration of mitochondria
Fewer myofibrils
Nuerous Gap junctions
Bi-nucleated

Question 15

Composition of the heart valve

Relationship to chordae tendiniae

Answer 15

Outgrowths of endothelium

On atrial side: Endothelial epithelium with underlying LCT (lamina spongiosa)

Fibro-elastic skeleton extending from a central fibrous body

chordae tendiniae tend to merge with fibrosa