HM Practical - Cardiac Histology

Embryology - 11 Dec 2023 Expand to Translate
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Introduction

Adult human cardiovascular system

HMA Practical 8 Virtual Slides

This page provides histology support information for cardiac histology.

Disclaimers

does not form part of the actual practical class based upon the virtual slides.
does not cover the pathology content.

Histology Links: Skeletal Muscle | Cardiac Muscle | Smooth Muscle

Cardiac Embryology

Introduction

Cardiac muscle, the myocardium, consists of cross-striated muscle cells, cardiomyocytes, with one centrally placed nucleus.

Nuclei are oval, rather pale and located centrally in the muscle cell which is 10 - 15 µm wide.
Cardiac muscle cells excitation is mediated by rythmically active modified cardiac muscle cells.
Cardiac muscle is innervated by the autonomic nervous system (involuntary), which adjusts the force generated by the muscle cells and the frequency of the heart beat.
Cardiac muscle cells often branch at acute angles and are connected to each other by specialisations of the cell membrane in the region of the intercalated discs.
- Intercalated discs invariably occur at the ends of cardiac muscle cells in a region corresponding to the Z-line of the myofibrils.
Cardiac muscle does not contain cells equivalent to the satellite cells of skeletal muscle.

Histology

Cardiac muscle histology

Image of primate heart stained with Alizarin blue.

Red Blood Cells (orange cells) Cardiac Muscle Cells (blue)
Cardiac muscle cells are cut longitudinally.
At high magnification see both striations and the large nuclei of the cardiac muscle cells.
Follow the course of individual cardiac muscle cells and note fine, dark blue lines which seem to cross (traverse) the fibres.
Intercalated Discs that connect the individual muscle cells and permit the conduction of electrical impulses between the cells.
- seen in longitudinal sections.

Unlabeled Images

Cardiac Layers

Endocardium

Inner layer of the heart, contains blood vessels. Has 3 sublayers
- Endothelium - innermost portion a simple squamous epithelium.
- Smooth Muscle and Connective Tissue - middle layer of the endocardium is mix of connective tissue and smooth muscle.
- Subendocardial Layer - outer layer of the endocardium is loose connective tissue joining the endocardium and myocardium.
equivalent to tunica intima.

Myocardium

Middle layer of the heart, thickest contains cardiomyocytes, blood vessels.
Muscular layer.
equivalent to tunica media.

Epicardium

Outer layer of the heart, contains blood vessels and lymphatics.
Visceral layer of pericardium rather thin.
equivalent to tunica adventitia.

Intercalated Discs

Cardiac muscle showing intercalated disc (electron micrograph)

seen in longitudinal sections.
connect the individual muscle cells.
permit the conduction of electrical impulses between the cells.

Histology "step-like" appearance due to:

transverse part - crossing fibres at right angle to myofibrils.
lateral part - runs in parallel to myofibrils.

Junctional Components

Adherens Junction	Desmosome	Gap junction
Fascia adherens – major portion of transverse component. Anchoring sites for actin, and connect to the closest sarcomere.	Macula adherens – (desmosomes) transverse and lateral components. Bind individual myocytes to one another. stop separation during contraction by binding intermediate filaments, joining the cells together. Macula adherens junctions are also called desmosomes.	Gap junctions - lateral component. Allow action potentials to spread between cardiac cells by passage of ions between cells, producing depolarization of the heart muscle. Allows muscle to act as syncytium.

Links: EM image - intercalated disc

Purkinje Fibres

Do not confuse these cardiac Purkinje fibres (cells) with neural Purkinje cells (neurons) located in the cerebellum.

modified cardiac muscle cells. Compared to ordinary cardiac muscle cells:
- contain large amounts of glycogen.
- fewer myofibrils.
- thicker cells.
can be binucleated (cell contains 2 nuclei).
extend from the atrioventricular node, pierces the fibrous body, divides into left and right bundles, and travels, beneath the endocardium, towards the apex of the heart.
bundle branches contact cardiac muscle cells through specialisations similar to intercalated discs.
conduct stimuli faster than ordinary cardiac muscle cells (2-3 m/s vs. 0.6 m/s).
discovered in 1839 by Jan Evangelista Purkyně).

Adult Heart Conduction System

Cardiac Valves

Note for the Semilunar valve slide is not anchored to the walls of the atria by chordae tendineae.

Only the mitral and tricuspid valves, located between the atria and the ventricles, are connected to the cardiac wall by chord tendineae and papillary muscles.

Terms

cardiomyocyte -
chordae tendineae - tricuspid and mitral valves connective tissue bands attached on the other end to the papillary muscles.
intercalated disc -
nodule - (of semilunar valve) small fibrous nodules located in the middle of the flaps, the nodules of the semilunar valve come closely together to fill the triangular opening.
Purkinje fibres -

Glossary Links

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Cite this page: Hill, M.A. (2023, December 11) Embryology HM Practical - Cardiac Histology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/HM_Practical_-_Cardiac_Histology

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