Confidential - International University of the Health Sciences

Heart Histology

January 2012

Dr. White, Ph.D.

Heart Histology Heart walls

• Contain/within the walls

– Cardiac muscle

– Fibrous skeleton

– Impulse-conducting system

• 3 layers make up the walls

– Epicardium

– Myocardium

– Endocardium

Dr. White, Ph.D.

Heart Histology Epicardium

• Faces pericardial space

• Serous membrane

– Simple squamous epithelium covering

– Connective tissue • Adipocytes

• Coronary vessels

• Nerves

Heart Histology Myocardium

• Cardiac muscle with connective tissue & blood vessels

• Myocardium of ventricles is thicker than that of the atria

X1000 blue arrows are capillaries

Heart Histology Endocardium

Gartner pg 162 & 163 figure 1 x 132

• Continuous with tunica intima of blood vessels

• 3 layers • Simple squamous epithelium & subendothelial CT

• Middle layer of dense collagenous & elastic fibers (even some smooth muscle cells)

• Borders myocardium composde of looser CT with blood vessels

Heart Histology Fibrous skeleton

• 4 fibrous rings surrounding valve openings

- Tricuspid

- Pulmonary

- Mitral

- Aortic

• 2 fibrous trigones connecting the rings

• Membranous part of the interventricular & interatrial septa

Heart Histology

Fibrous skeleton cardiac muscle and valve leaflets attach here Outer layer of heart: epicardium plus underlying loose CT Myocardium

Heart Histology

Endocardium: Endothelium simple squamous Subendocardial dense CT with elastic fibers, smooth muscle Subendocardium areolar ct with vessels nerves and conducting system

Heart Histology

Left ventricle – H and E – medium power

Lumen Endocardium Myocardium

Heart Histology

Left ventricle – H and E – medium power

Myocardium Epicardial fat Epicardial coronary artery

Heart Histology

Medium power High power Longitudinal sections of myocardium

Heart Histology

Cardiac muscle cells; central nucleus, joined by Intercalated disks (arrow)

Heart Histology

Heart Histology

Heart Histology

Heart Histology

Heart Histology

Heart Histology

Heart Histology

Heart Histology

Heart Histology

Atrial myocytes: Smaller than ventricle Less extensive t-tubule system, more gap junctions Contract more rhythmically

Heart Histology Impulse conducting system

• Functions for initiation & transmission of electrical impulses that result in cardiac muscle contraction • Purkinje fibers (specialized cardiac muscle cells) generate & conduct electrical impulses

Heart Histology

S-A Node generates electrical pulse

A-V Node conducts to ventricles

Right bundle branch Left bundle branch

Bundle Of His

Branches further into subendothelial branches also called Purkinje fibers

Heart Histology

Left side of interventricular septum – endocardium at top

Endocardium Purkinje cells Myocardium

Heart Histology

Heart Histology

The bundle of His is located immediately below the endocardium

Endocardium

Lumen

Bundle of His

Myocardium

Heart Histology

Heart Histology

Heart Histology Heart rate regulation

• Parasympathetic slows down the heart by release of acetylcholine causes constriction of the coronary arteries (bradycardia) and reduction in the force of heartbeat

• Sympathetic causes rate of contraction to increase thus increasing force of muscle contraction and inhibiting their constriction (tachycardia)

- Autonomic nerve fibers secrete norepinephrine which regulates impulses from the S-A node