Cardiac Structure and Myocardium Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary cause of worldwide mortality as mentioned?

Respiratory diseases

Cancer

Diabetes mellitus

Cardiovascular disease (correct)

Which of the following best describes cardiomegaly?

Decrease in chamber volume

Increased cardiac weight or size (correct)

Normal heart structure

Increase in heart rate

What contributes to the unique pumping function of the left ventricular myocytes?

Absence of connective tissue

Random arrangement of myocytes

Spiral circumferential orientation (correct)

Less robust contractile forces

Which layer is NOT part of the trilayered architecture of heart valves?

Myocte layer Signup and view all the answers

What change occurs in the left atrial cavity size during heart failure?

Increased left atrial cavity size Signup and view all the answers

How does aging affect the left ventricular cavity?

Left ventricular cavity size is reduced Signup and view all the answers

Which of the following describes a common mechanism contributing to heart failure?

Regurgitant flow Signup and view all the answers

What structural change is associated with the valves in heart failure?

Fibrous thickening of leaflets Signup and view all the answers

What is one of the endocrine functions of ventricular myocytes?

Contain B-Type Natriuretic Peptide Signup and view all the answers

What characteristic is observed in the right ventricular myocytes compared to the left?

Less structured organization Signup and view all the answers

Which of the following best describes the Frank-Starling mechanism?

Enhances contractility with increased filling volumes Signup and view all the answers

What is the role of the Renin-Angiotensin-Aldosterone System in heart failure?

Promotes water and salt retention Signup and view all the answers

Which component of the conduction system serves as the primary pacemaker of the heart?

Sinoatrial (SA) Node Signup and view all the answers

Which change occurs in epicardial coronary arteries during heart failure?

Increased atherosclerotic plaque Signup and view all the answers

Which of these is NOT a physiological mechanism that maintains arterial pressure during heart failure?

Myocardial necrosis Signup and view all the answers

What is characterized by a dilated ascending aorta and a rightward shift in heart failure?

Changes in the aorta structure Signup and view all the answers

What type of hypertrophy is characterized by new sarcomeres being assembled in series, primarily leading to ventricular dilation?

Eccentric Hypertrophy Signup and view all the answers

Which is NOT a cause of left-sided heart failure?

Congestive Heart Failure Signup and view all the answers

Which symptom is commonly associated with left-sided heart failure?

Cough and dyspnea Signup and view all the answers

What morphological change is typically seen in the lungs of patients with left-sided heart failure?

Pulmonary congestion and edema Signup and view all the answers

Which of the following is true about diastolic heart failure?

Hypertension is a common underlying cause. Signup and view all the answers

What is a common clinical manifestation of both systolic and diastolic heart failure?

Tachycardia Signup and view all the answers

What is the appearance of the liver in right-sided heart failure?

Nutmeg liver Signup and view all the answers

Which process leads to hypertrophy in response to pressure overload?

Parallel assembly of sarcomeres Signup and view all the answers

Study Notes

Cardiac Structure and Specializations

Heart weighs 0.4-0.5% of body weight
Hypertrophy: Increased heart weight or ventricular thickness
Dilation: Enlarged chamber size
Cardiomegaly: Increased cardiac weight or size (or both) resulting from hypertrophy and/or dilation
Normal Heart Weight: 250-320 g (F), 300-360 g (M)
Normal Ventricular Thickness: RV - 0.3-0.5 cm, LV - 1.3-1.5 cm

Myocardium

Pumping function of the heart is driven by coordinated contraction (systole) and relaxation (diastole) of cardiac myocytes.
Left ventricular myocytes are arranged in a spiral circumferential orientation to produce strong coordinated waves of contraction spreading from the apex to the base of the heart.
Right ventricular myocytes have a less structured organization, producing weaker contractile forces.
Heart also performs endocrine functions:
- Atrial cardiomyocytes contain Atrial Natriuretic Peptide
- Ventricular Myocytes contain B-Type Natriuretic Peptide
- Both peptides promote arterial vasodilation and stimulate kidneys to eliminate salt and water.

Valves

Atrioventricular Valves: Tricuspid and Mitral
Semilunar Valves: Aortic and Pulmonary
Valves are lined by endothelium
Valves have a three-layered architecture: Fibrosa Layer, Spongiosa Layer, Ventricularis or Atrialis Layer

Conduction System

The conduction system of the heart is responsible for the sequential contraction of the heart chambers
The components of the cardiac conduction system:
- Sinoatrial (SA) Node Pacemaker
- Atrioventricular (AV) Node
- Bundle of His (AV Bundle)
- Right and Left Bundle Branch Divisions
- Purkinje Network

Effects of Aging on the Heart

Size of the left ventricular cavity is reduced.
The basal ventricular septum protrudes into the left ventricular outflow tract.
There is a decrease in myocytes.
There is an increase in connective tissue.
There is a deposition of extracellular amyloid.
Valvular aging changes occur.
Progressive atherosclerosis occurs.

Six Principal Mechanisms of Heart Failure

Failure of the Pump: Systolic dysfunction or diastolic dysfunction
Obstruction to Flow: Examples include calcific aortic valve stenosis, systemic hypertension, or aortic coarctation
Regurgitant Flow: Backward flow of blood that results in increased volume workload and may overwhelm the pumping capacity of the affected chambers.

Heart Failure

Often called Congestive Heart Failure (CHF).
A heart cannot pump blood to adequately meet the metabolic demands of peripheral tissues, or can do so only at elevated filling pressures.
Common end stage of many forms of chronic heart disease.
Acute hemodynamic stresses, such as fluid overload, abrupt valvular dysfunction, or myocardial infarction, can all precipitate sudden CHF.
Physiologic mechanisms maintain arterial pressure and perfusion of vital organs:
- Frank-Starling mechanism: Increases filling volumes -> dilates the heart -> enhances contractility.
- Activation of Neurohumoral Systems: Augment heart function and/or regulate filling volumes and pressures.
- Release of Norepinephrine: Elevates heart rate, augments myocardial contractility and increases vascular resistance.
- Activation of Renin-Angiotensin-Aldosterone System: Promotes water & salt retention.
- Release of Atrial Natriuretic Peptide: Diuresis and vascular smooth muscle relaxation.
- Myocardial Adaptations: Ventricular remodeling - collective molecular, cellular, and structural changes that occur in response to injury or altered ventricular loading.

Cardiac Hypertrophy

The pattern of hypertrophy reflects the stimulus.
Pressure-Overload Hypertrophy: New sarcomeres are assembled in parallel to the long axes of cells. Ex: Concentric Hypertrophy due to hypertension or aortic stenosis.
Volume-Overload Hypertrophy: New sarcomeres are assembled in series within existing sarcomeres, leading primarily to ventricular dilation. Ex: Eccentric Hypertrophy due to valvular regurgitation.
Cardiac hypertrophy is not accompanied by a proportional increase in capillary numbers.
Cardiac hypertrophy is associated with heightened metabolic demands, deposition of fibrous tissue (interstitial fibrosis), and vulnerability to ischemia-related decompensation.

Molecular Changes in Hypertrophy

Expression of immediate-early genes (e.g., FOS, JUN, MYC, and EGR1).

Left Sided Heart Failure

Causes: IHD, Hypertension, Aortic and Mitral Valvular Diseases, Primary Myocardial Diseases
Effects: Congestion of pulmonary circulation, Stasis of blood in the left sided chambers, Hypoperfusion of tissues.
Morphology: Varies depending on the disease process. Nonspecific microscopic changes: Hypertrophy and interstitial fibrosis. Lung: Pulmonary congestion and edema. Heart failure cells.
Clinical Manifestations: Cough and dyspnea, Orthopnea or paroxysmal nocturnal dyspnea, Cardiomegaly, tachycardia, a third heart sound due to volume overload (S3), or a fourth heart sound (S4) due to increased myocardial stiffness. Reduced ejection fraction, Azotemia, Cerebral hypoperfusion - hypoxic encephalopathy.

### Left Sided Heart Failure Types:

Systolic Failure: Insufficient ejection fraction (pump failure) is caused by disorders that damage or derange the contractile function of the left ventricle.
Diastolic Failure: The left ventricle is abnormally stiff and cannot relax during diastole. Hypertension is the most common underlying etiology. May appear in older patients without any known predisposing factors as an exaggeration of normal stiffening of the heart with age.

Right Sided Heart Failure

Morphology: Varies with cause. Hypertrophy and dilatation of the right atrium and ventricle.
Liver: Congestive hepatomegaly- "nutmeg liver" appearance, Centrilobular necrosis, Cardiac cirrhosis.
Spleen: Congestive splenomegaly.
Bowel Wall: Chronic congestion and edema.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the intricate structures and specializations of the heart in this quiz. Learn about normal heart weight, hypertrophy, dilation, and the unique functions of myocardial cells. Test your knowledge on the cardiac myocytes' roles in pumping and endocrine functions.