Internal structure of Right Atrium and Right ventricle

In this chapter, we will delve into one of the most critical aspects of heart anatomy—the internal structure of the right atrium and right ventricle. These chambers play a crucial role in receiving and pumping deoxygenated blood to the lungs. To study this topic comprehensively, we will follow a structured approach, starting with the right atrium, followed by the right ventricle, and finally understanding how their structures contribute to their functions.

Right Atrium

Location and Overview

The right atrium is the upper chamber of the heart on the right side. Its primary function is to collect deoxygenated blood from the body and direct it to the right ventricle.

Internal Features of the Right Atrium

Auricle

The right atrium contains a small muscular appendage,ear like projection, called the auricle. This structure increases the atrial capacity and aids in accommodating fluctuating blood volumes.

Crista Terminalis

A muscular ridge separating the smooth posterior wall (sinus venarum) from the trabeculated anterior wall. It is a key anatomical landmark. SA Node is present on the anterior side of this ridge.

Pectinate Muscles

Parallel ridges of muscle on the anterior wall and auricle that enhance the contraction of the atrium.

Fossa Ovalis

A depression in the interatrial septum, marking the site of the fetal foramen ovale—a crucial bypass in fetal circulation that closes after birth.

Here is an interesting part about the location of AV node, it is present in the triange of Koch.This triangle of koch is bounded by Tendon of todaro, septal cusp of tricuspid valve and opening of coronary sinus.

Openings in the Right Atrium

1. Superior Vena Cava (SVC): Carries blood from the upper body.

2. Inferior Vena Cava (IVC): Drains blood from the lower body.

3. Coronary Sinus: Drains blood from the heart’s own circulation.

4. Tricuspid Valve Opening: Allows blood to flow into the right ventricle.

5. Thebesion veins: These are tiny veins,which opens in the right atrium.

Function

The right atrium ensures the smooth transfer of blood to the right ventricle, regulating venous return and maintaining cardiac efficiency.

Right Ventricle

Location and Overview

The right ventricle is the lower chamber of the heart on the right side. It pumps deoxygenated blood into the pulmonary circulation for oxygenation.

Internal Features of the Right Ventricle

Open structure of Right ventricle

Trabeculae Carneae

The walls are lined with irregular muscular ridges that prevent suction effects during ventricular contraction.

This muscle, inside the ventricle are arranged in three forms:

• Eleveted one called Ridges.
• Bridges
• Pillers (papillary muscle)

Papillary Muscles and Chordae Tendineae

Papillary Muscles: Cone-shaped muscular projections attached to valve leaflets.

Chordae Tendineae: Fibrous cords that anchor the tricuspid valve leaflets and prevent prolapse during contraction.It originates from the tip of the papillary muscle, which will go and join with the free end of the septal cusp.

Moderator Band (Septomarginal Trabecula)

A muscular band connecting the interventricular septum to the anterior papillary muscle, aiding in the conduction of electrical impulses for coordinated contraction(passage to right bundle branch).

Tricuspid Valve

A three-leaflet valve that regulates blood flow between the right atrium and right ventricle.

Conus Arteriosus (Infundibulum)

A smooth-walled outflow tract leading to the pulmonary valve, minimizing turbulence as blood enters the pulmonary artery.

Pulmonary Valve

A semilunar valve ensuring unidirectional blood flow into the pulmonary circulation.

Function

The right ventricle generates the force needed to pump blood into the lungs, ensuring efficient oxygenation.

Coordinated Functionality of the Right Atrium and Ventricle

The right atrium and right ventricle work in tandem to maintain the flow of deoxygenated blood. The atrium acts as a reservoir and primer pump, filling the ventricle efficiently. The ventricle, with its robust contraction, propels the blood into the lungs for gas exchange.

Clinical Relevance

Common Pathologies

1. Atrial Septal Defect (ASD): An abnormal opening in the interatrial septum, disrupting blood flow.

2. Tricuspid Valve Disorders: Such as tricuspid regurgitation, leading to inefficient blood flow.

3. Pulmonary Hypertension: Elevated pulmonary pressure affecting right ventricular function.

Conduction System Contribution

Both the right atrium and ventricle house parts of the cardiac conduction system. The sinoatrial (SA) node, located in the right atrium, acts as the pacemaker of the heart, while the atrioventricular (AV) node and parts of the conduction pathway are supplied by the right coronary artery.

By understanding the internal structure of the right atrium and ventricle, we gain deeper insights into their roles in maintaining circulatory homeostasis. This knowledge is foundational for diagnosing and managing cardiac conditions effectively.

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