Heart Anatomy Study Notes

Heart Anatomy: Overview

1. Introduction

The heart functions primarily as a "pump," ejecting blood into major vessels: the aorta and pulmonary trunk.
Blood distribution: After ejection, blood is distributed to the rest of the body through various vessels.
Anatomical structure: The heart is a living muscle, not a mechanical device.
Etymology of terminology: The term "cardiac" traces back to Latin "kardia." Cardiology is the study of the heart, and cardiologists are the relevant medical professionals.
Significance of the heart: A typical human heart contracts approximately 75 times per minute—amounting to about 108,000 times per day, over 39 million times per year, and nearly 3 billion times in a 75-year lifespan.
Blood ejection: Major pumping chambers of the heart eject approximately 70 mL of blood per contraction.
- This results in about 5.25 liters per minute and approximately 14,000 liters per day.
- This equates to 10,000,000 liters over one year, or 2.6 million gallons, circulated through around 60,000 miles of blood vessels.
Essential for understanding the anatomy and physiology of the heart to grasp how these functions occur.

2. Location of the Heart

Location: The heart is located within the thoracic cavity, medial to the lungs, specifically in the mediastinum.
Mediastinum: The heart is separated from other structures by the pericardium and sits in the pericardial cavity.
**Orientation:
- The base (superior surface) of the heart is at the level of the third costal cartilage.
- The apex (inferior tip) is just left of the sternum between the 4th and 5th ribs.
Position and orientation: Understanding this position is crucial for medical procedures like using a stethoscope to listen for heart sounds.

3. Shape and Size of the Heart

Shape: Similar to a pine cone, broad at the base tapering to the apex.
Size: A typical adult heart is approximately the size of a fist:
  - Length: 12 cm (5 in)
  - Width: 8 cm (3.5 in)
  - Thickness: 6 cm (2.5 in)
Weight:
- Male heart: approx. 300–350 grams (11 to 12 ounces)
- Female heart: approx. 250–300 grams (9 to 11 ounces)
Athlete's heart: Hearts of athletes can be larger due to a phenomenon called hypertrophy, similar to skeletal muscle responding to exercise.
Enlarged hearts: Not all enlarged hearts are from exercise; conditions like hypertrophic cardiomyopathy can cause pathological enlargement, which can lead to sudden death.

4. Chambers and Circulation Through the Heart

Structure: The heart has four chambers divided as follows:
  - Right atrium (receives blood from body)
  - Right ventricle (pumps blood to lungs)
  - Left atrium (receives blood from lungs)
  - Left ventricle (pumps blood to the rest of the body)
Circulation Process:
  - Right atrium receives deoxygenated blood via the superior and inferior venae cavae.
  - Blood moves to the right ventricle through the right atrioventricular valve.
  - Right ventricle pumps blood to the lungs via the pulmonary trunk.
  - After gas exchange, oxygenated blood returns to the left atrium through pulmonary veins.
  - Blood from the left atrium moves to the left ventricle through the left atrioventricular valve.
  - Left ventricle pumps oxygenated blood into the aorta for distribution throughout the body.
Overall path: Blood circulates continuously as long as the individual is alive, alternating between oxygenated and deoxygenated states according to its location.

Heart Anatomy: External Structure

1. Pericardial Membrane

The pericardium surrounds the heart, featuring two distinct layers:
  - Fibrous pericardium: Tough, dense connective tissue for protection and positioning.
  - Serous pericardium: Further divided into:
    - Outer parietal pericardium (fused to fibrous pericardium)
    - Inner visceral pericardium (epicardium, fused to heart wall).
Pericardial cavity: Contains serous fluid to reduce friction during heart contractions.
- Involves a simple squamous epithelium (mesothelium) reinforced with loose connective tissue, paramount for function.

2. Surface Features of the Heart

Auricles: Leaf-like extensions on atria resembling human ears; can fill with blood and drain into atria.
Sulci: Grooves filled with fat containing major coronary blood vessels.
- Coronary sulcus: Between atria and ventricles.
- Interventricular sulcus: Divides ventricles; comprises anterior and posterior segments.

3. Layers of the Heart Wall

**Composed of three layers: **
  - Epicardium: Outermost layer and also part of the visceral pericardium.
  - Myocardium: Thick, muscular layer responsible for contractions, organized in elegant swirling patterns for effective pumping.
  - Endocardium: Innermost layer made of simple squamous epithelium, linked to blood vessel endothelium, plays roles in contraction regulation.
Differences in wall thickness: The left ventricle has significantly thicker myocardium compared to the right due to higher pressure required for systemic circulation.

Heart Anatomy: Internal Structure and Chambers

1. Septa of the Heart

Septum: A wall dividing heart chambers (e.g., atrial septum, interventricular septum).
- Interatrial septum features: Contains fossa ovalis (remnant of fetal foramen ovale).
- Interventricular septum: Consistently intact, thicker due to higher pressure from ventricles.
Atrioventricular septum: Pathways for blood marked with valves;
- Atrioventricular valves: Between atria and ventricles.
- Semilunar valves: Along the pathway to the pulmonary trunk and aorta.
Cardiac skeleton: Dense connective tissue providing reinforcement around openings and supporting electrical conduction pathways.

2. Right Atrium

Serves as the blood receiving chamber from the body.
  - Major veins emptying:
    - Superior vena cava: blood from head, neck, and upper body.
    - Inferior vena cava: blood from lower body regions.
  - Features:
    - Smooth internal surface, presence of pectinate muscles, and fossa ovalis.

3. Right Ventricle

Receives blood from right atrium via right atrioventricular valve (tricuspid valve with three cusps).
- Chordae tendineae and papillary muscles prevent backflow during ventricular contraction.
- Ejects blood into the pulmonary trunk past the pulmonary semilunar valve.

4. Left Atrium

Receives oxygen-rich blood from the lungs via pulmonary veins:
- No pectinate muscles except in auricle.
- Assists in pumping blood into the left ventricle to maintain circulation.

5. Left Ventricle

Pumps oxygenated blood to the rest of the body via the aortic semilunar valve into the aorta:
- Thicker myocardium compared to right ventricle due to higher resistance of systemic circulation.
- Connected to the left atrium through the left atrioventricular valve (mitral valve with two cusps).

Heart Anatomy: Valve Structure and Function

1. Valve Structure and Function

All four valves ensure unidirectional blood flow:
- Right atrioventricular valve (tricuspid) with three flaps, and controlled by papillary muscles through chordae tendineae.
- Semilunar valves (pulmonary and aortic) consist of pocket-like folds of endocardium without chordae tendineae.

Key Concept

Valves open and close based on pressure differences:
- Blood flows from areas of high pressure to low pressure, causing valves to open or shut accordingly.

Heart Anatomy: Coronary Circulation

1. Coronary Arteries

Blood supply via left and right coronary arteries:
- Left coronary artery: Supplies left atrium, ventricle, and interventricular septum; branches into circumflex and anterior interventricular arteries.
- Right coronary artery: Supplies right atrium and portions of both ventricles; gives rise to marginal and posterior interventricular arteries.

2. Coronary Veins

Function parallel to the coronary arteries; major veins such as the great cardiac vein drain blood into the coronary sinus.

3. Heart Attack

Myocardial infarction (MI) occurs due to ischemia and hypoxia from blocked coronary arteries:
  - Causes include atherosclerotic plaques leading to tissue death.
  - Symptoms: Angina, difficulty breathing, and varying symptoms between males and females.
  - Diagnosis confirmed via EKG and blood tests; treatment includes oxygen, aspirin, nitroglycerin, thrombolytics, angioplasty, or bypass surgery.

Summary of Key Terms

Myocardial Infarction: Death of cardiac muscle due to a lack of blood flow.
Atherosclerosis: Accumulation of plaque causing blockage of coronary arteries, leading to ischemia.
Angioplasty: Procedure to widen occluded arteries, with stent placements often following.