RRB Group D Science Heart (हृदय) By Arti Mam

The heart is a vital organ in the human body, playing a crucial role in maintaining overall health. It functions primarily as a blood pump, circulating oxygen-rich blood to various organs and tissues while removing carbon dioxide and waste products. Located in the chest, the heart is the central component of the circulatory system, which also includes blood vessels and the blood itself. 

The heart's constant, rhythmic beating ensures the continuous flow of blood, supporting the body's ability to function effectively. Its proper functioning is essential for delivering nutrients and oxygen, vital for survival and optimal bodily performance.

Circulatory System Type

Humans possess a Double Circulatory System, meaning blood cycles through the heart twice for each complete circuit of the body.  This concept was first elucidated by William Harvey in 1628. The human circulatory system is also a closed circulatory system, where blood is always contained within vessels.

Heart Size, Shape, and Location

• Size: Approximately the size of an individual's fist.

• Shape: Resembles a clenched fist.

• Location: Situated in the mid of the chest, within the chest cavity.

• Tilt: The heart is tilted towards the left side, leading to a more prominent heartbeat sensation on the left. This tilt is anatomically due to the left lung having a notch where the heart is positioned.

• Weight:

• Newborns: 20-25 grams

• Average Adult: 250-350 grams

• Males: 280-340 grams

• Females: 230-280 grams

• Space: The space the heart occupies in the chest is known as the Mediastinum space.

Heart Chambers

The human heart is divided into four chambers (Think of the heart as having "rooms" or chambers). These four unequal parts are separated by a thick muscular wall called the Septum. The chambers are:

1. Right Auricle (Right Atrium)

2. Right Ventricle

3. Left Auricle (Left Atrium)

4. Left Ventricle

Heart Valves

The human heart contains four valves that are critical for ensuring unidirectional blood flow.

Heart Layers

The heart is enveloped by an outer protective layer called the Pericardium layer. This layer comprises two sub-layers:

1. Fibrous layer: Composed of fibrous tissue.

2. Serous layer: A thinner, inner layer.

Cardiac Fluid is present between these two layers, providing lubrication and cushioning.

Function of the Heart

The primary role of the heart is blood pumping, facilitating the circulation of oxygenated and deoxygenated blood throughout the body. The detailed blood circulation pathway is as follows:

1. Deoxygenated blood (impure blood) from the upper body (head, face, neck, arms) is collected by the Superior Vena Cava.

2. Deoxygenated blood from the lower body (stomach, back, legs) is collected by the Inferior Vena Cava.

3. Both Vena Cavae deliver this deoxygenated blood to the Right Auricle.

4. From the Right Auricle, blood passes through the Tricuspid Valve into the Right Ventricle.

5. The Right Ventricle pumps the deoxygenated blood into the Pulmonary Artery. (The Pulmonary Artery is an exception as it carries impure blood; all other arteries carry pure blood.)

6. The Pulmonary Artery transports blood to the Lungs.

7. In the Lungs, gas exchange occurs: carbon dioxide is removed, and oxygen is added, making the blood pure (oxygenated).

8. Oxygenated blood returns from the lungs to the Left Auricle via the Pulmonary Vein. (The Pulmonary Vein is an exception as it carries pure blood; all other veins carry impure blood.)

9. From the Left Auricle, blood passes through the Bicuspid/Mitral Valve into the Left Ventricle.

10. The Left Ventricle pumps the oxygenated blood into the Aorta (through the Aortic Valve).

11. The Aorta, the body's largest artery, branches into numerous arteries that distribute pure blood to all organs and tissues (Imagine two separate "roads" or "pipes" within the body: one for impure blood and one for pure blood, ensuring they don't mix).

Electrical System of the Heart: Natural Pacemaker

The heart's rhythmic pumping action is orchestrated by electrical impulses generated internally (The heart's electrical activity is like "electric shocks" or "currents").

Natural Pacemaker: Sino Auricular Node (SA Node)

• The Sino Auricular Node (SA Node), located within the heart, functions as the body's natural pacemaker.

• It acts as the "battery of the heart," initiating and regulating the electrical impulses that control the heartbeat (The SA Node is like the ignition system or battery that starts and regulates the heart's rhythm).

• Sodium ions are crucial for generating these electrical impulses. A deficiency in sodium can lead to a slowed heart rate and symptoms like dizziness.

Artificial Pacemaker

• If the SA Node malfunctions, an artificial pacemaker may be surgically implanted.

• These artificial pacemakers typically use Lithium batteries because lithium is the lightest metal, helping to keep the device's weight low (15-20 grams) to avoid burdening the heart.

Atrioventricular Node (AV Node)

• The Atrioventricular Node (AV Node), situated below the SA Node, is another key component of the heart's electrical conduction system.

Heartbeat and Heart Rate

Heart Sounds

• The characteristic sound of the heart is "Lub-Dub", not "dhak dhak" as often depicted.

Heartbeat Mechanism

• One complete heartbeat comprises two phases: Systole and Diastole.

• Systole: The contraction phase, where blood is ejected from a chamber.

• Diastole: The relaxation phase, when a chamber fills with blood (To remember which term means relaxation: DR (Diastole = Relaxation)).

Duration of a Heartbeat

• Systole: 0.3 seconds

• Diastole: 0.5 seconds

• Total for one heartbeat: 0.8 seconds

Heart Rate Variations (Beats Per Minute - bpm)

• Healthy Adult: Approximately 72 bpm.

• Embryo: Up to 200 bpm.

• Children: 130-150 bpm.

• Large Animals (e.g., Elephant, Whale): Lower heart rates (e.g., 20-25 bpm).

• Small Animals (e.g., Mouse, Bat): Very high heart rates.

• During Exercise: Heart rate increases (e.g., 90-95 bpm). Intense exercise can stress an unconditioned heart, potentially leading to issues like heart failure.

Doping and Heart Rate

• Athletes have used drugs to lower their heart rate (inducing Bradycardia) to delay fatigue.

• Bradycardia: Heart rate below 72 bpm.

• Tachycardia: Heart rate above 72 bpm.

Blood Pumped

• Per heartbeat: Approximately 70 ml of blood.

• Per minute: Approximately 5 liters of blood (70 ml/beat * 72 beats/minute).

Heart Conditions

Understanding distinctions between common heart-related conditions is vital.

Heart Procedures

Check below for common heart procedures, including angioplasty, bypass surgery, pacemaker implantation, and heart valve repair. These procedures are essential for treating heart-related conditions, improving blood flow, and ensuring the heart's proper function to maintain overall health.

Bypass Surgery / Angioplasty

• Purpose: To clear blocked arteries, typically caused by cholesterol buildup.

• Procedure: A thin wire or tube with a mesh-like structure (a stent) is inserted, usually through an artery in the leg. Guided by imaging to the blocked heart artery, the stent is expanded to push cholesterol plaque aside, restoring blood flow. For severely damaged arteries, an artificial artery may be used to bypass the affected section.

Control of Heart and Blood Pressure

• Gland: The Adrenal Gland influences heart function through hormones.

• Brain Part: The Medulla Oblongata in the brainstem regulates heart rate and blood pressure.

Heart Transplants

• First Heart Transplant: Performed by Dr. Christiaan Barnard in Cape Town, South Africa.

• First Heart Transplant in India: Performed by Dr. P. Venugopal in 1994.

Hole in the Heart (Septal Defect)

• Initial Stage: Most babies are born with 2-3 small holes in their heart, which typically auto-heal within 24 hours. These are remnants of fetal circulation.

• Problem: If a hole in the Septum persists, it allows pure and impure blood to mix, leading to health issues like breathing difficulties and reduced stamina.

• Treatment: Modern surgery can repair or reinforce the septum to close these holes.

Heart Chambers in Different Animals

The number of heart chambers varies across species:

• Fish: 2-chambered heart (single circulatory system; heart contains only impure blood, purified in gills).

• Amphibians: 3-chambered heart (2 auricles, 1 ventricle; pure and impure blood mix).

• Reptiles: 3-chambered heart.

• Mammals (including humans, dolphins, whales): 4-chambered heart.

• Birds: 4-chambered heart (2 auricles, 2 ventricles).