Structure & function of the heart

The Cardiovascular system

Responsible for the transport of substances throughout the body and plays a vital role in maintaining homeostasis

Consists of 3 main components:

• The heart

• Blood vessels

• Blood

Function of Cardiovascular system - Transport

Delivers O2, nutrients, and hormones to body cells

Removes metabolic wastes such as CO2

Function of Cardiovascular system - protection

Circulates white blood cells, antibodies, and complement proteins to defend against pathogens

Enables. bblood clotting to prevent excessive blood loss following injury

Function of Cardiovascular system - Regulation

Helps regulate body temperature

Maintains pH balance

Controls fluid, H2O content of cells

Structure & function of the heart

The heart is a muscular pump responsible for generating pressure to circulate blood throughout the body

It is located in the mediastinum, between the lungs, slightly to the left of the mifline

The adult human heart : Is approximately the size of a clenched fist , cone-shape

Coverings the heart ( pericardium )

The heart is enclosed by a double-walled sac called the pericardium

It consists of 2 layers with fluid between them

The fluid allows the layers to slide smoothly over each other as the heart beats, reducing friction

Functions of pericardium

Holds the heart in position within the chest cavity

Prevents the heart from overexpanding when it fills with blood

Reduces friction as the heart contracts and relaxes

Provides protection from infection and physical damage

Heart wall

3 layers: outer layer, middle layer, inner layer

The middle layer ( myocardium ) is made of cardiac muscle and varies in thickness:

• Thicker in the ventricles than the atria

• Thickest in the left ventricle due to higher pressure requirements

Cardiac muscle

Specialised muscle found only in the heart

It is a specialised to continuosly and repeatedly contract, providing circulation of blood throughout the body

Cardiac muscle

Striated muscle fibres

Cells are branched and interconnected

Typically contain a single, centrally located nucleus

Designed for continous, rhythmic contraction

Adjacent cardiac muscle cells are connected by intercalated discs, which locks cells together to allow for rapid transmission of electrical impulses

Pathway of blood around the body

External view of the heart

Chordae tendineae and papillary muscles

Trong connective tissue cords that attach AV valves to papillary muscles

During ventricular contraction:

-Papollary. muscles contract

Tension is applies to the chordae tendineae

This prevents valve cusps from inverting and stops backflow

Semilunar valves

Have 3 cusps

Lack chordae tendineae and capillary muscles

Function of Semilunar Valves

consist of pockey-shaped cusps reinforced with connective tiisue

whne ventricles relax:

• blood flows back toward the heart

• cusps fill with blood

• valves close, preventing backflow into the ventricles

double circulatory system

Humans have a double circulatory system, meaning blood passes through the heart tiwce per complete circut

Pulmonary circulation: Heart→ Lungs →heart

Systemic circulation: heart→ body→ heart

This allows efficient O2 delivery at high pressure

What causes blood to flow through the heart

Blood flows due to pressure differences created by the contraction and relaxtion of heart chambers

Blood moves from areas of high pressure to low pressure

Pressure changed result from:

• Systole ( contraction )

• Diastole ( relaxtion )

One complete sequence of events is called the cardiac cycle

Electrical control of the heart

The sinoatrial ( SA ) node:

• A cluster of specialised cardiac cells in the right atrium

• Acts as the heart’s natural pacemaker

• Initiates electrical impluses causing atrial contraction

Electrical control of the heart

The atrioventricular ( AV ) node:

• delays the electrical impluse

• Ensures atria fully contract before ventricles

• Transmits the impulse to the ventricles via specialised conducting fibres