Cardiovascular System - The Heart

Week 6

the heart is…

a muscular organ that functions as apump to circulate blood throughout the body

the heart maintains homeostasis by ensuring…

the continuous delivery of oxygen and nutrients and the removal of metabolic wastes

Heart location/orientation

• in the mediastinum, between the lungs in the thoracic cavity

• approx. two-thirds lies to the left of the midline

• the apex is formed bu the left ventricle and points downwards and to the left

• the base faces posteriorly and is formed mainly bu the atria

Heart External anatomy

• enclosed by the pericardium, a protective double-layered sac

• Surface groves - contain coronary blood vessels, which supply the heart muscle

Coronary sulcus

separates atria and ventricles

Anterior and posterior interventricul ar sulci

separated ventricles

Right Atrium

receives deoxygenated blood from the body vis the superior and inferior vena cava

Right Ventricle

pumps deoxygenated blood to the lungs via the pulmonary trunk

Left Atrium

Receives oxygenated blood from the lungs via the pulmonary veins

Left Ventricle

Pumps oxygenated blood to the body via the aorta

has the thickest wall due to higher pressure requirements

Superior and inferior vena cava

carry deoxygenated blood into the right atrium

Pulmonary trunk

carries blood from the right ventricle to the lungs

Pulmonary veins

carry oxygenated blood from the lungs to the left atrium

Aorta

carries oxygenated blood from the left ventricle to the systemic circulation

Atrium…

receives blood

Ventricle…

pumps blood

Interatrial septum

separated atria

Interventricul ar septum

separates ventricles

Trabecular carneae

muscular ridges in ventricles

Atrioventricular valves (AV)

Tricuspid (right) and Mitral (left)

Semilunar valves

pulmonary valve and aortic valve

supporting structures:

Chordae tendineae and papillary muscles

• prevent valve prolapse and ensure one-way flow

Bicuspid (mitral) valve function during cardiac cycle

• when valve is open, blood flows from the left atrium to the left ventricle, and the chordae tendineae are relaxed

• when the valve is closed, the papillary muscles contract, tightening the chordae tendineae to prevent backflow into the atrium

Pathway of bloodflow

Body → Vena cava → Right atrium → Tricuspid valve → Right ventricle → Pulmonary valve → Pulmonary trunk → Lungs → Pulmonary veins → Left atrium → Mitral valve → Left ventricle → Aortic valve → Aorta → Body

Blood moves in…

a continuous, one-directional pathway through the heart

specialised autorhythmic fibres

generate and conduct electrical impulses through the heart

Sinoatrial (SA) node

• located in the right atrium

• acts as the natural pacemaker and initiates each heartbeat

Cardiac output (CO) =

Heart rate x Stroke Volume

represents the volume of blood pumped per minute

Heart Rate (HR)

• number of heartbeats per minute

• regulated by the autonomic nervous system: Sympathetic → increases HR, Parasympathetic → decreases HR

Stroke Volume (SV)

• amount of blood pumped by each ventricle per beat

• influenced by Preload (venous return), Contractibility (strength of contraction) and Afterload (resistance to ejection)

Intrinsic regulation

Frank Starling mechanism: increased filling → increased contraction

Extrinsic regulation

• Autonomic control

• hormonal influences (e.g. adrenaline)

Cardiac output adjusts to ensure…

adequate blood flow based on body demand