Circulatory System - Part 3

The circulatory system is divided into 3 parts:

Circulatory System

Blood

Blood Vessels

HeartHeart

Heart is made of cardiac muscle

This type of muscle is branching and has ability to contract without being stimulated by a nerve (myogenic)

Heart Muscle

skeletal

smooth

cardiac

Histology of Cardiac Muscle

intercalated discs

nucleus

capillary

red blood cell

While these cells can contract on their own, a steady heart beat is maintained by specialized structures in heart

Heart MuscleHeart is made of cardiac muscle

This type of muscle is branching and has ability to contract without being stimulated by a nerve (myogenic)

Sinoatrial (SA) node is a neuromuscular mass in right atrium that sets heart’s tempoContraction is sensed by atrioventricular (AV) node, which conducts signal to Purkinje fibres

Nelson Biology 11 animation

SA nodeAV node

Purkinje fibres

Heart Rate

Stimulation by sympathetic nerves increases heart rate, while parasympathetic stimulation slows heart rate

Secretion of adrenaline speeds up heart rate

SA node is influenced by both autonomic nervous system and endocrine system

Heart Rate

Sound of a heart beat is sometimes described as a “lubb-dubb” and is caused by closing of heart valves

Heart Beat

After atria contract atrioventricular valves close, causing “lubb” soundAfter ventricles contract semilunar valves slam shut, causing “dubb” soundMitral valve viewed from left atrium Aortic valve viewed from aorta

Blood pressure is a measure of force exerted on arteries as blood moves away from heart

Blood pressure readings therefore consist of both values

Blood Pressure

Blood pressure : systolic pressurediastolic pressure

First atria contract, filling ventricles with blood (diastolic pressure) and then ventricles contract with much greater force (systolic pressure)

“Normal” blood pressure varies with age and is about 120/80 for young adults (units of measure are mm Hg)Blood pressure readings above 140/90 are considered high