Lecture 2 - Cardiovascular system

Describe the size, shape and location of the heart

• Size

Closed fist

• Shape

Apex is a blunt rounded point of cone Base is flat part at opposite of end of cone

• Location

Thoracic cavity, mediastinum

Describe what pericardium is and what it does

• Membrane that surrounds the heart

• Keeps the heart in place and limits its motion

• Prevents it from over expanding and acts as an anchor

What are the two layers of the pericardium called?

1. Outer layer fibrous pericardium

2. Inner layer serous pericardium

Name and describe the two layers of the serous pericardium?

1. Parietal layer Lines the fibrous pericardium

2. Visceral layer Covers the heart surface

• The two are continuous and have a pericardial cavity in between that reduces friction as the heart beats

Name and describe the three layers of the heart

1. Epicardium Smooth outer surface of heart

2. Myocardium Composed of cardiac muscle cell, responsible for heart contracting

3. Endocardium Smooth inner surface of heart chambers

Name and describe the four chambers of the heart and the two septums

1. Right atrium Receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus

2. Left atrium Receives oxygenated blood from pulmonary veins

3. Right ventricle Pumps deoxygenated blood to pulmonary trunk/artery

4. Left ventricle Pumps oxygenated blood to aorta

5. Inter-atrial septum Wall between the atria

6. Inter-ventricular septum Wall between the two ventricles

What is the primary function of heart valves?

Prevents back flow of blood

Where do the atrioventricular (AV) valves lie?

Between atria and ventricles are the tricuspid valve on the right side of the heart and bicuspid valve on the left

What are the valves attached to?

Each valve has leaf like cusps that are attached to cone shaped papillary muscles by tendons

What and where are the two semilunar valves?

1. Aortic valve - base of the aorta

2. Pulmonary valve - base of the pulmonary trunk

Outline the route of blood flow within the body

What are the three parts of the body's circulatory system?

1. Pulmonary

2. Coronary

3. Systemic

Describe systemic circulation

• The left side of the heart is the pump for the systemic circulation

• It pumps oxygenated blood from the lungs out into the vessels of the body

Describe pulmonary circulation

• The right side of the heart is the pump for the pulmonary circulation

• It receives deoxygenated blood from the body and sends it to the lungs for oxygenation

What is the blood volume distribution?

Pulmonary circulation - 18%
Coronary - 12%
Systemic - 70%

Describe coronary circulation

Provides blood flow to the myocardium

coronary artery disease

How is the myocardium specialised?

- Has intercalated discs with gap junctions to allow muscle action potentials to conduct from one muscle fibre to its neighbours

Describe what is meant by autorythmic cells

• Cells can spontaneously depolarise and generate action potentials

• Cells act as a pacemaker to set the rhythm for the entire heart

• Form their own conduction system

How do cardiac muscle cells contract?

• Action potential initiated in the conduction system is propagated across the sarcolemma of cardiac muscle cells

• Thin filaments and sarcomeres shorten within cardiac muscle cells

What does the conduction system do?

Heart regulates the rate and strength of contraction through an intrinsic conduction system, modified by external sympathetic and parasympathetic pathways

Describe the function of the SA node in relation to the conduction system

• mass of auto-rhythmic cells in the right atrial wall near the entrance of the superior vena cava

• generates impulses about 100x per minute and sets pace for entire heart

Describe the function of the AV node in relation to the conduction system

• mass of auto-rhythmic cells located in the inferior portion of the inter-atrial septum above the tricuspid valve

• each impulse is delayed briefly here, allowing atria to contract before ventricles

Describe the function of the bundle of His in relation to the conduction system

• Auto-rhythmic cells located in the inter-ventricular septum

• Only electrical connection between atria and ventricles

Describe the function of the Purkinje fibres in relation to the conduction system

- Run through the inter-ventricular septum, penetrate the heart apex, then turn upwards through the ventricular myocardium triggering ventricular contraction and pushes blood through the semilunar valves.

Define ECG

• Electrocardiogram

• A recording device for the heart's electrical events during each cardiac cycle

What does the P wave represent on the ECG?

• Depolarisation of atrial myocardium

• Signals onset of atrial contraction

What does the QRS complex represent on the ECG?

• Ventricular depolarisation and signals onset of ventricular contraction

• Repolarisation of atria simultaneously

What does the T wave represent on the ECG?

• Repolarisation of ventricles

• Precedes ventricular relaxation

What does the PQ interval represent on the ECG?

• Atria contract and begin to relax

• Ventricles begin to contract

What does the QT interval represent on the ECG?

- Ventricles contract and begin to relax

Label the waves on an ECG

What is the cardiac cycle made up of?

• Sequence of events that make up a heartbeat

• Consists of systole and diastole of both atria, rapidly followed by systole and diastole of both ventricles

How long does a complete cardiac cycle take?

75 beats/min = 0.8 secs

Define auscultation

Act of listening to heart sounds within the body

What is the 'lub' and 'dup' caused by?

• 'Lub' - blood turbulence associated with tricuspid and bicuspid valves closing

• 'Dup' - blood turbulence associated with pulmonary and aortic valves closing

Define cardiac output?

• Amount of blood pumped out by each ventricle in one minute

• Volume of blood ejected from the left ventricle into the aorta each minute

• heart rate x stroke volume

Define stroke volume

• Volume of blood pumped out by a ventricle with each contraction/heart beat

• Usually 70ml

What is stroke volume affected by?

• Venous return

• Force of contraction of heart regulated by

hormones sympathetic nervous system

Define heart rate

Number of times the heart beats in one minute

What is the heart rate regulated by?

• Parasympathetic nervous system - acts on SA node to decrease heart rate

• Sympathetic nervous system - acts on SA node to increase heart rate

• Hormones, age, exercise, body temperature

Define tachycardia

Heart rate greater than 100bpm

Define bradycardia

Heart rate slower than 60bpm

Define venous return

Amount of blood which returns to the heart

What is venous return regulated by?

• Blood volume - increases with exercise and decreases in event of a haemorrhage

• Skeletal muscle and respiratory pumps - muscles contracting around blood vessels aid venous return to the heart

State the formula for mean arterial pressure?

(1/3 x Systolic BP) + (2/3 x Diastole BP)