6. Anatomy of the Heart Flashcards
Describe the structure of the heart
Cone shaped muscular pump
Located in the thorax between the lungs.
Which ribs protect the heart
ribs 2-5
Which structure protects the heart
The rib cage
In relation to the rib cage, where can the apex of the heart be found
In the 5th intercostal space, in the midclavicular line.
What is the Pericardium?
The coverings of the heart - composed of an outer fibrous layer and an inner serous pericardium
Describe the structure of the fibrous pericardium
- An inelastic sac/bag of dense connective tissue.
- FP fuses interiorly with the diaphragm and superiorly with the great vessels (aorta etc that project out of top of heart)
What is the function of the fibrous pericardium?
Prevents over filling of the heart.
Anchors it into its position so it doesn’t get loose in the body!
Describe the structure of the serous pericardium
Double layered serous membrane – made up of parietal and visceral layers
Parietal layer lines the inner surface of the fibrous pericardium
Outer layer = Visceral layer (epicardium) adheres to the surface of heart
Inner layer = Pericardial cavity - potential space between the parietal and visceral layers, contains pericardial fluid
Describe the location of the heart
- located in thorax, between the two lungs
- protected by the ribs
- lies behind the sternum
- between ribs 2-5 (left of midline)
Where is the apex (bottom) of the heart found
Apex lies in the midclavicular line and is found in the 5th intercostal space,
Function of the Serous Pericardium
Prevents friction and allows heart to move smoothly
Layers of the Heart Wall
Endocardium: inner layer – endothelium
Myocardium: middle layer - cardiac muscle
Epicardium: outer layer - visceral pericardium
Describe the Fibrous Skeleton of the Heart and its function
- Bands of fibrous connective tissue between the atria and ventricles
- Electrically separates the atria from the ventricles
- Encircles the pulmonary trunk and aorta
- Heart valves suspended from it
Name the Atrioventricular (AV) Valves
Tricuspid (right AV valve)
Bicuspid/mitral (left AV valve)
Name the Semilunar Valves
Pulmonary Valve
Aortic Valve
What is the function of the AV Valves
- Opened by the blood flowing from atria to the ventricles
- Anchored by chordae tendinea to papillary muscles
- Contraction of papillary muscles prevents eversion of the valves and therefore backflow of blood into the atria
- Valve open when ventricular pressure is less than atrial pressure
What is the function of the Semilunar Valves
- Guard the entrances of the aorta and pulmonary trunk
- Pressure in ventricles increases
- Opened by the force of blood as the ventricles contract
- Heart relaxes and pressure decreases
- Blood flows backwards in the aorta and pulmonary trunk during ventricular relaxation, this pools in the cusps and pushes them shut
- Prevent backflow of blood into the ventricles
How does blood flow through the heart
- Blood enters heart into right atrium, through Inferior or Superior Vena Cava from body.
- Goes to Right Ventricle
- Leaves heart as it goes to the lungs through the pulmonary arteries
- Returns to heart through pulmonary veins. Goes into Left Atrium.
- Goes to left ventricle.
- Leaves heart through aorta as blood travels to body
How is blood delivered to heart muscles?
- The great, middle and small cardiac veins drain into the coronary sinus which empties into the right atrium.
- The anterior cardiac veins drain directly into the right atrium
Describe the Cardiac Conducting System
- Effective heart contraction is coordinated by the cardiac conducting system
- Consists of non-contractile cells that initiate electrical impulses
How does the heart beat?
- Sinoatrial (SA) nodes starts initiating the impulse so the right atrium contracts. We don’t want the atrium and ventricle to contract at the same time so they are separated by a fibrous skeleton. It slows down impulse.
- Atrioventricular (AV) node is the only way for the electrical impulse to pass through fibrous skeleton to the AV bundle (bundle of His)
- The impulse spreads down the heart through the right & left bundle branches and then through the purkinje fibres.
- Contraction of the ventricles occur
Why is foetal circulation different to normal circulation?
oxygen and nutrients are received from the placenta via the umbilical vein
Need to bypass non-functional lungs
What are the three circulatory shortcuts in the foetal circulatory system?
Foramen ovale connects the right to the left atria - bypassing right ventricle and pulmonary system
Ductus arteriosus connects the pulmonary trunk to arch of aorta – bypassing pulmonary system and left side of heart
Ductus venosus connects the umbilical vein to inferior vena cava - bypasses the liver
How does blood flow in a foetus circulatory system?
- Blood returns to right atrium. Blood entering through inferior vena cava from the umbilical artery is rich in oxygen and nutrients. Blood entering back from the head and neck is low in oxygen and high in CO2.
- Get pooling of blood - mixed blood.
- Blood from vena cava gets shunted across into left atrium.
- Blood coming down from head get pushed into the right atrium and up into the pulmonary trunk. Some of this blood goes to the lungs, however lungs are constricted and under high pressure, so blood flows into the aorta through the ductus arteriosus.
- Blood that returns to the heart from the lungs into the left atrium also goes up the aorta.
Changes to Ductus Ateriosus at Birth
- New born takes first breath
- Lungs expand
- Blood rushes into pulmonary circulation
- O2 levels rise
- Constricts ductus arteriosus to become Ligamentum Ateriosum
Changes to Formen Ovale at Birth
- New born takes first breath
- Left Atrium pressure increases
- Foramen vale closes to become fossa ovalis
Changes to Ductus Venosus at Birth
- New born takes first breath
- Umbilical cord tied
- Umbilical Venosus fibroses to become Ligamentum venosum
