W9 - cardiovascular system 1 the heart Flashcards
(21 cards)
Embryological development of the heart
Origin: Derived from mesoderm.
Timeline: Begins in week 3 when the embryo needs its own blood supply.
Formation: Two mesodermal heart tubes fuse into one primitive heart tube.
Development: The tube expands into regions that form the adult heart structures.
By Day 22: The heart starts beating and undergoes bending/folding.
Chamber Formation: The heart tube partitions into four chambers; great vessels develop.
Fetal Circulation: Two bypasses—foramen ovale and ductus arteriosus—allow blood to skip non-functional fetal lungs.
Describe the position of the heart in the thoracic cavity
Location: In the mediastinum, the central thoracic space between the lungs.
Orientation: Right side is more anterior, left side more posterior.
Apex: Points left; ~2/3 of heart lies to the left of midline.
Base: Opposite the apex, faces posteriorly (posterior surface).
Support: Heart rests on its inferior (diaphragmatic) surface, not the base.
Diaphragm connection: Inferior surface contacts the diaphragm; pericardium is fused with the central tendon of the diaphragm.
Describe the structure and function of the pericardium
Pericardium: Protective sac around the heart, fused with the central tendon of the diaphragm; anchors and stabilizes the heart.
2 Parts:
Fibrous Pericardium
Tough, outer layer made of dense irregular connective tissue
Fused to diaphragm’s central tendon
Serous Pericardium (thin, serous membrane)
Has parietal layer (lines fibrous pericardium) and visceral layer (lines heart surface = epicardium)
Pericardial cavity: space between layers
Pericardial fluid: reduces friction during heart movement
Describe the structure and function of the layers of the heart wall
Composed of 3 layers:
Outer epicardium
- Visceral layer of serous pericardium
- Made of simple squamous epithelium with an underlying layer of areolar connective tissue and fat
Myocardium
- Middle layer of the heart wall
- Thickest layer made of cardiac muscle tissue
Endocardium
- Inner layer of the heart wall
- Lines the internal surface of the heart, including the heart valves
- Made of simple squamous epithelium and a thin layer of areolar connective tissue
The endothelial layer is continuous with the internal lining of the large blood vessels leaving and entering the heart.
Describe the external and internal features of the heart
- The heart has four chambers – a left and right atrium and a left and right ventricle.
The two atria are the “receiving” chambers as they receive blood from either the lungs or the body, while the ventricles are the “pumping” chambers as they pump blood to either the lungs or the body.
External Features of the Heart - Anterior View:
- Auricle: small, ear-shaped outpouchings of the 2 atria. These increase the capacity of the atria.
- Coronary sulcus: groove running in between the atria and ventricles.
○ Runs around the entire heart like a crown
○ Has blood vessels running in it including the right and left coronary arteries which supply blood to the heart itself - Anterior interventricular sulcus: groove running in between the 2 ventricles on the anterior surface. It has blood vessels running through it.
Apex: formed by the left ventricle and points towards the left.
- Coronary sulcus: groove running in between the atria and ventricles.
External Features of the Heart - Posterior and Inferior Views:
- Posterior surface: This surface is more commonly referred to as the base of the heart and it is formed by the left atrium.
- Inferior surface: This surface sits on the diaphragm and is therefore also called the diaphragmatic surface
- Posterior interventricular sulcus: runs in between the two ventricles and the surface on which it is running is the inferior surface. It has blood vessels running in it.
Coronary sinus: continuation of the coronary sulcus can be seen with a large vein sitting in it (CS)
Internal Features of the Heart - Pulmonary and Systemic Circulation:
Internal Features of the Heart - Right Atrium - VEINS
- Receives deoxygenated blood from the body and there are three main veins that drain this blood into the right atrium – the superior vena cava, the inferior vena cava and the coronary sinus.
- Superior vena cava: large vein drains deoxygenated blood into the right atrium from all structures above the diaphragm, except the heart itself
- Coronary sinus: sits in the coronary sulcus on the posterior aspect of the heart and drains deoxygenated blood into the right atrium from the heart itself.
○ Opening seen in the right atrium in between the opening for the inferior vena cava and a structure on the wall of the right atrium called fossa ovalis.
Inferior vena cava: large vein drains deoxygenated blood into the right atrium from all structures below the diaphragm
Internal Features of the Heart - Right Atrium
Fossa Ovalis:
- This is an oval-shaped depression on the interatrial septal wall of the right atrium.
- It is an embryological remnant of a structure called foramen ovale, which is an oval-shaped hole that connects the right and left atria during foetal life.
- The function of foramen ovale is to allow blood to pass directly from the right atrium into the left atrium in order to bypass the non-functioning foetal lungs.
- When a baby is born, foramen ovale closes off, leaving the oval-shaped depression called fossa ovalis that we see in the adult heart.
Interatrial Septum
- This is the partition separating the right and left atria
Pectinate Muscles:
- These are also called musculi pectinati and are muscular ridges that are mainly found on the internal surface of the right auricle, but extend into the anterior wall of the right atrium.
However, the posterior wall of the right atrium is smooth. The exact function of the pectinate muscles is unknown, but it is thought that they assist with the shunting of blood from the right atrium into the left atrium through foramen ovale during foetal life.
Internal Features of the Heart - Right Ventricle part 1
- From the right atrium, deoxygenated blood flows into the right ventricle through an opening called the right atrioventricular orifice
- This opening is guarded by a valve called the right atrioventricular valve, which can be seen in the right ventricle.
- The other features that can be seen in the right ventricle are the chordae tendineae, papillary muscles, trabeculae carneae and the interventricular septum.
Right atrioventricular valve
- located between the right atrium and the right ventricle, guarding the right atrioventricular orifice. It is also called the tricuspid valve, as it has three cusps or leaflets
Chordae Tendineae
- These are tendinous cords that connect the cusps of the right atrioventricular valve to muscles in the right ventricle called papillary muscles.
Papillary Muscles
- These are pillar-like muscles that anchor the cusps of the right atrioventricular valve to the ventricular wall via the chordae tendineae.
- There are three papillary muscles in the right ventricle, as the right atrioventricular valve has three cusps.
Trabeculae Carneae
- Muscular ridges found on the walls of the right ventricle. Their exact function is unknown.
Interventricular Septum
This is the partition separating the right and left ventricles
Internal Features of the Heart - Right Ventricle part 2
- From the right ventricle, deoxygenated blood is pumped to the lungs to be oxygenated via a large artery called the pulmonary trunk.
○ It divides into right and left pulmonary arteries which go to the right and left lungs, respectively.- The entrance to the pulmonary trunk is guarded by a valve called the pulmonary semilunar valve, which can be seen from the right ventricle.
○ It has three cusps that are each shaped like a half-moom - Connecting the pulmonary trunk to the arch of the aorta is a structure called ligamentum arteriosum.
○ This is an embryological remnant of a structure called ductus arteriosus, which is a channel that connects the pulmonary trunk to the aorta during foetal life
○ The function of ductus arteriosus is to allow blood to pass directly from the pulmonary trunk into the aorta in order to bypass the non-functioning foetal lungs.
When a baby is born, ductus arteriosus closes off, leaving the ligament-like structure called ligamentum arteriosum that we see connecting the pulmonary trunk and aorta in an adult.
- The entrance to the pulmonary trunk is guarded by a valve called the pulmonary semilunar valve, which can be seen from the right ventricle.
Internal Features of the Heart - Left Atrium
- Once the deoxygenated blood from the right ventricle has been oxygenated in the lungs, this oxygenated blood returns to the left atrium of the heart.
- There are four veins that drain this blood into the left atrium called pulmonary veins, with two coming from each lung.
The walls of the left atrium are smooth and it does not have the same features as the right atrium, although there are some pectinate muscles on the internal surface of the left auricle and the interatrial septum can also be seen from the left atrium.
- There are four veins that drain this blood into the left atrium called pulmonary veins, with two coming from each lung.
Internal Features of the Heart - Left Ventricle
- From the left atrium, oxygenated blood flows into the left ventricle through the left atrioventricular orifice.
- This opening is guarded by the left atrioventricular valve, which can be seen in the left ventricle.
○ This valve is similar to the right atrioventricular valve, but it has two cusps instead of three. - The other features that can be seen in the left ventricle are the same as those in the right ventricle – chordae tendineae, papillary muscles, trabeculae carneae and the interventricular septum.
- The only difference is that there are two papillary muscles in the left ventricle rather than three, as the left atrioventricular valve has two cusps.
- From the left ventricle, oxygenated blood is pumped to the body via the largest artery in the body called the aorta.
The entrance to the aorta is guarded by a valve called the aortic semilunar valve, which can be seen from the left ventricle. Its structure is the same as that of the pulmonary semilunar valve.
- This opening is guarded by the left atrioventricular valve, which can be seen in the left ventricle.
Describe the flow of blood through the heart and explain how this relates to the phases of the cardiac cycle
- While the right atrium is receiving deoxygenated blood from the body and this blood is then flowing into the right ventricle, the left atrium is simultaneously receiving oxygenated blood from the lungs and this blood is then flowing into the left ventricle.
- Similarly, while the right ventricle is pumping deoxygenated blood to the lungs, the left ventricle is simultaneously pumping oxygenated blood to the body.
- These phases of heart filling and heart pumping are part of the cardiac cycle, which is the cycle of all events that occur within the heart over a single heartbeat.
- The pumping of blood from the ventricles occurs during ventricular systole, which is when the ventricles are contracting
The filling of the ventricles with blood occurs during ventricular diastole, which is when the ventricles are relaxing.
Describe the structure and function of the heart valves and the fibrous skeleton of the heart
Heart Valves
Important concepts:
1. The opening and closing of the heart valves is mediated by pressure differences
The 4 heart valves are never all open or all closed at the same time
Atrioventricular Valves
- FUNCTION: prevent the backflow of blood from the ventricles into the atria when the ventricles contract
CLOSED:- Contract (ventricular systole)
- The pressure inside the ventricles becomes greater than the pressure inside the atria
- Close due to blood pushing up on the valve cusps
- Papillary muscles pull tight on the chordae tendineae, which in turn pull tight on the valve cusps, keeping the atrioventricular valves closed and preventing the valve cusps from prolapsing into the atria
OPEN: - Relax (ventricular diastole)
- Pressure inside the atria becomes greater than the pressure inside the ventricles
Atrioventricular valves open to allow blood to flow passively from the atria into the ventricles
Semilunar Valves
- FUNCTION: prevent the backflow of blood from the pulmonary trunk and aorta into the ventricles when the ventricles relax
CLOSED:- When the ventricles relax (VD)
- Pressure inside the pulmonary trunk and aorta becomes greater than the pressure inside the ventricles
- The semilunar valves close due to blood pushing back on the valve cusps and filling them with blood.
- This prevents the valve cusps from prolapsing into the ventricles, thus preventing the backflow of blood from the pulmonary trunk and aorta into the ventricles.
OPEN: - Ventricles contract (ventricular systole)
- Pressure inside the ventricles becomes greater than the pressure inside the pulmonary trunk and aorta
The semilunar valves open to allow blood to enter the pulmonary trunk and aorta from the ventricles.
Fibrous Skeleton of the Heart
- Located in between the atria and the ventricles.
- It is made of dense connective tissue and consists of four fibrous rings that encircle the four heart valves, as well as fibrous tissue that connects these rings together.
- The fibrous skeleton anchors the cusps of the heart valves and provides a framework for the attachment of cardiac muscle tissue.
- It also acts as an electrical insulator between the atria and the ventricles.
This is very important as it prevents the ventricles from being stimulated to contract at the same time as the atria, which allows the ventricles to fill with blood before they contract.
Describe the components and function of the cardiac conduction system
Components of cardiac conduction system
