CVS 1 Flashcards
Four chambers of the Heart
Two upper ones: atria - receives blood that comes back to the heart
Two lower ones: ventricles – receives blood from the atria and generates the force that push blood away from the heart into the blood vessels.
Two sides of the heart
right: pulmonary (to the lungs)
left: systemic (to the rest of the body)
Define vasculature
system of blood vessels
What is the order of vessels from which the blood leaves and returns to the heart?
When blood leaves the heart, it travels through the arteries, which branch repeatedly into smaller vessels called arterioles which carry blood to the capillaries. From the capillaries, blood moves to larger vessels called venules, which lead to larger vessels called veins.
Arteries
Conducts blood away from heart to tissue.
Walls contain large amounts of elastic tissue; withstand high pressure. Stretches during systole and recoil during diastole.
Aorta- largest artery in the human body
Arterioles
Finest division of arterial tree.
Walls have little elastic tissue and more smooth muscle- control the release of blood into capillaries
Contractile activity is regulated by ANS and local chemical agents
Provides the greatest resistance to blood flow.
Capillaries
Single layer of endothelial cells and basement membrane (gives rigidity). No smooth muscle or elastic tissue.
Exchanges fluid, gas, nutrients, electrolytes and hormones
Venules/ veins
Collect blood from capillaries
Coalesce to form veins
Low resistance- transports blood back to the heart
Venules- thin walls with little to no smooth muscles.
Veins- muscular- contract or expand
Lymphatic vessels
An accessory route from which fluids can flow from interstitial spaces into the blood; ultimately empties the venous system.
Role of Blood
transports nutrients, metabolites, gases and heat.
The total volume of blood in a normal healthy adult is approximately 5.5 litres.
Composition of blood
Although blood is a fluid, nearly half of its volume is composed of cells.
The most numerous cells are erythrocytes; red blood cells. These contain haemoglobin; a protein that carries oxygen and gives blood its reddish colour.
The remainder of cells are leukocytes; white blood cells which protects the body from invading organisms.
There are also platelets; which are not cells but cell parts which help clotting.
These cellular components are suspended in plasma; the liquid portion of blood containing dissolved proteins, electrolytes and other solutes.
Haematocrit
the ratio of the volume of red blood cells to the total volume of blood
Flow of the CVS
check picture
Advantages of parallel arrangement of bloodflow
First, because each organ is fed by a separate artery, each receives fully oxygenated blood—that is, blood that has not been depleted of oxygen as a result of having already flowed through another organ.
Second, because blood reaches the organs via parallel paths, blood flow to the organs can be independently regulated. Thus blood flow can be adjusted to match the constantly changing metabolic needs of organs.
Three layers of the heart
The heart wall consists of three layers: an outer layer of connective tissue called the epicardium, a middle layer of cardiac muscle called the myocardium, and an inner layer of epithelial cells called the endothelium.
Which side of the heart is thicker?
Ventricular muscle is thicker than atria muscles as ventricles pump blood over relatively long distances. Also note LV’s muscle is thicker than RV, therefore allowing it to withstand greater pressure as blood is pumped to the whole body rather than just the lungs.
When do valves open?
The atrium and ventricle on each side are separated by atrioventricular valves (AV valves), which permit blood to flow from the atrium to the ventricle but not in the opposite direction. When atrial pressure is higher than ventricular pressure, the valves open; when ventricular pressure becomes higher than atrial pressure, the valves close.
What prevents blood from prolapsing?
When a ventricle contracts, the increased ventricular pressure exerts an upward force against the AV valve. Because of this force, there is a potential danger that one or more valve cusps could be pushed into the atria, a condition called prolapse. However, this is usually prevented because the valve cusps are held in place by strands of connective tissue (known as the chordae tendineae) that extend from the edges of the cusps to papillary muscles.
What are the three types of cardiac muscle?
Atrial
Ventricular
Specialised excitatory and conductive muscle fibres – contract feebly, exhibit rhythmicity and varying rates of conduction.
The Conduction System of the Heart
The heart does not require the CNS to contract, it has its own intrinsic system called the cardiac conducting system.
Thus it can be referred to as myogenic; originating in muscle tissue (rather than from nerve impulses).
The ability of the heart to generate its signals at its own rhythm is called autorhythmicity.
Two types of autorhythmic cells
Pacemaker cells, which initiate action potentials and establish the heart rhythm
Conduction fibres, which transmit action potentials through the heart in a highly coordinated manner.
Together, these cells make up the conduction system of the heart. The cells that generate the contractile force are called contractile cells.
Pacemaker Cells
Spontaneously generates action potentials and can determine its own pace of the heartbeat.
Although pacemaker cells are located in nearly all parts of the heart, they are concentrated primarily in two specific regions of the myocardium:
Sinoatrial node (SA node), located in the wall of the upper right atrium near where it joins with the superior vena cava, and the
Atrioventricular node (AV node), located near the tricuspid valve in the interatrial septum.
The rates at which SA node and AV node cells spontaneously generate action potentials differ; SA node have a faster inherent rate of spontaneous depolarization.
Spread of Excitation Between Cells
Once an action potential is initiated in pacemaker cells, the conduction system causes a wave of excitation to depolarise and contract the atria and then the ventricles.
Cell membrane fuse to form permeable communicating junctions called gap junctions- low resistance bridges for spread of excitation.
In the heart, gap junctions are concentrated in structures called intercalated discs.
Initiation and Conduction of an Impulse During a Heartbeat
- An action potential is initiated in the SA node. The signals spread through the atria.
- The impulse is conducted to cells of the AV node.
- From the AV node, the impulse travels through the atrioventricular bundle, also known as the bundle of His. The AV node and bundle of His are the only electrical connection between the atria and the ventricles.
- The signal travels a short distance before it splits into left and right bundle branches, which conduct impulses to the left and right ventricles, respectively.
- From the bundle branches, impulses travel through an extensive network of branches referred to as Purkinje fibres. From these fibres, impulses travel through the rest of the myocardial cells.
why are Impulses are normally generated by the SA node as opposed to the AV node.
Impulses are normally generated by the SA node as opposed to the AV node.
This is because:
Action potentials originating in the SA node travel through the AV node on their way to the ventricles, causing the AV node to go into refractory period during which they cannot generate their own action potentials.
SA node has a higher frequency of action potentials than the AV node (about 70 impulses per minute vs 50 impulses per minute).
