Cardiovascular system Flashcards
What surrounds the heart?
A fluid-filled sac called the pericardium surrounds the heart.
What is the function of the fluid within the pericardium?
The fluid acts as a shock absorber for the heart.
What are the two layers of the pericardium?
The serous (inner) layer and the fibrous (outer) layer.
How does the fibrous layer of the pericardium interact with the diaphragm?
It is attached to the diaphragm, allowing the heart to move during breathing (e.g., contraction of the diaphragm).
What is cardiac tamponade?
It occurs when the fibrous layer ruptures, increasing the fluid in the pericardium and causing pressure on the heart muscle.
What are the three layers of the heart wall?
The epicardium, myocardium, and endocardium.
What is the epicardium?
It is the outer layer of connective tissue that attaches to the serous layer of the pericardium.
What is the myocardium, and why is it important?
The myocardium is the thickest layer of the heart, consisting of cardiac muscle, blood vessels, and nerve fibers.
What is the endocardium?
The endocardium is a layer of connective tissue and endothelial cells on the inside of the heart.
How is blood supplied to the heart?
Blood is supplied by the left and right coronary arteries, which supply the left and right sides of the heart, respectively.
What happens if the coronary arteries are occluded?
Occlusion leads to reduced blood flow to the heart, which can result in angina pectoris and/or myocardial infarction.
Why is the extent and duration of coronary artery occlusion important?
It determines the extent of damage to cardiac tissue.
How many chambers does the heart have, and what are they called?
The heart consists of four main chambers:
Left atrium
Right atrium
Left ventricle
Right ventricle
Where are the left and right atria located in the heart?
The left and right atria are situated in the upper left and right portions of the heart.
Where are the left and right ventricles located in the heart?
The left and right ventricles are situated in the lower left and right portions of the heart.
What separates the left and right atria?
The left and right atria are separated by a thin muscular wall called the interatrial septum.
What separates the left and right ventricles?
The left and right ventricles are separated by the interventricular septum.
What is the purpose of the interatrial and interventricular septa?
These walls ensure that blood cannot move between the two atria or the two ventricles.
What is the role of the left atrium and left ventricle in circulation?
They act as a single pump, draining blood into the aorta and providing blood to the systemic circulation.
What is the role of the right atrium and right ventricle in circulation?
They act as a single pump, draining blood into the pulmonary artery and providing blood to the pulmonary circulation.
Why can blood not move freely between the left atrium and left ventricle or the right atrium and right ventricle?
Because of the existence of valves, which ensure unidirectional blood flow.
What is the function of heart valves?
Heart valves ensure that blood can only flow in one direction.
What is the name of the valve between the right atrium and right ventricle?
The tricuspid valve.
What is the name of the valve between the left atrium and left ventricle?
The bicuspid valve or mitral valve.
What structures are attached to heart valves, and what is their function?
Papillary muscles are attached to the valves and the ventricle walls via chordae tendineae, preventing valve prolapse.
What triggers the opening of valves during atrial contraction?
When pressure within the atria exceeds pressure in the ventricles, valves open, allowing blood to flow into the ventricles.
What is the function of the pulmonary and aortic valves?
- The pulmonary valve controls blood flow from the right ventricle to the pulmonary artery.
- The aortic valve controls blood flow from the left ventricle to the aorta.
How do the pulmonary and aortic valves respond to pressure changes?
These valves open when ventricular pressure exceeds vessel pressure, allowing blood to move into the circulatory system.
What are the main components of the circulatory system?
The circulatory system consists of arteries, arterioles, capillaries, venules, and veins.
What is the function of arteries and arterioles?
They carry blood away from the heart and can be compared to the efferent neurons of the nervous system.
What is the function of venules and veins?
They carry blood back to the heart and can be compared to the afferent neurons of the nervous system.
What is the primary role of capillaries in the cardiovascular system?
Capillaries perform the ultimate role of the cardiovascular system as the only site where gas exchange occurs.
What is the general structure of all elements in the circulatory system?
All elements of the circulatory system have a similar structure, consisting of:
- Tunica intima
- Tunica media
- Tunica externa
What does the tunica intima consist of?
The tunica intima is made up of:
- A thin layer of endothelium
- Some connective tissue
- In arteries, it includes a thin layer of elastic fibers called the internal elastic membrane.
What is the tunica media, and what is its primary component?
The tunica media consists almost entirely of smooth muscle.
The amount of smooth muscle varies among vessels, influencing the diameter of the vessel and the rate of blood flow.
What additional structure is present in the tunica media of arteries?
The tunica media in arteries contains a layer of elastic fibers called the external elastic membrane.
What is the function of the internal and external elastic membranes in arteries?
These membranes help arteries handle the large pressure exerted when blood is ejected from the heart and assist in returning to their resting state after expansion.
What is the tunica externa composed of, and what is its role?
The tunica externa is made of connective tissue, which acts as an anchor and stabilizes the vessel.
How does the thickness of the vessel wall differ between arteries and veins?
The vessel wall is generally thicker in arteries than in veins due to the greater thickness of the tunica media in arteries. However, the tunica externa is larger in veins.
Why is the tunica media thicker in arteries than in veins?
This is due to the need to withstand higher pressure in arteries compared to veins.
Why is the diameter of the lumen smaller in arteries than in veins?
The smaller lumen in arteries is due to the elastic recoil of arteries, reinforced by the internal and external elastic membranes, which are present only in arteries.
Why do capillaries allow gases to diffuse easily?
Capillaries have little or no tunica media or externa, and their vessel walls are very thin, allowing gases to diffuse efficiently.
How is deoxygenated blood returned to the right atrium?
Deoxygenated blood returns to the right atrium, and as pressure increases, the tricuspid valve opens, allowing blood to flow into the right ventricle.
What happens when pressure increases in the right ventricle?
Increased pressure causes the pulmonary valve to open, ejecting blood into the pulmonary artery.
Where does blood go after entering the pulmonary artery?
Blood flows to the pulmonary arterioles and then to the pulmonary capillaries, where it becomes oxygenated by diffusion of oxygen from the alveoli.
What happens to oxygenated blood after it leaves the pulmonary capillaries?
Oxygenated blood enters the pulmonary venules, moves to the pulmonary veins, and drains into the left atrium.
What happens when pressure increases in the left ventricle?
The aortic valve opens, allowing blood to be ejected into the aorta, which is a large systemic artery.
How does blood become deoxygenated in systemic circulation?
Blood is transported to systemic arterioles and capillaries, where oxygen diffuses to active tissues, resulting in deoxygenation.
How does deoxygenated blood return to the heart?
Deoxygenated blood flows through systemic venules and veins and returns to the right atrium via the inferior or superior vena cava.
What does the tunica intima layer contain, and what are its key functions?
The tunica intima contains a layer of endothelium, which:
- Provides protection to blood vessels.
- Prevents cells from sticking and forming plaques under normal conditions.
What can occur if the endothelium is damaged?
Damaged endothelium allows cells to stick and form plaques, leading to atherosclerosis.
How does the endothelium contribute to gas exchange?
The endothelium has a permeable membrane, allowing diffusion of gases and fluids in capillaries.
How does the endothelium regulate blood flow in arterioles?
It releases compounds that relax the surrounding smooth muscle, leading to an increase in blood flow through the arteriole.
What is angiogenesis, and how is it mediated?
Angiogenesis is the process of new capillary growth, mediated via the endothelium.
What role does the endothelium play in immune response and clotting?
The endothelium secretes various growth factors involved in immune response and substances central to the blood clotting process.
Why do arteries have relatively thick muscular walls?
Arteries have thick muscular walls due to the presence of large amounts of smooth muscle in the tunica media.
How does smooth muscle in arteries regulate vessel diameter?
- Contraction of smooth muscle causes vasoconstriction (reducing vessel diameter).
- Relaxation of smooth muscle causes vasodilation (increasing vessel diameter).
How are arteries classified, and what distinguishes them?
Arteries can be classified as:
- Muscular arteries
- Elastic arteries: These are large vessels like the aorta and have well-developed elastic membranes to absorb pressure.
What is the role of muscular arteries?
Muscular arteries have large amounts of smooth muscle and are responsible for distributing blood flow to various organs. The pulse in these arteries can also be measured.
What is the structure of arterioles?
Arterioles have a very small diameter and may have small amounts of smooth muscle in their tunica media.
Why are arterioles known as resistance vessels?
Arterioles regulate blood flow to tissues, determining the resistance within the circulatory system.
How do arterioles respond to smooth muscle activation?
- Smooth muscle contracts in response to the central nervous system and local factors, causing vasoconstriction.
- Relaxation leads to vasodilation.
Why are arterioles important in blood pressure regulation?
Due to their ability to regulate blood flow, arterioles have a major impact on blood pressure.
What makes capillaries the primary site of gas exchange?
Capillaries have very thin walls consisting of a single layer of tunica intima, enabling efficient gas exchange.
How does the structure of capillaries facilitate rapid gas exchange?
The thin walls of capillaries and the short distance between capillaries and the organs they serve allow for rapid gas exchange.
How do capillaries arise from arterioles, and what happens to blood flow in capillaries?
One arteriole gives rise to numerous capillaries that form a capillary bed around an organ. Blood flow rate decreases as the cross-sectional area increases, allowing maximum time for gas exchange.
Do capillaries act as a single unit?
No, capillaries do not act as a single unit. Each capillary is regulated by a pre-capillary sphincter, which can contract or relax to increase or decrease blood flow.
How are capillaries classified?
Capillaries are classified as either:
- Continuous
- Fenestrated
What are continuous capillaries, and what can pass through them?
Continuous capillaries have a continuous layer of endothelium, preventing proteins from passing through. However, gases, water, and some solutes can pass.
What are fenestrated capillaries, and what is their function?
Fenestrated capillaries have small pores in their endothelial layer, allowing for the rapid exchange of proteins. These are abundant in organs like the liver.
How do venules form from capillaries?
Each capillary drains into numerous venules.
Why can venules be difficult to distinguish from capillaries?
Venules have a very small diameter and poorly developed tunica media and externa, making them similar in structure to capillaries.
How are veins classified based on size?
Veins can be classified as medium-sized or large-sized.
What is the structure of medium-sized veins?
Medium-sized veins have a thin tunica media layer with little smooth muscle.
What is the structure of large-sized veins?
Large-sized veins have a more developed tunica media with large amounts of smooth muscle that can contract or relax in response to central nervous system activation.
How is blood flow back to the heart assisted in veins?
Blood flow back to the heart is assisted by the presence of valves, which ensure unidirectional movement of blood and prevent pooling.
What are the challenges blood faces when flowing back to the heart in veins?
- Blood pressure in veins is relatively low compared to arteries.
- Blood relies on gravity and valves to return to the heart.
- Problems with valves can lead to conditions like varicose veins.
How much blood is in the venous circulation at any time?
Approximately 60% of all blood is in the venous circulation at any given time.
What is the primary function of blood in the cardiovascular system?
Blood transports gases, nutrients, and hormones and provides an appropriate environment for cells.
How is blood structured?
Blood consists of:
- Cells (erythrocytes and leukocytes).
- Cell fragments (platelets).
- Plasma (suspending medium for cells and fragments)
What is plasma, and what does it contain?
Plasma is a fluid medium containing:
- Proteins: Albumin, globulins, clotting factors.
- Electrolytes and nutrients.
What happens when blood is centrifuged?
Blood is separated into its components:
- Red blood cells (percentage = haematocrit).
- Plasma.
- A thin layer of white blood cells.
What are erythrocytes, and what is their proportion in blood?
Erythrocytes (red blood cells) make up 99.9% of all cells in the blood.
What protein do erythrocytes contain, and what is its function?
Erythrocytes contain haemoglobin, which gives blood its red color and transports oxygen.
How are erythrocytes formed, and what hormone is involved?
Erythrocytes are formed via erythropoiesis in the bone marrow. The hormone erythropoietin stimulates their production and increases oxygen-carrying capacity.
Why is erythropoietin sometimes abused by athletes?
It is abused as it stimulates red blood cell production, enhancing oxygen delivery and endurance.
What is the shape of erythrocytes, and why is it important?
Erythrocytes have a biconcave disc shape, allowing flexibility and providing a high surface area for gas diffusion.
Why do erythrocytes have a limited lifespan?
Erythrocytes lack a nucleus, mitochondria, and organelles, giving them a lifespan of approximately 120 days.
How do erythrocytes generate energy without mitochondria?
Energy is obtained from the anaerobic breakdown of glucose in the plasma. This prevents erythrocytes from using the oxygen they transport.
What is haemoglobin, and what does it consist of?
Haemoglobin is a complex protein made of four chains of amino acids, each containing a heme molecule with iron.
How does haemoglobin bind oxygen?
Oxygen binds to the iron in the heme molecule of haemoglobin.
Why is oxygen released easily at active tissues?
There is a weak association between oxygen and haemoglobin, allowing rapid oxygen release where it is needed.
How many oxygen molecules can one haemoglobin molecule transport?
Each haemoglobin molecule can carry four oxygen molecules.
What is oxyhaemoglobin and carboxyhaemoglobin?
- When oxygen binds to haemoglobin, it forms oxyhaemoglobin.
- When carbon dioxide binds to haemoglobin, it forms carboxyhaemoglobin.
What are the structural levels of haemoglobin?
- Primary structure
- Secondary structure:
- Tertiary structure:
- Quaternary structure:
What primarily determines the exchange of oxygen and carbon dioxide?
The exchange depends on the plasma levels of the appropriate gas.
What happens when plasma oxygen levels are low and carbon dioxide levels are high (e.g., active tissue)?
Oxygen is released from haemoglobin, and carbon dioxide is bound.
What happens when plasma oxygen levels are high and carbon dioxide levels are low (e.g., around the lungs)?
Carbon dioxide is released from haemoglobin, and oxygen is bound.
What does blood pressure depend on in the walls of a vessel?
Blood pressure depends on:
- The volume of blood in the vessel.
- The compliance of the vessel’s walls.
How is pressure in an artery generated during systole?
Pressure increases when blood exits the ventricle during systole (ejection phase of the cardiac cycle) and is referred to as systolic pressure.
What is diastolic pressure?
Diastolic pressure is the lowest pressure in arteries, occurring at the end of diastole (the filling phase of the cardiac cycle).
How is blood pressure typically presented, and what is considered healthy?
Blood pressure is presented as systolic/diastolic pressure in mmHg.
A typical healthy blood pressure is 120/80 mmHg.
What is pulse pressure, and how is it calculated?
Pulse pressure is the difference between systolic pressure and diastolic pressure.
What is mean arterial pressure (MAP), and how is it calculated?
MAP is an indicator of the average pressure across the circulatory system. It is calculated as:
MAP = diastolic pressure + (pulse pressure / 3).
Why is MAP not simply the average of systolic and diastolic pressures?
Because the filling phase of the cardiac cycle (diastole) lasts longer than the ejection phase (systole), making MAP weighted more towards diastolic pressure.
How does pressure vary in different blood vessels?
Pressure in arteries is higher than in arterioles, which is higher than in capillaries, venules, and then veins. Pressure in veins can drop as low as 10–15 mmHg.
What ensures blood flow through the circulatory system?
The pressure gradient between various blood vessels.
What does Poiseuille’s law state about blood flow?
Blood flow (F) is proportional to the pressure gradient (ΔP) divided by the resistance (R): F = ΔP/R
Why are arterioles known as resistance vessels?
Arterioles create a pressure gradient by regulating blood flow to tissues and maintaining vascular resistance.
What happens when resistance in the arteriole increases?
- Blood flow through the arteriole is reduced.
- When resistance decreases, blood flow increases.
How is the resistance in arterioles controlled?
Resistance is altered by changes in the diameter of the arteriole through vasoconstriction or vasodilation.
What controls the diameter of arterioles?
The smooth muscle surrounding arterioles contracts or relaxes.
- Contraction increases resistance and reduces blood flow.
- Relaxation decreases resistance and increases blood flow.
What is the role of arterioles in oxygen delivery to organs?
Arterioles regulate blood flow and oxygen delivery to organs, directly affecting mean arterial pressure.
How does arteriolar smooth muscle respond to stimuli?
It relaxes or contracts in response to local or extrinsic factors.
What are the two local mechanisms affecting blood flow?
- Active hyperaemia.
- Autoregulation.
What is active hyperaemia?
It is an increase in blood flow due to increased metabolic activity in a tissue, caused by factors like:
- Increased carbon dioxide, hydrogen ions, bradykinin, and nitric oxide.
- Decreased oxygen levels.
How does autoregulation maintain blood flow?
Autoregulation adjusts blood flow through vasodilation in response to pressure changes in arterioles while maintaining constant metabolic activity, ensuring adequate blood supply.
What is the mechanism of autoregulation compared to active hyperaemia?
Both use vasodilation, but autoregulation is triggered by pressure changes, while active hyperaemia responds to metabolic demand.
What is the role of local control in blood flow?
Local controls ensure adequate blood flow to organs by adjusting arteriolar tone based on metabolic demands.
How is extrinsic control of blood flow mediated?
Extrinsic control involves activation of the central nervous system and circulating hormones, which regulate mean arterial pressure.
How do parasympathetic and sympathetic innervations affect most tissues?
- Most tissues receive sympathetic innervation, leading to arteriolar constriction or relaxation.
- Parasympathetic innervation is limited but important for specific functions.
What happens with increased sympathetic tone?
- Smooth muscle contraction in arterioles causes vasoconstriction, increasing resistance and blood pressure.
- Noradrenaline acts as a neurotransmitter in this process.
How does adrenaline affect arterioles?
Adrenaline can cause constriction or relaxation, depending on the receptor type it binds to.
What role do hormones like angiotensin II and vasopressin play?
These hormones increase vasoconstriction and smooth muscle tone, raising blood pressure.
How does blood flow back to the heart through veins?
Blood flow relies on:
- Small pressure gradients.
- Overcoming gravity.
- Venous smooth muscle contraction to increase pressure.
What happens with an increase in venous pressure?
Increased venous pressure enhances blood flow back to the right atrium. This is driven by venous smooth muscle contraction.
How is venous smooth muscle contraction enabled?
Venous smooth muscle contraction is enabled by an increase in central nervous system tone.
What happens when sympathetic nervous system activity increases?
Increased sympathetic nervous system activity leads to increased arteriolar and venous smooth muscle contraction, reducing blood flow through arterioles but increasing blood flow through veins.
How does skeletal muscle contraction influence blood flow in veins?
Skeletal muscle contraction (skeletal muscle pumps) increases blood flow through veins by reducing venous diameter and increasing pressure.
What role does the respiratory muscle pump play in blood flow?
The respiratory muscle pump increases venous blood flow by enhancing blood return through changes in pressure.
What is cardiac output and how is it calculated?
Cardiac output is the volume of blood ejected from the ventricle in 1 minute. It is the product of heart rate (number of beats per minute) and stroke volume (volume of blood emptied per beat).
What is total peripheral resistance?
Total peripheral resistance is the resistance of systemic vessels to blood flow.
How is mean arterial pressure calculated?
Mean arterial pressure is calculated by multiplying cardiac output by total peripheral resistance.
What factors influence mean arterial pressure?
Factors such as heart rate, stroke volume, and total peripheral resistance influence mean arterial pressure.
What is the main factor that affects stroke volume?
The main factor affecting stroke volume is venous return, which influences end-diastolic volume.
How is venous return determined?
Venous return is determined by venous pressure (influenced by sympathetic nervous system activation) and skeletal and respiratory muscle pumps.
What is the main factor that affects heart rate?
The main factor that affects heart rate is central nervous system activation.
What drives total peripheral resistance?
Arteriolar smooth muscle contraction drives total peripheral resistance, influenced by sympathetic nervous system activation, circulating hormones, and local factors.
What distinguishes cardiac muscle from skeletal and smooth muscle?
Cardiac muscle contracts without requiring input from the central nervous system, a property achieved through the conduction system.
What is the function of the sinoatrial (SA) node?
The sinoatrial node, located in the upper right atrium, generates electrical impulses as it contains specialized cells capable of producing pacemaker potentials.
What makes the cells of the sinoatrial node unique compared to other body cells?
Unlike most cells in the body, the cells within the sinoatrial node do not have a stable resting membrane potential.
Why does the resting membrane potential in sinoatrial node cells increase?
The membrane of sinoatrial node cells is porous, allowing ions to be easily exchanged, leading to a slow increase in resting membrane potential until it reaches the threshold and an action potential is produced.
What are gap junctions, and what role do they play in cardiac cells?
Gap junctions are specialized connections between cells that allow the movement of ions and, therefore, action potentials, between cells.
How do gap junctions contribute to coordinated heart contraction?
Gap junctions enable the action potential generated in the sinoatrial node to propagate to all cardiac muscle cells, resulting in a coordinated contraction of the atria.
What is the atrioventricular (AV) node, and where is it located?
The atrioventricular node is a small group of cells located in the bottom right-hand corner of the right atrium.
What role does the atrioventricular node play in heart contraction?
The AV node acts as a link between the atria and ventricles, briefly delaying the action potential to ensure atrial contraction is completed before ventricular contraction begins.
Why is the delay caused by the AV node important?
The delay ensures that the atria have time to fully contract and empty blood into the ventricles before the ventricles begin contracting, maximizing heart contraction efficiency.
What are the bundles of His, and what is their function?
The bundles of His are specialized cardiac cells that propagate the action potential from the atrioventricular node to the left and right ventricles.
Where do the left and right bundles of His extend?
The left and right bundles of His extend from the atrioventricular node down the interventricular septum to the bottom of each ventricle.
What is the purpose of an electrocardiogram (ECG)?
An electrocardiogram (ECG) depicts the electrical events of the heart and is used in clinical settings to identify potential conduction system problems that may result in arrhythmias.
What are the three main events depicted on a standard ECG trace?
The P-wave, the QRS complex, and the T-wave.
What does the P-wave on an ECG represent?
The P-wave represents the depolarization of the atria, which leads to atrial contraction.
What is represented by the QRS complex on an ECG?
The QRS complex represents the depolarization of the ventricles, leading to ventricular contraction.
What does the T-wave on an ECG represent?
The T-wave represents ventricular repolarization.
How long does one cardiac cycle take at rest?
At rest, one cardiac cycle takes approximately 0.7–0.8 seconds, although this varies depending on the individual.
What are the two main phases of the cardiac cycle?
The cardiac cycle is divided into:
- Systole (ejection phase, one-third of the cycle).
- Diastole (filling phase, two-thirds of the cycle).
What happens prior to the start of ventricular systole?
The atria and ventricles are relaxed, the atrioventricular valves are open, and the pressure in the ventricles is lower than in the atria, allowing blood to flow into the ventricles.
What is the end-diastolic volume (EDV), and how much is it?
The end-diastolic volume is the volume of blood in the ventricles at the end of diastole, just before ventricular systole starts. It is approximately 120–130 mL.
What are the two periods of ventricular systole?
Ventricular systole consists of:
- Isovolumic contraction: Pressure increases in the ventricles, but no blood is ejected because the aortic and pulmonary valves remain closed.
- Ejection period: When ventricular pressure exceeds arterial pressure, the aortic and pulmonary valves open, and blood is ejected.
What is end-systolic volume (ESV), and how much is it?
End-systolic volume is the volume of blood remaining in the ventricles after ejection. It usually amounts to 50–60 mL.
How is end-diastolic volume determined?
End-diastolic volume is determined by venous return. An increase in venous pressure leads to an increase in venous return, which increases end-diastolic volume and stroke volume.
What is afterload, and what determines it?
Afterload refers to the force against blood flow when blood is ejected from the left ventricle. It is primarily determined by aortic pressure.
How does aortic pressure affect blood flow?
If aortic pressure is high, the pressure gradient between the left ventricle and the aorta decreases, which reduces blood flow.
What are the two periods of ventricular diastole?
Ventricular diastole consists of:
- Isovolumic relaxation
- Filling phase
