Cardiovascular System

Question 1

Discussed Systems

Answer 1

The cardiovascular system is related to the heart and blood vessels. The circulatory is related to the heart, blood vessels and blood.

Question 2

Circulatory System Function

Answer 2

It acts in transport (O2, CO2, nutrients, wastes and hormones), protection (causes inflammation, limits infection spread, destroys microorganisms and cancers, neutralises toxins and initiates clotting) and regulation (fluid balance, stabilising pH of extracellular fluid and temperature control).

Question 3

Circuits of the Circulatory System

Answer 3

The system circuit supplies oxygenated blood to all tissues of the body and returns it to the heart. The pulmonary circuit carries blood to lungs for gas exchange and then back to the heart.

Question 4

Blood Flow

Answer 4

The heart consists of 2 pumps (right and left side). The atria receive blood and the ventricles pump blood. Valves ensure blood flows in one direction only. Arteries carry blood away from the heart, veins carry blood back to the heart. Capillaries are small vessels connecting arteries to the veins.

Question 5

Heart Position

Answer 5

It is found in the thoracic cavity/mediastinum. It is posterior to the sternum, anterior the the vertebral column, medial to the lungs, deep to the ribs and is surrounded by the pericardium.

Question 6

Pericardium

Answer 6

A double-walled sac that encloses the heart. It allows the heart to beat without friction, provides room for expansion of the heart but resists excessive expansion. It is anchored to the diaphragm inferiorly and the sternum anteriorly. This consists of the 2 layers the fibrous pericardium (outer wall, not attached to the heart) and serous pericardium (this is made up of 2 layers the parietal (lines fibrous pericardium) and the visceral (also known as epicardium which covers the hearts surface). There is also a pericardial cavity which is space between parietal and visceral layers of serous pericardium which is filled with pericardial fluid.

Question 7

Epicardium

Answer 7

The outer layer of the heart wall is the same as the visceral layer of serous pericardium, it is a serous membrane overlying the heart, it is made up of simple squamous epithelium overlying a thin layer of loose CT and coronary blood vessels are found within this layer.

Question 8

Myocardium

Answer 8

The middle layer of the heart wall consists of cardiac muscle which spirals around the heart and produces wringing motion and the fibrous skeleton of the heart which has a framework of collagen and elastic fibers which provides structural support and attachment for cardiac muscle and valves as well as electrical insulation between atria and ventricles.

Question 9

Endocardium

Answer 9

This is the smooth inner lining of the heart and blood vessels which is made of simple squamous epithelium overlying a thin layer of loose CT.

Question 10

Heart Chambers

Answer 10

There are 4 of these with a right atrium, right ventricle, left atrium and left ventricle.

Question 11

Semilunar Valves

Answer 11

These valves control blood flow into the pulmonary trunk (artery) and aorta. The pulmonary version of this valve is between the right ventricle and pulmonary trunk and the aortic version of this valve is between the left ventricle and aorta.

Question 12

Atrioventricular Valves (AV)

Answer 12

These valves control blood flow between the atria and ventricles with the right having 3 cusps (tricuspid valve) and the left having 2 (bicuspid valve). There are also structures called chordae tendineae which connect AV valves to papillary muscles on the floor of ventricles and prevent AV valves from flipping or bulging into atria (helping one-way flow).

Question 13

Blood Flow in the Heart

Answer 13

1. Blood returns from the lungs via the pulmonary veins to the left atrium (LA).
2. Blood in the (LA) flows through the left AV valve into the left ventricle (LV).
3. The LV then contracts (simultaneously with the right ventricle (RV))which forces the aortic valve open.
4. Blood flows through the aortic valve into the ascending aorta.
5. Blood in the aorta is distributed to every organ in the body where it unloads O2 and loads CO2.
6. Blood returns to the right atrium (RA) through the vena cava.
7. Blood in the RA flows into the RV through the right AV valve.
8. contraction of the RV forces the pulmonary valve open.
9. Blood flows through the pulmonary valve into the pulmonary trunk.
10. Blood is distributed by the left and right pulmonary arteries into the corresponding lungs where it unloads CO2 and load O2.

Question 14

Heart Sound

Answer 14

When ventricles contract the internal pressure rises and the AV valves close which is what causes the first part of the heart beat. The semilunar valves are pushed open blood flows into the aorta and pulmonary trunk. The ventricles then relax and expand causing a decrease in pressure. The semilunar valves close as blood attempts to back up into the ventricles which causes the second part of the heart beat.

Question 15

Coronary Circulation

Answer 15

5% of blood pumped by the heart goes to the heart itself through coronary circulation. The heart requires abundant O3 and nutrients to sustain its workload. Coronary blood returns to the RA through the coronary sinus and directly into the RV via cardiac veins.

Question 16

Cardiac Muscle

Answer 16

This consists of cardiomyocytes (heart muscle cells) these are striated, short, thick, branched cells with 1 central nucleus. They have intercalated discs which join cardiomyocytes end to end with interdigitating folds (folds which interlock each other and increase surface area of contact), desmosomes (mechanical junctions tightly joining the cells) and gap junctions (electrical junctions which allow ions to flow between cells).

Question 17

Intercalated Discs

Answer 17

The gap junctions at this point enable rapid communication of action potentials between cardiac muscle cells while the desmosomes enable the muscle cells to resist the mechanical stress that comes with contracting. The contractions of the heart originate within muscle cells (myogenic), these are triggered by pacemaker cells in the sinoatrial (SA) and AV nodes, an electrical signal is transmitted by a nerve-like conduction pathway in the myocardium, cardiac muscle cells contract on their own but are regulated by the autonomic nervous system.

Question 18

Conduction System

Answer 18

1. The SA node also known as the pacemaker cells are modified cardiomyocytes in the RA near the base of the superior vena cava initiates each heartbeat and determines the heart rate.
2. Excitation spreads through atrial myocardium.
3. The AV node near the right AV valve is an electrical gateway to the ventricles and allows excitation to spread to the AV bundle.
4. The AV bundle also known as the ‘bundle of his’ is splits into right and left bundle branches with these branches passing through interventricular septum toward the apex.
5. Subendocardial conducting network also known as ‘Purkinje fibers’ are nerve like processes that distribute excitation through the ventricular myocardium.

Question 19

Conduction Results

Answer 19

This signal is passed on from cell to cell via gap junctions meaning that the 2 atria and 2 ventricles act as a single unified cell. There is a fibrous skeleton which prevents current from getting to ventricles by any other route which keeps the adult heart rate 70-80bpm at rest (vagal tone).

Question 20

Pacemaker Cells (SA node)

Answer 20

These have an unstable resting membrane potential (RMP) due to a porous membrane which starts at -60mV which gradually depolarises to the threshold of -40mV causing an action potential (AP). When the SA node fires, it sets off the heartbeat after which the SA node stimulates both atria to contract almost simultaneously.

Question 21

Cardiomyocytes

Answer 21

These cells have a stable RMP of -90mV which only depolarise when stimulated. This causes an action potential with the depolarisation phase, plateau phase (sustains contraction for expulsion of blood from heart), repolarisation phase (returning to RMP) and an absolute refractory period (the time period when an AP can’t be initiated in that specific part of the cell).

Question 22

Electrocardiogram (ECG/EKG)

Answer 22

A composite of all AP’s of nodal and myocardial cells. The first part is a P wave when the SA node fires, atria depolarise and contract (atrial systole begins 100ms after SA signal). The PR interval is a signal conduction through the AV node before activating ventricles. The QRS complex is the period when the ventricles depolarise with a complex shape due to the different thickness and shape of the 2 ventricles. QT interval is the duration of ventricle depolarisation. ST segment is the period of ventricular systole which corresponds to a plateau in myocardial AP. T wave is the ventricular repolarisation and relaxation.

Question 23

Cardiac Cycle

Answer 23

The opening and closing of valves are governed by pressure changes. When ventricles relax they compact decreasing pressure, the AV valves limp meaning blood flows into the ventricle and semilunar valves close under the pressure of blood in the vessels. When ventricles contract they expand increasing pressure which causes AV valves to close and semilunar valves are pushed open as blood flows into the vessels. This can be put into 2 steps of diastole (relaxation/ventricular filling) and systole (contraction (isovolumetric contraction, ventricular ejection, isovolumetric relaxation)) which happens in <1 second.

Question 24

Ventricular Filling

Answer 24

The first step of the cardiac cycle also known as ventricular diastole when ventricles relax and expand which drops their pressure below that in atria. The AV valves then open and blood flows into the ventricles. Atria then contract to complete the filling of ventricles (P wave).

Question 25

Isovolumetric Contraction

Answer 25

The second step of the heart cycle which is in the beginning of ventricular systole. The atria repolarise, relax and remain in diastole for the rest of the cardiac cycle. The ventricles depolarise (QRS complex) and begin to contract. AV valves close as ventricular blood surges back against the cusps (part 1 of heart beat). The pressures in the aorta and pulmonary trunk is greater than in the ventricles so all 4 valves are closed so blood can’t go anywhere. Isovolumetric means that the volume stays the same as the ventricles contract but don’t eject blood.

Question 26

Ventricular Ejection

Answer 26

The third step of the heart cycle which is in the middle of ventricular systole. When the pressure of the ventricles is greater than that of the arteries the semilunar valves open. At first there is a rapid ejection of blood as it spurt out quickly however this ejection reduces in speed getting slower as the pressure in the ventricles decreases (T wave).

Question 27

Isovolumetric Relaxation

Answer 27

The fourth and final step of the heart cycle when ventricular diastole begins. The ventricles begin to expand (end of T wave). Blood from the aorta and pulmonary trunk flows back filling cusps and closing the semilunar valves (part 2 of heart beat). Isovolumetric means volume stays the same as AV valves close meaning no more blood enters the ventricles. When the AV valves open ventricular filling begins again and the cycle continues.

Question 28

Autonomic Innervation of the Heart

Answer 28

The heart rhythm and contractions are controlled by the cardiac centers in the medulla oblongata. This means the autonomic nervous system (ANS) doesn’t initiate the heartbeat however they can change the rate of heartbeat (rhythm). The sympathetic nerves increase heart rate and contraction strength. The cardiac nerve effects SA and AV nodes (increase heart rate) and atrial and ventricular myocardium (increase contraction strength). The parasympathetic nerves decrease heart rate. The right Vagus nerve effects the SA node while the left effects the AV node and there is very little effect on the myocardium meaning contraction strength isn’t really changed. Our heart is at a vagal tone resting heart rate is 60-80bpm.

Question 29

Cardiac Output

Answer 29

The amount ejected by each ventricle in 1 minute. To calculate this CO (L/min) = HR (bpm) * stroke volume (SV) (L/beat). A normal cardiac output is 4-6 liters per minute at rest. A RBC leaving the left ventricle will arrive back at the left ventricle in about 1 minute. During vigorous exercise CO increased to 21L/min in a fit person and >40L/min in athletes. The sympathetic nervous system increases CO (increases heart rate and stroke volume) while the parasympathetic decreases CO (decreases heart rate and doesn’t change stroke volume).

Question 30

Orricles

Answer 30

These are parts of the atria which act as expansion chambers. They can be seen best in an anterior view of the heart which is a good determinate for the orientation of a heart.

Question 31

Blood Vessels

Answer 31

There are 3 categories which consist of arteries which carry blood away from the heart, veins which carry blood back to the heart and capillaries which connect the smallest arteries to the smallest veins to create a circuit. Typically arteries carry oxygenated blood while veins carry deoxygenated blood however this is reversed when discussing the pulmonary artery and pulmonary vein.

Question 32

Tunica Interna

Answer 32

The innermost layer of blood vessel walls which lines the blood vessel and is exposed to blood which is made up of simple squamous epithelium and acts as a selectively permeable barrier.

Question 33

Tunica Media

Answer 33

The middle layer of blood vessel walls which is made up of smooth muscles, collagen and elastic tissue. It strengthens vessels and prevents blood pressure from rupturing them and contraction of the smooth muscles controls blood vessel diameter.

Question 34

Tunica Externa

Answer 34

The outermost layer of the blood vessel wall which consists of loose connective tissue. It anchors the vessel and provides passage for small nerves, lymphatic vessels and vasa vasorum which are small vessels that supply blood to the outer part of the larger vessels.

Question 35

Large Arteries

Answer 35

The largest type of artery which is also known as a conducting or elastic artery e.g. aorta, common carotid, subclavian and pulmonary trunk. There is an internal elastic lamina between the interna and media, an external elastic lamina between the media and externa and these expand during systole and recoil during diastole due to the elastic laminas which are present.

Question 36

Medium Arteries

Answer 36

These are the second largest type of artery which are also known as distributing or muscular arteries. They distribute blood to specific organs e.g. renal arteries. They have walls which are 3/4 the thickness of large arteries (less smooth muscle layers).

Question 37

Small Arteries

Answer 37

These are the also known as resistance arteries which have very small (little) tunica externa.

Question 38

Arterioles

Answer 38

These are the smallest of the resistance arteries as they only contain between 1-3 layers of smooth muscle. They control the amount of blood that is distributed to various organs.

Question 39

Metaarterioles

Answer 39

These are the smallest type of arteries and are also known as thoroughfare channels. These short vessels link arterioles directly to venules e.g. in mesenteries. They provide a shortcut which allows blood to bypass the capillary beds.

Question 40

Capillaries

Answer 40

These are also known as exchange vessels. They consist of endothelium (simple squamous epithelium) and a basement membrane. Gases, nutrients, wastes and hormones pass between the blood and tissue fluid and these are categorised into 3 categories of continuous, fenestrated and sinusoid which are categorised based on permeability.

Question 41

Continuous Capillaries

Answer 41

The simple squamous epithelium in these cells have tight junctions which form a continuous tube. This allows for the passage of solutes such as glucose. Pericytes wrap around the capillaries and contract in order to regulate blood flow. These are the least permeable form of capillaries.

Question 42

Fenestrated Capillaries

Answer 42

The epithelium cells have small holes (filtration pores). These are found near organs that require rapid absorption or filtration e.g. kidneys, small intestine etc. They allow for the passage of small molecules while proteins and larger particles stay in the bloodstream. These are the capillaries with medium permeability.

Question 43

Sinusoids

Answer 43

These are irregular blood-filled spaces with large fenestrations (holes/pores). These are found in the liver, bone marrow and spleen. They allow proteins and other molecules such as new blood cells to enter the circulation.

Question 44

Veins

Answer 44

These are thin-walled and flaccid blood vessels which collapse when empty and expand easily. They have a steady blood flow unlike the pulses in the arteries and a re subjected to relatively low blood pressure. These are also categorised by size.

Question 45

Postcapillary Venule

Answer 45

This is the smallest type of vein which is more porous than the capillaries. They exchange fluid with surrounding tissues with no smooth muscle present.

Question 46

Muscular Venules

Answer 46

These are the second smallest form of veins which receive blood from postcapillary venules. There are 1or 2 layers of smooth muscle in the tunica media and a very thin tunica externa.

Question 47

Medium Veins

Answer 47

These have a tunica interna that forms venous valves. It also has a thin tunica media and a thick tunica externa. The skeletal muscle pump propels venous blood back to the heart.

Question 48

Venous Sinuses

Answer 48

These have thin walls, large lumens and no smooth muscle. An example of one of these is the coronary sinus. These are the second largest type of vein.

Question 49

Large Veins

Answer 49

These have smooth muscle in all 3 of their layers with the tunica externa being the thickest. Examples of this are the vena cava, pulmonary vein and the renal vein. These are the biggest types of veins in the body.

Question 50

Neurovascular Bundle

Answer 50

This is a grouping of an artery, a vein and a nerve cell. These will follow the same path with relative proximity to one another creating a small grouping.

Question 51

Venous Return

Answer 51

The flow of blood back to the heart. This is mostly done through pressure gradient however other factors such as gravity (drains the neck and head) also assists this process. A skeletal muscle pump where muscles contract and squeeze deep veins which forces blood through valves which prevents backflow and when muscles relax blood flows downward due to gravity which only goes to close the nearest valve. A thoracic pump which causes the thorax to expand during inhalation which causes the pressure on the inferior vena cava (IVC) decrease, abdominal pressure on the IVC increases the blood that is forced upward toward the heart. Exercising will increase this while inactivity causes venous pooling.

Question 52

Normal Circulatory Pathway

Answer 52

The simplest and most common route for blood is starting at the heart -> arteries -> arterioles -> capillaries -> venules -> veins -> heart where the blood passes through 1 network of capillaries. There are also alternate pathways which may involve 2 (portal system) or 0 capillary beds.

Question 53

Portal System

Answer 53

This is an irregular/alternate circulatory path which occurs when blood flows from 1 capillary bed to another capillary bed before returning to the heart e.g. hypothalamus, anterior pituitary, intestines and liver.

Question 54

Anastomosis

Answer 54

This is an irregular/alternate circulatory path which occurs when there is a convergence between 2 blood vessels that aren’t capillaries which can occur in 3 different types. The arteriovenous or shunt form occurs when an artery flows directly into a vein, bypassing capillaries, venous occurs when one vein empties directly into another and arterial occurs when 2 arteries merge. All of these provide alternative routes of blood supply e.g. coronary circulation and will sometime occur around joints.

Question 55

Pulmonary Circuit

Answer 55

The pulmonary trunk is divided into the right and left pulmonary arteries carrying deoxygenated blood from the right ventricle to the lungs. The right and left pulmonary veins return oxygenated blood from the lungs into the left atrium.

Question 56

Major Systemic Arteries

Answer 56

These are the extensive set of arteries which travel all throughout the body. The important ones are the right and left common carotid artery, the right and left subclavian artery, the brachiocephalic trunk, aortic arch, the ascending and descending aorta, right coronary artery.

Question 57

Branches of the Abdominal Aorta

Answer 57

The left and right renal arteries which supply the kidneys, the celiac trunk and the superior and inferior mesenteric arteries which nourish the gut.

Question 58

Major Systemic Veins

Answer 58

The important ones are the subclavian vein, brachiocephalic vein, internal and external jugular vein, renal vein, hepatic portal vein and the inferior and superior vena cava.

Question 59

Blood

Answer 59

Adults have 4-6L of blood which is a connective tissue consisting of cells and extracellular matrix. Cells and cell fragments are the red blood cells (RBC), white blood cells (WBC) and platelets with the plasma making up the matrix.

Question 60

Erythrocytes

Answer 60

The principle function of these blood cells is gas transport by carrying O2 from lungs to tissues and CO2 from tissues to lungs. They are discoid cells with a biconcave shape with a 7.5 micrometer diameter and 2.0 micrometer thickness. The shape of these allows for a high surface area to volume ratio. These can stretch and bend as squeezed through small capillaries and lose nearly all organelles (mitochondria, nucleus/DNA) during development. The lack of DNA means no protein synthesis or mitosis meaning they have an average life span of 120 days. They have a special chemical called hemoglobin which carries oxygen.

Question 61

Blood Osmolarity

Answer 61

This is the total molarity of dissolved particles that can’t pass through the blood vessel wall. If its too high the blood absorbs too much water from tissues which increases blood pressure. It its too low too much water stays in tissue, blood pressure drops and edema (excess water in blood) occurs.

Question 62

Arterial Sense Organs

Answer 62

Sensory structures in the walls of major blood vessels monitor blood pressure and chemistry. They transmit information to the brainstem to regulate heart rate, blood vessel diameter and respiration via the autonomic nervous system. These sensory organs are the carotid sinuses, carotid bodies and aortic bodies.

Question 63

Carotid Sinuses

Answer 63

These are found in the internally in the carotid artery and contains baroreceptors which monitor blood pressure and transmit signal through the glossopharyngeal nerve (CN IX).

Question 64

Aortic & Carotid Bodies

Answer 64

These branch from the aortic arch and common carotids respectively and contain chemoreceptors which monitor blood chemistry. They transmit signals through the Vagus nerve (CN X) and glossopharyngeal nerve respectively to the brainstem respiratory centers. They help to adjust respiratory rate in order to stabilise pH through O2 and CO2 concentration.