The Cardiovascular System Lectures 14

Question 1

What does the mammalian cardiovascular system consist of?

Answer 1

Consists of the heart and circulatory system

Question 2

What is the role of the cardiovascular system?

Answer 2

To supply every cell in the body with oxygen and nutrients

Question 3

Where does deoxygenated blood enter the right atrium from?

Answer 3

From the inferior and superior vena cavae

Question 4

Where does deoxygenated blood pass through?

Answer 4

Passes through the right AV valve and enters the right ventricle

Question 5

Where is deoxygenated blood pumped into?

Answer 5

The pulmonary arteries through the pulmonary valve

Question 6

Where is oxygenated blood returned from?

Answer 6

From the lungs to the left atrium

Question 7

Where is oxygenated blood entered through?

Answer 7

Enters the left ventricle through the left AV valve

Question 8

How is oxygenated blood pumped through?

Answer 8

Pumped by the left ventricle through the aortic valve into the systemic circulation

Question 9

What does the CVS consist of?

Answer 9

Heart and blood vessels; arteries, arterioles, capillaries, venules and veins

Question 10

What are the functions of the CVS?

Answer 10

-collect and transport O2 (from lungs) and nutrients (from gastrointestinal tract) to all cells of the body
-collect and transport CO2 (cells main metabolic by product) and other waste products

Question 11

Excitation- contraction in the cardiac muscle;
What is cardiac action potential stimulated by?

Answer 11

-autorhythmic cells
*have an unstable resting membrane potential
*continuous depolarisation = produces pacemaker potentials that initiate APs

Question 12

Excitation- contraction in the cardiac muscle;
Difference between cardiac muscle + skeletal muscle?

Answer 12

Cardiac muscle=
-heart either contracts as a unit or doesn’t contract at all
-acts as a functional synctium; since electrical activity can spread from one cell to the next
-absolute refractory period= 250ms; nearly as long as the contraction

Skeletal muscle=
-each muscle fibre is attached to a motor nerve and will only contract when that motor nerve is stimulated
-absolute refractory period= 1-2ms

Question 13

What is the difference between non-contractile cells and contractile cells?

Answer 13

-non-contractile cells= auto rhythmic cells; comprise 1% of cardiac muscle fibres
-contractile cells= cardiac muscle cells; comprise 99% of cardiac muscle fibres

Question 14

What are the electrical events in cardiac contractile muscle cells?

Answer 14

Changes in membrane potential and permeability of contractile cardiac muscle cells
Phases of the Cardiac muscle AP;
• Depolarization
• Voltage-gated Na+ channels cause rapid depolarisation (Na+ channels inactivation ends this phase)
• Plateau phase of AP
• Slow Ca2+ channels (slow channels) open
• Repolarisation
• Slow Ca2+ channels inactivate and K+ channels open

Question 15

What happens during calcium induced calcium release?

Answer 15

-L-type Ca2+ channels in cell membrane= open in response to depolarisation caused by the opening of fast Na+ channels
-10-20% of Ca2+ enters here
-local influxes of Ca2+ triggers ryanodine receptors= causing opening of Ca2+ sensitive channels in the SR (called calcium induced calcium release; CICR)

Question 16

What does the SA node generate?

Answer 16

-Generates action potentials that spread through the atria
-The atria then contracts

Question 17

Where do the signals that are received from the pacemaker reach?

Answer 17

-reaches the AV node= which is then activated and fires

Question 18

What are the action potentials transmitted through?

Answer 18

Transmitted through a set of modified muscle fibres

Question 19

Where does the depolarisation spread from?

Answer 19

Spreads from the modified muscle fibres through the entire ventricle. The ventricles contract

Question 20

What is the difference between sympathetic stimulation and parasympathetic stimulation?

Answer 20

Sympathetic= speeds up the heart rate
Parasympathetic= slows down the heart rate

Question 21

What does the ECG consist of?

Answer 21

The ECG consists of the P wave (atrial depolarization),
QRS ventricular depolarization) and T wave (ventricular
repolarisation

SA node; activated and the atria contracts (P)
AV node; activated and the ventricles contract (QRS)
Ventricles repolarize and relax (T)

Question 22

Heart sounds:

Answer 22

2 major heart sounds:

“Lub”- AV valve closes , its louder and longer,ventricular pressure is larger than atrial pressure i.e. beginning of ventricular systole

“Dub”- SL valve closes, its short and sharp, beginning of ventricular relaxation (diastole)

Question 23

What are heart murmurs:

Answer 23

It’s result from turbulent blood flow due to valve malfunction

Question 24

Types of heart murmurs: stenotic valve

Answer 24

It’s stiff narrowed valves which don’t open completely, blood is forced through a high pressure producing a whistle sound

Question 25

Type of heart murmurs: insufficient/ incompetent valve

Answer 25

It’s valves that can’t close fully, backflow of blood causes turbulence and creates a swishing/gurgling sound

Question 26

Rhythmic changes in the cardiac cycle:

Answer 26

Rhythmic changes in electrical activity results in a cycle of contraction and relaxation which causes pressure changes which controls blood flow through the heart Blood flows down a pressure gradient through any available opening

Question 27

Systole vs diastole:

Answer 27

Systole- is the period of the cardiac cycle when the ventricles or atria is contracting Diastole- is the period of the cardiac cycle when the ventricles or atria are relaxing

Question 28

Cardiac output (CO):

Answer 28

Cardiac output is amount of blood pumped out by each ventricle in one minute Equation: CO= Heart rate(HR) x stroke volume (SV) SV is the volume pumped out by one ventricle with each beat (indicates the force of ventricular contraction)

Question 29

Resting vs maximum CO:

Answer 29

Resting CO = 5L/min Difference between resting and maximum CO is called cardiac reserve Non athletic people= 20-25 L/min Athletes= 35L/min

Question 30

What is stroke volume (SV)? Equation

Answer 30

SV is the volume of blood pumped out by one ventricle with each beat (indicates the force of ventricular contraction) SV represents the difference between end diastolic volume (EDV) and end systolic volume (ESV) SV= EDV-ESV

Question 31

What factors affect Stroke volume (SV)?

Answer 31

Preload Contractility Afterload

Question 32

Preload:

Answer 32

It’s the degree of stretch of the heart muscle - can produce dramatic increases in contractile force Intrinsic property of the cardiac muscle Most important is venous return is an increase in venous return e.g.exercise increases EDV

Question 33

Contractility:

Answer 33

Contractility is the contractile strength achieved at a given muscle length, independent of muscle stretch and EDV Increased sympathetic stimulation increases Contractility of heart E.g. mechanism by which no adrenaline influences heart Contractility

Question 34

After load:

Answer 34

After load is the back pressure exerted by arterial blood- must be overcome for the ventricles to eject blood In a healthy individual it is not a major determinant Becomes more important in those with hypertension

Question 35

How these factors affect SV?

Answer 35

Preload - increased EDV therefore increase in SV Contractility- decreased ESV therefore increase in SV Afterload- increased ESV therefore decrease in SV

Question 36

Regulation of heart rate:

Answer 36

Autonomic nervous system Sympathetic stimulation (NA & Adr) increased HR Parasympathetic decreased HR Chemical regulation Hormones: Adr, cortisol, thyroxine - all increased HR Ions: decreased [Ca2+]o and increased [K+]o - both decreased HR Other factors include age, gender, exercise and body temperature

Question 37

Coronary arteries:

Answer 37

Branch from aorta just beyond aortic valve Most arteriole flow occurs during diastole Blood flow normally adjusted to meet oxygen requirements

Question 38

Cardiovascular disease (CVD):

Answer 38

Most common cause of death in the UK; includes diseases of the heart and circulation including: coronary heart disease (angina and heart attack) stroke Occurs due to atherosclerosis: coronary arteries become narrowed by a gradual build-up of fatty material within their walls (atheroma). Angina – the pain resulting when coronary arteries cannot deliver enough oxygen containing blood to the heart muscle, particularly at times when there is more demand If atheroma becomes unstable, a piece may break off and lead to a blood clot forming.  Myocardial infarction (MI) - occurs if the blood clot blocks the coronary artery Stroke - may occur if the blood supply to part of the brain is cut off

Question 39

What is vasodilation?

Answer 39

Widening of blood. Occurs when smooth muscles (located in walls of arteries or large veins) relax which allows blood vessels to become more open. When blood vessels dilation the blood flow to the tissue is increased. Circulating Adrenalin acts on B2 receptors which causes vasodilation E.g. skeletal muscle; the adrenaline acts on B2 receptors causing vasodilation and increased blood flow

Question 40

What is vasoconstriction?

Answer 40

It is the narrowing of the blood vessels by contraction of circular smooth muscle in their walls. When blood vessels constrict, blood flow is slowed or blocked. Vasomotor fibres of sympathetic nervous system releases noradrenalin (NA) which acts on α1 receptors to cause vasoconstriction E.g. gastrointestinal tract; the noradrenaline acts on the a1 receptors to cause vasoconstriction

Question 41

What is haemodynamics?

Answer 41

It means the movement of blood. Blood flows down a pressure gradient (ΔP); this is the perfusion pressure. Perfusion is the passage of blood through the circulatory system Also depends upon resistance offered by the blood & blood vessels i.e., the peripheral resistance The relationship between blood flow, perfusion pressure (P) & total peripheral resistance (TPR) is described: BLOOD FLOW = ΔP / TPR

Question 42

Total peripheral resistance (TPR)

Answer 42

TPR is the sum of all frictional forces that oppose blood flow. Factors that affect TPR include: length of the system radius of blood vessel viscosity of the blood  a measurement of the thickness and stickiness of a person’s blood TPR (and thus blood flow) is most sensitive to changes in blood vessel radius (r). Blood flow is proportional to r4 – Poiseuille’s Law  so TPR is proportional to 1/r4

Question 43

Relationship between radius and flow

Answer 43

See slide 9 on lecture 16 CVS 3

Question 44

Blood pressure in various blood vessels of the systematic circulation

Answer 44

See slide 10 on lecture 16 CVS 3

Question 45

Maintaining blood pressure:

Answer 45

This is important to make sure adequate flow to all organs The blood pressure varies directly with; cardiac output(CO), peripheral resistance and blood volume Homeostatic mechanisms operate to ensure blood pressure is maintained

Question 46

Baroreceptors:

Answer 46

See slide 13- 17 on lecture 16 CVS 3

Question 47

What is normal blood pressure?

Answer 47

Healthy adult - systolic pressure usually < 140 mmHg & diastolic pressure < 90 mmHg Systolic: the pressure exerted by the blood on the blood vessel walls during contraction of the ventricle Diastolic: the pressure exerted by the blood on the blood vessel walls during relaxation of the ventricle Affected by age, gender, body size & disease Both pressures tend to be lower in young adults & children. Hypertension is persistently raised BP above 140/90mmHg on 3 consecutive occasions

Question 48

Mean arterial blood pressure (MAP)?

Answer 48

The mean pressure is time weighted average of arterial pressure over entire cardiac cycle MAP= Diastolic BP + 1/3 (systolic BP- diastolic BP)

Question 49

The relationship of Blood flow velocity and total cross sectional area in blood vessels:

Answer 49

The velocity of blood flow is lowest (i.e. slowest) in the capillaries due to the larger cross sectional area. This is necessary for exchange of materials Blood flow velocity is inversely proportional to the cross sectional area