Module 3 Flashcards Preview

BMA - SEMESTER 2 > Module 3 > Flashcards

Flashcards in Module 3 Deck (44):

what is the overall purpose of the circulatory system

to provide adequate blood flow to all tissues/organs according to their immediate needs


define blood flow

the volume of blood flowing through a vessel, organ or the entire circulation


what 2 factors determine blood flow

1. blood pressure
2. resistance


define blood pressure

the force exerted on a vessel wall by the blood in that vessel


define resistance

a measure of the amount of friction blood encounters as it flows through a vessel
(opposition to blood flow)


what are the 3 sources that affects total peripheral resistance (TPR)

- blood viscosity
- total blood vessel length
- blood vessel diameter


TPR: Viscosity

the thickness of fluid
- increase in RBC increases viscosity
- dehydration increases viscosity `


TPR: Vessel Length

resistance to flow increases as vessel length increases
(e.g. easier to drink a milkshake through shorter straw)


TPR: Vessel Diameter

the amount of contact between 2 surfaces determines friction

more contact blood has with the walls = more friction = more resistance to blood flow


what does increased vessel diameter result in

decreased contact between blood and vessel walls = decreased friction = decreased resistance to blood flow


what occurs as a result of vasoconstriction

decrease in daimeter = increases resistance = decreases blood flow


what occurs as a result of vasodilation

increases diameter = decreases resistance = increases blood flow


equation for blood flow

F= P/R


systemic blood pressure - when does the steepest drop in pressure occur and why

- arterioles
- resistance to blood flow = greatest


What are the 2 factors that reflects arterial pressure

1. how much elastic fibres can be stretched

2. The volume of blood forced into the elastic arteries by ventricular contraction


define systolic pressure

peak pressure generated in the large arteries when the ventricles contract


define diastolic pressure

pressure in the large arteries during ventricular relaxation


formula for pulse pressure

pp= systolic pressure - diastolic pressure


define mean arterial pressure (MAP)

the pressure that propels blood through the vessels


formula for MAP

MAP= diastolic pressure +(1/3 pulse pressure)

Map = COxR


why does an increase in CO result in higher BP

because an increase in CO pushes more blood into the arteries = increased MAP


what is the cause of chronic hypertension

sustained systolic pressure > 140mmHg


Why is thin capillary blood pressure required

1. High pressure would damage thin walled, fragile capillaries

2. Most capillaries are very permeable so low pressure is adequate to fluid exchange with tissues


Describe venous Blood Pressure

- constant at 15mmHg
- small pressure gradient
- too low to provide adequate census return to the heart


Characteristics of Venous Return (5)

1. Valves - prevent blood back flow; shifts blood in small volumes

2. Muscular Pump - contracts squeezed veins and pushes blood to heart

3. Respiratory Pump - pressure changes during breathing to help blood move toward the heart by squeezing abdominal veins as thoracic veins expand

4. Pulsation - in nearby arteries

5. Venoconstriction - pf tunica media under sympathetic control


what are the 3 factors that influence pressure, and therefore blood flow

1. Cardiac Output (rapid, short term)

2. Peripheral resistance (TPR) (rapid, short term)

3. Blood Volume (slower, long term regulation)


define cardiac output

CO = stroke volume x heart rate


how does cardiac output influence BP

increased Sv or HR = increased CO = increased BP

decreased SV or HR = decrease CO = decreased BP


how does Peripheral Resistance (TPR) influence BP

- vasoconstriction = increased resistance = increased BP but decreased BF

- vasodilation = decreased resistance = decreased Bp and increased BF


how is blood flow maintained

more pressure is applied which is generated by the heart


how does blood volume influence BP

- controlled by renal and endocrine mechanisms

- increased BV = more blood pushing on vessel walls = increased BP

vice versa


List the 4 different ways blood pressure is regulated

1. Autoreguation - occurs within tissues

2. Neural Regulation - involves the cardiovascular centres and the ANS

3. Renal Mechanisms

4. Endocrine Regulation


describe regulation in context to regulating blood pressure

tissues can regulate their own blood flow + pressure in response to local conditions by:

1. altering arteriole diameter
2. opening/Closing of pre capillary sphincters


describe how neural regulation regulates blood pressure

cardiovascular centres in the medulla oblongata contain 3 centres:

1. Cardioinhibitory centre

2. Cardioacceleratory centre

3. Vasomotor centre


Neural Regulation - Cardioinhibitory Centre

- provides parasympathetic input into the SA and AV nodes
- slows heart rate


Neural Regulation - Cardioacceleratory Centre

- provides sympathetic input to the SA and AV nodes and ventricular myocardium
- increases heart rate
- increases force of contraction and thus SV


Neural Regulation - Vasomotor Centre

Sympathetic vasomotor fires to the smooth muscle of the arterioles = change in vasomotor tone = change in vessel diameter

- increased sympathetic activity = increase in vasomotor tone = vasoconstriction

vice versa


Renal mechanisms and their influence on the regulation of blood pressure

1. Direct Mechanism
2. Indirect mechanism


Renal Mechanism - Direct Mechanism

- the rate of urine formation is determined by BP

increased BP = increased bf to kidneys = increased filtration = increased urine = decreased BV and BP

vice versa


Renal Mechanism - Indirect Mechanism

- involves hormones
(Renin Angioensins - Aldosterone SYstem = (RAAS)

- stimulates vasoconstriction = increased R = increased BP

- stimulates aldosterone = maintains/increases BV and thus BP

- stimulates DH = maintains/increases BV and BP


Endocrine regulation of blood pressure

hormones that increase BP
- adrenalin and noradrenalin
- angiotensin II

hormones that decrease BP



location of baroreceptors

- carotid sinuses
- aortic arch
- walls of most large arteries in the neck and thorax


role of carotid sinus reflex

monitors and protects blood flow to the brain


role of aortic arch baroreceptor reflex

monitors and maintains blood flow into the systemic circuit