NPB 101L-The Human Cardiovascular System

How does blood flow?

from areas of high pressure to areas of low pressure

Q= (change in P)/ R

---generally blood pressure remains fairly constant so flow is determined by resistance

Compare arterial pressure to venous pressure.

the heart works to keep arterial pressure higher than venous pressure

Cardiac Output (CO)

amount of blood pumped by each ventricle per minute

CO= HR x SV

HR= measured in BPM

SV= measured in volumes per beat

Describe arterial pressure.

-is a function in the change of volume since the capacity stays relatively constant

--only about 1/3 of the blood in the arteries flows out during systole

--the increased volume causes the arteries to distend slightly, increasing pressure

Describe the flow of blood in the arteries.

-pulsatile

--constant flow because of the continued blood flow in the arteries during diastole

Mean Arterial Pressure (MAP)

average effective pressure that pushes blood through the systemic organs

MAP = CO x TPR

Total Peripheral Resistance (TPR)

overall resistance to flow in the entire systemic circulation

MAP approximation

MAP = 1/3 SBP + 2/3 DBP

---the average is weighted because the blood spends more time in diastole

Pulse Pressure (PP)

PP = SBP - DBP

What is typical normal human blood pressure?

120/ 80 mm Hg

Blood pressure cuff

sphygmomanometer

auscultation

taking a blood pressure by listening to artery sounds

--the pressure cuff is inflated at the upper arm to occlude the brachial artery

Korotkoff sounds

"tapping" sounds that a partially occluded artery makes due to turbulent blood flow

Systolic BP

BP where the first Korotkoff sounds are heard

--peak pressure generated by the artery

Diastolic BP

BP where the sounds are no longer heard

Vascular Resistance

measurement of how hard it is for blood to flow through the vessel

R= 8Ln/(pi)(r^4)

L=length; n= viscosity ; r=radius of the vessel

Poiseuille's Equation

combines resistance with blood flow

Q= (change in P)(pi)(r^4)/ 8Ln

--flow rate is mainly controlled by the radius of the vessels

Compliance

the ease at which a vessel can be stretched

C= (the change in V)/(the change in P)

--veins are more compliant than arteries

-small changes in venous pressure can greatly alter the amount of blood in venous system

capacitance

holding volume

--vessels with high compliance also have high capacitance

--thus venous systems act as storage reservoirs?

What happens when you increase inflow and outflow?

the vessel volume will increase

What variables increase volume in arteries?

increases in SV, CO, HR, or increase in arterial resistance

What variables increase volume in veins?

-decrease in right hear pumping

-changing in body position from lying down to standing up

How do you decrease volume in the veins?

decreasing inflow or increasing outflow

Hydrostatic pressure

-produced by gravity

---a differences are made between 2 points of different hearts

Supine postion

laying down

-now the whole body is at heart level

--no added hydrostatic pressure

Describe the effects of laying down for an extended period and standing up quickly?

BP will initially decrease but slowly return to normal

--blood pools in the lower extremities due to hydrostatic pressure

---MAP decreases because there is less blood in the arterial system thus less venous return

Discuss how your body seeks to regulate the drop in blood pressure when you stand from the supine position.

baroreceptors sense the decrease in BP and signal to the brain to increase sympathtic activity and decrease parasympathetic activity

reactive hyperemia

transient increase in organ blood flow that occurs following a bried period of ischemia

--after the blood pressure cuff was removed, there was an increase in blood flow to the occluded area

----local metabolites in the area build up and cause vasodilation

ex: foot falls asleep then blood rushes back and it feels warm

Compare venous pressure to arterial pressure.

venous pressure is a lot smaller than arterial pressure

How does the venous system control the direction of blood flow?

valves in the venous system keep it from flowing the wrong direction

Explain the structure of the venous system and how that effects BP.

veins are highly distensible and able to hold large volumes of blood with out large increases in pressure

In response to exercise, what perimeters altered and how?

MAP, HR, PP, SV, and CO all increased and TPR decreased

Why did the response to exercise occur?

sympathetic activity increases with anticipation of exercise

-active hyperemia causes vasodilation to active skeletal muscles causing a decrease in TPR and an increase in blood flow

-the skeletal muscle pump is used increase venous return to sustain CO

dive reflex

allows prolonged submersion by limiting the rate of oxygen use and directing blood flow to essential organs

What is the mechanism of action for the dive reflex?

bradycardia (reduced HR) caused by increased vagal activity and vasoconstriction at nonessential organs due to increased SNS activity

electrocardiogram

atrial and ventricular deoplarization nd repolarization are recorded

P wave

first small wave of the ECG

--depolarization of the atria

QRS wave

spike of the ECG

-depolarization of the ventricles

T wave

larger ending wave of the ECG

-repolarization of the ventricles

Describe the relationship between the respiratory rate (RR) and the HR.

HR is inversely proportional to the RR interval

What causes the dizzy feeling following a rapid movement from laying don to standing?

the decrease in CO, VR, CO,and arterial blood pressure causing inadequate cerebral blood flow

Describe the baroreceptors.

they detect stretch in the carotid sinus and aortic arch

-they send afferent to the brain a.k.a. the CV center in the medulla

-changes in baroreceptor firing rate changes BP

---- increase BP= increased firing

-the response is mediated through sympathetic and parasympathetic input

Explain the sympathetic innervating in the cardiovascular system.

Sympathetic nerves release epinephrine

->binds to the A 1-adrenergic receptors on the smooth muscle cells in the vessel walls

-->vasoconstriction

---in arteries => decrease in diameter leads to an increase in resistance thus a decrease in blood flow venous side

---in veins => decrease in diameter leads to a decrease in capacitance, increasing the pressure causing an increase blood flow and venous return

in the heart norepinephrine is release by the SNS and binds to beta-adrenergic receptors causing an increase in HR and contractility (SV and CO)

Describe parasympathetic innervation in the cardiovascular system.

parasympathetic nerves only innervate certain vascular beds and locations

-release ACh to bind to mACh causing vasodilation via the nitric oxide pathway

--parasympathetic efferents in the heart release ACh to bind mACh leading to a decrease in HR and contractility

What is the ANS response to an increase in BP?

there is an increase firing rate of the baroreceptors, decreased sympathetic, and increased parasympathetic

--PNS: decrease in HR -> decrease in CO -> decrease in BP

--certain vessels

----increased vasodilation -> decreased resistance -> decreased BP

What is the ANS response to a decrease in BP?

decreased firing rate of the baroreceptors, decreased parasympathetic and increased sympathetic

--the increased SNS input leads to an increase in HR -> increased CO -> increased BP

---increased contraction -> increase SV

---arterioles: increased vasoconstriction -> increased resistance -> increased BP

---veins: increased vasoconstriction -> increased VR -> increased SV -> increased CO -> increased BP

What does the venous system experiment where the subject held their arm above their head demonstrate?

-demonstrates the response to gravity due to pooling/congestion

-pressure in the venous system is less than the arterial pressure

-oneway valves prevent back flow

-veins are highly distensible and are able to hold large volumes of blood without a large increase in pressure

active hyperemia

increased blood flow caused by an increase in metabolic activity, such as exercise

-mechanism: release of metabolites causes vasodilation and an increase in blood flow