circuitry, hemodynamics and cardiovascular pressures

8/11/2019 Circuitry, Hemodynamics and Cardiovascular Pressures

1/40


2/40

Circuitry of Cardiovascular System

Cost. Fig 4-1


3/40

3 Basic Principle of Circulatory

Function

1. The rate of blood flow to each tissue is almost

always precisely controlled in relation to the

tissues need

2. CO is controlled mainly by the sum of all localtissue flows

3. Arterial pressure regulation is generally

independent of either local blood flow control

or CO control


4/40

Hemodynamics:Relationship of Pressure, Flow, and Resistance

Flow (Q): movement of blood; always from high pressure to lowpressure

Pressure (P): force exerted by the blood

Force: generated by the heart and varies throughout the system

Resistance (R): measure of the friction that impedes flow

Cost. Fig 4-2

Q=P/R


5/40


6/40

Velocity of FlowCost. Fig 4-3


7/40

Velocity of FlowCost. Fig 4-6


8/40

Other Characteristics

Conductance:measure of the blood flowthrough a vessel for a given P. Expressed asml/sec/mmHg

Fluid Viscosity:amount of pressure requiredto force whole blood through a vessel ascompared to water.

Vascular distensibility: amount a vessel canaccommodate an increase in pressure byincreasing volume within the vessel.


9/40

Functions and Pressures

of the Arterial System

Arteries

Arterioles

Capillaries

Cost. Fig 4-2


10/40

Arteries

Strong vascular walls

Function as low-resistance

conduits and as pressure

reservoirs

Maintain blood flow to

the tissues during

ventricular relaxation

Compliance= vol/ P


11/40


12/40

Arterial Blood Pressure

Systolic P (SP)= max arterial P at the peak of systole

Diastolic P (DP)= min arterial P during diastole

Arterial P=Systolic/Diastolic

Pulse P= SystolicDiastolic

Mean Arterial P (MAP)= DP + 1/3 (SP-DP)

Cost. Fig 4-9


13/40

Arterial Baroreceptors

Baroreceptor reflex is a

homeostatic adjustment

to MAP in the short term

(seconds to hours)

Primary atrial

barorecptors:

2 carotid sinuses

Aortic arch

Firing rate is proportional

to MAP and PP


14/40

Operation of the Arterial Baroreceptor Reflex

Cost. Fig 4-31


15/40

Operation of the Arterial Baroreceptor

Reflex

Cost. Fig 4-32


16/40

Other Baroreceptors

Large systemic veins, the pulmonary vessels,

and the walls of the heart also contain

baroreceptors.


17/40

Blood Volume and Long-Term Regulation of

Arterial Pressure

Baroreceptor reflexes are short-term regulators of arterial pressure but adapt

to a maintained change in pressure.

The most important long term regulator of arterial pressure is blood volume.


18/40

A t i lC Fi 4 2


19/40

Arterioles

Dominant site of resistance to flow in the vascular system

Major role in determining MAP

Major role in distributing flow to organs and tissues

Since MAP is identical throughout the body, arterioles use

vasodilation and vasoconstriction of smooth muscle walls to alter

resistance to flow.

Cost. Fig 4-2


20/40

Capillaries

Thin walled tube of endothelial

cells one layer thick No smooth muscle, no elastic

tissue

Cells are separated by

intercellular cleft


21/40

Velocity of Capillary Blood Flow

Determined by R of arterioles and number of

open capillary sphincters


22/40


23/40

Veins

Low resistance

conduits for venous

return

Very compliant and

contain most of the

blood in the vascular

system


24/40

Determinants of Venous Pressure

SNS causes venoconstrictionto maintain pressure and

venous return

Skeletal muscle pump and

respiratory pump increase

venous pressure locally and

enhance venous return.

Venous valves allow pressure

to produce flow toward the

heart.

V PCost Table 4 1


25/40

Venous Pressures:

Right Atrial (Central Venous)

Regulated by a balance

between blood pumped

out and blood flowing in

Heart weakness elevates

RAP

Strong contractions

decreases RAP

Rapid venous return

increases RAP

Cost. Table 4-1

Cost Table 4-1


26/40

Venous Pressures:

Right Atrial (Central Venous)

Venous return can beincreased by:

Increased blood volume

Increased peripheral venouspressures

Dilation of arterioles

Normal value is 0 mmHg(equal to atmosphericpressure around body)

High RAPbacks up into

large veins

Cost. Table 4-1


27/40

Venous Pressures:

Intra-abdominal pressures

Normal value is 6 mmHg

One key determinant of peripheral venous

pressures (legs)


28/40


29/40

Venous valves

One way flow of blood toward the heart.

With any tension of skeletal muscle within the

legs, veins are compressed which squeezes

blood toward the heart.

Helps to regulate gravitational pressures.

With prolonged standing, blood will accumulate in

the legs and feet and increase the venous

pressure of the capillariesedema

Varicose veins


30/40

Microcirculation

Capillaries are the sites where nutrients and waste products are

exchanged between blood an tissues

Flow is less than anywhere else in body, intermittent due to

vasoconstriction, determined by NEEDS OF THE TISSUE


31/40


32/40

Net Filtration Pressure

(PC) (Pi)

(C) (i)

(PC) + (C) + (Pi) + (i) = net filtration P

if positive, fluid moves out of C

if negative, fluid moves into C

If positive

If negative

Cost. Fig. 4-34


33/40





Cost. Fig. 4 34

Cost. Fig. 4-34


34/40





Cost. Fig. 4 34


35/40


36/40

Increase Lymph Flow

(PC) (Pi)

(C) (i)

Changes in pressures

Increased permeability of the capillary

If positive

If negative


37/40

Acute Control of Tissue Blood Flow Tissue metabolism, Vasodilators (NO) and Vasoconstrictors (endothelin)

Local factors that change with metabolic activity cause arteriolar vasodilationand increased blood flow (active hyperemia)

Flow autoregulation (change in R to maintain Flow when P is changing) occurs

due to local factors and myogenic responses to stretch.

Cost. Table 4-7


38/40

Other Controls of Tissue Blood Flow

Long term controls: Vascularity (angiogenesis)

Humoral Control: Vasoconstrictors and

vasodilators

Ionic control


39/40


40/40

Integrative Cardiovascular Function:

Regulation of Systemic Arterial Pressure

circuitry, hemodynamics and cardiovascular pressures

Documents