Ohm’s Law of electrical circuitry indicates that 

the difference in the driving force difference between two points (V or voltage) = rate of flow of electrons (I or current) times the resistance (R); that is: V=IR 

   Ohm's Law of the entire CV System: 

 MAP = CO X TPR = (SV X HR) X TPR

(MAP = mean systemic arterial blood pressure; CO = cardiac output; SV = stroke volume; HR = heart rate;

 TPR=total peripheral vascular resistance.)

         THESE ARE THE THREE DETERMINANTS OF BLOOD PRESSURE!!!!!

FACTORS AFFECTING THE 3 DETERMINANTS OF MAP (i.e., what tools do blood pressure regulatory system have in order to control MAP?);

Affect heart rate

Affect stroke volume

 FACTORS AFFECTING HEART RATE

 Any factor which alters heart rate is called a chronotrope.  A positive chronotrope increase HR, while a negative chronotrope reduces HR. 

      The main factor controlling HR is the autonomic nervous system.  Parasympathetic (vagus nerve; post-ganglionic fiber; muscarininc receptors) stimulation of the SA node leads to a slowing of phase 4 depolarization and hence a slowing of the heart rate (negative chronotrope) , while sympathetic stimulation (cardiac nerves; post-ganglionic fiber; ß1) of the SA node exerts a positive chronotropic effect.

2. FACTORS AFFECTING STROKE VOLUME

   Preload:  The load the heart muscle faces immediately prior to contraction.  It is dependent upon the end diastolic volume (EDV).  Up to a certain point, an increase in EDV leads to increased strength of contraction.  Preload is largely determined by the heart rate (slow rate increases preload) and extracellular fluid volume (volume expansion increases preload). One of the most important concepts of myocardial function is the Frank-Starling Law of the heart, which states that the strength of cardiac contraction (and hence the stroke volume) increases in response to increased ventricular filling.

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Contractility:    

Any factor that affects ventricular contractility (the strength and effectiveness of cardiac contraction), is an inotrope.  A positive inotrope raises the Frank-Starling curve of a heart, which is equivalent to a higher SV for any given degree of ventricular filling.  Sympathetic stimulation (cardiac nerves; post-ganglionic fiber; ß1) of the ventricle is a positive inotrope. Parasympathetic (vagus nerve; post-ganglionic fiber; muscarininc receptors) stimulation of the ventricle leads to a reduction in contractility (primarily by reducing norepi release).

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Afterload: 

Recall Poiseuille's Law: 

IntrinsicControl: 

Extrinsic control

by the sympathetic division of the autonomic nervous system serves to contol TPR and thus alter MAP.

- α1 (vasoconstriction) and ß2 (vasodilation) adrenergic receptors for epinephrine/norepinephrine 

- the relative effect of sympathetic stimulation depends upon preponderance of subtype. Vascular smooth muscle in skeletal muscle has more ß2 and vascular smooth muscle in most viscera, such as the gastrointestinal tract, has relatively more α 1. Thus, if generalized sympathetic activation occurs, arterioles in skeletal muscle will tend to dilate and those in the gut will tend to constrict.  The net effect of extrinsic control, however, will always be an increase in TPR.

The hierarchy for most vital (strongest intrinsic mechanisms) is generally:

brain (vital) >heart (vital) >kidney (vital) >>>nonvital tissues (everything else, including viscera and skin).

1. It should be apparent that the only way to alter MAP is to change ______.

2. CNS Regulatory Center for control of the cardiovascular system located in the _______:

    Output from the Cardiovascular Regulatory Center affects:

 a. Peripheral vascular tone (TPR) - sympathetic

 b. Cardiac function: parasympathetic (vagus nerve) and sympathetic (cardiac nerves) control of HR and SV

Therefore, the autonomic nervous system is the effector for blood pressure control by the ______.  

Contractility (SV)

      β1 - stim by epi or norepi = + inotrope

      muscarinic - stim by Ach = - inotrope (a mild effect; main effect is to decrease norepinephrine release from sympathetic nerve endings)

Heart Rate (HR):

      β1 -  stim by epi or norepi = + chronotrope

      muscarinic - stim by Ach = - chronotrope

Total peripheral resistance (TPR):

      Β2 -    - stim by epi or norepi = vasodilation (arteriolar & venous)

      α1 - stim by epi or norepi = vasoconstriction (arteriolar & venous)

Where does input to the cardiovascular regulatory center arise from

C.    Input to the Cardiovascular Regulatory Center arises from higher centers in the CNS and a variety of reflex arcs from the peripheral nervous system (see Short Term Control) including exercise reflex (joint and muscle motion receptors) and central command (anticipation).

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MECHANISMS FOR CONTROL OF MAP  -

SHORT-TERM:

         LIMIT VARIABILITY IN BP (MINUTE TO MINUTE)

         DO NOT DETERMINE THE SET POINT ABOUT WHICH THIS VARIABILITY

            OCCURS

      LONG-TERM MECHANISMS FOR CONTROL OF MAP:

         DETERMINES THE SET POINT ABOUT WHICH BP VARIABILITY OCCURS

SHORT-TERM MECHANISMS FOR CONTROL OF MAP

MECHANISM 1. Baroreceptor Reflex:

receptor:

stimulus:

response:

purpose:

SHORT-TERM MECHANISMS FOR CONTROL OF MAP

MECHANISM 1. Baroreceptor Reflex:

      A. Receptor: stretch receptors in the walls of large arteries, especially in the    carotid sinus and the wall of the aortic arch. Afferents carotid sinus nerve (joins CN IX)  & aortic depressor nerve (joins CN X), respectively.  Afferent information transmitted to cardiovascular regulatory center.  Discharge slowly at normal MAP, discharge rate increases at higher MAP.  Most effective near physiologically normal MAP.

      B. Stimulus: change in MAP

      C. Response: reflex inhibition of the cardiovascular regulatory center to oppose the change in blood pressure.  For example, an increase in MAP is sensed by the baroreceptors which inhibit the vasoconstrictor center, leading to a reduction in sympathetic stimulation of arteriolar smooth muscle. What effect will this change in the autonomic nervous system have on MAP and its determinants?

                        D. Purpose: Oppose acute changes in blood pressure, thereby buffering the minute to minute variations in MAP

MECHANISM 2. (Hybrid System - Both Short and Long-Term Effects): The Renin-Angiotensin-Aldosterone System

receptor

stimulus

response purpose

A. Receptor: stretch receptors in the walls of afferent arterioles or receptors in the macula densa region of the distal tubule

      B. Stimulus: decrease in MAP

      C. Response: release of renin resulting in generation of angiotensin II      

      D. Purpose: Oppose changes in blood pressure, by directly altering TPR and by indirectly altering CO.    Angiotensin II has 3 important effects that allow it to achieve this purpose:

    i. directly produces vasoconstriction (short-term response)

             ii. stimulation of renal sodium reabsorption (long-term response) by aldosterone (secreted from the cortex of the adrenal gland                         

3.  There are 2 main types of capillaries: 

2. Capillaries form networks.  Distal arteriolar smooth muscle is often referred to as precapillary sphincter because ___.

The capillaries are 

Continuous: Limits macromolecular movement across wall to molecules <500 gm/mole.  Present in brain and skeletal muscle.  In brain, pericytes are astroglial cells, and the glial cells plus continuous capillary are often called the blood-brain-barrier. Question: Can Na⁺ and glucose get across? 

Fenestrated: 

Capillary Fluid Dynamics: 

LYMPH – 

REGULATION OF BLOOD VOLUME –