Physiology of Blood Pressure and Hypertension

TEST: The velocity of blood moving through systemic circulation is (directly/inversely) related to the total flow of blood and (directly/inversely) related to the total cross-sectional area of the vessel

DIRECTLY related to total flow INVERSELY related to total cross-sectional area

What is one really powerful CONSTRICTOR endothelial peptide? What kind of situations would cause the release of this? What is the general term describing these abnormal situations?

Endothelin Situations that cause the release of this include: - Hypertension damage to vascular endothelin (this may also REDUCE NO release) - Atherosclerosis - Anoxia - Inflammation Together, this is called ENDOTHELIAL DYSFUNCTION

RECALL: What is the primary catecholamine released in response to sympathetic nervous system activity?

Epinephrine

RECAP: Which of the following has TONIC activity on the heart under normal conditions? A) Nucleus tractus solitarius B) Nucleus ambiguus C) Rostral ventrolateral medulla D) Raphe nucleus E) A and B F) B and C G) All of the above

F) B and C! The NTS receives AFFERENT fibers, and the raphe nucleus has little or no tonic activity.

TRUE or FALSE: Only a limited number of factors that affect CO and TPR can cause HTN

FALSE! ANY factors that affect CO and TPR can cause HTN

TRUE or FALSE: Arteriolar dilation increases the pressure of the arteries upstream from them

FALSE! Dilation of arterioles lowers the arterial pressure!

TRUE or FALSE: Blood velocity progressively decreases as blood goes from capillaries to the vena cava

FALSE! It progressively increases because the total cross sectional area of the vessels DECREASES (while the FLOW increases as the vessel gets larger)

RECALL: What is the importance of the role of ADH?

It is an important factor in the compensatory responses to hypotension due to severe blood loss, dehydration, and other causes of low blood volume

TEST: In a PARALLEL arrangement of blood vessels, the total resistance is (greater/lesser) than any of the individual resistances. Why?

LESSER! When blood vessels are arranged parallel to each other, this means the blood has more than one possible pathway for flow through the network! This implies that the total resistance will be less than the individual resistances going down each pathway, as it is divided up among all of the parallel vessels

What does the term "Laminar Flow" refer to? In a tube, where do you expect the laminar flow to be?

Laminar flow refers to the flow through a tube where the FASTEST moving layer, called the LAMINA, is in the CENTER of the tube, and by moving toward the walls of the tube each PARALLEL LAYER is moving SLOWER

TEST: A relatively large compliance indicates the vessel is relatively (hard/easy) to distend by (increasing/decreasing) internal pressure

Large compliance = relatively EASY to distend by INCREASING internal pressure

TEST: What is the equation for MAP using CO and TPR?

MAP = Cardiac Output (CO) x TPR

TEST: What is one way of estimating MAP with diastolic and systolic pressures?

MAP = Diastolic pressure + 1/3 (pulse pressure) Pulse pressure = systolic pr - diastolic pr

TEST: From the arterial baroreceptors, where in the brain do they send signals to? List the nerves that carry these signals for the: - Carotid sinus baroreceptors - Aortic arch baroreceptors

MEDULLA! Carotid sinus baroreceptors send their signals via the HERING'S NERVES and CN IX Aortic arch baroreceptors send their signals via CN X

TEST: What specific nucleus in the medulla picks up AFFERENT signals from the baroreceptors?

Nucleus tractus solitarius (NTS)

TEST: (Sympathetic or parasympathetic) noradrenergic nerves are the only ones involved in in control of venous tone

SYMPATHETIC! This goes along with the theme that parasympathetics have little effect on blood vessels

What is the total resistance equal to in a system where the blood vessels are arranged in SERIES?

Simply the sum of the individual resistances (R(t) = R1 + R2 + R3 + etc...)

A stretch of the baroreceptors will cause an increase in the number of _______ _______ fired

Stretch in baroreceptors --> increase in number of ACTION POTENTIALS fired

TEST: What is the major NEURAL influence on total peripheral resistance? Why?

Sympathetic noradrenergic neurons! These play the biggest role on TPR because recall that the largest % of TPR is in the ARTERIOLES, which is under sympathetic control!

TRUE or FALSE: Laminar flow does not produce a sound

TRUE!

TRUE or FALSE: SMALL changes in arterial pressure causes LARGE changes in urinary output rate. Is this beneficial?

TRUE! This is beneficial in LONG TERM arterial pressure regulation!

TRUE or FALSE: Mean arterial pressure at REST is usually lower than the average of the values of systolic and diastolic pressures

TRUE! At rest, the period of ventricular diastole is much longer than systole, and because mean arterial pressure takes durations into account, at REST the MAP should be lower due to the long duration of diastole compared to diastole during vigorous activity (for example).

TRUE or FALSE: Primary HTN is much more prevalent than secondary HTN

TRUE! Primary, or essential HTN, accounts for at least 90% of all hypertensive patients

TRUE or FALSE: An increase in intracranial pressure will trigger sympathetic output from the medulla

TRUE! The increased intracranial pressure restricts cerebral blood flow by compression of the cerebral vessels, so you would want to increase the blood flow to the brain to compensate!

TRUE or FALSE: Compliance essentially contributes to how well a blood vessel adapts to a change in internal pressure

TRUE! The more compliant the vessel wall is, the more it is able to enlarge or shrink based on changes in volume

List at least 4 other reflexes/responses that influences arterial pressure.

1) Cardiopulmonary reflex (involved more with blood VOLUME change) 2) Chemoreceptor reflex 3) Cerebral ischemic response 4) Emotional CV response (increase in stress has an impact on BP)

TEST: What two major receptors sense changes in arterial pressure?

1) Carotid sinus 2) Aortic arch baroreceptors

TEST: What are 4 major vasoactive hormones that play a huge role on arteriolar tone and vascular resistance?

1) Epinephrine 2) Norepinephrine 3) Arginine Vasopressin (ADH) 4) Angiotensin II

What are three endothelial derived VASODILATOR factors?

1) Nitric oxide (Endothelium-derived relaxing factor, EDRF) 2) Endothelium-derived hyperpolarizing factor, EDHF) 3) Prostacyclin (PGI2)

Vascular tone is the result of contributions of what two primary factors?

1) Spontaneous, nerve/humoral stimuli-INDEPENDENT (makes the BASAL tone) 2) Neural and humoral stimuli (dependent on hormones and NTs, such as NorE)

TEST/TEST/TEST: List the effect of a DECREASE in blood pressure on the following: 1) Sympathetic activity 2) Parasympathetic activity 3) HR 4) CO 5) Venous tone 6) Capillary pressure 7) Peripheral venous pressure 8) Total peripheral resistance

1) Sympathetic activity INCREASES 2) PS activity DECREASES 3) HR INCREASES 4) Cardiac output INCREASES 5) Venous tone INCREASES 6) Capillary pressure DECREASES! 7) Peripheral venous pressure INCREASES 8) Total peripheral resistance INCREASES!

What are the two major determinants of mean arterial pressure?

1) Total peripheral resistance (TPR) 2) Cardiac output

RECALL: What is the effect of norepinephrine on blood vessels?

Activates alpha-1 receptor, causes arteriolar constriction and an increase in TPR

What is the total resistance equal to in a system where the blood vessels are arranged in PARALLEL?

1/R(t) = 1/R1 + 1/R2 + 1/R3 + etc...

In GENERAL, would you expect a higher change in arterial pulse pressure with an increase in volume in a 20 year old or a 70 year old? Explain.

A higher change in arterial pulse pressure should be seen in the 70 year old, because as you get older your arteries become LESS COMPLIANT (due to buildup and wear and tear). A less compliant vessel would mean an increase in blood volume will increase the arterial pressure MORE than if the vessel was more compliant.

Give a general example of blood vessels in parallel

All arterioles or capillaries in a particular organ

TEST: (Arterioles/capillaries) have the greatest total resistance. Why?

ARTERIOLES! You would think capillaries because they are the smallest, but the sheer number of them arranged in PARALLEL actually decreases their total resistance! Arterioles on the other hand, though larger than capillaries, are still relatively small compared to arteries, and there aren't nearly as many of them as there are capillaries. This small size and lower number contributes to increased FRICTION and RESISTANCE TO FLOW, which increases the total resistance and correlates with the largest drop in pressure!

TEST: Total peripheral resistance, also known as ______ _______ resistance, is defined as what? Where is the greatest percentage of TPR located?

Also known as SYSTEMIC VASCULAR RESISTANCE Definition: TOTAL resistance of ALL systemic vessels Greatest TPR % in ARTERIOLES, as that is where the total resistance is the highest

When blood vessels in the body are arranged in (parallel/series), the blood travels the same pathway in sequence.

Arranged in SERIES

AGAIN: What is a major determinant of systemic arterial blood pressure that isn't CO or HR or SV or TPR? (think big picture and simple)

Arterial blood VOLUME!! As well as total blood volume in the entire CV system

Give a general example of blood vessels in series

Artery --> arteriole --> capillary --> venule --> vein

TEST: What is the definition of mean arterial pressure (MAP)?

Average arterial pressure during a SINGLE cardiac cycle, not only averaging the values of peak systolic and minimum diastolic pressures, but also the DURATIONS of systole and diastole

TEST: The baroreceptor reflex is considered a (long/short) term mechanism, while fluid balance is considered a (long/short) term mechanism

Baroreceptor reflex: SHORT term Fluid balance: LONG term

Why do capillaries have a much higher total cross-sectional area than arteries, if they are overall smaller than arteries?

Because the wall thickness of capillaries is significantly thinner (1 micrometer) than arteries (2 mm), which means the radius is much larger and thus the A is much greater. Functionally, this makes sense because the thin walls provide a much more efficient means of solute and gas exchange!

TEST/AGAIN: Why do veins have a relatively higher compliance than arteries?

By being more compliant, it can hold a LARGER VOLUME of blood at relatively LOW PRESSURES, so it can act as a reservoir of blood that can be mobilized to the arterial side if need be!

TEST: Which vessel has the GREATER total cross sectional area, arteries or capillaries? What does this mean about the velocity of blood through the greater cross sectional area vessel?

CAPILLARIES! This means the velocity of the blood should be SLOWEST at the capillaries, because velocity is inversely related to the total cross sectional area!

One way to express the elastic properties of blood vessel walls is by calculating _________, which is equal to what?

COMPLIANCE Complicant = (Change in volume) / (change in internal pressure )

TEST: Changes in diameter of venous vessels primarily affects the ______ of blood in the veins

Changes in diameter of venous vessels primarily affects the VOLUME of blood!

What is the baroreceptor reflex in very general terms?

Changes in mean arterial blood pressure occurs, which acts as the stimulus and triggers the BARORECEPTOR reflex in attempt to normalize that pressure.

Nitric oxide contributes to a _______ vascular tone. What are two things that can cause nitric oxide to be released by the endothelium?

Contributes to a VASODILATOR vascular tone Two things can cause release of NO from the endothelium: 1) Increased rate of blood flow 2) Shear stress on endothelium

TEST: What is arterial pulse pressure directly proportional to?

DIRECTLY proportional to: Left ventricular stroke volume INVERSELY proportional to: Arterial compliance

REVIEW: Briefly describe the renin-angiotensin-aldosterone system, starting with a DROP in arterial pressure

Drop in arterial pressure triggers the baroreceptor reflex --> INCREASED renal SYMPATHETIC activity + DECREASED glomerular capillary pressure --> DECREASED GFR --> INCREASED RENIN RELEASE --> INCREASED angiotensin II --> INCREASED aldosterone --> INCREASED sodium retention --> INCREASES fluid retention!! Whew!

TEST/TRUE or FALSE: The most common neural mechanism of VASODILATION in blood vessels is from the parasympathetic nerves, just as how vasoconstriction is from the sympathetic nerves

FALSE! Parasympathetic innervation of blood vessels is NOT extensive and does NOT play a substantial role in regulating arterial blood pressure. What causes vasodilation is actually a REDUCED SYMPATHETIC activity from the noradrenergic neurons! - In some animals, there appears to be a sympathetic vasodilator NT, which is ACh. However, in humans this isn't well established

TRUE or FALSE: As a whole, arteries typically have a much higher compliance than veins

FALSE! Remember, artery walls are more rigid than veins, so they can keep the internal arterial pressure high and drive blood systemically!

TEST/TRUE or FALSE: The baroreceptor reflex is most sensitive to slow changes and is a very important player in the long-term management of blood pressure

FALSE! The baroreceptor reflex is most responsive to RAPID changes and is meant as a SHORT-TERM management for changes in blood pressure. After a few days, these receptors RESET and now have a new baseline BP (this is why the baroreceptor reflex DOES NOT play a role in CHRONIC HTN management)

TRUE or FALSE: You can't really hear turbulent flow with a stethoscope

FALSE! Turbulent flow creates vibrations that you can pick up with your stethoscope!

TRUE or FALSE: Vascular smooth muscle either contracts all the way or it doesn't contract at all, like in skeletal and cardiac muscle

FALSE! VSM is able to maintain partial contractions for long periods of time, and with LOW ENERGY COST!

TRUE or FALSE: It is impossible to cure secondary hypertension. What is the caveat to this?

FALSE, especially when a specific cause is evident Example: Surgically correcting renal artery stenosis CAVEAT: If the HTN has existed for a prolonged period, PERMANENT structural changes in the vasculature may result

What is the difference between the FLOW of blood and the VELOCITY of blood?

Flow = VOLUME/time Velocity = DISTANCE/time

RECALL: What is the effect of: - HIGH dose epi - LOW dose epi on blood vessels?

HIGH dose epi: Activate alpha-1 receptors, causing CONSTRICTION of SMOOTH muscle and keeping an increase in BP as you're running away from the bear Low dose epi: Activate beta-2 receptors, causing DILATION of SKELETAL muscle so you can increase blood flow to those muscles that help you run away!

TEST: Arteriolar constriction will cause an (increase/decrease) in ARTERIAL pressure and an (increase/decrease) in CAPILLARY pressure. Overall, arteriolar constriction will (increase/decrease) the blood flow to that organ

INCREASE in arterial pressure DECREASE in capillary pressure Overall, arteriolar constriction --> DECREASE blood flow to that organ

TEST: An increase in arterial blood pressure causes an (increase/decrease) in urinary output rate, but with time and a _______ fluid intake will cause an (increase/decrease) in blood volume and cardiac output

INCREASE! You have higher blood pressure, you pee more! However, over time with a CONSTANT fluid intake, you will ultimately DECREASE the blood volume and cardiac output because you aren't increasing your fluid intake to adequately replace all the volume you lose in your pee! This loss in blood volume will DECREASE the arterial pressure back to the original level!!!!!!

TEST: Increased sympathetic activity causes systemic venous (relaxation/constriction) via _______ receptors, which reduces the _______ of blood in the veins and also forces movement of blood toward the right ________. This in effect leads to increased _______ ______ and ______ _______, which makes sense as a _________ response to (low/high) arterial blood pressure.

Increased sympathetic activity --> systemic venous CONSTRICTION via ALPHA-1 receptors, which reduces the VOLUME of blood in the veins. This also forces the movement of blood toward the right ATRIUM. This in effect --> increased STROKE VOLUME and CARDIAC OUTPUT, which makes sense as a COMPENSATORY response to LOW arterial blood pressure!!

TEST: Most vessels in the systemic circulation are arranged in (series/parallel). What is the advantage of this?

PARALLEL The advantage of systemic vessels organized in parallel is that the total resistance of blood flow is much LOWER than it would be if the vessels were all in series. This REDUCES the amount of WORK the heart must do in order to pump blood through the systemic vessels!

TEST: List the EFFERENT fiber origins of the baroreceptor reflex for: - Parasympathetics - Sympathetics (which has an excitatory and inhibitor component, list both nuclei)

Parasympathetic: Nucleus Ambiguus (Vagal center) Sympathetic: - Excitatory: Rostral ventrolateral medulla (RVLM) - Inhibitory: Raphe nucleus

TEST: What is the main difference between primary and secondary hypertension?

Primary: Specific causes CANNOT be identified Secondary: Specific cause CAN be identified

RECALL: What is the equation for blood flow (Q)? Flow is MOST directly proportional to which variable, and why?

Q = Change in pressure / Resistance (R) Resistance = (8 x Length x Viscosity) / (pi x radius^4) Flow is MOST directly proportional to the RADIUS of the vessel, as that variable is raised to the fourth power and would have the most impact on the flow if it changed.

In a patient with HTN, the arterial baroreceptor reflex _______ to a (higher/lower) level, which then causes it to regulate arterial around this new pressure

RESET to a HIGHER level

In turbulent flow, the _______ to flow is greatly increased. Give two examples of where this might occur.

RESISTANCE to flow is greatly increased Examples: 1) High velocity blood flow but blood viscosity is low 2) At branch points or abnormal narrowing of a vessel (stenosis for example)

TEST: Many, if not all, chronically hypertensive patients requires a (lower/higher) mean arterial pressure in order to increase urinary output rate.

Requires a HIGHER MAP to increase urinary output rate

Why do we see a drop in blood pressure as we move from arteries to veins? Where does the largest drop in blood pressure occur, and why?

The drop in blood pressure moving from arteries to veins is the result of LOSS OF FLUID ENERGY due to friction and increasing resistance of flow (as vessel size gets smaller) Largest drop in ARTERIOLES, which is where the TOTAL resistance is the greatest`

The sympathetic efferents, both excitatory and inhibitory, have an effect on what? (4 things)

The heart, arterioles, venules, and veins

What is the equation for the velocity of blood?

Velocity = Flow (Q)/Cross-sectional area (A)

TEST/AGAIN: Why does blood have the lowest velocity in capillaries? (What is the purpose of this)

To facilitate capillary exchange of solutes and fluid!!!!!

TEST: In a SERIES arrangement of blood vessels, the total resistance is (greater/lesser) than any of the individual resistances in series

Total resistance is GREATER in series (than any individual resistances)

AGAIN: What is the role of the parasympathetic nervous system on blood vessels?

VERY MINIMAL, and only in a few organs. Their increased activity does indeed cause vessels to dilate, but the effects on TPR is really negligible compared to the sympathetic nerve activity.

TEST: What is the single most common effector for all types of vascular control?

Vascular smooth muscle (VSM!)

Venous diameter changes have significantly greater effects on venous _____ capacity than on venous ______ to blood flow. This is why they are often called ________ vessels.

Venous diameter changes have significantly greater effects on venous VOLUME capacity than on venous RESISTANCE to blood flow. This is why they are often called CAPACITANCE vessels

TEST: At rest, where is the greatest percentage of total blood volume located, the venules/veins or the arteries/arterioles? Why?

Venules/veins! The large volume (60-67%) of blood in the veins acts as a reservoir to shift to the arterial side in case of sudden drops in arterial pressure

RECALL: Angiotensin II is a very potent ________ agent. What is the enzyme responsible for forming this, and what hormone does it lead to the secretion of?

Very potent VASOCONSTRICTOR agent Enzyme responsible for forming this: ACE Leads to the secretion of ALDOSTERONE!

TEST/AGAIN: When daily fluid intake rate is constant, an increase in arterial pressure will lead to an (increase/decrease) in urinary output rate, which will (increase/decrease) blood volume and this (increases/decreases) the blood pressure.

When daily fluid intake is constant, an INCREASE in arterial pressure --> INCREASE in urinary output --> DECREASE in blood volume --> DECREASE in blood pressure!