WEEK 4: PERIPHERAL RESISTANCE; CONTROL OF BP

Question 1

State the normal pressures of the CVS.

1.Systemic (Aortic) pressures
2.Pulmonary artery pressure

Answer 1

1.*At systole = 120 mm Hg

*Diastole = 80 mm Hg

*Pulse pressure = (120 – 80) mm Hg

2.*Systolic = 15 – 18 mm Hg

*Diastolic = 8 – 10 mm Hg

Question 2

What is mean arterial blood pressure?

Answer 2

Mean arterial pressure (MAP) is the average pressure in a person’s arteries during one cardiac cycle.

Question 3

State the formula for MAP.

Answer 3

DP + 1/3 (SP-DP)

Question 4

Describe the determinants of blood pressure.

Answer 4

*Total peripheral resistance (TPR): Total peripheral resistance (TPR) is the amount of resistance to blood flow present in the vascular system of the body.

*Cardiac Output (CO): Cardiac output is the amount of blood pumped by the heart per unit time.

Question 5

What is the formula for Cardiac output?

Answer 5

Cardiac output= Stroke volume x Heart rate

Question 6

State the determinants for Cardiac output.

Answer 6

Heart rate (HR)
Stroke volume (SV)

Question 7

What is stroke volume?
What is the average resting Stroke volume?

Answer 7

Volume of blood pumped out (ejected) by each ventricle per minute.
The average resting SV is approximately 70 ml.

Question 8

State factors affecting stroke volume.
*Intrinsic
*Extrinsic

Answer 8

INTRINSIC FACTORS
-Venous return (Pre-load/EDV = 135 ml)

-Frank-Starling Law of the heart:

*The strength of the heart’s systolic contraction is directly proportional to its diastolic expansion.

The energy produced by the heart during systole is a function of the end-diastolic length of its muscles.

EXTRINSIC FACTORS (Sympathetic)

-Increase force of contraction which decreases End Systolic Volume (ESV) decreases below 65 (135 – 70) ml therefore increase venous return

-Vasoconstriction of veins increases venous return and EDV

NOTE:
*Venous return (VR) is the flow of blood back to the heart.
*EDV: Is the volume of blood in the right or left ventricle at end of filling in diastole which is amount of blood present in ventricle at the end of diastole systole.

Question 9

State the formula for BP?

Answer 9

*Blood Pressure= Total peripheral resistance x Cardiac Output

*BP = SV X HR X TPR

Question 10

State factors favoring arterioles resistance.

Answer 10

Highly muscular (circular)
Small radius
High sympathetic supply
Lacks parasympathetic supply
Capacity to vary diameter (vasoconstriction/ vasodilatation)
Responsiveness to local chemicals /hormone

Question 11

State the short-term mechanisms of BP regulation.

Answer 11

*Short term: within seconds to minutes

Baroreceptor reflex
Nervous system
Stress/relaxation
Fluid shift at capillary membrane

Question 12

State the long-term mechanisms of BP regulation.

Answer 12

*Takes much longer, begins after some hours and lasts days

-Kidney response: Renin – Angiotensin – Aldosterone System (RAAS)

-Hormonal:

Question 13

What are baroreceptors?

Describe the Baroreceptor feedback loop for controlling MAP.

Answer 13

Baroreceptors are a type of mechanoreceptor sensory neuron that are excited by a stretch of the blood vessel.

Thus, increases in the pressure of blood vessel triggers increased action potential generation rates and provides information to the o neurons within the solitary nucleus which lies in the medulla.

The solitary nucleus in the medulla oblongata of the brain recognizes changes in the firing rate of action potentials from the baroreceptors and influences cardiac output and systemic vascular resistance.

This sensory information is used primarily in autonomic reflexes that in turn influence the heart cardiac output and vascular smooth muscle to influence vascular resistance.

Baroreceptors act immediately as part of a negative feedback system called the baroreflex, as soon as there is a change from the usual mean arterial blood pressure,
returning the pressure toward a normal level.

increased MAP—-Stretch of baroreceptors resulting in increased firing— Glossopharyngeal or vagus nerve takes afferents to the NTS in medulla— Cardio-inhibitory area and vasomotor area—which sends efferent via sympathetic and parasympathetic to the heart, blood vessels, adrenal medulla, skin and sweat glands.

These reflexes help regulate short-term blood pressure.

Question 14

What are the functions of cardio-inhibitory and vasomotor areas in the medulla?

Answer 14

*The cardioinhibitory center slows cardiac function by decreasing heart rate and stroke volume via parasympathetic stimulation from the vagus nerve.

*The vasomotor center controls vessel tone or contraction of the smooth muscle in the tunica media.

Question 15

Where are baroreceptors located?
Give their examples.

Answer 15

Baroreceptors are sensors located in the carotid sinus (at the bifurcation of common carotid artery into external and internal carotids) and in the aortic arch.

*Carotid sinus receptors and aortic arch receptors.

Question 16

Describe the ANS regulation of BP.

Answer 16

PARASYMPATHETIC ACTIONS
*Vagus nerve releases ACH
INNERVATES: SA node and myocardium
*HR and conduction velocity
R side SA node (HR)
L side contractility (slight

MECHANISM
*Muscarinic receptors (M2)
*ßγ subunit (HR)
*Nitric oxide (weak inotropic effect)

Decreased HR—–Decreased cardiac output—-Decreased BP

Question 16

Describe the PARASYMPATHETIC regulation of BP.

Answer 16

PARASYMPATHETIC ACTIONS
*Vagus nerve releases ACH
INNERVATES: SA node and myocardium
*HR and conduction velocity
R side SA node (HR)
L side contractility (slight

MECHANISM
*Muscarinic receptors (M2)
*ßγ subunit (HR)
*Nitric oxide (weak inotropic effect)

Decreased HR—–Decreased cardiac output—-Decreased BP

Question 17

Describe the SYMPATHETIC regulation of BP.

Answer 17

ACTIONS on the heart
*Nerve fibers release NE
INNERVATES: SA node, atria, and ventricles
↑ HR and contractility

MECHANISM
*ß1 receptors – pacemaker activity
*ß1 myocardium contraction

ACTIONS on blood vessels
*Activated -Vasoconstriction throughout body
INNERVATES: Skin/kidney BVs most abundant
De-activated – vasodilation

MECHANISM
Norepinephrine α > ß
Epinephrine ß > α

Vasoconstriction – α1
Vasodilation – ß2

Question 18

What are chemoreceptors?
What stimuli do they respond to?
State the two types of chemoreceptors.
State their general function.

Answer 18

1.Chemoreceptors are sensory cells or organs that respond to chemical stimuli.

2.Respond to a ↓PaO2 , ↑ PaCO2, fall in pH.
Normal O2 changes not significant stimulus.
Severe hypoxia is potent stimulus.

3.*Peripheral chemoreceptors: Carotid sinus and Aortic bodies.
*Central chemoreceptors: located in MEDULLA OBLANGATA

4.Coordination of inputs to cardiovascular centers and respiratory centers.
Exert a positive drive on vasomotor area.
Exert a positive drive on cardio-inhibitory area.

Question 19

Describe the action of peripheral chemoreceptors.

Answer 19

*Located at the bifurcation of Carotid artery and at Aortic arch.
*Senses low oxygen in blood
*Synapses with Glossopharyngeal and Vagus nerve and send impulses to Medulla and Pons respectively.
*Initiates changes to restore Partial pressure of Oxygen.

Question 20

Describe the action of Central chemoreceptors.

Answer 20

*Primarily sense low pH in the brain (High CO2)
*Initiates changes in ventilation to restore partial pressure of Carbondioxide.

Question 21

Describe the RAAS system of long-term BP regulation.

Answer 21

1.When your blood pressure falls, your kidneys release the enzyme renin into your bloodstream.

2.Renin splits angiotensinogen, a protein your liver makes and releases, into pieces. One piece is the hormone angiotensin I.

3.Angiotensin I, which is inactive (doesn’t cause any effects), flows through your bloodstream and is split into pieces by angiotensin-converting enzyme (ACE) in your lungs and kidneys. One of those pieces is angiotensin II, an active hormone.

4.Angiotensin II causes:
* The muscular walls of small arteries (arterioles) to constrict (narrow), which increases blood pressure.

*Thirst

*Angiotensin II also triggers your adrenal glands to release aldosterone and your pituitary gland to release antidiuretic hormone (ADH, or vasopressin).

5.Together, aldosterone and ADH cause your kidneys to retain sodium. Aldosterone also causes your kidneys to release (excrete) potassium through your urine.

6.The increase in sodium in your bloodstream causes water retention. This increases blood volume and blood pressure, thus completing the renin-angiotensin-aldosterone system.

Question 22

How is renin released in the kidneys.

Answer 22

Renin is secreted from juxtaglomerular kidney cells, which sense changes in renal perfusion pressure, via stretch receptors in the vascular walls.

Question 23

1.What are the 2 atrial and ventricular peptides involved in BP regulation?
2.Where are they released form?
3.Describe the function of Atrial and ventricular peptides in BP regulation.

Answer 23

1.Atrial Natriuretic Peptide (ANP): Released by atria muscle cells
Brain Natriuretic Peptide (BNP): Released from ventricles and brain.

2.The (hormones) peptides reduce BP by inhibiting:
-Na+ & H2O reabsorption in distal nephron
-Renin secretion
-Aldosterone secretion
-Secretion and action of ADH

NOTE: they oppose the effects of ANGIOTENSIN II