Regulation of blood pressure and flow

Question 1

Arterial Baroreceptors

Answer 1

pressure sensors
Baroreceptor neurons function as sensors in the homeostatic maintenance of mean arterial pressure (MAP)

Located in the aortic arch and carotid sinuses where they monitor pressure.
Located in thinner walls that can be stretched (by pressure)

Baroreceptor nerve endings are sensitive to stretch and pressure in artery

Question 2

Rate of baroreceptor nerve firing is

Answer 2

proportional MAGNITUDE and CHANGES in the mean arterial pressure

Baroreceptor response is lost in minutes (can only act as a short term sensor of blood pressure)

Question 3

Arterial baroreceptors act as part of a

Answer 3

negative feedback pathway that regulate mean arterial pressure via the brain (central control)

Actions are coordinated by the medulla oblongata (medullary cardiovascular
centre)

Autonomic Nervous System
Sympathetic (increase MAP)
Parasympathetic (decrease MAP)

Hormonal
Adrenaline (increase MAP)
Angiotensin II and Vasopressin
(increase MAP)

Question 4

Autonomic nervous system (central control)- Sympathetic nerves

Answer 4

mediated by noradrenaline via b-adrenergic receptors
a1-adrenergic receptors in arterioles (except skeletal muscle which is a2-adrenergic )
increase cardiac output and peripheral resistance

Question 5

Autonomic nervous system (central control)
-Parasympathetic nerves

Answer 5

mediated by acetycholine via muscarinic receptors
inhibit heart rate

Question 6

Arterial baroreceptors and the regulation of hypotension (and exercise induced dehydration

Answer 6

Causes of hypotension (reduction in arterial pressure)

Loss of blood (hemorrhage)

Loss of salts
burns and sweating
diarrhea or vomiting

Stress or emotions (fainting

Question 7

standing up

Answer 7

Orthostasis
Standing is associated with a drop in mean blood pressure (and possible fainting)

Why does this occur and how does the cardiovascular system compensate?

Standing and effect of gravity leads to blood pooling in legs (up to 500ml)
Reduced blood volume and lowering of central venous pressure
Reduced venous return, reduced end-diastolic pressure, reduced stroke volume and reduced blood pressure
Baroreceptor reflex will compensate

Question 8

Blood volume is an important

Answer 8

long term regulator of mean arterial pressure
Baroreceptors can regulate short term (seconds-minute) changes in blood pressure
Changes in blood volume regulated by the kidneys are responsible for long-term regulation of blood pressure (renin-angiotensin system)

Question 9

Mean Arterial Pressure

Answer 9

Cardiac Output x Total Peripheral Resistance

Question 10

Local flow is regulated

Answer 10

by both local, neural and hormonal factors (varies between different tissues)

Question 11

Intrinsic (local) control of arteriole vasodilation and vasoconstriction

Answer 11

Local factors

Myogenic Response
Vasoconstriction of arterioles caused by stretch of smooth muscle
Brain, kidney and heart – not skin

Vasodilation induced by metabolites:
O2 ↓, CO2 ↑,
H+ ↑, adenosine ↑, K+ ↑, osmolarity↑

Autocoids
Mainly release as a result of inflammation and bleeding
Histamine, bradykinin, prostaglandins etc

Endothelial cells (sheer stress)

Release local factors (paracrine)
Nitric oxide and prostacyclin (vasodilation)
Endothelin-1 (vasoconstriction)

Question 12

Increase metabolic activity leading to

Answer 12

ACTIVE HYPEREMIA

1. metabolic activity of organ increased
2. decrease in oxygen increase in metabolites in organ interstitial fluid
3. Arteriolar dilation in organ
4. increased blood flow to organ

Question 13

Reduce blood flow in organ leading to

Answer 13

FLOW AUTOREGULATION

1. decrease in arterial pressure in organ
2. decrease in blood flow to organ
3. decrease in oxygen increase in metabolites decreases in vessel-wall stretch in organ
   4.Arteriolar dilation in organ
   5.Restoration of blood flow toward normal in organ

Question 14

Arterioles are regulated by both local, neural and hormonal factors

Answer 14

Vasoconstriction
Internal blood pressure
(myogenic response)
Endothelin-1

Vasodilators
Oxygen ↓
CO2, K+, H+
Osmolarity
Adenosine
Eicosanoids
Bradykinin
Nitric Oxide

Question 15

Neural control of arterioles vasodilation and vasoconstriction (from brain)

Answer 15

Skin

Room Temperature
arterioles constricted by moderate rate of sympathetic discharge

Cold, Fear or Loss of blood
Sympathetic discharge increased and arterioles vasocontriction
Divert blood to essential organs

Increased Body Temperature
Sympathetic discharge reduced and arterioles vasodilation
Blood flow to skin to facilitate body cooling

Question 16

Angiotensin II

Answer 16

vasoconstriction
renin-angiotensin system

Question 17

Vasopressin

Answer 17

vasoconstriction
posterior pituitary gland

Question 18

Atrial Natriuretic Peptide

Answer 18

vasodilation
cardiac atria

Question 19

Exercise and the response of the
Cardiovascular system

Answer 19

Boost O2 uptake and CO2 removal (increased cardiac output)

Increase blood flow to muscles, heart and skin (changes peripheral resistance)

Stabilise arterial blood pressure (despite changes in cardiac output and peripheral resistance)

Question 20

Increased blood flow strenuous exercise to:

Answer 20

Skeletal muscle
Skin (cooling)
Heart (cardiac output)

Vasodilation of arterioles

Question 21

Decreased blood flow to non-essential organs:

Answer 21

Kidneys
Abdominal organs

Vasoconstriction of arterioles

Question 22

Valsalva Manoeuvre
Why do people have heart attacks when they are trying to have a poo?

Answer 22

Valsalva was a 18th Century Physiologist
Forced expiration against a closed or narrowed airway
Coughing, lifting heavy weights, clearing ears and defecation
Leads increase in intrathoracic (chest) pressure