Download File - Dr. Jerry Cronin

Autoregulation
• The Renin-angiotensin-aldosterone (RAA)
system is an important endocrine component of
autoregulation.
• Renin is released by kidneys when blood
volume falls or blood flow decreases.
• It is subsequently converted into the active
hormone angiotensin II which raises BP
by vasoconstriction and by stimulating
secretion of aldosterone from the
adrenal glands.
Autoregulation
• Epinephrine and norepinephrine are also
released from the adrenal medulla as an
endocrine autoregulatory response to
sympathetic stimulation.
• They increase cardiac output by increasing rate and
force of heart contractions.
• Antidiuretic hormone (ADH) is released from the
posterior pituitary gland in response to
dehydration or decreased blood volume.
Autoregulation
• Atrial Naturetic Peptide (ANP) is a natural
diuretic polypeptide hormone released by cells
of the cardiac atria.
• ANP participates in autoregulation by:
• Lowering blood pressure (it causes a direct vasodilation)
• Reducing blood volume (by promoting loss of salt and
water as urine)
Circulation
• In an autoregulatory response, important
differences exist between the pulmonary and
systemic circulations:
• Systemic blood vessel walls dilate in response to
hypoxia (low O2) or acidosis to increase blood flow.
• The walls of the pulmonary blood vessels constrict
to a hypoxic or acidosis stimulus to ensure that
most blood flow is diverted to better ventilated
areas of the lung.
Circulation
• A measure of peripheral circulation can be done
by checking the pulse. The pulse is a result of the
alternate expansion and recoil of elastic arteries
after each systole.
– It is strongest in arteries closest to the heart and
becomes weaker further out.
– Normally the pulse
is the same as
the heart rate.
Circulation
• Blood pressure is the pressure in arteries generated by
the left ventricle during systole and the pressure
remaining in the arteries when the ventricle is in diastole.
Alterations Of Blood Pressure
• About 50 million Americans have hypertension
(HTN).
• It is the most common disorder
affecting the CV system
and is a major cause of
atherosclerotic vascular
disease (ASVD), heart
failure, kidney disease
and stroke.
Alterations Of Blood Pressure
• Hypertension is defined as an elevated systolic
blood
pressure (SBP), an elevated diastolic blood
pressure (DBP), or both. Depending on severity,
it is classified as pre-hypertension, Stage 1 HTN,
or stage 2 HTN.
Alterations Of Blood Pressure
• Hypotension is defined as any blood pressure
too low to allow sufficient blood flow (hypoperfusion) to meet the body's metabolic
demands (to maintain homeostasis).
• Many persons, especially some thin, young
women, have very low BP, yet experience no
dizziness, fatigue, or other symptoms – they are
not hypotensive, and in fact are probably very
healthy (cardiovascular wise).
• Hypotension leading to hypo-perfusion
(pressure and flow are related) of critical organs
results in shock
Shock And Homeostasis
• The 4 basic types of shock are:
•
•
•
•
Hypovolemic shock, due to decreased blood volume
Cardiogenic shock, due to poor heart function
Obstructive shock, due to obstruction of blood flow
Vascular shock, due to excess vasodilation - as seen
in cases of a massive allergy (anaphylaxis) or sepsis.
In the U.S., septic shock causes >100,000 deaths/yr.
and is the most common cause of death in hospital
critical care units.
Shock And Homeostasis
• The same negative feedback mechanism
discussed in autoregulation of blood
pressure/flow is activated to restore blood and
nutrient flow in cases of shock.
• Heart will respond with  rate and force of
contraction.
• Selective tissue beds will vasoconstrict to shunt
blood flow to those tissue most necessary to life
(brain).
• The other neural, hormonal, and chemical pathways
will be recruited to restore balance.
Shock and Homeostasis
• Heart rate & force increase
• Vasoconstriction or vasodilation
depending on type of shock
• ADH released  conserve water
• Renin released  Angiotensin II
• Aldosterone released  conserve Na+
• ANP inhibited
The body responds via negative feedback to restore homeostasis