Title: In the power company they keep the voltage in your house constant (110 V) and you vary the resistance of what you plug in to determine how much power you want to use.
1In the power company they keep the voltage in
your house constant (110 V) and you vary the
resistance of what you plug in to determine how
much power you want to use.
2The body works the same way. 100 mmHg is
maintained in the aorta and autoregulation
controls blood flow in each organ in the
periphery.
Overall aim of the system is to keep aortic
pressure constant and let the organs regulate
their own flow through autoregulation.
3- Blood pressure control is based on negative
feedback. - Negative feedback requires a
- Detector
- Integrator
- set point
- effector
Your furnace
4Set Point
Integrator
Detector
Effector
5Arterial baroreceptors are located in the
carotid sinus and arch of aorta
The sensor
6Stretch receptors in the carotid sinuses are
innervated by the Herrings nerve (sinus nerve).
It is a branch of the glossopharyngeal.
7The aortic arch has similar receptors that are
innervated by the aortic nerve, a branch of the
cervical vagus. AKA depressor branch of the
vagus.
8Increased blood pressure stretches the walls and
increases their frequency of action potentials.
A fall in pressure would decrease the frequency.
9Like most mechanoreceptors they are
rate-sensitive and respond to pulsatile pressures
better than a steady pressure
10The carotid sinus receptors have a wider dynamic
range than the aortic
11The integrator
12 The first synapse for all afferent signals is in
the Nucleus tractus solitarius (NTS)
13 Activity in the NTS also activates neurons in
the nucleus ambiguous.
14 Activity in the NTS inhibits neurons in the C1
region.
15The sympathetic nervous system acts to increase
pressure by increasing heart rate, contractility
and constricting the arteries and veins
Parasympathetic nervous system acts to decrease
pressure by slowing heart rate only.
Acetylcholine acts to inhibit cAMP in the heart
and lowers contractility. However, very few
vagal fibers go to the human ventricle.
To decrease the hearts contractility or dilate
blood vessels the CNS can only decrease
sympathetic tone.
16The sympathetic and parasympathetic nerves to the
heart and blood vessels have resting tone and act
reciprocally during reflex activity. AOP CO
x TPR
17Cutting sympathetics in the spinal cord causes a
precipitous drop in blood pressure due to loss of
peripheral vascular tone (spinal shock).
18Parasympathetic nerves do not innervate most of
the peripheral vessels.
Parasymapthetic nerves in salivary glands and
intestine cause dilation that is secondary to
increased metabolism (active hyperemia). They
also dilate erectile tissue
None of the parasympathetic nerves to blood
vessels are stimulated in the baroreflex.
19So what vessels do the sympathetic nerves
constrict?
Vessels in the resting skeletal muscles,
intestine or kidney
If the organ becomes active it undergoes an
active hyperemia that will over-ride any signal
from the sympathetic nerves to constrict (such
the skeletal muscle dilation seen in exercise).
20The baroreflex acts primarily to control
minute-to-minute blood pressure.
- Blood pressure changes due to
- Active hyperemia
- Hydrostatic columns
Note that mean pressure is not changed by
denervation. That is controlled by blood volume
21- The sequence of events with exercise will be
- An active hyperemia in the exercising muscles,
- A drop in peripheral resistance and thus blood
pressure. - Detected by the baroreceptors
- Initiate a reflex to move pressure back toward
the set point
In heavy exercise blood pressure will actually
increase. That is because the CNS increases the
set point during heavy exercise.
22Cardiopulmonary mechanoreceptors
23A and B type stretch receptors are found in the
left atrium. A-fibers respond to atrial systole
and report heart rate while B-fibers respond
during ventricular systole and report atrial
volume.
24- Atrial stretch activates B-fibers which will
- Increase the heart rate (Bainbridge reflex)
- Decrease sympathetic tone to the kidney causing
increased filtration and urine formation. - Decrease production of vasopressin (anti-diuretic
hormone)
25Atrial stretch also causes the atria to make
atrial natriuretic peptide (ANP)
All of these effects act to lower blood volume
26mean arterial pressure cardiac output x
peripheral resistance cardiac output filling
pressure of the heart blood volume Thus blood
pressure can be controlled by controlling blood
volume.
27The rate at which the kidney loses sodium is
determined by the blood pressure
Loss curve
28The kidney is the ultimate controller of blood
pressure.
29A defect in the kidneys ability to control fluid
balance leads to hypertension.
Just raising peripheral resistance does not cause
hypertension. Otherwise all amputees would
suffer from hypertension.
Restricting salt and giving diuretics is an
effective way to treat hypertension.
30Peripheral chemoreceptors Primarily control
pulmonary function but their effects spill over
into the CV system Carotid and Aortic Bodies
31Carotid and aortic bodies are stimulated by 1.
Low PO2 2. High PCO2 3. Low pH 4. Low aortic
pressure
32Stimulation of the chemoreceptors directly
decreases heart rate and constricts the
peripheral blood vessels.
33Systemic hypoxia actually causes a tachycardia
due to the increased respiratory activity. The
overall effect is to raise the blood pressure.
34Head injury or a ruptured aneurysm can cause an
intracranial bleed.
Bleeding inside the cranial vault raises CSF
pressure and collapses the brains blood vessels.
35Ischemia in the CNS causes intense stimulation of
both the sympathetic and parasympathetic outflow
The patient will present with bradycardia and a
very high blood pressure.
The vagus is dominant over the sympathetics at
the SA node
36A summary of the known controllers of blood
pressure.