Download Circulation of Blood

Circulation of Blood
• Overview: Two Circuits
• Goal: Get Blood to Capillaries
• Capillary Beds
• Arteries and Veins
• Blood Pressure
• Control of Circulation and Blood Pressure
Larry M. Frolich, Ph.D., Yavapai College
Overview—Two circuits
• Pulmonary Circuit:
Right side of heart
pumps blood to lungs
to pick up oxygen
• Systemic Circuit: Left
side of heart pumps
blood to rest of body to
deliver oxygen
• Schematic does not
show left/right
symmetry for most of
circulatory system
Goal—get blood to capillaries
• Pulmonary circuit—right side of
heart pumps blood through
pulmonary arteries to capillaries
• Oxygen diffuses into blood and
RBC’s in lungs at alveoli
surrounded by capillaries
• Pulmonary veins return blood to
left side of heart
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Systemic left side of heart
pumps blood through
systemic arteries to
capillaries
Oxygen diffuses out of
blood and into interstitial
fluid around cells making
oxygen available for
cellular metabolism. This
is the grand goal of the
circulatory system—where
the real action happens
Besides oxygen, water,
glucose and other nutrients
are delivered; CO2, waste
products are picked up
Systemic veins return
blood to right side of heart
Action at the capillary beds
• Every cell of every tissue of body
must be close to a capillary
• Capillaries are microscopic—often
just one RBC in diameter
• Remember—diffusion is the way
substances (like oxygen, nutrients)
to move in and out of cells and
across membranes (like capillary
wall)
Capillaries form “beds” or
networks that connect from
artery to vein
Capillaries—more realistic views
More realistic drawing
showing network of capillaries
connecting arteries to veins
and threading through tissue.
Open-ended lymph capillaries
pick up excess fluid from
tissue and also give immune
cells route back into blood
circulation
Photomicrograph of
stained blood vessels of
retina showing intricate
capillary network
Electron micrograph
showing arterioles,
tiniest of arteries,
splitting into virtual sheet
of capillary network that
brings blood into very
close proximity with
almost every cell in the
tissue.
Histology of the
capillary wall
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Wall of capillary is simple
squamous epithelium
Basal lamina is thin collagen
layer on external surface
that gives structure
Fenestrated capillaries with
pores in the epithelial cells
are found where rapid
exchange of water or
solutes is needed: e.g.
absorptive parts of
intestines, choroid plexus in
ventricles of brain, endocrine
glands like hypothalamus,
pituitary
Smooth muscle sphinchters
control flow through capillary
bed (somatic or
visceral/autonomic or no
innervation?)
Fluid flow at capillary—from filtration to reabsorption
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As blood moves
through capillary, fluid
first diffuses out
(filtration), along with
dissolved solutes that
will fit through spaces
between endothelial
cells
Then, fluid is
reabsorbed close to
veins
This transition will
become especially
important when we
study kidney
Arteries and Veins—almost always run together in NAV
Artery/Vein differences
Arteries (aa.)
Direction Blood Away from
of flow
Heart
Pressure Higher
Veins (vv.)
Blood to Heart
Walls
Lumen
THICKER: Tunica
media thicker than
tunica externa
Smaller
THINNER: Tunica
externa thicker
than tunica media
Larger
Valves
No valves
Valves (see next)
Lower
• William Harvey (1578-1627)
• Exercitation Anatomica de
Motu Cordis et Sanguinis in
Animalibus (An Anatomical
Exercise on the Motion of
the Heart and Blood in
Living Beings) (1628)
• Famous veinous flow valve
experiment
• Easy to repeat—just try it if
you’ve got the veins
Where’s the blood? Mostly in your veins
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“Venous reserve” is
about 20% of
blood– pooled in
skin, liver, lungs
Veins can be
constricted to move
this blood out and
to vital organs like
brain, muscles
when needed
Venous blood is
under almost no
pressure to move it
along
Skeletal muscle
action moves
venous blood
ahead of next valve
Long periods of
inactivity can lead
to pooling of blood
Heart pushes blood
through vessels
against resistance
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Factors
that
affect
blood
pressure
Heart contracts to push blood into
vessels
Friction causes resistance of
movement of any fluid through a pipe
or tube
Heart has to pump enough volume to
create enough pressure to overcome
resistance, but not too much which will
cause high blood pressure
(hypertension) and can lead to many
secondary problems
Blood Pressure—overview
Blood pressure in arteries is
constantly changing to counteract
variability in resistance
• Gravity alone makes for huge
differences in amount of pressure
needed to overcome resistance
and get blood to organs
• Standing up from lying creates an
instant need for total change in
blood distribution—lat-time leads
to dizzy sensation and even
fainting.
• Exercise also changes the
amount of blood (and pressure
that blood is under) needed in
different parts of the body
• What about a giraffe or dinosaur!
Online text about Dinosaur Evolution with great images and links, by David Esker
Blood Pressure—the
body’s fundamental
challenge
• Vessels provide resistance, heart pumps to overcome
resistance
• How does body use feedback information to control
vessel size and resistance as well as heart output. This
is what maintains blood pressure in a normal range
• High blood pressure results when size of artery dilation
is too small for the volume of blood being pumped (or the
volume of blood being pumped is too great for arterial
dilation)
• So we need to understand two things:
– INPUT: How does body “know” what blood circulation needs are
– OUTPUT: How does body control response to those needs
Input on blood pressure to brain
• Chemoreceptors
– aortic bodies, carotid bodies
– Sense CO2, pH, O2
• Barroreceptors
– stretch receptors sense blood
pressure pushing on vessel wall
– aortic sinus, carotid sinus
Bonus A and P I Review:
Cranial Nerve that carries aortic
receptor input to brain? IX. Vagus
Cranial Nerve that carries carotid
receptor input to brain?
IX. Glossopharyngeal
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If CO2 is high, what is needed?
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Response to chemoreceptor (aortic, carotid bodies) input:
(Physiology is common sense—think it through)
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If O2 is low, what is needed?
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Arteries: constrict or dilate?
Heart output: more or less?
Arteries: constrict or dilate?
Heart output: more or less?
Is this sympathetic or
parasympathetic response?
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If blood pressure rises, what is needed?
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Response to Baroreceptor
(aortic, carotid sinus) input:
•
(Physiology is common sense—think it
through)
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Arteries: constrict or dilate?
Heart output: more or less?
If blood pressure falls, what is needed?
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Arteries: constrict or dilate?
Heart output: more or less?
Which response is sympathetic (NE); which is
parasympathetic (ACH)?
Reflexive output: heart rate
• Baro- and chemo-receptor
input arrives to medulla
oblongata (A and P I review!)
• Autonomic motor output (A and
P I review) to AV node of heart
– Sympathetic will speed heart
rate (where do sympathetic
neurons originate? What is
path to heart?
– Parasympathetic will slow
heart (where do
parasympathetic neurons
originate? What is path to
heart?)
• Bonus (common sense
physiology!): Will blood
vessels constrict or dilate with
sympathetic response?
A and P I Review
Sympathetic = “fight or flight” =
NE (norepinephrine)
Parasympathetic = calming =
ACH (acetylcholine)
Reflexive output: vessel
dilation and constriction
• Baro- and chemo-receptor
input arrives to medulla
oblongata (A and P I review!)
• Autonomic motor output (A
and P I review) directly to
blood vessel smooth muscle
and capillary sphincters?
• Autonomic output to
stimulate secretion of
adrenalin (E, NE)
• Adrenalin will cause vessel
constriction
– Physiolog common sense:
– Does this increase or
decrease blood pressure?
– Does this work with
increase or decrease in
heart rate?
So, what causes high blood pressure?
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Too much heart volume output or too much fluid/blood in system?
Vessels are too constricted?
Easy case: High blood sugars in diabetes damages small blood vessels leading to increased
resistance—thus hypertension frequently accompanies diabetes
Most of the time, root cause is difficult to determine.
Control is much more complex than just general input from chemo- and baro-receptors and
generalized reflexive output response.
Local input and response is very important. Remember capillary sphincters…
Regulating fluid and salt levels is crucial—why? (common sense physiology…think it through)
Site of action of
medications to
control high
blood pressure
Holistic approaches to hypertension which are scientifically proven to work.
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Reduction is salt intake. This reduces the circulating fluid. Therefore blood pressure falls.
Proof: Take a lot of salt, you will drink plenty and your blood pressure will increase because
your circulatory system has too much fluid. You can reverse this process and see the results
for yourself. You do not need to be a scientist.
Regular activity. Doing exercises (or physical activity as part of your daily routine) will lower
your blood pressure. The reasons are two fold. First, the heart becomes stronger and beats
more efficiently and secondly the blood vessels become more elastic and therefore have
more recoil (elasticity). Proof: Stop exercising for two months and you will loose all the
benefits of your exercises.
Healthy Diet: Reduce cholesterol and red meat intake. The elasticity of your blood vessels
will improve. There will be minimal or no plaque deposits in your blood vessels. This is
important because the plaque decreases available space for your blood to travel around the
body.
Zero Cigarettes: The vasoconstriction brought about by cigarettes increases blood pressure.
Coffee and other vasoconstrictors should be avoided.
Stress, job related or not, must be reduced. Relaxation has a BP reducing effect on the body.
Watch what medications you are taking. Many non-steroidal anti-inflammatory drugs, diet
pills, steroids, antidepressants and monoamine oxidase inhibitors are known to be major
causes of hypertension.
Weight. If you weigh too much your heart has to supply oxygenated blood to all the fat you
are carrying. So it has to produce a higher blood pressure, otherwise the oxygenated blood
will not reach all the fatty and not so fatty tissues.
Alcohol. Research shows that consuming more than 3 to 4 ounces of 80-proof alcohol per
day will result in hypertension. One to two drinks per day is considered satisfactory.
Question your holistic practitioner’s motives. Does he get a commission on his sale to you. Is
there a professional body to verify what he/she is telling you is correct. If in doubt, move on.
BRAINSTORM:
How should
increased
activity level or
exercise affect
blood pressure
readings?
(do exercise
physiology lab
to find out!)
Guyenet Nature Reviews Neuroscience 7, 335–346 (May 2006) | doi:10.1038/nrn1902
Numerous factors cause rises in blood pressure (BP), for example, pain and physical exercise. Increases in BP are brought about
predominantly through three mechanisms. One involves the stimulation of glutamatergic rostral ventrolateral medulla (RVLM)
barosensitive neurons via spinoreticular afferents (pain and muscle receptors) or inputs from more rostral structures (central command)
1). A second mechanism is a reduction of the baroreceptor feedback due to a biasing of the transmission between baroreceptor afferents
and second-order neurons in the nucleus of the solitary tract (NTS) (2). The mechanism relies on pre- and postsynaptic inhibition
mediated by GABA ( -aminobutyric acid) and other substances such as vasopressin (not represented). Last, the baroreflex is also under
humoral control (3). Circulating angiotensin II (Ang II), for example, also reduces transmission between baroreceptor afferents and
second-order neurons. The mechanism of angiotensin II control of the baroreflex involves the production of nitric oxide (NO) by the
capillary endothelium, and this mechanism could have a role in neurogenic hypertension 75. CVLM, caudal ventrolateral medulla; Glu,
glutamate; SGN, sympathetic ganglionic neuron; SPGN, sympathetic preganglionic neuron.