Download System Responses to Exercise and Disease

System Responses to
Exercise and Disease
Hemodynamic
changes in response
to hemorrhage
A drop in systemic arterial pressure
initiates the baroreceptor reflex and
greatly increases sympathetic outflow.
This accounts for the increases in
heart rate and TPR. Remember that
the regulated variable here is mean
arterial pressure. In this example, the
blood loss is mild (no more than about
1 liter for a 60-70 Kg person) and the
reflexive compensation is able to
protect MAP while slower responses
can restore the lost fluid, electrolytes
and blood cells. Note that cardiac
output is not a regulated variable and
cannot return to normal until volume
restoration occurs.
Irreversible Hemorrhagic Shock
If the immediate responses were inadequate, a rapid
positive-feedback cycle would cause hemorrhagic shock.
Cardiac depression: heart fails to pump enough blood to
meet the needs of itself and the CNS, leading to
Vasomotor Failure: depressed blood flow to brain is the
most potent of sympathetic stimulants, but after a few
minutes of depressed blood flow, sympathetic outflow
drops and those arterioles that had been constricted by
their adrenergic inputs then dilate, causing a collapse of
MAP.
Hemodynamic changes during exercise
Organ
Resting
Perfusion
Dominant effect
Perfusion during Exercise
(L/min)
(L/min)
Brain
1
1
autoregulation
Heart
0.5
1
autoregulation
Skeletal Muscle
1
12
autoregulation + beta
adrenergic effect
Skin
0.5
4
thermoregulation
Splanchnic
2
1
Alpha adrenergic effect
Kidney
2
1
Alpha adrenergic effect
TOTAL CO
7
20
How is a 3X increase in CO possible during exercise?
• Can it be the result of cardiac effects only? Use the
model to find out.
CO
RAP
Exercise responses are
multifactorial
The magnitudes of MAP, CO and
TPR changes in exercise are
affected by multiple factors,
including
Conditioning
Muscle mass
Exercise intensity level
Environmental temperature
In some highly muscular
individuals, MAP may
decrease significantly in
intense exercise, due to a
profound decrease in diastolic
pressure.
Capillary Filtration, Interstitial
Fluid and the Lymphatic System
Capillaries and Capillary Filtration
• Capillaries are the major sites of exchange of
materials between tissues and bloodstream
• Materials may move across capillary walls only
by diffusion and bulk flow, with exceptions:
– brain capillaries actively transport glucose into the
brain ISF
– Ordinarily, capillary slits are not permeable to
molecules as large as plasma proteins, but in order
for protein hormones to enter the bloodstream and to
reach their targets, and for antibodies to reach sites of
infection, selected proteins can move across capillary
endothelial cells by transcytosis.
There are 3 basic capillary types
The most common
type – clefts are 1015 nm wide, but
smaller in brain
capillaries, which form
the blood-brain barrier
A fenestra is a
window.
Endothelial cells
are perforated like
a shower head – to
increase bulk flow
- found in epithelia
like intestine and
exocrine glands.
Large gaps are
present – this
allows the capillary
to pass proteins –
this form is found in
liver, where plasma
proteins are
synthesized.
Capillary filtration
3
28
Osmotic pressure gradient is due to
plasma proteins and doesn’t change along
capillary length – little protein is filtered.
3
28
Arteriolar end
Venular end
Total
pressure
= 10
outward
35
~0
15
Capillary hydrostatic pressure
decreases along capillary length due
to friction
~0
Total
pressure =
10 inward
Edema is an excess of ISF that reflects an imbalance
between rates of formation and drainage of ISF
Hydrostatic factors that promote systemic edema:
–
–
–
–
–
–
Hypertension
Vasodilation
Increased venous pressure
Erect posture or compression of central veins
Lymphatic blockage
Right Heart failure
Osmotic factors that promote systemic edema:
Loss of serum proteins (protein undernutrition)
inflammation with increased capillary leakiness and release of
tissue proteins
Edema and congestive
heart failure
“Congestive” refers to the fact that
the disease-weakened heart must
operate in a larger range of EDV
and ESV to be able to generate
enough force to sustain MAP.
The edema results from increased
venous pressure that backs up to
increase capillary hydrostatic
pressure, favoring filtration over
absorption.
Patients with generalized congestive
heart failure typically experience
peripheral edema during the day
and pulmonary edema at night.
The Lymphatic System
• Lymphatic capillaries are
blind-ended tubes with flap
valves that permit entry of
ISF
• Lymphatic veins have 1way valves like blood
veins, so periodic
compression of lymphatics
improves lymph flow.
• Ultimately, lymph drains
back into the blood
vascular system through
two ducts – the thoracic
duct (to left subclavian
vein) and right lymphatic
duct (right subclavian
vein).
Lymph drainage
• opposes edema
• recovers proteins that escape across
capillary walls
• delivers information about presence of
infectious agents and non-self antigens to
lymph nodes for immune surveillance
Overview of blood and
lymph transport
Note that:
Cardiac output is a really large
number
The fluid cycle between blood and
ISF is a large number
Diffusional exchanges of water and
glucose between tissues and blood
are truly huge numbers, compared to
filtrative flows
Major Issues to know/understand about
Cardiovascular Physiology
•
•
•
•
Heart cycle – sequence of events and cause-effect relationships
EKG: correlate waves with heart processes, determine axis, and recognize
simple abnormalities.
Baroreceptor reflex and control of heart and vasculature by ANS
System properties: what they are, how they can change, and how they
interact to determine the system variables.
– Know which tissues are dominated by extrinsic control and which by
autoregulation
– As demonstrated in class, be able to use the model to predict outcomes for
system variables in exercise, blood loss, disease, and application of drugs that
affect specific system properties
•
•
Capillary filtration and lymphatic function – forces involved in ISF formation,
and how they can change in disease states.
Know approximate normal values of the following variables for humans:
–
–
–
–
Resting CO/min and daily CO
MAP for systemic and pulmonary loops
RAP
Daily values of capillary filtration and lymph flow