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Aims
• Blood clotting (cont.).
– Coagulation cascade
• Regulation of blood pressure.
• Regulation of blood volume.
• Reading; Sherwood, Chapters 10 &11,
Chapter 15 pages 569-570 ; Robbins, pages
84-90
Coagulation Cascade
• Very complex
– >50 substances effect coagulation
– procoagulants
– anticoagulants
• Key Steps
– Formation and/or Activation of prothrombin
activator/s (Factor X)
– Conversion of prothrombin to _________________
– Conversion of fibrinogen to ___________________.
Coagulation Cascade
Activation of Prothrombin activator/s is the
rate limiting step.
Sherwood’s Human Physiology 11-12
Intrinsic Pathway
Guyton’s Textbook of Medical Physiology 36-4
Extrinsic Pathway
Guyton’s Textbook of Medical Physiology 36-3
Summary
Sherwood’s Human Physiology 11-13
Fibrinolytic System
•
•
•
•
Limits the size of the clot.
Plasminogen is a plasma protein trapped in the clot.
It is cleaved into plasmin by tPA.
Plasmin breaks down __________________ and
interferes with its polymerization.
Robbins’ Basic Pathology 4-12
Leukocytes
• White blood cells (WBC’s) that serve in the
immune system.
• Primary functions:
– Defend against pathogens via phagocytosis.
– Identify and destroy cancer cells.
– Phagocytose debris resulting from dead or
injured cells.
Factors Involved in Blood Pressure
• mean arterial pressure = cardiac output X total peripheral
resistance
Sherwood’s Human Physiology 10-35 (10-34 6th Edition)
Factors Involved in Blood Pressure
• There are both short term and long term
adjustments made to normalize blood
pressure.
• Short Term (within seconds to minutes)
– Alterations in cardiac output and total peripheral
resistance (______________________________)
• Long Term (minutes to days)
– Adjusting total blood volume
Sherwood’s Human Physiology 10-35 (10-35 6th Edition)
Arterial Baroreceptors
• Constantly monitor mean arterial pressure and
pulse pressure.
• Mechano-receptors in the walls of several
large arteries.
Sherwood’s Human Physiology 10-36 (10-36 6th Edition)
Arterial Baroreceptors
• Cardiovascular Control Center
• Located in the __________________
• Autonomic nervous system “feedback”
Guyton’s Textbook of Medical Physiology 18-5
Arterial Baroreceptor
• Increased arterial
pressure =>
Increased CNS
signal.
• Decreased arterial
pressure =>
decreased CNS
signal.
Guyton’s Textbook of Medical Physiology 18-6
Arterial Baroreceptor
Sherwood’s Human Physiology 10-37 (10-36 6th Edition)
Baroreceptor Reflex
• Increased CNS signal (increased BP)
– Inhibit vasoconstrictor center of medulla.
• Vasodilation of veins and arteries => decreasing
peripheral resistance.
– Excite vagal parasympathetic center.
Sherwood’s Human Physiology 10-38 (10-37 6th Edition)
Baroreceptor Reflex
• Decreased CNS signal (decreased BP)
– Excite vasoconstrictor center of medulla.
• Vasoconstriction of veins and arteries => increasing peripheral
resistance.
– Excite vagal _____________________________________ center.
Sherwood’s Human Physiology 10-38 (10-37 6th Edition)
Effects of changing body position
on the arterial baroreceptor
Standing from a supine position (lying down)
-BP in upper body and head decreases and
can cause a loss of consciousness.
-Decreased pressure elicits a an immediate
reflex resulting in a strong sympathetic
response.
Arterial baroreceptor as a pressure
buffer system
• Important in
maintaining pressure
during changes in body
position.
• Functions as a “pressure
buffer system” since
without an arterial
baroreceptor there is an
increase in pressure
variability.
Guyton’s Textbook of Medical Physiology 18-8
Arterial baroreceptor is a short term
regulator
• Arterial baroreceptors
are responsible for
reducing the minute
by minute variations
in arterial pressure by
1/2-1/3.
• ____________ Term
Regulation
Guyton’s Textbook of Medical Physiology 18-9
Summary of Baroreceptor Reflex
Increased BP
Sherwood’s Human Physiology 10-39 (10-38 6th Edition)
Summary of Baroreceptor Reflex
Decreased BP
Sherwood’s Human Physiology 10-39 (10-38 6th Edition)
Chemoreceptor Reflex
• Located in the ______________________
and adjacent to the aorta.
• Sensitive to:
– Decreased O2
– Excess CO2
– Excess H+ (low pH)
Guyton’s Textbook of Medical Physiology 18-5
Chemoreceptor Reflex
• Excite nerve fibers in the vasomotor center
of the brain stem.
• Decreased pressure => decreased O2,
increased CO2, increased H+ => stimulates
chemoreceptors => maintain vasoconstrictor
tone => increased pressure back to normal.
• Not a powerful reflex
– Because it is only activated at pressures below
80mm Hg.
Blood Pressure Control Mechanisms
Guyton’s Textbook of Medical Physiology 19-15
CNS Ischemic Response
“Last ditch stand”
• Control of arterial pressure in response to
diminished brain blood flow.
• Neurons in the vasomotor center respond directly
and strongly.
• Their stimulation results in systemic arterial
pressure as high as the heart can pump.
– Due to elevated level of CO2 stimulating sympathetic
nervous system in medulla.
– One of the most powerful activators of the sympathetic
vasoconstrictor system.
Blood Pressure Control Mechanisms
Guyton’s Textbook of Medical Physiology 19-15
Cushing Reaction
• In response to elevated cerebrospinal fluid
pressure.
• When cerebrospinal fluid pressure > arterial
pressure, the brain’s vessels collapse and
blood flow stops.
• This initiates the CNS ischemic response
and the elevation of arterial pressure > than
the cerebrospinal fluid pressure.
Volume Reflex
• Left
atrial volume
receptors and
osmoreceptors are
involved in H2O and NaCl
balance.
•They play a role in
___________________
Term regulation of BP by
increasing blood volume
& vasoconstriction.
Sherwood’s Human Physiology 15-4
Renal-Body Fluid System for
Arterial Pressure Control
• Primitive: dates back to the hag fish.
• Long Term regulation of BP.
• Pressure diuresis is the increase in output
volume as arterial pressure rises.
Renal-Body Fluid System for Arterial
Pressure Control
Guyton’s Textbook of Medical Physiology 19-1
Blood Pressure Control Mechanisms
Guyton’s Textbook of Medical Physiology 19-15
Water and Salt Intake vs. Renal Output
Renal output of water and salt
8
4
More output than input
Equilibrium point
Water and salt intake
1
More input than output
50
100
Arterial pressure
150
Blood Volume Increases
• If you increase the
volume of blood
there is an
immediate
response to
increase CO, Urine
out flow, and
arterial pressure.
Guyton’s Textbook of Medical Physiology 19-2
Renin-Angiotensin System
• When the Kidneys experience ________________
arterial pressure their Juxtaglomerular cells release
a small protein, Renin.
• Renin is not a vasoactive substance it is an enzyme
which cleaves a plasma protein angiotensinogen to
angtensin I which is a mild vasoconstrictor.
• Angiotensin I is cleaved in the lungs into
Angiotensin II which is a strong vasoconstrictor
and decreases renal excretion of both water and
salt.
Renin-Angiotensin System
Decreased arterial pressure
Renin release from Kidneys
Angiotensinogen
Angiotensin I (mild vasoconstriction)
Converting enzyme (in lung)
Angotensinase
Angiotensin II
(inactive)
Renal retention of
salt and water
Strong vasoconstriction
Next Time
• Cardiovascular pathology
– Hypertension
– Atherosclerosis
Readings; Robbins, Atherosclerosis 328338, Hypertension 338-341.
Objectives
1. Describe the coagulation cascade.
2. Describe how blood pressure is regulated
(short term vs long term).
1.
2.
3.
4.
Baroreceptors and baroreceptor reflex
Chemoreceptors and chemoreceptor reflex
Ischemic response
Volume reflex and the role of the kidney (reninangiotensin system)