Chapter 14 Flashcards
Flow Rule
- Flow occurs from high pressure to low pressure
- P is the force pushing blood against the various factors resisting the flow of liquid in a pipe
- flow = p/r
Pressure gradients drive flow from ___ pressure to ___ pressure
high; low
P =
(systemic circuit)
pressure in aorta minus pressure in vena cava just before it empties into right atrium
Pressure in aorta =
mean arterial pressure (MAP) = 90 mm Hg
Pressure in vena cava =
central venous pressure (CVP) = 0 mm Hg
Pressure gradient across the circuits formula
P = MAP – CVP = 90 – 0 = 90 mm Hg
P =
( pulmonary circuit)
pressure in pulmonary arteries minus pressure in pulmonary veins
Pulmonary arterial pressure =
15 mm Hg
Pulmonary venous pressure =
0 mm Hg
Which pressure gradient is larger systemic or pulmonary
systemic
T/F: Flow through both circuits is equal (systemic v. Diastole)
true
Factors affecting resistance to flow
- Radius of vessel
- Length of vessel
- Viscosity of fluid, depends on amount of RBCs and proteins
Total peripheral resistance
combined resistance of all blood vessels within the systemic circuit
Vasoconstriction in network ->______ ->_______
increased resistance; decreased flow
Vasodilation in network-> ______-> _______
decreased resistance; increased flow
Flow =
cardiac output (CO)
P =
mean arterial pressure (MAP)
R =
total peripheral resistance (TPR)
CO =
MAP / TPR
Arteries
carry blood away from heart
whats involved in microcirculation
Arterioles
Capillaries: site of exchange
Venules
Veins:
return blood to heart
label artery and vein diagram
____ cells line inner layer of all blood vessels
Endothelial
components of blood vessel walls:
Smooth muscle
Fibrous connective tissue
Collagen
Elastic connective tissue
Elastin
Arteries
- Rapid transport pathway
- Large diameter
- Little resistance
- Walls contain elastic and fibrous tissue
- Under high pressure
- Muscular arteries
Arteries expand as blood? And Recoil?
enters arteries during systole; during diastole
Compliance
measure of how the pressure of a vessel will change with a change in volume
Small increase in blood volume causes a
large increase in pressure
Large increase in blood volume is required to
produce a large increase in pressure
Systolic blood pressure =
maximum pressure
Diastolic blood pressure =
minimum pressure
Diastolic blood pressure =
minimum pressure
Arterial Blood Pressure
- Pressure in the aorta
- Varies with cardiac cycle
- Not zero due to elastic recoil
Pressure cuff and sphygmomanometer
- Compressed artery
- Turbulent flow produces Korotkoff sound
- Pressure at first Korotkoff sound = systolic blood pressure
Uncompressed artery
- Laminar flow, no sound
- Pressure when sound disappears = diastolic blood pressure
The measured BP is shown as
SP/DP
Pulse pressure =
SP – DP
MAP =
SP + (2DP) / 3
Arterioles
- resistant vessels
- Part of microcirculation
- Connect arteries to capillaries
- Contain rings of smooth muscle to regulate radius and, therefore, resistance
____ provide greatest resistance to blood flow
Arterioles
Arteriolar tone
Contraction level (radius) is independent of extrinsic influences
Vasoconstriction
Increased contraction = decreased radius
Vasodilation
Decreased contraction = increased radius
Functions of varying arteriole radius
- Controlling blood flow to individual capillary beds
- Regulating mean arterial pressure
Changes associated with increased metabolic activity generally cause
vasodilation
Carbon dioxide
Potassium
Hydrogen ions
Changes associated with decreased metabolic activity generally cause
vasoconstriction
Active hyperemia
increased blood flow in response to increased metabolic activity
Steady state
(active hyperemia)
- O2 is delivered as fast as it is consumed
- CO2 is removed as fast as it is produced
Increased metabolic rate
(active hyperemia)
- O2 is consumed faster than it is delivered
- CO2 is produced faster than it is removed
Response to low O2 and high CO2
- Vasodilation
- Vasodilation increases blood flow
Increased blood flow
Delivers more O2
Removes more CO2
Reactive hyperemia
increased blood flow in response to a previous reduction in blood flow
Blockage of blood flow to tissues causes?
- Metabolites increase and oxygen decreases
- Vasodilation
When blockage is released what occurs?
- Increased blood flow due to low resistance
- Metabolites removed, oxygen delivered
Myogenic response:
change in vascular resistance in response to stretch of blood vessels in the absence of external factors
Myogenic autoregulation of blood flow
- Increased perfusion pressure increases blood flow and pressure in arterioles
- Increased pressure in arteriole stretches arteriole wall
- Stretch of vascular smooth muscle induces contraction of vascular smooth muscle—inherent property of smooth muscle
- Vasoconstriction decreases blood flow
Purpose of Myogenic autoregulation of blood flow
keep blood flow constant (autoregulate)
Radius of arterioles is regulated by
extrinsic mechanisms to control mean arterial pressure
Extrinsic Control of Arteriole Radius and Mean Arterial Pressure is sympathetic or parasympathetic
sympathetic
Epinephrine
Released from adrenal medulla
Vasopressin (ADH)
- Secreted by posterior pituitary
- Increases water reabsorption by kidneys
- Vasoconstriction
Angiotensin II
- Vasoconstriction
- Increases TPR
Capillaries
Site of exchange between blood and tissue
Capillary walls
- One cell layer
- Small diffusion barrier
- Have greatest total cross-sectional area
- Have slowest velocity of blood flow, which enhances exchange
Continuous capillaries
- Most common
- Small gaps between endothelial cells
- Allow small water-soluble molecules to move through
Fenestrated capillaries
- Large gaps between endothelial cells forming pores or fenestrations (windows)
- Allow proteins, and in some cases blood cells, to move through
Metarterioles
- Intermediate between arterioles and capillaries
- Directly connect arterioles to venules
- Function as shunts to bypass capillaries
Contraction of metarterioles->
increase blood flow through capillaries
Relaxation of metarterioles
decrease blood flow through capillaries
Precapillary sphincters
- Rings of smooth muscle that surround capillaries on the arteriole end
- Contract and relax in response to local factors only
Contraction of precap sphincters ->
constricts capillary decreases blood flow
Relaxation of precap sphnicters->
increases blood flow
Metabolites cause
relaxation
label venule and arteriole diagram
Lipophilic
across membrane
Lipophobic
through channels
Transcytosis
exchangeable proteins
Bulk flow of fluid across capillary wall based on?
pressure gradients
Protein-free plasma moves across _____
capillaries
Filtration =
movement out of capillary into interstitial space
Absorption =
movement into capillary from interstitial space
Forces for bulk flow
hydrostatic and osmotic pressures
Hydrostatic pressure gradient
force due to fluid
Osmotic pressure:
osmotic force exerted on water by nonpermeating solutes
Only nonpermeating solute
proteins
Oncotic pressure
osmotic force of proteins
Capillary hydrostatic pressure
- capillary BP
- Arteriole end = 38 mm Hg
- Venous end = 16 mm Hg
- Favors filtration
Interstitial hydrostatic pressure =
0–1 mm Hg
Favors reabsorption
Capillary oncotic osmotic pressure
25 mm Hg
Favors reabsorption
Interstitial fluid oncotic osmotic pressure
0–1 mm Hg
Favors filtration
Osmotic pressure gradient
25 – 0 = 25 mm Hg
Favors reabsorption
Net filtration pressure =
filtration pressure – absorption pressure
Net across capillary:
filtration > absorption
Factors affecting filtration and absorption across capillaries
- Standing on feet
- Injuries
- liver disease
- kidney disease
- heart disease
- venules
- veins
Veins
- Expand with little change in pressure
- Function as blood reservoir
- 60% total blood volume in systemic veins at rest
Skeletal muscle pump
- Squeezes on veins, increasing pressure
- Blood moves toward heart
- Blood cannot move backward due to valves
Factors That Influence Venous Pressure and Venous Return
- skeletal muscle pump
- respiratory pump
- Blood volume
- Venomotor tone
Inspiration
- Decreases pressure in thoracic cavity
- Increases pressure in abdominal cavity
Pressure on veins in abdominal cavity creates gradient favoring?
blood movement to thoracic cavity
Increased blood volume->
increased venous pressure
Decreased blood volume->
decreased venous pressure
Venomotor tone
-Smooth muscle tension in the veins
- Increases central venous pressure
- Decreases venous compliance
- Increases venous return
Smooth muscle in walls of veins is innervated by
sympathetic nervous system
Lymphatic System
-system of vessels, nodes, and organs
- Vessels are involved in returning excess filtrate to circulation
- Vessels form an open system starting at the capillaries
- Lymph moves from capillaries to veins
- Lymphatic veins drain into the thoracic duct, which empties into the right atrium
- Lymph moves through the lymphatic veins in the same way as blood flows through regular veins
- Also part of immune system (macrophages)
Determinants of Mean Arterial Pressure
Heart rate
Stroke volume
Total peripheral resistance
Short-term regulation of MAP
- Regulates cardiac output and total peripheral resistance
- Involves the heart and blood vessels
- Primarily neural control
Long-term regulation of MAP
- minutes to days
- Regulates blood volume
- Involves the kidneys
- Primarily hormonal control
Baroreceptors
- pressure receptors
- Sometimes called stretch receptors
Arterial baroreceptors
- sinoaortic receptors
- Aortic arch
-Carotid sinuses - Respond to stretching due to pressure changes in arteries
Regulation of Mean Arterial Pressure
- Cardiovascular control center
- Medulla oblongata
- Integration center for blood pressure regulation
Cardiovascular control center: Input
Arterial baroreceptors
Low-pressure baroreceptors
Chemoreceptors
Proprioceptors
Higher brain centers
Autonomic output to cardiovascular effectors
Parasympathetic input to
SA node (decreases HR)
Sympathetic input to
- SA node (increases HR)
- Ventricular myocardium (increases contractility)
- Arterioles (increases resistance)
- Veins (increases venomotor tone)
Baroreceptor reflex
negative feedback loop to maintain blood pressure at normal level
Hemorrhage
- Decreases blood volume
- Triggers the baroreceptive reflex
- Increases sympathetic activity
- Decreases parasympathetic activity
Adrenal medulla releases?
epinephrine in response to sympathetic activity
Vasopressin and angiotensin II
Vasoconstrictors
Increase TPR
Increase MAP
