2 - Circulatory Flashcards
What percentage of blood is in the veins at any given moment?
64%
What is the average functional pressure in most vascular beds?
In glomerulus?
17 mmHg
60 mmHg
What is Ohm’s Law?
Calculation for flow through a vessel:
F = (Delta P)/R
F is blood flow
Delta P is the pressure difference between the two ends of the vessel
R is resistance
What is the overall blood flow of an adult person at rest?
5000 ml/min
What is laminar flow?
When blood flows through a long smooth vessel, it flow in streamlines, with each layer of the blood remaining the same distance from the vessel wall
Why is parabolic velocity in blood vessels important?
MUCH faster
fluid in the middle of the vessel can move rapidly becuase many layers of the slipping molecules exist between the middle of the vessel and the vessel wall
Is turbulence higher in large or small vessels?
Large, especially with:
pulsatile flow
sudden change in vessel diameter
high velocity of flow
What is the definition of blood pressure?
force exerted by the blood against any unit area of the vessel wall
____ mmHG equals _____ cmH20
1 mm
1.36 cm
Mercury has a specific gravity 13.6 times that of water
Why do large diameter vessels conduct blood faster than small?
Laminar flow
Poiseuille’s Law
The ______ blood vessels in circuit,
the _____ the total vascular resistence
more
lower
Which is more distensible: veins or arteries?
Veins!
About 8x more distensible.
What is vascular compliance?
Total quantity of blood that can be stored in a given portion of the circulation
The compliance of a vein is about 24x higher than a corresponding artery
What two major pressures affect pulse pressure?
Stroke Volume
Vessel compliance/distensibility
What are four examples of specific blood resevoirs?
- The spleen (100 ml)
- the sinuses of the liver (several hundred)
- Large abdominal veins
- Venous plexus beneath the skin
What is the rough total surface area of the peripheral circulation?
500 to 700 square meters
How far is a single cell from a capillary (usually)?
20-30 micrometers
What is the intercellular cleft?
Pore in the capillary membrane that allow movement across the membrane
Brain capillary endothelial cells have what kind of cell junctions?
Tight junctions
Only allow water, O2 and COd to pass in or out
Describe the capillary intercellular clefts of the liver
Wide open, allowing almost all disolved substances in the plasma to pass into the liver (including plasma proteins)
Describe the endothelial clefts in the glomerular capillaries of the kidney
numerous oval windows (fenestrae) allow tremendous amounts of small molecular and ionic substances (but not plasma proteins) to filter through
What is vasomotion?
intermittent contraction of the metarterioles and precapillary sphincters
causes intermittent flow instead of continuous flow in capillaries
What is the #1 regulator of vasomotion? How?
Oxygen concentration in the tissue
When VO2 is increased, the intermittent periods of blood flow occur more often, allowing increased DO2
What is the interstitium?
The space between cells
Contains interstitial fluid
What is a brush pile?
in the interstitium, the proteoglycans form a mat of extremely fine filaments called a brush pile
How does free fluid usually exist in the interstitium?
As rivulets of free fluid and small free fluid vessicles
It doesn’t flow easily through the interstitial gel
With edema, these rivulets expand tremendously
capillary pressure moves fluid ______
out of the capillary
Plasma colloid osmotic pressure moves fluid ____
into the capillary
Interstital fluid pressure moves fluid ______
into the capillary
interstitial fluid colloid osmotic pressure moves fluid______
Out of the capillary
What is the net filtration pressure?
Sum of the four forces, determines which way filtration will occur
Why is the interstitial fluid pressure slightly negative?
The lympatic system pumps extra fluid and protein/molecules/debris from the interstitial space into the blood circulation, and this creates a slight negative pressure in the interstitial space
All the lymph vessels from the lower body empty into the _____, which empties into the blood system at the ________
thoracic duct
L IJ
2/3 of all lymph is derived from the ______
liver and intestines
Total estimated lymph flow
120 ml/hr
2-3 L/day
How are tissues held together in the body?
connective tissue fibers, but also the negative interstital fluid pressure!!!!
What happens with interstitial tissues lose their negative pressure?
Edema
what is beriberi?
Thiamine (vit B12) deficiency
Reactive Hyperemia
mechanism for local blood flow
WHen the blood supply to a tissue is blocked, once it’s unblocked the blood flow increases 4-7x normal. Lasts for seconds or hours.
Active Hyperemia
When a tissue becomes highly active with increased VO2, rate of blood flow increases
Increases skeletal blood flow 20 fold during exercise
Myogenic Theory of acute autoregulation
when the smooth mm cells of the vascular walls are stretched, they contract, and vice versa
this means flow in the arterioles remains almost exactly the same regardless of fluctuations in MAP
Myogenic contraction is initiated by ________
stretch induced vascular depolarization
Describe Tubuloglomerular Feedback
in the distal tubule, macula densa sense an increase in the amount of blood filtering through the glomerulus and constrict afferent arterioles, reducing renal blood flow back to normal
The level of excitability in the brain is highly dependent on concentrations of what?
CO2
H+
The most important endothelium-dervied relaxing factor is _______
nitric oxide
What does NO do in vascular smooth muscle?
activates a cascade that leads to vasodilation
How does NO contribute to effective local blood flow control?
When microvascular flow increases, NO is released upstream and dilates the feeding vessel, so that pressure isn’t excessive
Why does Angiotensin II trigger NO synthesis and release?
Protect against excessive vasoconstriction
How does Sildenafil work?
prevents degradation of cGMP (the secondary messenger that NO triggers) and prolongs the actions of NO that cause vasodilation
What is endothelin?
When is it released?
Why?
extremely potent vasoconstrictor
Released by the endothelium when it’s been damaged
Prevents extensive bleeding from the damage
Hypertension damages endothelium, worsening vasoconstriction by triggering release of ______
endothelin
what causes retrolental fibroplasia?
Hyperoxia in preemies causes blindness after they are removed from the hyperoxic environment becuase the relative hypoxia causes uncontrolled angiogenesis in the retina and overgrows to the point of causing blindness
Name four angiogenic factors
- VEGF
- Fibroblast growth factor
- PDGF
- Angiogenin
What is the role of HIF in angiogenesis?
Reduced tissue oxygen induces expression of HIF (hypoxia inducible factors) which upregulate angiogenic factors
Is vascularity determined by maximum or average blood flow need?
Maximum
(you’re not always exercising, but when you exercise consistently your body remembers the blood flow you needed during peak performance and creates enough vascularity to meet that maximum demand
Laplace’s Equation for vessels
T = r x P
where t is vascular wall tension
radius is the radius of the vessel
and P is its pressure
How do small blood vessels respond to prolonged hypertension?
constrict
inward eutrophic remodeling
smooth mm cells arrange themselves around the smaller diameter, basically bunching up to hold the smaller size permanently
How do larger arteries respond to chronic hypertension?
Cannot constrict
vessel wall is exposed to increased wall tension
undergo hypertrophic remodeling
vascular smooth mm cells get bigger and develop collagen/fibrin to make the vessel wall stronger
MAKES BLOOD VESSELS STIFFER
If veins have thin walls, why can you use a saphenous vein to replace an artery in a CABG?
Once it’s anastamosed, the increased pressure leads to hypertrophy of vascular smooth muscle cells
gets thicker and stronger, and after several months will be about as thick as an artery
what does humoral control of the circulation entail?
substances secreted or absorbed into the body fluids affect blood pressure
What are the humoral vasoconstrictors?
Norepinephrine/Epinephrine
Angiotensin II
Vasopressin
Which is a more powerful vasoconstrictor: NE or Epi?
Norepinephrine
During sympathetic stimulation, NE and epi function as both neurotransmitters and ______
hormones
adrenal medullae secretes NE and epi into the blood, causing direct vasoconstriction
Angiotensin II constricts the ______
arterioles
Where is vasopressin produced?
Where is it secreted?
Hypothalamus
Posterior Pituitary
What are the humoral vasodilators?
Bradykinin
Histamine
What are kinins?
substances that cause powerful vasodilation
Bradykinin causes ______ and _______
Arteriolar dilation
increased capillary permeability
Most histamine is derived from _____ in damaged tissues and ______ in the blood.
mast cells
basophils
Histamines cause _____ and _____
arteriolar vasodilation
increased capillary permeability (edema)
Increases in which ions cause vasodilation?
Increased potassium
Increased Magnesium
Increased Hydrogen
Increased acetate and citrate
Increased CO2
Increased calcium causes vasodilation or vasoconstriction?
constriction
An increase in CO2 will cause ________ in the brain
marked vasodilation in the brain, but stimulates brain vasomotor center which leads to widespread vasoconstriction in the body
Sympathetic vasomotor nerve fibers leave the spinal cord through spinal nerves at:
T1-L2
Once sympathetic nerves leave the vertebral column, they pass immediately in _______
a sympathetic chain
one on each side of the vertebral column
In most tissues, all the vessels except ______ are innervated
capillaries
Precapillary sphincters and metarterioles are innervated
Sympathetic vasoconstriction is most potent in what tissues?
kidneys
intestines
splen
skin
Sympathetic vasoconstriction is less potent in what tissues?
skeletal muscle
heart
brain
Where is the vasomotor center?
bilateral
medulla and lower third pons
The vasomotor center transmits parasympathetic impulses through the _______ to the _______, sympathetic impulses through the ______ and _____ to ________
vagus nerves to the heart
spinal cord and peripheral sympathetic nerves to virtually all arteries, arterioles, and veins of the body
Which portion of the vasomotor center transmits excitatory impules to the heart?
Lateral
Which portion of the vasomotor center decreases heart rate and contractility?
How?
Medial
sends signals to the adjacent dorsal motor nuclei of the vagus nerves
What is the reticular substance/formation?
complex network of brain and brainstem nuclei that can excite or inhibit the vasomotor center
________ is the sympathetic vasoconstrictor.
Norepinephrine
Norepinephrine acts directly on _______ receptors in vascular smooth muscle.
A adrenergic
When sympathetic impulses are sent to the blood vessels, they are also sent to the ________
adrenal medullae
Sympathetic stimulation of the adrenal medullae causes what?
medullae secret epinephrine and norepinephrine into the circulating blood
When rapid control of arterial pressure is needed, what three things happen in the autonomic nervous system?
- Arterioles are constricted, increasing SVR
- The veins especially are strongly constricted
- the heart is directly stimulate by the autonomic nervous system, enhacing pumping
Your nervous system can double or halve your BP in as little as ________
10 seconds
Baroreceptors are extremely abundant in which two areas?
wall of each internal carotid artery (carotid sinus)
the wall of the aortic arch
Signal from carotid baroreceptors travel to the brain via _______.
Signals from the aortic baroreceptors travel to the brain via _______.
Both pathways lead to the ________
Herings nerves to glossopharyngeal nerve
vagus nerves
nucleus tractus solitarius of the medulla
Baroreceptors respond much more rapidly to a pressure that is ______ than a pressure that is ________
rising
stationary
What happens when high pressure baroreceptor signals enter the nucleus tractus solitarius of the medulla?
secondary signals inhibit the vasoconstrictor center and excite the vagal parasympathetic center
How long does it take for baroreceptors to reset when BP is chronicly increased/decreased?
1-2 days
This is due to resetting of the sensors themselves, not the vasomotor center
Where are the chemoreceptor organs?
2 carotid bodies in the common carotid artery
1-3 aortic bodies adjacent to the aorta
What nerves do chemoreceptor excite?
Same as baroreceptors:
Hering’s in the carotid
Vagus in the aorta
At what blood pressure are chemoreceptors generally excited?
80mmHG
has to be really low before they’ll take action, so not a strong arterial pressure controller unless profound hypotension is present
What effect does atrial stretch have on renal sympathetic activity?
ADH?
ANP?
Decreases renal
Decreases ADH
Increases ANP
What are low-pressure receptors?
Why are they important?
Stretch receptors in the atria and pulmonary arteries
Helpful in adjusting BP when large changes in volume are present
What is the bainbridge reflex?
Atrial stretch increases heart rate
What is the CNS ischemic response?
When decreased blood flow (and therefore elevated CO2) in the vasomotor center are severe, the vasomotor center excites the vasoconstrictor and cardioaccelerator neurons.
SBP and HR skyrocket
CNS ischemic response only occurs at severely low BP, so it’s often referred to as _______
Last-ditch stand presure control mechanism
What is the Cushing Reaction?
Special type of CNS ischemic response
triggered by increased CSF pressure
When CSF pressure is higher than SBP, this stimulates and increase in SBP so that the brain can be perfused
What is the abdominal compression reflex?
When baroreceptors or chemoreceptors are activated, skeletal nerves to the abdomen are stimulated and compress the abdomen
Increases venous return
Why is it that people who have been paralyzed are considerably more prone to hypotensive episodes?
Unable to mount abdominal compression reflex
How does skeletal muscle increase CO and BP during exercise?
Increases venous return
