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A&P 2 Physiology Exam 2
Chapter 19- Blood Vessels
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Cardiovascular System consists of the
blood
,
heart
and
blood vessels.
60,000 miles of blood vessels in the body.
Blood vessels made of
living cells
Three main kinds of blood vessels:
Arteries
- away from heart
Veins
- toward the heart
Capillaries
- gas exchange (1 tunica interna, tight junctions)
The walls of arteries & veins have 3 layers: *
Lumen
- space inside blood vessel*
Tunica
Interna
- innermost (lymphatics), may elastic
Tunica
Media
- Muscle (vasoconstruction/vasodilation), elastic fiber.
Tunica
Externa
- outermost, plastic fibers (lymphatics).
Tunica Media - Muscle (vasoconstruction/vasodilation), elastic fiber.
Vasoconstruction
= decrease diameter of blood vessel
Vasodilation
= increase diameter of blood vessel
Less tunic media, lots of
elastic fibers
-> aorta/pulmonary trunk
constrict
dilate
Venous System:
Large
Veins
Small
Veins
Venules
Arterial System:
Elastic
Arteries (ex: aorta)
* elastic fibers, no constrict/dilate "conducting arteries"
2.
Muscular
Arteries "disturbing arteries"
* ex: ulnar/radial
3.
Arterioles
* ex: resistance vessels
4.
Capillaries
* tunica interna, thinnest, exchange vessels, left-communication
The
arterial
system - high pressure, thickest layer is tunica media, all layers have more elastic fibers.
(a) Elastic arteries stretch during ventricular
contraction.
(ex: aorta)
(b) Elastic arteries recoil during ventricular
relaxation.
(ex: brachial, radial)
The tunica media allows muscular arteries and arterioles to
constrict
and
dilate
:
Muscular arteries therefore can regulate blood flow into blood supply to specific
organs.
Arterioles therefore can regulate blood flow into
capillaries.
The
capillaries
are the exchange vessels:
5-10 micrometers in diameter
Tunica
interna
only - thin walls
Tight junctions join cells together
Clefts
- gaps between neighboring cells
There are 3 types of capillaries:
Continuous
Capillaries - least permeable, no pores (slow exchange)
Locations: throughout
body
,
skin
,
muscle
2.
Fenestrated
Capillaries - very permeable, has pores (fast exchange)
Locations:
small
intestine,
kidneys
3.
Sinusoids
- extremely permeable, large pores and clefts (fastest exchange)
Locations:
Liver
(krupfter cells),
bone marrow
,
spleen
, sinusoids
Capillary Exchange - movement of substances between
blood plasma
and
interstital fluid.
Capillary exchange is aided by:
Diffusion
- going from high to low concentration
Transcytosis
- ex: exocytosis, pinocytosis
Bulk flow
- passive process by which large numbers of ions, molecules or particles in a fluid move together in the same direction.
Capillary transport mechanism
Diffusion through
plasma membrane.
Bulk flow through
clefts
Bulk flow through
fenestrations
Transcytosis using
vesicles
Bulk flow is directional : High -> Low
Filtration
(high pressure in
capillaries
> low pressure in interstitial fluid)
Reabsorption
(high pressure in
interstital fluid
> low pressure in capillaries)
*pressure differences determine the direction of
bulk flow
*
Definitions
Hydrostatic
Pressure (HP) <- ->
forced exerted by a fluid against a wall.
Osmotic
Pressure (OP) -> <-
force opposing hydrostatic pressure due to non-diffusing molecules
Net Filtration
Pressure (NFP)
calculated using several HP and the OP
(a) when blood HP > blood OP, then filtration occurs at the beginning of capillary (≈ 20 L of fluid/day)
(b) when blood OP > blood HP, then reabsorption occurs at the end of capillary (≈ 17 L of fluids reabsorbed day)
Filtration
occurs at the beginning of capillary (NFP is +10 mmHg)
Reabsorption
occurs at the end of capillary (NFP is -9mmHg)
Venous System
Low
pressure system compared to arterial system
Has
thinner
walls and
wider
lumens than arteries (tunica externa is thickest layer) compared to arterial system.
Blood reservoirs
of vascular system (veins)
The Venous System consists of :
Venules
(smallest diameter) - connect cap, to veins
Veins
(large diameter) ex:
valves
present in veins
Venous sinuses
- specialized, broad veins supported by surrounding tissue ; only has the tunica
interna.
ex: coronary sinus
⬇️⬇️⬇️⬇️
deoxygenated
blood
going outwards in
different directions
Anastomoses provide detours for blood flow.
(a) The major coronary artery :
anatomosis
(b) The major cardiac :
coronary sinus
Blood pressures drop along the
vascular
system
Arterial system -
highest
pressure (120 -> 35 mmHg)
*must know*
capillaries
(35 -> 16 mmHg)
Venous system -
lowest
pressure (16 -> 0 mmHg)
Blood Pressure moves areas of high pressure -> low pressure
Aorta
Arteries
ex: muscular arteries
Arterioles
Capillaries
Venules
Veins
Venae Cavae
(back to RA)
Venous return of blood is aided by:
Muscular pump
(squeeze
deep
veins -> heart)
Respiratory pump
(squeeze
local
veins -> heart)
Valves
(back flow, ex.
varicose
veins 'incompetent valve')
Also
large
lumens (decrease resistance)
Some definitions:
Blood flow (F) =
ml
/
min
Blood pressure (P) =
mmHg
Resistance (R)
F = ΔP/R
F:
blood flow
per
min.
ΔP: change in
BP
*
hydrostatic
Smaller Lumen/diameter:
As
resistance
⬆️
Flow
⬇️
Larger Lumen/diameter:
As
resistance
⬇️
Flow
⬆️
ΔP⬆️,
F⬆️
(vice versa)
Contraction of the ventricles
increases
blood pressure ->
increase
blood flow. (blood pressure)
Increases in the resistance
decrease
blood flow :
Greater blood viscosity (thickness) increases resistance.
⬆️Plasma p vot. (ex:
polycythemia
)
Greater total blood vessel length
increases
resistance.
Vasoconstruction
increase resistance
Vasodilation
decreases resistance
Systolic P (≈120)
max P when ventricle
contracting
Diastolic P (80 mmHg)
max P when ventricle is
resting
Mean arterial P
diastolic
P
pulse pressure
(systolic - diastolic)
Blood Pressure -
hydrostatic
pressure exerted by
blood.
Systolic
Pressure
Diastolic
Pressure
Pulse
Pressure (systolic P - diastolic P)
Mean Arterial
Pressure (MAP)
diastolic
P
avg pressure from
arterial
system
Neural Regulation of Blood Pressure (BP) is short-term
⬆️HR, ⬆️BP (
sympathetic
),
vasoconstrict
(sym ON/activated)
⬇️HR, ⬇️BP (
parasympathetic
),
vasodilation
(sym OFF/
deactivated
)
*Only the
sympathetic
division of the autonomic nervous system can change the diameter of blood vessels*
Hormonal Regulation of BP is short-term.
Hormones that raise BP:
Angiotensin
II
Epinephrine
& norepinephrine
Antidiuretic Hormone
(ADH)
(opposite dehydration)
bp med: for hypertension ⬇️BP ex: diuretic ⬆️dehydration ⬇️BP
Hormones that lower BP:
Atrial natriuretic peptide
(ANP)
change in
NA
(decrease)
Renal Regulation of BP is long-term:
Kidneys increase BP by
increasing
blood volume.
Kidneys decrease BP by
decreasing
blood volume.
Short-term regulation by:
Nervous system
(para + sym)
Hormones
Long-term regulation by:
Kidneys
adjusting
blood volume
Normal BP is about
120
/80
Disorders of the Vascular System:
Hypertension
- high blood pressure
(>
140
/90)
Hypotension
- low blood pressure
(systolic pressure <
100
mmHg)
Hypotension may be due to different causes:
Orthostatic hypotension, due to
position
of body
Chronic
hypotension (circulatory shock),
allergies
, bacterial
infections
*hives
Acute
hypotension (sudden)
Circulatory
shock - condition when there is not enough blood in the blood vessels and blood cannot circulate normally.
Hypovolemic shock - loss of
volume
Vascular shock -
vasodilation
Cardiogenic shock -
weak
heart
Hypertension
⬆️ Afterload
High pressure in SL valves
Harder for the heart to
reopen
valve in next contract.
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