Lecture 11/8: CV Biophysics Overview Pt 2 Flashcards
Final
Is CVP measured before or after the high resistance?
After
Hence why CVP is a low value
Where are pressures highest at in blood vessels?
Upstream or proximal to the high resistance or “choke points”
What blood vessel is primarily for nutrient exchange and waste product collection?
Capillaries
What blood vessel is responsible for blood flow through the capillaries?
Arterioles
What are arterioles made of? What is this assist with?
Multiple layers of smooth muscle tissue
Good for contracting and relaxing to regulate SVR & blood flow to capillaries
There are ______ capillaries in the body that make up ________ square meters of surface area. What does this help with?
10+ billion
500-700
This large surface area helps with rapid nutrient exchange & waste product collection
Which vessels have multiple layers of smooth muscle tissue? What is the importance of this?
Arterioles & small arteries
Allows vessels to contract/relax which is important for BP regulation
What happens at the capillaries in the peripheries?
Nutrient delivery: glucose, fats, cholesterol
Gases: offloading of O2
Picking up CO2 & carrying to lungs for removal from body
All tightly controlled by metabolic rate of specific tissue
SVR =
Systemic vascular resistance
Equation: xsection
xsection = π(d/2)2 x (amount)
Describe the capillary walls
thin 1 endothelial cell layer
thin so good for exchange
No resistance to force/pressure = things move easily in and out of capillary
No smooth muscle = Cannot contract/relax
What veins return blood to the heart?
Large veins: Superior/inferior venae cava
Which vessel has the slowest velocity?
Capillaries
What is the internal diameter to wall thickness ratio in arterioles?
3:2
What is the internal diameter of the aorta?
2.5 cm
What is the internal diameter of the arterioles?
30 um
What is the wall thickness of the arterioles?
20 um
What is the wall thickness of the capillaries?
1 um
What is the internal diameter of the vena cava?
3 cm
What blood vessel has the fastest velocity?
The aorta during systole/ejection
When the xsection is low the velocity is _______. When the xsection is high velocity is ________.
high
low
What is normal MAP?
100 mmHg
What is pressure at the arterial end of the capillary?
30 mmHg
What is pressure at the Venus end of a capillary?
10 mmHg
What is ∆P the capillaries? What is the importance of this?
20 mmHg
∆P = 30 mmHg - 10 mmHg
∆P = P1 - P2
driving force behind blood flow; allows us to get blood from beginning of capillary to the end.
What are the different names for the beginning of the capillary?
Arterial end
Arteriole end
The arterial end of the capillary has forces that favor _________.
filtration
The venous end of the capillary has forces that favor_________.
reabsorption
Which end of the capillary has a higher pressure?
Arterial end
What does filtration mean?
Moving fluid/waste out of the capillaries
What does reabsoprtion mean?
moving fluid/nutrients into the capillaries
T/F: the lymphatics is a circulatory system
T
Surgeons needs to know where they are cutting bc if they knick the wrong area with lymphatics, can have a swollen limb for the rest of their life.
What are the channels in capillaries that allow movement water & nutrients?
Vesicular channel
Describe the BBB cell wall
BBB = blood brain barrier
cells are right next to each other = tight junctions –> less permeable to Na+ & Cl -
What are the factors that determine if fluid will be filtered out of a capillary?
Starling Capillary Forces
What are the Starling Capillary Forces?
- Hydrostatic Pressure in Capillary
- Hydrostatic Pressure in ISF
- Plasma Colloid Osmotic/Oncotic Pressure
- Interstitial Fluid Colloid Osmotic Pressure
What is hydrostatic pressure in the capillary?
Arterial end: Pcap = 30 mmHg
Venous end: Pcap = 10 mmHg
What is the Hydrostatic Pressure in ISF in the capillary?
PISF = -3 mmHg
Why is hydrostatic pressure in ISF negative?
Lymphatic pull excess fluid out of ISF –> causes pressure to be negative and FAVOR FILTRATION
Favoring filtration = pulling fluids out
arterial end = this increases filtration
venous end = this reduces reabsorption
If there was something wrong with your lymphatic system and it wasnt draining, how would this effect your starling forces?
PISF would increase and no longer be negative. It would be a positive number
-Reduced filtration at arterial end
-promote reabsorption at venous end
Increases blood/fluid volume
Think pathologies that have involvements with increased fluid volume
What is plasma oncontic pressure?
πcap = 28 mmHg
Dissolved colloids in the capillary
Force wants to pull fluid into capillary
What is the Interstitial Fluid Colloid Osmotic Pressure?
πISF = 8 mmHg
Dissolved colloids in ISF
Force wants to pull fluid into ISF
BUT IS OUTWEIGHTED BY STRONGER PLASMA ONCOTIC PRESSURE
T/F: Capillary wall is permeable to colloids
F
Impermeable
What are pathologies that can cause capillary wall to become permeable to colloids? What will happen?
Sepsis
ARDS
Severe Burn injuries
Colloids from capillaries will leak out into ISF. This will make it difficult to keep your BP up. And replacing the colloids wont work bc they will just continue to leak out until capillaries are healed.
What is the Capillary Filtration Coefficient?
Kf = 12.5 mL/min/mmHg
that shows how permeable the capillaries are to FLUID; factors in surface area
– capillary expands = More surface area = more fluid movement
What 3 things make up plasma oncotic pressure?
Albumin<– primary
Fibrinogen - 2nd most important
Immunoglobulin/globulin
What pathologies can drop your plasma oncotic pressure? What happens with this?
Hemmorhage
Liver failure
It becomes hard to keep fluids in the CVS because we don’t have colloids needed for the osmotic pressure to actually create that pressure.
T/F: when capillary walls become more permeable to proteins, those proteins lose some of the osmotic pressure associated with them.
T
double whammy :(
That means that capillary walls becoming more permeable to proteins becomes a PROBLEM before those proteins start leaking out the capillary
Keep looking at this card until you understand
Osmotic pressure is dependent on a ____________ membrane
semi permeable
Describe the pathology for capillary death
Localized capillaries severely damaged –> colloids from inside the capillaries are now in ISF –> increases localized πISF –> pulls fluid out of localized capillaries –> SWELLING/EDEMA
The ______ has more dissolved colloids
Capillary
What is interstitial fluid? What does it consist of?
Matrix protein & substances that sit between cells (intersitual space)
Proteins: Collagen
Proteoglycan filaments
Hylauronic acid
How does swelling go down after capillaries walls have healed from being permeable to colloids? How?
The lymphatics!
The extra fluid in the ISF is able to be sucked up by the lymphatics and taken back up into the CVS! How fun :(
Where does lymphatics deposit excess fluid into the CVS?
The top of the thorax/chest
lymphatic ducts at the top of the thorax connect to large veins for emptying of excess lymphatic fluids
The lymphatics _______ rate when muscles are contracting and relaxing, but they _______ rate if you are bedbound.
Increase
Decrease
Why do the lymphatics take longer to work if you are bed bound?
They are based on movement. The lymphatics depend on a valve opening and closing which depends on your muscles relaxing and contracting. This allows fluid to move; the fluid cannot move if muscles are not contracting/relaxing.
Lymphatics can scavange FLUID ______ fold increase. What does this require?
20-30x fold increase
Requires you to be moving
What are lymph nodes?
Areas of collection that lymphatic vessels tie into.
__________ drives flow through the venous and lymphatic circulation
Light muscle activity (moving around)
Compare/contrast the lymphatic and venous circulatory system
Venous: 1-way valve system
-returns blood to heart
against the lymphatic system
depends on skeletal muscle movement
Lymphatic: 1-way valve system
-takes excess ISF/colloids to top of thorax to CVS
against venous system
depends on skeletal muscle movement
What is the lymphatic pumping system?
as the skeletal muscle contracts/relaxes it opens/closes the 1-way valves which encourages flow of fluid
What will happen to lymph fluid if you are not moving?
Skeletal muscles not contracting/relaxing –> 1-way valves not able to open –> fluid stuck in lower extremities
What helps with lymph circulation if bed bound?
SCDs
Passive ROM
What do SCDs help with?
Lymphatic circulation
Venous circulation
What capillary starling force is effected if we are bedbound? How?
PISF
It will increase
this will decrease filtration at arterial end and increase reabsorption at venous end
Equation: Net Filtration Pressure
NFP = (PCAP - PISF) - ∂(πCAP - πISF)
∂ = protein permeability: (1 = impermeable; 0 = permeable)
assume ∂ = 1 unless stated capillary is permeable to proteins
What is the NFP at the arterial and venous end? What does this mean?
Arterial end = 13 mmHg
Venous = -7 mmHg
There’s more fluid being filtered into the ISF than being reabsorbed into the CVS. This extra fluid is NORMAL IN A HEALTHY PERSON and is scavanged by the lymphatics
What is the BP in the center of a capillary? Why?
17.3 mmHg
Capillaries get larger from front to end –> average pressure is lower than half (would expect to be 20)
What is the NFP in the capillaries?
0.3 mmHg
NFP = (17.3 - (-3)) - 1(28 - 8)
NFP = (PCAP - PISF) - ∂(πCAP - πISF)
The ______ the molecular wt the less likely it is to fit in between the space between the endothelial cell. It has ________ permeability.
higher
decreased
Albumin has a ______ molecular wt therefore it has a ________ capillary permeability
high
low
T/F: Glucose is important to the brain therefore it can cross its barrier freely
F
It is important to the brain, but the brain has tight junctions
Glucose gets into the brain via GLUT1 & GLUT3 transporters
What is the pressure going into the renal artery? What is the pressure leaving the renal vein? Why? Calculate ∆P
100 mmHg
0 mmHg
Vascular resistance encountered throughout the kidney decreases the pressure.
∆P = 100 mmHg
What is Glomerular filtration rate?
GFR = 125 ml/min
rate of fluid moving from GC to Bowman’s capsule (nephron)
AA =
Afferent Arterioles
Describe the AA
-High resistance arterioles
-immediately upstream from GC
- determines BP in GC
Reason for drop in pressure in GC
GC =
Glomerular Capillaries
What is the pressure in the GC? why?
60 mmHg
Blood passes through the AA which reduces pressure
What is the driving force behind GFR?
High pressure in the GC (60 mmHg)
It is double that of a normal capillary (30) therefore it pushes fluids out (drives filtration)
What is the 1st capillary bed we encounter in the kidneys?
GC
How many capillary beds are in each nephron?
2
Where does filtration happen?
GC (pushes fluids out)
Bowman’s capsule (catches what’s filtered)
What is the nephron forming?
urine
How much of glucose managed in the kidney?
All is filtered and all should be reabsorbed if WNL
T/F: RBC are easily filtered at the GC
F
Not small and not filtered unless something is wrong
T/F: No proteins are filtered
F
A few proteins are actually filtered, but not a large amount. The few that are filtered get handled by the kidney.
