A & P 2 - Hemodynamics

Front 1

What are the types of blood flow?

Back 1

1. Laminar (streamlined) flow:
-normal blood flow in CVS under normal conditions
-organized in layers (laminae)
-velocity is zero at vessel wall and maximum in center
-requires minimal energy and not accompanied by sounds

2. Turbulent Flow:
-molecules hit each other - turbulences
-produces sound when velocity exceeds critical level
-occurs during obstruction of blood flow
-requires extra energy

3. Single-file flow in capillaries:
-RBC --> cells occupy the full width of capillary --> bolus of plasma moves trapped between cells because laminar flow is impossible

Front 2

What is the velocity of Blood flow?

Back 2

Volume velocity (Q):
-volume movement per unit time (ml/s or L/min)
-equal to CO
-equal all throughout CVS
-for laminar flow Q directly related to pressure gradient and inversely related to length of tube (Q = Pr^4 / L n)
n = viscosity

Linear velocity (V):
-distance blood displaced over time (mm/sec)
-inversely proportional to cross-sectional area of blood vessels
- V = Q / A
-circulatory time is time required for a drop of blood to go from RA all through through back to RA (1 min)

capillaries have the slowest blood flow due to the highest cross sectional area

Front 3

What are the factors that affect blood flow?

Back 3

driving force:
-hydrostatic pressure gradient (fluid flows from lower to higher hydrostatic P); effective P

Resistance to flow:
-results from friction between molecules
-opposes blood flow

rate of blood flow = P / R

Front 4

What is Blood Pressure?

Back 4

lateral hydrostatic P exerted by blood on unit area of vessel wall

BP is determined by COP, blood volume, and vascular resistance

higher in aorta than systemic arteries

Arterial BP:
Systolic:
-highest P recorded during ventricular systole
maximal work of heart
-N range = 100-140 mm Hg
Diastolic:
-lowest P at end of diastole
-affected by total peripheral R
-N range = 60-90 mm Hg
How to measure:
-stethoscope placed over brachial artery in antecubital fossa
-air pumped until P is above systolic P (no sound heard)
-P in cuff lowered slowly until artery becomes turbulent leading to kortokov sound, this first sound is systolic P
-when korotkov sound disappears = diastolic P

Front 5

What is Pulse pressure?

Back 5

difference between systolic and diastolic pressures (PP = SP - DP)

most important determinant is SV

decrease in capacitance = increase in pulse pressure

Front 6

What is the Mean Arterial Blood Pressure?

Back 6

MAP

average BP in arteries during the cardiac cycle

MAP = DP + (SP-DP)/3

N ratio SP:DP:PP = 3:2:1

CO = MAP/TPR

Front 7

What are the factors that affect peripheral resistance?

Back 7

R = L n / r^4

L = length of vessel; n = viscosity of blood; r = radius of vessel

Lumen size:
-decrease lumen of blood vessel = increase resistance to blood flow

Total blood vessel length:
-increase length = increase resistance (ex obesity)

Viscosity of blood:
-increase viscosity = increase resistance
-depends on hematocrit

Front 8

What is the Arterial Pulse?

Back 8

rhythmic stretch and recoil of arterial wall produced by rhythmic cardiac ejection

originates in aorta

velocity increases with age due to increasing rigidity of arteries

palpated on large arteries near body surface

Front 9

What is Venous Return and factors that ensure VR?

Back 9

volume of blood returning to right atrium

increase P right atrium --> decrease VR

when TPR decrease --> increase VR

Skeletal muscle pump:
-depend of presence of valves in veins

Respiratory pump:
-breathing movement
-decrease in intrathoracic P during inspiration (increase in intra-abdominal pressure) --> faciliation of VR from extrathoracic veins

Gravity:
-standing and sitting positions speeds up VR in regions above heart and lowers VR in regions below heart

Front 10

What is Microcirculation and Capillary Exchange?

Back 10

Microcirculation:
-adapted to exchange of water, nutrients, electrolytes, gases between blood and tissues
-slow linear blood flow (high cross-sectional area)
-thin vascular wall and proximity to tissue cells

Capillary exchange by:
Diffusion:
-low molecular weight substances
-intracellular pores (water-soluble)
-cell membrane of endothelial cells (lipid soluble)
-low permeability (BBB)

bulk flow:
-movement of solvent and solutes in same direction (down hydrostatic P gradient)
-filtration - water and solutes down pressure gradient from arterial end into interstitial fluid
-reabsorption - ISF into venous end of capillaries

endocytosis/pinocytosis:
-vesicular transport or transcytosis
-large lipid molecules (ex. insuline and Ab)

Front 11

What is the Starling Hypothesis of Transcapillary exchange?

Back 11

Starling forces:
1. Blood/capillary hydrostatic P (BHP):
-drives fluid out of capillary (filtration)

2. Interstitial fluid hydrostatic P (IFHP):
-opposes BHP and drives fluid into capillary (absorption) if positive, if negative - facilitates filtration

3. Blood Colloid osmotic (oncotic) P (BCOP):
-retains fluid and facilitates absorption of fluid in capillaries

4. Interstitial fluid osmotic P (IFOP):
-retains fluid in interstitial space, facilitates filtration. opposes PCOP

Front 12

What are the forces that favor filtration and reabsorption?

Back 12

Blood hydrostatic P:
-35 mm Hg at arterial end and 16 mm Hg at venous end

Interstitial fluid hydrostatic P:
-close to 0, varies from small positive to small negative values

Blood colloid osmotic P:
-26 mm Hg

Colloid osmotic P of interstitial fluid:
-1 mm Hg, small amount of proteins present, proteins are sent to lymph and eventually returned to blood

Front 13

What is the Net Filtration P (NFP)?

Back 13

NFP = BHP + IFOP - (BCOP+IFHP)

pressure that promotes filtration - pressure that promotes reabsorption

at arterial end:
-net outward pressure of 10 mm Hg, fluid moves out of capillary

venous end:
-net INWARD pressure of 9 mm Hg, fluid moves into capillary (reabsorption)

Front 14

What is Edema?

Back 14

presence of excess fluid

causes:
excessive filtration of fluid:
-increase capillary hydrostatic pressure
-venous obstruction (local - embolism or thrombus, general - right sided heart failure)
-lowered plasma colloid P (liver diseases (cirrhosis, hepatitis), loss or proteins in urine (nephrotic syndrome)
-increase capillary permeability

Decreased reabsorption from interstitial compartment:
-increase ISF colloid osmotic P (myxedema)
-blocked lymphatic drainage