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physiology module 2 > Microcirculation > Flashcards

Microcirculation Flashcards

(54 cards)

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1
Q

Describe capillary walls and their permeability.

A

Capillary walls are one cell thick of endothelium about 42mm thick .
Small and lipophilic substances can pass thru cells . The walls have small gaps called clefts that let other small substances pass through . Any other substance that must diffuse into / out of capillary use vesicles called Caveolae .Different capillaries have different permeabilities based on needs / brain , liver, GI , kidney

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2
Q

Microcirculation

A

Over 10 billion capillaries with surface area of ~500-700 m2
Transport of nutrients to the tissues
Removal of cell waste
Very thin walls
Controlled by arterioles in each tissue along with precapillary sphincters
Local control

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3
Q

Capillary Walls

A

One cell thick endothelium
Basement membrane
~0.5 μm total thickness
Contains pores
Intercellular cleft
Caveolae

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4
Q

Brain

A

Tight junctions – continuous capillaries

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5
Q

Liver

A

Large clefts - sinusoids

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6
Q

GI tract

A

Clefts smaller than liver, but still large

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7
Q

Kidney glomeruli

A

Small oval windows – fenestrated capillaries

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8
Q

Vasomotion

A

Intermittent flow of blood through capillaries due to regulation via precapillary sphincters and metarterioles or small arterioles
Due to O2 levels of tissue

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9
Q

Bulk Flow in Systemic Capillaries

A

Transcapillary movement is by bulk flow diffusion
Diffusion is the main method of exchange between plasma and interstitial fluid (fluid in interstitium, found between cells; gel consistency)
Lipid soluble substances pass through cell membrane
Lipid insoluble pass through intercellular clefts
Enhanced by concentration differences

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10
Q

Hydrostatic Pressure

A

pressure fluid puts on walls

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11
Q

Colloid Osmotic Pressure

A

pressure solutes put on water, drawing water toward solutes

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12
Q

Capillary Hydrostatic Pressure (Pc)

A

Tends to push fluid out of capillaries

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13
Q

Interstitial Fluid Hydrostatic Pressure (Pif)

A

Would tend to pull fluid into capillaries, BUT pulls fluid out of capillaries due to lymphatic drainage

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14
Q

Capillary/Plasma Osmotic Pressure (πp)

A

Tends to pull water into capillaries by osmosis
Due to presence of proteins (albumin/globulins) in plasma

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15
Q

Interstitial Fluid Osmotic Pressure (πif)

A

Tends to pull water out of capillaries by osmosis
Due to proteins in interstitium (very low)

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16
Q

Net Filtration Pressure

A

NFP = outward pressures – inward pressures
NFP = (Pc + πif) – (πp + Pif)

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17
Q

Bulk Flow in Systemic Capillaries

A

90% of filtered fluid is reabsorbed at venous end
10% is collected by lymphatic system

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18
Q

Lymphatic System

A

Returns fluid and proteins to the blood
(2-3L/day)
Fluid in lymphatic vessels is called lymph
Prevents edema
Absorbs lipids from GI tract
Role in immune system

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19
Q

lymph flow

A

aided by smooth muscle and the skeletal muscle pump.

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20
Q

Describe the lymphatic vessel system & its role in preventing fluid accumulation in the interstitial space.

A

90% of filtered fluid is reabsorbed at the venous end of the capillary .
The remaining 10% is collected by lymphatic capillaries as lymph .
Lymph collecting into the thoracic cavity where , after it has been filtered by lymph nodes , empties back into the veins to contribute to blood volume . lymph flow is aided by smooth muscle and the skeletal muscle pump.

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21
Q

Local Control of Blood Flow

A

Each tissue controls its own blood flow
Based on tissue needs
Delivery of O2
Delivery of other nutrients: glucose, amino acids, fatty acids
Removal of CO2 and H+
Maintenance of ion concentrations
Transport of hormones and other substances
Flow proportional to metabolic needs

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22
Q

Mechanisms of Blood Flow Control

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A

Acute Control (seconds)
Vasodilation/vasoconstriction
Arterioles, metarterioles, precapillary sphincters
Long-term Control (days, weeks, months)
Increase/decrease in size/number of blood vessels

23
Q

Acute Control of Local Blood Flow

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A

Increases in metabolism increase flow
Decreases in O2 increase flow

Two theories
Vasodilator theory
O2 demand theory

24
Q

Vasodilator Theory

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A

Metabolism produces vasodilator substances
Adenosine
Adenosine phosphate compounds
Histamine
CO2
K+
H+
Metabolism produces vasodilator substances
Substances reduce resistance
Flow increases

25
O2 Demand Theory
O2 decrease in tissues leads to relaxation of smooth muscle Because O2 is needed for contraction Relaxation reduces resistance Flow increases
26
Reactive Hyperemia
Increase in flow in response to blocked flow
27
Active Hyperemia
Increase in flow in response to increased metabolism
28
Explain the factors that control local blood flow
Each tissue controls its own blood flow , directly proportional to metabolic needs . During high metabolic activity of a certain tissue ex. Skeletal muscle, GI trait) , flow will increase in that area and decrease in lower energy areas. 2 theories on how this is accomplished 1. Vasodilator theory : high metabolism produces Vasodilating substances (CO2 , H+) that reduce resistance and increase flow 2. O2 demand theory : low O2 delivery or high metabolism causes less contraction , which reduces resistance and increases flow Reactive hyperemia : increase in flow after removal of blocked flow Active hyperemia : increase flow in response to decrease in metabolism
29
List several substances involved in local and circulating metabolic control of vascular tone and describe how they affect vascular tone.
Vascular tone can be controlled humorally through vasodilators like Bradykinin , histamine, ANP, Serotonin and prostaglandins and vasoconstrictors like NE , Epi , angiotensin II , and ADH. It can also be controlled by Vasodilating ions like K+ , Mg" , H+ and Vasoconstricting ions like Ca++.
30
Two Theories of Autoregulation
Metabolic theory Myogenic theory
31
Myogenic Theory of Autoregulation
Sudden stretch of small vessels leads to contraction Theory: Stretch of smooth muscles opens mechanically-gated Ca++ channels Increase in Ca++ in vascular smooth muscle leads to increased contraction
32
Law of LaPlace
Tension =P ✗ r Increase pressure - increase tension and decrease radius Decrease Pressure- decrease tension and increase radius
33
Describe the myogenic response of blood vessels.
The myogenic theory of response is that in a sudden stretch in small vessels , a contraction of the vessel will occur. This is due to the opening of Mechanically Ca++ Channels in vascular smooth muscle. This mechanism is the default, which can be overridden . The law of Laplace = Tension =P ✗ r ← allows for constant tension
34
Explain long-term control of blood flow.
Longterm control is more effective than short term and is due to changes in vascularization. Angiogenesis requires vascular growth factors , which are proteins. These can also be inhibited.
35
Acute Flow in Specialized Tissues (Kidneys)
Tubuloglomerular Feedback (in Urinary)
36
Brain
Also regulated by CO2/H+
37
Skin
Tied to body temperature regulation
38
Vasodilators
NO Released from endothelial cells in response to shear stress (important in larger vessels) Half life of ~6 sec Activates guanylate cyclase, which converts GTP to cGMP, which activates PKG, causing relaxation
39
Vasoconstrictors
Endothelin Released in response to vessel injury Prevents blood loss
40
Autoregulation of Blood Flow
Long term regulation is more effective than short term Long term changes are due to changes in vascularization Angiogenesis – formation of new vessels In response to O2 demand (maximal, not average) Requires vascular growth factors VEGF – vascular endothelial growth factor FGF – fibroblast grown factor PDGF – platelet-derived growth factor Angiogenin Inhibition of vascularization Angiostatin Endostatin
41
Long term regulation
is more effective than short term
42
Long term changes
are due to changes in vascularization
43
Angiogenesis
formation of new vessels In response to O2 demand (maximal, not average) Requires vascular growth factors VEGF – vascular endothelial growth factor FGF – fibroblast grown factor PDGF – platelet-derived growth factor Angiogenin
44
Inhibition of vascularization
Angiostatin Endostatin
45
Humoral Control of Circulation (Vasolidators)
Bradykinin Inflammation Histamine Tissue damage/inflammation Atrial naturetic peptide High blood volume Serotonin Prostaglandins
46
Vasolidators (Bradykinin)
Inflamation
47
Vasolidators (Histamine)
Tissue damage/inflammation
48
Vasolidators (Atrial naturetic peptide)
High blood volume
49
Humoral Control of Circulation (Vasoconstrictors)
NE (and Epi) Sympathetic stimulation Angiotensin II To increase TPR ADH To increase BP
50
Vasoconstrictors (NE and Epi)
Sympathetic stimulation
51
Vasoconstrictors (Angiotensin II)
To increase TPR
52
Vasoconstrictors (ADH)
To increase BP
53
Control by Ions & Other Factors (Vasodilators)
K+ Mg++ H+ Acetate & citrate (mild) CO2 (esp. in brain)
54
Control by Ions & Other Factors (Vasoconstrictors )
Ca++

physiology module 2 (4 decks)

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