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physiology module 2 > Microcirculation > Flashcards

Microcirculation Flashcards

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

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

A

Increases in metabolism increase flow
Decreases in O2 increase flow

Two theories
Vasodilator theory
O2 demand theory

24
Q

Vasodilator Theory

A

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

25
Q

O2 Demand Theory

A

O2 decrease in tissues leads to relaxation of smooth muscle
Because O2 is needed for contraction
Relaxation reduces resistance
Flow increases

26
Q

Reactive Hyperemia

A

Increase in flow in response to blocked flow

27
Q

Active Hyperemia

A

Increase in flow in response to increased metabolism

28
Q

Explain the factors that control local blood flow

A

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
Q

List several substances involved in local and circulating metabolic control of vascular tone and describe how they affect vascular tone.

A

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
Q

Two Theories of Autoregulation

A

Metabolic theory
Myogenic theory

31
Q

Myogenic Theory of Autoregulation

A

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
Q

Law of LaPlace

A

Tension =P ✗ r
Increase pressure - increase tension and decrease radius
Decrease Pressure- decrease tension and increase radius

33
Q

Describe the myogenic response of blood vessels.

A

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
Q

Explain long-term control of blood flow.

A

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
Q

Acute Flow in Specialized Tissues
(Kidneys)

A

Tubuloglomerular Feedback (in Urinary)

36
Q

Brain

A

Also regulated by CO2/H+

37
Q

Skin

A

Tied to body temperature regulation

38
Q

Vasodilators

A

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
Q

Vasoconstrictors

A

Endothelin
Released in response to vessel injury
Prevents blood loss

40
Q

Autoregulation of Blood Flow

A

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
Q

Long term regulation

A

is more effective than short term

42
Q

Long term changes

A

are due to changes in vascularization

43
Q

Angiogenesis

A

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
Q

Inhibition of vascularization

A

Angiostatin
Endostatin

45
Q

Humoral Control of Circulation (Vasolidators)

A

Bradykinin
Inflammation
Histamine
Tissue damage/inflammation
Atrial naturetic peptide
High blood volume
Serotonin
Prostaglandins

46
Q

Vasolidators (Bradykinin)

A

Inflamation

47
Q

Vasolidators (Histamine)

A

Tissue damage/inflammation

48
Q

Vasolidators (Atrial naturetic peptide)

A

High blood volume

49
Q

Humoral Control of Circulation (Vasoconstrictors)

A

NE (and Epi)
Sympathetic stimulation
Angiotensin II
To increase TPR
ADH
To increase BP

50
Q

Vasoconstrictors (NE and Epi)

A

Sympathetic stimulation

51
Q

Vasoconstrictors (Angiotensin II)

A

To increase TPR

52
Q

Vasoconstrictors (ADH)

A

To increase BP

53
Q

Control by Ions & Other Factors (Vasodilators)

A

K+
Mg++
H+
Acetate & citrate (mild)
CO2 (esp. in brain)

54
Q

Control by Ions & Other Factors (Vasoconstrictors
)

A

Ca++

physiology module 2 (4 decks)

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