Week 4- Cardiovascular Physiology Flashcards
1
Q
What is the microcirculation?
A
Vessels from the first-order arteriole to the first-order venule
2
Q
What happens in the microcirculation?
A
This is the site of nutritional exchange
3
Q
What/where can the microcirculation serve non-nutritional functions?
A
- Glomeruli of the kidneys (filtration)
- Skin (temperature regulation
- Signaling and host defense
4
Q
What do precapillary sphincters do?
A
- If metabolic demands are greater further down the line, the sphincters contract
- This creates a high pressure spot, pushing the blood away
5
Q
What is another name for arteriold?
A
Resistance vessels
6
Q
How innervated are arterioles?
A
Highly innervated
7
Q
Structure of the capillary wall
A
- Endothelial cells (stacks)
- Basement membrane
8
Q
What holds the endothelial cells together?
A
Tight junctions
9
Q
What is made possible by the range of permeability in the tight junctions?
A
- If they are very tight, very impermeable
- If they are more loose, there is room for cells (think inflammatory response, WBC)
10
Q
Types of capillaries
A
- Continuous
- Fenestrated
- Sinusoidal
11
Q
Which type of capillary is most predominant?
A
Continuous
12
Q
Where might continuous capillaries be found?
A
- Skeletal muscle
- Blood-brain barrier
13
Q
How permeable are continuous functions?
A
Highly impermeable
14
Q
Where might fenestrated capillaries be found?
A
- Small intestine
- Kidney
15
Q
What are fenestrae?
A
Pores that allow transport of substances from the inside to the outside
16
Q
Why are the fenestrated capillaries more permeable?
A
They are located in places like the small intestine where absorption of nutrients is very important
17
Q
Where might sinusoidal capillaries be found?
A
Liver
18
Q
What is another name for sinusoidal capillaries?
A
Discontinuous capillary
19
Q
What component of capillary structure is missing from sinusoidal capillaries?
A
The basement membrane
20
Q
What makes sinusoidal capillaries so leaky?
A
The large fenestrations and gaps between endothelial cells
21
Q
What kind of substances pass directly through the capillary membrane?
A
Lipid-soluble substances like O2 and CO2
22
Q
What do lipid-insoluble substances pass through?
A
Intercellular clefts
23
Q
Ultimately, what determines the permeability of the membrane?
A
- Diameter of the cleft (larger = easier)
- Size of the molecule (smaller = easier)
24
Q
In skeletal muscle, what percentage of capillaries are perfused?
A
~20%, more become active during exercise
25
What are the implications for delivery and diffusion of substances when many capillaries are closed?
Less efficient delivery, since a single capillary is responsible for providing nutrients for more tissue
26
What determines PO2?
The amount of O2 in the plasma
27
What factors impact the PO2 in the capillary?
- [O2]
- O2 content of blood
- Capillary blood flow (F)
- Capillary radius
- Radius of tissue cylinder
- O2 consumption of surrounding tissues
- Axial distance (x) along the capillary
28
What does PO2 determine?
Rate of diffusion
29
Interstitium
Space between cells
30
Interstitial fluid
Fluid filling the interstitum
31
What major types of solid structures are in the interstitum?
- Collagen fibers
| - Proteoglycan filaments
32
What are proteoglycan filaments?
Coiled molecules composed of hyaluronic acid
33
What makes up most of the fluid in the interstitum?
- Gel, fluid proteoglycan mixtures
| - Little free fluid under normal conditions
34
What are Starling forces?
Forces governing the passive exchange of fluids across a semipermeable membrane
35
Compartments at play with cardiovascular system Starling forces
- Capillary
| - Interstitial space
36
Types of forces with the Starling forces
- Hydrostatic forces
| - Colloid osmotic forces
37
What are hydrostatic forces
Pressure of the fluid in either the capillary or the interstitial fluid
38
What are colloid osmotic forces
Osmotic forces produced by molecules such as proteins that generate osmotic pressure
39
What are the capillary Starling forces?
- Capillary pressure (Pc)
| - Plasma colloid osmotic pressure (IIp)
40
What direction does the capillary pressure go?
Out of the capillary against the capillary wall
41
What direction does the plasma colloid osmotic pressure go?
Into the capillary (water flows in)
42
What are the interstitial fluid Starling forces?
- Interstitial fluid pressure (Pif)
| - Interstitial fluid colloid osmotic pressure (IIif)
43
What direction does the interstitial fluid pressure go?
Into the capillary against the capillary wall
44
What direction does the interstitial fluid colloid osmotic pressure go?
Out of the capillary (water flows out)
45
What is the equation for net filtration?
NFP = Pc - Pif - IIp + IIif
46
What does a positive NFP indicate?
Water out of the capillary into the interstitial space (filtration)
47
What does a negative NFP indicate?
Water into the capillary from the interstitial space (reabsorption)
48
Which end of the capillary will have a positive NFP?
Arterial
49
Which end of the capillary will have a negative NFP?
Venous
50
Between the capillary and interstitial forces, which one will change most from the arterial to the venous end?
Capillary forces (Pc and IIp)
51
Classic Starling Model
The four forces acting together to filter and absorb fluids
52
How are the predictions different in the revised Starling model?
Absorption is much less
53
Osmotic asymmetry
The amount of fluid filtered does not equal the amount of fluid absorbed
54
What is the normal capillary hydrostatic pressure?
17 mmHg
55
What is the interstitial fluid pressure in most tissues?
- 3 mmHg (mostly loose subcutaneous tissue)
56
What interstitial fluid pressures do encapsulated have?
5-10 mmHg
57
What kind of pressure do natural cavities of the body have?
Negative
58
What cavities have this negative pressure?
- Intrapleural space
- Joint synovial space
- Epidural space
59
Pressure of intrapleural space
-8 mmHg
60
Pressure of joint synovial space
-4 to -6 mmHg
61
Pressure of epidural space
-4 to -6 mmHg
62
What purpose does the negative interstitial fluid pressure serve?
- Caused by pumping of lymphatic system
| - Sucks excess fluid into the lymphatic system
63
What causes the colloid osmotic pressure?
Presence of large proteins
64
What proteins cause colloid osmotic pressure?
- Albumin
| - Globulins
65
What percentage of total colloid pressure comes from albumin?
80%
66
What percentage of total colloid pressure comes from globulin?
20%
67
What is the average protein concentration and colloid pressure?
- 3g/dl
| - 8 mmHg
68
Edema
Excess fluid accumulation
69
Why does edema occur?
Abnormal Starling forces
70
What kind of edema could abnormal hydrostatic forces cause?
- Pulmonary edema
| - Generalized peripheral edema
71
What will cause pulmonary edema?
Left-sided heart failure
72
How is pulmonary edema caused?
- Left-sided HF may cause increased Pc in pulmonary capillaries
- Arises from left atrium and ventricle not pumping blood into systemic circuit well enough
73
What will cause generalized peripheral edema?
Right-sided heart failure
74
How is generalized peripheral edema caused?
- Right-side HF may cause increased Pc in systemic veins
| - Arises from right atrium and ventricle not pumping blood into the pulmonary circuit well enough
75
What happens with nephrotic syndrome?
Proteins are lost in the urine
76
What kind of edema can nephrotic syndrome cause?
Generalized peripheral edema
77
How does nephrotic syndrome cause edema?
Decreased IIp causes decreased ability to retain fluids in the capillaries
78
What happens during pregnancy to cause edema?
- Synthesis of plasma proteins does not keep up with increase in plasma volume
- Results in decreased IIp and generalized peripheral edema
79
How can inflammation in capillary walls cause edema?
- Release vasodilators and cytokines which cause interendothelial clefts to widen
- Results inn tissue swelling
80
How do head injuries result in edema?
- Cause cerebral edema
| - Breakdown tight junctions in cerebral vessels
81
What about impaired lymphatics causes edema?
- Damaged lymph nodes may reduce lymphatic drainage
| - Lead to local edema upstream from the affected nodes
82
What is the lymphatic system?
- An accessory route where fluids and protein can flow from interstitial spaces to the blood
- Important for immunity
83
What does the lymphatic system prevent?
Edema
84
What is lymph is derived from?
Interstitial fluid that flows into the lymphatics
85
What is the connection between the lymphatic system and the GI tract?
Absorption of nutrients from GI tract
86
What happens to fluid that does not re-enter the capillary at the venous end?
- Brought back into circulation via lymphatic vessels
| - ~1/10 of fluid
87
How much lymph circulates daily?
2-3 L
88
What is the structure of initial lymphatics?
Endothelial cells anchored to surrounding connective tissue with anchoring filaments
89
What do overlapping endothelial cells form?
Valves preventing backflow
90
What is the effect of pressure from the interstitial fluid (Pif)?
As P(if) increases, lymph flow also increases to a certain point
91
At what point does increases in P(if) fail to drive greater lymph flow?
~2 mmHg
92
Why does the increase in pressure fail to create more lymph flow?
Excessive pressure actually compresses the lymph vessels
93
Phases of lymph flow
- Expansion phase
| - Compression phase
94
What happens during the expansion phase?
- Hydrostatic pressure in the interstitial fluid exceeds what's in the initial lymphatic
- Microvalves open and fluid enters
95
What happens during the compression phase?
- Hydrostatic pressure inside the initial lymphatic increases, which closes the microvalves
- Increasing pressure opens the secondary lymph valves, fluid flows downstream
96
In lymphatic vessels, where is smooth muscle present?
After the secondary lymph valves
97
What causes lymph to flow?
- Lymphatic pump
| - External pumps
98
How does the lymphatic pump function?
Lymph vessels stretch --> smooth muscle contracts
99
How much pressure can the lymphatic pump inn large lymph vessels?
50-100 mmHg
100
What are the external pumps for the lymphatic system?
- Muscles
- Movement
- Adjacent arterial pulsations
- Compression of tissues by external objects
101
How much does lymph flow increase during exercise?
10-30x
102
Key roles of lymphatic system
- Controls concentrations of proteins in the ISF (increased IIif can cause edema)
- Controls volume of ISF
- Controls ISF pressure (Pif)
