26 Microcirculation

Question 1

At the entrance of capillaries, smooth muscle
fibers are arranged to form _________ which are not innervated.

The venous ends of capillaries unite to form
__________ with no smooth muscle in the
wall, which are high permeable to water and
important in the development of inflammation.

Answer 1

pre-capillary sphincters

pericytic venules

Question 2

Blood flow is of arterioles that is regulated by smooth muscle contraction increased by
_________ stimulation by ___ receptors.

Answer 2

sympathetic

a1

Question 3

Are capillaries innervated?

Answer 3

No

Question 4

As pre-capillary sphincters are not innervated, how are they regulated?

Answer 4

They are relaxed by local metabolite products such as adenosine or nitric oxide.

Question 5

What is the equation to the Net filtration pressure due to fluid movement across capillary membrane? (Starling’s principle)

What does it mean when the value is negative?

Answer 5

(Hydrostatic pressure in capillary + oncotic pressure in interstitial fluid) - (hydrostatic pressure in interstitial fluid + oncotic pressure in vessel)

Net absorption instead of filtration

Question 6

Fluid filtered by microcirculation (~8L/day) is returned to bloodstream by the ________ .

Answer 6

lymphatic system

Question 7

The wall of lymphatic vessels contains _________.

Answer 7

smooth muscle.
Lymph is propelled by smooth muscle contraction and finally to lymphatic nodes, where bacteria and other foreign materials are removed by phagocytes.

Question 8

What is the impact of orthostasis on fluid balance?

Answer 8

= standing position.

Increases capillary pressure below heart level and raises filtration rate into tissues

Question 9

Exercise increases the filtration rate and causes
plasma volume reduction due to?

(3 reasons)

Answer 9

1. Local dilation of resistance arteries by metabolic dilators to raise hydrostatic pressure
2. Increased interstitial osmolarity due to accumulation of small solutes such as K+ and lactic acid (increased interstitial osmotic pressure)
3. Increases intracellular osmolarity during skeletal muscle contraction due to breakdown of creatinine phosphate and formation of lactate, causing muscle swelling

Question 10

Inflammation can cause ______ in any tissue. It is not usually detectable until the interstitial volume has _______ , which corresponds to ~10% swelling
of the limb.

Answer 10

edema;

doubled

Question 11

What are the impacts of peripheral edema?

Answer 11

1. impairs cell communication
2. increases diffusion distance
3. deformity
4. skin ulceration and blistering

Question 12

Pulmonary edema is caused by __________, which
raises __________ pressure and __________ pressure.

The lung of patients with pulmonary edema is
difficult to inflate and therefore causes _____.

Answer 12

left ventricular failure
left ventricular filling;
pulmonary venous;

dyspnea (difficulty
in breathing)

Question 13

What are the 5 causes of edema?

Answer 13

1. High arterial blood pressure
2. Obstruction of lymphatic drainage
3. Decreased plasma protein concentration
4. Leakage of plasma proteins into interstitial fluid
5. Venous obstruction

Question 14

When does high-protein edema = inflammatory swelling occur?

Answer 14

Increased endothelial
permeability to water and proteins.

Due to increased transcellular gaps in vascular endothelium.

Question 15

_________ can evoke endothelial intracellular
Ca2+ levels to trigger production of NO, loosening
gap junctions letting plasma proteins to leak out.

Answer 15

Inflammatory mediators like histamine and thrombin

Question 16

How can congestive heart failure cause edema? (2 ways and 2 types of edema)

Answer 16

Reduced CO causes an
1. increase in pulmonary pressure > pulmonary edema

2. increase in central venous pressure > peripheral edema

(why decrease CO will increase CVP?

A decrease in cardiac output either due to decreased heart rate or stroke volume (e.g., in ventricular failure) results in blood backing up into the venous circulation (increased venous volume) as less blood is pumped into the arterial circulation. The resultant increase in thoracic blood volume increases CVP. )

Question 17

Why would renal disease cause edema?

Answer 17

the ability to excrete salt
in the urine is limited.

amount of salt in the body increases, which causes
the patient to retain water and develop edema.