7 - Microcirculation

Question 1

What are the features of the pressure in the circulation?

Answer 1

• mostly stays the same in arteries
• only changes when reaches arterioles
• arterioles: major resistance vessels of circulation (drop of BP greatest)

Question 2

What is elephantiasis?

Answer 2

parasitic blockage of lymph nodes

Question 3

What are the labels of the lymphatic system?

Answer 3

1. blood capillary
2. arteriole
3. lymphatic endothelium
4. anchoring filament
5. interstitial fluid
6. opening
7. tissue cell
8. lymphatic capillary

Question 4

What is the difference between vasodilation and vasoconstriction?

Answer 4

• vasoconstriction: decreased radius and flow, increased resistance (contraction)
• vasodilation: increased radius and flow, decreased resistance (relaxation)

Question 5

What is the pressure gradient?

Answer 5

• pressure a - pressure b
• difference in pressures arriving and leaving capillaries
• generally MAP as venous pressure so low its negligible

Question 6

What is blood flow rate?

Answer 6

• volume of blood passing through vessel per unit time
• flow rate (Q) = pressure gradient (P) / resistance (R)
• increased pressure gradient increases resistance

Question 7

What are the 3 types of capillaries and their features?

Answer 7

• continuous: small water-soluble molecules diffuse through, lipid soluble molecules diffuse across cells
• fenestrated: allow for larger molecules to diffuse through
• discontinuous: allow for alot of space for wasy access

Question 8

What is the blood brain barrier?

Answer 8

• continuous structure with tight junctions (not gap junctions so no space between capillary cells)
• gives brain tighter controls over substances entering

Question 9

What is capillary exchange?

Answer 9

delivery of metabolic substrates to cells of organism

Question 10

What are the general features of capillaries?

Answer 10

• single endothelial cell
• diameter big enough for one cell (7μm)
• extensive branching
• 1μm cell width
• pre-capillary sphincters allow for certain capillaries to be shut down
• highly metabolically active tissues have denser capillary networks

Question 11

What is Fick’s law in relation to capillary density?

Answer 11

• minimises diffusion distance
• maximises surface area and time for diffusion

Question 12

Under what conditions does ultrafiltration and reabsorption occur?

Answer 12

• ultrafiltration: pressure inside capillary > in interstital fluid
• reabsorption: inward driving pressures > outward pressures across capillary

Question 13

How does fluid move in the capillary network?

Answer 13

• bulk flow: volume of protein-free plasma filters out of capillary, mixes with surruonding interstitial fluid and is reabsorbed
• hydrostatic (pushing) force: higher at arterial end - fluids leave blood vessels
• oncotic (pulling) force: constant throughout length - counteracts hydrostatic force

Question 14

How do the radii of arterioles vary?

Answer 14

• local intrinsic control: match blood flow to metabolic needs of specific tissues
• extrinsic control: help regulate arterial BP

Question 15

How does matching blood flow to metabolic needs of tissue operate in adjusting arterial radii?

Answer 15

• chemically driven (active hyperaemia): increased metabolites/O2 usage leads to vasodilation (skeletal muscle arterioles)
• physically driven (autoregulation): decreased blood temperature/increased stretch leads to vasoconstriction (small intestine arterioles)

Question 16

How does regulating arterial blood pressure operate in adjusting arterial radii?

Answer 16

• neural: cardiovascular control centre in medulla leds to vasoconstriction
• hormonal: vasopressin, AGTii and adrenaline lead to vasoconstriction

Question 17

What is the lymphatic system and its features?

Answer 17

• large filled water channel that reabsorbs excess interstitial fluid (interwoven with blood vessels)
• blind-ended capillaries with single endothelial cell layer
• no pump to induce flow
• drainage into right lymphatic duct (thoracic duct) and right and left subclavian veins
• lymph nodes have defense mechanisms (immune detection)