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What is the length and diameter of capillaries?
- Length: 1 mm
- Diameter: 5-10 um
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What are the properties of capillaries in regards to vessel area and velocity of blood?
- Greatest cross-sectional area
- Slowest velocity of blood flow - enhances exchange
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What are the 2 types of capillaries? List one property for each.
Continuous Capillaries - small gaps btwn endothelial cells that allow small water molecules to move through
Fenestrated Capillaries - large gaps btwn endothelial cells (pores) that allow proteins and sometimes blood cells to move through
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What type of capillary is this?
Continuous
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What type of capillary is this?
Fenestrated
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What are Metarterioles and their function?
- Intermediate btwn arteriolesand capillaries
- Directly connect arteriole to venule (bypass capillary)
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What are precapillary sphincters?
Rings of smooth muscle that surround capillaries on the arteriole end
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What do precapillary sphincters respond to?
- Local factors only
- Metabolites cause relaxation
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- 1. Arteriole
- 2. Precapillary Sphincter
- 3. Venule
- 4. Metarteriole
- 5. Rings of smooth muscle
- 6. Capillary
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What are the 3 exchange mechanisms across capillary walls?
- Diffusion
- Transcytosis
- Mediated transport
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What is bulk flow and what is it's purpose?
- Movement of water + solutes
- Distrubute ECF
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What drives bulk flow and what are the 2 forms of movement?
Pressure Gradient
- Filtration - movement out of capillary into interstitial space
- Absorption - movement into capillary from interstitial space
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What are the 2 types of pressure that act as forces for bulk flow?
- Hydrostatic - force due to fluid
- Osmotic - force exerted on water by proteins (non-permeating solutes)
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What is oncotic pressure?
Osmotic force of proteins
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What are the capillary hydrostatic pressures? What does it favour?
- Arteriole end = 39 mm Hg
- Venous end = 16 mm Hg
Filtration
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What is the insterstitial hydrostatic pressure? What does it favour?
0-1 mm Hg
Reabsorption
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What are the hydrostatic pressure gradients and what do they favour?
- Arteriole end: 38-1 = 37 mm Hg, filtration
- Venous end: 16-1 = 15 mm Hg, reabsorption
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What is capillary oncotic osmotic pressure?
- 25 mm Hg
- Favors reabsorption
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What is instertitial fluid oncotic pressure?
- 0-1 mm Hg
- Favours filtration
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What is the osmotic pressure gradient? What does it favour?
25 - 0 = 25 mm Hg
Favours reabsorption
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What is the net filtration pressure (NFP) of arteriole and venouse ends?
Arteriole (38+0) - (25+1) = 12 mm Hg, filtration
Venous (16+0) -(25+1) = -10 mm Hg, absorption
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What is the net filtration per day?
3L/day
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What factors can affect filtration and absorption across capillaries?
- Standing on feet - increases hydrostatic pressure
- Injuries - damaged capillaries leak fluid/proteins, histamine increases capillary permeability
- Liver disease - decrease in plasma proteins
- Kidney disease - increase blood volume/pressure, decrease plasma proteins
- Heart disease - pulmonary edema
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What are some properties of venules?
- Smaller than arterioles
- Connect capillaries to veins
- Little smooth muscle in walls
- Some exchange between blood and interstitial fluid
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What are some properties of veins?
- Large diameter
- Thin walls
- Valves = unidirection blood flow (not in central veins)
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What is meant by "veins are a volume reservoir"?
Veins hold a large volume (60% of blood at rest) with small pressure change due to high compliance
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What do skeletal muscle pumps do?
Contract - squeeze veins = increased pressure, blood moves toward heart, valves ensure no back flow
Relax - blood flows into veins btwn muscles
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How does the respiratory pump affect blood flow?
Inspiration - decreases pressure in thoracic cavity, increases P in abdominal cavity (creates gradient that favors blood mvmt to thoracic cavity)
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What is the long-term regulation of blood pressure regulated through?
Blood volume
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What is the relationship between blood volume and venous pressure?
Proportional
- Increase in BV = increase in VP
- Decrease in BV = decrease in VP
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What is venomotor tone?
Smooth muscle tension in the veins
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What is an increase in venomotor tone cause by?
Contraction of smooth muscle in wall of vein
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What does venomotor tone do (increases/decreases...)?
- Increases central venous pressure
- Decreases venous compliance
- Increases venous return
- Increases stroke volume
- Increases cardiac output
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What is the smooth muscle wall of veins innervated by?
Sympathetic nervous system - alpha adrenergic receptors, norepinephrine
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What is part of the lymphatic system?
- Vessels, nodes, organs
- Vessels involved in returning excess filtrate to circulation
- Vessels from open system starting at capillaries
- Part of the immune system
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What are some propterties of lymph movements?
- Moves from capillaries to veins
- Lymph veins drain into thoracic duct which empties into R atrium
- Movement through lymphatic veins is same as regular veins
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What do lymph nodes do?
- Contain macrophages
- Filter lymph flowing through the node
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