AN SC 310 - 17
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What is the length and diameter of capillaries?
- Length: 1 mm
- Diameter: 5-10 um
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
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
What type of capillary is this?
What type of capillary is this?
What are Metarterioles and their function?
- Intermediate btwn arteriolesand capillaries
- Directly connect arteriole to venule (bypass capillary)
What are precapillary sphincters?
Rings of smooth muscle that surround capillaries on the arteriole end
What do precapillary sphincters respond to?
- Local factors only
- Metabolites cause relaxation
- 1. Arteriole
- 2. Precapillary Sphincter
- 3. Venule
- 4. Metarteriole
- 5. Rings of smooth muscle
- 6. Capillary
What are the 3 exchange mechanisms across capillary walls?
- Mediated transport
What is bulk flow and what is it's purpose?
- Movement of water + solutes
- Distrubute ECF
What drives bulk flow and what are the 2 forms of movement?
- Filtration - movement out of capillary into interstitial space
- Absorption - movement into capillary from interstitial space
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)
What is oncotic pressure?
Osmotic force of proteins
What are the capillary hydrostatic pressures? What does it favour?
- Arteriole end = 39 mm Hg
- Venous end = 16 mm Hg
What is the insterstitial hydrostatic pressure? What does it favour?
0-1 mm Hg
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
What is capillary oncotic osmotic pressure?
- 25 mm Hg
- Favors reabsorption
What is instertitial fluid oncotic pressure?
- 0-1 mm Hg
- Favours filtration
What is the osmotic pressure gradient? What does it favour?
25 - 0 = 25 mm Hg
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
What is the net filtration per day?
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
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
What are some properties of veins?
- Large diameter
- Thin walls
- Valves = unidirection blood flow (not in central veins)
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
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
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)
What is the long-term regulation of blood pressure regulated through?
What is the relationship between blood volume and venous pressure?
- Increase in BV = increase in VP
- Decrease in BV = decrease in VP
What is venomotor tone?
Smooth muscle tension in the veins
What is an increase in venomotor tone cause by?
Contraction of smooth muscle in wall of vein
What does venomotor tone do (increases/decreases...)?
- Increases central venous pressure
- Decreases venous compliance
- Increases venous return
- Increases stroke volume
- Increases cardiac output
What is the smooth muscle wall of veins innervated by?
Sympathetic nervous system - alpha adrenergic receptors, norepinephrine
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
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
What do lymph nodes do?
- Contain macrophages
- Filter lymph flowing through the node
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