Questions and Answers
What is the primary mechanism of gas and nutrient exchange in capillaries?
Which pressure is responsible for pushing fluid out of the capillary at the arterial end?
What is the value of the hydrostatic pressure of the interstitial fluid (HPIF)?
What is the pressure differential at the arterial end of the capillary?
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What is the primary function of the lymphatic system?
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Which component of the lymphatic system is responsible for 'cleansing' the lymph?
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What would occur if the lymphatic system failed to return excess fluid and proteins to the vascular system?
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What is the net fluid loss per minute in the given example?
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What is the main reason why fluid enters the lymphatic capillaries?
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Where are lacteals, specialized lymphatic capillaries, located?
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What is the purpose of the valves in the lymphatic vessels?
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What is the name of the enlarged sac that collects lymph from the lumbar trunks and intestinal trunk?
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What is the primary mechanism of lymph transport?
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What is the name of the type of lymph that is whitish in color and absorbed from the intestinal mucosa?
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Where do the right and left lymphatic ducts empty into the venous system?
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What type of cells manage the immune response and directly attack antigens?
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Study Notes
Capillary Dynamics
- Exchange of gases and nutrients occurs through diffusion, accompanied by bulk fluid flow.
- Hydrostatic pressure (HP) is the force exerted by a fluid pressing against a wall, with capillary HP (HPC) equal to capillary blood pressure (filtration pressure).
Hydrostatic Pressure
- HPC is greater at the arterial end (35mmHg) than at the venous end (16 mmHg).
- HPC is opposed by the hydrostatic pressure of the interstitial fluid (HPIF), which is approximately 0mmHg due to excess fluid being reclaimed by the lymphatic vessels.
Osmotic Pressure
- Osmotic pressure (OP) is created by the presence of large, non-diffusible molecules (plasma proteins) in a fluid, drawing water towards them.
- OPC = 26mmHg, OPIF = 5mmHg.
Fluid Flow and Lymphatic System
- At the arterial end, fluid leaves the capillary because Net HP > Net OP, with a pressure differential of 14mmHg.
- At the venous end, some fluid is reclaimed by the capillary because Net OP > Net HP, with a pressure differential of 5mmHg.
- There is a net fluid loss of 1.5mL/min, which is picked up by the lymphatic system and returned to the vascular system (blood).
- The lymphatic system prevents the body from being depleted of plasma in a day.
Lymphatic System
Components and Functions
- Lymphatic vessels: transport excess fluid from interstitial spaces and return it to the venous system.
- Lymphoid tissues and organs: phagocytic cells (lymphocytes) "cleanse" lymph and provide body defense.
Lymphatic Pathways
- Fluid leaves the arterial end of a capillary, with most being reclaimed at the venule end.
- Excess fluid remaining in the interstitial space causes a temporary increase in HPIF.
- This increase in HPIF, along with the design of lymphatic capillaries, allows fluid to enter the lymphatic capillaries.
Lymphatic Capillaries
- Blind-ended (open at one end) and found almost everywhere blood capillaries occur, except in bones, teeth, bone marrow, and the central nervous system.
- Fluid moves in one direction, and backflow is prevented by valves.
- Specialized lymphatic capillaries include lacteals in the intestinal mucosa, which absorb fatty lymph (chyle).
Lymphatic Pathway
- Lymphatic capillaries → afferent lymphatic vessels → lymphatic organs (nodes) → efferent lymphatic vessels → lymphatic trunks → two lymphatic ducts (right lymphatic duct and thoracic duct).
- Thoracic duct:
- Begins as the cisterna chyli, collecting lymph from the lumbar trunks (legs) and intestinal trunk (digestive organs).
- Collects lymph from the left side of the head, neck, and thorax (including the left arm) and the abdomen and legs.
- Empties lymph into the venous system at the juncture of the left subclavian vein and left internal jugular vein.
- Right lymphatic duct:
- Collects lymph from the right side of the head, neck, and thorax (including the right arm).
- Empties lymph into the venous system at the juncture of the right subclavian vein and right internal jugular vein.
Lymph Transport
- Pumpless, with low pressure conditions (3L/Day).
- Movement controlled by:
- Skeletal muscle contraction
- Actions of breathing
- Contraction of smooth muscle in lymph vessel wall
- Valves preventing backflow
- Lymph flow increases with physical activity, highlighting the importance of immobilizing an infected area.
Cells, Tissues, and Organs
- Lymphocytes: T cells and B cells
- Activated T cells manage the immune response and directly attack antigens.
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Description
Learn about the exchange of gases and nutrients through diffusion and bulk fluid flow in capillaries, and how hydrostatic pressure affects capillary function.
