CFR blood vessels FLOW

Starling Forces and Fluid Dynamics

  • Starling forces are key in fluid movement between capillaries and interstitium, discovered by Rex Stahl.

Forces Involved

  • Capillary Hydrostatic Pressure:

    • High in arterial capillaries, decreases in venous capillaries, exerting pressure that pushes fluid out into the interstitium.

    • Measured at +8.3 mmHg on the arterial side and -6.7 mmHg on the venous side, average net: +1.6 mmHg, indicating more fluid is pushed out than pulled in.

  • Plasma Osmotic Pressure:

    • Pulls fluid back into the capillaries; works against hydrostatic pressure.

    • Higher protein concentration in plasma than in interstitium (7-8% vs. 2%).

  • Interstitial Fluid Pressure:

    • Negatively pressured interstitium sucks fluid out of capillaries.

  • Interstitial Osmotic Pressure:

    • Weaker osmotic pull due to lower protein concentration in interstitium, but still contributes to overall fluid movement.

Mechanism of Fluid Movement

  • Outflow:

    • Fluid moves into the interstitium primarily due to hydrostatic pressure.

  • Reabsorption:

    • On the venous side, due to decreased pressure, fluid moves back into capillaries.

    • Overall, balance maintained between fluid entering the interstitium and returning to capillaries.

Lymphatic System Functions

  • The lymphatic system collects excess fluid from interstitium (approx. 10%) which is then returned to the circulatory system.

  • Role in Immune Function:

    • Lymphatic vessels transport lymphocytes and mount immune responses.

  • Fluid Regulation:

    • Removes excess fluid to prevent edema.

Fluid Homeostasis

  • Daily loss of fluids through:

    • Urine (0.5 to 1.5 liters)

    • Breathing (100-200 mL, varies with environment)

    • Perspiration (0.2 to 1 L)

  • Balance maintained through hydration and fluid intake matching losses.

Edema Causes

  • Increased Capillary Pressure:

    • Blockage or thrombus formation causing fluid backpressure in capillaries.

    • Slow blood movement leads to cell accumulation, potentially damaging structures.

  • Heart Failure:

    • Inefficient heart function leads to blood accumulation in veins, resulting in edema.

  • Kidney Dysfunction:

    • Leaky kidney tubules due to inflammation or infection increase fluid in the interstitium by reducing plasma osmotic pressure.

  • Liver Damage:

    • Conditions like alcoholism lead to low albumin production, affecting fluid homeostasis and causing edema.

  • Capillary Permeability Damage:

    • Caused by burns or allergic reactions, increasing capillary porosity.

Lymphatic Vessel Structure

  • Lymphatic capillaries have overlapping endothelial cells, allowing for fluid entry.

  • One-way Valves:

    • Prevent backflow, allowing unidirectional fluid movement towards circulation.

  • Movement of Fluid:

    • Relies on skeletal muscle movement rather than a central pump like the heart.

Lymph Fluid Transport

  • Thoracic duct and right lymphatic duct are main conduits back to venous circulation.

Cancer and the Lymphatic System

  • Staging of Cancer (TNM Classification):

    • T (Tumor size): Sizes categorized (<2cm, 2-5cm, >5cm).

    • N (Node involvement): Indicates spread to nearby lymph nodes, more serious with nodal involvement.

    • M (Metastasis): Spread to distant body parts, severity and treatment options affected by stage.

Diagnosis and Sentinel Lymph Node Mapping

  • Lymph Node Biopsy:

    • Involves injecting dye near tumor to visualize lymphatic drainage for assessing cancer spread.

    • Critical for determining treatment path including need for surgery or radiotherapy for metastatic tumors.

Summary of System Importance

  • The intricate balance of fluid movement through Starling forces, lymphatic system function for fluid homeostasis, and the relationship with cancer staging emphasizes the body's complexity and need for precise mechanics in health and disease.