Microcirculation Lecture Notes

Overview

• Focus on microcirculation, specifically blood flow through capillary beds.
• Discusses anatomy and function of various components involved in microcirculation.

Diagram Components

• Brain and CNS: Central nervous system.
• Lungs: Respiratory system.
• Skeletal Muscle Tissue: Represents muscular system.
• Blood Vessels: Serve specific tissues.
• Lymphatic Vessel: Represents lymphatic system.
• Skin: Includes epidermis and dermis.
• GI Tract: Includes esophagus, stomach, and small intestine.

Anatomy of Microcirculation

• Terminal Arteriole: Precedes capillary bed.
• Metarteriole: Connects to true capillaries, part of arterio-venous shunt.
• True Capillaries: Around 10-100 capillaries per bed.
• Thoroughfare Channel: Connects metarteriole to venous side.
• Vascular Shunt: Includes metarteriole and thoroughfare channel.
• Postcapillary Venule: Drains blood from thoroughfare channel.

Precapillary Sphincters

• Rings of smooth muscle regulating blood flow into capillaries.
• Controlled by sympathetic nervous system and local chemicals.

Capillary Bed Pressures

• Hydrostatic Pressure (HPc): Pushes substances out, ~35 mmHg.
• Osmotic Pressure (OPc): Regulated by albumin, pulls water in, ~25-26 mmHg.
• Interstitial Fluid Pressures: Hydrostatic ~0 mmHg, Osmotic ~1 mmHg.

Net Filtration Pressure

• Calculated to determine net flow of fluid.
• Arterial: ~11 mmHg net flow out.
• Venous: ~-7 mmHg net flow in.

Conditions Affecting Pressure

• Hypoproteinemia: Low plasma proteins leading to edema.
• Lymphatic Occlusion: Can lead to edema due to increased interstitial fluid pressure.

Types of Anastomoses

• Definition: Alternative channels for blood flow.
• Types:
  • Arterial-arterial
  • Venous-venous (most common)
  • Arterio-venous (in capillary beds)
• Examples: Circle of Willis (important for brain circulation)

Blood Flow Regulation in Specialized Areas

• Muscles: Active hyperemia during exercise due to lactic acid and CO2.
• Brain: Controlled by mean arterial pressure (MAP).
  • High MAP: Vasoconstriction to prevent vessel rupture.
  • Low MAP: Vasodilation to increase perfusion.
• Lungs:
  • Low O2 concentration causes vasoconstriction to redirect blood flow.
  • High O2 concentration causes vasodilation for better oxygenation.
• GIT and Skin: Blood diverted away during sympathetic response.

Arterio-Venous Malformations

• AV Malformation: Direct artery to vein connections causing potential issues.
• Risks: High pressure can lead to aneurysms and complications.
• Treatment: Often involves embolization therapy.

Conclusion

• Comprehensive overview of microcirculation mechanisms and related physiological and pathological aspects.