Cardiovascular | Microcirculation

Micro Circulation Overview

• Introduction to micro circulation, including key structures like the brain, lungs, skeletal muscle tissue, and blood vessels.

• Overview of capillary beds and lymphatic vessels; introduction to the gastrointestinal tract components.

• Focus on anatomy of micro circulation; terminal arterial prepares for capillary bed entry.

Key Components of Micro Circulation

• Terminal arterial is identified as feeding into the capillary bed.

• Meta arterial connects to true capillaries; important for understanding blood flow.

• True capillaries are present in varying numbers per capillary bed (10 to 100).

Understanding Vascular Structures

• Thorofare Channel connects true capillaries and drains into post-capillary venule.

• The vascular shunt is defined as the distance from meta arterial to thorofare channel.

• Arterio venous anastomosis is explained through vascular shunt example.

Blood Flow Dynamics

• Recap of blood flow structure: terminal arterial → meta arterial → true capillaries → thorofare channel → post-capillary venule.

• Importance of understanding this structure for gas exchange processes in tissues.

Role of Precapillary Sphincters

• Precapillary sphincters control blood flow into true capillaries based on smooth muscle contraction.

• Constriction prevents blood from entering true capillaries; dilation allows it.

Fluid Exchange Mechanisms

• Blood consists of cells and plasma; focus on plasma's role in fluid dynamics.

• Hydrostatic pressure (HP), specifically within capillaries, pushes substances out during circulation.

Understanding Capillary Bed Pressures

Capillary Hydrostatic Pressure

• Capillary hydrostatic pressure averages about 35 mmHg, influenced by systolic blood pressure.

• Proteins like albumin generate osmotic pressure, crucial for retaining water in the bloodstream.

Osmotic Pressure Dynamics

• Oncotic pressure (osmotic pressure from proteins) averages around 25 mmHg, helping to pull water into capillaries.

• Fluid accumulation outside capillaries leads to net changes in pressures affecting fluid movement.

Interstitial Fluid Pressures

• Hydrostatic pressure of interstitial fluid is typically zero mmHg, pushing fluid into capillaries.

• Osmotic pressure of interstitial fluid averages about 1 mmHg, pulling substances out into the interstitial space.

Net Filtration Pressures in Capillaries

Arterial vs. Venous Side Pressures

• Hydrostatic pressure in capillaries drops to approximately 17 mmHg on the venous side after plasma filtration.

• Osmotic pressure remains at about 25 mmHg if plasma proteins are intact.

Calculating Net Filtration Pressure

• Net filtration involves combining pressures that push fluids out and those that pull them back in.

• Key factors include hydrostatic pressures (35 mmHg arterial; 0 mmHg interstitial), and osmotic pressures (25 mmHg capillary; 1 mmHg interstitial).

Summary of Forces at Play

Understanding Capillary Pressure and Flow

Average Filtration Pressure

• The average pressure for filtration in veins is approximately 10 to 11 mm of mercury.

• Capillary hydrostatic pressure changes to 17 mm of mercury, resulting in a net flow calculation.

Net Flow Dynamics

• There is a net flow out from the capillaries, while the net flow into the capillaries is also significant.

• Understanding these pressures helps clarify what occurs at the capillary bed.

Impact of Protein Loss

• Conditions like nephrotic syndrome can lead to protein loss, decreasing osmotic pressure and increasing fluid push-out.

• This situation can result in edema due to reduced reabsorption of fluids.

Effects of Lymphatic Blockage

Consequences of Cancer on Fluid Dynamics

• Cancer causing lymphatic vessel occlusion prevents proper drainage, leading to swelling and edema.

• Increased hydrostatic pressure in interstitial fluid results from this blockage.

Types of Anastomosis

Definition and Importance

• Anastomosis refers to alternative or collateral channels for blood flow, crucial during vessel blockages.

Types of Anastomoses

• Three main types: arterial anastomosis, venous anastomosis, and arteriovenous anastomosis.

Clinical Relevance

Understanding Blood Flow and Anastomosis

Capillary Beds and Blood Flow

• Adequate blood flow is maintained despite reduced arterial anastomosis; capillary beds play a crucial role.

• Arterio-venous anastomosis serves as a vascular shunt; the Circle of Willis is a key example in pathophysiology.

The Circle of Willis

• The Circle of Willis includes several arteries: vertebral, basilar, posterior cerebral, and anterior communicating arteries.

• Understanding the anatomy of the Circle of Willis is essential for discussing clots and aneurysms later.

Alternative Blood Routes

• If a clot forms in the posterior communicating artery, alternative routes can still supply blood to tissues.

• While collateral circulation exists, it may not be as effective; risks include transient ischemic attacks or strokes.

Localized Blood Flow Changes

• Discussion shifts to localized blood flow changes during muscle activity; exercise increases lactic acid production.

• High CO2 and H+ levels from metabolism can lead to localized regulation affecting smooth muscle cells.

Active Hyperemia Explained

Mean Arterial Pressure and Its Effects

• Mean arterial pressure (MAP) is crucial for understanding blood flow.

• High MAP can lead to rupture of fragile cerebral blood vessels.

• Myogenic mechanism: vasoconstriction occurs to protect smaller vessels from high pressure.

Responses to Low and High MAP

• Vasoconstriction protects cerebral vessels when MAP is high.

• Vasodilation occurs with low MAP to increase blood flow and prevent syncope.

• Proper perfusion is essential for oxygen delivery in capillary beds.

Oxygen Levels in the Lungs

• Low partial pressure of oxygen leads to vasoconstriction in affected lung areas.

• Blood is redirected to areas with higher oxygen concentration for effective oxygenation.

• This mechanism ensures efficient use of available oxygen in the lungs.

Blood Flow Regulation During Stress

• Non-vital organs like the GI tract and skin receive less blood during stress responses.

• Blood shunting occurs towards vital organs when under sympathetic stimulation.

• This process prioritizes blood flow to critical areas such as muscles, heart, and brain.

Arteriovenous Malformation (AVM)

• AVMs lack true capillaries, leading to direct artery-vein connections.

AV Malformation and Its Implications

• AV malformations can cause high pressure from arteries to veins, leading to complications.

• Coiling of blood vessels may occur, resulting in a condition known as aitis.