Reactions of Blood Vessels in Acute Inflammation

Slide 1 · Reactions of Blood Vessels

in Acute Inflammation

Vasodilation • permeability • exudation • stasis

An integrated vascular mechanism of acute inflammation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain the changes in vascular caliber and blood flow after injury.

Connect permeability changes with exudation and tissue edema.

Distinguish exudates, transudates, edema, and purulent exudates.

Explain how stasis favors leukocyte margination.

From vascular change to tissue defense

Slide 3 · Vascular responses deliver inflammatory defense

Local injury or microbes

Inflammatory mediators

Altered blood flow + permeability

Plasma proteins + leukocytes in tissues

Local host defense requires regulated transfer across the microvascular wall.

Slide 4 · Three major components of acute inflammation

Vascular dilation

Increases local blood flow

Microvascular leakage

Allows plasma proteins into tissue

Leukocyte recruitment

Delivers circulating effector cells

Slide 5 · A microvessel separates plasma from injured tissue

The endothelial lining is the key interface.

In normal conditions, most plasma proteins remain intravascular.

Inflammation alters both local flow and endothelial barrier function.

Schematic microvessel (not histology)

Slide 6 · Vascular reactions have two distinct axes

Hemodynamics

Changes in vessel caliber

Changes in blood flow

Stasis and vascular congestion

Barrier function

Increased vascular permeability

Loss of protein-rich fluid

Edema and exudate formation

Slide 7 · The response is spatially targeted

Stimulus in tissue

Local sentinel-cell mediators

Nearby small vessels respond

Plasma and cells reach injury

Circulating leukocytes and plasma proteins are redirected to the focus of injury.

Slide 8 · Order of early vascular events

Mediator release

Vasodilation

Permeability ↑

Fluid loss + stasis

Leukocyte margination

Slide 9 · Vasodilation is an early vascular event

Chemical mediators act on vascular smooth muscle.

Affected small vessels increase in caliber.

Local blood flow initially rises.

This contributes directly to erythema and warmth.

Early: Greater caliber → greater local flow

Slide 10 · Histamine is a prominent vasodilator

Histamine as a notable mediator.

The mediator acts on vascular smooth muscle.

Vasodilation begins soon after the inflammatory stimulus.

The same mediator can also participate in vascular leakage.

One mediator, multiple vascular effects

Slide 11 · Postcapillary venules are central responders

The source emphasizes postcapillary venules.

These vessels participate in permeability changes.

They also provide an interface for leukocyte adhesion and exit.

Schematic microvessel (not histology)

Slide 12 · Increased caliber raises blood flow locally

Vasodilation expands the functional vascular channel.

More blood reaches the site of injury initially.

The inflamed area therefore appears red and warm.

Schematic microvessel (not histology)

Slide 13 · Why acute inflammation causes redness

Inflammatory mediator

Vasodilation

Increased local blood volume/flow

Erythema (redness)

Slide 14 · Why the inflamed area feels warm

Dilation of small vessels

Increased warm blood delivery

Local heat (calor)

Slide 15 · Hyperemia and congestion describe different flow states

Early hyperemia

Vessels dilate

Local blood flow rises

Supports warmth and redness

Developing congestion

Microvascular flow slows

Red cells accumulate in vessels

Engorgement becomes apparent

Slide 16 · Vasodilation precedes the major fluid leak

Increased vascular caliber

Microvascular permeability rises

Protein-rich fluid escapes

Tissue swelling develops

Slide 17 · Microvascular permeability controls exudation

Endothelial barrier integrity regulates protein escape.

Inflammatory mediators can increase passage between endothelial cells.

Injury can cause a more sustained barrier defect.

Increased permeability is the defining vascular change in exudation.

A protein-permeable vessel generates an exudate

Slide 18 · Inflammatory permeability is especially venular

Postcapillary venules are a key leakage site.

Junctional changes allow plasma components to exit.

The response supplies tissue with soluble host-defense proteins.

Endothelial gap

Schematic microvessel (not histology)

Slide 19 · Endothelial contraction creates temporary gaps

Histamine / kinins / leukotrienes

Endothelial contraction

Interendothelial gaps

Protein-rich fluid exits

Slide 20 · The immediate transient leak is short-lived

Interendothelial gaps appear rapidly after mediator exposure.

A usual duration of 15–30 minutes.

The underlying mechanism is endothelial contraction.

This is the most common described leakage mechanism.

Immediate transient response: Usually 15–30 min

Slide 21 · Different mediators can converge on a gap response

Histamine

Induces endothelial contraction

Bradykinin

Promotes junctional leakage

Leukotrienes

Can increase permeability

Slide 22 · Delayed prolonged leakage has a different tempo

In some mild injuries, leakage begins after 2–12 hours.

It may continue for several hours or even days.

Contraction or mild endothelial damage may contribute.

Immediate and delayed leakage can lie on a continuum.

Delayed onset does not exclude inflammatory leakage

Slide 23 · Sunburn illustrates delayed vascular leakage

Slide 24 · Endothelial necrosis produces sustained leakage

Severe insults can injure and detach endothelial cells.

Direct barrier destruction permits vascular contents to escape.

Leakage can continue until vessels thrombose or repair.

Endothelial injury

Schematic microvessel (not histology)

Slide 25 · Thermal burns combine several leakage mechanisms

Chemically mediated endothelial contraction may occur first.

Direct endothelial injury can extend the permeability defect.

Adherent leukocytes may add endothelial damage.

Extensive leakage can cause dangerous fluid loss.

Severe burns can produce life-threatening fluid depletion

Slide 26 · Microbes and toxins may directly injure endothelium

Microbe / microbial toxin

Endothelial damage

Loss of barrier integrity

Sustained leakage

Slide 27 · Adherent neutrophils can amplify vascular injury

Activated endothelium

Neutrophil adherence

Leukocyte-mediated injury

Additional vascular leakage

Slide 28 · Vascular permeability mechanisms can overlap

Mediator-driven contraction

Endothelium retracts

Gaps are created

Often rapid and transient

Endothelial cell injury

Cells may undergo necrosis

Cells detach from vessel wall

Leakage may be sustained

Slide 29 · An injured vessel is not equivalent to a retracted vessel

Contraction preserves living endothelial cells.

Injury disrupts or removes part of the endothelial lining.

The mechanism influences the duration of the leak.

Endothelial injury

Schematic microvessel (not histology)

Slide 30 · Exudation is escape from the vascular compartment

Vessel becomes permeable

Fluid + proteins cross wall

Contents accumulate in tissue/cavity

Exudation

Slide 31 · Exudates indicate an inflammatory permeability defect

An exudate is an extravascular protein-rich fluid.

It may contain cellular debris and sometimes blood cells.

Its presence implies increased permeability of small vessels.

Exudation connects vascular alteration to tissue findings.

Exudate → inflammatory vessel leak

Slide 32 · Exudates contain fluid and plasma proteins

Inflammation allows more than water to leave vessels.

Plasma proteins move into the interstitial space.

An inflammatory exudate can also contain cell fragments.

Vascular lumen

Interstitial compartment

Water + proteins

Slide 33 · The protein content distinguishes exudates

Exudate

Relatively protein-rich

Inflammatory permeability increased

Cells or debris may be present

Transudate

Relatively protein-poor

No primary permeability increase

Few or no cells

Slide 34 · A transudate is essentially a plasma ultrafiltrate

Fluid escapes without an inflammatory barrier defect.

Protein content is low, largely albumin.

Little or no cellular material is present.

Pressure or osmotic imbalance drives formation.

Transudate → hydrostatic / oncotic imbalance

Slide 35 · Hydrostatic pressure can cause transudation

Raised vascular hydrostatic pressure

Increased outward filtration

Low-protein fluid accumulation

Transudate

Slide 36 · Reduced colloid osmotic pressure also causes transudation

Loss / reduced synthesis of plasma proteins

Reduced inward oncotic pull

Predominantly water leaves vessels

Transudate

Slide 37 · Typical pressure-related transudate settings

Venous outflow obstruction

Raised hydrostatic pressure

Liver disease

Reduced protein synthesis

Kidney disease

Increased protein loss

Slide 38 · Exudate and transudate: Causal comparison

Feature

Exudate

Transudate

Primary disturbance

Endothelial permeability ↑

Pressure / osmotic imbalance

Protein content

High

Low

Cells / debris

May be present

Little or none

Main implication

Inflammatory process

Noninflammatory fluid shift

Vascular wall

More permeable

No primary increase in permeability

Slide 39 · Edema means excess extravascular fluid

Edema can occur in interstitial tissue.

It may also collect in serous cavities.

Edema describes the location and volume of fluid, not its composition.

Either an exudate or a transudate can produce edema.

Edema is not synonymous with exudate

Slide 40 · Two distinct pathways can produce edema

Inflammatory edema

Vascular permeability increases

Proteins accompany fluid

Exudate forms

Noninflammatory edema

Hydrostatic / oncotic imbalance

Mainly fluid leaves vessels

Transudate forms

Slide 41 · A purulent exudate is not merely watery edema

Pus is an inflammatory exudate.

It is rich in leukocytes, mainly neutrophils.

Dead-cell debris is present.

Microbes are present in many, but not necessarily all, cases.

Pus = neutrophils + necrotic debris ± microbes

Slide 42 · Fluid terminology follows a hierarchy

Extravascular fluid

Edema (site of accumulation)

Exudate or transudate (composition)

Purulent exudate if pus

Slide 43 · Loss of plasma fluid changes microvascular flow

Plasma fluid leaves vessels

Relative red-cell concentration rises

Flow becomes slower

Stasis develops

Slide 44 · Hemoconcentration accompanies vascular leakage

Inflammatory fluid loss removes plasma from the vessel.

Red cells become more concentrated in remaining blood.

The dilated vessel now contains more slowly moving blood.

These changes promote microvascular stasis.

Plasma loss + dilation → slower flow

Slide 45 · Stasis develops after the early hyperemic phase

Blood flow progressively slows in small vessels.

Red cells accumulate within the dilated vascular lumen.

Vessels appear engorged, a state described as congestion.

Schematic microvessel (not histology)

Slide 46 · The hemodynamic sequence is not static

Normal flow

Early vasodilation

Later stasis + margination

Schematic; Vessel diameter and cell density are illustrative, not quantitative

Slide 47 · Vascular congestion is a histologic observation

Congestion means small vessels are engorged with erythrocytes.

It reflects accumulation of slowly moving red cells.

The accompanying edema may separate tissue structures.

The diagram is schematic rather than an actual H&E image.

Morphologic correlate: Engorged small vessels

Slide 48 · Stasis shifts leukocytes toward endothelium

Slower flow favors peripheral positioning of leukocytes.

Neutrophils collect along the endothelial surface.

This redistribution is termed margination.

Schematic microvessel (not histology)

Slide 49 · Margination bridges vascular and cellular responses

Dilation + plasma loss

Stasis

Neutrophil margination

Endothelial attachment

Slide 50 · Endothelial activation enables firm cellular contact

Injury-associated mediators activate endothelial cells.

Endothelial adhesion-molecule expression rises.

Leukocytes attach to the endothelium.

The next phase is migration across the vessel wall.

Vascular changes set the stage for leukocyte exit

Slide 51 · Vascular change precedes leukocyte emigration

Stasis + margination

Rolling / adhesion

Transmigration

Leukocytes in injured tissue

Slide 52 · The lymphatic system helps clear extravascular fluid

Leaky blood microvessel

Interstitial edema fluid

Lymphatic drainage

Increased lymph flow can remove some of the accumulating extravascular fluid.

Slide 53 · Lymph flow rises during acute inflammation

Lymphatics normally collect small amounts of extravascular fluid.

Inflammatory edema increases the drainage load.

Lymph can carry leukocytes, debris, and microbes.

This provides context for spread toward draining nodes.

Lymph drainage is a companion, not a substitute, for vascular defense

Slide 54 · Inflamed lymphatics and nodes can become clinically visible

Lymphangitis denotes inflammation of lymphatic vessels.

Lymphadenitis denotes inflammation of lymph nodes.

A red streak extending from a wound suggests lymphangitis.

Enlarged painful draining nodes can accompany it.

Regional lymphatic findings can indicate local infection

Slide 55 · Redness and swelling arise by different mechanisms

Redness and warmth

Early vasodilation

Greater local blood flow

Engorgement may persist during stasis

Swelling

Increased vascular permeability

Protein-rich fluid enters tissue

Edema becomes visible

Slide 56 · Small local inflammation produces a coordinated response

Local tissue damage

Vasodilation

Permeability / edema

Stasis / leukocyte margination

Cellular response

Slide 57 · Severe systemic fluid loss is a possible consequence

Barrier disruption may involve many vessels in severe burns.

Large quantities of plasma fluid may leave the circulation.

Vascular reactions that protect locally can be harmful when extensive.

Potentially life-threatening fluid loss.

Extent of leakage determines systemic significance

Slide 58 · Clinical interpretation: An erythematous warm wound

Clinical setting

Following a superficial injury, the surrounding skin becomes red and warm before pronounced swelling develops.

Interpretation question

Which vascular event is most directly responsible for the initial signs?

Source-based explanation

Early mediator-induced vasodilation with increased local blood flow.

Erythema and warmth precede or accompany the later permeability-related swelling.

Slide 59 · Clinical interpretation: Delayed sunburn edema

Clinical setting

After ultraviolet exposure, local tissue swelling develops several hours after the exposure.

Interpretation question

Is a delayed leak necessarily noninflammatory?

Source-based explanation

No. It is compatible with delayed prolonged inflammatory leakage.

Robbins explicitly describes sunburn as a delayed-onset permeability response.

Slide 60 · Clinical interpretation: Fluid in heart failure

Clinical setting

A patient with venous congestion develops a relatively protein-poor edema fluid without local vascular injury.

Interpretation question

Is the fluid best interpreted as exudate or transudate?

Source-based explanation

Transudate.

A hydrostatic pressure abnormality can generate low-protein fluid without increased vessel permeability.

Slide 61 · Clinical interpretation: A purulent wound

Clinical setting

A wound contains thick fluid rich in neutrophils and necrotic cellular debris.

Interpretation question

Which form of extravascular fluid is present?

Source-based explanation

Purulent inflammatory exudate (pus).

The cellular composition identifies pus rather than simple transudative edema.

Slide 62 · Clinical interpretation: Major thermal injury

Clinical setting

A patient with extensive burns develops widespread tissue swelling and substantial intravascular fluid loss.

Interpretation question

Why can local permeability mechanisms become dangerous?

Source-based explanation

Extensive, sustained plasma leakage reduces circulating fluid volume.

Endothelial contraction, direct injury, and leukocyte-mediated injury may all contribute.

Slide 63 · A single causal chain explains many findings

Mediators → vasodilation

Blood flow initially ↑

Leakage → edema

Plasma loss → stasis

Margination → cell recruitment

Slide 64 · Distinguish a permeability defect from a pressure defect

Finding

Interpretation

Reason

Protein-rich swelling

Inflammatory exudation

Barrier permeability increases

Low-protein swelling

Transudation

Hydrostatic / oncotic shift

Slow red-cell-filled venules

Congestion / stasis

Plasma loss and dilation

Neutrophils along endothelial wall

Margination

Slowing changes leukocyte distribution

Slide 65 · Assessment: Which finding implies vascular leakage?

An extravascular fluid has high protein content and scattered cell debris. What does this imply?

A. Isolated increase in hydrostatic pressure

B. Increased permeability of small vessels

C. Reduced plasma protein synthesis alone

D. An unchanged endothelial barrier

Rationale: High-protein inflammatory exudates indicate permeability increase.

Slide 66 · Assessment: What prepares neutrophils for adhesion?

After vasodilation and plasma-fluid loss, which event positions neutrophils near the vessel wall?

A. Transudation

B. Margination during stasis

C. Immediate endothelial thrombosis

D. Reduced endothelial adhesion

Rationale: Slowed blood flow shifts leukocytes to the endothelial periphery.

Slide 67 · Five distinctions to retain

Dilation

Initial ↑ local flow → warmth/redness

Leakage

Plasma proteins escape → exudate

Edema

Excess extravascular fluid of either type

Stasis

Flow slows; Red cells concentrate

Margination

Leukocytes move toward endothelium

Slide 68 · Primary source and figure provenance

Core reading

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th edition (2026).

Chapter 3: Inflammation and Repair; acute inflammation, pp. 67–69.

Assigned section: Reactions of Blood Vessels in Acute Inflammation.

All instructional drawings were constructed as native PowerPoint schematics; no synthetic micrographs or unlicensed pathology images are used.