Learning Objectives • Define edema • Recognize and be able to describe the gross and microscopic appearance of edema • Know the four pathophysiological mechanisms by which edema develops • Understand the different mechanisms under which generalized and localized edema develop • Know the terminology for edema/fluid accumulation in different tissues / regions of the body • Understand the clinical significance and pathogenesis of edema at important sites (eg lung and brain) • Understand the clinical significance, gross appearance, and pathogenesis of dehydration EDEMA
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Learning Objectives
• Define edema
• Recognize and be able to describe the gross and microscopic appearance of edema
• Know the four pathophysiological mechanisms by which edema develops
• Understand the different mechanisms under which generalized and localized edema develop
• Know the terminology for edema/fluid accumulation in different tissues / regions of the body
• Understand the clinical significance and pathogenesis of edema at important sites (eg lung and brain)
• Understand the clinical significance, gross appearance, and pathogenesis of dehydration
EDEMA
Circulatory Disturbances 1: Introduction and Edema
Shannon Martinson, January 2017
http://people.upei.ca/smartinson/ VPM 152 General Pathology
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Distribution of fluid is carefully controlled (homeostasis)
Deviations from normal can have profound pathological effects
Normal function requires intact blood and lymph vessels
Endothelial cells are important!
Important concepts
Components of the Circulatory System
PumpDistribution
system Collection
system
Microcirculation system
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Components of the Circulatory System
Endothelial cells
Image: Zachary PBVD 2017
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
• All components of the circulatory system are lined by a single layer of endothelium
• Critical site for fluid balanceImage: Mescher, Junqueira’s Basic Histology, 12 ed
Capillaries
Capillary wall is semipermeable membrane
Direct diffusion• Most small molecules move by passive diffusion through endothelial cell membrane or
interendothelial pores• Normal interendothelial pores too small to allow escape of large proteins*• With inflammation→ endothelial cells contract, allowing larger molecules to escape*
Mechanisms for transport of substance across capillary walls
GasLipid soluble molecules
Water, Ions, Glucose,Amino acids
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Transcytosis• With some endothelial cells, fluids / macromolecules can be
transported across a cell by vesicles
Capillary wall is semipermeable membrane
Mechanisms for transport of substance across capillary walls
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Fluid distribution and Homeostasis
Total Body Water
Extracellular Fluid
Plasma Interstitial
fluid
Intracellular fluid
5%15%
40%20%
60%
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
• The space between microcirculation and the cellsInterstitium
Function
• Binds cell/structural elements into discrete tissue and organs
• Medium through which metabolic products pass between circulation and cells
Structure
• Composed of extracellular matrix (ECM) and supporting cells
• ECM provides structural support and has adhesive absorptive properties
• Distribution of fluids, nutrients & wastes between blood→
interstitium→ cells controlled by physical structures, pressure gradients and ion concentration gradients
Distribution of Fluids
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
• Capillaries (endothelial cells + basal lamina):• Allow the free passage of H2O & ions • Oppose the passage of plasma proteins• Water distribution between plasma & interstitium is primarily determined by
hydrostatic and osmotic pressure differences between the two compartments.
Water Ions
Protein
Distribution of Fluids
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
The osmotic pressure exerted by proteins is referred to as oncotic pressure
Hydrostatic pressure is the pressure exerted by a fluid in a confined space
• Hydrostatic pressure in the vascular system + interstitial osmotic pressure moves fluid out of the vascular system
Plasma hydrostatic pressure
Tissue colloidal osmotic pressure
Distribution of Fluids
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Starlings Equation
• The osmotic pressure of the plasma proteins and tissue hydrostatic pressure contains the fluid within the vascular system.
Plasma hydrostatic pressure
Tissue colloidal osmotic pressure
Plasma colloidal osmotic pressure
Tissue hydrostatic pressure
Starlings EquationDistribution of Fluids
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Hydrostatic pressure drops along the length of the capillary bed!
Distribution of Fluids
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Starlings Equation
Hydrostatic pressure drops along the length of the capillary bed!
Plasma hydrostatic pressure
Tissue colloidal osmotic pressure
Plasma colloidal osmotic pressure
Tissue hydrostatic pressure
Excess fluid Lymphatic drainage
Starlings Equation → Net movement of fluid out of the capillaries
Distribution of Fluids
INTRODUCTION – NORMAL CIRCULATORY SYSTEM
Excess fluid is drained via lymphatics
CIRCULATORY DISTURBANCES
Edema
Hyperemia and congestion
Shock
Hemorrhage
Thrombosis and embolism
Infarction
Gross Appearance of Edema
• Organs wet (± gelatinous) and heavy
• Organs swollen and fluid may weep from cut surface
• Fluid present in the body cavities
• Abnormal (excess) accumulation of fluid in interstitial tissue spaces or body cavities
EDEMA
EDEMA
Edema in the stomach wall
EDEMA
Edema in the stomach wall
Histologic Appearance of Edema
• Lightly staining eosinophilic fluid (if some protein content)
• Clear / no staining (if protein content low)
• Lymphatics usually dilated
hronic local passive hyperemia
1) ↑Intravascular hydrostatic pressure
2) ↓Plasma colloidal osmotic pressure
3) ↓ Lymphatic drainage
4) ↑Vascular permeability
Edema – 4 Pathophysiological Mechanisms of Development
EDEMA
• Generalized edema: eg Heart failure**
• Localized edema: eg tight bandage causing local obstruction of venous return
Due to impaired venous blood flow
NORMAL
1. Increased intravascular hydrostatic pressure
EDEMA - Pathophysiological Mechanisms of Development
• Proteins not produced
• Liver disease
• Proteins lost
• Kidney (glomerular) disease
• Intestinal damage
• Proteins not absorbed
• Starvation
• Malabsorption
• Causes generalized edema
Due to hypoproteinemia
NORMAL
2. Decreased plasma colloidal osmotic pressure
Plasma colloidal osmotic pressure is exerted mostly by plasma protein
EDEMA - Pathophysiological Mechanisms of Development
• Surgery / trauma (fibrosis)
• Neoplasm (tumour) or mass
• Inflammation (lymphangitis)
• Typically localized
Due to lymphatic obstruction / damage
NORMAL
3. Decreased lymphatic drainage
EDEMA - Pathophysiological Mechanisms of Development
• Mostly due to inflammatory / immune reactions release of inflammatory mediators
• “inflammatory edema”
• Endothelium can also be directly damaged by specific agents (eg viruses, toxins)
• Subcutis on the ventrum of the abdomen / thorax (“brisket edema”)• Subcutis of the ventral cervical / mandibular region (“bottle jaw”)• Subcutis of the limbs (“stocking up”)
LOCALIZED VS GENERALIZED EDEMA
Generalized Edema
• When pressure is applied to an area of edema and a depression or dent resultsPitting edema