Disorders of the Circulatory System

Study Notes

Gangrene is massive tissue necrosis followed by putrefaction
Putrefaction is the breakdown of necrotic tissue proteins by saprophytic organisms
Gangrene causes a foul-smelling discharge and discoloration of the affected area
Causes of gangrene include ischemia (lack of blood flow) or toxins
Sites of gangrene affect all tissues in the affected organ
Types of gangrene include dry, moist (wet), and infective. Gas gangrene is a type of moist gangrene.

Pathogenesis: occlusion of arterial blood supply to an organ, often with patent (open) veins and poor collaterals
Causes of dry gangrene include thrombosis (atherosclerosis), embolism, surgical ligation, and ergot poisoning-induced arterial spasm
Steps of dry gangrene development:
- Gradual obstruction of arteries leading to slow spread
- Initially, the affected area is pale, numb, cold, and painful
- Necrosis begins, causing the area to turn red due to blood cell lysis and blood pigment diffusion
- Saprophytic bacteria cause putrefaction of the necrotic tissue, causing black discoloration, bad odor, and surface/subsurface discoloration
- Tissue fluid drains through lymphatics and veins
- Surface evaporation happens
- The affected area eventually becomes shrunken and mummified
- The gangrene stops upon reaching areas of good collateral circulation.
- Inflammation and formation of a line of demarcation begin, which separates necrotic from healthy tissue.
- Granulation tissue forms in the healthy tissue bordering the necrotic area, further isolating the affected tissue.
- Necrosis continues until a conical stump separates the affected area from the healthy tissue.

It affects internal organs, especially when there is sudden arterial AND venous occlusion
Causes of moist gangrene include strangulated hernia, crush injuries, and diabetic gangrene
Steps:
- Venous obstruction causes edema (fluid accumulation)
- Intestinal loops swell or become congested with fluid.
- Arterial occlusion leads to necrosis
- Saprophytic bacteria cause putrefaction
- Black coloration and foul odor develop

A type of moist gangrene caused by pathogenic bacteria, which cause tissue necrosis and putrefaction
Pathogenesis:
- Pathogenic bacteria produce toxins, causing tissue necrosis
- Saprophytic bacteria then act on dead proteins, causing putrefaction
Types of infective gangrene include: lung gangrene, bed sores, cancrum oris, and gas gangrene.

A moist, infective gangrene caused by anaerobic bacteria (Clostridium)
Pathogenesis
- Bacteria present in deep wounds (often contaminated by soil or feces)
- Anaerobic bacteria produce excessive gases (hydrogen sulfide, hydrogen, carbon dioxide)
Characterized by the production of gases, leading to tissue damage.

Definition: abnormal accumulation of fluid in interstitial tissue and serous membranes
Causes:
- Increased capillary hydrostatic pressure (obstructions, heart failure)
- Decreased capillary colloid osmotic pressure (protein deficiency)
- Increased capillary permeability (inflammation, infection, burns)
- Lymphatic obstruction (congenital, inflammatory).
Types of edema:
- Generalized (throughout the body) vs. localized (in specific areas)
- Soft pitting vs. hard pitting (depending on the amount of readily displaced interstitial fluid)
Causes of generalized edema
- Cardiac: right-sided heart failure
- Renal: proteinuria
- Nutritional: decreased protein intake leading to decreased osmotic pressure
Causes of localized edema:
- Inflammatory
- Venous obstruction
- Lymphatic obstruction