Oedema, Congestion, Infarction and Shock Flashcards
What is edema, and how does it manifest?
Edema is the accumulation of fluid in tissues, either localized or generalized. It can manifest as mild swelling (e.g., shoes fitting tighter after a long day) or severe conditions like alveolar fluid accumulation, leading to life-threatening hypoxia.
What can cause edema?
◾ Increased hydrostatic pressure;
◾ Reduced plasma osmotic pressure;
◾ Lymphatic obstruction;
◾ Sodium and water retention
What are the causes of increased hydrostatic pressure leading to edema?
◾ Impaired venous outflow (e.g., deep vein thrombosis, heart failure);
◾ Increased arterial pressure
What are the effects of reduced plasma osmotic pressure?
Loss of fluid from circulation into tissues;
It is commonly caused by reduced albumin levels due to:
◾ nephrotic syndrome,
◾ liver cirrhosis,
◾ protein malnutrition
How does lymphatic obstruction contribute to edema?
Prevents fluid reabsorption from interstitial spaces;
Causes include inflammatory or neoplastic obstruction and parasitic infections (e.g. filariasis)
What happens in nephrotic syndrome regarding plasma proteins?
Increased permeability of glomerular capillaries resulting in loss of plasma proteins (e.g., albumin) in urine.
What is the mechanism of edema in heart failure?
◾ In heart failure, the heart’s ability to pump blood is compromised. This leads to a backup of blood in the veins, increasing the pressure within the capillaries. This forces fluid out of the capillaries and into the surrounding tissues, hence oedema results.
◾ Additionally, heart failure reduces the cardiac output, leading to decreased renal blood flow. In response, the kidneys activate mechanisms to retain sodium and water (e.g. RAAS) in an attempt to increase blood volume and improve perfusion. This will result in an increase in overall fluid volume in the body, contributing to oedema.
What are the clinical features of nephrotic syndrome that contribute to edema?
◾ Massive protein loss in urine (proteinuria);
◾ Hypoalbuminemia, leading to reduced plasma osmotic pressure;
◾ Secondary hyperaldosteronism due to decreased plasma volume
How does inflammation lead to edema?
Increased vascular permeability due to endothelial cell contraction;
Leakage of protein-rich fluid (exudate) into interstitial spaces
What is anasarca?
Severe, generalized edema affecting the entire body; Typically associated with hypoalbuminemia or severe systemic conditions
Briefly describe the morphology of cerebral oedema.
Briefly describe the morphology of pulmonary oedema.
What is effusion?
Effusion refers to the escape of fluid into a body cavity or tissue.
What are the different forms of effusion based on fluid type?
◾ Transudate: Low protein content, specific gravity < 1.012 (e.g., heart failure)
◾ Exudate: Protein-rich, specific gravity > 1.020 (e.g., inflammation)
Give the medical term for the following:
(a) fluid in the pleural cavity
(b) fluid in the pericardial sac
(c) fluid in the peritoneal cavity
(a) Hydrothorax
(b) Hydropericardium
(c) Ascites
Define:
(a) serous effusion
(b) serosanguinous effusion
(c) haemorrhagic effusion
(d) chylous effusion
(a) serous effusion: accumulation of clear, pale yellow fluid that is similar to serum
(b) serosanguinous effusion: this type of effusion contains both serous fluid and blood; typically light red
(c) haemorrhagic effusion: this type of effusion involves the presence of a significant amount of blood in the effusion fluid. It appears red.
(d) chylous effusion: this type of effusion contains a milky fluid rich in triglycerides, known as chyle. It is often caused by damage to the lymphatic system.
Define congestion.
This refers to the abnormal accumulation of blood within the blood vessels of an organ or tissue.
State the two broad types of congestion and give a brief description of each.
(1) Active congestion (Hyperemia)
This occurs when there is increased blood flow to a particular area due to the dilation of blood vessels. It is often a result of increased metabolic activity, inflammation, or exercise. The affected area typically appears red and warm due to the increased blood supply.
(2) Passive congestion (Venous congestion)
This occurs when there is an obstruction to the outflow of blood, leading to the accumulation of blood in the affected area. It is often caused by conditions such as heart failure or venous thrombosis. The affected area may appear bluish or purplish due to the deoxygenated blood.
Outline consequences of impaired venous outflow.
◾ Congestion: stasis of deoxygenated blood.
◾ Haemorrhage: increase in capillary pressure which can lead to capillary rupture
◾ Oedema: due to increased intravascular pressure
◾ Chronic hypoxia
Differentiate between shock and infarction.
◾ Shock is a condition where the body’s organs and tissues do not receive enough blood flow, leading to a lack of oxygen and nutrients. It is as a result of overall failure of the circulatory system.
◾ Infarction refers to the death of tissue due to a lack of blood supply. This is usually caused by a blockage in an artery, e.g. a blood clot, which prevents blood from reaching the affected area.
List the types of shock.
🩺 Cardiogenic shock
🩺 Hypovolemic shock
🩺 Septic shock
🩺 Neurogenic
🩺 Anaphylactic
What are the common causes of shock?
◾ Hypovolemia;
◾ Cardiogenic failure;
◾ Sepsis;
◾ Anaphylaxis
What is the main pathological feature of shock?
systemic hypoperfusion
What is the sequence of vascular events in shock?
Vasoconstriction during compensatory stage;
Progressive vasodilation in later stages
What are the stages of shock progression?
(1) Non-progressive (compensated)
(2) Progressive
(3) Irreversible
