Homeostasis and Body Fluid Composition

### Homeostasis

• The internal environment or milieu interieur refers to the state of the body where interstitial fluid and plasma maintain normal cell and tissue functions.
• Homeostasis is the mechanism maintaining the constancy of the internal environment.
• Membranes like vascular endothelium and cell walls play a crucial role in fluid, electrolyte, nutrient, and metabolite exchange.

Body Fluid Composition

• Water is the primary component, comprising 50-70% of body weight in males and 50% in females.
• Total body water is divided into intracellular fluid (33% body weight, mainly in muscles) and extracellular fluid (27% body weight).
• Intracellular fluid has high potassium and magnesium, and low sodium and chloride.
• Extracellular fluid has high sodium and chloride, and low potassium and magnesium.

### Oedema

• Oedema is excessive fluid accumulation in interstitial spaces and serous cavities.
• Intracellular oedema is fluid accumulation within cells, also known as hydropic degeneration.
• Ascites refers to fluid in the peritoneal cavity, hydrothorax/pleural effusion in the pleural cavity, and hydropericardium/pericardial effusion in the pericardial cavity.
• Pitting oedema occurs in subcutaneous tissues, where pressure creates a depression.
• Non-pitting or solid oedema occurs in conditions like myxoedema and lipedema.
• Localised oedema affects a specific organ or limb, while generalised oedema (anasarca or dropsy) is systemic.
• Oedema fluid can be transudate (in cardiac and renal diseases) or exudate (in inflammatory oedema).

### Blood Loss

• Losing up to 20% of blood volume has minimal clinical effects due to compensatory mechanisms.
• Sudden loss of 33% of blood volume can be fatal, while loss of 50% over 24 hours may not be fatal.
• Chronic blood loss causes iron deficiency anaemia while acute haemorrhage leads to hypovolaemic shock.

### Shock

• Shock is a life-threatening syndrome of cardiovascular collapse with reduced effective circulating blood volume and inadequate cell and tissue perfusion.
• Primary shock is a transient, usually benign vasovagal attack caused by reduced venous return to the heart due to neurogenic vasodilatation.
• Anaphylactic shock is caused by type 1 immunologic reaction and is not due to circulatory derangement.
• “True” shock is a circulatory imbalance between oxygen supply and demand.

Shock Etiology

• Hypovolemic Shock: Caused by reduced circulating blood volume due to haemorrhage or plasma loss.
• Cardiogenic Shock: Caused by acute heart disease leading to reduced cardiac output, not blood volume reduction.
  • Deficient emptying (Myocardial infarction, cardiomyopathies, heart rupture)
  • Deficient filling (Cardiac tamponade)
  • Outflow obstruction (Pulmonary embolism, tension pneumothorax)
• Septic Shock: Caused by severe bacterial infections or septicaemia, more commonly from Gram-negative bacteria (endotoxic shock) than Gram-positive bacteria (exotoxic shock).
• Other types:
  • Traumatic Shock: Caused by trauma, initially hypovolaemic, but continues with plasma loss into injured tissue.
  • Neurogenic Shock: Caused by interruption of sympathetic vasomotor supply.
  • Hypoadrenal Shock: Caused by adrenal insufficiency, preventing normal stress response.

### Shock Pathogenesis

• Reduced Effective Circulating Blood Volume: Loss of blood volume or reduced cardiac output.
• Reduced Oxygen Supply: Hypoperfusion causes cellular anoxia.
• Inflammatory Mediators and Toxins: Released from shock-induced cellular injury.

Shock Complications

• Pulmonary Hypoperfusion: Worsened perfusion leading to tachypnoea and ARDS.
• Tissue Ischaemia: Anaerobic glycolysis causes lactic acidosis, lowering tissue pH and leading to vasodilatation.
• Decompensated Shock: Progressive deterioration despite compensatory mechanisms and treatment.

### Decompensated Shock

• Clinical Features: Low blood pressure, subnormal temperature, weak & irregular pulse, shallow & sighing respiration, pale face, sunken eyes, weakness, cold & clammy skin.
• Life-threatening Complications:
  • Acute Respiratory Distress Syndrome (ARDS)
  • Disseminated Intravascular Coagulation (DIC)
  • Acute Renal Failure (ARF)
  • Multiple Organ Dysfunction Syndrome (MODS)
  • Stupor, coma, and death.

This quiz covers the concepts of homeostasis, fluid composition, and oedema in the human body. Explore how the internal environment is maintained and the significance of body fluids in cellular functions. Test your knowledge on the various compositions and the impact of fluid accumulation disorders.