Pathophysiology: Homeostasis and Feedback Mechanisms

Study Notes

Homeostasis is the dynamic process of maintaining internal balance, regulating nutrient concentrations, pH, O2/CO2 levels, electrolytes, and temperature.
Disruption of homeostasis can lead to illnesses such as infections, injuries, and nutrient deficiencies.
Feedback mechanisms consist of a sensor (detects disruption), control center (regulates response), and effector (restores balance).
Two main types of feedback:
- Negative feedback corrects disruptions (e.g., high blood glucose levels).
- Positive feedback moves systems further from homeostasis (e.g., labor contractions).

Hypoxic cell injury refers to decreased oxygen supply to blood cells, often initiated by lung injury.
Ischemia is a common cause of cell injury due to inadequate oxygen reaching tissues.
Irreversible cell injury causes include cell membrane damage, lysosomal membrane rupture, and necrosis.
Cellular swelling occurs due to ATP depletion, anaerobic glycolysis, and lactic acid accumulation, impairing cell volume regulation.

Non-specific (innate) immunity comprises natural barriers and inflammation, while specific (adaptive) immunity involves B- and T- lymphocytes.
Vascular response involves vasodilation, increased permeability, and white blood cell (WBC) migration to injury sites.
Plasma protein cascade components include the complement system, clotting system, and Kinin system.
Chemotaxis is the movement of immune cells directed by chemical signals, often involving cytokines.
Key roles in inflammation:
- Complement system: recruits WBCs and can lyse pathogens.
- Clotting cascade: forms a fibrinous meshwork to trap pathogens and aid in healing.
- Bradykinin: causes vasodilation and increases permeability, activating pain receptors.
- Mast cells: release histamine during inflammatory responses.
- Dendritic cells: process antigens and activate T-cells.
- Types of immune cells:
  - Neutrophils: primary responders for phagocytosis.
  - Eosinophils: combat allergies and parasites.
  - Macrophages: derived from monocytes for tissue phagocytosis.

Osmosis is the passive movement of water from high to low concentration; hydrostatic pressure is the force of water against membranes.
Major intracellular cation: K+; major extracellular cation: Na+; proteins predominantly remain intracellular.
Aldosterone promotes sodium reabsorption and water conservation, while ADH regulates water excretion based on blood osmolarity and pressure.
Edema can arise from:
- Increased capillary permeability due to inflammation.
- Increased hydrostatic pressure from conditions like CHF.
- Decreased oncotic pressure from low plasma protein levels.
- Loss of plasma proteins affects fluid balance.

Risk factors for coronary heart disease include modifiable factors (HTN, smoking, etc.) and non-modifiable factors (age, gender, genetics).
Atherosclerotic plaque development follows endothelial injury, leading to inflammation, monocyte migration, and LDL oxidation.
Various types of chest pain:
- Stable angina: triggered by exertion, relieved by rest.
- Unstable angina: occurs at rest, risks heart ischemia.
- Prinzmetal angina: transient ischemia at rest.

Left-sided heart failure involves diminished ventricular function and pulmonary congestion, leading to pulmonary edema and systemic effects.
Right-sided heart failure typically stems from left-sided failure or conditions like COPD, increasing systemic vascular resistance.
Clinical manifestations include dyspnea, fatigue, and fluid retention.

Blood pressure classification divides systolic and diastolic categories; higher blood volume increases pressure.
Types of shock:
- Cardiogenic shock: results from heart failure and low cardiac output.
- Hypovolemic shock: due to significant fluid loss.
- Neurogenic shock: caused by spinal cord injury leading to vasodilation.
- Anaphylactic shock: severe allergic reaction causing widespread vasodilation.
- Septic shock: results from systemic infections leading to multiple organ dysfunction.

Normal PCO2: 35-45 mmHg; normal PO2: 80-100 mmHg.
Hypoxemia is low oxygenation in arterial blood; causes include altitudes, diffusion issues, and ventilation-perfusion imbalances.
Hypercapnia results from reduced breathing effectiveness, potentially leading to acid-base imbalance.
Hypoventilation results in inadequate CO2 removal, while hyperventilation exceeds the body's ventilatory demands.