Advanced Notes on Altered Cells, Tissues, and Electrolyte Imbalance

Anatomic Organization and Cellular Components

• Levels of Anatomic Organization: Biological hierarchy progresses from fundamental units to complex systems:

  • Cells: The basic unit of life.

  • Tissues: Groups of similar cells working together.

  • Organs: Structures composed of different tissues performing specific functions.

  • Organ systems: Groups of organs working together for a common purpose.

• Cellular Components and Functions:

  • Plasma membrane: Maintains cell integrity and controls the entry and exit of substances.

  • Cytoplasm: A jelly-like fluid where organelles are suspended and where chemical reactions occur.

  • Nucleus: Controls all cell activities and contains DNA. Components include the nuclear envelope, nuclear pores, nucleoplasm, nucleolus, and chromatin.

  • Endoplasmic Reticulum (ER):

    • Rough ER: Synthesis of proteins; associated with fixed ribosomes.

    • Smooth ER: Synthesis of lipids and detoxification.

  • Golgi Apparatus: Modifies, sorts, and packages proteins and lipids from the ER.

  • Lysosomes: Act as the recycling center and are involved in excretion and breaking down waste materials.

  • Peroxisomes: Break down fatty acids; they generate and degrade hydrogen peroxide ($H_2O_2$).

  • Proteasomes: Provide protein quality control by degrading damaged or misfolded proteins.

  • Mitochondria: The "powerhouse of the cell," responsible for producing ATP ($Adenosine$ $Triphosphate$).

  • Cytoskeleton: Provides cell support and shapes the cell; composed of microfilaments and microtubules.

  • Additional structures:

    • Ribosomes: Can be "fixed" to the ER or "free" in the cytoplasm.

    • Polyribosome: Multiple ribosomes translating a single mRNA.

    • Cilia: Hair-like projections for movement.

    • Microvilli: Finger-like projections to increase surface area.

    • Vesicles: Small membrane-bound sacs (e.g., exocytotic vesicles, secretory vesicles).

    • Centrioles: Structures involved in cell division.

Transport Mechanisms

• Passive Transport: Does not require energy ($ATP$). Substances move from high concentration to low concentration, moving "down" the concentration gradient.

  • Diffusion: Movement of molecules (gases or solutes) from high to low concentration areas. Example: Oxygen moving into a cell and carbon dioxide moving out.

  • Osmosis: Movement of water molecules across a semipermeable membrane from low solute concentration to high solute concentration. The goal is to balance solute concentration. The pressure generated is called osmotic pressure.

  • Facilitated Transport: Movement from high to low concentration using specific transport proteins.

    • Specificity: Each protein is specific to a substance (e.g., glucose, ions).

    • No Energy: Follows the concentration gradient.

    • Use Case: For molecules too large or polar to cross the lipid bilayer directly.

• Active Transport: Requires energy in the form of $ATP$. It moves molecules against the concentration gradient (low to high).

  • Mechanism: $ATP \rightarrow ADP + energy$.

  • Key Features: Involves specific carrier proteins/pumps, such as the sodium-potassium ($Na/K$) pump. It maintains critical gradients for nerve and muscle cell function.

• Ingestion Mechanisms:

  • Endocytosis: Form of active transport using energy to bring large substances into the cell.

  • Pinocytosis: "Cell drinking"; engulfing small liquid droplets or dissolved substances into vesicles.

  • Phagocytosis: "Cell eating"; specialized cells like macrophages and neutrophils engulf large particles (bacteria, debris).

• Exocytosis (Secretion):

  • Active transport where vesicles (packaged by the Golgi apparatus) fuse with the plasma membrane to release contents outside the cell.

  • Process Flow: Ingestion (forming a phagosome) $\rightarrow$ Lysosome fusion (digestion) $\rightarrow$ Exocytosis (waste expulsion).

Cellular Metabolism, Communication, and Reproduction

• Cellular Respiration: Metabolic processes transforming fuel (glucose) into usable energy ($ATP$), $CO_2$, and water.

  • Aerobic Respiration: Highly efficient; occurs in most animal cells.

    • Requirement: Uses Oxygen.

    • yield: High ($36–38$ $ATP$ total).

    • Breakdown: Glycolysis ($2$ $ATP$), Krebs cycle ($2$ $ATP$), and Electron Transport Chain ($32-34$ $ATP$).

    • Location: Mitochondria.

  • Anaerobic Respiration: Occurs in microorganisms or human muscle during intense activity.

    • Requirement: No Oxygen.

    • Yield: Low ($2$ $ATP$ total).

    • Product: Lactic acid.

    • Location: Cytoplasm (Glycolysis only).

• Cell Communication:

  • Signals: Essential for coordinating functions like growth, immune response, and tissue repair.

  • Receptor-Ligand Binding: A ligand (hormone or neurotransmitter) binds to a specific receptor, triggering signal transduction inside the target cell.

  • Feedback Mechanisms: Regulate activity; negative feedback prevents overstimulation and damage.

• Reproduction and Differentiation:

  • Cellular Differentiation: Cells become specialized for specific functions (e.g., muscle, nerve, skin).

  • Meiosis: Produces four genetically unique gametes (haploid cells). Occurs only in reproductive cells.

  • Mitosis: Produces two identical daughter cells for growth and repair. Occurs in somatic (body) cells.

Cellular Adaptation and Response to Stress

1. Atrophy: Decrease in cell size due to reduced workload, blood supply (ischemia), nutrition, or use. Example: Muscle shrinking in a casted limb.

2. Hypertrophy: Increase in cell size, leading to larger tissue/organs. Example: Cardiac muscle enlargement due to high blood pressure; reproductive cells enlarging during puberty due to sex hormones.

3. Hyperplasia: Increase in the number of cells. Example: Proliferation of endometrial lining; Benign Prostatic Hyperplasia (BPH); increased red blood cells at high altitudes.

4. Metaplasia: Reversible replacement of one adult cell type with another better suited for stress. Example: Columnar epithelium in respiratory tracts becoming squamous cells in smokers.

5. Dysplasia: Abnormal changes in cell size, shape, uniformity, and organization. Often pre-cancerous.

   • Example 1: Cervical dysplasia from Human Papillomavirus (HPV) detected via Pap smear.

   • Example 2: Bronchopulmonary dysplasia (BPD), which prompts chronic, irreversible tissue changes.

Cellular Injury and Death

• Mechanisms of Death:

  • Apoptosis: Programmed cell death; energy-dependent and controlled. Does not cause inflammation. Example: Removal of webbing between fingers during fetal development.

  • Necrosis: Uncontrolled death due to injury; causes cell rupture, inflammation, and tissue damage. Example: Tissue death after a myocardial infarction.

• Causes of Injury:

  • Physical: External forces (e.g., blunt trauma from a fall).

  • Mechanical: Structural stress (e.g., shearing injuries or lacerations).

  • Thermal: Extreme temperatures (e.g., burns or frostbite).

  • Chemical: Toxins (e.g., lead poisoning, strong acids/bases).

Electrolyte Dynamics

• Electrolytes: Electrically charged particles (ions) in body fluids.

  • Cations: Positive charge.

  • Anions: Negative charge.

  • Electroneutrality: Determines the balance across compartments.

• Normal Electrolyte Concentrations:

  • Sodium ($Na^+$): Extracellular ($135-145\,mEq/L$); Intracellular ($10-14\,mEq/L$).

  • Chloride ($Cl^-$): Extracellular ($98-106\,mEq/L$); Intracellular ($3-4\,mEq/L$).

  • Potassium ($K^+$): Extracellular ($3.5-5\,mEq/L$); Intracellular ($140-150\,mEq/L$).

  • Calcium ($Ca^{2+}$): Extracellular ($8.5-10.5\,mg/dL$); Intracellular ($< 1\,mEq/L$).

  • Bicarbonate ($HCO_3^-$): Extracellular ($24-31\,mEq/L$); Intracellular ($7-10\,mEq/L$).

Electrolyte Imbalances and Manifestations

• Sodium ($Na^+$):

  • Hyponatremia ($< 135\,mEq/L$): Muscle cramps, twitching, weakness, volume deficit, hypotension, oliguria, headache, anxiety, altered consciousness.

  • Hypernatremia ($> 145\,mEq/L$): Thirst, dry skin/mucous membranes, decreased excretions, headache, restlessness, altered consciousness.

• Potassium ($K^+$):

  • Hypokalemia ($< 3.5\,mEq/L$): Dizziness, muscle weakness, leg cramps, cardiac arrhythmia, hypotension, thirst, nausea, anorexia, polyuria (impaired renal concentration).

  • Hyperkalemia ($> 5\,mEq/L$): Cardiac arrest, abdominal cramping, flaccid paralysis.

• Chloride ($Cl^-$):

  • Hypochloremia ($< 98\,mEq/L$): Hypertonicity, twitching, weakness, tetany, shallow/depressed breathing, respiratory arrest, mental confusion.

  • Hyperchloremia ($> 108\,mEq/L$): Hyperchloremic metabolic acidosis, deep/rapid breathing, weakness, headache, diminished cognitive ability, cardiac arrest.

• Calcium ($Ca^{2+}$):

  • Hypocalcemia ($< 8.5\,mg/dL$): Enhanced neuromuscular irritability, anxiety, irritability, seizure, muscle twitching/cramps/spasm, tetany, laryngospasm, hypotension, arrhythmia.

  • Hypercalcemia ($> 10.5\,mg/dL$): Decreased neuromuscular irritability, confusion, fatigue, headache, constipation, nausea, vomiting, arrhythmia.

• Magnesium ($Mg^{2+}$):

  • Hypomagnesemia ($< 1.5\,mEq/L$): Tetany, muscle cramping, seizures, cardiac arrhythmia, hypotension.

  • Hypermagnesemia ($> 2.5\,mEq/L$): Reduced neuromuscular transmission/excitability, flaccid paralysis, diminished reflexes, muscle weakness, hypotension, respiratory depression.

• Phosphate ($PO_4^{3-}$):

  • Hypophosphatemia ($< 2.5\,mg/dL$): Muscle weakness, tremor, paresthesia, weight loss, bone deformity.

  • Hyperphosphatemia ($> 4.5\,mg/dL$): Often asymptomatic; may show muscle tetany or calcium deposits in soft tissues.

Fluid Balance and Regulation

• Fluid Transport: Water moves via aquaporins (specialized channels) through osmosis.

  • Osmolality: Osmolar concentration in $1\,kg$ of water.

• Regulation Mechanisms:

  1. Thirst: Triggered by high osmolality or low volume.

  2. RAAS (Renin-Angiotensin-Aldosterone System): Activated by low BP/sodium. Renin $\rightarrow$ Angiotensin I $\rightarrow$ Angiotensin II (via ACE) $\rightarrow$ Vasoconstriction and Aldosterone release (sodium/water retention).

  3. Antidiuretic Hormone (ADH): From posterior pituitary; promotes water reabsorption and concentrated urine.

  4. Diuretics: Medications (e.g., Furosemide, HCTZ) used for hypertension or edema by promoting urine output.

• Tonicity: The osmotic pressure gradient between two fluids:

  • Isotonic: Equal concentration (e.g., $0.9\%$ sodium chloride). No net water movement.

  • Hypotonic: Lower solute concentration outside cell (e.g., $0.45\%$ sodium chloride). Water enters cell; cell ممکن است swell/burst.

  • Hypertonic: Higher solute concentration outside cell (e.g., $3\%$ sodium chloride). Water leaves cell; cell shrinks/shrivels.

Pathological Fluid Shifts

• Mechanisms of Edema:

  1. Increased Capillary Hydrostatic Pressure: Pressure inside vessels pushes fluid out (e.g., heart failure).

  2. Decreased Capillary Oncotic Pressure: Low albumin levels fail to pull fluid back into capillaries (e.g., liver disease, malnutrition).

  3. Increased Capillary Permeability: "Leaky" walls due to inflammation, burns, or trauma.

  4. Lymphatic Obstruction: Blocked drainage (e.g., after breast cancer surgery).

• Hypervolemia: Extracellular volume expansion.

  • Cues: Hypertension, bounding pulses, muscle weakness, cramps, fatigue, headache, confusion, depressed deep tendon reflexes ($DTRs$).

• Dehydration:

  • Causes: Low intake, high output (diarrhea), fluid shifts (ascites).

  • Classification: Hyponatremic, isonatremic, or hypernatremic.

  • Recognizing Cues: Thirst, dry mucous membranes, weight loss, flattened neck veins, diminished skin turgor, prolonged capillary refill ($>3\,seconds$), decreased/absent urine output, tachycardia (increased heart rate), hypotension, altered consciousness, depressed fontanelles (in infants), and sunken eyes.