Cells

• Homeostasis is the process through which the body maintains a stable internal environment, including the balance of fluid, electrolytes, and pH levels
• Fluid Balance:

  • Thirst Mechanism: Specialized cells in the brain detect decreased fluid levels and trigger thirst to prompt drinking fluids
  • Kidney Function: Filters waste products and excess water from the blood, excreting them as urine. Also reabsorbs water and important electrolytes when necessary
• Electrolyte Balance:

  • Kidney Function: Regulates levels of electrolytes (sodium, potassium, calcium, magnesium) by excreting or retaining them as needed
  • Hormonal Regulation: Hormones like aldosterone regulate electrolyte balance by promoting sodium reabsorption and potassium excretion
• pH Balance:

  • Buffer Systems: Help maintain pH balance by absorbing or releasing hydrogen ions. Examples include bicarbonate, phosphate, and protein buffer systems
  • Respiratory Regulation: Controls CO2 levels in the body to adjust acidity. Increased CO2 levels lead to increased acidity, so the respiratory system adjusts breathing rate to expel excess CO2
  • Renal Regulation: Kidneys reabsorb or excrete hydrogen ions and bicarbonate ions to adjust blood pH and maintain acid-base balance
• These mechanisms work together to maintain fluid balance, electrolyte balance, and pH balance within narrow ranges
• Feedback mechanisms are activated to restore equilibrium and ensure proper functioning of cells and organs in the body when there is an imbalance
• Sodium (Na+):

  • Role: Main extracellular cation crucial for maintaining proper fluid balance, nerve function, muscle contraction, and acid-base balance
  • Too much: Excess sodium in extracellular fluid can lead to water retention, increased blood pressure, strain on the cardiovascular system, and an increased risk of conditions like hypertension and edema
  • Too little: Low sodium levels (hyponatremia) can result in symptoms such as weakness, fatigue, confusion, muscle cramps, seizures, and, in severe cases, it can even be life-threatening
• Potassium (K+):

  • Role: Primary intracellular cation essential for maintaining proper nerve and muscle function, regulating heartbeat, balancing fluids within cells, and supporting kidney function
  • Too much: Excessive potassium (hyperkalemia) in extracellular fluid can disrupt the electrical activity of the heart, leading to abnormal heart rhythms and potentially life-threatening conditions
  • Too little: Low potassium levels (hypokalemia) can cause muscle weakness, fatigue, irregular heartbeat, constipation, and impaired kidney function
• Calcium (Ca2+):

  • Role: Vital for maintaining strong bones and teeth, proper nerve function, muscle contraction, blood clotting, and enzyme activity
  • Too much: Elevated calcium levels (hypercalcemia) in extracellular fluid can lead to kidney stones, bone pain, digestive issues, muscle weakness, and abnormal heart rhythms
  • Too little: Low calcium levels (hypocalcemia) can cause muscle spasms, numbness or tingling in extremities, osteoporosis, and increased risk of fractures
• Magnesium (Mg2+):

  • Role: Involved in hundreds of enzymatic reactions, including energy production, protein synthesis, muscle and nerve function, and maintaining a healthy immune system
  • Too much: Excess magnesium (hypermagnesemia) can lead to muscle weakness, low blood pressure, respiratory distress, and cardiac abnormalities
  • Too little: Low magnesium levels (hypomagnesemia) can cause muscle cramps, tremors, weakness, fatigue, irregular heartbeat, and impaired nerve function
• Maintaining proper electrolyte balance is crucial for overall health

  • Electrolyte imbalances can be caused by various factors such as certain medical conditions, medications, dehydration, hormonal disorders, or kidney problems
  • If an electrolyte imbalance is suspected, it's essential to seek medical attention for appropriate diagnosis and treatment
• Key characteristics of epithelial tissue:

  • Cellularity: Composed of closely packed cells with minimal extracellular matrix
  • Polarity: Cells have distinct apical (upper) and basal (lower) surfaces
  • Attachment: Anchored to a basement membrane separating it from underlying connective tissue
  • Avascularity: Does not have blood vessels but receives nutrients and oxygen through diffusion
  • Regeneration: High rate of cell division, can regenerate and repair damaged tissue quickly
• Classification of epithelial tissue based on:

  • Cell morphology: Squamous (flattened and scale-like), cuboidal (cube-shaped), and columnar (tall and rectangular) epithelia
  • Number of layers: Simple (single layer) or stratified (multiple layers) epithelia
• Adaptive features used in naming epithelia and their functions:

  • Specializations: Cilia for movement, microvilli for increased surface area, goblet cells for mucus production
  • Secretory function: Some epithelia have secretory cells producing substances like hormones, enzymes, or mucus
  • Barrier function: Acts as a protective barrier against mechanical injury, pathogens, and loss or absorption of substances
  • Sensory function: Contains sensory cells detecting stimuli
• Epithelial tissue found in specific areas:

  • Skin: Stratified squamous epithelium for protection against mechanical stress, pathogens, and dehydration
  • Buccal cavity, oropharynx, trachea, alveoli: Different types of epithelia for protection and foreign particle removal
  • Esophagus, stomach, ileum: Each with specific epithelium for protection, secretion, absorption, and nutrient absorption
  • Vagina: Stratified squamous epithelium for protection and elasticity
  • Urinary bladder: Transitional epithelium for stretching and accommodating changes in urine volume without leakage
• Basic characteristics of neurons:

  • Excitability: Neurons can respond to various stimuli by generating and propagating electrical impulses
  • Conductivity: Neurons can transmit electrical impulses over long distances
  • Secretion: Neurons can release neurotransmitters at synapses to communicate with other neurons or target cells
  • Longevity: Neurons are typically long-lived cells
  • Nondivisibility: Most neurons lose their ability to divide and replicate after development
• Structural classification of neurons:

  • Multipolar neurons: Have multiple processes (dendrites and one axon), involved in motor control and sensory information integration
  • Bipolar neurons: Have two processes—one dendrite and one axon, specialized for sensory functions like vision and olfaction
  • Unipolar neurons: Have a single process that divides into two branches, involved in sensory functions transmitting information to the central nervous system
• Functional classification of neurons:

  • Sensory neurons (afferent neurons): Transmit sensory information to the central nervous system
  • Motor neurons (efferent neurons): Transmit signals from the central nervous system to muscles or glands
  • Interneurons (association neurons): Located in the central nervous system, facilitate communication between sensory and motor neurons
• Neuroglia (glial cells):

  • Astrocytes: Provide structural support, regulate the chemical environment, contribute to the blood-brain barrier, assist in neuronal development and repair
  • Oligodendrocytes: Produce and maintain the myelin sheath in the central nervous system for faster impulse transmission
  • Schwann cells: Produce the myelin sheath in the peripheral nervous system
  • Microglia: Act as immune cells, defend against pathogens, remove damaged cells or debris, contribute to the inflammatory response
• • Ependymal cells: Line the ventricles of the brain and central canal of the spinal cord, assist in the production and circulation of cerebrospinal fluid, provide a barrier between cerebrospinal fluid and neural tissue