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Unit II. Cells, Tissues, Glands and Membranes

Cells

  • Basic unit of life; growth determined by replication.
  • General cell functions: provide structure; absorb nutrients for energy to carry out functions.

Cell Structure and Organelles

  • Cell membrane: outer semi-solid covering; facilitates movement of organelles and provides protection.
  • Cytoplasm (Protoplasm): filling fluid where organelles float; site of many metabolic activities.
  • Nucleus: controls/regulates cell activities and carries hereditary information; contains DNA.
  • Nucleolus: ribosome synthesis.
  • Chromatin: DNA packaging inside the nucleus.
  • Rough Endoplasmic Reticulum (RER): production, folding, quality control, and dispatch of some proteins; ribosomes on surface synthesize proteins.
  • Smooth Endoplasmic Reticulum (SER): lipid/phospholipid synthesis; fat metabolism.
  • Golgi apparatus: modifying, sorting, and packaging of proteins for secretion; involved in lipid transport and lysosome creation.
  • Golgi vesicles: pinch off membranes and transport contents through the cell.
  • Ribosomes: protein builders; synthesize amino acids into proteins.
  • Mitochondria: powerhouse; site of cellular respiration providing energy.
  • Peroxisome: oxidation of fatty acids and amino acids; neutralize free radicals.
  • Lysosome: digest excess/worn-out organelles, food particles, viruses, and bacteria.
  • Vacuole: store nutrients and water; house waste to protect other cells.
  • Centrosome: microtubule organizing center; regulates the cell cycle via microtubule assembly.
  • Microtubules: move chromosomes during cell division; attach to daughter cells.
  • Microfilaments: thin protein strands; provide shape and aid movement.
  • Intermediate filaments: mechanical support for the plasma membrane; not involved in motility.

Cytoskeleton & Proteins

  • Cytoplasm: gel-like matrix hosting organelles.
  • Ribosomes, Golgi, ER, mitochondria, lysosomes, peroxisomes: coordinated in protein/lipid synthesis and trafficking.

Tissues

  • Tissues: groups of cells with common origin functioning together for specialized activities; histology is the study of tissues; pathologist analyzes cells/t tissues for diagnoses.

Epithelial Tissues

  • Functions: protection, secretion, absorption, excretion, filtration, diffusion, sensory reception.
  • Lines and roles: lines air sacs, heart and blood vessel linings; ducts and secretory portions of glands; ciliated and non-ciliated varieties in respiratory/digestive tracts.

Connective Tissues

  • Connects and supports; ranges from avascular to highly vascular; extracellular matrix separates cells.
  • Examples: fat, bone, cartilage, tendons, blood.
  • Fibers:
    • Collagen fibers: about 25\% of body protein; tough, resistant, yet flexible.
    • Elastin fibers: stretchable up to 150\% and return to normal.
    • Reticular fibers: form internal framework in organs (e.g., spleen, lymph nodes).

Muscle Tissues

  • Skeletal muscle: striated, tubular, multinucleated; usually attaches to skeleton; voluntary.
  • Cardiac muscle: striated, branched, typically one nucleus; found in heart walls; involuntary; intercalated discs.
  • Smooth muscle: spindle-shaped, non-striated, single nucleus; in walls of internal organs; involuntary.

Nervous Tissues

  • Found in brain, spinal cord, and nerves.
  • Function: transmits impulses; regulates activities, emotions, memory, and reasoning.
  • Types:
    • Neurons: primary impulse transmitters.
    • Neuroglial cells: support neurons.

Membranes

  • Membranes cover and line cell surfaces and many organs.
  • Functions: contain cellular components, regulate movement of molecules, enable communication, provide reaction sites, facilitate mobility.
  • Types:
    • Mucous membranes: line digestive, respiratory, urinary, and reproductive tracts; secretions from mucous glands.
    • Serous membranes: line closed body cavities (peritoneal, pleural, pericardial); secrete serous fluid; have parietal and visceral layers.
    • Cutaneous membrane: skin; protects external surface.

Glands

  • Definition: glandular tissue secreting substances for body use or release.
  • Classification:
    • Endocrine glands: secrete hormones into bloodstream; no ducts (e.g., hypothalamus, pituitary, thyroid, parathyroids, thymus, adrenal, pancreas [endocrine part], ovary, testis).
    • Exocrine glands: secrete products into ducts (e.g., sweat, ear wax, saliva, digestive enzymes).
  • Unicellular vs multicellular glands
    • Unicellular: goblet cells.
    • Multicellular: various duct structures.
    • Duct patterns: simple vs compound; tubular, acinar, tubuloacinar; and combinations (e.g., simple tubular, simple branched tubular, simple branched acinar, simple branched alveolar, compound tubular, compound alveolar, compound tubuloalveolar).

Inflammation

  • Definition: localized defensive response to injury or tissue destruction.
  • Cardinal signs (5): Pain, Heat, Redness, Swelling, Loss of Function.
  • Major events in local inflammatory response:
    • Activated macrophages/mast cells release chemical signals; nearby capillaries widen and become permeable.
    • Fluid, antimicrobial proteins, and clotting elements move to the site; clot forms.
    • Chemokines attract more phagocytes (neutrophils and macrophages) from blood.
    • Phagocytosis of pathogens and debris; tissue heals.