Classification of Tissues – Practice Flashcards

Epithelial Tissue

Simple Cuboidal Epithelium

• Description
  • Single layer of cube-shaped cells
  • Large, centrally located, spherical nuclei
• Function
  • Secretion
  • Absorption
• Typical Locations
  • Kidney tubules
  • Ducts & secretory portions of small glands
  • Surface of ovary
• Microscopic Clues / Photomicrograph
  • Lumen surrounded by simple cuboidal cells
  • Basement membrane separates epithelium from underlying connective tissue
  • Photomicrograph magnification 430x (kidney tubule)

Simple Columnar Epithelium

• Description
  • Single layer of tall, column-shaped cells
  • Nuclei round ➜ oval and usually basal in non-ciliated form
  • May contain goblet cells (unicellular mucus glands)
  • Some variants display surface cilia and/or dense microvilli (brush border)
• Function
  • Absorption of nutrients & fluids
  • Secretion of mucus, enzymes, other substances
  • Ciliated subtype propels mucus or reproductive cells by ciliary action
• Typical Locations
  • Non-ciliated: most of digestive tract (stomach ➜ rectum), gallbladder, excretory ducts of some glands
  • Ciliated: small bronchi, uterine tubes, some uterine regions
• Photomicrograph Details
  • Small intestine section shows goblet cells and tall absorptive cells
  • Magnification 640x

Pseudostratified Columnar Epithelium

• Description
  • Single layer, but cell heights differ → nuclei at varying levels → false impression of multiple layers
  • Often contains goblet cells; ciliated surfaces common
• Function
  • Secrete mucus (esp. goblet cells)
  • Propel mucus via coordinated ciliary beating
• Typical Locations
  • Non-ciliated: male sperm-carrying ducts, large gland ducts
  • Ciliated: trachea, most upper respiratory tract
• Microscopic Clues
  • Irregular nuclear “staggering” + cilia + mucus within goblet cells
  • Photomicrograph magnification 530x (human trachea)

Stratified Squamous Epithelium

• Description
  • Several layers
  • Basal layer: cuboidal/columnar, mitotically active
  • Surface layer: flattened (squamous)
  • Keratinized variant: surface cells dead, filled with keratin
• Function
  • Protection against abrasion & minor chemical attack
• Typical Locations
  • Non-keratinized: moist linings of esophagus, mouth, vagina
  • Keratinized: epidermis (dry, protective skin surface)
• Photomicrograph
  • Esophagus lining; magnification 280x

Stratified Cuboidal Epithelium

• Description: usually two layers of cube-shaped cells
• Function: Protection in large ducts
• Locations: Largest ducts of sweat, mammary, and salivary glands
• Photomicrograph magnification 290x (salivary gland duct)

Stratified Columnar Epithelium

• Description
  • Several layers; basal cells cuboidal, superficial cells elongated & columnar
• Function: Protection & secretion
• Location: Rare—male urethra, large ducts of some glands
• Photomicrograph magnification 290x (male urethra)

Transitional Epithelium

• Description
  • Basal cells: cuboidal/columnar
  • Surface cells: dome-shaped when relaxed, squamous-like when stretched
• Function: Permits stretching & organ distension by urine
• Typical Locations: Ureters, urinary bladder, part of urethra
• Photomicrograph: Urinary bladder wall (relaxed); magnification 365x – note bulbous superficial cells

Connective Tissue

Hallmark Characteristics (All Sub-types)

• Common origin: all arise from embryonic mesenchyme
• Variable vascularity
  • Bone: richly vascularized
  • Dense regular CT: poorly vascularized
  • Cartilage: avascular
• Abundant extracellular matrix (ECM) separates living cells
  • ECM = ground substance + fibers
  • Ground substance: interstitial fluid + cell-adhesion proteins + proteoglycans ➜ consistency ranges liquid → gel → very hard
  • Fibers for support: collagen (white, strong), elastic (yellow, stretch/recoil), reticular (fine collagen, supportive networks)
• Prototype = Areolar CT (shows all fiber types, sparse arrangement, many cell types)

Embryonic CT: Mesenchyme

• Description: Gel-like ground substance, delicate fibers, star-shaped mesenchymal cells
• Function: Precursor for all other connective tissues
• Location: Primarily embryo
• Photomicrograph magnification 627x

Loose Connective Tissues

Areolar CT

• Description: Gel-like matrix; all three fibers; cell types include fibroblasts, macrophages, mast cells, WBCs
• Function
  • Wraps & cushions organs
  • Macrophages phagocytize bacteria
  • Important in inflammation (holds interstitial fluid)
• Location: Widely under epithelia (lamina propria of mucous membranes), packages organs, surrounds capillaries
• Microscopy
  • Abundant empty spaces (“areolae”)
  • Identify starlike fibroblasts, collagen vs elastic fibers
  • Look for mast cells (granule-filled; histamine release)
  • Magnification 365x

Adipose CT

• Description: Sparse matrix, closely packed adipocytes; nucleus displaced peripherally by large fat droplet ("signet ring")
• Function: Energy storage, insulation, cushioning/protection
• Location: Subcutaneous layer, around kidneys & eyeballs, abdomen, breasts
• Microscopy: Minimal matrix; magnification 110x

Reticular CT

• Description: Network of reticular fibers with reticular cells (fibroblast-like)
• Function: Soft internal skeleton (stroma) supporting WBCs, mast cells, macrophages
• Location: Lymph nodes, bone marrow, spleen
• Photomicrograph: Spleen; magnification 350x

Dense Connective Tissues

Dense Regular CT

• Description: Parallel collagen fibers; few elastic fibers; fibroblast nuclei compressed between fibers
• Function: Withstands tensile stress in one direction; forms tendons (muscle→bone), ligaments (bone→bone), aponeuroses
• Photomicrograph: Tendon; magnification 590x

Elastic CT

• Description: Dense regular CT, but high proportion of elastic fibers
• Function: Recoil after stretching; maintains pulsatile blood flow (arteries); aids passive recoil of lungs
• Locations: Large artery walls (e.g., aorta), some vertebral ligaments, bronchial tube walls
• Photomicrograph: Aortic wall; magnification 250x

Dense Irregular CT

• Description: Irregularly arranged collagen fibers; some elastic; fibroblasts predominant
• Function: Structural strength; withstands tension from many directions
• Locations: Dermis of skin, fibrous joint capsules, organ capsules, submucosa of GI tract
• Photomicrograph: Dermis; magnification 210x

Cartilage (Avascular; Chondrocytes in Lacunae)

Hyaline Cartilage

• Matrix: Amorphous, firm; imperceptible collagen network
• Function: Support & reinforce; resilient cushion; resists compressive stress
• Locations: Embryonic skeleton, costal cartilages, articular cartilage (ends of long bones), nose, trachea, larynx
• Photomicrograph: Costal cartilage; magnification 470x

Elastic Cartilage

• Similar to hyaline but with more elastic fibers
• Function: Maintains shape + flexibility
• Locations: External ear (auricle), epiglottis
• Photomicrograph: Ear auricle; magnification 510x

Fibrocartilage

• Matrix: Less firm than hyaline; thick collagen bundles dominate
• Function: Tensile strength & shock absorption
• Locations: Intervertebral discs, pubic symphysis, knee menisci
• Photomicrograph: Intervertebral disc; magnification 160x (blue-stained collagen)

Bone (Osseous Tissue)

• Matrix: Hard, calcified; many collagen fibers
• Cells: Osteocytes in lacunae arranged in concentric lamellae around central (Haversian) canal
• Functions
  • Support & protection
  • Levers for muscles
  • Mineral (Ca^{2+}, PO_4^{3-}) & fat storage
  • Blood cell formation (hematopoiesis) in marrow
• Vascularity: Extensive
• Photomicrograph magnification 175x

Blood

• Description: Plasma (fluid ECM) + formed elements (erythrocytes, leukocytes, platelets)
• Function: Transport of gases, nutrients, wastes, hormones, heat, etc.
• Location: Contained within cardiovascular system
• Photomicrograph: Peripheral smear; magnification 1000x
• Unique Note: Only CT with liquid matrix

Nervous Tissue

• Cell Populations
  • Neurons – excitable, conduct action potentials
  • Features: Cell body with nucleus; long cytoplasmic processes (axon, dendrites) – may reach \approx 1\,\text{m} length
  • Neuroglia – supporting, protective, insulating cells
• Function: Receive stimuli and transmit electrical signals to effectors
• Locations: Brain, spinal cord, peripheral nerves
• Photomicrograph: Spinal cord smear; magnification 370x (dim light reveals processes)

Muscle Tissue

Skeletal Muscle

• Description
  • Long, cylindrical fibers; multinucleate (nuclei peripheral)
  • Prominent cross-striations
• Control: Voluntary
• Function: Body movement, facial expression, posture, heat production
• Location: Attached to bones (sometimes skin)
• Photomicrograph magnification \approx 550x

Cardiac Muscle

• Description
  • Branching fibers, single central nucleus
  • Striated; cells connected by intercalated discs (desmosomes + gap junctions)
• Control: Involuntary (autorhythmic + autonomic modulation)
• Function: Pump blood through circulatory system
• Location: Heart wall (myocardium)
• Photomicrograph magnification 775x

Smooth Muscle

• Description
  • Spindle-shaped cells; single central nucleus; no striations
  • Arranged in sheets, often orthogonal layers
• Control: Involuntary
• Function: Propels substances (food, urine, fetus); regulates lumen diameter (blood vessels, bronchioles)
• Locations: Walls of hollow organs—GI & urinary tracts, uterus, blood vessels, respiratory passages
• Photomicrograph magnification 265x

Practical Microscopy & Study Tips

• Distinguish matrix vs cells—especially in CT subtypes
• Collagen vs elastic fibers: collagen → thick/pink; elastic → thin/dark/coiled
• In dense regular CT, fiber orientation is parallel; in dense irregular CT, criss-cross
• Look for lacunae to identify cartilage or bone; identify chondrocytes vs osteocytes
• Identify specific staining artifacts (e.g., blue fibrocartilage due to special stain)
• Use magnification values (e.g., 430x, 590x) as context for size comparison
• Recognize functional link between structure & location (e.g., cilia + mucus ➜ respiratory defense)

Integrative Connections & Significance

• Epithelial barriers often rest on areolar CT—lamina propria provides vascular support for avascular epithelia
• Transitional epithelium’s domed surface cells withstand toxic, variable-volume urine ➜ clinical relevance: urinary tract pathology may flatten these cells prematurely
• Dense regular CT’s parallel collagen alignment echoes direction of mechanical force (tendons/ligaments) ➜ injuries (sprains/strains) heal slowly due to poor vascularity
• Cartilage avascularity explains poor regenerative capacity; contrast with richly vascularized bone
• Intercalated discs in cardiac muscle allow synchronized contraction; damage (myocardial infarction) disrupts this unity ➜ arrhythmias
• Neuroglia outnumber neurons \approx 10:1, emphasizing supportive importance; demyelinating diseases (e.g., MS) stem from glial dysfunction