Anatomy: Connective Tissue & Integumentary System

Connective Tissue: Overview

  • Four main classes: connective tissue proper, cartilage, bone, blood.
  • Cells and matrix: matrix with fibers + ground substance; CT proper cells are primarily fibroblasts and fibrocytes.
  • Cell maturity: blast = immature cell; mature cells include fibrocytes, osteocytes, etc.
  • Origin: mesenchyme (embryonic stem cells) give rise to CT components.
  • Cartilage vs bone: cartilage is avascular and tends to be in joints; bone is vascularized and highly organized.

Bone

  • Immature bone cells are called blasts; mature bone cells are osteocytes.
  • Two basic bone types: compact bone (outer surface) and spongy (trabecular) bone (inside).
  • Compact bone contains osteons (concentric rings around a central canal).
  • Bone is vascularized; blood formation occurs in bone marrow.
  • Joints and contact surfaces often involve cartilage near bones to reduce friction.

Cartilage

  • Cells: chondrocytes reside in lacunae.
  • Characteristic: avascular and has limited healing.
  • Common joint context: glassy smooth surface = hyaline cartilage for low-friction articulation.
  • Areas of high compression often show fibrocartilage.
  • Cartilage arises from mesenchymal tissue during development.

Connective Tissue Proper

  • Cells: fibroblasts (produce fibers) and fibrocytes (mature cells).
  • Fibers in matrix: collagen, elastin, reticular fibers (general CT framework).
  • Dense vs loose types vary by fiber density and arrangement.
  • Dense connective tissue includes regular, irregular, and elastic categories.
  • Under each CT class, note which forms the base of membranes and supports subcutaneous tissues.

Blood

  • Blood is a connective tissue with a liquid matrix called plasma.
  • Plasma is mostly water; components include formed elements: erythrocytes, leukocytes, thrombocytes.
  • Erythrocytes = mature red blood cells; leukocytes = white blood cells; thrombocytes = platelets (clotting).
  • Blood provides transport, immunity, and clotting functions.

Muscle Tissue

  • Three types: skeletal, cardiac, smooth.
  • Skeletal: attached to bones, voluntary control, striated.
  • Cardiac: only in the heart, involuntary, striated, with intercalated discs.
  • Smooth: lines hollow organs, involuntary, non-striated.
  • Key distinctions: striations and voluntary vs involuntary control.

Nervous Tissue

  • Primary cell type: neurons (large, highly branched cells).
  • Main functions: receive sensory information, process it (in brain/spinal cord), and respond with an effect.
  • Neurons have long processes and specialized junctions; nervous system coordinates all body activities.

Integumentary System (Skin & Accessories)

  • Skin organization: epidermis (outer, avascular) and dermis (beneath, vascular, contains vessels, nerves, hair follicles).
  • Dermis houses receptors and various structures; epidermis contains multiple keratinocyte layers.
  • Epidermis is keratinized and waterproof; outermost strata are dead cells.
  • Key epidermal layers (from bottom to top):
    • Stratum basale (deepest, mitotically active)
    • Stratum spinosum
    • Stratum granulosum (granules; cells begin to die)
    • Stratum lucidum (thick skin only; optional in thin skin)
    • Stratum corneum (outermost, dead keratinocytes; waterproof)
  • Keratinization: process that creates the waterproof, tough outer layer.
  • Epidermis is avascular; blood vessels are in the dermis and subcutaneous tissue.
  • Subcutaneous tissue (hypodermis) is loose connective tissue that anchors skin to underlying tissues.
  • Practical note: understanding the epidermal layers helps predict healing and sensation patterns after injury.