Primary Tissues Notes

Primary Tissues

Tissues

• Four primary tissue types:

  • Epithelial tissue

  • Connective tissue

  • Muscle tissue

  • Nervous tissue

Epithelial Tissue

• A sheet of cells that:

  • Covers a body surface.

  • Lines a body cavity.

  • Examples:

    • Skin

    • Inner linings of hollow organs and cavities

    • Lining of all blood vessels

• Forms most of the body’s glands.

• Occurs at the interface of two different environments.

Classifications of Epithelial Tissue

• Each type has two names:

  1. Number of cell layers.

  2. Shape of the cells.

• Based on number of cell layers:

  1. Simple: A single cell layer.

  2. Stratified: More than one layer of cells.

• Based on cell shape:

  1. Squamous: Flat cells.

  2. Cuboidal: Cube-shaped cells.

  3. Columnar: Column-like cells.

Epithelial Surfaces

• Two primary surfaces:

  • Apical: Opens inward.

  • Basal: Connects to deeper tissues (usually connective tissue).

Epithelial Tissue Types

• Simple Squamous:

  • Walls of capillaries.

  • Skin.

  • Linings of pleural and peritoneal cavities.

• Simple Cuboidal:

  • Pancreas

  • Salivary glands

• Simple Columnar:

  • Ciliated or non-ciliated.

  • Female reproductive tract, uterus.

• Stratified Squamous:

  • Non-keratinized: Mucosal lining of oral cavity.

  • Keratinized: Epidermis of palm and dorsum of foot.

• Stratified Cuboidal:

  • Sweat glands, mammary glands, salivary glands.

• Stratified Columnar:

  • Rare.

  • Male urethra and vas deferens, conjunctiva.

• Transitional:

  • Lines the ureters, bladder, and part of the urethra

• Function related to tissue type:

  • Squamous: Diffusion and filtration (Simple), Protection (Stratified)

  • Cuboidal: Secretion and absorption (Simple), Protection (Stratified)

  • Columnar: Secretion and absorption; ciliated types propel mucus or reproductive cells (Simple), Protection (Stratified)

  • Transitional: Protection; stretching to accommodate distension of urinary structures

  • Thinner the tissue, easier to push; thicker the tissue, more for protection

Epithelial Tissue: Glands

• Formed by epithelial cells that make and secrete products.

  1. Endocrine: Secrete substances directly into the bloodstream.

  2. Exocrine: Ducts carry products onto epithelial body surfaces or into cavities.

• Examples of exocrine glands:

  • Salivary glands (parotid, submandibular, sublingual)

  • Liver and pancreas

Cilia

• Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces.

Connective Tissue

• Most diverse and abundant tissue type.

• Two main types of connective tissue proper:

  • Loose connective tissue (e.g., collagen, reticular, and elastic fibers; interstitial fluid; defense cells; adipose cells).

  • Dense connective tissue (regular or irregular) (e.g., fibrous capsules of certain organs; ligaments and tendons; fascia membranes surrounding muscles, vessels, or nerves).

• Specialized forms of connective tissue:

  • Cartilage, bone, and blood.

Characteristics of Connective Tissue

• Cells are situated in an extracellular fluid.

• Ground substance:

  • A clear, colorless, viscous fluid.

  • Fixes the body water and fibers (collagen) within the intercellular space.

• The matrix of connective tissue is formed by the ground substance and fiber content.

• Loose vs. dense connective tissue is determined by the ratio of ground substance to fiber content.

• Cell types:

  • Fibroblast. Macrophage. Lymphocyte. Fat cell. Mast cell. Neutrophil.

Connective Tissue Fiber Component

• Collagenous:

  • Bind bones and other tissues to each other.

  • Tendons, ligaments, cartilage, intervertebral disc, etc.

• Elastic:

  • Allow organs to recoil.

  • Arteries and lungs.

• Reticular:

  • A scaffolding matrix.

  • Liver, bone marrow, lymph, etc.

Connective Tissue Types

• Embryonic Connective Tissue: Mesenchyme

• Connective Tissue Proper:

  • Loose Connective Tissue:

    • Areolar.

    • Adipose.

    • Reticular.

  • Dense Connective Tissue:

    • Dense Irregular.

    • Dense Regular.

    • Elastic.
      *Note: Elastic is a dense regular connective tissue containing a high proportion of elastic fibers.

• Cartilage:

  • Hyaline

  • Elastic

  • Fibrocartilage

• Bone (Osseous Tissue)

• Blood

Cartilage

• A specialized type of connective tissue; firm yet flexible.

• Functional properties:

  • Reinforcement and support.

  • Shape maintenance.

  • Ability to absorb compressive shock.

• Found in several parts of the skeleton:

  • Ends of the long bones in the skeleton, cartilages of the ribs, trachea – protection and support, cushioning properties.

  • Framework of the ear and the nose – shape maintenance.

  • Discs between individual vertebrae – shock absorption.

Bone (Osseous Tissue)

• Bones make up the skeletal framework of the body.

• Functions:

  • Supports and protects by enclosing subdivisions of the dorsal body cavity.

  • Provides levers for muscles to act on and produce movements at various joints.

  • Stores calcium, other minerals, and fat.

  • Site for blood cell formation (hematopoiesis).

• Two types:

  • Compact bone

  • Spongy bone

• Cross-section of a typical long bone:

  • Proximal epiphysis, Diaphysis, Distal epiphysis

    • Articular cartilage, Epiphyseal line, Periosteum, Compact bone, Medullary cavity, Yellow bone marrow.

    • Perforating (Sharpey's) fibers, Nutrient arteries.

    • Endosteum

Blood

• The most atypical connective tissue type as it does not serve the functions of binding elements together or providing support.

• Vehicle of the cardiovascular system that allows the transport of respiratory gases, defense cells, nutrients, wastes, and other substances throughout the body.

• Components:

  • Red blood cells (erythrocytes)

  • White blood cells (leukocytes)

  • Platelets

  • Plasma: Fluid matrix

Nervous Tissue

• The main component of the nervous system:

  • Brain

  • Spinal cord

  • Nerves (neurons and support cells)

• Two types of cells:

  1. Neurons: Highly specialized cells which generate and conduct impulses.

  2. Supporting cells (neuroglia): Nutrition, insulation, and protection.

• Function: Transmit electrical signals from sensory receptors and to effectors (muscles and glands) which control their activity.

Muscle Tissue

• Three types of muscle tissue:

  • Skeletal: The major component of skeletal muscles that pull on different bones to produce movements.

  • Smooth: Occurs primarily in the walls of hollow visceral organs; acts to propel substances through these organs by generating sequences of contraction and relaxation.

  • Cardiac: Unique type of muscle tissue that only occurs in the walls of the heart.

The basics of tissue organization

• Generally speaking, the four basic tissues are organized in such a fashion that they are always in close association to one another.

  • Epithelium always rest upon or is supported by connective tissue

  • Peripheral nerves are surrounded by, or embedded within, connective tissue.

  • Muscle tissue is enmeshed by connective tissue.

  • Blood vessels (organs in their own right, built from all four basic tissues) travel within connective tissue.

• These relationships hold true throughout the body, so that CT is found everywhere with the muscles, nerves and vessels running through it, and epithelium rest upon it.

FYI: Connective tissue vocab

• Connective tissue is found everywhere, and there are names given to the geographic location of certain CT.

  • Adventitia: CT closest to (surrounding an organ)

  • Serosa: CT surrounding (enclosing) an organ that is adjacent to a body cavity.

  • Organ sheath: Sometimes CT will form a tough sheet of tissue that strongly envelopes an organ. (Think Rectus sheath in the abdomen).

  • Fascia: Generally CT that is found in places other than mentioned above and/or deep to the skin (i.e. Superficial fascia).

Tubular vs. glandular organs

• The body’s organs are built in such a way, that they fall into one of two categories: Glandular organs or Tubular organs.

  • Glandular organs: Salivary glands, pancreas, lacrimal gland, lungs, liver, kidneys, etc.

  • Tubular organs: Oral cavity, esophagus, stomach, small intestine, large intestine, rectum, and anal canal (the gastrointestinal tract); nasal passages and trachea (the upper respiratory tract); ureters, bladder, and urethra (the urinary tract); fallopian tube, uterus, vas deferens (the female and male reproductive tracts); and vessels of the circulatory system and the heart.

• While there are obvious differences and many we will discuss as we progress through this course; there are some basic foundations:
  * In both organizations, epithelium rests (is supported by) upon connective tissue.
  * In the tubular plan, epithelium forms the internal lining of the organ.
  * In the glandular plan, the bulk of the secretive portion of the organ (the parenchyma) is epithelium.

Glandular organs

• Glandular organs pack a large number of epithelial cells into a small volume.

• Furthermore, glandular organs allow a large number of secretive epithelial cells to function, without being exposed to the outside environment.

• Glandular epithelial cells are generally well protected by surrounding tissues.

• Some organs that are not generally thought of as ‘glands’, like the kidneys and lungs follow this pattern.

• Glandular epithelium is still supported by underlying CT.

Membranes

• Epithelium + Connective tissue

• Function: cover and line surfaces outside and inside the body.

• Classification: 3 types of membranes:
  * Cutaneous – skin, a dry membrane.
  * Mucous (mucosa) – line the internal surface of every hollow organ that opens to the outside of the body (respiratory, digestive, urinary, and reproductive tracts).
  * Serous (serosa) – slippery membranes that line closed cavities inside the body (the pleural, pericardial, and peritoneal cavities).

Cutaneous Membranes

• Dry membrane

• External to the body and protective of everything underneath it.

• Epithelium layer is the epidermis and CT layer is the dermis.

Mucous Membranes

• Lines body cavities open to the external environment: Oral cavity, nasal cavity, anus, urethra, vagina, etc.

• Wet/moist membrane.

• Most secrete mucous, but not all.

Serous Membranes

• Serous membranes are slippery and line the closed cavities of the body: Pleural, Pericardial and Peritoneal

• The epithelial layer produces a slippery, lubricating serous fluid

• Serous cavities contain two layers the parietal layer (lining the body wall) and the visceral layer covering the organ(s).

• The parietal layer and visceral layer move freely against each other because of the presence of the lubricating serous fluid.

• This construct allows for the beating of the heart, movement of the guts and inspiration (which happens thousands of times a day) to occur without any irritation on either layer.