The Cell Theory

  1. developed 1838-9 by Matthias Schleiden (plants) and Theodore Schwann (animals).
    1. All organisms are composed of cells
    2. Every cell comes from preexisting cell
    3. All vital funtions occur within cells
    4. Cells carry hereditary information for metabolism and reproduction.

Animals have a level of organization

  1. Cells form tissues
  2. Different tissues make up organs
  3. Several organs are found within an organ system
  4. Organ systems make up the organism

Embryological development: multicellular life with a single cell

Divides to produce three fundamental layers  

I. Ectoderm (outer layer)

  1. Epidermis of skin
  2. Epithelial lining of mouth and rectum
  3. Nervous system

II. Mesoderm (middle layer)

  1. 1. Notochord
  2. 2. Skeleton
  3. 3. Muscular system
  4. 4. Dermis of skin
  5. 5. Circulatory system
  6. 6. Excretory system
  7. 7. Reproductive system
  8. 8. Outer layer of respiratory and digestive systems

III. Endoderm (inner layer)

  1. 1. Epithelial lining of respiratory & digestive tracts
  2. 2. Associated glands of these systems
  3. 3. Epithelial lining of urinary bladder

Tissue: group of closely related cells, adapted to carry out specific functions

There are 4 major types of tissue in complex animals:

  1. 1. Epithelial tissue: covers body surface, lines body cavities
  2. 2. Connective tissue: binds and supports body parts
  3. 3. Muscular tissue: Causes body parts to move
  4. 4. Nervous tissue: responds to stimuli and transmits impulses from one body part to another

Epithelial Tissue (epithelium)

cells tightly fitted together, forms continuous sheet, covers body surface, lines cavities


  1. 1. protection - epidermis (skin) against injury, bacteria, water loss
  2. 2. absorption - digestive tract
  3. 3. secretion - glands: hormones, enzymes, sweat
  4. 4. sensation - skin receptors, nose

Epithelium may be simple or stratified

  1. "Simple" means the tissue has single layer of cells
  2. "Stratified" means layers piled on top of each other

Five basic types of epithelium [fig. 3.24]

  1. 1. simple squamous (fig. 3.24a): composed of flat cells in a single layer; diffusion across in air sacs, blood vessels
  2. 2. simple cuboidal (fig. 3.24b): single layer of cube_shaped cells; some microvilli; secretion and adsorption in kidney tubules, gland ducts
  3. 3. simple columnar (fig. 3.24c, d): single layer of cells that resemble pillars or columns; secretion of mucus [pseudostratified], absorption in kidney tubules, upper respiratory tract
  4. 4. stratified squamous (fig. 3.24e): two to many layers, protection - skin, mouth vagina
  5. 5. transitional: stratified, accomodates stretching, bladder, urinary tract

gland: one or more epithelial cells that secretes a special product, e.g.

  1. goblet cells (fig. 3.24d): glands in columnar epithelium that secrete mucus; lubricates, facilitates movement.
  2. A gland can contain a single cell or numerous cells
  3. Exocrine glands: Secrete product into ducts
  4. Endocrine glands: Secrete product directly into blood stream

CONNECTIVE TISSUE: Connective tissues may have several purposes:

  1. Binds structures together and supports them
  2. Provides support and protection; repairs damage
  3. Fills spaces
  4. Store fat
  5. Forms Blood cells
  6. source cells for muscular and skeletal cells in animals that can regenerate lost parts

Fibroblasts: cells of loose and fibrous connective tissues

  1. relatively few cells separated by an extracellular ground substance (matrix)
  2. Lies beneath epithelium in the skin
  3. Present in lungs, arteries, and the urinary bladder
  4. allows the organs to expand
  5. Forms protective covering for many organs e.g., muscles, nerves, blood vessels

matrix: noncellular material between cells secreted by fibroblasts

gel of polysaccharides containing three types of fibers

  1. 1. collagen: protein; high tensile strength; resists stretching
  2. 2. elastic: snaps back; lines blood vessels
  3. 3. reticular: forms supporting network for tissues and organs

Types (8) of Connective Tissue

  1. 1. loose ordinary (figure 3.24g): commonest - support; fluid and salt reservoir; wraps nerves, blood vessels, muscles; attaches skin to muscles.
  2. 2. fibrous-dense ordinary (figure 3.24h): very strong - collagen; found in dermis; tendons (connect muscles to bone).
  3. 3. fibrous-elastic: parallel elastic fibers - ligaments (connects bones); lines arteries, lungs
  4. 4. reticular: stroma (framework) for many organs - liver, spleen, etc.
  5. 5. adipose tissue (figure 3.24f)
    1. Type of loose connective tissue with cells which can enlarge and store fat
    2. Found particularly beneath the skin (subcutaneous), around kidneys, and on surface of heart
    3. Insulates the body; cushions internal organs
  6. 6. cartilage (figure 3.24i, j, k): cells lie in small chambers called lacunae. Fetal skeleton is cartilage (embryonic support); also adult sharks, nose, ear, lacks nerves and blood vessels; no blood supply, relies on diffusion
  7. 7. bone (figure 3.24l): osteocytes - living tissue; highly vascular; cells, blood vessels, nerves, fluid, fat; matrix of calcium salts is deposited around protein fibers. Minerals give bone rigidity (withstands compression) and protein fiber provides elasticity and strength (resists extension)
  8. 8. blood (figure 3.24m) and lymph: A connective tissue in which the cells are separated by a liquid called plasma (fluid intercellular substance).


Muscle Tissue [fig. 3.24o, p, q]: specialized for contraction; most abundant animal tissue; usually fibers - long narrow cells, arranged in bundles; 3 types: smooth, cardiac, skeletal.

Nervous Tissue

  1. neurons (figure 3.24n): cell body, axon, dendrites - receives and transmits messages
  2. gllial cells: support neurons


different tissue types cooperating to perform a particular biological function; brain, stomach, eye, etc.


  1. tissues and organs coordinated for specialized functions; working together to make an organism
  2. 11 different kinds - integumentary; skeletal; muscular; nervous; endocrine; circulatory; lymphatic; respiratory; digestive; urinary; reproductive.


" skin and structures derived from it, such as nails and hair. protects the body, helps regulate temperature; receives external stimili such as pressure, pain, heat.


" consists of bones and cartilage. supports and protects the body.


" large skeletal muscles for movement, cardiac muscle of the heart, smooth muscle of internal organs


" brain, spinal cord, sense organs. principal regualtory system.


" ductless glands that release hormones. helps regulate metabolic activity.


" heart and blood vessels. the transportation system of the body.


" a subsystem of the circulatory system. returns excess tissue fluid and defends body against disease.


" lungs and air passageways. supplies oxygen to blood, removes CO2


" digestive tract and glands that secrete digestive juices. mechanically and enzymatically breaks down food and eliminates wastes


" kidneys and associated organs. main excretory system, removes nitrogenous wastes, maintains salt balance.


" gonads and associated structures. maintains the sexual characteristics and perpetuates the species.