Learning Outline

Tissues, Organs, and Systems

A&P 1

This outline is for your own review of tissues (in the context of organs and systems) and is provided as a brief overview of tissues. Although you will learn this material in the lab course (and again, bit by bit, in the lecture course), I will not test you specifically on this material now.

Tissues

• Review Levels of Organization
  
  
• Tissues are the "fabric" that make up organs
  
  
• Four main types of tissues: epithelial, connective, muscle, nervous

Extracellular matrix (ECM)

Complex, nonliving material filling the spaces between cells

• Some tissues (epithelial) has little ECM and a lot of cells; some tissues (connective) have a lot of of ECM and few cells
  

Made up of

• Water
  
  
• Proteins
  
  
• Glycoproteins
  
  
• Proteoglycans
  

Functions

• Help hold tissues together
  
  
• Communication between ECM and cell or among cells

Extracellular matrix (ECM)
Immunofluorescent staining of fibroblast cells reveals the extracellular matrix (bluish and turquoise areas)

Epithelial tissues

Function

• Cover and line (form membranes)
  
  
• Secrete (form glands) — "secretory tissue"
  
  
  • Endocrine glands (ductless glands) secrete hormones into blood
    
    
  • Exocrine glands (ducted glands) secrete fluids onto surface (incl. into tubes)
    

Structure

• Cellular junctions
  
  
  • Cohesion
    
    
  • Junctional complexes
    
    
    • Desmosomes — "tangled filaments" hold cells together as in Velcro fasteners
      
      
    • Gap junctions — channels in adjacent plasma membranes form "tunnels" that hold cells together structurally and functionally
      
      
      • Syncytium — group of cells held together by gap junctions and acting (in some ways) as a single, giant cell
        
        
    • Tight junctions — rows of connecting proteins, like "snaps" on a jacket form a collar-like seal all the way around a cell (as the plastic yoke on a six-pack)
      
      
• Basal surface is anchored; apical surface is "free"
  
  
  • Basal layer attached to underlying connective tissue by glue-like basement membrane (BM)
    
    
• Epithelial types are named for
  
  
  • Number of layers
    
    
    • Simple = one layer of cells
      
      
    • Stratified = more than one layer of cells (from stratum = layer)
      
      
    • Pseudostratified = looks like more than one layer, but because all cells touch the basement membrane it's really just one layer
      
      
  • Shape of cells in outermost ("free surface") layer (as seen in cross-section)
    
    
    • Squamous = flat, scale-like cells
      
      
    • Cuboidal = about as tall as wide
      
      
    • Columnar = taller than wide
      
      
    • Transitional = shape depends on how stretched the membrane is
      
      
• Examples of epithelial tissue types
  
  
  • Simple squamous
    
    
  • Simple cuboidal
    
    
  • Simple columnar
    
    
  • Pseudostratified columnar
    
    
  • Stratified squamous
    
    
    • Keratinized (has outer layers of dead cells that have filled with tough, waterproof protein called keratin—as in skin)
      
      
    • Nonkeratinized
      
      
  • Transitional (stratified)

Connective tissues

Function

• Connects body parts in any of several ways
  
  
• Many different functions, really
  

Structure

• Dominated by extracellular material ("extracellular matrix" or ECM)—with few, scattered cells
  
  
• Matrix contains fibers (made by fibroblast cells) and other materials
  
  
  • Elastic fibers — made of elastin and stretch easily, then recoil (also called yellow fibers)
    
    
  • Collagen fibers — made of collagen and do not stretch (much) but are strong and flexible (also called white fibers or collagenous fibers)
    

Major types of connective tissues

• Fibrous connective tissues
  
  
  • There are several ways to classify fibrous connective tissues—most commonly, they are categorized by the structure of the matrix (type and arrangement of fibers)
    
    
  • Loose (areolar) connective tissue has collagen and elastin fibers scattered loosely
    
    
  • Adipose tissue forms when fat-storing cells in areolar tissue enlarge as they accumulate more [triglyceride] fat
    
    
  • Dense fibrous connective tissue has a dense arrangement of collagen fiber bundles
    
    
    • Regular — has rougly parallel bundles of collagen fibers
      
      
    • Irregular — has hodgepodge, irregular arrangement of collagen fibers
      
      
  • Reticular tissue is a netlike meshwork of fine collagen fibers that helps hold tissues in place and sometimes helps to filter particles from fluids passing through it

Three types of fibrous connective tissue.
The third image is regular dense fibrous connective tissue.

• Cartilage
  
  
  • Chrondrocytes make cartilage matrix
    
    
    • Found within spaces called lacunae (sing. lacuna = "lake") giving cartilage a "Swiss cheese" appearance
      
      
  • Hyaline cartilage — some collagen in matrix
    
    
  • Elastic cartilage — some collagen and some elastin in matrix
    
    
  • Fibrocartilage — dense collagen in matrix

Swiss cheese.
A model for cartilage. Compare this image to that of hyaline cartilage (below).

• Bone
  
  • Osteocytes (within lacunae) surrounded by collagen fibers encrusted with calcium salts
    
    
  • Spongy bone — irregular beams of bone surrounded by red bone marrow (soft, blood-forming tissue); also called cancellous bone
    
    
  • Compact bone — denser type of bone made up of cylindrical units composed of concentric layers (lamellae) of bone matrix
    
    
• Blood
  
  
  • Liquid matrix (blood plasma) and circulating blood cells
    
    
  • Blood cells are also called "formed elements" because plasma is "unformed" taking the shape of its container
    
    
  • RBCs = red blood cells, WBCs = white blood cells, platelets = thrombocytes

Blood, bone and cartilage
Bone is sometimes called "osseous" which means "bony" (compact bone is shown)

Muscle tissue

Function

• Contraction
  
  
• May be "voluntary" or "involuntary"
  

Structure

• Cylindrical cells or "muscle fibers"
  
  
• Muscle fibers have highly organized cytoskeleton that "slides together" like a split deck of cards to contract the fiber
  

Three types: skeletal, smooth, cardiac

• Skeletal muscle
  
  
  • Also called "striated" because of striped appearance of overlapping filaments of cytoskeleton
    
    
  • Voluntary muscle
    
    
  • Connected to skeleton
    
    
• Cardiac muscle
  
  
  • Faintly striated
    
    
  • Branched fibers held together end-to-end by gap junctions, forming intercalated disks
    
    
  • Involuntary
    
    
  • In heart wall
    
    
• Smooth muscle
  
  
  • Not striated (cytoskeleton organized differently)
    
    
  • Involuntary
    
    
  • In walls of hollow organs (except heart)

Muscle tissue types.

Nervous tissue

Neurons

• Conducting cells
  
  
• Connected at synapses that act as switches, allowing information storage and processing
  

Glia (also called neuroglia)

• Support cells (functional and structural support)
  
  
  • Involved in modulating neuron function

Brain tissue.
Click the image to see a larger view, where a mixture of neurons and glia can be seen.

 

Click here to explore a comprehensive visual review of tissues

 

Organs and systems

Organs

Organs are made up of different tissues

Organs are organized into different body systems

Organs may belong to more than one system

Different biologists organize them differently

• Example
  
  
  • Nervous system could be subdivided
    
    
    • Central nervous system (brain and spinal cord)
      
      
    • Peripheral nervous system (nerves)
      
      
  • Nervous system could be joined to other systems
    
    
    • Neuroendocrine system (nervous and endocrine systems)
      
      
    • Neuroskeletomuscular system (nervous, skeletal, and muscular systems)