Biology  2401   A & P I                Lecture Notes   Tissues               

TISSUES....group of closely related cells that are similar  in structure and perform a common function. 
The study of tissues on a microscopic level is called Histology.

Four basic tissues                                                       Function

1. Epithelium                                                                 covering

2. Connective tissue                                                      support

3. Muscular tissue                                                         movement

4. Nervous tissue                                                          communication

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I. Epithelial Tissue Divisions:

Membranous Epithelium is a cellular tissue arranged in continuous sheets bound together by tight junctions and desmosomes.  These cells form a membrane that lines all surfaces of the body.
The arrangement of tissues determines an organs structure and capabilities.

    Special characteristics :

    Functions: protection, absorption, filtration, excretion, secretion.    

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There is a connective tissue structure associated with the epithelium called the BASAL LAMINA, that is one part of the basement membrane. This tissue is made up of a fluid (glycoproteins) and a fibrous structural component.

ALL epithelium rests on the BASAL LAMINA.

The second part of the basement membrane is the Lamina Propria, now called the Reticular Lamina and it is formed by reticular fibers and ground substance and will connect with the basal lamina. Helps to reinforce and defnine boundary between epithelium and underlying structures.

Summary: Basement Membrane = Basal Lamina + Reticular Lamina (propria)

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   Classification of epithelial membranes is based on structural appearance.

      The number of layers seen can be

Therefore we have the following possible groupings :

1. Simple squamous epithelium....a sheet of flat cells

2. Simple cuboidal epithelium.....a sheet of square cells

        these can be found lining some ducts and renal tubules function for secretion & absorption

3. Simple columnar epithelium..... a sheet of tall cells

4. Stratified squamous....a layer of cells in which the TOP, apical layer  is flat. 

    The cells in the lower layers beneath the top layer can be any shape. Stratified must have a minimum of 2 layers thick.

     Major function is protection

                 i.e. The epidermis of the skin called cutaneous membrane.

                       Lines openings of all body cavities that are directly continuous with the skin

5. Stratified cuboidal....a rare form, nuclei will be in a row

6 . Stratified columnar.....rare form, found in some glands, and the male urethra

Variations of membranous epithelium include:

7. Pseudostratified epithelium

                appears stratified, and the nuclei will appear at  different levels.

                All cells reach the basal surface, but not all reach the apical surface.

                Seen in the lining of the trachea and upper respiratory tract.

     + / - cilia     

8. Transitional Epithelium

                Seen in the urinary bladder, ureters, part of urethra.  

    Basal cells will be cuboidal or columnar in layers with the top cells having a curved aspect

    Cell appearance will change in the relaxed state vs. when are stretched and under pressure  they will stretch out.

 

9. Specialized Epithelium : Glandular Epithelium

                found in the glands and also for sensory needs in the neuroepithelium.

Glands --> one or more cells that make or secrete a particular product 

Two types of Glands :

     1. Exocrine...those glands are separated from the surface or body cavity by a duct

     2. Endocrine.. ductless glands produce hormones (regulatory chemicals) that travel through the blood to target organs that have the proper receptor.

EXOCRINE Glands

 Cell shape is primarily cuboidal or columnar

            Can be simple (lacking a duct system) or compound (compound duct system).

            Unicellular or multicellular

Therefore, the possible groupings of exocrine glands include

1. One simple unicellular gland

2. Simple multicellular

Single unbranched duct that has a tubular appearance,  projected beneath the surface

The tubular portion can have

3. Compound Glands are characterized by complex duct system that branch.

Shapes can be acinar, alveolar or a combination of the two.

Multicellular glands secrete their products in different ways.

1. Merocrine glands --> secrete products by exocytosis

2. holocrine glands --> accumulate product then rupture

3. apocrine glands --> accumulate product at apex of cell and then pinch off

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Connective tissue

One of the four primary tissues, arise from mesenchymal mesoderm

Various Function : support, protection, binding, transportation

Connective Tissue has three common components :

1. Ground substance --

Composed of ISCF, adhesion protiens, proteoglycans, hyaluronic acid and sulfates to create an unstructured material that fills the space between cells and creates a filter or sieve for diffusion processes.

2. Fibers -- 3 types

found at the junction of CT & other tissue types

3. Cells  -- each CT has fundamental immature and mature cell type :

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In connective tissue, the fibrous and ground substance together form the extracellular compartment and is called the MATRIX.

Connective tissue can be classified into two groups

1. Embryonal C.T.

2. Adult C.T.

Embryonal Connective Tissue develops from 3 germ layers.

Adult Connective Tissue has 3 major categories ::

The connective tissue proper consists of :

a. Loose C.T. - a loose arrangement of randomly spaced fibers and cells (fibroblasts / fibrocytes)

                    e.g. the superficial fascia that helps create the bodies framework

b. Dense C.T. -

c. Specialized C.T. proper

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II. Supportive tissues -- two types: Bone and Cartilage

Bone:
has a dense irregular outer collagenous C.T. layer surrounding it, called the periosteum. Inside of bone this irregular CT forms the endosteum and houses immature bone cells, such as osteoblasts and osteoclasts.

Bone has a matrix composed of fibers and fluid. The collagen fibers can be layed down in an orderly fashion to create layers that form an osteon. If the collagen fibers are laid down in a lattice fashion, it is called spongy or trabecular bone.

The osteoblasts lay down a collagenous matrix that in most cases will be replaced by ossified bone. Once the cells mature, they are called osteocytes which lie in spaces called lacunae. 

Cartilage
consists of dense irregular collagenous C.T. matrix and have cells called chondrocytes (from chondroblasts) that lie in spaces called lacunae. Cartilage has good rebound properties but is avascular, so that repair is slow and based on interstital fluid composition.

Different types of cartilage include :

1. Hyaline cartilage --

2. Elastic cartilage --

3. Fibrocartilage B

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III. BLOOD

 a connective tissue consisting of a liquid fluid matrix portion known as plasma. It also contains a cellular formed element  component and a fibrous portion, fibrin, that is only seen during the clotting process.

These formed elements are

1. RBC's usually have no nucleus and are made up of hemoglobin.

2. WBC -- Leukocytes

a. Agranulocytes  (no granules)

b. Granulocytes

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VI. Membranes --- are combinations of epithelia and C.T.

1. Mucous membranes  (mucosa)

2. Serous membranes

3. Cutaneous membranes

4. Synovial membranes

5. Basement membrane :: basal lamina + Reticular lamina Propria

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IV. Muscle Tissue

Body tissue made up of cells called fibers that are highly  specialized.    

Have the ability to contract due to the interaction  between actin and myosin, the contractile proteins

to create two types of contractions : Isometric and Isotonic.

 

Two types of muscle tissue based on arrangement of these contractile proteins

Classification can also be based on physiologic control of contraction

1. Voluntary contraction :  skeletal muscle cells

2. Involuntary contraction : smooth and cardiac

  Comparison for the striated muscles:

Cardiac                                                            Skeletal

loosely arranged myofibrils                                 myofibrils organized into  bundles

one nucleus near center                                     May have more than one nucleus of cell

branching                                                          Muscle fibers can increase in size when exercised called Hypertrophy.

intercalated discs                                                          This is an increase in size not number

Smooth muscle

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V. Nervous Tissue

Basic tissue made up of neurons to form the nerves of the brain, spinal cord, and peripheral extensions called Cranial Nerves and Spinal Nerves.

Support cells called Neuroglia which will insulate, protect, and possible myelinate.

Function : Neurons conduct electrical impulses by ionic changes.

 

            Neurons have three main parts.

1. Cell body (soma) that has a nucleus

2. Processes -- called nerve fibers, a bundle of nerve fibers is called a nerve.

 

The nervous system has two Anatomical parts

A. Central Nervous System (CNS) --

B. Peripheral Nervous System

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To maintain homeostasis, tissues need to be able to respond to an injury.

    Tissue repair occurs in 2 major ways :

1. Regeneration....replacement of same kind of tissue

2. Fibrosis...replacement with fibrous C.T., scar tissue

After injury, the tissue continues to degenerate or necrosis. These changes start an

(1) inflammatory response by stimulating mast cells.  Mast cells release chemicals that attract macrophages and white blood cells to attack and clean up.
(2) Once this is complete, fibroblasts lay down collagen framework along with capillaries to form granulation tissue that is (3) further remodeled depending on the organ type. 
Some organs regenerate well like the skin, and others regenerate poorly like smooth muscle, and some do not normally regenerate without help. (i.e. most of the central nervous system).

 

Factors Affecting Repair Process ::

Tissues will change with age.

Structure and composition are altered and repair & maintenance becomes less efficient.

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Problems ::

I. Tissue WILL NOT heal in the face of infection (pus)