Chapter 4: Histology - the Study of Tissues

Chapter 4: Histology - The Study of Tissues

Cells are grouped together into specialized functional and structural groupings to perform a common function. These groupings are called TISSUES.

The four basic types of tissues in the human body are:

1. EPITHELIAL

2. MUSCULAR

3. CONNECTIVE

4. NERVOUS TISSUES.

EPITHELIAL TISSUES: (Epi upon; thelium to cover)

I.Locations of Epithelial Tissues

A. line internal cavities

B. line urinary, reproductive, digestive and respiratory organs

C. cover outer surfaces

II.Functions of Epithelial Tissues

A. protection consists of several layers [skin, lining of mouth, lining of vagina, etc.]

B. secretion consists of single layers [glands]

C. absorption consists of single layers [small intestines, kidneys]

D. filtration consists of single layers [capillaries, glomeruli]

III.Characteristics of Epithelial Tissues

A. exists in sheets (attached to "Basement Membrane" for support and nourishment)

B. lacks blood vessels (avascular)

C. cells replaced by mitosis

D. very little intercellular material (cells close together)

IV. Types of Epithelial Tissues

A. Covering and Lining Epithelium:

1. Simple - one layer of cells in thickness [lining of internal cavities and blood vessels]

a. Simple Squamous flat cells [found in the lining of the alveoli of the lungs]

1) Endothelium lines the heart, blood & lymph vessels;forms the walls of capillaries

2) Mesothelium lines the serous membranes of the thoracic and abdominal cavities

b. Simple Columnar two types of cells: (columnar & goblet)

1) Ciliated outer surface possesses cilia [respiratory passages; Fallopian tubes; uterus]

2) Non-ciliated lack cilia [digestive tract]

c. Simple cuboidal [line the tubules of the liver, kidneys and thyroid gland]

2. Stratified - several layers in thickness

a. Stratified squamous

1) Keratinized tough, waterproof layer by the secretion of KERATIN

2) Non-keratinized surface cells lack keratin [lining of the oral cavity, throat & vagina]

b. Stratified columnar [excretory ducts, male urethra]

c. Stratified cuboidal [ducts of sweat glands]

d. Pseudostratified cells similar to columnar some cells donot reach the surface of the tissue BUT all the cells are attached to the basement membrane Cells are ciliated. Nuclei appear at various levels making the tissue appear stratified. [lines the larger respiratory passages, male reproductive ducts]

3. Transitional - surface cells are large and rounded and become flattened, scalelike when the organ is stretched [urinary bladder being filled with urine]

V. Glandular Epithelium

1. Endocrine secretes directly from the cells into the blood. Secretions called HORMONES.

2. Exocrine secretes through a duct to the surface of a hollow organ or to the exterior surfaces. [Sweat, sebaceous and digestive glands]

a. Structural Classification of Exocrine Glands

1. Unicelluar - onecelled glands

Examples:Goblet Cells in the digestive tract; respiratory tract; urinary tract

reproductive tract

Function:produce MUCUS to lubricatesurfaces

2. Multicellular Glands - has ducts

a. simple (duct does not branch out)

• Tubular (intestinal glands)
• Branched Tubular (stomach & uterus)
• Coiled sudoriferous
• Acinar [flasklike] - (seminal vesicle in males)
• Branched Acinar

b. compound (ducts branch out)

• Tubular (liver)
• Acinar - (salivary glands)
• Tubuloacinar (pancreas)

b. Functional Classification of Exocrine Glands

1. Holocrine cells form product in their cytoplasm; cells die and secretion is discharged to the exterior; cells replaced by cell division [Sebaceous Glands of the skin]

2. Merocrinecells form product which is released from cells to form the secretion

3. Apocrinecells form and accumulate substances at their apex apex breaks off to form the secretion [Mammary Glands]

VI.Cell Junctions in Epithelial Tissues

A. General Functions

1. Cell to Cell attachments

2. Barrier prevents movements of certain substances through. epithelial tissues.

3. Communication between cells

B. Structural Classification of Cell Junctions:

1. Desmosome:

a. locations stratified epithelium

b. functions attach adjacent cells

2. Tight Junctions:

a. locations epithelial lining of digestive system

b. functions circle cells below the microvilli

• prevents substances from moving through between the cells

3. Intermediate Junction:

a. locations epithelial lining of digestive tract (below the Tight Junctions)

b. functions forms firm connections between cells

4. Gap Junctions:

a. location - between smooth muscle cells and cardiac muscle cells

b. function - allows adjacent cells to communicate by passage of ions (e.g. Na+, K+, Cl-)

VII. Connective Tissues

Most widely distributed tissue, found everywhere in the body. Contains an abundant intercellular material, called the MATRIX.

A. General Functions of Connective Tissues

1. Binding tissue organs held together, and muscles attached to bones (by way of tendons), bones attached to other bones (by way of ligaments)

2. Fat storage adipose connective tissue

3. Support and Protection bones and cartilage

4. Blood cell formation (hemopoiesis) occurs in the bone marrow.

5. Defense against bacterial invasionreticuloendothelial tissue in bone marrow

B. General Characteristics of Connective Tissues:

1. Vascularity abundant blood supply

2. Cells widely dispersed abundant intercellular material [MATRIX]

a. Matrix is a nonliving intercellular material that has been secreted by the cells of the connective tissue; the matrix may be fluid, semifluid, mucoid, gellike or ri gid

C. Types of Cells in Connective Tissues

1.Fibroblasts most of the connective tissue cells

a. large, flat cells

b. produce collagenous and elastic fibers needed for growth and repair of tissues

2. Macrophages large ameboid cells

a. function in phagocytosis of bacteria

b. found in liver, lymph organs and bone marrow

3. Plasma Cells small, rounded cells

a. produce ANTIBODIES for the immune system

4. Mast Cells found along blood vessels

a. HEPARIN an anticoagulant

b. HISTAMINE dilates capillaries &increases their permeability

D.Types of Fibers

1. Collagenous strong, tough resists pulling forces, yet is flexible

a. each collagenous fiber composed of tiny fibrils in bundles.

b. fibrils are composed of the protein - COLLAGEN

2. Elastic or Yellow Fibers small, branching fibers

a. elastic means that th material returns to its original shape after stretching

b. fibers are composed of the protein ELASTIN

3. Reticular Fibers delicate, branching fibers may be the same as collagenous fibrils.

E. Types of Connective Tissues

1. Embryonic Connective Tissue present only in the embryo or fetus

a. Mesenchyme found only in the embryo (under the skin and near bones); gives rise to all connective tissue

2. Mucous Connective Tissue found only in the fetus as a jell-like substance [umbilical cord]

3. Areolar <loose, ordinary connective tissue>

a. consists of fibers imbedded in a soft, jellylike matrix

b. found in all parts of the body and is flexible, due to loose arrangement of fibers.

c. functions as an important packing tissue

4. Adipose

a. consists of closely packed fat cells with elastic and collagenous fibers

b. fat cells are modified fibroblasts with stores of fat droplets [Signet Rings]

c. located under the skin, around the kidneys, around theheart, behind the eyeballs, and around joints

d. functions as food reserve, insulator against heat loss,support and protection for organs

5. Dense Regular (white) or Fibrous or Collagenous

a. consists mainly of densely packed bundles of collagenous and elastic fibers

b. functions as a binding tissue in the following structures:

Tendons attaching muscles to bones

Ligaments attaching bones to bones at joints

Aponeuroses broad sheet of connective tissue attachingmuscles to muscles [abdomen]

Serous Membranes surrounds visceral organs

- Fasciae wrapping around muscles

6. Elastic

a. consists mainly of densely packed bundles of elastic fibers

b. found in larynx, arterial walls and trachea

7. Reticular Connective Tissue

a. consists of interlacing reticular fibers

b. forms the framework of the liver, spleen, lymph nodes

8. Dense Irregular

a. irregularly arranged collagen fibers

b. submucosa of digestive tract; capsules around organs and joints

8. Bone and Cartilage (studied with the Skeletal System)

9. Hemopoietic Tissue blood cell formation in the bone marrow (studied with Blood)

VIII. Muscle Tissues

A. General Functions of Muscular Tissue

1. pumping blood (cardiac muscle tissue]

2. moving extremities [skeletal muscle tissue]

3. pumping air into and out of the lungs [skeletal muscle tissue]

4. movement of food through the digestive tract[visceral muscle tissue

5. movement of urine through the urinary tract [visceral muscle tissue

6. contriction of blood vessels [visceral muscle tissue]

B. Types of Muscular Tissue

1. Skeletal attached to bones

a. also called striated due to its microscopic appearance

b. also called voluntary because it is under control of the will

c. consists of bundles of long, cylindrical fibers

d. each fiber is a multinucleated cell that has resulted from several cells fusing together

2. Smooth striations not very noticeable

a. also called Visceral Muscle - associated with organs

b. also called Involuntary because it is not under the control of the will

c. consists of long, tapered cells, with a single nucleus

3. Cardiac only located in the heart

a. forms the muscular wall of the heart

b. myofibrils are similar to skeletal muscle, but transverse striations are less distinct

c. composed of elongated branching cells that are irregular at their junctions forming trans verse thickenings called INTERCALATED DISCS

IX. Nervous Tissue (studied with Nervous System)

X. Membranes

The four principle types of membranes are: MUCOUS, SEROUS, SYNOVIAL, AND CUTANEOUS

A. Mucous Membranes

1. General functions

a. Protection against bacterial invasion, water loss dust the air.

b. Secretion mucus for lubrication and protection, and secretion of digestive enzymes.

c. Absorption water, digested foods, salts

2. Location of Mucous Membranes:

a. mouth and nasal cavities

b. digestive organs

c. respiratory tract

d. urinary and reproductive tract

B. Serous Membranes

1. General Functions

a. Reduces friction between the body walls and organs

2. Location of Serous Membranes

a. Thoracic cavity called the pleura

b. AbdominalPelvic cavity called the peritoneum

c. Pericardial cavity called the pericardium

3. Structure of the Serous Membranes consists of TWO LAYERS

a. Visceral Layer part touching the organ itself

b. Parietal Layer part touching the wall of the cavity where organ is located

c. Serous Fluid - fills the space between the two layers to reduce friction