Chapter 4 -1

HistologyTissues and Membranes

Common Course Objectives

• Identify tissues and their specific characteristics

• Define membrane structure, and its importance for cell integrity, function and identity

Tissues

• Groups of similar cells in close association with each other that work and perform similar functions.

• Four basic types we will learn in detail:• Epithelial

• Connective• Nervous• Muscle

Four basic types we will learn

Epithelial Tissue

• Consists of cells arranged in continuous sheets of either single or multiple layers supported by a connective tissue underlayment (basement membrane).

• They are closely packed and held together by specialized cell junctions (tight junctions, gap junctions, desmosomes).

• There is an intercellular space between adjacent cells.• Contain 3 surfaces: Apical (superficial), lateral

(intercellular space), and basal (deep).

Intercellular connections

• Tight junctions formed by fusion of lipid layers between cells prevent substances from entering between cells.

• Gap junctions consist of interlocking membrane proteins that allow ions and small molecules to pass from one cell to another.

• Desmosomes formed by a thin layer of intercellular cement reinforced by protein filaments resulting in strong junctions holding adjacent cells together.

Intercellular connections

Epithelial Tissue• Cell surface orientation

- Apical surface is in the lumen-Basal infrastructure of cell (foundation)

Epithelial Tissue

• Is avascular and receives nutrients from a connective tissue layer below via diffusion.

• It is innervated and highly sensitive to touch, pain and pressure.

• May be divided into 2 types: Covering and lining epithelium (e.g. skin, vessels, body cavities, etc.) and Glandular epithelium (secreting portion of glands – (e.g. thyroid, sweat, adrenal).

• It is capable of regenerating itself as it is worn off or abraded away.

Classification of Epithelia

• Classified by layers:– Simple vs. Stratified

• Classified by cell shape:– Squamous– Cuboidal– Columnar

Types of Epithelia

Simple Cells vs. Stratified Cells

Simple Stratified

Single lining layer Cell layers stacked up.

Simple cells vs. Stratified cells

• Simple is a single layer of cells (i.e. the cells are not stacked on top of each other).– Function in diffusion, osmosis, filtration, secretion

and absorption.

• Stratified is composed 2 to 20+ layers. Only the deepest layers rest on a basement membrane. – Found in locations where there is considerable

wear and tear.

Simple epithelial cells

• Squamous = arranged like floor tiles and are thin and flat.

• Cuboidal = shaped like cubes or hexagons.

• Columnar = much taller than wide and protect underlying tissues.

• Transitional = may be any of the 3 above and exhibits variable cell shapes.

Simple Squamous Epithelium

Single layer of flat cells.

-Lines internal surface of

internal body cavities,

blood vessels, heart,

renal tubules & alveoli

of lungs.

Allows for easy diffusion,

filtration or secretion.

Simple Cuboidal Epithelium

Single layer of cuboidalshaped cells.

-Found in gland ducts,kidney tubules, and thyroid follicles.

-Act in secretion and absorption.

Simple Columnar Epithelium

Single layer of tall, column-shaped cells with oblong nuclei. May be ciliated or non-ciliated.

-Non-ciliated found in stomach, small and large intestine and gall bladder.

-Ciliated found in uterine (fallopian) tubes.

Ciliated Simple Columnar Epithelium

Ciliated found in uterine (fallopian) tubes and large bronchioles.

Why would cilia be

found here??

Stratified vs. Pseudostratified

• Stratified consists of 2 or more layers of cells that protect underlying tissues. Found in locations where there is considerable wear and tear (skin, mouth, intestines, etc.).

• Pseudostratified contains only a single layer of epithelial cells, but appears to have

multiple layers because the cell nuclei lie at different levels and not all cells reach the apical surface.

Stratified vs. Pseudostratified Stratified Pseudostratified

Stratified Squamous EpitheliumConsists of 2 different

types: Keratinized and

Non-keratinized.

Bottom layer is either

cuboidal or columnar cells

that are active in cell

division.

-Keratinized is found in

the epidermis of the skin.

-Non-keratinized is in

mouth, pharynx, anus, esophagus, and vagina.

Stratified Squamous Epithelium

Keratinized is found

in epidermis of skin.

Stratified columnar epithelium

• Basal cells tend to be more cuboidal and the

apical surface cells are columnar in shape.

• Found in ducts of larger glands as in the

submucosa of the esophagus.

Pseudostratified columnar epitheliumA single row of cells.

Most cells look columnar

while others cells may

look cuboidal shape. Note that all cells are

attached to basal lamina.

-Ciliated epithelium is

found in nasal cavity,

trachea and bronchi.

-Non-ciliated is in ducts of

male reproductive tract

Transitional epithelial cells

• Cells change shape, from cuboidal to flat and back.

• Occurs in organs that stretch to a larger size and then collapse to a smaller size.

• Present only in the urinary system. Lines ureters, urinary bladder, urethra and renal pelvis.

• In relaxed state, it looks like cuboidal cells at basal surface, columnar in middle and large dome shaped at surface. When stretched dome shaped cells flatten out.

Transitional epithelium

Glandular epithelium

• Functions in secretion and is performed by glandular cells that lie deep to the lining epithelial cells. Keep the membranes moist.

• May consist of a single cell or a group of cells that secrete substances into ducts or onto a surface (exocrine) or directly into the blood (endocrine).

Shapes of Exocrine Glands

Glandular secretions• Merocrine – vesicles synthesized by ribosomes

are secreted in small portions. Most exocrine glands are of this type in the body. – (Ex. salivary, gastric and pancreatic glands).

• Apocrine – accumulate their secretion at the surface and then pinch off from the rest of the cell. - (Ex. Sweat glands in armpit and groin).

• Holocrine – whole cell is released as a secretion and is then replaced by mitosis.– (Ex. Sebaceous glands of skin).

Exocrine secretions

Connective Tissues

• Are all derived from Mesenchymal cells of embryo.

• Four types in body:-Fibrous connective tissue (2 Types; 6

kinds)

-Cartilage (3 kinds)

-Bone (2 kinds)

-Blood [liquid connective tissue composed of plasma, and formed elements (cells)].

Fibrous Connective TissueTwo broad categories: Loose and Dense

Loose

1. Areolar connective tissue

2. Adipose connective tissue

3. Reticular connective tissue

Dense

1. Dense regular connective tissue

2. Dense irregular connective tissue

3. Elastic connective tissue

Fibrous connective tissue functions to support and protect the body and its organs as well as bind tissues and organs together.

Areolar (loose) CT matrix

• Characterized by:1. Protein fibers: collagen; reticular; elastic2. Ground substance/ interstitial fluid3. Defensive cells: macrophages, mast cells,

plasma cells, neutrophils, lymphocytes and eosinophils

4. Fat cells: store triglycerides as nutrientsAreolar connective tissue is found under epitheliaas in the lamina propria and around organs andcapillaries.

Areolar Connective Tissue

Areolar Connective Tissue

Protein fibers in connective tissue

• Collagen fibers- occur in parallel bundles, strongest (stronger than steel) and most abundant. Withstand tremendous pulling forces.

• Reticular fibers- short bundles of specialized collagen fibers. Important in support of vessels and tissues.

• Elastic fibers- smaller in diameter, branching and form networks. Consist of protein elastin and fibrillin. Highly stretchable (150%) but strong and return to original length.

Areolar Connective Tissue

Ground substance

• Binds, supports and provides medium for transport and exchange between cells.

• Consists of water, proteoglycans, hyaluronic acids, glycosaminoglycans (GAGs), fibronectin and other substances that hold the cells together.

• Interstitial fluid - liquid faction that bathes tissues and contains all of the preceding substances and cells.

Connective tissue cells• Fibroblasts- large flat branching cells secrete

fibers and ground substance in the matrix

• Macrophages- derived from monocytes, large irregular shape. Phagocytic action.

• Plasma cells- derived from B lymphocytes, secrete antibodies= immune response

• Mast cells- produce histamine

• Adipocytes- store triglycerides

• White blood cells- neutrophils, eosinophils, and lymphocytes for fighting infection