Lecture 3 - histology epithelial tissues

Functions of epithelial tissue

1. physical protection from dehydration, abrasion, and physical chemical and biological agents in the atmosphere. it is very strong and doesn't rip easily. 2. selective permeability regulates the passage of certain molecules in or out of certain regions of the body 3. secretion some epithelial cells called exocrine cells produce secretions such as sweat or oil 4.sensation epithelial cells possess nerve ending that can detect light, taste, sound, smell, hearing, heat, cold, and pain

Types of intercellular junctions

1. tights junctions surrounds the epithelial cells near their apical surface and attaches each cell to its neighboring cells. It forces most materials to move through/get absorbed into the cell instead of between epithelial cells. Tight junctions are like zippers around the cells. not on the whole apical surface but rather links the apical cells together. 2. gap junctions provide a direct passageway for small molecules to travel between cells 3. adhering junctions located deep the tight junctions and completely encircles the cell. It supports the apical surface and provides a small space between the neighboring cells in the direction of the basal surface. It allows for materials that passed through the apical surface to exit cell on lateral surface to travel to the basement membrane. 4.desmosomes act as buttons/snaps between cells. Holds the cells together and provides resistance to mechanical stress. Hemidesmosomes attach the basal layer of epithelial cells to the basement membrane.

Tissue

a group of similar cells and extracellular matrix that perform a common function

Simple epithelium

a single layer of cells with all cells have an apical surface and attached to the basement membrane

Extracellular matrix

a substance produced by the cells of a specific tissue and can contain protein, salts, H2O, and dissolved molecules. located outside of cells.

Avascularity of epithelial tissue

all epithelial tissues lack blood vessels. The cells of epithelial tissue receive their nutrients by diffusion from underlying tissues

Transitional epithelium

appearance varies depending on whether the tissue is stretched or relaxes function: distension and relaxation to accommodate urine volume location: lining of the urinary bladder, ureters, and part of the urethra

Pseudostratified epithelium

appears layered because the cells nuclei are distributed at different levels between the apical and basal layer and no all cells reach the apical layer HOWEVER it is singular layered. Every cell is attached to the basement membrane

Attachment of epithelial tissue

basal surface is attached to a thin basement membrane

Ciliated simple columnar epithelium

columnar epithelial cells - some have cilia on their apical surface function: (remember that cilia moves things along) secretion of mucus and movement of mucus along the apical surface and movement of oocyte alone the uterine tube location: lining of uterine tubes and lining of respiratory bronchi

Cellularity of epithelial tissue

composed almost entirely of cells with little extracellular matrix (because the cells are so tightly bound to each other.) They are bound together by intercellular junctions.

Innervation of epithelial tissue

epithelial tissue are richly innervated (filled with nerves) to detect sensation - heat, cold, pain, taste, etc.

Cell shapes - squamous

flat wide irregular in shape

Specialized structure of epithelial tissue - basement membrane

found between the epithelium and underlying connective tissue provides physical support and anchoring of epithelial tissue it acts as a barrier to regulate passage of large molecules between epithelium and the underlying connective tissue

Epithelial tissue

lines every body surface and all body cavities. Forms both the external and internal lining of many organs. The majority of glands are derived from epithelial tissue. Epithelial tissue possesses tightly packed cells and little to no extracellular matrix

Stratified cuboidal epithelium

multiple layers of cells apical cells are cuboidal function: protection and secretion location: large ducts in exocrine glands (such as sweat glands) and some parts of the male urethra

nonkeratinized stratified squamous epithelium

multiple layers of cells apical cells are squamous function: protection of underlying tissue location: lining of oral cavity, part of the pharynx, esophagus, vagina, and anus

Keratinized stratified squamous epithelium

multiple layers of cells apical cells are squamous and contain keratin function: protection of underlying tissue location: epidermis/skin surface

Cell shapes - cuboidal

same size on all sides the nucleus is centrally located

Specialized structures of epithelial tissue - Intercellular junction

sharing membrane specializations that strongly bound epithelial cells to each other (laterally on the apical surface) they are gatekeepers between the external and internal environment intercellular junctions allow adjacent cells to communicate by allowing flow of ions and other small molecules and preventing molecules from traveling between cells

High regeneration capacity of epithelial tissue

since the apical surface of epithelial tissue is constantly exposed to the environment, epithelial cells are frequently damaged/die. They are replaced as quickly as they are lost. Such as when you swallow you take away epithelial cells and new ones get built up

Pseudostratified columnar epithelium

single layer of cells with varying heights, not all cells reach apical surface function: protection and secretion and movement of mucus (ciliated form) location: ciliated form: nasal cavity, pharynx, larynx, traches, bronchi nonciliated form (rare): lines part of the male urethra and the epididymis

Simple squamous epithelium

single layer of flat cells with tile-like appearance function: rapid diffusion (because it only has 1 layer), filtration (bcz of the 1 layer), some secretion/serous membranes (such as the pleura around your lungs) location: alveoli (lungs), lining of heart chambers, blood vessels, lymph vessels, serous membranes of body cavities there are keratenized and nonkeratinized

Non ciliated simple columnar epithelium

single layer of tall narrow cells no cilia at the apical surface function: absorption and secretion of mucus (goblets) location: lining of most of the digestive tract

Simple cuboidal epithelium

single layered cuboidal cells (cube shaped, even height and width) function: absorption and secretion location: kidney tubules, thyroid gland follicles, ducts and secretory regions of most glands, surface of the ovaries

Cell shapes - columnar

taller than wider nucleus is oval and located in the basal region of the cell

Histology

the study of tissues and their relationships within organs

How to classify epithelial tissue

there are 2 criteria: 1. number of layers of cells 2. shape of the cells

Cell shapes - transitional

these cells can change shape and cycles between distended and relaxed states

Statified columnar epithelium

they are rare multiple layers of cells apical cells are columnar function: protection and secretion location: large ducts of some exocrine glands (such as salivary glands)

Polarity of epithelial tissue

they have apical (top) surface and a basal (bottom) surface. the basal surface attaches to underlying cells

Stratified epithelium

two or more layers of cells not all cells have an apical surface (only the very top layer does) not all cells attach to the basement membrane since the shape changes around the cell, the apical surface is what identifies the shape of the cell