lecture day 2 epithelium and glands

Epithelium and Glands

Histology – The study of tissues

What is a tissue?

A group of cells that work together for a specific function

Tissue classes:

• epithelial -

• connective – support, protection, storage, transport

• muscle  - move things

• nervous – communication

Epithelial Tissue: skin, lines cavities, blood vessels, glands, ducts

• Functions

  • Protection - skin

  • Produce / control secretions

  • Controls Absorption, excretion and filtration

  • Provides Sensation

  • Glands – produce secretions (sweats, oils,)

• Characteristics of epithelial tissue

  • polarity:  

    • apical surface (top surface)

      • cilia – protection from outside germs

      • microvilli – increase surface area for absorption

    • lateral surface (sides of the cell)

    • basal surface (bottom of the cell)

      • basal lamina (basement membrane) surface under the cell

• attachment: cells must attach to an underlying structure

• avascularity: without vessels (uses connective tissue to bring up nutrients into epithelial tissue)

• regeneration: fast replacement of cells, undergoes a lot of stress

• cellularity:

  • Cell junctions  

·        Tight junction – impermeable, zipper-like, (space between two cells), prevents things from going between cells and going to the other side

·        Gap junction – allow movement of small substances from one cell to another, allows electric signals to go from one cell to another

·        Button desmosome – holds 2 cells together, has proteins on each cells and filaments between them, still allows substances to get through

·        Hemidesmosome – attach the cell to the basement membrane

Classification of epithelial cells  

• simple – one layer

• stratified – more than one layer

Simple squamous                  thin, flat, fried egg shape, nucleus is flattened; very thin layer

Function: rapid diffusion, if a substance has to get through

Locations: air sacs of lungs, inner lining of heart and blood vessels, serous membranes of stomach, intestines and other organs, pericardium, peritoneum, mesenteries.

Stratified squamous   multiple layers of cells that get flatter as they reach the surface, thick layer

Function: protection

Locations: nonkeratinized- surface cells are alive, located in moist areas; mouth, throat, esophagus, anal canal, vagina.

Keratinized- surface cells are dead, contains keratin; skin

Simple cuboidal   square, nucleus is round and locate toward the center of the cell

Function: secretion, absorption, diffusion (lungs), not rapid diffusion but can be found occurring through kidney tubules and our glands

Locations: kidney tubules and glands

Stratified cuboidal  two or more layers of cuboidal cells; rare

Function: protection, movement of substances (moving it through the dock to get it to the surface)

Locations: ducts of sweat glands and salivary glands

Simple columnar  tall, narrow cells, nucleus is jelly-bean shaped and located near the bottom of the cell, may have microvilli or cilia on apical surface

Function: absorption and secretion

Locations: uterine tube, GI tract, bronchioles

Pseudostratified columnar    single layer of cells; all cells attached to the basement membrane but

not all cells are tall enough to reach the apical surface; nuclei are at different levels so it looks stratified; almost

always ciliated.

Function: protection (lower airways from thing that could cause damage like pathogens and dust an debris and things like that)

Locations: respiratory tract from nasal cavity to bronchi

Transitional   varying shapes ranging from cuboidal (empty bladder) to squamous (full bladder)

Function: allows stretch and recoil

Location: Urinary bladder

Glandular epithelium

• endocrine glands – (endo – inside) ductless glands – produces hormones and secreted into blood or interstitial fluid

• exocrine glands – (exo – outside) connected by ducts to the surface – secrete sweat, oils, digestive enzymes

Exocrine glands  

• Gland structure  

  • unicellular glands: single-celled  - goblet cells – mucous

  • multicellular glands: all other exocrine glands

    • branched (multiple branches) or unbranched (one branch)

      • simple gland (one duct)

      • compound gland (multiple ducts)

    • secretory portion:

      • tubular: shaped like a U

      • acinar or alveolar: has a flask shape

• Modes of secretion  

  • merocrine glands: product gets packaged into a vesicle and gets released into a duct

  • apocrine glands : products accumulate towards the apical surface of the cell, then when ready to release, the portion will pinch off and leave a small portion of the cell behind and the product released into the cell membrane

  • holocrine glands: cell makes product, undergoes apoptosis and rupture open, then product releases, cell dies and gets replaced

• Types of secretions

  • serous - watery

  • mucous - thicker

  • mixed exocrine – both