11.09.11+-+Introduction+to+Histology+&+Epithelia

Introduction to Histology & Epithelia


 * 1. List and define the four primary tissue types**

Epithelium: Generally form in a membrane with little extracellular space Muscle: Contractile, cells are elongated, little extracellular space Connective: Much extracellular space; provides support, form, protection, and/or transport Nervous: Neurons and support cells


 * 2. List five general distinguishing characteristics of epithelial tissues.**

Epithelial tissues are diverse isolated covering cells without blood or nerve bodies.

Their characteristics could be seen as following logically from one to another. Once you know that they are isolated from the other cell types by a basement membrane, the rest of the characteristics could be intuited. We know that other cell types include the vascular and neural cells, so it could be reasoned that vascularization or neural cell bodies (there are nerve endings) do not exist in epithelium. Also, since they are separated from other cell types, it could be reasoned that they must be on the surface of whatever tissue they are on, covering either the inside or the outside. Since they are on the inside and outside of structures, they seem like useful structures to secrete substances to lumens or the surface. Finally, since there's no mention that they are only in one region of the body, so it would make sense that they could be derived from multiple germ layers.


 * 3. List the primary embryonic germ layers that can give rise to epithelial tissues.**

All 3: ectoderm, mesoderm, and endoderm.


 * 4. Describe four broad functions of membranous epithelia.**

This is an interesting question because the lecture gave us six functions, which I put into the amazing mnemonic: T-SCABS.

T - Transport S - Secretion C - Contraction A - Absorption B - Barrier S - Sensation


 * 5. Describe three functions of basement membranes/basal laminae. Be aware of which cell types have a basal lamina and which don't.**

Another mini-mnemonic: STD Support - It provides an attachment point for the basal layer of epithelial cells Transport - It serves as a semi-permeable membrane to compartmentalize tissues through filtration Direction - It orients the epithelial cells to know which side is apical and which side is baso-lateral


 * 6. Describe the distinguishing features of the following classifications of epithelia:**

Simple - 1 cell layer thick Stratified - >1 cell layer thick Pseudostratified - 1 cell layer thick, but the sample cut stacked several cells to make the nuclei look stacked Squamous - flat cell Cuboidal - height and width of cell equal Columnar - height of cell 2-3x of width of cell Transitional - only present in urinary tract; appears cuboidal when unstretched (5-6 cells thick) and squamous when stretched Endothelium - lines blood vessels and lymphatic vessels mesothelium - lines surfaces of many organs (along with the connective tissue portion forms serous membrane) Keratinized - squamous cells can be keratinized (have apical extracellular surface keratin) or nonkeratinized Ciliated - apical extracellular surface of columnar cells can have cilia (thick, dense membrane projections to increase surface area)


 * 7. Describe the distinguishing structural features of exocrine and endocrine glands.**

Exocrine: Connected by a duct to a surface; an invagination of epithelial cells into ECM; product ends up on surface. Endocrine: Develops from an invagination of epithelial cells into ECM, but duct breaks down so gland isolated in ECM; product diffuses to blood flow.


 * 8. In general terms, describe the functional differences between secretory products characteristic of exocrine and endocrine glands.**

Because endocrine secretory products get picked up by blood vessels, they can have a global effect on the body. Exocrine secretory products have local effects.


 * 9. Describe the classification of exocrine glands according to the following criteria:**

Duct arrangement - Exocrine vs. Endocrine Shape of the secretory portion - Unicellular vs. Multicellular; Tubular vs. Alveolar; Simple vs. Branched Manner of secretion - Merocrine (exocytosis) vs. Holocrine (apoptotic sluffing) vs. Apocrine (disintegration of large portion of cell)


 * 10. Define parenchyma and stroma**

The stroma is the supporting framework of an organ. The parenchyma is the organ specific tissue (e.g. for a liver the hepatocytes).


 * 11. Identify the following micro anatomical structures in photomicrographs of histological sections:**

Simple squamous epithelium Simple cuboidal epithelium Simple columnar (ciliated or nonciliated) epithelium Stratified squamous (keratinized or nonkeratinized) epithelium Stratified cuboidal epithelium Stratified columnar epithelium Transitional epithelium Endothelium Mesothelium