Class Notes (807,458)
Canada (492,633)
ANAT 261 (42)

2. Skin epithlelium cell junctions and connective tissue.pdf

14 Pages
Unlock Document

McGill University
Anatomy & Cell Biology
ANAT 261
Craig Mandato

Naveen Sooknanan McGill Fall 2011 Skin: The skin is made of 3 layers: the epidermis (packed cells), the dermis (fibers) and the hypodermis (fat cells and reticular fiber). The skin has 7 functions: Protection: blocks entry of foreign material and also resist penetration and abrasion Containments: prevents loss of body fluid Thermoregulation: Controls the transfer of heat across the bodys surface, i.e. it regulates the body temperature through sweat, vasodilation, etc. Immunological defence: physical barrier against pathogens Sensory abilities: receptors for pains, heat, etc. Also why your hair stands up sometimes Communication: releases visual (e.g. blushing) and pheremonal signals Appendages: hair, nails, sebaceous glands, sweat glands The epidermis is made of a stratified squamous keratinized epithelium. We will discuss exactly what this means in a bit, but there are 4 main layers to the epidermis, going from the bottom up: The basements membrane: all epithelium lies on a basements membrane, which in this case separates the epidermis from the dermis o The basement membrane is invisible under LM everywhere except for the hair follicles and the respiratory tract, where they are enflamed Stratum germinativum (or stratum basili) is right on top of the basement membrane and is a single layer of columnar cells o These are the stem cells of the epithelium, and will differentiate into the layers above it The stratum spinosum are spiny, polygonal cells which are part of intracellular junctions o As the stem cells continue to grow, these cells begin to grow protein granules and are pushed up into the next layer, the stratum granulosom The stratum granulosom is made up of flat cells filled with protein granules o These cells begins to release their proteins granules at this layer o The stratum spinosum and granulosom attach laterally The stratum corneum Is made up of 10-15 layers of flat, dead cells that came from the stratum germinativum o The nuclei in these cells has been squeezed out of the cell, and therefore the cell dies 1 Naveen Sooknanan McGill Fall 2011 Below all of this is the dermis, which is made up of more fibrous elements called connective tissue. This connective tissue contains collagen fibers, as well as others such as extracellular membrane proteins Invaginations of the dermis begin to push into the epidermis; these are called papillae o Sometimes, because of plane of sections, these papillae will appear detached from the dermis, but they always remains attached The layer below this is the hypodermis, which contains mainly fat cells Because of the fixation procedure, these fat cells cannot be seen because they were removed when the sample was dehydrated with ethanol Characteristic of all epithelium: The cells are squished together, meaning there is little extracellular space The cells are strongly attached due to intercellular junctions They line the bodys surface and cavities They have specializations; they can be used for absorption, secretion, sensation and contractility The cells are polarized (doesnt mean charged); they have top and bottom which are different All epithelial tissue rests on a basement membrane (BM o Sometimes the BM will also be called basal lamina Epithelial tissue can either be covering epithelia or glandular epithelia. For now, we will only look at covering epithelia, we will do glandular later A simple epithelium has only one layer of cells, and can be further classified by the shape of the cells o Simple cuboidal (cube shaped) I.e. sebaceous gland o Simple columnar (tall, thin cells) I.e. intestines o Simple squamous (flat cells) I.e. respiratory tract, capillaries A stratified epithelium has many layers of cells, and its shape is determined by the outermost layer of cells o Stratifies squamous (either keratinized, like the skin, or non- keratinized) has flat cells on the top layer (like the skin) o Transitional epithelium, in which the top layer changes shape This will be seen in the kidney and urinary bladder The outermost layer is made of 2-5 layers of facet cells, 2 Naveen Sooknanan McGill Fall 2011 which can change their shape The epithelium can also be pseudostratified columnar, meaning it has the appearance of multiple layers, but in reality there is only one layer of columnar cells o An example of this is in the trachea o The nuclei appeared scatter, until simple columnar epithelium where they are all lined up, but there is still only one layer of cells Epithelium can also be ciliated (i.e. contain cilia, which arte little cells, at the outermost layer) or have a brush border, which are microvilli (hairs just like cilia, but much smaller) o These help increase surface area of the epithelium, useful in absorption As we have seen in the epidermis, keratinized epithelium has a layer of dead cells on top, which are full of keratin granules. We will talk about these more later on Non-keratinized epithelium does not have any keratin containing cells, and therefore there is no stratum corneum layer The BM is made up of proteoglycans, glycoproteins, collagen, and a layer of reticular fibers which underlies it. The basement membrane has 5 main functions: Structural attachment: of epithelial tissue to connective tissue (CT) Compartmentalization: separates epithelial cells from muscle cells Filtrations: Helps move molecules using their ionic charge, important in the kidney Helps establish polarity of the epithelial cells Tissue scaffolding: acts as a scaffold during regeneration when the epithelium is damaged A proteoglycan is made up of 50% sugars, 50% proteins. It consist of a core protein and several branches The core protein is attached to many glycosaminoglycan (GAGs) o An example of a GAG is heparan sulfate, which is made by epithelial cells The GAG is attached to a carbon atom in the core preteen through link trisaccharide o The link trisaccharide are three sugars which link the C of the core protein to the O of the GAG o This reaction is caused by glucaronic acid and N-acetylglucosamine 6-sulfate Physically, the proteoglycan resembles a test tube brush, the GAGs being the bristles Since GAGs are negatively charged they can retain water and have a spongy texture A glycoprotein, another component of the BM, is composed of 10% sugars, 90% protein. They are located everywhere in the body and help blood cells fight infection 3
More Less

Related notes for ANAT 261

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.