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Anatomy and Cell Biology
Anatomy and Cell Biology 3309
Kem Rogers

Desmosomes (macula adherens) hold cells together at individual spots o Here, there is a 30 nm space between the two cells that is ELECTRON DENSE This is due to the cadherins proteins (desmoglein and desmocollin) o Again, there are electron-dense plaques on the cytoplasmic sides of both cells Inserting into these plaques are 10 nm filaments (i.e. intermediate filaments) The plaques contain desmoplakin, plakoglobin, and plakophilin On the basal surface of cells, we can find hemidesmosomes o These hold basal epithelial cells onto the basal lamina o They contain the same materials in the cytoplasmic side of the cells In the skin disease Pemphigus folaceus, there is an autoimmune response to desmoglein-1 o Desmoglein-1 is predominant in the upper layers of the stratified squamous epithelium in skin while desmoglein-3 is found in the lower layers o As a result of the autoimmune response, there is a loss of macula adherens junctions between the upper and lower layers because of a loss in desmoglein-1 function In cells, the complexes discussed above are grouped together as the junctional complex o Therefore, this includes zonula occludens (tight junctions), zonula and fascia adherens, and macula adherens (desmosomes) Junctional complexes can be seen in light microscopes, where they are called terminal bars Gap junctions are the 3 type of cell-cell junction o They are involved in transmitting electrical signals and metabolites between cells They have a very important function in transmitting electrical impulses in the myocardium o They are made up of proteins known as connexins 6 connexins form a connexon 2 connexons come together to form a full channels between 2 cells There are 3 types of cell surface modifications: o Cilia These are motile projections An extremely long cilium is known as a flagellum o Microvilli These are immotile projections that function to increase SA o Stereocilia These are really long projections that arent cilia They are more like long microvilli They are found in the hair cells of the vestibular and auditory systems Cilia contain within their cores axonemes, which are the underlying structures (they are a collection of MTs with a specific 9+2 pair organization) o There are dynein arms in cilia, which act as ATPase motors that use ATP hydrolysis energy to facilitate MT sliding and thus, ciliary beating o The MTOCs of cilia are basal bodies, which are essentially the same as cilia Microvilli are found on the surface of epithelial cells and they function to increase SA o In their core, they contain 6 nm filaments (i.e. microfilaments) associated with proteins to form a structure called a terminal web These 6 nm filaments allow for some movement They project into the cytoplasm Along with being found in the auditory and vestibular systems, the stereocilia are also found in the epididymis o They can be viewed as extremely long microvilli After epithelium, another tissue type in the body is connective tissue o Its function is to join, support, and provide structure for tissues and organs o It mediates exchange of nutrients, metabolites, and waste products between tissues and circulation There are 2 main types of connective tissue: o Loose (many cells, few fibers) = embryonic, lymphatic, hematopoietic, mesenteric, adipose o Dense (few cells, many fibers) = tendons, ligaments Regular Irregular o Bone and cartilage are highly specialized types of dense CT In connective tissue, we can find: o Cells o Extracellular matrix (ECM) Fibrous components that provide structure (easy to see microscopically) Non-fiber components that are important in bone and cartilage (harder to see because many histological techniques get rid of these) The many cell types in connective tissue can be permanent or transient o Examples of permanent cell types: Fibroblasts these are the main cell type in CT, where they synthesize and maintain the ECM of connective tissue Endothelial cells these line blood and lymphatic vessels Pericytes these are found on the outside blood vessels and capillaries; they are stem-cells that are a potential source of fibroblasts and smooth muscle cells; they are particularly found in adult tissue and are involved in fibrosis/scarring and angiogenesis (therefore, they can respond in a pathological manner) o Transient cell types: Tissue macrophages Mast cells these release histamine and are therefore very granular; they are usually difficult to find Plasma cell these are often very transient; they deal with inflammation, allergic reactions, and immune responses Adipocytes these cells fill space, store fat/lipid, and provide energy storage The skin is the bodys first line of defence o It contains connective tissue o The bodys 2 line of defence are the macrophages, mast cells, and plasma cells The fibrous components of CT include: o Collagen (type I collagen is very common!) There are 28 types in vertebrates The most important ones are type I, II, and III; the rest are mostly collagen-binding proteins that act to stabilize the regular collagens o Elastin o Reticular fibers Collagen assembly is an intracellular and an extracellular process o Collagen genes are transcribed into procollagen strands, which come together as 3 alpha- helices to form a procollagen triple helix The triple helix can be homo or heterotrimeric o The tropocollagen t
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