A&P Tissue level of organization Flashcards
Tissue Level of Organization
Histology – the study of tissues
There are 4 main types of tissue found in the body:
Epithelial, Connective, Muscular, Nervous (know this!!!)
N-ot E-very M-an C-an
3 Primary germ layers: (first types of tissues in embryonic development)
- Endoderm – epithelial, GI, respiratory, & urinary tract
- Mesoderm – epithelial, most muscle, & all connective tissue (including blood)
- Ectoderm – epithelial, & nervous tissue
cell junctions
defined as: the junction and adherence between the plasma membranes of cells.
5 types found in the body
-Tight *keep things out!
-Adherens *actin morcrofiliments velcro
-Desmosome * keratin intermediate filaments keeps things in place
-Hemidesmosome * found on the bottom only, transmembrane protein: Integrin, attaches to external membrane protein called Laminin
-Gap * essential for communication (heart…like a wave)
tunnel like connections called Connecons made of glycoprotein: Connexin
1) Tight junctions:
Transmembrane proteins that fuse the outer surface of adjacent cells to prevent passage of substances into or out of blood and tissues.-
*Found in the stomach, intestines, bladder
2) Adherens junctions
– contains a density of proteins called plaque (found on the inside of a cell’s membrane) that is associated with actin microfilaments which in turn attach to
cadherin proteins (a trans-membrane protein) that projects between cells onto the adjacent cell’s plaque. In certain types of cells, they form adhesion belts which
help with preventing separation of the layer of cells
(often the adhesion belts circumnavigate the entire cell membrane).
(think of velcro)
3) Desmosomes
– similar to the adherens junctions in that they have plaques at specific locations on the inside of the cell membrane as well as attachments to the trans-membrane protein cadherin,
however, they instead attach to
intermediate filaments
which, as you recall, is for internal structure of the cytoplasm (rather than the cell membrane).
This is made up of the protein KERATIN which is the protein found in skin.
These are like the “buttons” of a shirt - found in epidermis and cardiac muscle cells.
b. Intermediate filaments
b. Intermediate filaments – Medium sized
- Made of keratin protein
- Aids in internal stability of cell
- Helps in cell to cell junctions
4) Hemidesmosomes
– similar to structure of desmosomes but the glycoprotein is ** which INTEGRIN attaches to another external membrane protein called laminin and the function is not to attach to adjacent cells but to the basement membrane - found between epidermis and dermis
(only occur on the bottom)
5) Gap junctions
– tunnel like connections called Connexons, made up of the glycoprotein connexin, which attach adjacent cells but
allows communication or transfer of substances
such as
wastes, chemical or electrical signals, ions, & *nutrients.-
found in the corneal cells, muscles & nerve cells, and various GI or urinary cells.
FYI:
Gap junctions are how nerve or muscle cells in your body conduct electrical impulses*.
An example is the conductive system of your heart => 1 cell fires off an electrical signal, which passes through gap junctions stimulating the next cell etc. This is what causes your heart to contract in a coordinated fashion (keeping you alive)!
B. Epithelial tissue: “aka epithelium”
Consists of cells arranged in *layers. May be single or multiple layer, depending on the area of the body.
Has ample nerve supply but *no substantial blood supply (avascular)**. respiratory system, outside of body and different body cavities
Key roles of the epithelium include:
Protection against chemical & physical damage absorption of nutrients (ex gastro intestinal tract) excretion of wastes secretion of hormones P E A S
3 surfaces of epithelial cells:
lumen is inside of the tube
(a) apical surface* – “free” side that opens up into the body cavity, lumen or an organ, or lumen of a vessel and may contain cilia or microvillus. Ex. In the stomach, this is the surface that is closest to the outside environment.
(b) lateral surface* – the side shared with adjacent cells. This is where the different forms of cell to cell junctions are found.
(c) basal surface* – the side opposite to the apical surface; responsible for attachment to the basement membrane and underlying connective tissue.
basement membrane
– layer that attaches the epidermis to connective tissues.
(Analogous to the underlay that connects the carpet to the ground).
Consists of:
i. basal lamina – contains collagen fibers, laminin (protein), glycoproteins, and proteoglycans.
ii. reticular lamina – contains fibrous proteins
(tends to be stronger) created by fibroblasts
C. Cell arrangement types:
- Simple epithelium – single layer of cells. E.g. The capillaries or alveolar sacs of the lungs. The reason for this type of arrangement is for ease of exchange of substances. (squamous cells)
- Pseudostratified epithelium – appears multi layered but is in actuality only 1 layer – cells have projections that give it a stratified look. (tends to be more secretory columnar cells)
*Stratified – multiple layers of cells – tends to be in areas requiring strength & reinforcement. Also found in areas where a layer of cells may slough off easily
protection (skin)
D. Cell shapes:
Squamous – flat* – allows high rate of absorption – ie. lungs & capillaries
Cuboidal – cube shaped with microvillus – allows secretion and absorption
Columnar – column shaped with microvillus – allows secretion and absorption
Transitional – flat to cuboidal shaped – allows for distension and stretch (rare really only exists in urinary tract bladder can stretch)
E. Glands
secretory organs– specialized epithelial/dermal tissues that produce secretions and release them into:
Ducts (tubes) (where they secrete determines what kind of gland they are) or skin
The blood stream (arteries, veins, & capillaries) or
Onto the surface of the organs.
2 main types of GLANDS:
(a) Exocrine – secretes into ducts to be carried away into the lumen or onto skin surfaces
E.g. Suderiferous (sweat), sebaceous (oil), lacrimal (tears).
3 functional classifications of exocrine glands:
i. Merocrine – secretions are made in the cell and when ready, released in vesicles. E.g. Pancreatic & salivary ii. Apocrine - secretions are accumulated on apical surfaces until ready for release. Ex. Mammary glands iii. Holocrine – secretions are accumulated in the cytosol and when ready, released as a large excretory vesicle. Ex. Sebaceous glands
Structural classifications of Exocrine glands:
not needed for test
simple: tubular branched coiled tubular acinar branched acinar
compound:
tubular
acinar
tubuloacinar
(b) Endocrine
– secreted into the blood stream** for functioning locally or elsewhere.
Secretions from endocrine glands are called HORMONES.
E.g. Testes, ovaries, pancreas, pituitary etc. These organs contain tissues with cells that produce hormones that they release into the blood stream to affect locally or somewhere else in the body.
CONNECTIVE TISSUE – IT IS EVERYWHERE! UBIQUITOUS
LOCATION:
- Surrounds organs and muscles, layer deep to the epidermis, surfaces of joints (cartilage), bones themselves, blood, and MUCH MORE.
