Chapter 4: Tissue Level of Organization Flashcards
Epithelial Tissues
A group of cells that usually have a common origin in an embryo and function together
Tissues
Epithelial Tissues
covers body surfaces and lines hollow organs, body cavities and ducts and also forms glands
Allows the body to interact with both internal and external environment
Connective tissue
Protects and supports the body and its organs
Various types of tissues bind organs together, store energy reserves as fat, and help provide the body with immunity to disease causing organisms
Muscular Tissue
is composed of cells specialized for contraction and generation of forces
In the process, muscular tissue generates heat that warms the body
Nervous Tissue
detects changes in a variety of conditions insides and outside of the body and responds by generating electrical signals called nerve action potentials that activate muscular contractions and glandular secretions
Cell Junctions
Contact points between plasma membranes of tissue cells; 5 types
The five types of cell junctions
- Tight junctions
- adherens junctions
- desmosomes
- hemidesmosomes
- Gap junctions
Tight junctions
- fuse togeher the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells
- web like strands of transmembrane proteins
eg. stomach or bladder cells are adhered with tight junctions to prevent leakage of contents into other tissues
Adherens junctions
- contain plaque - a dense layer of proteins on the inside of the plasma membrane that attaches both to the membrane proteins and to microfilaments of the cytoskeleton
- it forms an adhesion belt
- transmembrane glycoproteins join the cells
What are the transmembrane glycoproteins that join the cells in an adheren junction; they link together on the outside of the cell membranes o-o-o-o-o
Cadherins
Adhesion belts
formed by adherens junctions in epithelial cells and encircle the cell.
help epithelial surfaces resist separation during various contractile activities
eg. digestive tract contractions
Desmosomes
contain plaque and have transmembrane glycoproteins (cadherens) that extend into the intracellular space between adjacent cell membranes and attach cells to one another
however, the plaque of desmosomes does not attach to microfilaments, but rather intermediate filaments inside the cell
Found in skin and heart tissue cells
spot weld junctions
Hemidesmosomes
Look like desmosomes but do not link adjacent cells; instead anchor cells to the basement membrane
transmembrane proteins in hemidesmosomes are integrins rather than cadherins
When do integrins attach to in hemidesmosomes?
Intermediate filaments on the inside of the plasma membrane made of protein keratin
On the outside of the cell, they adhere to the protein laminin on the basement membrane
Gap Junctions
Connect neighboring cells via membrane proteins called connexions that make connexons (tiny fluid filled tunnels)
Intercellular gap between them, not completely connected
Allows passage of ions, nutrients and wastes between avascular tissues cells like lens and cornea of the eye
Allows communications
Epithelial Tissue (vs)
Many cells tightly packed with little or no extracellular matrix
No blood vessels
Usually forms surface layers and isn’t covered by another tissues (one expection is the blood vessel since blood is a tissue)
Connective Tissue
Large amount of extravellular material that separates cells that are usually widely scattered
Most have significant networks of blood vessels
Why is epithelial tissue always found adjacent to connective tissue?
Because it lacks blood vessels and forms surfaces and the blood vessel rich connective tissues enables it to make exchanges with blood
Describe epithelial tissue (epithelium)
cells arranged in a continuous sheet in either single or multiple layers
Two general patterns of epithelial cells in the body
- covering and lining various surfaces
- forming the secreting portion of glands
What is the function of epithelial tissues?
- protects, secretes, absorbs and excretes
Apical Surface
(aka free surface) outermost / most superficial layer
faces the body surface, cavity, the lumen of an internal organ or tubular duct
may contain cilia or microvilli
Lateral epithelial cell surfaces
Face adjacent cells on either side
may contain cell junctions (not hemidesmosome)
Basal surface of epithelial cells
Opposite the apical surface - the deepest layer
Adhere to extracellular materials like the basement membrane
Contain hemidesmosomes
Basement membrane
thin extracellular layer that consists of two layers
two layers of basement membrane
- basal lamina
- Reticular lamina
Basal lamina
the layer of the basement membrane that is closest to, and secreted by, the epithelial cells
Contains laminin protein that adheres to the integrin in the hemidesmosome of the basal layer of the epithelial tissues
Reticular Lamina
Closer to underlying connective tissues
Contains proteins like collogen that is produced by connective tissue cells called fibroblasts
Which tissue is avascular but has its own nerve supply?
epithelial tissue
What process allows the exchange of substances between teh epithelial tissue and the connective tissue
diffusion
Most important roles of epithelial tissues in the body
- protection, filtration, secretion, absorption, and excretion
-also combine with nervous tissue to create sensory organs
Two types of epithelial tissue
- Covering and lining epithelium (surface epithelium)
- Glandular epithelium
Surface epithelium location/function
outer covering of the skin and some internal organs
inner lining of blood vessels, ducts, body cavities
interior lining of the respiratory, digestive, urinary, and reproductive systems
Glandular epithelium
makes up the secreting portion of glands such as thyroid, adrenal, sweat and digestive glands
Two characteristics used to classify cover and lining (surface) epithelium
- Arrangement of cells in layers
- Shape of the cells
3 Types of Classifications for tissue based on arrangement of cells in layers
- Simple epithelium
- Pseudostratified epithelium
- Stratisfied epithelium
Simple Epithelium
a single layer of cells that function in diffusion, osmosis, filtration, secretion and absorption
Pseudostratisfied Epithelium
Appears to have mulitple layers because cell nuclei lie at different levels and not all cells reach the apical surface
It is a simple epithelium - it is a single layer of cells that rest on the basement membrane
Cells that do not reach apical usually contain cilia or secrete mucous (goblet cells)
Stratisfied Epithelium
Two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear (eg skin)
4 cell shape classifications for epithelial tissues
- Squamous cells (flat)
- Cuboidal cells (cubes or hexagons)
- Columnar Cells
- Transitional Cells
Describe squamous cells
Flat thin cells that allow rapid passage of substances through them
Cuboidal cells
cubes or hexagon shape
may have microvilli
secrete or absorb
Columnar Cells
Column structure
Protect underlying tissues
Apical surface may have cilia or microvilli
Often specialized for secretion and absorption
Transitional Cells
change shape from squamous to cuboidal and back
seen in stretch organs like stomach and bladder
I. Simple epithelium
a. simple squamous epithelium
- endothelium
-mesothelium
b. simple cuboidal epithelium
c. simple columnar epithelium
- nonciliated
-ciliated
d. Pseudostratisfied columnar epithelium
- nonciliated
-ciliated
II. Stratified epithelium
a. stratified squamous epithelium **
- nonkeratinized
- keratinized
b. stratified cuboidal epithelium
c. stratified columnar epithelium
d. Transitional epithelium or urothelium
The function of glandular epithelium?
secretion
This structure consists of epithelium that secretes substances into ducts, onto a surface, or eventually into the blood in the absence of ducts
Endocrine or exocrine
Glands
Endocrine glands
secrete hormones
interstitial fluid -> diffuse into blood stream
No duct
Systemic effects
Exocrine Glands
Secrete products into ducts that empty onto a surface of a covering and lining epithelium
Local effects only
Sweat, mucous, etc
Structural classifications of exocrine glands
Unicellular or multicellular
Unicellular Exocrine Glands
Single celled glands
eg goblet cells
Multicellular Glands
most exocrine glands are multicellular
many cells that form a distinctive microscopic structure or macroscopic organ
Sweat (sudoriferous), oil (sebasceous), and salivary glands
2 criteria for classifications of multicellular glands
- Branched or unbranched ducts
- the shape of the secretory portions of the gland
An exocrine gland that does not branch
Simple gland
An exocrine gland that branches
compound gland
Glands with tubular secretory parts
Tubular glands
Glands with rounded secretory parts (berry; alveolar)
Acinar Gland
Glands that have both tubular and more rounded secretory parts
Tubuloacinar Glands
Structure Classification Scheme for Multicellular Exocrine Glands
I. Simple:
1. Simple Tubular
2. Simple branched tubular
3. Simple coiled tubular
4. Simple Acinar
5. Simple branched Acinar
II. Compound
1. Compound Tubular
2. Compoud acinar
3. Compound tubuloacinar
Function Classifications of exocrine Glands
Merocrine GLands
Apocrine Glands
Holocrine
Merocrine Glands
- released from the cell in secretory vessciles via exocystosis (eg. sailvary glands)
Apocrine Glands
accumulate their secretory product at the apical surface of secreting cell, then that portion of the cell pinches off from the rest of the cell to release the substance by exocytosis (mammary glands)
Holocrine Glands
Collect secretion in cytosol and then as the cell matures, it ruptures and becomes the secretions (sebasceous gland)
Secretion contains a large amount of lipids from the cells membranes
