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Characteristics of Epithelial Tissues some answers too study guide
Terms in this set (54)
What are the 4 basic types of tissues in the body?
Epithelial tissue, connective tissue, muscular tissue, nervous tissue
What are the 4 major characteristics of epithelial tissues?
1. Covers and lines body surfaces
2. Cells are densely packed together with minimal amount of intercellular substance
3. Cells are firmly attached by intercellular junctions
4. Cells rest on a basement membrane partly derived from underlying connective tissue
What are the 2 functions of a basement membrane?
1. Anchors epithelium to underlying connective tissue
2. Acts as a selective barrier for diffusion
How does epithelial tissue derive its nutrients?
Diffusion from underlying connective tissue
Describe the nerve supply of epithelial tissue.
It is richly supplied with nerve fibers
Describe the vascularity of epithelial tissue.
It is avascular
The epithelium develops from what 3 germ layers?
Ectoderm, mesoderm, endoderm
What specific parts of the body does each germ layer form?
1. Ectoderm- epidermis of skin
2. Endoderm- epithelium of digestive tract
3. Mesoderm- the serous lining of body cavities
What are the classifications of epithelial tissue?
1. Covering/lining epithelium
2. Glandular epithelium (endocrine and exocrine)
3. Neuroepithelium (taste buds)
What is the covering of epithelial tissue classified by?
The number of layers of cells and the shape of surface cells
What are the specific classifications for the number of layers of cells?
Simple (one layer of cells) and stratified (2 or more layers of cells)
What are the specific classifications for the shape of surface cells?
Squamos (flat), cuboidal (square), and columnar (tall)
What are simple epithelial tissues?
They are formed of one layer of cells resting on a basement membrane
What are the functions of simple epithelial tissues?
Absorption, diffusion, secretion, excretion
What are the 4 types of simple epithelial tissues?
1. simple squamos
2. simple cuboidal
3. simple columnar
4. pseudostratified columnar
What is the function of simple squamos epithelium and where is it found in the body?
1. Its major function is diffusion
2. Found in bowman's capsule in kidney, lining of blood vessels (endothelium), lining of body cavities (mesothelium), and alveoli of lungs
What is the function of simple cuboidal epithelium and where is it located in the body?
1. Absorption, secretion
2. Convoluted tubules of kidney, thyroid gland, and germinal epithelium of ovary
What is the function of simple columnar epithelium and where is it located?
1. Functions are absorption and secretion
2. Simple columnar ciliated epithelium is located in the lining of the uterus and uterine tube. Simple columnar non-ciliated epithelium is located in the lining the stomach, small intestine, large intestine, and gall bladder
What is meant by "pseudostratified"?
There is one layer of cells and all cells touch the basement membrance, but not all cells reach the luminal surface. This is due to cells of different sizes being lined up next to each other.
How do nuclei appear in pseudostratified epithelium?
The nuclei appear to be arranged in more than one layer. This is a false appearance.
What are the 2 subtypes of pseudostratified columnar epithelium and where is each found in the body?
1. Pseudostratified columnar ciliated with goblet cells, which is found in the respiratory system (nasal cavity, trachea, and bronchi)
2. Pseudostratified columnar with stereocilia, which is found in the male reproductive system
What are stereocilia?
What is the main functin of stratified epithelial tissues?
Protection- they have the ability to withstand wear and tear
What are the 4 types of stratified epithelial tissues?
1. Stratified squamos
2. Stratified cuboidal
3. Stratified columnar
What are the 2 types of stratified squamos epithelium and in what tissues are they found?
1. Keratinized: epidermis of skin
2. Non-Keratinized: oral cavity, pharynx, esophagus, vagina (wet), cornea
Where is stratified cuboidal epithelium found?
This is a rare type of epithelium. It is only found in the small ducts of sweat glands of the skin and in ovarian follicles
Where is stratified columnar epithelium found?
This is a rare type of epithelium. It is present in the large ducts of the salivary glands, conjuctiva (mucus membrane that lines eyelids), and penile urethra
What is transitional epithelium and where is it found?
A type of stratified epithelium that changes shape and can resemble either stratofied squamos or stratified cuboidal epithelium, depending on whether it is stretched or contracted. It is found in the urinary system (calyces of kidney, ureter, urinary bladder, and prostatic urethra in males and females)
How does transitional epithelium appear in its relaxed and stretched state?
1. Relaxed (empty): 4-6 layers and the surface cells are cuboidal, binucleate cells
2. Stretched (distended, full): appears to have only 2-3 layers and surface cells look cuboidal with convex free border and rounded nuclei
Name and desribe the 5 types of cell junctions in epithelial tissues.
1. Tight or occluding junction: tight seal that obstructs transmission between cells
2. Adherent junctions: are sites of strong adhesion between cells
3. Gap/communicating junctions: allow the transmission of ions and small molecules between cells
4. Desmosomes: are adherent junctions that connect adjacent cells at certain spots only
5. Hemidesmosomes: connect epithelial cells to underlying connective tissue
How to desmosomes connect adjacent cells?
Tonofilaments/intermediate filaments are inserted into electron-dense plaques of material on the cytoplasmic surfaces of the junctional membranes
What are the 3 types of surface specialization of epithelial tissues?
2. Microvilli (brush border)
What types of epithelium contain cilia?
simple/pseudostratified columnar ciliated epithelium
What are some important characterisitcs of cilia and where are they found?
It is attached to basal bodies (same structure as centrioles), composed of microtubules covered with cell membrane, and they beat to move things along a surface. They are located in the respiratory tract (move things away from lungs) and fallopian tubes (move ovum towards uterus)
What is a brush border and where is it found?
The name for the microvilli-covered surface of simple cuboidal epithelium and simple columnar epithelium cells. They are found in the small intestine and proximal convoluted tubules of the kidney.
Describe the appearance and function of microvilli.
They are very short and formed of folds of cell membrane and a core of actin filaments. They increase the surface area for absorption.
Describe the appearance of stereocilia and comment on its location.
It contains long microvilli that project from the luminal pole of the cell. It is composed of a core of actin filaments and only found on columnar cells. It is located in male genital passages (epididymis and vas deferens).
What is the function of stereocilia?
To absorb testicular fluid in the epididymis and vas deferens that was produced by cells in the testes.
What are goblet cells and where are they found?
Modified columnar cells that synthesize and secrete mucus, which are found in the GI tract and the respiratory tract.
What type of gland is a goblet cell?
What are myoepithelial cells and where are they found?
They are cells that contain contractile actin proteins and surround and squeeze secretory units and ducts. They are found in exocrine glands inlcuding the lacrimal, salivary, mammary, and sweat glands.
What is glandular epithelium and its function?
An organized collection of cells derived from covering epithelial cells. They synthesize, secrete, and store the secretion.
Is glandular epithelium vascular or avascular?
What are the 2 major classifications of glandular epithelium?
1. Exocrine: contains ducts and maintains connection with surface cells
2. Endocrine: do not have ducts, secrete directly into blood, loses connection with surface cells
How are glands formed?
1. Proliferation of surface cells
2. Downward growth and invasion of the underlying connective tissue
3. Differentiation into exocrine and endocrine
What are exocrine glands?
Glands formed of secretory units formed of secretory epithelial cells that release secretion into a lumen and a duct that conveys secretion to a surface.
What are the 4 criteria for classification of exocrine glands?
1. Branching of the duct
2. Shape of the secretory unit
3. Type of secretion
4. Method/mode of secretion
What are the 2 types of branching of exocrine glands? Define each.
1. Simple: ducts do not branch
2. Compound: branched duct system
What are the 2 shapes of secretory units? Define each.
1. Tubular: tube-like
2. Acinar/alveolar: bulbous-like
What are the 3 types of secretions? Define and give example of each.
1. Serous: watery secretion containing enzymes. Ex-parotid (contains salivary amylase)
2. Mucous: thick mucous secretion. Ex- goblet cells
3. Mixed: has both serous and mucous acini. Ex- submandibular gland
What are the 3 modes of secretion of exocrine glands? Define and give examples of each.
1. Eccrine/merocrine: secretion released without loss of cell. Ex- sweat glands
2. Apocrine: apex of cell is lost with secretion. Ex- mammary glands
3. Holocrine: cell is lost as part of the secretion. Ex- sebaceous glands of skin
How are endorcrine glands classified?
By their arrangements
What are the 2 classifications of endocrine glands? Describe and give examples of each.
1. Follicular: arranged in rings called follicles (secretion stored inside follicles), lined with simple cuboidal epithelium, and follicles are surrounded with blood capillaries to transport secretion. Ex- thyroid gland.
2. Anastomosing cords: granules are stored inside cells, every cell must be in contact with a capillary for transport of secretion. Ex- parathyroid gland.
What are the 7 functions of epithelial tissue? Cite locations in the body with each function.
1. Protection: covers body surfaces (epidermis of skin, cornea) or lines hollow organs (digestive tube, urinary/reproductive passages), blood vessels, and body cavities
2. Absorption (intestines and kidney)
3. Secretion (glandular epithelium)
4. Excretion (kidney)
5. Sensation (neuroepithelium- taste buds)
6. Contractility (myoepithelial cells of glands)
7. Reproduction (germinal epithelium of ovary and testis)
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