L3 EPITHELIAL TISSUE Flashcards
What is tissue?
A group of cells that come together
What are the four basic tissues of human body?
- Muscle tissue
- Epithelial tissue
- Connective tissue
- Nervous tissue
What is Epithelial tissue?
One or more layers of closely packed cells (with very little intercellular spaces) avascular and is nourished by diffusion from the underlying capillaries
Extends to form glands
Where is Epithelial tissue found?
Outer surface of the body – Interior of tubular organs and body cavities (mesothelium) – Lines the interior of heart and blood vessels (endothelium) – Ducts and secretory elements of glands
Describe the arrangement of epithelium?
Epithelium may consist of one layer or many layers of closely packed cells • The cells rest on a basement membrane • In case of multilayered epithelia, deepest layer of cells rest on a basement membrane • Basement membrane or basal lamina is made up fibrous tissue
Functions of epithelium?
- Protection of underlying tissues of the
body from abrasion and injury - Secretion of mucous, hormones, enzymes
from various glands
3.Absorption of material from the lumen
(intestinal tract or certain kidney tubules).
4.Detection of sensations (olfactory
epithelium of nose, taste buds and
receptors in the internal ear)
What are the two main classifications of epithelia?
- Simple
2. Stratified
What are the four types of simple epithelia ?
Simple squamous epithelium
Simple cuboidal epithelium
Simple columnar epithelium
Pseudostratified columnar epithelium
What are the five types of stratified epithelia?
1. Stratified squamous non-keratinized epithelium • Stratified squamous keratinized epithelium • Stratified cuboidal epithelium • Stratified columnar epithelium • Transitional epithelium
What is simple squamous epithelium?
Function? Example?
One layer of flat cells resting on a basement membrane
• Width of the cell is more than the height
• Nucleus is flat, seen as a bulge on the cell surface
• Thin layer of cytoplasm
• This epithelium allows passage of materials by diffusion and filtration
• eg. Alveoli of lung, blood vessels, bowman’s capsule of kidney
What is simple cubodial epithelium?
Function? Example?
One layer of cells, have equal height and width • Centrally placed round nucleus • Function – secretion and absorption • Eg. follicles of thyroid gland, renal tubules
What is simple columnar epithelium cells?
Cells are almost 3 times taller than their width • Oval shaped nucleus placed near the basal part of cell • Function: – Absorption, secretion of mucus, enzymes – ciliated type propels mucus (or reproductive cells) by ciliated action found in stomach
What are the four types of simple columnar epithelium cells?
- Simple columnar epithelium
2.Simple columnar epithelium with microvilli or
brush border
3.Ciliated columnar epithelium - Simple columnar epithelium with Goblet cells
– Simple columnar epithelium with microvilli or
brush border
free surface presents fine
projections called microvilli e.g. gall bladder,
small intestine
Ciliated columnar epithelium –
– free surface has
projections called cilia – eg uterine tube
Simple columnar epithelium with Goblet cells
contains Goblet cells which produce mucous e.g.
large intestine
What is Pseudo stratified ciliated columnar epithelium?
Example?
Single layer of cells with different heights
• All the cells lie on the basement membrane
• Some cells are short, only some cells reach the
surface of the epithelium
• Their nuclei are located at different levels, giving
the impression of a stratified epithelium even
though it is composed of single layer of cells
• Function: Secretion, particularly of mucus,
propulsion of mucus by ciliary action.
• E.g. trachea, vas deferens
What is Stratified (compound) squamous epithelium?
Seen in areas where there is maximum friction, and
cells are constantly replaced
• Thick, several layers of cells, only the deeper layer
of cells are in contact with the basement membrane
What is Stratified squamous non-keratinized epithelium:
Contains 3 types of cells
• Deepest single layer of cells resting on basement
membrane are columnar cells
• Intermediate 3 to 6 layers of polyhedral cells
• Most superficial 2 to 5 layers of squamous cells
• E.g. esophagus
Stratified squamous keratinized
epithelium:
Contains 3 types of cells • Deepest single layer of columnar cells resting on the basement membrane • 3 to 6 layers of polyhedral cells • 2 to 5 layers of squamous cells • Layer of keratin over the squamous cells • E.g. skin
What is Transitional epithelium (urothelium)?
Function? Example?
Capable of considerable distension
• Epithelium is 4 to 6 layers in thickness
• Deepest cells are cuboidal or columnar cells
located on the basement membrane
• Middle 2-4 layers of polyhedral or pear
shaped cells
• Superficial layer of umbrella shaped cells
• Function: stretches readily and permits
distension of urinary organ by contained urine
Stratified columnar epithelium
Usually made up of 2 layers of cells • Deeper layer of cuboidal cells in contact with the basement membrane • Superficial layer of columnar cells. • E.g. large excretory ducts of the salivary glands
Stratified cuboidal epithelium
- Two layers of cuboidal cells.
* E.g. Ducts of sweat glands
What are glands?
Glands are epithelial invaginations of the surface epithelium These are cells or aggregation of cells whose function is secretion
What are the two classification of glands?
– Exocrine glands
– Endocrine glands
What are endocrine glands?
Function? Example?
• Are composed of groups of cells lying close to blood and lymph vessels • The secreting cells mostly occur in groups or cords • These glands don’t have ducts and discharge their secretion directly into the blood and lymph vessels • These produce hormones • eg. thyroid gland, pituitary gland etc
What are exocrine glands?
Exocrine glands discharge their secretions
through the ducts
• Exocrine gland secretions include saliva,
perspiration, oil, earwax, milk, mucus, and
digestive enzymes
What are the classification of exocrine glands according to the
branching of ducts?
- Simple glands
2. Compound glands
What are simple glands?
Example?
Simple glands:
• Secretion of these glands is discharged
through single or unbranched duct
• eg. gastric glands of stomach, sweat glands
What are compound glands?
Example?
The ducts of these glands divide into many
branches
• eg. Parotid salivary gland
What are the classification of glands according to the shape of secretory unit?
Tubular glands
– Acinar glands
– Alveolar glands
What are tubular glands ?
Example?
Tubular glands:
• Secretory unit is tubular in
shape
• eg. gastric glands of stomach
What are Acinar glands?
Secretory unit is rounded or oval in shape – which is called acinus • eg. parotid salivary gland, pancreas
What are alveolar glands?
Secretory unit is in the form of
flask-shaped sac called
alveolus
• eg. mammary gland
What are the classification of glands according to the method of discharge of secretion from the secreting cells?
Holocrine glands, Apocrine glands, Merocrine glands
What are Holocrine glands?
These glands accumulate their secretions in each cell’s
cytoplasm and release the whole cell into the duct
• The entire secreting cell forms a part of secretion
eg. sebaceous glands
What are Apocrine glands?
Only a portion (apical part) of secreting cell is lost during
secretion and becomes a part of secretion
eg. mammary glands
What are merocrine glands?
The secretion passes through the free surface of the cells
into the lumen of the acinus.
• Wall of the secreting cell remains intact
eg. parotid salivary gland
What are the classification of glands according to the type of secretion?
Serous glands
Mucous glands
Mixed glands
What are Serous glands?
Secretion of these glands is a watery clear fluid
• The secreting cells have rounded nuclei close to their
base
eg. Parotid salivary gland
What are Mucous glands?
Secrete the glycoprotein mucin, which by the uptake of
water is converted into a slippery secretion called
mucous
• The secreting cells have flat, peripheral nucleus lying
against the base of the cell
e.g Sublingual salivary gland
What are mixed glands?
Sublingual salivary gland
eg. Submandibular salivary gland
What are the classification of glands according to number of secreting cells?
Unicellular glands
Multicellular glands
What are unicellular glands?
Gland consisting of single cell that functions as a gland • These are situated in the epithelium of trachea and intestine along with other epithelial cells and secrete mucous eg. goblet cells
What are Multicellular glands?
These glands consists of clusters of secreting cells • Most of the glands in the body are multicellular glands eg. parotid salivary gland, gastric glands.
