Week 3 - Epithelia Flashcards
How are epithelial tissues formed and what are some of their functions?
- they are formed by layers of cells that line the body surfaces both inside and outside the body and the organs
- they provide lining/ covering of body surfaces and provide boundaries between environments
- protect the body (skin)
- allow easy movement into and out of the body (gas exchange)
Epithelial tissues cover and line body surfaces or organs.
How is this beneficial?
- Lining on external surfaces provide protection
- Lining on internal body surfaces allow transport of substances into the body
- Coverings define structural boundaries and aid frictionless movement between structures
• Protection – Epithelial tissue protects the organs and body
• Selective permeability – compartmentalisation and separate parts of the body
• Secretion – Release of compounds on to the Epithelial surface
• Excretion - Release of compounds to the outside of the body
• Absorption – Taking stuff in
• Transport – lining on internal body surfaces are often designed to allow
transport of substances into the body
• Sensory perception – work with nervous cells to detect stimuli
Epithelial Architecture= important for epithelial to perform their functions
Name the 6 characteristics
- Adhesions: between ep cells helps form layers and barriers
- Polarity: ep has inner and outer surfaces
- Proliferative Capability: the ability to reproduce rapidly
- Anchored/ supported by CT: All eps are lined by basal lamina (layer of CT adjacent to inner ep surface and where ep rests on)- gives support and helps ep integrate into organs
- Avascular: ep receives nutrition through diffusion and doesn’t have its own blood vessels (not in direct contact with blood supplies, which is a good thing)
- Glands: synthesize and secrete molecules
3 types of epithelia?
Simple- single layer of cells that allow easy transport across ep
Stratified- multiple layers, makes transport impossible
Pseudostratified- consist of multiple layers but have cells of differing height for complex function
3 cell shapes for epithelia?
Squamous- very thin and flat. Few cytoplasm and found where rapid filtration or exchange is happening
Cuboidal- square cells, important for secretion and absorption
Columnar- tall and thin, for secretion and absorption. Many show microvilli
Epithelial Type: Simple Squamous
Single layer of flattened cells with few cytoplasm.
Functions: diffusion and filtration
Eg, in kidneys, lining of heart, blood vessels, air sacs of lungs
Epithelial Type: Simple Cuboidal
Single layer of cube like cells, large spherical nuclei
Function: secretion and absorption
Eg, kidneys, ducts, ovary surface
Epithelial Type: Simple Columnar
Single layer of tall and thin cells, with oval nuclei
Function: Absorption and Secretion
Non-ciliated: line digestive tract and gallbladder
Ciliated: line small bronchi, uterine tubes
Epithelial Type: Stratified Squamous
Thick membrane, several layers of cells
Function: protection of underlying areas subjected to abrasion
Eg, external part of the skin, lining of oesophagus, mouth and vagina
Epithelial Type: Pseudostratified Columnar
Single layer of cells with different heights
Nuclei seen at different heights, giving the appearance of layers
Functions: secretion and propulsion of mucus
Non-ciliated= male sperm carrying ducts
Ciliated= Trachea
Transition between stratified squamous and stratified columnar:
Transitional Epithelia
Has several cell layers, basal cells and cuboidal
Surface cells are dome-shaped
Allows distention of urinary bladder, lines the urinary bladder and uterus
What is epithelial specialization?
Glands develop from epithelia
Cells in epithelia differentiate and become cells that can produce and secrete aqueous product
Happens to single cells to form unicellular/ multicellular glands
Exocrine Glands:
Unicellular Glands and Multicellular?
Unicellular; secrete their products directly via exocytosis
Eg, goblet cells and mucous cells. Goblet cells secrete mucin that dissolves in water to make mucous
Multicellular; have an epithelium derived duct and a secretory unit consisting of secretory cells. deliver their product to the epithelial surface via epithelia lined ducts.
During Epithelial specialization multicellular glands are formed, what else happens?
Development of a multicellular secretory gland from an epithelia also involves invagination of the epithelia into the underlying CT
Allows for larger secretion production and allows the product to be stored away from epithelial surface so that secretion can be controlled
eg, secretory cells of mammary glands
What are the 4 modes of secretion? Explain.
Merocrine- secretion is where vesicle of product is released by exocytosis
eg, salivary glands and pancreas
Halocrine- accumulate a secretory product in their cytosol. As the secretory cell matures, it ruptures and becomes the secretory product. (when the whole cells contents are release in secretion.)
Apocrine - where part of the cytoplasm of a cell is released with the vesicle and secretory product The cell repairs itself and repeats the process.
Endocrine- secretion is directly into the blood
What are the 3 types of epithelial membranes?
Cutaneous:
Epidermis- karatinized stratified squamous epithelium
Dermis- very thick and supports epidermis
combine to form skin
Serous- moist membrane found in closed ventral body cavity, produces serous fluid
- lungs, digestive system, heart
- parietal layer, the outer layer which lines the body cavity
-visceral layer, the inner layer which covers the organ
2 layers separated by serous fluid
Mucous -lines many hollow internal structures in the body
-epithelial lining: contains mucosal glands
-lamina propria: loose connective tissue layer
-muscularis mucosae: thin layer of smooth muscle
eg, GI tract, respiratory tract
3 functions of epithelial tissue.
(1) a selective barrier that limits or aids the transfer of substances into and out of the body
(2) a secretory surface that releases products produced by the cells onto its free surfaces
(3) a protective surface that resists the abrasive influences of the environment.
What is the apical surface?
The apical (free) surface of an epithelial cell faces the body surface, a body cavity, the lumen (interior space) of an internal organ, or a tubular duct that receives cell secretions
May contain cilia or microvilli
The most superficial layer of cells
What is the lateral surface?
The lateral surfaces of an epithelial cell, which face the adjacent cells on either side, may contain tight junctions, adherens junctions, desmosomes, and/or gap junctions.
What is the basal surface?
The basal surface of an epithelial cell is opposite the apical surface.
The basal surfaces of the deepest layer of epithelial cells adhere to extracellular materials such as the basement membrane.
Hemidesmosomes in the basal surfaces of the deepest layer of epithelial cells anchor the epithelium to the basement membrane.
What is the basement membrane?
- basal lamina
- reticular lamina
A thin extracellular layer that commonly consists of two layers
Basal: is closer to—and secreted by—the epithelial cells. It contains proteins such as laminin and collagen, as well as glycoproteins and proteoglycans. The laminin molecules in the basal lamina adhere to integrins in hemidesmosomes and thus attach epithelial cells to the basement membrane
Reticular: closer to the underlying connective tissue and contains proteins such as collagen produced by connective tissue cells called fibroblasts
Explain how the epithelial cell is avascular.
Relies on the blood vessels of adjacent connective tissue to bring nutrients and remove waste
2 types of epithelial tissue
- Glandular
- Covering and Lining
Glandular- makes up the secreting portion of glands such as the thyroid gland, adrenal glands, and sweat glands.
Covering and lining- forms the outer covering of the skin and some internal organs. It also forms the inner lining of blood vessels, ducts, and body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems.
How are multicellular glands categorized?
(1) whether their ducts are branched or unbranched
- does not branch, it is a simple gland
- duct branches, it is a compound gland
(2) the shape of the secretory portions of the gland
endocrine glands?
internally secreting (blood)
hormones are produced and released into the blood
ductless
not all derived from epithelia
