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Histo, Anat & Physiol > Epithelial Tissue > Flashcards

Epithelial Tissue Flashcards

1
Q

Epithelial Tissue

A
  • Protective coverings of surfaces both inside and outside of the body
  • Includes the skin surface and the linings of the heart, blood vessels, digestive tract, respiratory tract, urinary tract and body cavities
  • Includes secretary cells and glands
  • Function is predicted by the cell organisation/histology
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2
Q

Functions of epithelium

A
  • Physical protection
    - Protect exposed and internal surfaces from abrasion, dehydration, and destruction by chemical or biological agents
    - Outer layer of skin, lining of the gut, respiratory tract
  • Control permeability
    - Allow water, gases and nutrients to cross into and out of the body
    - Prevent toxins and microorganisms from entering
  • Provide sensation
    - Provide information on the external and internal environment
  • Produce specialized secretions
    - Epithelial cells that produce secretions are called gland cells
    - Hormones, sweat, mucous and joint fluid
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3
Q

Classification of Epithelia

A
  1. Based on shape
    • Squamous epithelia: thin and flat
    • Cuboidal epithelia: square shaped
    • Columnar epithelia: tall, slender rectangles
  2. Based on layers
    • Simple epithelium: single layer of cells
    • Stratified epithelium: two or more layers of cells
  3. Based on surface specializations
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4
Q

Examples of Columnar epithelium

A

Intestine

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5
Q

Examples of Simple Squamous epithelium

A

Capillary and alveoli

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6
Q

Examples of Cuboidal epithelium

A

Sweat duct

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7
Q

Simple Squamous epithelium

A
  • Role in secretion and absorption
  • Endothelium – lines blood vessels and heart
  • Mesothelium – lines body cavity
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8
Q

Simple Squamous epithelium Locations

A

Mesothelia lining pleural, pericardial, and peritoneal cavities; endothelia lining heart and blood vessels; portions of kidney tubules (thin sections of nephron loops); inner lining of cornea; alveoli of lungs

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9
Q

Simple Squamous epithelium Functions

A

Reduces friction; controls vessels permeability; performs absorption and secretion.

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10
Q

Stratified Squamous epithelium Location

A

surface of the skin; lining of the mouth, throat, oesophagus, rectum, anus and vagina.

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11
Q

Stratified Squamous epithelium Functions

A

Provides physical protection against abrasion, pathogens and chemical attack

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12
Q

Simple Cuboidal epithelium Locations

A

Glands; Ducts; portions of kidney tubules; thyroid gland

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13
Q

Simple Cuboidal epithelium Functions

A

limited protection, secretion and absorption

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14
Q

Stratified cuboidal epithelium Functions

A

protection, secretion and absorption

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15
Q

Stratified cuboidal epithelium Locations

A

lining of some ducts (rare) e.g. sweat gland duct

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16
Q

Stratified columnar epithelium Functions

A

Protection

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17
Q

Simple columnar epithelium Locations

A

Lining of stomach, intestine, gallbladder,uterine tubes and collecting ducts of kidneys

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18
Q

Simple columnar epithelium Functions

A

protection, secretion and absorption

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19
Q

Pseudostratified columnar epithelium Locations

A

Lining of the nasal cavity, trachea and bronchi; portions of male reproductive tract

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20
Q

Stratified columnar epithelium Locations

A

Small areas of the pharynx, epiglottis, anus, mammary glands, salivary gland ducts and urethera

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21
Q

Pseudostratified columnar epithelium Functions

A

Protection, secretion and move mucus with cilia

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22
Q

Transitional epithelium Locations

A

Urinary bladder; renal pelvis; ureters

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23
Q

Transitional epithelium Functions

A

Allows repeated expansion and recoiling after stretching
Returns to previous shape without damage

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24
Q

Application – GIT Epithelia (Epithelium)

A

changes with function; protection, secretion and absorption:
* Stratified squamous at mouth, oesophagus and anus
* Simple columnar in stomach and intestine

25
Q

Application – GIT Epithelia (Gland Cells)

A

found among epithelial cells, submucosal and in accessory structures (salivary glands, pancreas and liver)
Gland cells in GIT may be mucous, hormone or serous (enzyme secreting)

25
Q

Application – GIT Epithelia (Microvilli)

A

increase surface area for absorption

26
Q

Glandular Epithelia

A
  • Epithelia containing gland cells are specialised for secretion- these are
    known as glandular epithelia
  • Epithelial cells can produce secretions:
    - Goblet cell – secretions by a single cell
    - Gland – secretions by a group of cells
27
Q

Types of Glands

A

Endocrine Glands
Exocrine Glands

28
Q

Endocrine Glands

A
  • Produce endocrine secretions – called hormones
  • Hormones enter bloodstream for distribution throughout body
  • Ductless glands – secretions not released into ducts
  • Hormones regulate or coordinate activities of tissues, organs, and organ systems.
  • E.g. Insulin hormone
29
Q

Exocrine Glands

A
  • Release secretions directly onto epithelia
    surface or into passageways (ducts) that
    open onto epithelia surface
  • e.g. Sweat Gland releases secretions to
    surface of body
30
Q

Goblet Cells

A

Mucous Glands
in the GIT and respiratory tract secrete mucous.
Secretion protects the surface cells.
In respiratory tract mucous moistens and warms the incoming air and traps any dust particles.

31
Q

Mucositis

A
  • Inflammation of the mucosa - the mucous membranes that line the mouth and gastrointestinal tract
  • Common side effect of chemotherapy or radiation cancer therapy
32
Q

Submucosal Exocrine Glands

A
  • In some structures where more protection is required submucosal glands are found below the surface but attached to the surface by a duct (tube)
  • Allow increased secretions
33
Q

Exocrine gland structure

A

-Unicellular gland
-Multicellular glands

34
Q

Unicellular exocrine glands

A
  • Single cells called goblet cells that are specialised for secretion
  • Goblet cells secrete mucin – mixes
    with water to form a sticky lubricant
    called mucus
  • individual secretory cells in epithelia that have independent, scattered gland cells
35
Q

Multicellular exocrine glands

A
  • include glandular epithelia and aggregations of gland cells that produce exocrine or endocrine secretions into an inner compartment e.g., salivary glands
    produce mucins and digestive
    enzymes
36
Q

Characteristics when describing the structure of multicellular exocrine glands

A
  1. Structure of the duct:
    • Simple
    • Compound
  2. Shape of the secretory portion of the gland
    • Tubular
    • Alveolar or acinar
    • Tubulo-alveolar or tubulo-acinar
  3. Relationship between ducts and glandular area
    • Branched (refers to glandular areas
      and not to the duct)
37
Q

Exocrine Gland – modes of secretion

A

Merocrine secretion
Apocrine secretion
Holocrine secretion

38
Q

Merocrine secretion

A
  • Product is released from an exocrine cell by secretory vesicles through exocytosis
  • Most common method of exocrine secretion
  • E.g., mucin is a merocrine secretion: mucous secretions of the salivary glands coat food and reduce friction during
    swallowing; merocrine sweat glands in the skin produce perspiration that cools body on a hot day
39
Q

Apocrine secretion

A
  • Involves the loss of cytoplasm as well as the secretory product
  • Apical portion of cytoplasm is packed with secretory vesicles and then shed
  • E.g. milk production in the mammary glands involves merocrine and apocrine
    secretions
40
Q

Holocrine secretion

A
  • Superficial cell in a stratified glandular epithelium becomes packed with secretory vesicles and then burst – releasing secretion but also killing the cell
  • Further secretion dependent on replacing destroyed gland cells by division of underlying stem cells
  • E.g., sebaceous glands of hair follicles produce oily hair coating by holocrine secretion
41
Q

Mammary Gland

A
  • Mammary gland cells produce and store milk
  • Have an outer epithelial cells layer with some contractile proteins
  • MYO – refers to muscle function
  • The muscle proteins form part of the lower layer of cells just above the basement membrane
42
Q

Hormones

A
  • Chemical messengers released from endocrine glands
  • Transported in the bloodstream
  • Reach target cell/organ(s)
  • Alter metabolism of target cell
43
Q

Insulin secretion – the pancreas

A

The pancreas has islets of Langerhans that produce insulin (and other hormones)

44
Q

Insulin secretion

A
  • Food is converted into glucose in the stomach and intestinal tract
  • Glucose then enters the bloodstream
  • Glucose reaches the pancreas, resulting in
    the pancreas releasing insulin
  • Insulin will cause glucose uptake in target
    cells (liver, muscle, adipose tissue)
  • Glucose is stored as glycogen in liver and
    muscle, stored as fat in adipose tissue
45
Q

Reasons for Epithelial cells specialisation

A
  1. The movement of fluids over the epithelial surface, providing protection and lubrication
  2. The movement of fluids through the epithelium to control permeability
  3. The production of secretions that provide physical protection or act as chemical messengers
46
Q

Specialised epithelial cells types

A
  • Apical surface – cell is exposed to internal or external environment
  • Lateral surface – side surfaces, where the cell contacts its neighbours
  • Basal surface – cell attached to underlying epithelial cells or deeper tissues
47
Q

Apical Surface Specialisations

A
  • Cell is exposed to internal or external environment
  • At surface of layer of cells – in contact with exterior surface (air), lumen (tube interior) e.g. blood, chyme, urine, or body cavitiesn
  • The epithelial cells surfaces may be
    * smooth
    * may have cilia
    * may have microvilli
  • Some skin surfaces have a protein called keratin in the cells that provides additional strength
47
Q

Cilia

A
  • move substances (fluids or secretions) over epithelial surface
  • Each ciliated cell may have up to 250 cilia that beat in a co-ordinated fashion
  • Behave like escalator:
    * In the trachea cilia or hairs on the
    surface of the epithelial cells move the
    mucous along the respiratory tract
    * Moving mucus up from lungs, mucus
    traps particles such as pollen,
    pathogens, dust
    * Ciliated epithelium carries mucus to
    throat; mucus is swallowed or expelled
    by coughing
  • Smoking one cigarette immobilises the cilia for one hour
  • The epithelium of the trachea is a classified as a ciliated pseudostratified epithelium with goblet cells.
  • also found in the fallopian tubes
48
Q

Microvilli

A
  • increase the surface area of the epithelial cells
  • Increase the capacity for absorption by a factor of 20
  • Important in the jejunum of the gut for absorption of nutrients
  • Important in the early part of the kidney tubules (PCT) for absorption
49
Q

Keratin

A
  • produced by the epithelial cells of skin (keratinocytes)
  • a protein that forms granules in the cytoplasm
  • Keratinised epithelia are found in the oesophagus in some animals – depends on the diet
50
Q

Tight (Occluding) junctions

A
  • between two plasma membranes
  • Adhesion belt forms and attaches to terminal web
  • Prevents passage of water and solutes
  • Isolates wastes in the lumen
50
Q

Lateral Surface Specialisations

A

May be:
* Tight junctions
* Gap junctions
* Anchoring junctions (desmosomes)

51
Q

Gap junctions

A
  • allow rapid communication
  • Held together by channel proteins (junctional proteins, connexons)
  • Allow ions to pass so cells can communicate
  • Allow the coordination of cilia beating or coordinating muscle cell contractions
51
Q

Anchoring junctions (desmosomes)

A
  • Very strong, can resist stretching and twisting
  • At a desmosome CAMs and proteoglycans link opposing plasma membranes
  • Spot desmosomes:
    * Small disks connected to bands of
    intermediate filaments
    * Tie cells together
    * Allow bending and twisting
  • Hemidesmosomes
    * attach cells to the basal lamina
    * Helps stabilise position of epithelial cell
    CAMs – cell adhesion molecules, dense areas, and intercellular cement
52
Q

Basal lamina

A
  • closer to the epithelium
  • functions as selective filter – restricts movement of proteins from underlying connective tissue
53
Q

Epithelium repair/dead

A
  • Epithelia may last a few days before being worn off or destroyed
  • E.g., exposed to enzymes, pathogenic bacteria, physical distortion
  • Cells lost are replaced by division of stem cells
  • Stem cells are found in the basal layer of stratified epithelia
54
Q

Reticular lamina

A
  • Gives the basement membrane strength
  • Attachments between fibres of basal lamina and reticular lamina hold the two layers together
  • Acts as filter determining substances that can diffuse between epithelium and adjacent tissues
  • Hemidesmosomes attach epithelial cells to basement membrane

Histo, Anat & Physiol (12 decks)

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