Unit 1: Epithelial Tissue

Question 1

What is a cell?

Answer 1

An aggregate of cells similar in structure and function
- About 200 types, differentiated in embryonic stage
- Their specialization leads them to lose their ability to survive on their own, they depend on functions of different cell types in the organism

Question 2

4 cell type categories

Answer 2

1. Epithelial: covers surfaces of body, lines cavities, secrete
2. Connective: binds organs together, protection/support
3. Nervous: coordinates body functions via transmission of nerve impulses
4. Muscle: contract to enable movement

Question 3

Epithelial tissue composition

Answer 3

Sheets of closely packed cells (single/multiple layer) that cover other tissues
- Sides that attach to neighboring cells by junctional complexes -> forms sheets
- Rapidly regenerate by mitotic division, destroyed and replaced daily

Question 4

Epithelial tissue functions

Answer 4

• Protects, covers
• Filters biochemical substances
• Absorbs nutrients
• Provides sensory input (some! others lack nerves)
• Makes secretions (inside - mucus, hormones, enzymes) and excretions (outside - sweat, milk)

Question 5

2 classifications of epithelial tissue

Answer 5

Covering and lining
Glandular

Question 6

Glandular epithelial tissue

Answer 6

Produce secretions in exocrine and endocrine glands

Question 7

The 2 ends of epithelial tissue

Answer 7

POLAR
Apical surface: surface of cell exposed to body cavity, lines internal organ (facing lumen), exposed to exterior
Basal surface: surface of the cell attached to basement membrane (faces underlying tissue)

Question 8

Do epithelial cells have a blood supply?

Answer 8

NO, avascular. Rely on underlying tissue for nutrients and waste exchange

Question 9

What are the ways cells are held together?

Answer 9

• Sides fit interlocking
• Matrix-filled channels running between cells
• Membranes joined w/junctional complexes (3 types)

Question 10

3 Intercellular junctions?

Answer 10

Tight, Anchoring, Communicating

Question 11

Tight junctions

Answer 11

• Fluid-tight seal (no penetration of substances. eg. bladder leakage, digestive tract stops enzymes from getting out into the body)
• The outer layers of plasma membrane between 2 cells are fused
• Found around circumference of cell

Question 12

Desmosomes/Anchoring junctions

Answer 12

Fastens cells to one another OR to extracellular materials (basement membrane)
- Plaque of interlocking filaments (some filaments penetrate into cytoplasm to stabilize)
- Area with stretching (skin, heart, uterus)

Question 13

Gap/Communicating junctions

Answer 13

Fluid-filled tunnels between cells
- Connexons: tubular channel proteins, join cytoplasm of adjoining cells together
- Exchange of nutrients, ions, electrical impulses
- Help coordinate action of cells
- Intestine, heart, smooth muscle

Question 14

Basement membrane

Answer 14

Attaches epithelium to underlying connective tissue
- Function: resists rubbing
- Not a true membrane, so often referred to as ‘basal lamina’
- Acellular
- Helps with movement of oxygen, nutrients, and waste from blood vessels in connective tissue below -> basement membrane of epithelium

Question 15

Surface specialization

Answer 15

• According to location and function
• Blood vessel epithelia = very smooth
• Microvili = fingerlike projections (increase surface area up to 20x, found in intestine and urinary tract, help absorb/secrete)
• Cilia = tiny hairlike projections (help move stuff like mucus/debris)
• Keratin = waterproofing that fills mature epithelial cells

Question 16

How are epithelial tissues classified?

Answer 16

• Cell shape at exposed surface (squamous = scale, cudoidal = cube, columnar = elongated)
• Presence of surface specialization
• # of layers (simple = 1, stratified = multiple)

Question 17

Simple epithelium

Answer 17

• 1 layer of cells
• Squamous, cuboidal, or columnar (->ciliated or non-ciliated)
• Occur where diffusion/secretion/filtration happens OR where smooth surface is required

Question 18

Simple squamous epithelium

Answer 18

Single flat layer of scalelike cells
Irregular outlines
Central nucelus
Function: nutrient exchange, reduce friction, weak
Location: air sacs of lungs, inner surface of vessels/heart walls (‘endothelium’)
- Line peritoneal, pleural, pericardial cavities (‘mesothelium’)
- Also called serous membranes because they secrete

Question 19

Simple cuboidal epithelium

Answer 19

Single-layer cube shaped w/central nucelus
Location: lining of kidney tubules, smaller ducts of exocrine glands (salivary, pancreas), secretory part of endocrine gland (thyroid), surface of ovary, lens, retina

Function: lining, sectretion (thyroid), absorption (kidney)

Question 20

Simple columnar epithelium - Non-ciliated

Answer 20

Single layer of elongated cells
Smooth apical surface
Location: lines GIT, ducts of many glands

Functions:
- Cells with microvilli: absorption and secretion
- Goblet cells: secret mucin, lubricative barrier

Question 21

Simple columnar epithelium - Ciliated

Answer 21

Single layer of ciliated elongated cells
Nucelus towards basal surface
Goblet cells in some spots

Location: uterus, respiratory, spinal cord

Function: move fluid/particles along through ciliary action

Question 22

Stratified epithelium

Answer 22

More than 1 layer of cells
More resistant to abrasion
Only the inner layers produce new cells (mitosis), pushed to the surface where cells die/are lost to abrasion
Named according to shape of cells at surface

Function: protect underlying tissue

Question 23

‘Weird’ stratified epithelium? (2)

Answer 23

Pseudostratified columnar
Transitional

Question 24

Stratified squamous epithelium

Answer 24

Several layers of cells
Basal layer: cudboidal -> columnar
- actively growing/multiplying
- start cuboidal, become more flattened as they die and move
to surface
Middle: irregular cells
Surface: squamous

2 types: keratinized/non
- Keratinized: skin
- Non: Upper GIT, epiglottis, vagina, cornea

Function: protection, thickest epithelia

Question 25

Keratinization

Answer 25

Keratin = waterproofing protein incorporated into the outer layer of stratified squamous epithelium, protects against water loss to external environment
- AKA cornification

Usually at sites with lots of friction, become callouses

Question 26

Stratified cuboidal epithelium

Answer 26

2+ layers of cells, surface cell cube shaped

Location: ducts (sweat, mammary, salivary glands)

Function: protection

Question 27

Stratified columnar epithelium

Answer 27

Rare: male urethra, large excretory ducts, pharynx, anal mucous membranes, conjunctiva of eye

Function: protection and secretion (mucus in goblet cells)

Question 28

Pseudostratified Columnar Epithelium

Answer 28

All cells attached to the basement membrane, but not all reach su rface
- Plain or ciliated
- Plain: male urethra, lining of large glandular ducts
- Ciliated: upper respiratory, auditory tubes
- Often have goblet cells for mucus production.
- Function: protection, secretion, movement of mucus via ciliary action

• Mucus protects host from disease

Question 29

Transitional epithelium

Answer 29

Changes shape according to degree of stretching (can stretch to a single layer of cells)
- Superficial cells: large dome when relaxed, flat squamous when stretched
- Deep layers: cuboidal, columnar, polyhedral. Not as closely packed as other epithelium

Location: bladder, kidneys, ureters/urethra (so urine can accumulate)
Function: distension without leakage

Question 30

Glandular epithelia

Answer 30

Gland: cells that make and secrete
- Usually make protein in RER, package in Golgi Apparatus, and release from cell
- Originally an inward folding during embryo development
- Some cut off from contact with environment (endocrine glands)

Question 31

Endocrine glands

Answer 31

Lack ducts - secretions released into blood/lymph to be carried
Function: produce hormones to be carried around blood and impose humoral control on body’s activities

Location: pituitary, thyroid, ovaries, GIT, pancreas, testes, thymus, kidneys

Question 32

Exocrine glands

Answer 32

Have ducts (small tubes) that carry secretions to specific areas, usually an epithelial surface
Location: salivary, sweat, liver, pancreas, sebaceous, ceruminous (ear wax) glands

Classified by:
- Structure (uni/multicellular. tubular/alveolar. simple/compound)
- Manner of secretion (holocrine/merocrine/apocrine)
- Type of secretion (serous, mucous, mixed)

Question 33

Unicellular exocrine glands

Answer 33

Only one is goblet cell
Location: columnar cells of respiratory and GIT and conjunctiva of eyes

Function: Secrete mucin (sticky protein/carb mixture that becomes mucus when H2O added -> traps bacteria)

Question 34

Multicellular exocrine gland

Answer 34

Divided into: secretory unit (secretions made) and duct (secretions carried out)
- May be surrounded by myoepthilial cells to help squeeze the secretion

Shape: tubular or alveolar (secretory unit - either looks like a tube or a ball… or tubuloalveolar if combo)
- Simple or compound (duct branches or not)
- Compound subdivided into: lobes or lobules (ducts draining the glands also interlobar/interlobular ducts)

Question 35

Holocrine gland (exocrine)

Answer 35

Cells fill with secretory material and discharge the entire cell contents into the gland lumen, destroying cell (eg. sebaceous)

Question 36

Merocrine gland (exocrine)

Answer 36

Creates vesicles which pass secretory products through the membrane without major loss of cytoplasm (eg. pancreas, sweat, salivary glands)
- Most common

Question 37

Apocrine gland (exocrine)

Answer 37

Intermediate to holocrine/merocrine (some cytoplasm and membrane lost, but cell not destroyed)
- Mammary tissue, prostate, some sweat glands

Question 38

Serous secretions (exocrine)

Answer 38

Watery, lots of enzymes

Question 39

Mucous secretions (exocrine)

Answer 39

Thick, viscous, glycoproteins
Common in digestive and respiratory tracts

Question 40

Mixed secretions (exocrine)

Answer 40

Produce both serous and mucous
- Mandibular salivary glands (some cells make mucous, others enzymes)