The Tissues of the Human Body: Epithelia

Question 1

CELL JUNCTIONS

Lateral junctions

Answer 1

Tight junction
Adherens junction
Gap junction
Desmosome

Question 2

CELL JUNCTIONS

Basal junction

Answer 2

Hemidesmosome

Question 3

Cytoskeleton

细胞骨架

Answer 3

Microfilaments e.g. ACTIN
微丝
bundles beneath cell membrane and cytoplasm; strength, alter cell shape; link cytoplasm to membrane; tie cells together; muscle contraction

Intermediate filaments e.g. KERATIN
中间纤丝
Strength;
move materials through the cytoplasm

Question 4

TIGHT JUNCTIONS

Answer 4

• Individual sealing strands transmembrane
• More strands the tighter the junction
• Many proteins involved but two key ones: claudins& occludins
• Join the cytoskeletons of adjacent cells e.g. via ZO-1 to actin
• Keep cell polarity by preventing migration of proteins between apical and basal surfaces

Question 5

Tight junctions

Answer 5

Lots of these found in the stomach, intestines, bladder

Question 6

ADHERENS JUNCTIONS

Answer 6

• “Belt desmosome” or adhesion belts (zonula adherens) in some epithelial cells
• Other cells are less continuous and are called “adhesion plaques”
• More basal located than tight junctions
• Have a plaque layer of proteins on the inside of the cell to join actin to cadherins
• Cadherins(span the gap)
• Cateninslink the Cadherinsto Actin(microfilament in cell cytoplasm)
• Adherens junctions prevent cell separation from tension forces like in contractions

Question 7

DESMOSOME JUNCTIONS

细胞桥粒连接

Answer 7

• Lateral wall
• Have “plaque” just like adherens junctions
• Resist shearing forces
• Example: they bind muscle cells
• Cadherinspans the gap
• BUT link cell surface to Keratin(a cytoskeletal intermediate filament)
• Keratin spans from one desmosome to another on the other side of the cell – structural integrity
• Most common in skin epithelium and cardiac cells of the heart to prevent pulling apart

Question 8

GAP JUNCTIONS

间隙连接

Answer 8

• Direct connection between cells
• 6 connexin联接蛋白 protein molecules form connexion连接 or hemichannel半通道
• 2 hemichannels make up gap junction
• Allow ~1kDa molecules through

Question 9

Hemidesmosome

半桥粒

Answer 9

• Connect epithelia to the basement membrane
• Links cellular basal intermediate filament(Keratin) to the basement membrane
• Hemidesmosome –(INTEGRINlinker protein (instead of cadherin) binds to LAMININin the BM and to Keratinintermediate filament in the cytoplasm)

Question 10

The Basement Membrane

Answer 10

All epithelia overlay a basement membrane composed of two parts:
BASAL LAMINA(secreted by the epithelial cells) containing collagen, laminin, other proteoglycans, glycoproteins, etc
RETICULAR LAMINA(produced by cells of the underlying connective tissue known as fibroblasts) containing fibrous proteins such as fibronectin, collagen etc

Question 11

Functions of the Basement Membrane

Answer 11

Supports the overlying epithelium

Provides a surface along which epithelial cells migrate during growth and wound healing

Acts as a physical barrier

Participates in the filtration of substances in the kidney

Question 12

The basement membrane can act as a barrier to invasion by malignant melanoma.

Answer 12

Once the barrier has been penetrated, the chances of metastasis(spread) occurring increase.

Question 13

There are TWO types of Epithelial tissue

Answer 13

Covering and Lining Epithelia

Glandular Epithelia

Question 14

Covering and Lining Epithelia

a. ARRANGEMENT

Answer 14

i. Simple: single layer (secretion; absorption; filtration)
ii. Stratified: two or more layers (protective)
iii. Pseudostratified: appears to have multiple layers as judged by positions of nuclei.

Question 15

Covering and Lining Epithelia

b. SHAPE

Answer 15

i. Squamous: flat and thin (helps allow passage by diffusion)
ii. Cuboidal: about as tall as they are wide (secretion; absorption)
iii. Columnar: more tall than wide (secretion; absorption)
iv. Transitional: a stratified epithelium in which the cells can change shape from cuboidal to flat shape depending on organ shape (allow stretch e.g. urinary bladder)

Question 16

Covering and Lining Epithelia

Answer 16

Simple squamous*
Simple cuboidal*
Simple columnar* 
Stratified squamous*
Stratified cuboidal 
Stratified columnar
Transitional 
Pseudostratified columnar*

Question 17

Simple Squamous鳞状的 Epithelium

Features

Answer 17

Features

• Most delicate epithelium
• Where there is filtration (kidney); diffusion (lung); secretion where slippery surface needed (e.g. outer layer of serous membranes);

Question 18

Simple Squamous Epithelium

Appearance

Answer 18

Appearance

• Thin flat and somewhat irregular like a jigsaw
• Cells are “like fried eggs” or paving stones

Question 19

Simple Squamous Epithelium

Specialised Subtypes

Answer 19

Specialised Subtypes

• Mesotheliumlines pericardial, pleural, peritoneal cavities
• Endotheliumlines inside of heart and blood and lymphatic vessels

Question 20

Simple Squamous Epithelium

Location examples:

Answer 20

Location examples:

In Bowman’s capsule of the kidney, lines cardiovascular and lymphatic systems, inside the eye, alveoli of lungs, visceral cavity linings, inside blood vessels and inside the heart

Question 21

Simple Cuboidal立方形的 Epithelium

Answer 21

Features

Where there are SECRETION and ABSORPTION

Question 22

Simple Cuboidal Epithelium

Answer 22

Appearance

• Cuboidal or hexagonal boxes.
• The distance between adjacent nuclei is approx. the height of the epithelium

Question 23

Simple Cuboidal Epithelium

Answer 23

Specialised Subtypes

Nil

Question 24

Simple Cuboidal Epithelium

Answer 24

Location examples:

pancreas ducts; parts of kidney tubules, smaller ducts of many glands; secretory chambers of thyroid; the anterior surface of the lens; pigmented epithelium at posterior of the retina; secretory part of some glands like the thyroid

Question 25

Simple Columnar柱状的 Epithelium

Answer 25

Features More cytoplasm so more organelles

Question 26

Simple Columnar Epithelium Come in two major subtypes

Answer 26

i.Non-ciliated simple columnar epithelium. Ciliated simple columnar epithelium

Question 27

Simple Columnar Epithelium

Answer 27

Appearance * Rectangular * Often hexagonal but taller and more slender than cuboidal * Nuclei often elongated and near the base of the cell * Height of cell is several times the distance between adjacent nuclei

Question 28

Simple Columnar Epithelium

Answer 28

Specialised Subtypes Simple columnar epithelium can have:cilia or microvilli

Question 29

Non-Ciliated Simple Columnar Epithelium

Answer 29

Features •Single layer •Microvilli on the apical surface •Have goblet cells interspersed

Question 30

Location examples of non-ciliated columnar epithelium:

Answer 30

Examples: lines gut mucosa from the stomach to anus; ducts of many glands; gall bladder. Function: secretion and lubrication (mucus goblet cells); absorption;

Question 31

Ciliated Simple Columnar Epithelium (move materials)

Answer 31

Features •Single layer •Have goblet cells as well

Question 32

Ciliated Simple Columnar Epithelium (move materials)

Answer 32

Location examples: Examples: some bronchioles, uterine fallopian tubes, sinuses; central canal of the spinal cord, ventricles of the brain Function: synchronous movement assists motility of mucus and foreign objects or oocytes

Question 33

Stratified Squamous Epithelium

Answer 33

Features * Located where mechanical or chemical stresses are severe严重的 * All forms protect against microbes微生物 * In some places where mechanical stress and dehydration major issue apical顶端 cells are packed with keratin角蛋白 – makes the surface tough and waterproof防水.

Question 34

Stratified Squamous Epithelium

Answer 34

Appearance * Cells form layers like plywood夹板 or pancakes in upper layers * Lower layers may be cuboidal立方形的 or columnar柱状 * Cells furthest最远的 from nutrition is thinner and less active.

Question 35

Stratified Squamous Epithelium

Answer 35

Specialised Subtypes * Keratinised 角质化的 * Non-keratinised

Question 36

Stratified Squamous Epithelium

Answer 36

Location examples: * Keratinised: skin * Non-keratinised: mouth, throat, tongue, oesophagus食管, anus, and vagina

Question 37

Stratified Squamous Epithelium (non-keratinized)

Answer 37

Examples: mouth, throat, tongue, oesophagus, anus, and vagina Function: protection from abrasion擦伤, defence from microbes, require secretions from glands

Question 38

Psuedo伪-stratified分层 Columnar Epithelium柱状上皮

Answer 38

Features * All cells contact BM but not all reach the apical surface of the tissue * Actually a simple epithelium

Question 39

Psuedo-stratified Columnar Epithelium

Answer 39

Appearance * Nuclei at all different levels * Appears to have several layers but it is not actually the case

Question 40

Psuedo-stratified Columnar Epithelium

Answer 40

Specialised Subtypes i)Pseudo-stratified ciliated有纤毛的 columnar epithelium 1. )Cilia on some cells 2. )Secrete mucus (from goblet cells) ii)Pseudo-stratified non-ciliated columnar epithelium 1. )No cilia 2. )Lack goblet cells

Question 41

Glandular腺的 Epithelia

Answer 41

Glands consist of a single cell or a group of cells that secrete substances into ducts导管, onto a surface or into the blood.

Question 42

Endocrine gland | 内分泌腺

Answer 42

Secrete directly into blood usually via traversing interstitial fluid通过穿越组织液 Example Pituitary脑垂体 pineal松果体 thyroid 甲状腺 parathyroid甲状旁腺

Question 43

Exocrine gland | 外分泌腺

Answer 43

Secrete into ducts that empty onto the surface of a covering or lining epithelium. Example Sweat and salivary glands汗腺和唾液腺 oil glands脂腺 wax glands蜡腺 pancreas胰腺