Histology: Epithelial tissues

Question 1

Define the term histology

Answer 1

Study of tissues

Question 2

List four major tissue types

Answer 2

epithelial tissue (lining cavities on surfaces of body)
connective tissue (support)
muscle tissue
nervous tissue (brain, spinal cord,etc.)

Question 3

Describe characteristics of tight junctions, anchoring junctions, and gap junctions

Answer 3

1. Tight junctions - fusion of proteins on lateral surface of cell membrane, form a ring like tight seal
   preventing material from passing between cells (e.g bacteria, proteins, sometimes fluid or ions)
2. Anchoring junctions - proteins that fasten cells together and/or to extracellular material (“rivets” cells together; hold cells together but gaps in between so material can pass through)
3. Gap junctions - open channels (proteins) through adjacent cell membranes, interconnecting the cytosols of cells
   - allows passage of ions and small molecules from cell to cell - Tissues then can work as a unit
   - IMPORTANT IN CARDIAC and SMOOTH MUSCLE (allows synchronization of contractions) also found in EPITHELIAL TISSUE

Question 4

Describe the structural characteristics common to all types of epithelia

Answer 4

Has one free surface
Little extracellular space between cells
avascular = no blood vessels
basement membranes (velcro)
- extracellular layer
- Attaches epithellium to underlying connective tissue layer (formed by both tissues)

Question 5

Classify epithelial tissue into subtypes giving examples where possible

Answer 5

Simple Epithelia (all one layer)
1. simple squamous: single layer “squished” (flat) cells
- ex) lungs

2. simple cuboidal: single layer: single layer of cube-shaped cells
   - ex) kidneys
3. simple columnar: single layer: column-shaped (tall and thin)
   - ex) small intestine, stomach

2. Stratisfied Epithelia (all more than one layer)
1. stratisfied squamous: apical cells “squished” (flat)
- ex) common - skin

2. **straistfied cuboidal **: apical cells cubed shape
   - ex) rare - some ducts salivary glands?
3. Statisfied columnar: apical cells column shaped (tall and thin)
   ex) rare

Other subtypes that dont fit in these classifications
Pseudostratisfied epithelia
ex) lines most of respiratory tract (+ciliated)
Transitional Epithelium
ex) found only on inner lining of urinary system

Exception
Glandular epithelium used for secretion
- epithelial cells form a gland -> classification no longer used
- two subtypes: Exocrine and endocrine

**1. Exocrine gland (unicellular and multicellular) **
ex) goblet cells - secrete mucus into cavity (unicellular)
-found on reproductive, respiratory, urinary and digestive tracts
ex) glands: sudiferous (sweat), sebacous (oil), mammary, digestive (multicellular)

2. Endocrine gland
ex) thyroid gland secretes throid hormones

Question 6

Tissue

Answer 6

group of cells with similar structure

Question 7

Cell connections

What are they? where are they? What are they formed by?

Answer 7

points of contact between adjacent cells
- seen in epithelial tissue, some nervous and muscle cells (3 majors types)
formed by cell membrane proteins

most CT cells are far a part

Question 8

Tight junctions

Answer 8

PARTIAL FUSION of SPECIFIC PROTEINS on the LATERAL SURFACE (side) of the cell membrane
forms ring like tight seal, preventing from materials to pass through (e.g proteins, bacteria, sometime fluid or ions (depending on tissue))

Question 9

Anchoring junctions

What are they and give an example

Answer 9

ex) desmosomes
fasten cells together or extracellular material

Question 10

Gap junctions

Answer 10

open protein channels, connect cytosols of each cell helps the passage of material from cell to cell
Tissues then work as a unit
- important in cardiac and smooth muscle (allows sycnhronization of contractions b/c the ctyosols are synchronized
- epithelial tissue

Question 11

where is Epithelial Tissue located

Answer 11

Covers body surface (skin)
Lines body/organ cavities (lumen)

Question 12

Desosomes

Answer 12

an example of an anchoring junction

Question 13

Lumen

Answer 13

A part of epithelial Tissue (linings)
lumen is the Organ cavity (abdominal and inner cavities)

Question 14

Basement memebranes

Answer 14

Extracellular layer
attaches epithellium tissues to underlying of connective tissue layer (connective tissue is always going to have epithelium)
formed by both tissues “velcro”

Question 15

Classification of Epithelial Tissues

Answer 15

Subtypes are classified and named according to number of cell layers sitting on the basement membrane
Simple: one layer
Stratisfied: more than one layer

Shapes of cells in the apical layer (layer forming the free surface) **
- squamous (flattened)
- cubical (cube/round)
- columnar** (taller than wide)

Question 16

Apical layer

Answer 16

a layer forming the free surface

Shape of cells in apical layer

Question 17

Simple Epithelia

Define and Name the different types

Answer 17

(all one layer)
allow exchange of molecules (gases, nutrients, etc) - asborption/secretion b/c of the fewer layers = less time it takes for nutrients to pass through

1. simple squamous: “squished” (flat) cells
   - ex) lungs
2. simple cuboidal: single layer: cube-shaped cells
   - ex) kidneys
3. simple columnar: single layer: column-shaped (tall and thin)
   - ex) small intestine, stomach,

Question 18

Stratisfied Epithelia
Define and Name the different types

Answer 18

(all more than one layer)
protective areas of abrasion = multiple layers
1. stratisfied squamous: apical cells “squished” (flat)
- ex) common - skin

2. straistfied cuboidal : apical cells cubed shape
   - ex) rare - some ducts salivary glands?
3. Statisfied columnar: apical cells column shaped (tall and thin)
   ex) rare

Question 19

Other subtypes that dont fit in classification of Epithelium

Answer 19

Pseudostratisfied epithelia
looked straisfied (because nuceli are at different levels) but it really is simple
- all cells sit on basement membrane, cells jammed together (makes it simple)
ex) lines most of respiratory tract (+ciliated)

transitional epithelium
- cell shape (and layering) varies with stretching
ex) found only on inner lining of urinary system

Question 20

Glandular epithelium

Answer 20

An exception of epithelium classification
If the epithelial cells form a gland, the cell layer(s)/cell shape classification is no longer used and the tissue is therefore classified as Glandular epithelium
- used for secretions

Question 21

Subtypes of Glandular epithelium

Answer 21

exocrine and endocrine

Exocrine glands secretes products onto body surface or into a body cavity
has two subtypes (unicellular or multicellular)
1. Unicellular ex) goblet cells
- secret mucus (into a cavity)
- in digestive, urinary, reproductive and respiratory tracts
2. Multicellular ex) glands: sudorigerous (sweat, sebacous (oil), mammary, digestive
- consist of secretory and duct cells (ducts connect secretions to surface of cavity)

Endocrine glands: thyroid gland secretes thyroid hormone
- no ducts (ductless)
- secretions (hormones released directly into blood (dont need ducts!)

Question 22

Pseudostratisfied epithelia

Answer 22

looked straisfied (because nuceli are at different levels) but it really is simple
- all cells sit on basement membrane, cells jammed together (makes it simple)
ex) lines most of respiratory tract (+ciliated)

Question 23

Transitional Epithelium

Answer 23

cell shape (and layering) varies with stretching
ex) found only on inner lining of urinary system

Question 24

Functions of Epithelia

Answer 24

Protection: often stratified squamous (ex. skin)
Secretion: glandular epithellium (ex. thyroid (endocrine) and sweat glands(exocrine;multicellular))
Control permeability: typically simple epithelial
- exchange of simple material (ex. kidneys, intestine, capillaries)

Question 25

Goblet cells

Answer 25

Apart of the glandular epithellium Example of an exocrine gland and they are unicellular secrete mucus (into a cavity) in the digestive, urinary, reproductive and respiratory tracts

Question 26

Exocrine glands

Answer 26

A subtype of glandular Epithelium secretes products onto body surface or into a body cavity has two subtypes (unicellular or multicellular) 1. Unicellular ex) goblet cells - secret mucus (into a cavity) - in digestive, urinary, reproductive and respiratory tracts 2. Multicellular ex) glands: sudorigerous (sweat, sebacous (oil), mammary, digestive - consist of secretory and duct cells (ducts connect secretions to surface of cavity)

Question 27

Endocrine glands

Answer 27

A subtype of Glandular Epithelium thyroid gland secretes thyroid hormone - no ducts (ductless) - secretions (hormones released directly into blood (dont need ducts!)