Histology (Tissues)

Question 1

What is Histology?

Answer 1

The study of Tissues

Question 2

What is Tissues?

Answer 2

• A group of cells with similar structure and function
• Cells of most tissues are surrounded by an extracellular fluid called interstitisl fluid (mostly water and ions)

Question 3

What is the 4 major tissues types?

Answer 3

1. Epithelial Tissue
2. Connective Tissue
3. Muscle Tissue
4. Nervous Tissue

Question 4

What is Cell Junction?

Answer 4

• Points of contact between adjacent cells - seen in epithelial tissue, some nervous and muscle cells
• Formed by cell membrane proteins

Question 5

What are the 3 examples of cell junctions?

Answer 5

1. Tight Junctions
2. Anchoring Junction (e.g. desmosomes)
3. Gap Junction

Question 6

Tight Junctions

Answer 6

• Holds cell membrane together
• Are a partial fusion of specific proteins on the lateral surface of the cell membrane
• Form ring-like tight seal
• Prevents material from passing between cells e.g. bacteria, proteins, sometimes fluid or ions (depending on the tissue)
• Stops integral proteins from moving between apical (lumen exposed surface) and basolateral (attached) surfaces of the cell

Question 7

Anchoring Junction (e.g. desmosomes)

Answer 7

• Proteins that fasten cells to each other and/or extracellular material (“rivets” cells together)

Question 8

Gap Junction

Answer 8

• Gaps between the cells
• Open channels (formed by proteins) through the adjacent cell membranes interconnecting the cytosois of the cells
• Allows ions/small molecules to pass from one cell to another
• Tissues can then work as a unit:
  
  • Important in cardiac and smooth muscle (allows synchronization of contractions)
  • Also found in epithelial tissue

Question 9

What are the 4 Major Tissue Types? (Overview)

Answer 9

1. Epithelial Tissue (Lining tissue)
2. Connective Tissue (Connecting tissue)
3. Muscle Tissue (Contractile tissue)
4. Nervous Tissue (Sensation and signalling tissue)

Question 10

What is the Epithelial Tissue?

Answer 10

• Covers body surface
• Lines body/organ cavities
  
  • Organ cavity = lumen

Question 11

What are the characteristics of Epithelia?

Answer 11

• Has one free surface
• Little extracellular space between cells
• Avascular - no blood vessels
• Basement membrane
  
  • Extracellular layer
  • Attaches epithelium to underlying connective tissue layer (formed by both tissues and aacts like “velcro”)

Question 12

What is the classification of Epithelia?

Answer 12

• Most subtypes are classified and named according to:
  1. The number of cell layers sitting on the basement membrane
  
  • One layer = simple
  • More than one layer = stratified
    
    2. Shapes of the cells in the apical layer (= layer touching the free surface)
  • Flattened = squamous
  • Round or cube shaped = cuboidal
  • Rectangular = columnar

Question 13

What are the types of Epithelial tissues?

Answer 13

1. Simple Epithelia ( = 1 layer)
2. Stratified Epithelia ( = > 1 layer)
3. Pseudostratified Epithelia
4. Transitional Epithelia ( = cell shape & layering varies with stretching)
5. Glandular Epithelium ( = for secretion)

Question 14

Simple Epithelia ( = 1 layer)

Answer 14

Allow exchange of molecules (gasses, nutrients, ions) - absorption/secretion

Question 15

What are the subtypes of Simple Epithelia?

Answer 15

1. Simple Squamous
2. Simple Cuboidal
3. Simple Columnar

Question 16

Simple Squamous

Answer 16

• 1 layer of squished (flat) cells
• e.g. lungs

Question 17

Simple Cuboidal

Answer 17

• 1 layer of cube shaped cells
• e.g. kidney

Question 18

Simple Columnar

Answer 18

• 1 layer of column shaped (tall & thin) cells
• e.g. stomach, small intestine

Question 19

Stratified Epithelia ( = > 1 layer)

Answer 19

• Protective (areas of abrasion)
• predominant subtype is stratified squamous = apical cells squished (flat)
  
  • e.g.epidermis of skin

Question 20

Pseudostratified Epithelia

Answer 20

• Columnar cells that appear stratified (some cells are shorter and nuclei appear at different levels), but all cells sit on basement membrane (=simple!)
• e.g. lines most of respiratory tract (where the cells are also ciliated = ciliated pseudostratified epithelium)

Question 21

Transitional Epithelia ( = cell shape & layering varies with stretching)

Answer 21

• Only in inner lining of urinary system
• Cuboidal to squamous when stretched

Question 22

Glandular Epithelium ( = for secretion)

Answer 22

If the epithelial cells form a gland, the cell layer(s)/cell shape classification is no longer used & tissue is called a glandular epithelium

Question 23

What are the 2 subtypes of Glandular Epithelium?

Answer 23

1. Exocrine Glands
2. Endocrine Glands

Question 24

Exocrine Glands

Answer 24

• Secrete products onto body surface or into a body cavity
• Can be:
  
  • Unicellular
  • Multicellular

Question 25

Unicellular

Answer 25

• e.g. Goblet cells
• Secrete mucus (into a cavity)
• In the digestive, urinary, reproductive, respiratory tracts

Question 26

Multicellular

Answer 26

• Consists of secretory and duct cells (ducts connect secretions to surface or cavity)
• e.g. glands: sudoriferous (sweat), sebaceous (oil), mammary, digestive

Question 27

Endocrine Glands

Answer 27

• No ducts (ductless)
• Secrete hormones into the extracellular fluid (interstitial fluid) surrounding glandular cells that then enter the blood plasma for transport to target cells/tissues
• e.g. thyroid gland secretes thyroid hormone

Question 28

What are the 3 Functions of Epithelia?

Answer 28

1. Protection
2. Secretion
3. Allows selective passage of materials (nutrients, waste, water, ions) across membrane

Question 29

Protection

Answer 29

• Often stratified squamous
• e.g. epidermis of skin

Question 30

Secretion

Answer 30

• Glandular epithelium
• e.g. thyroid gland, sweat gland

Question 31

Allows selective passage of materials (nutrients, waste, water, ions) across membrane

Answer 31

• Typically simple epithelia
• e.g. kidney, intestine, capillaries