Host Barriers

Question 1

What is the main epithelial type that provides protection?

Answer 1

Stratified squamous epithelium

Question 2

Why is stratified squamous epithelium called “squamous” ?

Answer 2

The upper most layer of epithelial cells are squamous (squished)

Question 3

Langerhans Cells

Answer 3

aka. Dendritic Cells

• Located among keratinocytes
• Derived from the bone marrow
• Mildly phagocytic
• Antigen-presenting cell to contact antigens

Question 4

Birbeck Granules

Answer 4

Paddle-shaped organelles that are in dendritic cell cytoplasm.

Question 5

Basic Organization of GI Tract

Answer 5

1. Mucosa
   - Epithelium
   - Lamina Propria (loose CT with glands like goblet cells)
   - Muscularis Mucosae (smooth muscle)
2. Submucosa
   - Dense Irregular CT
3. Muscularis Externa
   - Inner smooth muscle
   - outer smooth muscle
4. External Layer
   - Adventitia (loos CT)
   - Seros (loose CT with mesothelial-peritoneum)

Question 6

Three Main Intercellular Adherens Junctions

Answer 6

1. Tight Junction (Zonula Occludens)
2. Zonula Adherens (belt desmosome)
3. Desmosomes (Macula Adherens)

Question 7

Tight Junction Components & Functions

Answer 7

• Has claudins and occludins
• Prevents leaking b/w cells
• Prevents movement of membrane proteins

Question 8

Zonula Adherens Componenets & Functions

Answer 8

• Has E-Cadherins that is calcium dependent and binds to actin in cellular terminal web.
• Adheres epithelial cells

Question 9

Desmosomes Components & Functions

Answer 9

• Has desmoplakins and plakoglobins
• Adheres epithelial cells
• Strongest

Question 10

Gap Junction

Answer 10

Communication junction composed of connexins.

Question 11

Hemidesmosomes

Answer 11

Connects the cell to the basement membrane so it is NOT an intercellular junction.

Question 12

What are some epithelial products/components of intestine that provide immunity?

Answer 12

• Acidic pH
• Pancreatic enzymes
• Bile
• Intestinal secretions
• mucus
• Lysozyme (Released by Paneth Cells)
• Gut normal flora

Question 13

Mechanism of Mucosal Immunity in Intestine

Answer 13

1. Antigens in the gut lumen are bound by M Cells and undergo transcytosis into the intraepithelial pockets.
2. Dendritic cells phagocytose the antigen and present it to helper T cell.
3. B cells differentiate into plasma cells to secrete IgA.
4. IgA is transported to the gut lumen and binds to the antigen.

Question 14

Lysozyme

Answer 14

A glycoside hydrolase that hydrolyze linkages in peptidoglycan cell wall.

Question 15

Components of Oral Cavity

Answer 15

1. Epithelium
   - Langerhans cells
   - Intraepithelial lymphocytes
2. Lamina Propria
   - Macrophages
   - Dendritic Cells

Question 16

What’s in Saliva?

Answer 16

1. Lysozyme
2. Lactoferrin
   - Binds to iron and deprives microbes of nutrient
3. Histatins
   - inhibit Candida albicans & streptococcus mutans (cause decay)
4. Salivary IgA
   - aggregates oral bacteria to prevent against dental plaques.

Question 17

MALT & More ALTs

Answer 17

Mucosa Associated Lymphoid Tissue

• GALT (Gut)
• BALT (Bronchus & Trachea)
• NALT (Nose)
• VALT (Vulvovaginal)

Question 18

Peyer’s Patch

Answer 18

Especially large lymphoid nodule that press outward into the submucosa of ILEUM.