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Epithelial Tissue Histology
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Epithelial Tissue Histology
Epithelial Tissue Histology
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1
Question
What are the five core histological features that define epithelial tissue?
Page 1
Answer
1. Closely aggregated cells with minimal matrix. 2. Sit on a basement membrane. 3. Exhibit morphologic and functional polarity. 4. Bound by cell-to-cell adhesion molecules. 5. Avascular tissue nourished via diffusion.
2
Question
How is the naming and classification of stratified epithelia determined?
Page 1
Answer
It is named strictly according to the shape of the cells located in the most superficial or outermost layer.
3
Question
What are the three parameters used to classify lining epithelium?
Page 1
Answer
1. Number of cell layers (Simple vs. Stratified). 2. Shape of surface cells (Squamous, Cuboidal, Columnar). 3. Specialization of the apical cell surface domain.
4
Question
What are the specific histological names for simple squamous epithelia lining vessels and heart cavities?
Page 2
Answer
Endothelium refers to the lining of blood and lymphatic vessels, while Endocardium refers to the lining of the heart's ventricles and atria.
5
Question
Where is mesothelium located, and what type of epithelium is it?
Page 2
Answer
Mesothelium is simple squamous epithelium that lines the walls of closed serous body cavities (abdominal, pleural, peritoneal, and pericardial).
6
Question
What are common locations for simple cuboidal epithelium, and how do the nuclei appear?
Page 2
Answer
It is found in thyroid follicles, small ducts of glands, and kidney tubules. The nuclei are centrally located and rounded.
7
Question
What defines pseudostratified columnar epithelium, and where is its classic respiratory variant found?
Page 2
Answer
It appears stratified because nuclei are at different levels, but all cells rest on the basal lamina. The respiratory variant lines the trachea and primary bronchi.
8
Question
What are the defining features of transitional epithelium (urothelium) in relaxed versus distended states?
Page 2
Answer
When relaxed, the surface has large, dome-shaped 'umbrella' cells. When distended, the epithelium stretches and the surface cells flatten.
9
Question
Describe the structure and primary function of microvilli.
Page 3
Answer
Microvilli are cytoplasmic projections containing an actin filament core. They increase surface area 20- to 30-fold for absorption.
10
Question
What are stereocilia, and how do they differ from microvilli in structure and location?
Page 3
Answer
Stereocilia are longer, immobile actin-based projections that show distal branching. They are found in the epididymis, ductus deferens, and inner ear.
11
Question
What is the internal molecular architecture of a motile cilium?
Page 3
Answer
It features an axoneme with a 9+2 assembly: 9 peripheral microtubule doublets surrounding 1 central microtubule pair.
12
Question
What are primary cilia, and how does their organization differ from motile cilia?
Page 4
Answer
Primary cilia have a 9+0 axonemal organization (lacking the central pair), are non-motile, and act as sensors (chemosensors, osmosensors, or mechanosensors).
13
Question
What is the specific role of nodal cilia during embryonic development?
Page 4
Answer
They perform a clockwise rotational movement to target signaling molecules, establishing correct left-right organ asymmetry.
14
Question
What are the position, components, and functions of the Tight Junction (Zonula Occludens)?
Page 4
Answer
Located most apically, it is composed of claudins and occludins. It seals cells to prevent paracellular leakage and maintains cell polarity.
15
Question
Compare Zonula Adherens and Desmosomes regarding their cytoskeletal attachments.
Page 4
Answer
Zonula Adherens connects actin filaments of adjacent cells. Desmosomes (Macula Adherens) connect intermediate filaments (cytokeratins).
16
Question
What are Gap Junctions, and what specific conditions cause them to close?
Page 5
Answer
They are communicating junctions made of connexon channels. They close in response to decreased cytosolic pH or increased cytosolic \(Ca^{2+}\) concentration.
17
Question
Distinguish between the two layers of the basement membrane visible under electron microscopy.
Page 5
Answer
1. Basal Lamina (lamina lucida and lamina densa) produced by epithelial cells. 2. Reticular Lamina produced by connective tissue cells.
18
Question
What are the three main mechanisms of glandular secretion?
Page 6
Answer
1. Merocrine (exocytosis, no loss of cytoplasm). 2. Apocrine (cytoplasm pinched off). 3. Holocrine (whole cell disintegrates).
19
Question
Define Autocrine, Paracrine, and Endocrine secretions based on their target distance.
Page 6
Answer
Autocrine stimulates the secreting cell itself. Paracrine reaches nearby cells via diffusion. Endocrine travels via blood to remote tissues.
20
Question
Distinguish between mucous and serous acini under H&E staining.
Page 7
Answer
Mucous glands appear empty/washed out with flattened basal nuclei. Serous glands have round nuclei and eosinophilic apical cytoplasm with zymogen granules.
21
Question
What are myoepithelial cells, and what is their functional role in glands?
Page 7
Answer
Contractile cells that wrap around secretory acini. They contain actin and squeeze the acinus to help express secretions into the duct system.
22
Question
What is metaplasia, and what classic example occurs in the respiratory tract of heavy smokers?
Page 7
Answer
Metaplasia is a reversible transformation of one mature epithelium into another. In smokers, respiratory epithelium transforms into stratified squamous epithelium.
23
Question
Define neoplasia and differentiate between carcinoma and adenocarcinoma.
Page 8
Answer
Neoplasia is uncontrolled tumor growth. Carcinoma is a malignant tumor of lining epithelium; adenocarcinoma is a malignant tumor of glandular epithelium.
24
Question
From which three embryological germ layers does epithelial tissue originate?
Page 8
Answer
Ectoderm (e.g., epidermis), Mesoderm (e.g., endothelium, mesothelium), and Endoderm (e.g., GI and respiratory lining).