Epithelial Tissue Overview

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Questions and Answers

What is a defining characteristic of epithelial tissue?

It consists of loosely arranged cells.

It has a basement membrane only in stratified types.

It is avascular and receives nutrients through diffusion. (correct)

It is highly vascularized.

Which domain of an epithelial cell faces the lumen or external environment?

Basal Domain

Lateral Domain

Apical Domain (correct)

Ciliary Domain

Which type of epithelium consists of multiple layers of cells?

Stratified epithelium (correct)

Simple epithelium

Transitional epithelium

Pseudostratified epithelium

What shape does cuboidal epithelium exhibit?

Cube-shaped cells with equal height and width. Signup and view all the answers

Pseudostratified epithelium appears stratified due to what feature?

The arrangement of cell nuclei at different heights. Signup and view all the answers

What is a key feature of transitional epithelium?

Its shape changes depending on the organ's distension. Signup and view all the answers

Which type of epithelial cells line blood vessels?

Endothelial cells Signup and view all the answers

What distinguishes the basal domain of an epithelial cell?

It faces the basement membrane and provides adhesion. Signup and view all the answers

Which of the following correctly describes microvilli?

Finger-like protrusions that increase surface area for absorption Signup and view all the answers

What is a distinct structural characteristic of stereocilia?

Absence of myosin and presence of ezrin Signup and view all the answers

Which axoneme structure is associated with motile cilia?

9+2 axoneme Signup and view all the answers

Which protein is responsible for connecting the actin filaments to the plasma membrane in microvilli?

Myosin I Signup and view all the answers

Which statement is true regarding primary cilia?

They have a 9+0 axoneme structure Signup and view all the answers

What is the role of the terminal web in microvilli?

To anchor actin filaments at the base of microvilli Signup and view all the answers

Which type of cilia is responsible for generating left-right asymmetry during embryonic development?

Nodal cilia Signup and view all the answers

Which of the following cells would contain microvilli enhancing absorption?

Columnar epithelial cells in the small intestine Signup and view all the answers

What is a key composition difference between microvilli and cilia?

Microvilli are made of actin while cilia are made of microtubules Signup and view all the answers

Study Notes

Epithelial Tissue

Epithelial tissue forms a protective covering of body surfaces and lines body cavities.
It's avascular; nourished by diffusion from underlying connective tissue.
It always rests on a basement membrane, a specialized type of connective tissue.
Cells display polarity (structural and functional differences between sides).

Epithelial Cell Polarity

Apical Domain: Faces the lumen or external environment; possesses microvilli, cilia, stereocilia.
Lateral Domains: Contact adjacent cells; responsible for cell-to-cell adhesion.
Basal Domain: Faces the basement membrane; attaches to it, facilitates nutrient transport.

Epithelial Tissue Classification

Simple epithelium: Single layer of cells.
Stratified epithelium: Multiple layers of cells.

Classifying Epithelial Cells Based on Shape

Squamous epithelium: Flattened cells, width greater than height.
Cuboidal epithelium: Cube-shaped cells, equal height and width.
Columnar epithelium: Tall, column-shaped cells, height greater than width.

Pseudostratified Epithelium

Appears stratified due to varying cell heights and nuclei positions.
All cells connect to the basement membrane.
Primarily pseudostratified columnar epithelium, found in the respiratory system..

Transitional Epithelium

Also known as urothelium, found in the ureters, bladder, urethra.
Stratified epithelium where the top layer of cells changes shape based on organ distension.
Top layer (umbrella cells) covers underlying cells.

Specialized Epithelial Cells

Endothelial cells: Simple squamous, line blood vessels.
Mesothelial cells: Simple squamous, cover organ surfaces.

Apical Domain Modifications

Microvilli: Finger-like projections increasing surface area for absorption; found in intestines (striated border), kidneys (brush border).
Cilia: Hair-like projections moving substances along the cell surface; found in the respiratory system.
Stereocilia: Long, non-motile microvilli found in the inner ear and the male reproductive system.

Microvilli Structure and Proteins

Core: Contains 20-30 parallel actin filaments.
Actin Filaments: Connected by fimbrin, villin, and fascin.
Myosin I: Links actin filaments to the plasma membrane
Villin: Maintains actin filament arrangement at the microvillus tip.
Terminal Web: Anchoring structure; composed of cross-linked actin filaments and myosin II.

Microvilli, Stereocilia, and Cilia

Microvilli:
- Projections of the apical domain for increased absorption.
- Contain actin filaments, connected by fimbrin, villin, fascin.
- Myosin I links actin to the membrane; villin anchors the core.
- Terminal web anchors at the base, composed of cross-linked actin filaments, and myosin II.
Stereocilia:
- Highly modified microvilli, found in epididymis (absorb testicular fluid).
- Actin filaments with alpha-actinin, but no villin.
- Ezrin connects actin filaments to the plasma membrane
- They do not contract due to the absence of myosin, in contrast to microvilli.
Cilia:
- Hair-like structures responsible for movement.
- Composed of microtubules in a 9+2 axoneme arrangement; 9 peripheral doublets & 2 central microtubules.
  - 9+0 axoneme is also possible
- Dynein: Motor protein involved in cilia motion.
- Basal body: Microtubule organizing center located in the apical domain

Types of Cilia

Motile Cilia:
- 9+2 axoneme and dynein, moving substances.
- Abundant in respiratory system to clear mucus/foreign material.
Primary Cilia:
- 9+0 axoneme, non-motile; sensory function.
Nodal cilia:
- 9+0 axoneme and dynein. Development of left/right body symmetry.

Other Relevant Tissues and Structures

Simple Columnar Epithelium:
- Single layer columnar cells found in the small intestine; possess a brush border (microvilli).
- Goblet cells: Mucus-secreting cells, appear empty in H&E after clearing. PAS staining highlights them
Mesentery:
- Tissue covering small intestines; composed of mesothelial cells; visible in Silver & H stains (silver stains lipids)
Blood vessels:
- Endothelial cells (simple squamous) lining blood vessels.
- Veins appear collapsed in H&E staining
Lymphatic vessels:
- Lined by endothelial cells, do not contain red blood cells.
Basement membrane: A thin, red line underneath the epithelium in H&E staining.
Terminal web: At the base of microvilli, composed of cross-linked actin filaments and myosin II. Not present under cilia.

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Description

This quiz focuses on the characteristics and functions of epithelial tissue, including its structure and polarity. Understand the significance of avascularity and the roles of the apical, lateral, and basal domains in epithelial cells. Test your knowledge on these fundamental concepts in histology.