Epithelial tissue - Introduction to histology PDF

Preview

Summary

Epithelial tissueFour basic tissue types:1. Epithelial tissues – lining and secretion 2. Connective tissue – support and protection 3. Muscle tissue – contraction and body movement 4. Nervous tissue – transmission of nerve impulsesThe principal function of epithelial tissue: Covering, lining and pro...

Description

Thursday, May 6, 2021

Epithelial tissue Four basic tissue types: 1. 2. 3. 4.

Epithelial tissues – lining and secretion Connective tissue – support and protection Muscle tissue – contraction and body movement Nervous tissue – transmission of nerve impulses

The principal function of epithelial tissue: 1. Covering, lining and protecting surfaces (skin) 2. Absorption (small intestine) 3. Secretion (stomach), e.g., hormones, Characteristics of epithelial cells: shapes 1. Squamous 2. Cuboidal- cube-like shape 3. Columnar- tall, elongated, absorption and secretion.

Basement membrane composed of macromolecules, mostly proteins, connect between the special side to the basal side. 

Epithelial cells line lamina and rest on a thin sheet of macromolecules called basement membrane and divided into two parts- basal lamina, reticular lamina. 1. Basal lamina- nearest the epithelial cells, type 4 collagen 2. Reticular lamina- below the basal laminae. Type 3 & 8 collagen

Epithelial cells

Basement membrane Connective tissue

Thursday, May 6, 2021

Intracellular adhesion & anther junction Three main types 1. Tight junction 2. Anchoring junction 3. GAP junction

1. Tight junction: Function  

Seal adjacent cell to each other Separate apical and basolateral membrane domains

Proteins  

Occluding Claudin

Cytoskeleton component: 

Actin filaments

Medical significance 

Neurologic disorders

Apical domain- the highest part of the cell

2. Anchoring junctions Functions  

Provides point linking the cytoskeletons of the adjacent cell Strengthens and stabilizes nearby tight junctions

Proteins  

Cadherins Catenin

In cancer, cadherins is not produced and the cell is permeable for tumors

Cytoskeleton components 

Actin filaments

Medical significance

Thursday, May 6, 2021 

Tumor invasion- loss of cadherin in neoplasms

Types of anchoring junction: Desmosomes Function  

Provide points of string intermediate filament coupling between adjacent cell strengthening the tissue

Proteins 

Cadherins

Cytoskeleton components 

Actin filaments

Medical significance 

Autoimmune disease

Hemidesmosomes Function 

Anchor cytoskeleton to the basal lamina

Proteins  

Keratins Integrins

Medical significance 

Epidermolysis- mutation in integrin β4 gene

3. Gap junctions Functions

Thursday, May 6, 2021 Allows direct transfer of small molecules and ion from one cell to another. Heart and visceral muscles produce rhythmic contraction

 

Proteins Connexin



Cytoskeleton components None



Medical significance Deafness and peripheral neuropathy



Specialization of the apical cell surface Three mains characteristics 1. Microvilli 2. Stereocilia 3. Cilia Microvilli    

For absorption Visible in light microscope as brush border Actin filaments Terminal web at the base of the microvilli

Stereocilia    

Absorptive epithelial cells of the male reproductive systems (epididymis) Motion detecting function in the ear Actin filaments Much longer than microvilli and less motile

Cilia     

Long Highly motile No actin filaments An internal array of microtubules (ciliary axoneme) Primary cilium- not motile, detects light, odors, motion, and flow of liquid past the cells.

9+2 assembly   

Ciliary axoneme The core structure of nine microtubules doublets arranged around two central microtubules Rapid beating patterns

Thursday, May 6, 2021  

Move a current of fluid and suspended matter in one direction along the epithelial (respiratory) Propel a cell (sperm cell)

Two Types of epithelia 1. Covering -lining 2. Secretory- glandular

1. Covering epithelia Cell are organized into one or more layers that comprise the surface or line that cavities of an organ Classification a. By number of the cell layer (simple, pseudostratified or stratified) b. By cell shape (squamous, cuboidal or columnar) c. By characteristics of the surface (microvilli, stereocilia or cilia) Number of the cell layer One cell layer → simple epithelium Many cell layers → stratified epithelium One cell layer that looks like many layers → pseudostratified epithelium ----------------------------------------------------------------------------------------------------1. Simple epithelium 

One layer only

2. Stratified epithelium  Two or more layer of the epithelial cell  Epithelial cells are stacked one above the other  Only one epithelial layer is attached to the basement membrane Transitional epithelium o A unique type of stratified epithelium o Also called urothelium o Lines much of the ordinary tract o Superficial layer of umbrella cells o Specialized epithelium that allows destination of the bladder 3. Pseudostratified  Just one layer  Cells with different highest, shapes and size

Thursday, May 6, 2021    

A unique type of epithelium All epithelial cells are attached to the basement membrane, but no all reach the surface Give false stratifies appearance Mostly commonly observed in the respiratory system

Cell shape   

Thin/flat cells → squamous Same height and width → cuboidal Higher than they are wide → columnar epithelium

Surface characteristics   

Production of keratin → keratinized Non-production of keratin → non-keratinized Presence of cilia → ciliated

Common types of epithelia

Produce only with stratified epithelia

Thursday, May 6, 2021

Secretory epithelia – glands Calls produce and secrete various macromolecules; proteins, lipids, carbohydrates & mucus Two major types of glands present in the body 1. Exocrine glands o Glands remain connected with the surface epithelium o Deliver their products to the surface through tubular ducts (always) Exocrine glands   -

Simple glands – ducts do not branch Compound glands- ducts have two or more branches The secretary portion may be tubular, acinar or branched

Mechanism of exocrine secretion – three main types 1. Merocrine o Proteins and glycoproteins secretion o Products is released by typical exocytosis o Most common 2. Holocrine a. Cells undergo terminal differentiation b. Their disintegration for the final secretary products c. Sebaceous glands 3. Apocrine a. Products if resales tighter with a small amount of the cytoplasm and cell membrane b. Mammary gland

Thursday, May 6, 2021 2. Endocrine glands o Glands lose their connection to their original epithelium o Secrete hormones o Deliver their products through blood vessels...