Tissues are group of cells organized to perform specific function



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Tissues



Tissues are group of cells organized to perform specific function

Tissues of human body

Human body composed of 4 basic tissue types, which are:

1. Epithelial tissue = epithelium it covers the body surfaces

and lines cavities and lumen and formed glands. There are:

a) Surface epithelium

b) Glandular

c) Special epithelium
2. Connective tissue, which surrounds or underlies and

support the other three basic tissues.

It is classified into:

a) Connective tissue proper

1- loose C.T

2- Dens C.T "regular, irregular"

b) Haemopoitic tissue

c) Blood and lymph

d) Supportive tissue" cartilage, bone"
3- Muscular tissue is made of contractile cells. responsible

for body movement" smooth, skeletal, cardiac"



4- Nervous tissue transmits and integrates information

From outside and inside the body to control its

activities and function.

Epithelial tissues



  • The epithelial tissues having diverse functions and structural multiformity

General features of the epithelia




The cells that make up the epithelium tissues have three principal

Characteristics:

a) They adhere to one another by mean of junctions

b) They exhibit functionally distinct surfaces, free or apical,

lateral and basal surface.

c) The basal surface is attached to the underlying basement

Membrane. EM = basal lamina



Function:


1. Act as selective barrier.

2. Facilitate differentiation and proliferation.

3. Provide attachment to underlying tissue.


Nourishment occurs by diffusion.

  • Epithelial tissues lined all surfaces and cavities of the body except joint. e.g. : - Lined skin (epidermis)

- Lines digestive system, respiratory, urinary passages

- Lines closed coelomic cavities, peritoneum, pleura,

Pericardial called mesothelium

- Lines cardiovascular channels by endothelium.

- Lines all derivatives of surface epithelium such as

glands.


  • All the body surfaces are active i.e. there is continuos flow of materials either in unidirectional or bi-directional across the epithelial lining.

  • Glands of the body exocrine gland retained its connection with surface, but endocrine lost it.

  • Epithelia have a remarkable capability of renewal and regeneration

This shedding off epithelium used in diagnostic aspect (Pap

smear)


Exofoliative Cytology to study the cervix to detect any cervical

carcinoma.



  • The epithelial tissues have ability to change their morphology and function. Change of one epithelium to another is called metaplasia e.g urinary stone in U.B (transitional squamous cell)

Pseudo stratification of bronchi of smokers’ str. sq. may be reversal Tumor arising from epithelium carcinoma for gland adenocarcinoma

  • They have diversity of function include: Protection, lubrication, secretion, absorption, digestion, transport, excretion, sensation, reception, transduction and reproduction.

Give examples of different secretion secreted by epithelial



gland??

Milk – breast

Sweat gland sweat

Sebaceous sebum

Gland in the external ear wax

Digestive gland enzymes

Endocrine gland hormones

Urine, reproductive cells


Classification of epithelium


There are three types of epithelium

I- Surface epithelium (SE)

According to the cell number and the height and shape of surface layer,

SE divides into:

a. Simple

b. Stratified

II - Glandular epithelium

a. Endocrine gland.

b. Exocrine gland.

c. Mixed.
111- Neuro-epithelium = special epithelia have certain special

properties

Concern with:


  • Sensory perception

  • Reproduction


1- Sensory perception

    • Olfactory

    • Visual

    • Gastatory

    • Auditory



2- Reproduction

germinal epithelium lined seminefrous tubules of the



testis and surface of the ovary.



I- Surface epithelium
a-Simple
b- Stratified
There are 4 simple and 4 stratified.
a. Simple

Consists of single layer of cells it can be classified as follow:



1. Simple squamous epithelium: allow exchange of gas, fluid

on metabolites.

The cells are flat with flattened nuclei.
Site:


  • Endothelium of blood vessels

  • Serous membrane, pleura, pericardium, peritoneal (mesothelium).

  • Alveoli of the lung. Small bronchioles

  • Cardiac channels ( endothelium)

  • Bowman's capsule (parietal layer )

  • Thin segment of loop of Henle

  • Inner aspect of tympanic membrane


2. Simple cuboidal (cubical) epithelium

It is formed of one layer of cubical cells with central rounded

Nuclei resting on a basement membrane.
Function:


  1. Play important role in secretion or absorption.

  2. Line glandular ducts


Site:

  • Kidney tubules, proximal & distal convoluted tubules and small collecting ducts

  • Rete testis and free surface of the ovary

  • Ducts of many gland.


3. Simple columnar epithelium

It is formed of tall columnar cells with basal oval nuclei



Function:

- It is primarily responsible for secretion and absorption.


Site:

  • Line ducts of many glands e.g. stomach, intestine (absorption),

gall bladder.

  • Lining the large collecting tubules of the kidney ( secretion)

  • Oviduct (secretion).



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