Syllabus requirements 3.2 Cell Practical Work:structure Animal tissues should include the and following epithelia: Squamous,function cuboidal, columnar, ciliated, pseudostratified and stratified epithelium.
Epithelial tissue is arranged in single or multilayered sheets covers the internal and external surfaces of the body of an organism
Epithelium arises from germ layers ectoderm mesoderm endoderm
What is a ‘germ layer’? Any of the three primary cellular layers, the ectoderm, endoderm, or mesoderm, into which most animal embryos differentiate and fromwhich the organs and tissues of the body develop.
[IMP: all animals develop from a blastula] Blastula: a hollow ball of cells
True epithelial tissue arises embryonically from:Either the ectoderm which Or the endoderm, whichprovides epithelium for provides epithelium forthe the: skin remainder of the nervous system alimentary canal parts of the fore- & liver hindgut pancreas
The inner lining of blood vessels, called endothelium : is not true epithelium as it is derived from embryonic mesoderm Artery Vein
Epithelial cellsAre held together by: Rest on a basement small amounts of membrane:cementing substance composed of a containing a carbohydrate network of collagenous derivative called fibres usually secreted hyaluronic acid by underlying tissues
Epithelial cells have two surfaces Apical surface(faces the lumen or space) Basement membraneBasal surface(faces the basement membrane)
Epithelial cells are not supplied with blood vessels So how do they get oxygen & nutrients?
By diffusion from lymph vessels which ramifyadjacent intercellular spaces
Functions of epithelial tissue: to protect underlying structures from injury: through abrasion or pressure from infectionBacteria on skin surface.
How is stress combatted by the tissue? the tissue becomes thickened & keratinized where cells are sloughed off due to constant friction the epithelium shows a very rapid rate of cell division so that lost cells are speedily replaced
The free surface of the epithelium:Is often highly differentiated and may be: absorptive secretory or excretory in functionHas sensory nerveendings specialized forstimulus reception
Epithelial tissues are classified : according to the: 1. number of cell layers 2. shape of the individual cells
In many areas of the body: the different cell types intermix the epithelia cannot be classified into distinct types
Squamous epithelium cells are thin flattened contain little cytoplasm (irregular) (to bind cells)
Squamous epithelium occurs in: Bowman’s capsules of the kidney Alveolar lining of the lungs Blood capillary walls
Being thin, squamous epithelium permits fast diffusion SimpleSimple Simple ColumnarSquamous Cuboidal Basement membrane
Squamous epithelium provides smooth linings to hollow structures e.g. blood vessels & the chambers of the heartSmooth linings are important toallow the relatively friction-freepassage of fluids through them
Cuboidal epithelium the least specialised of all epithelia cells: cube-shaped possess a central spherical nucleus
Cuboidal cells viewed from the surface are: pentagonal or hexagonal in outline
Occurrence of cuboidal epithelium: forms the lining of many ducts e.g.: non-secretory salivary pancreatic cuboidal collecting ducts of the epithelium kidney in many glands e.g.: salivary mucus secretory sweat cuboidal thyroid glands epithelium
Columnar epithelium cells are: tall quite narrow[thus providing morecytoplasm per unitarea of epithelium] basement membrane nucleus is situated at basal end of cell
Secretory goblet cells are often interspersed among the epithelial cells epithelium may be: secretory and/or absorptive in function Goblet cell Goblet cell in small intestine
Microvilli frequently occur at the free end of each cell increase the surface area of the cell for absorption and secretion Part of a villus in the small intestine
Columnar epithelium lines the: stomach: mucus secreted by the goblet cells protects the stomach lining from: 1. the acidic contents of the stomach 2. digestion by enzymes intestine: mucus: 1. protects it from self-digestion 2. lubricates the passage of food
Columnar epithelium lines the: many kidney ducts
Columnar epithelium : is a component of the: thyroid gland gall bladder
Ciliated epithelium cells of this tissue are usually columnar in shape but bear numerous cilia at their free surfaces
Ciliated epithelium is always associated with mucus-secreting goblet cells producing fluids in which the cilia set up currents ciliated epithelium serves to move materials from one location to another
Ciliated epithelium lines the:1. oviducts2. ventricles of the brain3. the spinal canal4. respiratory passages
Compare appearance of:Simple columnar Simple cuboidal epithelium epithelium LS LSTS TS Duct or tubule Duct or tubule
Pseudostratified epithelium cilia when viewed in section the nuclei of this type of epithelium appear to be at several different levels because all the cells do not reach the free surface the epithelium is only one layer of cells thick : each cell is attached to the basement membrane
Pseudostratified occurs in the lining:1. urinary tract2. trachea (as pseudostratified columnar)3. other respiratory passages (as pseudostratified columnar ciliated) as a component of the olfactory mucosa
Stratified epithelium this tissue: comprises a number of layers of cells is correspondingly thicker than simple epithelium forms a relatively tough, impervious layer Stratified squamous
The cells are formed by mitosis: of the germinal layer which rests on the basement membrane germinal layer Germinal layer: a layer of cells from which new tissue is constantly formed
The first-formed cells are cuboid in shape but : as they are pushed outwards towards the free surface of the tissue they become flattened The flattened cells are called squames.
Stratified epithelial cells may: become cornified: the squames are transformed into a dead horny layer of keratin which ultimately flakes away as on external skin surfaces, lining the buccal cavity & vagina where it affords protection from abrasion
Stratified epithelial cells may be:Uncornified: as in the oesophagus Stratified squamous Columnar epithelium epithelium
Uncornified stratified squamous epithelium inthe oesophagus protects: the underlying tissues against mechanical damage by friction with food just swallowed
Name of stratified epithelium is according to the shape of the cells present: stratified squamous: – located in parts of the oesophagus stratified cuboidal: – in sweat gland ducts stratified columnar: – in the mammary gland ducts
Essay TitleDifferent cells are adapted to perform differentfunctions. Discuss. [MAY, 2010][hint: mention both plant & animal cells]
Question: SEP, 2005The diagram in Figure 1 shows three forms ofepithelium:
2.1 What is an epithelium? (2) A tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs.
2.2 Identify the forms of epithelium shown inFigure 1 and name one place in the human bodywhere you would expect to find each form. (6) Form ofLabel Location in body epithelium alveoli / capillary walls / cheek A squamous lining / Bowman’s capsule lines convoluted tubules / in B cuboidal glands e.g. salivary, sweat ciliated lines the stomach, intestines, C columnar kidney ducts, thyroid gland
2.3 Give ONE function of each of the three formsof epithelium represented in Figure 1. (3)A – provides smooth linings / being thin it permits diffusionB – secretory function in glandsC – secretory or absorptive function
3. The diagram shows a section of a vein.a) Name the type of epithelium making up the ‘lining layer’. (1) Simple squamous epithelium
b) Explain how the structure of this type of epithelium is adapted for the efficient functioning of the vein. (1) Provides a smooth surface to reduce friction. Blood flows without clumping to the sides of the vessel.