Epithelium and Mcgraw-hill Companies Essay

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Classification of

Grozdena Yilmaz
BIO 150
Lab 3

• Tissue—a group of similar cells and cell products that arise from the same region of the embryo and work together to perform a specific structural or physiological role in an organ
• Organ—structure with discrete boundaries that is composed of two or more tissue types
• Histology- the study of tissues is called

• Types of tissues
• Epithelial- covers the body's external and internal surfaces and most glands
• Connective- binds and support parts

Muscle- makes movement possible

• Nervous-conducts impulses from one part of the body to another and help to control and coordinate body activities

Interpreting Tissue Sections
• Preparation of histological specimens
– Fixative prevents decay (formalin)
– Histological sections: tissue is sliced into thin sections one or two cells thick
– Stains: tissue is mounted on slides and artificially colored with histological stain
• Stains bind to different cellular components

• Sectioning reduces three-dimensional structure to two-dimensional slice

Longitudinal, Cross, Oblique Sections
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Longitudinal sections

Longitudinal section (l.s.)
– Tissue cut along long direction of organ

Cross section (c.s. or x.s.) or transverse section (t.s.)

Cross sections

– Tissue cut perpendicular to length of organ •
Oblique sections

Oblique section
– Tissue cut at angle between cross and longitudinal sections

Figure 5.2


Interpreting Tissue Sections

• Smear—tissue is rubbed or spread across the slide – Spinal cord or blood

• Spread—cobwebby tissue is laid out on a slide
– Areolar tissue

Epithelial Tissue
• Consists of a flat sheet of closely adhering cells
• One or more cells thick
• Upper surface usually exposed to the environment or an internal space in the body
• Covers body surface and lines body cavities
• Forms the external and internal linings of many organs • Constitutes most glands


Epithelial Tissue
• Extracellular material is thin
• Epithelia allow no room for blood vessels-

• Lie on a layer of loose connective tissue and depend on its blood vessels for nourishment and waste removal


Epithelial Tissue
• Basement membrane—layer between an epithelium and the underlying connective tissue
– Collagen

• Anchors the epithelium to the connective tissue below it
• Basal surface—surface of an epithelial cell that faces the basement membrane
• Apical surface—surface of an epithelial cell that faces away from the basement membrane

Epithelial Tissue

• Stratified epithelium

Simple epithelium
– Contains one layer of cells
– Named by shape of cells

– All cells touch the basement membrane

– Contains more than one layer
– Named by shape of apical cells
– Some cells rest on top of others and do not touch basement membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(a) Classes of epithelium Simple

Pseudostratified columnar Stratified




(b) Cell shape s

Figure 5.3


Simple Epithelia

• Four types of simple epithelia
• Three named for their cell shapes
– Simple squamous (thin, scaly cells)
– Simple cuboidal (square or round cells)
– Simple columnar (tall, narrow cells)


Simple Epithelia
• Fourth type
– Pseudostratified columnar
• Not all cells reach the free surface
• Shorter cells are covered over by taller ones
• Looks stratified
• Every cell reaches the basement membrane

• Goblet cells—wineglass-shaped mucus-secreting cells in simple columnar and pseudostratified epithelia 5-12

Stratified Epithelia
• Range from 2 to 20 or more layers of cells
• Some cells resting directly on others
– Only the deepest layer attaches to the basement membrane

• Three stratified epithelia are named for the shapes of their surface cells
– Stratified squamous
– Stratified cuboidal
– Stratified columnar