1. The Tissue Level of Organization
Chapter 4
Anatomy and Physiology

2. Types of Tissue Four Primary Types I. Epithelial II. Connective
III. Nervous
IV. Muscle

3. Epithelial Covers body surfaces
e.g. skin, but also “internal” body surfaces:
Lines the internal passageways and body cavities:
Digestive system
Respiratory system
Reproductive system
Urinary system
Cells are in layers: one layer or multiple layers.
Always have a “free surface” exposed to the environment or internal chamber or passageway.

4. Epithelial Tissue Epithelial tissue:
Avascular: (does not contain blood vessels) the cells of the epithelium obtain nutrients by diffusion or absorption from deeper tissues or exposed surfaces.
Network of protein fibers called the BASEMENT MEMBRANE connects the epithelium to the rest of the body.

5. Epithelium Functions 1. Physical protection: 2. Permeability control:
From abrasion, dehydration, chemical agents, biological agents.
2. Permeability control:
Some are impermeable others allow movement of molecules as large as proteins
3. Provision of sensation-
touch, smell taste.
4. Provision of specialized secretions
Digestive enzymes, perspiration, milk, hormones

6. Types of Epithelial Tissues
Classified according to:
A. Number of cell layers
B. Cell Shape

7. A) Number of Cell Layers
Simple Epithelium
Are thin
Are relatively fragile
Line internal passageways:
Chambers of heart, blood vessels
Line regions where secretions or absorption occurs
Short amount of time for materials to pass
Stratified Epithelium
Have several layers
Cover areas which are exposed to mechanical stress.
e.g.
Skin
Lining of mouth

8. Simple
Stratified

9. B. Cell Shape Squamous: Cuboidal Columnar Thin flat cells
Nucleus is the thickest portion
Viewed form the surface they look like “fried eggs”
Cuboidal
Hexagonal cells of equal height
In sectional view they appear square with the nuclei near the center of each cell
Columnar
Similar to cuboidal
Taller and more slender
Nuclei closer to basment membrane

10. Squamous Cell
Cuboidal Cell
Columnar Cell

11. Types of Epithelial Tissue
Simple Squamous-
Consists of flat irregularly shaped cells
Is the most delicate epithelium
Covers the heart and lungs where it secretes lubricating fluids which reduce friction in the operation of these organs
Found in blood vessels and aveoli
ANATOMICAL TERMINOLOGY
Mesothelium- simple squamous epithelial tissue that lines the pleura, peritoneum and pericardial cavities.
Endothelium- simple squamous epithelial tissue that lines the heart and blood vessels.

12. Simple Squamous

13. Types of Epithelial Tissue
Stratified Squamous Epithelium-
The squamous type cells form several layers
Is found in lining of mouth and esophagus
Surface of skin
Protect against mechanical injury
Outer layers may become non-living and fall off.

14. Stratified Squamous

15. Types of Epithelial Tissue
Simple Cuboidal Epithelium
Are hexagonal cells of equal height and width
In cross section they appear square
Provides limited protection where secretion and absorption take pace
Tubules of kidneys
Salivary glands
May secrete enzymes and buffers

16. Simple Cuboidal

17. Types of Epithelial Tissue
4. Stratified Cuboidal Epithelium 1. Are rare 2. Found along ducts of sweat glands and mammary glands 3. Provide protection, secretion, absorption of various biochemicals

18. Stratified Cuboidal

19. Types of Epithelial Tissue
5. Transitional Epithelium
Unusual epithelium that lines urinary bladder where large changes in volume take place
Appearance changes as stretching occurs.
In empty bladder the epithelium seems to have many layers and the outermost cells look like plump cuboidal cells.
Layered appearances is due to overcrowding of cells
Actual structure can be seen in the full urinary bladder (few 1-2 layers)

20. Transitional

21. Types of Epithelial Tissue
6. Simple Columnar Epithelium
Are similar to cuboidal epithelium but they are taller and more slender
Is found in the small intestine, stomach and large intestine
This is the epithelium that provides protection from the chemical stress of the digestive system.

22. Simple Columnar

23. Types of Epithelial Tissue
Pseudostratified
Is a mixture of epithelial cell types
The cells appear to be in layers due to the various shapes of the cells and the apparent location of the nuclei
However…all cells are in contact with the basement membrane
Actually is a simple epithelium
Found lining trachea, nasal cavities, bronchi, and parts of the male reproductive tract.
Always possess cillia
They provide protection and secrete protective fluids

24. Pseudostratified

25. Types of Epithelial Tissue
Stratified Columnar Epithelium
Are rare
Occur in large salivary gland ducts and in small areas of the pharynx, anus, mammary glands, and urethra
Their function is to provide protection

26. Stratified Columnar

27. Glandular Epithelia Produce exocrine or endocrine secretions.
Exocrine Secretions: produced by exocrine glands that discharge their secretions through a duct, tube, or onto some external surface.
Endocrine Secretions (hormones): produced by ductless glands and released into blood or tissue fluids

28. Mode of Secretion
Merocrine Secretion: product released through exocytosis (leaves cell intact)
e.g. mucus in digestive and respiratory tracts
Apocrine Secretion: involves loss of both cytoplasm and secretory product (leaves cell intact)
e.g. Mammary gland milk, perspiration
Holocrine Secretion: entire cell becomes packed with secretion and bursts (cell is no longer intact)
e.g. skin oils and waxy coating of hair