1. Unit 3 Histology Part 3.1: Germ layers and Epithelial Tissue

2. Objectives Define tissue
Describe the germ tissue layers, their location, and what tissues they produce in eucoelomate animals (humans).
List the 4 major types of tissues of the human body.
Describe the characteristics, cell types, function, and the location of epithelial tissues.

3. Histology
Histology is defined as the study of the microanatomy of animal and plant tissues

4. Germ tissue layers We all start as a single cell called a zygote.
This cell begins to divide, and gives rise to germ cells or stem cells that eventually form the developing embryo.
Because humans are eucoelomate (true body cavity) animals, like earthworms, we have three germ tissue layers.
We develop from these three germ tissues which give rise to all other tissue, such as muscle, nerve, connective, and epithelial tissues.

5. Development of three germ layers

6. Germ tissue layers
1. The endoderm layer is the innermost layer, which forms the lining in our digestive tract.

7. Germ tissue layers The mesoderm layer is the middle layer.
It surround the endoderm layer and is the layer where our large body cavities develop.
The mesoderm gives rise to our muscle and connective tissues.

8. Germ tissue layers The ectoderm layer is the outermost layer.
It is the tissue layer which gives rise to our skin and nervous tissue.

9. True tissues
A tissue is a group of like cells of similar specialized structure which carry out specific functions.
Groups of tissues compose and work together to form organs.
All organs are composed of two or more types of tissues.
There are four major tissue types:
a. Epithelial
b. Connective
c. Muscle
d. Nervous

10. Epithelial tissue
Epithelial tissues are tissues that are found on the outer surface or linings of internal cavities and organs.
They are also found in many glands and produce materials that are secreted by the glands (skin, lining of trachea, esophagus, urinary bladder, and digestive tract, sweat glands, kidneys).

11. Apical surface, basal surface and basement membrane of a tissue

12. Epithelial tissue
These cells are rapidly dividing because they are constantly being sloughed away or rubbed off.
Therefore they must constantly be replaced.

13. Epithelial tissue
They all have a lower layer which consists of germ cells that are constantly dividing to produce new cells.
They are all avascular, meaning they do not have a direct blood supply.

14. Epithelial tissue
They are nourished by blood vessels in the tissue layer below them.
They often contain gland cells which secrete lubricating substances such as mucous and form mucous membranes (nose, mouth, urogenital tract) and serosa membranes which form the outer covering of the digestive organs.

15. General Structural Characteristics of Epithelial Tissues:
Epithelial tissues are also classified according to how many layers compose them.
a.Simple epithelial tissues are only one cell layer thick.

16. General Structural Characteristics of Epithelial Tissues:
Stratified epithelial
tissues are
several layers thick.

17. General Structural Characteristics of Epithelial Tissues:
c. Pseudostratified epithelial tissues appear to be composed of multiple layers but on close examination are actually only one cell layer thick.

18. General Structural Characteristics of Epithelial Tissues:
Epithelial tissues have three basic shapes:
a. Squamous - flattened cells, fried egg shape in appearance.

19. General Structural Characteristics of Epithelial Tissues:
b. Cuboidal - square or cubed shaped. Cells are as wide as they are tall.
c. Columnar - cells are taller than they are wide. Shaped like columns or rectangles.

20. General Structural Characteristics of Epithelial Tissues:

21. Naming (Nomenclature) Epithelial Tissues
Epithelial tissues are named in the following manner:
First word: Number of layers (simple, stratified, pseudostratified)
Second word: Shape of cell (squamous, cuboidal, columnar)
Third word: Describes the apical surface; if there are structures (cilia or microvilli) or materials present (keratin).

22. Naming epithelial tissues
From the name given you can tell much about the tissue. For example: pseudostratified columnar ciliated epithelial.
What can you tell from the name about the tissue?
1. It is one cell-layer thick
2. It is column shaped.
3. It has cilia on its apical surface

23. Types of epithelial tissues
SIMPLE SQUAMOUS:
Location: This type is found lining blood vessels and is called endothelium.
It is also found in the alveoli (or “air sacks”) of the lungs.
Function: This tissue allows the rapid exchange of materials by diffusion and osmosis from cell to cell.

24. Types of epithelial tissues
2. STRATIFIED SQUAMOUS:
Location: This type of epithelium is present in areas where there is wear and tear on the tissue, where cells are continually being sloughed away, or rubbed off, by abrasion.
There are two types of Stratified squamous tissue:
Keratinized
Non Keratinized

25. Types of epithelial tissues
What is Keratin?
Keratin is a layer of waterproof protein on the apical surface of stratified squamous keratinized epithelium (skin).
Examples of :
Keratinized- Skin
B. Non Keratinized- lining of the esophagus and the vagina of the female reproductive system

26. Types of epithelial tissues
3. SIMPLE CUBOIDAL:
Location: (i)Simple cuboidal cells are common in secretory glands and ducts
(ii)They are also found in the walls of kidney tubules where they are involved with reabsorption of materials as urine is being produced
(iii)found on the surface of mammalian ovaries

27. Types of epithelial tissues
4. SIMPLE COLUMNAR:
Location: Commonly found in the lining of the small and large intestine where it is involved with absorption of molecules from digested food and re-absorption of water.
microvilli on apical surface

28. Types of epithelial tissues
In the small intestine the apical surface of these cells have microvilli present on their surface and specialized gland cells called goblet cells which produce and secrete mucus.
microvilli on apical surface

29. Types of epithelial tissues
5. PSEUDOSTRATIFIED COLUMNAR CILIATED:
This tissue appears to be stratified but is actually one layer of irregularly shaped cells.
Location: This tissue forms the lining of the trachea, bronchi, and lining of the Fallopian tubes (oviducts) of female.
The apical surface of these cells have tiny, hair-like projections called cilia, which are involved with the movement across the surface of the cells.
This epithelial tissue also has the mucus secreting goblet cells present.

30. Types of epithelial tissues
PSEUDOSTRATIFIED COLUMNAR CILIATED

31. Types of epithelial tissues
6. STRATIFIED TRANSITIONAL:
Location: This epithelium is unique to the urinary bladder and a small portion of the ureters.
It has the unique property of expansion and contraction. This allows the tissue to adjust to the urinary bladder’s expansion and contraction when it is full or empty.

32. songs https://www.youtube.com/watch?v=B7JHaq66w3o