1. Tissues

2. Impermeable junctions
Cell Junctions
Tight Junctions
Desmosomes
Gap Junctions
Impermeable junctions
Anchoring junctions bind to adjacent cells like Velcro
Allow for intercellular communication
Prevent molecules from passing through intercellular space
Form internal tension-reducing network of fibers; plaques on surface of membrane attach to protein filaments
Allow ions and small molecules to pass through channels formed by connexon protein cylinders
Example:
Lining of the digestive tract
Found in tissues subject to stress like skin; heart muscle
Found in electrically excitable tissue (heart; smooth muscle) to synchronize

4. Intercellular Junctions
Tight junctions
Close space between cells
Located among cells that form linings
Cell membrane
Tight junction
Desmosomes
Form anchors between cells
Located among outer skin cells
Cell membrane
Desmosome
Gap junctions
Tubular channels between cells
Located in cardiac muscle cells
Cell membrane
Gap junction

5. Four Primary Tissue Types:
Tissue = a group of similar cells that function together to carry out specialized activities. Histology = the study of microscopic anatomy (tissue). The body has different kinds of tissues, some highly organized and some not. *Form (structure) fits function.
Four Primary Tissue Types:
Epithelium
Connective
Muscle
Nervous

6. Epithelium: Basic Info.
Cover internal and external body surfaces
Lines body cavities & hollow organs.
1. Protection (cells tightly packed)
2. Absorption
3. Secretion
4. Excretion
5. Sensory reception
Epithelium: Basic Info.

7. Epithelium: General Characteristics
Consists mostly or entirely of closely packed cells that are arranged in continuous sheets.
Has an apical surface (one side is always exposed to the external or internal environment), and a basement membrane. Basement membrane connects epithelium to connective tissue and other structures
It’s a thin matrix of fibers that anchor the tissue.
Avascular (no blood supply), but innervated.
Nutrients must diffuse into the tissue from the blood vessels of the connective tissue.
High capacity for renewal by cell division.
Epithelium: General Characteristics

8. Epithelial tissue
Basement membrane
One side of the tissue is exposed to the outside and the tissue is connected by a basement membrane.

9. Epithelium: Nomenclature
Epithelial tissue is categorized according to the shape of the cells and number of layers.
Three basic shapes:
Squamous
Cuboidal
Columnar
Layers:
Single layer = “simple”
Multiple layers = “stratified”

10. Squamous cells are flat.

11. Cuboidal epithelium cells are shaped like cubes.

12. Columnar epithelium cells are rectangular in shape.

13. Simple squamous epithelium: look for a thin layer of flat (squamous) cells.
Common site for passive transport (filtration & diffusion).
Found in the lungs, walls of capillaries and inside of blood and lymphatic vessels.

14. Stratified squamous epithelium: as the cells reach the surface, they flatten out. Many cell layers. Top cells = flat
This is a slide of the most superficial layer of the skin known as the epidermis.
Keratin is found at the top of the epidermis: protein that keeps cells from being very moist
Stratified squamous is also found lining orifices, like the oral cavity (non-keratinized here so cells are relatively moist)

15. Simple Cuboidal Epithelium: only one layer
Commonly found in ovaries, kidney tubules, ducts.
Stratified cuboidal epithelium also lines ducts. It can be found in the ducts of mammary glands, sweat glands, salivary glands, pancreas. (2-3 layers)

16. Simple columnar epithelium: can be ciliated or non-ciliated.
Ciliated is found in the female reproductive tract.
Non-ciliated is found in the uterus and digestive tract.
Columnar epithelium can also be stratified. This tissue is found in the vas deferens and pharynx. It provides a thicker lining for some tubular structures in the body.

17. A special type of cell known as a goblet cell is usually associated with columnar epithelium. The goblet cell secretes mucus.

18. Cilia and microvilli may also be present on columnar cells.
The cilia and goblet cells work together to move substances along the cells, like in the respiratory tract.
Cilia

19. Stratified columnar: Top layer of elongated cells
Cube-shaped cells in deeper layers
Line part of male urethra and part of pharynx
(b)
(a)
Lumen
Stratified
columnar
epithelium
Connective
tissue
Basement
membrane
Free surface
of tissue

20. Epithelium: Exception to the Rule #1
Pseudostratified columnar epithelium
Looks like it’s stratified (more than one layer), but it’s not.
It looks stratified because the nuclei of the cells are at various levels, but there is really only one layer.
May have cilia, line resp. passages

21. Pseudostratified vs. Simple columnar epithelium
Nuclei don’t line up—pseudostratified.
Nuclei all line up nicely in one row—simple.
Pseudostratified vs. Simple columnar epithelium

22. Epithelium: Exception to the Rule #2
Transitional epithelium Looks somewhat like stratified squamous, but there is a difference. Many layers; cube-shaped & elongated cells; can stretch In transitional epithelium, the cells are rounded both at the base of the tissue and the section exposed to the outside. Urinary bladder: multiple layers allow for the bladder to distend and contract. Forms a barrier to help protect the bladder from infection.

23. The cells of this tissue are specialized to change shape in response to pressure.
When the bladder is empty, these cells are more or less cuboidal in shape.
As the bladder fills, the cells become compressed and flattened.
Transitional epithelium

24. Epithelium: Glandular
Glandular epithelium Can secrete substances into the bloodstream (endocrine glands), or into ducts (exocrine glands).
Epithelium: Glandular

25. Exocrine Glands Can be classified by method of secretion:
Merocrine—release substance via exocytosis
Also called “eccrine”
Ex: salivary glands, pancreatic glands, some sweat glands
Apocrine—lose small portion of cell body.
Examples: mammary glands, some sweat glands
Holocrine—release entire cell.
Examples: sebaceous glands (hair follicles)
Exocrine Glands

26. Duct
Secretory portion
Tissue surface
Simple tubular
Simple branched
tubular
alveolar
Simple coiled
Compound tubular
Compound alveolar

27. Merocrine Glands Apocrine Glands Holocrine Glands Fluid product
Salivary glands
Pancreas
Sweat glands (also called eccrine)
Apocrine Glands
Cellular product
Portions of cells
Mammary glands
Ceruminous glands
Holocrine Glands
Secretory products
Whole cells
Sebaceous glands
(a) Merocrine gland
(b) Apocrine gland
(c) Holocrine gland
Secretion
Pinched off
portion of cell
(secretion)
Intact
cell
Disintegrating cell
and its contents
New cell
forming by
mitosis and
cytokinesis