1. Ch. 4 Part 1
Tissues and Junctions

2. Histology Science that deals with the study of tissues
Tissue – group of similar cells that usually have a common embryonic origin and functions together to carry out specialized activities
Pathology – study of cells and tissues for the purpose of diagnosis

3. 4 Main Types of Tissues Epithelial Connective Muscular Nervous
Cover body surfaces and line hollow organs, body cavities, and ducts; also forms glands
Connective
Protects and supports the body and its organs; bind organs together, store energy reserves, help provide immunity
Muscular
Generates physical force needed to make body structures move
Nervous
Detects changes in body conditions and responds by generating action potentials to help maintain homeostasis

4. Primary Germ Layers
All 4 body tissues arise during embryonic period from:
Ectoderm – epithelial, nervous
Endoderm – epithelial
Mesoderm – epithelial, connective, muscular

5. Checkpoint Define a tissue.
What are the four basic types of human tissues?
What are the 3 primary germ layers and which tissue is derived from each?

6. Cell Junctions
Cell junctions – contact points between the plasma membrane of tissue cells
5 types:
Tight junctions
Adherens junctions
Desmosomes
Hemidesmosomes
Gap junctions

7. Tight Junctions
Consist of weblike strands of transmembrane proteins that fuse the outer surfaces of plasma membranes together
Where in the body?
Epithelial tissue of stomach, intestines, and bladder
Function:
Prevent passage of substances between cells
Prevent leaking of contents into blood

8. Tight Junction

9. Adherens Junctions
Contain plaque – dense layer of proteins on the inside of the plasma membrane
Cadherins (proteins) attach to the plaque in each cell and create a belt around the cells
Where in the body?
Epithelial tissue
Function:
Resist separation during contractile activities (ie: moving food through intestines)

10. Adherens Junctions

11. Desmosomes Contain plaque and cadherins that connect cells together
Do not create belt
Where in the body?
Epidermis (skin), cardiac (heart) muscle cells
Function
Prevent separation during tension and contraction

12. Desmosomes

13. Hemidesmosomes Hemi = half
Look like desmosomes, but don’t actually connect cells
Use integrins instead of cadherins
Where in the body?
Epithelial tissue
Function:
Connect cells to basement membrane

14. Hemidesmosomes

15. Gap Junctions
Use connexins to form tiny fluid-filled tunnels call connexons that connect cells
Cells have space between them
Where in the body?
Eye tissue, embryos, nerve and muscle cells, heart, intestinal tract, uterus
Function:
Allow communication through passage of ions, chemical and electrical signals

16. Gap Junctions

17. Checkpoint Which type of cell junctions allow cellular communication?
Which types of cell junctions are found in epithelial tissues?