Ch. 4 Part 1

Tissues and Junctions

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

4 Main Types of Tissues• Epithelial

– 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

Primary Germ Layers

• All 4 body tissues arise during embryonic period from:– Ectoderm – epithelial,

nervous– Endoderm – epithelial– Mesoderm –

epithelial, connective, muscular

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?

Cell Junctions

• Cell junctions – contact points between the plasma membrane of tissue cells

• 5 types:– Tight junctions– Adherens junctions– Desmosomes– Hemidesmosomes– Gap junctions

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

Tight Junction

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)

Adherens Junctions

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

Desmosomes

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

Hemidesmosomes

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

Gap Junctions

Checkpoint

• Which type of cell junctions allow cellular communication?

• Which types of cell junctions are found in epithelial tissues?