Post on 22-Feb-2016
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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?