Histology

1. Histology The study of….webs?

2. Histo- Greek for ‘web’ • Tissue-groups of similar cells ‘webbed’ together

3. Epithelial • Protects outer body and lines inner organs • Sheets/tubes of tightly-packed cells • Polarity- has a top (apical) and a bottom (basal) • Apical- surface that can be exposed to air or fluid • Sometimes has cilia (hair-like growth) • Moves material over cell surface • Or microvilli (finger-like projections) • Increases surface area for absorption • Basal attaches to a connective tissue

4. Classification by layers- • Single-layered: simple • Multi-layered: stratified • Pseudostratified epithelium- appear multilayered because of differing cell lengths but it is only simple epithelium

5. Simple columnar epithelium with very regular line-up of nuclei EM of apical (top) surface of two epithelial cells whose cell membranes lie next to each other. The microvilli (1) of the striated border are very straight and regimented in appearance. Microfilaments within them can be seen extending down into the terminal web (2), which is an aggregate of fine filaments lying in the cell cytoplasm. Several junctional complexes are seen including tight junction (zonula occludens =3); intermediate junction (zonula adherens =4); and desmosome (macula adherens =5). Thickly cornified stratified squamous epithelium. The cells in the bright red layer and in the pale layers above it are completely flattened and dead, and have lost their nuclei.

6. Shape classification

7. Key functions • Protection • Protects more vunerable structures in the body • Barrier • Prevents foreign objects from entering the body • Sensation • Sensory nerve endings in epithelial tissue connect with outside stimuli • Secretion • Can be specialized to secrete enzymes, hormones, and fluids

8. Connective Tissue • It is the frame-work and support for organs, stores fat, transports substances, protects against disease, repairs tissue damage. • Classified by the extracellular matrix- what they lay in. • Collagen- fibrous protein • Gives the tissue the strength it needs • Connective tissue is made up of a mix of collagen, elastic, and reticular fibers

9. Primary types of connective tissue • Dense regular connective tissue: in tendons used as bundles of collagenous fibers to attach muscle to bone. In ligaments as elastic fibers from bone to bone, surrounding a joint, and anchoring organs. • Dense irregular connective tissue: fibers twist and weave to form thick tissue that withstands stress from any direction. Makes up inner skin layer called the dermis and the outer capsule of organs like the kidney and the spleen. • Reticular tissue:thin, branching fibersmade of collagenous fibers. It is a filter found in the spleen, lymph nodes, and bone marrow.

10. Areolar (loose) tissue: almost everywhere in the body, it binds structures together and fills space. Made of collagenous protein fibers (wavy ribbons), elastic fibers (cylindrical threads), and amorphous ground substance (semisolid gel). • Adipose tissue: made from fat cells. Forms padding for internal organs, reduces heat loss, and stores energy in fat molecules (triglycerides). Have a ring-like structure bc fat molecules fill cells forcing the nuclei against the cell membranes. Has an intracellular matrix, not extracellular.

12. Cartilage: firm, flexible tissue made of collagen and elastic fibers with no blood vessels or nerve cells. Contains openings called lacunae that enclose mature cells (chondrocytes). There are 3 types: • Hyaline- foundation for embryonic skeleton, forms the rib cartilages, makes nose cartilage, and covers articulating surfaces of bones • Fibrocartilage- thick, compact collagen fibers. Its sponge-like structure makes it a good shock-absorber. Found in intervertebral discs and symphysis pubis (front of pelvis). • Elastic cartilage- more tightly packed lacunae and chondrocytesbeween parallel elastic fibers than hyaline. Makes the ear lobe and other structures with specific form. It tends to ‘bounce back’ into its original shape. • Bone (osseous) tissue: repeating patterns called Haversian systems. TheHaversiancanal (center of each system) contains blood vessels, lymph vessels, and nerves. It is surrounded by thin membranes called lamellae. • Blood: extracellular matrix is plasma. Erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets) are suspended in it.

13. Muscle Tissue • Made of fibers called myocytes • Cytoplasm in the fiber is called sarcoplasm • In the cytoplasm is myofibrils • They contain the protein filaments actin and myosin • These filaments slide past each other during muscle contractions to shorten the fiber. • There are 3 types

14. Smooth muscle tissue- contracts without conscious control. Made of spindle-shaped fibers with large, central nuclei. Found in internal organ walls. It is not striated. • Cardiac muscle tissue- known as myocardium. Branching fibers with a central nucleus and alternating light and dark striations make it. Intercalated discs are the dark structures between fibers. Controlled by the autonomic nervous system. • Skeletal, striated, muscle tissue- it attaches to the skeleton and is used throughout the central nervous system for movement. Fibers are cylindrical with several nuclei in each cell.

15. Neurons are the only type of nerve tissue It generates and conducts electrical signals throughout the body Sense receptors receive a stimulus which then sends electrical impulses through finger-like cytoplasmic projections called dendrites. It moves through the body through axons. Nerve Tissue