Introduction to Tissues and Selected Epithelial Tissues

What is a tissue? Tissue = cells + matrix Non-living material around/between the cells cells

Tissues are the building blocks of organs Different tissues have different characteristics, capabilities, and functions Organs are made with tissues Organ are made with tissues that have the capabilities that the organs need in order to do there jobs.

Four Basic Types of Tissues Epithelial Tissues: –covering, barriers, secretion/absorption Connective Tissue: –connects, protects, bears weight Muscle Tissue: –Contracts, produces movement, stabilizes and/or propels substances through the body Nervous Tissue: –controls and regulates with electrical impulses and neurotransmitters

Shared ET Characteristics 1.Very Cellular (little matrix) –Cells are tightly packed 2.Covers/lines surfaces –Enables tissue to act as a barrier 3.Polarity –“top”—apical surface –“bottom”—bottom surface 4.Attached to the material it covers by a basement membrane 5.Avascular –No direct blood supply –obtains O 2 and nutrients by diffusion from nearby blood vessels 6.cells divide rapidly (mitotically active/regenerative) most cancers are epithelial (due to high rate of division  higher mutation rate) 7. Innervated Contains sense receptors and neurons/nerves

ET is classified/described base on: Number of Layers simple=1 layer of cells stratified=2+ layers of cells Shape squamous=flattened cuboidal=cube (square) columnar=tall and thin

Cell Volume and Cell Activity: functional consequence of cell volume Amount of cytoplasm/organelles related to cell’s ability to be active and perform work More cytoplasm  more work/active squamous cuboidalcolumnar Least active More active Most active

Functional Consequences of thickness/layers Thicker  less permeable & more proctective Thinner  more permeable & less protective Simple epithelium  thin layer  easy to pass through --”highly permeable” -- less physically protective stratified epithelium  THICK layer  difficult to get through -- very protective -- “low permeability” “most permeable” “least permeable” DistanceTime to diffuse ųm msec 0.01 ųm0.05 msec 0.1 ųm5 sec 1 mm8.3 min 1 cm14 hr

Simple Squamous: one layer of thin, flat cells Thin, low volume cells Quick & easy to get through (highly permeable) Diffusion & filtration Passive processes Example Locations Alveoli of lungs –Rapid diffusion of O2 and CO2 Capillaries –Movement of substances in and out of blood vessels (diffusion & filtration) Kidneys: movement of wastes out of blood by filtration –Serous membranes—forms a smooth, slick, low-friction surface –endothelium = mesothelium = simple squamous ET

Simple Cuboidal: single layer of “cube-shaped” cells Thin enough to be readily passed through Cells are large enough to be active Absorption –Active transport into cells and/or across epithelial layer –E.g. transport proteins, endo/exocytosis Secretion –Active creation of substances for release Example Location Kidney Tubules –reabsorption of needed substances into blood –Active transport of substances out of blood into “urine”

Simple columnar; single layer of tall cells Thin enough to be readily passed through Cells are large enough to be active Absorption –Active transport into cells and/or across epithelial layer –E.g. transport proteins, endo/exocytosis Secretion –Active creation & release of chemicals Goblet cells Produce mucin Mucin + water  mucus Example Location intestines –Production of enzymes for digestion –Transport of nutrients out of intestines through epithelium –Release of materials into intestines

Psuedostratified ciliated columnar: single layer of irregular cells with cilia Found in respiratory Tract: Nasal cavity, pharynx, larynx, trachea, bronchi Goblet Cells –Mucin + water  mucus –Mucus traps inhales particles –Protects and cleans with mucus Cilia sweep away dirty mucus –(toward esophagus)

stratified squamous; many layers of cells, apical cells squamous in shape Thick layer Difficult to pass through (“low permeability”) Highly protective Example Location Skin Protects underlying tissue, barrier to pathogens/water loss Oral cavity, pharynx, esophagus, vagina, anal canal Protects underlying tissue against abrassion/damage

Glands Clump of epithelial cells designed for producing and releasing substances –secretion –e.g., sweat, saliva, enzymes, hormones –Exocrine: secretion released through a duct (tube) –Endocrine secretions released directly into blood or interstitial space

exocrine duct Exocrine glandEndocrine gland: Exception to free edge rule

Cell Junctions: not limited to ET found in other tissues too Tight Junctions Adhering junctions Desmosomes/hemidesmosomes Gap junctions

Apical features Microvilli –Increase absorptive INTO cell Cilia –“beat”, “sweep” materials ALONG apical surface