Tissues -Whole body contains only 200 different cells types that are organized into tissues Four primary tissue classes –epithelial tissue –connective tissue –muscular tissue –nervous tissue The extracellular fluid surrounding the cells within tissue is called interstitial fluid Histology (microscopic anatomy) –study of tissues and how they form organs

Epithelial Tissue -Covers the entire surface of the body –includes skin, lining of the lung, lining of the digestive tract, lining of the urinary tract, lining of the reproductive tract -barrier between what is IN the body and what is OUT of the body -controls what substances enter/exit the body and what substances stay in/out of the body Primary tissue type found in glands –exocrine glands secrete substances outside of the body (sweat, salivary, digestive) –endocrine glands secrete substances (hormones) into the blood (thyroid, adrenal, pituitary, pancreas

Epithelial Tissue: Basic Structure Made of epithelial cells that are connected to adjacent cells by proteins called tight junctions –make the tissue leakproof –create “sheets” of epithelial cells –similar in structure to a six-pack of cans Epithelial cell surfaces face 2 different environments –apical surface of the cell faces toward the OUTSIDE of the body –basal surface of the cell faces toward the INSIDE of the body Anchored to the body by a structure called the basement membrane

Classification of Epithelial Tissues Epithelial tissue is classified based on 2 criteria: Cell shape –squamous (flattened cells) cell width is larger than cell height –cuboidal (cube-like cells) cell width is equal to cell height –columnar (column-like cells) cell height is larger than cell width

Classification of Epithelial Tissues Number of layers of epithelial cells –Simple one cell layer thick transports substances into or out of the body –Stratified more than one cell layer thick protects body from mechanical damage (abrasion, puncture…) –Pseudostratified one cell layer thick made of different cell types

Epithelia: Simple Squamous single layer of squamous epithelial cells with flat nuclei Small intestine and cheek

Epithelia: Simple Cuboidal single layer of cuboidal epithelial cells with spherical nuclei Kidney

Epithelia: Simple Columnar single layer of columnar cells with oval nuclei Interior of small intestine

Epithelia: Pseudostratified Columnar single layer of cells with different heights; some do not reach the surface of the body the shape of the nuclei is similar to the shape of the cell Trachea

Epithelia: Stratified Squamous thick epithelium composed of several layers of squamous cells with flat nuclei Vagina

Epithelia: Stratified Cuboidal and Columnar Rare in the body Stratified cuboidal –2-3 layers of cuboidal cells with spherical nuclei Sweat gland

Epithelia: Transitional The shape of the cells change based on the amount of stress (stretch) on the tissue can appear as cuboidal or columnar when not stretched or squamous when stretched Umbilical cord and Urinary bladder

Connective Tissue -Most abundant and variable tissue type Consists of widely spaced cells separated by fibers and ground substance -4 primary types –Connective tissue proper characterized by histological appearance –loose –dense –Cartilage –Bone –Blood Functions –connects organs to each other –gives support & protection (physical & immune) –storage of energy & heat production –transport of materials

Structural Elements of Connective Tissue 3 structural elements (components) of connective tissue Ground substance unstructured (gel-like) material that fills the space between cells (interstitial space) Fibers very large proteins outside of the cell which make a web-like structure to hold the tissue together -Ground substance + fibers = Extracellular Matrix Cells create the extracellular matrix by exocytosis

Structural elements of connective tissue

Fibers 3 primary types of extracellular protein fibers Collagen –very thick and strong, do not stretch –provides tough structure to tissue Elastic –thin and strong, allow for stretch and then recoil (return to original length) when released –made from the protein elastin Reticular –thin collagen fibers –provide delicate structure to tissue

Cells There are 4 different cell types which are responsible for making the 4 different types of connective tissue Fibroblasts –connective tissue proper Chondroblasts –cartilage Osteoblasts –bone Hemocytoblast –blood blast = “to build”

Loose Connective Tissue Proper: Areolar Walls of abdomen

Loose Connective Tissue Proper: Adipose stores lipids for use as fuel, insulates and protects Under skin

Loose Connective Tissue Proper: Reticular Kidney

Dense Connective Tissue Proper: Regular many parallel collagen fibers with a few elastic fibers attaches muscles to bone (tendons) and bone to bone (ligaments) Tendons and ligaments

Dense Connective Tissue Proper: Irregular many non-parallel collagen fibers with a few elastic fibers Skin - Dermis

Connective Tissue: Cartilage 3 types –Hyaline –Fibrocartilage –Elastic made of chondrocytes found in a lacuna (“pit”) within the firm but flexible extracellular matrix comprised of a network of collagen fibers

Ossification is the gradual replacement of cartilage with bone Occurs slowly so that by adulthood cartilage remains in a limited number of places - such as the ears, trachea, nose and between the bones