 Define tissue  Describe the germ tissue layers, their location, and what tissues they produce in eucoelomate animals (humans).  List the 4 major types of tissues of the human body.  Describe the characteristics, cell types, function, and the location of epithelial tissues.  Describe the characteristics, cell types, functions, and the location of connective tissues.  Describe the characteristics, cell types, functions, and the location of muscle tissues.  Describe the characteristics, cell types, functions, and the location of nervous tissues.

 Histology is defined as the study of the microanatomy of animal and plant tissues  A tissue is a group of like cells of similar specialized structure which carry out similar specific functions.

 We all start as a single cell called a zygote.  This cell begins to divide, and gives rise to germ cells or stem cells that eventually form the developing embryo.  Because humans are eucoelomate (true body cavity) animals, like earthworms, we have three germ tissue layers: A. Endoderm B. Mesoderm C. Ectoderm

 The endoderm layer is the innermost layer, which forms the epithelial lining in our digestive tract from mouth to rectum.  The endoderm also forms many organs: the stomach, the liver, the pancreas, the urinary bladder, the epithelial parts of trachea, the lungs, and the intestines

 The mesoderm layer is the middle layer.  It surrounds the endoderm layer develops into our large body cavities.  The mesoderm also gives rise to: muscle, bone, connective tissue, adipose tissue, the circulatory system, the kidneys, the dermis

 The ectoderm layer is the outermost layer.  It is the tissue layer which gives rise to our skin, hair, nails, eyes and nervous tissue (brain, spinal chord, nerves).

 A tissue is a group of cells with similar specialized structure which carry out specific functions.  Groups of tissues compose and work together to form organs.  All organs are composed of two or more types of tissues.  There are four major tissue types: 1. Epithelial 2. Connective 3. Muscle 4. Nervous

 General Locations  Body coverings  Body linings  Glandular tissue  Including:  Skin, lining of trachea, esophagus, urinary bladder, and digestive tract, sweat glands, kidneys

 General Functions a. Protection b. Absorption c. Filtration d. Secretion

 Functions (continued): e. These cells are rapidly dividing because they are constantly being sloughed away or rubbed off. f. Therefore they must constantly be replaced.

 General Characteristics: a. Cells fit closely together and often form sheets b. The apical (top) surface is the free surface of the tissue i. They face the air (skin, lungs) or a fluid- filled organ cavity (the lumen of the gut). ii. Apical ends may have cilia or be highly folded to increase surface area (microvilli).

 Characteristics (cont’d): d. The basal (lower layer) consists of germ cells, which are constantly dividing to produce new cells. e. The basal surface of the epithelium rests on a basement membrane. i. Basement membrane: a layer of extracellular matrix and proteins (desmosomes) anchoring the epithelium to the connective tissue underneath

Apical surface of simple cuboidal epithelial with microvilli present. Basement membrane where the cells are attached to the non-living basal lamina. Nucleus Microvilli

 Characteristics (cont’d): e. Epithelial are avascular (no direct blood supply) f. Regenerate easily if well nourished (by diffusion through other cells)

Apical surface Basal surface Simple Apical surface Basal surface Stratified (a) Classification based on number of cell layers Figure 3.17a

 Epithelial tissues are classified in two ways: A. Number of cell layers B. Shape of cells

A. Number of cell Layers: i. Simple epithelial tissues are only one cell layer thick. ii. Stratified epithelial tissues are several layers thick. iii. Pseudostratified epithelial tissues looks like multiple layers, but on close examination are actually only one cell layer thick.

 c. Pseudostratified epithelial tissues appear to be composed of multiple layers but on close examination are actually only one cell layer thick.

 Classification by shape – three basic shapes: a. Squamous b. Cuboidal c. Columnar

a. Squamous - flattened cells, fried egg shape in appearance.

b. Cuboidal - square or cubed shaped. Cells are as wide as they are tall.

c. Columnar - cells are taller than they are wide. Shaped like columns or rectangles.

 Epithelial tissues are named in the following manner: 1. First word: Number of layers (simple, stratified, pseudostratified) 2. Second word: Shape of cell (squamous, cuboidal, columnar) 3. Third word: Describes the apical surface; if there are structures (cilia or microvilli) or materials present (keratin).

 You can tell a lot about a tissue from its name  For example: pseudostratified columnar ciliated epithelium  What can you tell from the name about the tissue? 1. It is one cell-layer thick 2. It is column shaped. 3. It has cilia on its apical surface

I. Simple Squamous II. Simple cuboidal III. Simple Columnar IV. Stratified Squamous I. Non-keratinized II. Keratinized V. Pseudostratified columnar VI. Stratified transitional VII. Glandular

a. Name: Simple squamous epithelium  Single layer of flat cells b. Location: usually forms membranes Lines body cavities Lines lungs and capillaries c. Function: diffusion, filtration, or secretion in membranes

d. Unique Facts:  Found lining blood vessels and is called endothelium.  Found in alveoli (or “air sacks”) of the lungs.  Allows the rapid exchange of materials by diffusion and osmosis from cell to cell.

Figure 3.18a Nucleus of squamous epithelial cell Basement membrane (a) Diagram: Simple squamous Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (185×). Nuclei of squamous epithelial cells Air sacs of lungs

a. Name: Simple cuboidal epithelium  Single layer of cube-like cells b. Locations: Common in glands and their ducts Form walls of kidney tubules Covers the ovaries c. Functions: secretion and absorption; ciliated types propel mucus or propel reproductive cells

d. Unique Facts:  Simple cuboidal cells are common in secretory glands and ducts  Found in the walls of kidney tubules where they are involved with reabsorption of materials as urine is being produced  Found on the surface of mammalian ovaries, where their ciliated surfaces move the ovum (egg cell) from the co

Figure 3.18b (b) Diagram: Simple cuboidal Nucleus of simple cuboidal epithelial cell Photomicrograph: Simple cuboidal epithelium in kidney tubules (250 × ). Basement membrane Connective tissue Basement membrane Simple cuboidal epithelial cells

a. Name: Simple columnar epithelium  Single layer of tall cells  Often includes mucus-producing goblet cells b. Location: lines digestive tract c. Functions: in secretion and absorption; ciliated types propel mucus or reproductive cells; microvillate types absorb nutrients

d. Unique Facts:  Commonly found in the lining of the small and large intestine where it is involved with absorption of molecules from digested food and re-absorption of water.  Some are microvillate (have microvilli on their apical surface)

microvilli on apical surface  Microvillate epithelium: In the small intestine the apical surface of these cells have microvilli present on their surface and specialized gland cells called goblet cells which produce and secrete mucus.

microvilli on apical surface

 Stratified cuboidal and columnar epithelia:  Rare in human body  Found mainly in ducts of large glands  Stratified cuboidal — two layers of cuboidal cells; functions in protection  Stratified columnar — surface cells are columnar, cells underneath vary in size and shape; functions in protection

a. Name: Stratified squamous epithelium  Cells at the apical surface are flattened b. Functions: as a protective covering where friction is common c. Locations: linings of the… i.Skin ii.Mouth iii.Esophagus

Figure 3.18e Stratified squamous epithelium Basement membrane (e) Diagram: Stratified squamous Photomicrograph: Stratified squamous epithelium lining of the esophagus (140×). Connective tissue Stratified squamous epithelium Nuclei Basement membrane

d. Unique Facts:  Present in areas where there is wear and tear on the tissue, where cells are continually being sloughed away, (or rubbed off) by abrasion.  Two types of stratified squamous epithelial tissue: Keratinized and Non-keratinized.

e. Stratified squamous non-keratinized epithelium:  Lines the oral cavity and the esophagus and the vagina of the female reproductive system.  The surface of these epithelia are moist and protected by mucosa

f. Stratified squamous keratinized epithelium  Keratin is a layer a waterproof protein  Produced on the apical surface of these epithelia

a. Name: Pseudostratified columnar  Single layer, but some cells are shorter than others  Often looks like a double layer of cells but all cells rest on the basement membrane b. Location: respiratory tract, where it is ciliated c. Functions: in absorption or secretion

d. Unique Facts:  Can be ciliated: The apical surface of these cells have tiny, hair-like projections called cilia, which are involved with the movement across the surface of the cells.

Figure 3.18d Pseudo- stratified epithelial layer Basement membrane (d) Diagram: Pseudostratified (ciliated) columnar Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (430×). Pseudo- stratified epithelial layer Basement membrane Connective tissue Cilia

a. Name: Transitional epithelium  Composed of modified stratified squamous epithelium  Shape of cells depends upon the amount of stretching b. Location: lines organs of the urinary system c. Functions: stretching and the ability to return to normal shape

d. Unique Facts:  This epithelium is unique to the urinary bladder and a small portion of the ureters.  It has the unique property of expansion and contraction.  This allows the tissue to adjust to the urinary bladder’s expansion and contraction when it is full or empty.

Figure 3.18f Transi- tional epithelium Basement membrane Photomicrograph: Transitional epithelium lining of the bladder, relaxed state (215×); surface rounded cells flatten and elongate when the bladder fills with urine. (f) Diagram: Transitional Connective tissue Transitional epithelium Basement membrane

 Glands  One or more cells responsible for secreting a particular product  Secretions contain protein molecules in an aqueous (water- based) fluid

 Two major gland types: 1. Endocrine gland Ductless since secretions diffuse into blood vessels All secretions are hormones 2. Exocrine gland Secretions empty through ducts to the epithelial surface Include sweat and oil glands