Lecturer Dr. Twana A. Mustafa Histology Lecturer Dr. Twana A. Mustafa

Why Study Histology? Knowing the difference between normal and abnormal tissue is the first step in diagnosis and treatment of patients.

Tissues: groups of cells closely associated that have a similar structure and perform a related function Tissue classification based on structure of cells, composition of noncellular extracellular matrix, and cell function Major types of adult tissues Epithelial Connective Muscle Nervous Histology: Microscopic Study of Tissues Biopsy: removal of tissues for diagnostic purposes Autopsy: examination of organs of a dead body to determine cause of death

* made of all four tissue types Skin, our largest organ * made of all four tissue types

Embryonic Tissue 3 major germ layers that form the embryonic disc (source of stem cells) Endoderm Inner layer Forms lining of digestive tract and derivatives Mesoderm Middle layer Forms tissues as such muscle, bone, blood vessels Ectoderm Outer layer Forms skin and neuroectoderm

Epithelial tissue Cellularity - Consists almost entirely of cells Covers body surfaces, lines hollow organs, and forms glands Outside surface of the body Lining of digestive, respiratory and urogenital systems Heart and blood vessels Linings of many body cavities Polarity - Has apical, basal, and lateral surfaces Rests on a basement membrane Specialized cell contacts bind adjacent cells together Avascular - no blood vessels Regenerative -Replaces lost cells by cell division

Locations of Epithelial Tissues Covers the body (epidermis) Found on the inside of hollow organs and the outside of all organs Found above a connective tissue layer (epi = above) Lines the cavities, tubes, ducts, and blood vessels inside the body

Functions of Epithelia Protecting underlying structures; e.g., epithelium lining the mouth Acting as barriers; e.g., skin Permitting the passage of substances; e.g., cells lining air sacs in lungs and nephrons in kidney Secreting substances; e.g., pancreatic cells Absorbing substances; e.g., lining of stomach and small intestine

Terms referring to the layers Terms that help us understand what kinds of tissues we are identifying: Terms referring to the layers Simple = one layer Stratified = more than one layer Pseudostratified = false layered (appears to be more than one layer, but only one); ciliated = with cilia Terms referring to the cell shapes Squamous = flat Cuboidal = cube Columnar = rectangular (column) Transitional = ability to change shape

Classification of Epithelium Number of layers of cells Simple- one layer of cells. Each extends from basement membrane to the free surface Stratified- more than one layer. Pseudostratified- tissue appears to be stratified, but all cells contact basement membrane so it is in fact simple Shape of cells Squamous- flat, scale-like Cuboidal- about equal in height and width Columnar- taller than wide

Apical surface Basal surface Simple Apical surface Basal surface Stratified Classification based on number of cell layers.

Squamous Cuboidal Columnar Classification based on cell shape.

The following types of epithelial tissues are covered in this activity: 1. Simple squamous epithelial tissue (lungs) 2. Simple cuboidal epithelial tissue (kidneys) 3. Simple columnar epithelial tissue (small intestine) 4. Pseudostratified (ciliated) columnar epithelial tissue (trachea lining) 5. Stratified squamous epithelial tissue (mouth lining) 6. Stratified cuboidal epithelial tissue (salivary glands, sweat glands) 7. Stratified columnar epithelial tissue (male reproductive tract) 8 Transitional epithelial tissue (bladder) a. The tissue may show a full bladder b. The tissue may show an empty bladder

Figure 4.3a Epithelial tissues. (a) Simple squamous epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (125x). Air sacs of lung tissue Nuclei of squamous epithelial cells

Figure 4.3b Epithelial tissues. (b) Simple cuboidal epithelium Description: Single layer of cubelike cells with large, spherical central nuclei. Simple cuboidal epithelial cells Function: Secretion and absorption. Basement membrane Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (430x).

Figure 4.3c Epithelial tissues. (c) Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus- secreting unicellular glands (goblet cells). Simple columnar epithelial cell Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Basement membrane Photomicrograph: Simple columnar epithelium of the stomach mucosa (860X).

Figure 4.3d Epithelial tissues. (d) Pseudostratified columnar epithelium Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus- secreting cells and bear cilia. Cilia Mucus of mucous cell Pseudo- stratified epithelial layer Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in male’s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Basement membrane Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (570x). Trachea

Stratified Epithelia Contain two or more layers of cells Regenerate from below Major role is protection Are named according to the shape of cells at apical layer

Figure 4.3f Epithelial tissues. (f) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch. Transitional epithelium Function: Stretches readily and permits distension of urinary organ by contained urine. Location: Lines the ureters, urinary bladder, and part of the urethra. Basement membrane Connective tissue Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine.

Epithelium: Glandular A gland is one or more cells that makes and secretes an aqueous fluid Two types of glands formed by infolding of epithelium: Endocrine: no contact with exterior of body; ductless; produce hormones (pituitary, thyroid, adrenals, pancreas) Exocrine: open to exterior of body via ducts (sweat, oil) Exocrine glands classified either by structure or by the method of secretion Classified by structure Unicellular: goblet cells Multicellular: sweat, oil, pituitary, adrenal

Multicellular Exocrine Glands Classified on the basis of types of ducts or mode of secretion Types of ducts Simple: ducts with few branches Compound: ducts with many branches If ducts end in tubules or sac-like structures: acini. Pancreas If ducts end in simple sacs: alveoli. Lungs