Tissues and Histology Tissues - collections of similar cells with same embryonic origin performing a similar function

Tissues and Histology Tissues - collections of similar cells with same embryonic origin performing a 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

I. 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

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

Special Characteristics of Epithelia Figure 4.1

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

Classifications of Epithelia

Simple Squamous Epithelium Figure 4.3a

Simple Cuboidal Epithelium Figure 4.3b

Simple Columnar Epithelium Figure 4.3c

Pseudostratified Ciliated Columnar Epithelium Figure 4.3d

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

Stratified Squamous Epithelium Description Many layers of cells – squamous in shape Deeper layers of cells appear cuboidal or columnar Thickest epithelial tissue – adapted for protection

Stratified Squamous Epithelium Specific types Keratinized – contain the protective protein keratin Surface cells are dead and full of keratin Non-keratinized – forms moist lining of body openings

Stratified Squamous Epithelium Function – Protects underlying tissues in areas subject to abrasion Location Keratinized – forms epidermis Non-keratinized – forms lining of esophagus, mouth, and vagina

Stratified Squamous Epithelium Figure 4.3e

Transitional Epithelium Figure 4.3h

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

Lateral Surface Features Tight junctions Desmosomes Gap junctions

Membrane Junctions: Tight Junction Integral proteins of adjacent cells fuse together Completely encircle the cell and form an adhesion belt. Form an impermeable junction. Common near apical region

Lateral Surface Features – Cell Junctions Desmosomes – two disc-like plaques connected across intercellular space Plaques of adjoining cells are joined by proteins called cadherins Proteins interdigitate into extracellular space Intermediate filaments insert into plaques from cytoplasmic side

Membrane Junctions: Desmosome Linker proteins extend from plaque like teeth of a zipper. Intermediate filaments extend across width of cell. Common in superficial layers of skin; skin peels after a sunburn Reduces chance of tearing, twisting, stretching Figure 3.5b

Membrane Junctions: Gap Junction Connexon proteins are trans- membrane proteins. Present in electrically excitable tissues (heart, smooth muscle)

Basal Feature: The Basal Lamina  Noncellular supporting sheet between the epithelium and the connective tissue deep to it  Consists of proteins secreted by the epithelial cells  Functions:  Acts as a selective filter, determining which molecules from capillaries enter the epithelium  Acts as scaffolding along which regenerating epithelial cells can migrate  Basal lamina and reticular layers of the underlying connective tissue deep to it form the basement membrane

Epithelial cells Basal lamina Collagen fibers

Epithelial Surface Features Apical surface features Microvilli – finger-like extensions of plasma membrane Abundant in epithelia of small intestine and kidney Maximize surface area across which small molecules enter or leave Cilia – whip-like, highly motile extensions of apical surface membranes Movement of cilia – in coordinated waves

Connective Tissue

Connective Tissue Most diverse and abundant tissue Main classes Connective tissue proper Cartilage Bone tissue Blood Characteristics Vascular Nonliving extracellular matrix, consisting of ground substance and fibers Cells are not abundant as in epithelium

Connective Tissue: Embryonic Origin Figure 4.5

Functions of Connective Tissue Enclose organs as a capsule and separate organs into layers - Areolar Connect tissues to one another - Tendons and ligaments. Support and movement - Bones Storage and Insulation - Fat Transport - Blood Protection - Bone, cells of the immune system

Structural Elements of Connective Tissue Ground substance – unstructured material that fills the space between cells Fibers collagen elastic reticular Cells fibroblasts chondroblasts osteoblasts hematopoietic stem cells, and others

Connective Tissue Cells Fibroblasts - secrete the proteins needed for fiber synthesis and components of the extracellular matrix Adipose or fat cells (adipocytes). Common in some tissues (dermis of skin); rare in some (cartilage) Mast cells. Common beneath membranes; along small blood vessels. Can release enzymes in response to injury. Leukocytes (WBC’s). Respond to injury or infection Macrophages - Phagocytic; provide protection Chondroblasts - form cartilage Osteoblasts - form bone Hematopoietic stem cells - form blood cells

Extracellular Matrix - ECM ECM has 3 major components 1. Protein fibers 2. Ground substance 3. Fluid Protein fibers Collagen fibers. Made of protein collagen. Strong, flexible, inelastic; great tensile strength (i.e. resist stretch). Perfect for tendons, ligaments Elastic fibers. Made of protein elastin that resemble coiled springs. Found in lungs, large blood vessels Reticular fibers. Made from fine collagenous fibers; fill spaces between tissues and organs.

Ground Substance Interstitial fluid within which are one or more of the molecules listed below: Hyaluronic acid: a polysaccharide. Very slippery; serves as a good lubricant for joints. Proteoglycans: protein and polysaccharide complex. Able to trap large amounts of water. Adhesive molecules: hold proteoglycan aggregates together. Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells

Areolar Connective Tissue Figure 4.12b

Adipose Tissue Figure 4.12c

Reticular Connective Tissue Figure 4.12d

Dense Irregular Connective Tissue Figure 4.12e

Dense Regular Connective Tissue Figure 4.12f

Connective Tissue: Cartilage Composed of chondrocytes (cells) located in matrix-surrounded spaces called lacunae. Type of cartilage determined by components of the matrix. Firm consistency. Ground substance: Proteoglycans and hyaluronic acid complexed together trap large amounts of water (microscopic sponges). Allows tissue to spring back after being compressed. Avascular and no nerve supply. Heals slowly. Types of cartilage Hyaline Fibrocartilage Elastic

Hyaline Cartilage Figure 4.12g

Elastic Cartilage Figure 4.12h

Fibrocartilage Figure 4.12i

Tissues and Aging Cells divide more slowly Collagen fibers become more irregular in structure, though they may increase in number Tendons and ligaments become less flexible and more fragile Elastic fibers fragment, bind to calcium ions, and become less elastic Arterial walls and elastic ligaments become less elastic Changes in collagen and elastin result in Atherosclerosis and reduced blood supply to tissues Wrinkling of the skin Increased tendency for bones to break Rate of blood cell synthesis declines in the elderly Injuries don’t heal as readily

Bone Tissue Figure 4.12j

Blood Tissue Figure 4.12k

Muscle Tissue Characteristics Cells are referred to as fibers Contracts or shortens with force when stimulated Moves entire body and pumps blood Types Skeletal:attached to bones Cardiac: muscle of the heart. Smooth: muscle associated with tubular structures and with the skin. Nonstriated and involuntary.

Skeletal Muscle Tissue Figure 4.14a

Cardiac Muscle Tissue Figure 4.14b

Smooth Muscle Tissue Figure 4.14c

Nervous Tissue Figure 4.15

Tissues and Aging Cells divide more slowly Collagen fibers become more irregular in structure, though they may increase in number Tendons and ligaments become less flexible and more fragile Elastic fibers fragment, bind to calcium ions, and become less elastic Arterial walls and elastic ligaments become less elastic Changes in collagen and elastin result in Atherosclerosis and reduced blood supply to tissues Wrinkling of the skin Increased tendency for bones to break Rate of blood cell synthesis declines in the elderly Injuries don’t heal as readily