Histology Lecture 3

Tissues

Cells organized into more complex units

Histology

Groups of similar cells and extracellular material

Physical Protection

Protects external and internal surfaces

Selective permeability

Relatively impermeable to some substances

Secretions

• May be scattered among other cell types

• May form exocrine or endocrine glands

Sensations

• Contain nerve endings

• Specialized epithelium, termed neuroepithelium

• House cells responsible for sight, taste, smell, hearing,equilibrium

Epithelium

• Composed of one or more layers of closely packed cells

• Little/no extracellular matrix

Cellularity

• Composed almost entirely of tightly packed cells

Polarity

• Has apical surface-modifications

• Lateral surface with intercellular junctions

• Has basal surface

Basement Membrane

• Contains collagen fibers and specific proteins and carbohydrates

• Forms a selective barrier between epithelium and connective tissue

Avasularity

How does chemical change occur

Extensive innervation

Detects changes in the environment in that region

High regeneration capacity

• Frequent mitosis of deepest epithelial cells

• Stem cells, adjacent to basement membrane

• Continual replacement of lost cells

Simple epithelium

• Found where filtration, absorption, or secretion primary function

• Ex; lining of air sacs of lungs, intestines, blood vessels

Stratified epithelium

• Found in areas subjected to mechanical stress

• Ex; skin, lining of the pharynx, esophagus

• Cells in basal layer continuously regenerate

Pseudostratified epithelium

• Type of simple epithelium

• All cells attached to basement membrane but appears layered

• Some cells not reaching apical surface

Squamos cells

• Arranged like flattened floor tiles

• Nucleus flattened

Cuboidal cells

Nucleus spherical and in center of cell

Columnar cells

Nucleus oval

Transitional Cells

• Occur where epithelium stretches and relaxes

• Polyhedral in shape when epithelium relaxed

• More flattened when epithelium stretched

Simple Columnar Epithelium

• Single layer of columnar cells

• Ideal for secretory and absorptive function

• Can be conciliated or ciliated

Conciliated

• Often contains microvilli-brush border

• Often contains unicellular glands, termed goblet cells

• Secrete glycoprotein, mucin

• Lines most of digestive tract from stomach to anal canal

Ciliated

• Has cilia projecting from apical surface

• Move mucus along

• Goblet cells interspersed

• Present in the bronchioles

• Lines uterine tubes

• Helps move oocyte from ovary to uterus

• Houses goblet cells

• Found in large passageways of the respiratory system

Pseudostratified Columnar Epithelium

• Appears to consist of multiple cell layers

• Not really stratified

• Can be ciliated or conciliated

Conciliated

• Lacks goblet cells and cilia

• Occurs mainly in male urethra and epididymis

Stratified squamous epithelium

• Protects against abrasion and friction

• Has multiple cell layers; only deepest in direct contact with basement membrane

• Apical cells with squamous shape

• Basal layers with cubical shape

• Stem cells in basal layer that continuously divide

• Replace lost cells

• Exists in nonkeratinized and keratinized forms

Transitional Epithelium

• Limited to the urinary tract

• In relaxed and stretched state

• Contains binucleate cells (two nuclei)

• Allows for stretching as bladder fills

Connective Tissue

• Most diverse, abundant, widely distributed tissue

• Designed to support, protect, and bind organs

• All with cells, protein fibers, and ground substance

• Examples include: tendons and ligaments, body fat, cartilage and bone, blood

• Three basic components: cells, protein fibers, and ground substance

Cells in a Supportive Matrix

• Each class of connective tissue with specific types of cells

• Most cells not in direct contact with each other

Fibroblasts

• Produce fibers and ground substance of extracellular matrix

• Flat cells with tapered ends

Adipocytes

• Appear in small clusters with some types of connective tissue proper

• If dominate an area, tissue termed adipose connective tissue

Mesenchymal Cells

• Type of embryonic cell

• Divided cell becomes committed connective tissue cell

Fixed macrophages

Derived from monocytes, type of white blood cells

Wandering Cells

Are primarily types of leukocytes, white blood cells

Mast cells

• Small, mobile cells close to blood vessels

• Secrete heparin and histamien

Plasma cells

• Formed when B-lymphocytes activated by foreign material

• Produce antibodies

Free macrophages

• Mobile phagocytic cells

• Function like fixed macrophages

Other leukocytes

• Include neutrophils

• Include lymphocytes

Protein fibers

Strengthen and support tissue

Collagen Fibers

• Unbranched, strong, flexible and resistant to stretching

• Appear white in fresh tissue

• Numerous in tendons and ligaments

Reticular fibers

• Similar to collagen fibers but thinner

• Form branding, interwoven framework

• Tough but flexible

• Abundant in storma of: lymph nodes, spleen and liver

Elastic fibers

• Yellow in color when fresh

• Help structures return to normal shape after stretching

• Found in skin, lungs and arteries

Physical Protection

Bones and adipose tissue

Support and structural framework

• Bones and cartilage

• Supportive tissues around kidney and spleen

Binding of structures

• Ligaments and tendons

• Dense irregular tissue anchoring skin to muscle and bone

Storage

Adipose tissue and bone

Transport

Blood carrying nutrients, gases, wastes

Immune protection

• Leukocytes protecting body against disease

• Extracellular matrix restricting movement of infectious organisms