Histo 2) Epithelium

What is epithelium and where is it found?

A cluster or sheet of structurally similar closely attached cells with little intercellular space that covers body surfaces and lines cavities and tubes while attaching to underlying connective tissue

What does epithelial polarity and avascularity mean?

Epithelial cells have distinct apical-lateral-basal regions and contain no blood or lymphatic vessels /

nutrients and oxygen diffuse from vessels in underlying CT / nerve endings may be present

How are epithelial cells maintained and what changes can they undergo?

Cells are continually shed and replaced often by stem-cell mitosis near CT /

sensitive to environmental conditions: epithelia can undergo atrophy / hypertrophy / hyperplasia / metaplasia / dysplasia / specialized epithelia include glandular / myoepithelial / neuroepithelial / germinal

How do simple and stratified epithelia differ and how are they named?

Simple = one layer with all cells touching basal lamina and named by cell shape / Stratified = multiple layers with only basal cells touching basal lamina and named by surface-cell shape

How should you identify and classify epithelium on a histology slide?

Look along tissue edges or lumens → find the boundary with CT → determine number of layers → determine cell shape using cell borders or flat-round-oval nuclear shape

What are the appearance function and locations of simple squamous epithelium?

One layer of thin flat cells with flat nuclei / diffusion-filtration-ion or gas exchange / blood and lymphatic vessels / lung alveoli / kidney nephron / body cavity linings / vessel lining = endothelium / body cavity lining = mesothelium

What are the appearance function and locations of simple cuboidal epithelium?

One layer of square cells with round nuclei / secretion and absorption function / glands / gland ducts / lung bronchioles / kidney nephrons / microvilli or cilia may be present

What are the appearance function and locations of simple columnar epithelium?

One layer of tall cells with oblong nuclei / secretion and absorption function/ stomach / intestines / gallbladder / uterus-uterine tube / bronchioles / microvilli or cilia may be present

What are the appearance function and locations of pseudostratified epithelium?

One layer with all cells touching basal lamina but nuclei at different heights create a false multilayered appearance / secretion or absorption / trachea-bronchi and male reproductive system including ductus deferens / cilia or microvilli may be present

What are the appearance function and locations of nonkeratinized stratified squamous epithelium?

Multiple layers with flat nucleated surface cells /

function- protection from abrasion and irritation in moist areas

/ oral cavity / esophagus / anal canal / vagina / cornea / internal areas continuous with epidermis

What are the appearance function and locations of keratinized stratified squamous epithelium?

Multiple layers with dead flat anucleated keratin-filled surface cells /

function- protection from abrasion and irritation /

epidermis and hard palate

What are the appearance function and locations of transitional epithelium?

Multilayered urothelium with rounded dome-shaped umbrella cells that flatten during distension but never become as flat as stratified squamous /

function- protects from urine and permits stretching

/ bladder / ureter / urethra

What are stratified cuboidal and stratified columnar epithelia?

Multilayered epithelia named by cuboidal or columnar surface cells /

mainly protective /

found in transition areas such as gland ducts and are not commonly present

What are the basal lamina and basement membrane?

Basal lamina = specialized extracellular fibrous sheet with fibers and sticky molecules attaching epithelium to CT

basement membrane = thick visible version under LM and consists of basal lamina plus reticular lamina when resolved by EM

What are the major functions of the basal lamina?

Anchors and supports epithelium / filters material between epithelium and CT / attachment is required for normal epithelial function / provides a scaffold for regeneration after injury

What other cells have a basal lamina and why is it clinically important?

Adipose / muscle / Schwann cells produce an external lamina and basal-lamina disruption occurs in diseases of lung / kidney / vascular system / skeletal muscle / cancer

What are cilia and what do they do?

Motile microtubule projections with a 9+2 doublet axoneme and 9-triplet basal body / move mucus in respiratory tract / ovum in female tract / CSF in ventricles / sperm flagellum is related

What are microvilli and what are their alternate names?

Stiff actin-microfilament projections that increase surface area mainly for absorption / striated border = small intestine / brush border = kidney / stereocilia = very long microvilli in male reproductive system

What are the terminal web and terminal bar?

Terminal web = apical microfilament layer that anchors microvilli /

terminal bar = junctional complex visible by light microscopy where several junction types occur together

What is a tight junction or zonula occludens?

Most apical junction that completely encircles the cell and seals adjacent membranes

/ blocks paracellular passage / creates blood-tissue barriers / separates apical from basolateral membrane domains

What is an intermediate junction or zonula adherens?

Encircling junction containing actin and cadherin-family proteins / anchors terminal-web actin to the membrane / stabilizes cytoskeleton and nearby tight junctions / present as fascia adherens in cardiac muscle

What is the difference between desmosomes and hemidesmosomes?

Desmosomes or macula adherens are strong spot cell-to-cell attachments linked to intermediate filaments and also occur in smooth-cardiac muscle / hemidesmosomes are half-desmosome-like attachments anchoring epithelial cells to basal-lamina proteins

What is a gap junction?

Communicating or nexus junction forming channels between neighboring cells / allows ions and small regulatory molecules to pass directly between cells / electrically couples cells / also important in smooth and cardiac muscle

What is special about the ileum plastic section and what should you identify?

Plastic embedding produces thinner sections with better high-power resolution / identify simple columnar / microvilli-striated border / terminal bars / simple squamous epithelium

What are atrophy hypertrophy and hyperplasia?

Atrophy = decreased cell size and organelles / hypertrophy = increased cell size and organelles with increased function / hyperplasia = increased cell number in cells capable of division

What is metaplasia?

Reversible replacement of one fully differentiated cell type by another after stress such as cigarette smoke / stem cells are reprogrammed so normal-appearing tissue better suited to the stress appears in the wrong location

What is dysplasia?

Disordered abnormal tissue maturation with altered cell size-shape called pleomorphism / abnormal architecture / increased mitotic figures / possibly reversible but considered precancerous

What is a neoplasm and how is it classified?

New uncontrolled cell proliferation classified using resemblance to precursor cells / growth rate and mitotic activity including abnormal mitotic locations / ability to invade and metastasize

How do benign and malignant neoplasms differ?

Benign tumors are localized and usually differentiated without invasion or metastasis / malignant tumors invade nearby tissue and can metastasize to distant sites

What is anaplasia and how do malignant epithelial cells change?

Anaplasia = loss of differentiated characteristics / malignant epithelial cells can lose polarity and cell junctions / separate from neighboring cells / detach from basement membrane / become motile

What are the benign and malignant names for epithelial and glandular tumors?

Epithelium: epithelioma → carcinoma /

Glandular epithelium: adenoma → adenocarcinoma

What tumor names are listed for connective adipose cartilage bone and adult CNS glia?

Connective: fibroma → fibrosarcoma / Adipose: lipoma → liposarcoma / Cartilage: chondroma → chondrosarcoma / Bone: osteoma → osteosarcoma / Adult CNS glia: glioma → glioblastoma

What is a sarcoma?

A malignant neoplasm derived from mesenchyme which is embryonic connective tissue

What is carcinoma in situ?

A carcinoma with abnormal anaplastic cells of varying size and shape plus many mitotic figures that remains confined to the epithelium above an intact basal lamina

How does an epithelial carcinoma metastasize?

Cells lose polarity and junctions → detach → secrete proteases to breach basal lamina → enter CT → become amoeboid and migrate → enter blood or lymphatic vessels → reach distant sites

What are exocrine glands?

Epithelial cells specialized to secrete a product onto an epithelial surface / may be isolated cells or multicellular glands connected to the surface by epithelial ducts / examples studied include salivary glands and pancreas

What are goblet cells and how do they look?

Unicellular mucus-secreting cells scattered in epithelial sheets

/ appear clear or empty because mucus dissolves during processing / dark heterochromatic nucleus lies at the base / identify in small intestine and trachea

What are serous cells and how do they look?

Cells secreting watery protein-rich material / basophilic granular cytoplasm / round nucleus at the base

What are mucous cells and how do they look?

Mucus-secreting cells with clear cytoplasm and a flat heterochromatic nucleus at the base

How are serous mucous and mixed glands classified?

Serous gland = only serous cells / Mucous gland = only mucous cells / Mixed or seromucous gland = both serous and mucous cells

How do you recognize a gland duct?

Look for an open lumen surrounded by epithelial cells / duct epithelium can range from simple to stratified squamous

What is a serous demilune?

A crescent-shaped group of serous cells associated with mucous secretory units in a mixed gland

How can you quickly distinguish serous mucous and mixed glands histologically?

Serous = darker basophilic granular cells with round basal nuclei / Mucous = pale-clear cells with flat dark basal nuclei / Mixed = both cell types

Why is simple squamous epithelium well suited for diffusion and filtration?

Its extremely thin flat cells create a short barrier for rapid exchange

Why are cuboidal and columnar epithelia suited for secretion and absorption?

Their larger cells can contain more cellular machinery needed for secretion and absorption

Why do microvilli improve absorption?

They increase apical surface area available for absorption

Why are cilia suited for transport?

Their motile microtubule-based projections move material across an epithelial surface

How do pseudostratified epithelium goblet cells and cilia work together in the respiratory tract?

Goblet cells produce mucus and cilia move that mucus along the epithelial surface

Why is keratinized stratified squamous epithelium protective?

Multiple cell layers plus dead keratin-filled surface cells resist abrasion and irritation

Why is transitional epithelium suited for the urinary tract?

Umbrella cells change shape as the organ stretches while maintaining a protective multilayered lining

What is the relationship between epithelial avascularity and connective tissue?

Epithelium lacks vessels so oxygen and nutrients must diffuse from vessels in underlying connective tissue

Why is the basal lamina important when evaluating carcinoma invasion?

Carcinoma in situ remains above an intact basal lamina while invasive carcinoma breaches it and enters connective tissue

What is the key difference between metaplasia and dysplasia?

Metaplasia = replacement by another normal differentiated cell type in the wrong location / Dysplasia = abnormal maturation with abnormal cells and tissue architecture

What is the key difference between benign and malignant tumors?

Benign = localized without invasion or metastasis / Malignant = capable of tissue invasion and distant metastasis