Cytology Histology
Description: This video gives an overview of cytology, cell growth, cell death, chromatin, the nucleus, the cell cycle, and cell populations.
Lecture Notes
I. Overview of Integumentary System
Study of cellular structure and function
Clinically, cytology is the examination of a single cell type versus histology, which consists of reviewing a tissue in whole
Collected as tissue scrapings (e.g. pap smear), fluid samples, and biopsies
Used for screening and diagnosing cancer, infectious organisms, and fetal abnormalities
II. Epidermis
§ Most superficial layer of the skin that consists primarily of stratified squamous epithelium
○ Predominant cell is the keratinocyte
§ Consists of multiple layers:
○ Stratum basale (germinativum)
○ Stratum spinosum
○ Stratum granulosum
○ Stratum lucidum
○ Stratum corneum
III. Stratum Basale
§ Single layer of cuboidal epithelial cells at the base of the epidermal epithelium
○ Derived from the ectoderm
§ Contains germinal stem cells that continuously undergo mitosis to produce new keratinocytes
§ Also functions to connect the epidermis to the dermis via hemidesmosome connecting with integrins (basal lamina)
§ Histological appearance
○ Large oval nuclei
○ Basophilic cytoplasm
IV. Stratum Spinosum
§ Intermediate layer containing keratinocytes with a spiny appearance
§ Radiating bundles of tonofilaments (cytokeratin) forming desmosomes between cells
○ Spaces observed between cells are shrinkage artifact
○ Cells closer to the surface are flatter than cells closer to the stratum basale
V. Stratum Granulosum
§ Composed of keratinocytes that produce the stratum corneum layer
§ Basophilic inclusion bodies that contain keratohyalin granules composed of histidine- and cystine-rich proteins (filaggrin) that stimulate keratin filament aggregation
§ Undergo modified apoptosis, resulting in nuclear degradation, while maintaining cell structure
VI. Stratum Lucidum
§ Layer of thick stratum corneum composed of anucleate keratinocytes
§ Only found in areas of body with thicker skin, such as palms and soles of feet
§ Appear translucent and homogenous due to intracellular aggregation of keratin
VII. Stratum Corneum
§ Most superficial layer
§ Composed of anucleate (cornified) keratinocytes filled with keratin filaments and lamellar bodies
○ Coated with glycolipids that serve to create the water barrier feature of skin
§ Thick skin has a thicker, dense stratum corneum
§ Thin skin has a thinner, soft stratum corneum
VIII. Cells of the Epidermis
§ Keratinocytes
§ Melanocytes
§ Langerhans cells
IX. Keratinocytes
§ Epithelial cell of the epidermis
§ Produce keratin filaments that form bundles called tonofilaments that contribute to desmosomes linking adjacent keratinocytes
§ Undergo the process of keratinization that transforms granular cells into cornified cells
○ Involves increased aggregation of keratin filaments to form soft keratin
§ Stratum spinosum layer produces lamellar bodies which contain mixture of lipids for coating the epidermis to form the epidermal-water barrier
X. Melanocyte
§ Responsible for producing melanin
§ Derived from neural crest
§ Found between keratinocytes of the stratum basale, stratum spinosum, and within hair follicles
§ Attached to the basal lamina via hemidesmosomes
○ Not attached to keratinocytes (no desmosomes)
§ Histological appearance
○ Large ovoid nuclei
○ Pale staining cytoplasm
§ Produce melanin via oxidation of tyrosine to 3,4-dihydroxyphenylalanine (DOPA) to melanin
○ Melanin protects against damage from UV light
§ Multiple cytoplasmic extensions into the stratum spinosum
○ Facilitate transfer of filamentous melanin in melanosomes from melanocytes to keratinocytes via cytocrine secretion
§ Number of melanocyte cells is equal among all races
§ Skin and hair color are influenced by the degree of melanosome aggregation in keratinocytes
○ Rate melanin production, transfer of melanosomes, and lysosomal degradation vary among races
XI. Langerhans Cells
§ Dendritic macrophages that act as antigen presenting cells
○ Utilize major histocompatibility complex (MHC) II to present foreign antigens to T-cells
§ Able to travel to lymph nodes via dermal lymphatic vessels
§ Usually found in the stratum spinosum
§ Histological appearance
○ Dense, basophilic, indented nucleus
○ Pale cytoplasm
§ Electron microscopy reveals unique “paddle-shaped” intracellular granules known as Bierbeck bodies (unknown function)
XII. Merkel Cells
§ Cells found within the stratum basale layer that function as mechanoreceptors
○ Associated with unmyelinated nerve endings to provide touch sensation
§ Form attachments with adjacent keratinocytes via desmesomes
§ Histological appearance
○ Indented nucleus
○ Pale cytoplasm
○ Electron-dense, perinuclear vesicles
XIII. Dermis
§ Layer of skin deep to the epidermis with two layers:
○ Papillary dermis (superficial 1-20%) = loose connective tissue
○ Reticular dermis = dense irregular connective tissue
§ Composed of a fibrous network of collagen type I and III fibers with elastic fibers
§ Contains blood vessels, sweat glands, nerves, including sensory receptors
§ Site of immune response to infections, skin wounds, and cutaneous allergic reactions
I. Hypodermis
§ Underlying region composed of loose connective tissue and adipocytes
○ Provide cushioning and insulation
§ Some hair follicles and sweat glands may extend into the hypodermis
§ Sometimes contains smooth muscle
XV. Epidermal-Dermal Junction
§ Dermal papillae interdigitate with epidermal ridges to increase contact surface area between the two layers
○ Microanatomical basis for fingerprints and footprints
§ Most prominent in areas of skin that withstand significant shearing forces
○ Fingertips, palms, soles
XVI. Thick vs. Thin Skin
