Lecture 1 & 2: Glands & Integumentary System

Glands are what type of organs?

Secretory organs:

make and release chemical substances

they are made of epithelium & supportive connective tissue

Two Types of Glands formed by Infolding of Epithelium:

Endocrine

Exocrine

Endocrine Glands

Ductless glands that secrete hormones directly into blood or interstitial fluid. (No ducts! Extensive capillary supply)

Exocrine Glands

Glands that release secretions onto epithelial surfaces through ducts. (YES DUCTS! ie. saliva & sweat)

- classified by mode of secretion

Exocrine Duct Structure & Type

Structure: Unicellular vs Multicellular

Duct Type: Simple vs Compound branching

Three Modes of Secretion by _____ Glands

Exocrine Glands mode of secretion:

- Merocrine

- Apocrine

- Holocrine

Merocrine (Eccrine) Secretion

Secretion mechanism where contents are released via exocytosis or active transport (w/ ATP) without cell damage (loss of cytoplasm).

- ie. sweat glands

Apocrine Secretion

- Secretion mechanism where the apical portion of the cytoplasm is shed with product.

- APO- A PART OF cell & cytoplasm pinches off and is released.

ie. Mammary gland

Holocrine Secretion

- Secretion mechanism where entire cell ruptures, dies, and forms the secretory product.

- ie. sebaceous gland

Unicellular Exocrine Glands

• Single isolated secretory cells found in an epithelium (e.g., goblet cells).

Multicellular Exocrine Glands

• Glands composed of multiple secretory cells and supportive connective tissue.

• many cells acting as one unit

Simple Exocrine Glands

Glands with a single unbranched duct leading to secretory units.

Compound Exocrine Glands

Glands with a branched duct system leading to multiple secretory units.

Acini / Acinar (Alveolar)

- Sac-like or bulbous clusters that produce or hold secretions

Integumentary System Consist of

Skin

Accessory organs: hair, nails, cutaneous glands

T/F - Skin is the most vulnerable organ

True: skin is exposed to radiation, trauma, infection, and toxic chemicals

- receives more medical treatment than other organ systems.

General Functions of the Skin

- Resistance (Trauma & Infection)

- Barrier (Waterproofing, UV Light (melanin), Chemicals)

- First Step for Vitamin D Synthesis

- Sensation & Thermoregulation (vasodilation/constriction)

- Nonverbal communication (acne, birthmark,scar)

- Transdermal absorption (drug patch)

What makes this skin resistant to infection

• Keratinized epidermis does not contain live cells that can act as hosts fo pathogens

• Acid mantle…

Three Layers of Integumentary System (which is not a part of the skin?)

Skin Layers: Epidermis & Dermis

Non Skin, Fat & Neuro-Vascular Layer below Dermis: Hypodermis

Thick vs Thin Skin & Glands

Thick Skin =

- on palms and sole & digits (epidermis) 0.5mm thick

- has sweat glands, no hair follicles or sebaceous (oil) glands

Thin Skin =

- covers rest of body (epidermis) 0.1 mm thick ;

- has sweat glands, hair follicles, and sebaceous glands

continuously shedding & regenerating

What type of epithelium does the Epidermis have & general characteristics

- keratinized stratified squamous epithelium:

- dead cells packed with keratin (tough protein)

- lacks blood vessels

- sparse nerve ending for touch & pain

5 Types of Cells in Epidermis

- stem cells

- keratinocytes

- melanocytes

- tactile (merkel) cells

- dendritic (langerhans) cells

Stratum Basale

• Deepest epidermal layer containing stem cells (which keratinizes cells), melanocytes, and tactile (Merkel) cells.

• above basement membrane where nutrients diffuse..*

Stratum Spinosum

• Above Basale

• Epidermal layer of thick keratinocytes attached by desmosomes; contains dendritic cells.

Stratum Granulosum

Epidermal layer containing keratohyalin granules and lamellar granules for water barrier.

Stratum Lucidum

• Thin, Clear epidermal layer containing eleidin;

• found exclusively in thick skin (palm & soles) ; cells are dead

Stratum Corneum

Outermost epidermal layer of dead, fully keratinized, highly resistant squames.

Keratinocytes

Principal epidermal cell type synthesizing keratin for structural protection.

Melanocytes

Cells in stratum basale that produce melanin to shield nuclear DNA from UV.

Dendritic (Langerhans) Cells

Macrophage-like immune cells found mainly in stratum spinosum and granulosum.

Tactile (Merkel) Cells

Sensory receptors located in stratum basale associated with nerve fibers for touch.

Epidermal Stem Cells

Undifferentiated mitotic cells in stratum basale that give rise to keratinocytes.

Keratinocyte Life Cycle

30 to 40 day transition of keratinocytes from stratum basale to surface exfoliation.

Epidermal Water Barrier

Hydrophobic barrier between granulosum and corneum formed by lipids and tight junctions.

Filaggrin

Protein from keratohyalin granules that aggregates keratin filaments into tough bundles.

FLG Gene

Gene located on chromosome 1q21 encoding profilaggrin.

Profilaggrin

Large precursor protein stored in keratohyalin granules that cleaves into filaggrin.

Natural Moisturizing Factor (NMF)

Breakdown products of filaggrin (PCA, UCA) that maintain skin hydration and pH.

trans-Urocanic Acid (trans-UCA)

Filaggrin breakdown product in stratum corneum that absorbs UV-B radiation.

Pyrrolidone Carboxylic Acid (PCA)

Filaggrin breakdown product that serves as a potent hygroscopic humectant in skin.

Ichthyosis Vulgaris

Autosomal semi-dominant skin disorder caused by FLG loss-of-function mutations.

Atopic Dermatitis (Eczema)

Chronic inflammatory skin disease associated with filaggrin deficiency and skin barrier loss.

Atopic March

Progression from eczema in infants to asthma, allergic rhinitis, and food allergies.

Thick Skin

Epidermis (~0.5 mm) with stratum lucidum and prominent ridges; lacks hair and oil glands.

Thin Skin

Epidermis (~0.1 mm) covering most of body; lacks stratum lucidum; contains hair and glands.

Papillary Layer of Dermis

Superficial dermal layer composed of areolar connective tissue and dermal papillae.

Reticular Layer of Dermis

Deep dermal layer composed of dense irregular connective tissue providing strength.

Dermal Papillae

Upward finger-like projections of dermis that interlock with epidermal ridges.

Epidermal Ridges

Downward projections of epidermis into dermis forming friction ridges (fingerprints).

Cleavage (Langer's) Lines

Predominant orientation of collagen bundle fibers within reticular layer of dermis.

Striae (Stretch Marks)

Dermal tears resulting from severe stretching of collagen fibers.

Hypodermis (Subcutaneous Layer)

Subepidermal layer of loose areolar and adipose tissue anchoring skin to fascia.

Subcutaneous Fat

Adipose deposit within hypodermis providing thermal insulation and energy storage.

Eumelanin

Dark brownish-black pigment produced by melanocytes.

Pheomelanin

Reddish-yellow sulfur-containing pigment produced by melanocytes.

Tyrosinase

Enzyme required for synthesis of melanin from tyrosine in melanocyte melanosomes.

Carotene

Yellow-orange dietary pigment accumulating in stratum corneum and subcutaneous fat.

Hemoglobin

Iron-bearing red pigment of red blood cells imparting pinkish skin tones.

Cyanosis

Blueness of skin resulting from oxygen deficiency in circulating blood.

Erythema

Abnormal skin redness due to dilated dermal cutaneous blood vessels.

Pallor

Pale or ashen skin shade from diminished cutaneous blood flow.

Albinism

Genetic deficiency of melanin production due to absent/defective tyrosinase.

Jaundice

Yellowish staining of skin and sclera from elevated serum bilirubin.

Hematoma

Localized collection of clotted blood outside blood vessels (bruise).

Friction Ridges

Markings on fingertips/soles created by dermal papillae enhancing grip.

Flexion Lines

Marks on skin where skin folds over joints during movement.

Freckles

Flat melanized patches of skin resulting from localized melanin aggregation.

Nevus (Mole)

Elevated melanized patch of skin, often containing hair.

Hemangioma

Benign tumor of cutaneous blood capillaries (birthmark).

Hair Shaft

Visible portion of hair extending above skin surface.

Hair Root

Portion of hair embedded beneath skin surface within hair follicle.

Hair Bulb

Swollen base of hair root situated in deep dermis or hypodermis.

Hair Papilla

Vascular connective tissue projection into hair bulb providing nutrients.

Hair Matrix

Mitotic layer of growth cells resting directly over hair papilla.

Hair Medulla

Innermost core layer of hair follicle containing soft keratin and air spaces.

Hair Cortex

Middle layer comprising bulk of hair tissue containing hard keratin.

Hair Cuticle

Outermost layer of hair shaft composed of overlapping scaly cells.

Epithelial Root Sheath

Extension of epidermal strata surrounding hair root.

Dermal Root Sheath

Derived from dermal connective tissue surrounding epithelial root sheath.

Arrector Pili Muscle

Smooth muscle bundle extending from dermal collagen to epithelial sheath.

Lanugo

Fine, unpigmented fetal hair present during last trimester.

Vellus

Fine, pale hair covering majority of children and female body surface.

Terminal Hair

Coarse, heavily pigmented hair on scalp, eyebrows, axillary, and pubic regions.

Anagen Phase

Active growth stage of the hair cycle where matrix cells undergo active mitosis.

Catagen Phase

Degenerative transition phase of hair cycle where follicle shrinks and matrix dies.

Telogen Phase

Resting phase of hair cycle prior to hair shedding and new growth re-entry.

Alopecia

Hair thinning or baldness resulting from follicle aging or disease.

Pattern Baldness

Genetic condition where hair loss occurs selectively in specific regions due to DHT.

Hirsutism

Excessive body hair growth in areas atypical for female sex due to androgen surge.

Nail Plate

Hard external portion of nail including free edge, body, and root.

Nail Body

Visible attached portion of nail plate overlying nail bed.

Nail Root

Proximal hidden portion of nail plate extending beneath skin fold.

Nail Bed

Skin layer situated directly beneath nail plate.

Nail Matrix

Thickened stratum basale at proximal nail fold responsible for nail growth.

Eponychium (Cuticle)

Narrow zone of dead skin overhanging proximal end of nail plate.

Hyponychium

Epidermis of skin underlying free edge of nail plate.

Lunule

White crescent-shaped area at proximal base of nail plate.

Sebaceous Glands

Holocrine glands associated with hair follicles that secrete oily sebum.

Sebum

Oily secretion rich in lipids produced by sebaceous glands.

Merocrine (Eccrine) Sweat Glands

Simple tubular cutaneous glands producing watery perspiration for thermoregulation.