SKIN

Question 1

Skin, general structure, vascular supply and innervation

• • Dermal-epidermal junction
    
    • Consists of a basement membrane that anchors the epidermis to the dermis
    • The basement membrane consists of two layers.
      
      • Lamina lucida (superficial)
      • Lamina densa (deeper)
• Hemidesmosomes: connect the epidermis to the basal cell layer
• Collagen fibrils: connect the basal cell layer to the papillary layer
• Dermis: derived from mesoderm;
• contains blood vessels and provides structural integrity to the skin Papillary dermis
  
  • Consists of fine, loosely arranged collagen fibers
  • Supplies the epidermis with nutrients
  • Plays an important role in temperature regulation
  • Forms dermal ridges, which connect dermal papillae (extension of the papillary dermis into the epidermis) to epidermal downgrowths known as epidermal ridges or rete ridges
  • Contains Meissner corpuscles (for fine-touch and two-point discrimination) and free nerve endings
  • Contains immune cells (mast cells and macrophages)
• Reticular dermis
  
  • Consists of thick, densely packed fibers (e.g., reticular, elastic, and collagenous)
  • Provide structure and support to the skin and its components
  • Contains elastic fibers that provide elasticity
  • Contains Ruffini corpuscles (mechanoreceptors)
    
    • Responsible for mechanical pressure and the sensation of distortion
  • Contains sweat glands, sebaceous glands, and the roots of hair follicles
  • Langer lines
    
    • Topographic lines that correlate with the natural orientation of the reticular fibers of the reticular dermis
    • Important for wound healing and guiding surgical incisions
• Subcutis (also called hypodermis)
  
  • Derived from mesoderm
  • Consists mainly of fat that protects from cold and trauma
  • Contains superficial veins and free nerve endings
  • Contains Pacinian corpuscles (mechanoreceptors)
  • Responsible for the sensations of vibration and pressure
  • Collagenous and elastic fibers in this area anchor the skin (epidermis, dermis) to the deep fascia.
  • Allows for the subcutaneous administration of medication

Answer 1

Skin and its derrivatives are appart of the integumentrary system

• The skin is the largest organ of the body, covering an area of approximately 2m² , 15-20% of body mass
• Integumentary system
  
  • ​Skin and its derivatives and appendages
    
    • Skin
      
      • Dermis, epidermis, and subcutaneous tissue)
    • Skin appendages
      
      • Nails, hair, and several types of sweat and sebaceous glands.

General structure:

• Epidermis:
  
  • Epithelial layer: keratinized stratified squamous
  • Ectodermal origin
  • Nonvascularized
  • Consists of five layers
  • Maintains the skin’s barrier function
• Dermis:
  
  • Layer of the connective tissue
  • mesenchymal origin
  • a) papillary layer (loose CT)
  • b) reticular layer (dense irregular CT)
  • Epidermal derivatives of the skin:
    
    • hair follicles and hair,
    • sweat and sebaceous glands,
    • nails,
    • and mammary glands
• Hypodermis
  
  • (subcutaneus connective tissue)
  • contains variable amounts of adipose tissue,
  • binds skin to the underlying tissues

FUNCTIONS OF THE SKIN

• Acts as a barrier that protects against physical, chemical, and biologic agents in the external environment
• Provides immunologic information obtained during antigen processing to the appropriate effector cells in the lymphatic tissue
• Participates in homeostasis by regulating body temperature and water loss
• Conveys sensory information about the external environment to the nervous system
• Synthesizes of the vitamin D3 from the vitamin precursor (action of the UV light), cytokines, and growth factors
• The exocrine secretion: the eccrine and apocrine sweat glands, sebaceous glands, and mammary glands

CATAGORIES:

• Refer mostly to thickness of epidermal layer
• Thin skin
  
  • Epidermis 75-150 μm thick,
  • thin stratum corneum,
  • indistinct stratum granulosum
• Thick skin
  
  • Thick epidermal layer, hairless
  • palm, sole of the foot
  • Epidermis 400 – 1400 μm thick
    
    • keratinized stratified squamous epithelium
  • DERMIS:
    
    • papillary layer (loose CT), reticular layer (dense irregular CT)
    • Hypodermis - subcutaneous connective tissue, lobules (pads) of the adipose tissue

INNERVATION:

• Autonomic nerve fibers:
  
  • Skin glands, arrector pili muscles, vessels
• Sensory nerve fibers:
  
  • Free nerve endings
    • ​Lack CT or schwan cell investment
    • in the epidermis: detect pain and temperature extremes (stratum granulosum)
    • and in dermal papillae, root hair plexus
• Encapsulated nerve endings, tactile receptors
  
  • Meissner corpuscle (tactile receptor in the dermal papilla)
  • Krause bulb (pressure and low-frequency vibrations)
  • Ruffini corpuscle (sensitive to skin stretch and torque)
  • Pacinian (pressure and high-frequency vibration)

1- Meissner corpuscle

• Location
  
  • Dermal papillae in hairless skin;
• Structure:
  
  • Thin capsule derived from the perineurium
  • Attached by bundles of collagen fibrils to the epidermis.
  • The cellular component of MC consists of flattened Schwann cells that form several irregular lamellae through which the axons course to the pole of the corpuscle.
• Function:
  
  • Mechanical impression results in the depolarization of axolemma.

2- Krause bulb ???

• Location:
  
  • Nerve terminals in skin, mucosa of the oral cavity, conjunctiva, and other parts,
• Structure:
  
  • consisting of a laminated capsule of connective tissue enclosing the terminal, branched, convoluted ending of an afferent nerve fiber;
• Function:
  
  • Sensitive to pressure and low-frequency vibrations

3- Ruffini’s corpuscles

• Simplest encapsulated mechanoreceptors.
• Structure:
  
  • They have an elongated fusiform shape and

measure 1 to 2 mm in length

* Consist of a **thin connective tissue capsule** that **encloses a fluid-filled space.**
* Collagen fibers from the surrounding connective tissue pass through the capsule.
* The neural element:

    * Single myelinated fiber
    * Enters the capsule and loses myelin sheath
    * Branches to form a dense arborization of fine axonal endings, each terminating in a small **knoblike bulb.** * **Function**
* Respond to **skin stretch and torque**
    * Axonal endings respond to displacement of the collagen fibers
    * Induced by sustained or continuous mechanical stress * Functionally belong to the family of rapidly adapting receptors (phasic receptors)

* Generate short action potentials at the beginning and end of a stimulus.

4- Pacinian corpusle

• Location:
  
  • In the deeper dermis and hypodermis,
  • Or in the association with joints, periosteum, and internal organs
• Structure:
  
  • Hacroscopic dimensions.
  • Myelinated nerve ending surrounded by a capsule structure
    • Nerve enters capsule at one pole with its myelin sheath intact.
    • The myelin is retained for one or two nodes and is then lost.
    • Inner core of the corpuscle/ inner lamellae
      
      • The unmyelinated portion of the axon extends toward the opposite pole
      • Covered by a series of tightly packed, flattened Schwann cell lamellae
    • Outer core/ outer lamella
      
      • Series of concentric lamellae;
      • Seperated by narrow space containing lymph like fluid
        
        • Also collagen fibrils are present and occasional capillaries.
• Function:
  
  • Pacinian corpuscles respond to pressure and vibration through the displacement of the capsule lamellae.
  • Displacement effectively causes depolarization of the axon.
• OL form concentricly arranged flattened fibroblasts; be- tween the lamellae is a lymphlike fluid, collagen fibrils and some capillaries. Axon entering PC loses its myelin sheath, is surrounded by ramified and interdigitating Schwann cells, which form IL. PC responds to pressure and vibration through the displacement of the capsule lamellae causing the depolarization of the axon.

Question 2

Structure and function of the epidermis

Answer 2

General:

• Ectodermal origin
• Stratified squamous epithelium
• The average thickness is approximately 0.3-1.5 mm.

5 layers according to the type of cells:

• Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum.

The life cycle of keratinocytes and layers

Differentiation of keratinocytes constitute a specialized form of apoptosis.

• Str. basale:
  
  • Contains mitotic active cells, cells begin to synthesize keratin.
    
    • Basal cells
    • AKA: stratum germinativu
    • Closely spaced nuclei, in combination with the basophilic cytoplasm of these cells, impart a noticeable basophilia to the stratum basale.
    • Cell junctions
      • Desmosomes: Connected to each other and to karatinocytes
      • Hemidesmosomes: Connected to the underlying basal lamina
  • The basal cells also contain various amounts of melanin (described later) in their cytoplasm that is transferred from neighboring melanocytes interspersed in this layer.
• Str. spinosum
  
  • Cytoplasmic processes or spines, which gives this layer its name
    
    • The processes are attached to similar processes of adjacent cells by desmosomes.
    • In the light microscope, the site of the desmosome appears as a slight thickening called the node of Bizzozero.
  • As the cells move to the surface, they increase in size and become flattened in a plane parallel to the surface.
  • Synthesis of keratins (major structural proteins of epidermis),
    
    • Formation of keratin intermediate filaments, aggregation keratin filaments into bundles called tonofibrils.
  • In the upper part of the spinous layer the keratinocytes begin to produce the keratohyalin and membrane-bounded lamellar granules.
• Str. granulosum
  
  • Keratohyaline granules are distinctive feature of cells.
    
    • Basophilic granules
    • Contain keratin filament-associated proteins (filaggrin) that aid in the aggregation of keratin filaments.
  • Production of lamellar granules (unique for mammalian epidermis)
    
    • Composed of lipids
    • Which are exocytozed into intercellular spaces, where they form the lipid envelope coating cell surfaces, contribute to the formation of epidermal water barrier.
  • Transformation of a keratinocyte into a cornified cell also involves breakdown of the nucleus and other organelles and thickening of the plasma membrane.
• Str. corneum
  
  • Composed of cornified cells
    
    • completely filled with bundles of keratin filaments.
    • Thickened plasma membrane of cells contains insoluble proteins on its inner surface
  • Desquamation of surface keratinocytes is regulated by enzymatic degradation of desmosomes (kallikrein-related serin protease).
  • Layer that varies most in thickness, being thickest in thick skin.
• Stratum lucidum
  
  • Can be considered a subdivision of the stratum corneum by some histologists
  • Normally only well seen in thick skin.
  • This highly refractile layer contains eosinophilic cells in which the process of keratinization is well advanced.
  • The nucleus and cytoplasmic organelles become disrupted and disappear as the cell gradually fills with keratin.

Epidermal water barrier

• Responsible for maintaining body homeostasis.
• Consists of two structural parts:
  
  • Cell envelope and lipid envelope
• Lipid envolope:
  
  • Lamellar bodies
    
    • Granules; heterogenous mixture of glycosphingolipids, phospholipids and ceramides
    • Produced in Golgi complex
    • Are secreted by exocytosis into the intercellular spaces between cells of str. granulosum and corneum,
    • Form the lipid envelope placed just bellow the thickened plasma membrane.
      
      • (its major components are ceramides; cholesterol, and free fatty acids)
• Cell membrane
  
  • The layer adjacent to the plasma membrane contains tightly packed proteins, involucrin.
  • Keratin filaments bound by filaggrin are anchored into the envelope.
• Cell envelope- innermost part:
  
  • Consists of loricrin molecules (pink spheres) that are cross-linked by small proline-rich proteins (SPR) and elafin.

Specilized cells:

Langerhans cells

• Antigen-presenting dendritic cells in epidermis
  
  • Bone marrow-derived cells, capable binding, processing, and presenting antigens toT lymphocytes.
    
    • Migrate from the epidermis to a regional lymph node
• Their processes penetrate between keratinocytes
• Birbeck granules contain proteins langerin and CD1a, involved in the uptake and delivery of antigens.

Melanocyte

• Neural crest–derived cells,
• Rounded cell body resides in the basal layer
• Extends long processes between the keratinocytes of the stratum spinosum.
• Melanocytes produce and transfer melanin into keratinocytes by cytokrine secretion.
• Melanin granules form nuclear shield against UV radiation.

Merkel cells

• Mechanoreceptors derived from neural crest cells,
• Located in basal layer of epidermis
  
  • (or at bases of hair follicles)
  • bound to adjoining keratinocytes by desmosomes
• Contain dense core neuroendocrine granules in the basal cytoplasm
  
  • Related also to the diffuse neuroendocrine system.
• Basolateral surface of cells contact expanded terminal disc, a nerve ending of the sensory fibers.

Question 3

Structure of dermis and the subcutaneous tissue

Answer 3

Attachment of epidermis to dermis

• Enhanced by an increased interface between the two tissues.
• Dermal papillae
  
  • Fingerlike connective tissue protrusionsthat project into the undersurface of the epidermis
    
    • Loose CT, contains capillary loops supplying the nutrients to epidermis.
  • Complemented by similar epidermal protrusions, called epidermal ridges or rete ridges, that project into the dermis.
• True dermal ridges are present in thick skin in addition to dermal papillae.
  
  • Parallel arrangement, with the dermal papillae located between them.
  • Form a distinctive pattern that is genetically unique to each individual and is reflected in the appearance of epidermal grooves and ridges on the surface of the skin.
  • Basis of dermatoglyphics/ fingerprint and footprint identification.
• ​The dermis is composed of two layers:
  
  • Papillary layer
    
    • Superficial layer, relatively thin
    • Loose connective tissue immediately beneath the epidermis
    • Delicate collagen network
      
      • I and type III collagen molecules.
      • Elastic fibers are threadlike and form an irregular network.
    • Contains blood vessels that serve but do not enter the epidermis.
    • Contains nerve processes that either terminate in the dermis or penetrate the basal lamina to enter the epithelial compartment.
      • Because the blood vessels and sensory nerve endings are concentrated in this layer, they are particularly apparent in the dermal papillae.
  • Reticular layer
    
    • Considerably thicker and less cellular than the papillary layer.
    • Characterized by thick, irregular bundles of mostly type I collagen and by coarser elastic fibers.

Hypodermis

• (subcutaneus connective tissue)
  
  • contains variable amounts of adipose tissue, binds skin to the underlying tissues
    
    • Major energy storage site
    • Insulation
• Individual smooth muscle cells or small bundles of smooth muscle cells that originate in this layer form the arrector pili muscles that connect the deep part of hair follicles to the more superficial dermis.
  
  • Contraction of these muscles in humans produces the erection of hairs and puckering of skin called “goose flesh.” In other animals, the erection of hairs serves in both thermal regulation and fright reactions.
• A thin layer of striated muscle, the panniculus carnosus,lies deep to the subcutaneous fascia in many animals. Althoughlargely vestigial in humans, it remains well defined in the skin of the neck, face, and scalp, where it constitutes the platysma muscle and the other muscles of facial expression.
• The subcutaneous tissue has a mesenchymal origin. There are ligaments, blood vessels, nerves, nerve endings and sweat glands. Thinnest on the eyelids, strongest on the buttocks, abdomen and thighs.

Question 4

Skin appendages

Answer 4

Skin appendages

• Derived from downgrowths of epidermal epithelium during development.
  
  • Hair follicles and their product: hair
    
    • specific roles in the regulationof body temperature
  • Sebaceous glands and their product: sebum
    
    • an oily substance that may have protective functions
  • Eccrine sweat glands and their product: sweat
    
    • specific roles in the regulation of body temperature
  • Apocrine sweat glands and their mixed product containing:
    
    • Form of sweat with a high concentration of carbohydrates, lipids, and proteins
    • specific roles in the regulation of body temperature????
    • serous secretion containing pheromones that act as a sex attractant in other animals and possibly in humans.

1- Hair Follicles and Hair

Hair follicle

• Responsible for the production and growth of a hair.
• The hair follicle is divided into three segments:
  
  • Infundibulum
    
    • Extends from the surface opening of the follicle to the level of the opening of its sebaceous gland.
    • Apart of the pilosebaceous canal, which is used as a route for the discharge of the oily substance sebum.
  • Isthmus
    
    • From the infundibulum to the level of insertion of the arrector pili muscle.
  • Inferior segment
    
    • Uniform diameter except at its base,
    • Bulb: expantion at base
      
      • Dermal papilla
        
        • Vascularized loose connective tissue that invaginated at base of the bulb
      • Matrix cells:
        • Adjacent to the dermal papilla
        • Represent the germinative layer of the follicle.
        • Division and proliferation of these cells accounts for the growth of the hair.
          
          • differentiate into the keratinproducing cells of the hair and the internal root sheath
        • Scattered melanocytes are also present in this germinative layer.
        • The dividing matrix cells in the germinative layer
• Hair shaft: protudes beyond epidermis
  • ​yellow-keratin, brown-melanin​
  • Medulla:
    
    • imcompleatly keritinied cells
    • only in large hairs
  • Cortex:
    
    • Cuboidal and fusiform cells
    • compleatly keritinized cells, spindle shape
  • Cuticle
    
    • keritinized cells, in upwards orientation
• The internal root sheath
  • Multilayered cellular covering that surrounds the deep part of the hair.
    
    • Three layers:
      
      • Cuticle
        
        • Squamous cells
        • downwards orientation
      • Huxley’s layer
        
        • Single or double layer of flattened cells that form the middle plate of the internal root sheath.
      • Henle’s layer
        
        • Outer single layer of cuboidal cells.
        • These cells are in direct contact with the outermost part of the hair follicle
• External root sheeth
  • Extension of the epidermal basal layer which envelopes the entire hair follicle
  • non keritinized germinal layer
• Glassy membrane
  
  • A thick basal lamina
  • separates the hair follicle from the dermis.
• Follicular bulge
  
  • A niche of epidermal stem cells
  • Resides within the of the external root sheath provides stem cells for hair growth.
• Fibrous sheath
  
  • Dense irregular connective tissue sheath containing follicular bulge.
    
    • inner circular
    • outer longitudinal

By the time the hair emerges from the follicle, it is entirely keratinized as hard keratin.

The internal root sheath, consisting of soft keratin, does not emerge from the follicle with the hair but is broken down at about the isthmus level where sebaceous secretions enter the follicle.

The arrector pili muscle is attached to follicular bulge which, as was indicated above, also serves as a epidermal stem cell niche.

Hairs are elongated

2- GLANDS OF THE SKIN

Sweat glands are classified according their structure, the formation and release their secretion:

Innervation of sweat glands

• Smpathetic portion of the autonomic nervous system.
  
  • Eccrine sweat glands are stimulated by cholinergic transmitters (usually identified with the parasympathetic component of the autonomic system)
    
    • Respond to heat and stress
  • Apocrine glands are stimulated by adrenergic transmitters.
    
    • Respond to emotional and sensory stimuli but not to heat.
• Eccrine sweat glands
  
  • Location
    
    • Distributed over the entire body surface except of the lips and part of the external genitalia.
  • Structure:
    
    • Simple coiled glands
    • Independent structure
    • Secretory segment
      
      • located deep in the dermis or in the upper part of the hypodermis lined with:
      • Clear cells
        
        • (transport of the extracelullar fluid from capillary into the tubular lumen),
      • Dark cells
        
        • (eccrine type; synthesis of the glycoproteins which are involved in the innate immu- nity).
      • Myoepithelial cells
        
        • Limited to the basal aspect of the secretory segment.
        • Between the secretory cells,with their processes oriented transversally to the tubule.
      • Secretion: watery solution low in protein, contains varying amounts of sodium chloride, urea, uric acid, and ammonia.
    • Duct segment
      
      • Directly continuous, less coiled
      • Leads to the epidermal surface
      • Lined with stratified epithelium
        • consisting of two layers of cuboidal cells;
        • cells absorb Na+ from the secretion into blood capillary to prevent its excessive loss.
  • Function:
    
    • Regulate body temperature.
    • cooling that results from the evaporation of water from sweat on the body surface.
    • Sweating is response to the increased temperature and stress.
• Apocrine sweat glands
  
  • Location:
    
    • Limited to the axilla, areola and nipple of the mammary gland; skin around the anus and the external genitalia; ceruminous glands of the external acoustic meatus canal and glands of Moll of the eyelashes.
  • Structure:
    
    • Coiled tubular glands, sometimes branched.
    • Secretory portions
      
      • located deep in the dermis or, in the upper region of the hypodermis.
      • Secretory tubules
        
        • Wide lumen: a store their secretory product in the lumen.
        • Lined with simple epithelium
        • Cells according the secretory phase are low cuboidal, cuboidal or columnar;
      • Myoepithelial cells are located at the basement membrane
    • Duct portions
      • Similar to that of the eccrine gland;
      • Narrow lumen, is stratified cuboidal, usually two cell layers.
      • Relatively straight path to empty into the follicle canal.
• Secretions:
  • Merocrine type
  • Secretory product is not altered in its passage through the duct.
  • Protein-rich, containing
    
    • pheromones, carbohydrate, ammonia, lipid, and certain organic compounds that may color the secretion.
  • In the axilla, the secretion is milky and slightly viscous. When secreted, the fluid is odorless; through bacterial action on the skin surface, it develops an acrid odor.

Sebaceous glands

• Holocrine type of secretion
• Location:
  
  • Most of the body surface except of thick hairless skin; Meibomian glands in the tarsal plate.
• Development:
  
  • As outgrowths of the external root sheath of the hair follicle, usually producing several glands per follicle
  • Growth and secretory activity are stimulated by androgenes.
• Structure:
  
  • Branched alveolar (acinar) glands located in the dermis.
  • Secratory portion:
    
    • Cells: Spongiocytes
    • Secretory alveoli consist of a basal layer of stem cells, liked by desmosomes
    • These cells proliferate and differentiate into secretory cells which fill the alveolus.
    • The entire cell produces and becomes filled with the fatty product while it simultaneously undergoes programmed cell death (apoptosis) as the product fills the cell.
  • ​Short duct:
    
    • Ultimately, both the secretory product and cell debris are discharged from the gland as sebum into the infundibulum of a hair follicle
      
      • Forms the pilosebaceous canal with the short duct of the sebaceous gland.
    • Lined with stratified squamous epithelium
    • Usually empties into the upper portion of hair follicle.
    • In certain hairless regions, directly onto the epidermal surface:
      
      • Nipple, Meeibomian glands of the eyelid, outer margin of red portion of lip, glands penis and glands clitoridis
  • Secretion release – contraction of the arrector pili muscle
• Secretion:
  
  • Sebum,
  • Mixture of lipids (triglycerides, waxes, cholesterol and its esters),
  • Maintains the stratum corneum of epidermis and hair,
  • Also has weak antibacterial and antifungal properties.

Nails are plates of keratinized cells containing hard keratin.

• The nail bed:
  
  • Consists of basal and spinous epidermal layers
• The nail root:
  
  • Is covered by the proximal skin fold.
• The nail plate
  
  • Arises from the nail matrix.
  • The stem cells of the matrix divide, migrate toward the root of the nail, and there differentiate.
• Nail keratin is a hard keratin, like that of the hair cortex. Unlike the soft keratin of the epidermis, it does not desquamate. It consists of densely packed keratin filaments embedded in high sulfur matrix proteins. Keratin formation does not involve keratohyalin granules. The nail plate contains closely packed interdigitating corneocytes lacking nuclei and organelles.

Question 5

Structure and function of the mammary gland

Answer 5

Mammary glands

• Structurally dynamic organs, varying with age, menstrual cycle, and reproductive status of the female.

Multiple glands develop along paired epidermal thickenings called mammary ridges (milk lines) that extend from the developing axilla to the developing inguinal region.

In females, mammary glands develop under the influence of sex hormones.

• Until puberty, both females and males mammary glands develop in similar fashion.
• At the onset of puberty in males, testosterone acts on the mesenchymal cells to inhibit further growth of the mammary gland.
• Mammary glands in women undergo further development under hormonal influence of estrogen and progesterone.
  
  • Estrogen stimulates mesenchymal cells further development.
  • The mammary gland increases in size, mainly due to the growth of interlobular adipose tissue. The ducts extend and branch into

the expanding connective tissue stroma. Proliferation of epithelial

cells is controlled by interactions between the epithelium

and the specialized intralobular hormone-sensitive loose

connective tissue stroma. By adulthood, the complete ductal

architecture of the gland has been established.

General:

• Modified tubuloalveolar apocrine sweat glands.
• Derived from modified sweat glands in the epidermis, lie in the subcutaneous tissue.

Structure:

• Areola (the pigmented area surrounding the nipple)
  
  • Nipple
  • areolar tubercles of montgomery
  • areolar glands of montgomery
• Mammary glands
  
  • Composed of 15-20 distinct lobes
    
    • Separated by fibrous bands of connective tissue:
      
      • Interlobular connective tissue
        
        • Dense irregular connective tissue
      • Intralobular connective tissue
        
        • Loose connective tissue
  • Lobules: terminal duct lobular units (TDLUs)
• alveoli ???
• Ducts
  
  • interlobular ducts
    
    • Intralobular; Interlobular ducts; Main ducts
    • Intralobular ducts
      • Lined with a simple cuboidal or columnar epithelium, and exhibit interspersed lymphocytes
      • numerous myoepithelial cells are located between the epithelial cells and basement membrane
    • To the nipple:
    • Lactiferous ducts :
      
      • Form a tree branched system connecting the  lobules of th e mammary glan d to the tip of the  nipple.
      • Lined by a simple columnar  epithelium  supported by  myoepithelial cells.
      • When a woman is not lactating, the lactiferous duct is frequently blocked by a keratin  plug. This plug prevents bacteria from entering the duct in non-lactating women.
    • Sinus lactiferous
      
      • Dilation of the lactiferous duct just before it entrance to nipple.
      • In nursing mothers, this stores a droplet of milk that is expelled as the infant begins to suckle.
      • Porus lactiferous - contains many adipocytes
• Opening: stratified squamous keratinized epithelium.
• Gradual transition from stratified squamous to two layers of cuboidal cells in the lactiferous sinus and finally to a single layer of columnar or cuboidal cells through the remainder of the duct system.
• The epidermis of the adult nipple and areola is highly pigmented
• and somewhat wrinkled and has long dermal papillae
• sinus
• Suspensory ligament of brest/ Cooper’s ligaments
  
  • Some of the fibrous bands that connect with the dermis.
• Mammary fat pad

Inactive adult mammary gland

• *
• They radiate from the mammary papilla, or nipple, and are further subdivided into numerous lobules known as terminal duct lobular units (TDLUs)
• Some of the fibrous bands, called suspensory or Cooper’s ligaments, connect with the dermis. Abundant adipose tissue is present in
• the dense connective tissue of the interlobular spaces.
• Each gland ends in a lactiferous duct that opens through a
• constricted orifice into the nipple. Beneath the areola, the pigmented
• area surrounding the nipple, each duct has a dilated
• portion, the lactiferous sinus. Near their openings, the lactiferous
• ducts are lined with stratified squamous keratinized epithelium.
• The epithelial lining of the duct shows a gradual
• transition from stratified squamous to two layers of cuboidal
• cells in the lactiferous sinus and finally to a single layer of columnar
• or cuboidal cells through the remainder of the duct system.
• The epidermis of the adult nipple and areola is highly pigmented
• and somewhat wrinkled and has long dermal papillae

Mammary gland -

• Specific type of apocrine gland - tuboalveolar secretory unit
• Influenced by estrogen and progesterone
• Lactation starts to increase due to secretion of prolactin

Structure:

The gland is composed of 15-20 distinct lobes embedded in fibro collagenous tissue

Interlobular connective tissue composed from dense irregular connective tissue

Intralobular is loose connective tissue

Ducts -

Intralobular; Interlobular ducts; Main ducts

To the nipple -

Lactiferous ducts -

Form a tree branched system connecting the lobules of the mammary gland to the tip of the nipple.

Lactiferous ducts are lined by a simple columnar epithelium supported by myoepithelial cells. When a woman is not lactating, the lactiferous duct is frequently blocked by a keratin plug. This plug prevents bacteria from entering the duct in non-lactating women.

Sinus lactiferous -

A circumscribed spindle shaped dilation of the lactiferous duct just before it enters the nipple. In nursing mothers, this stores a droplet of milk that is expelled as the infant begins to suckle.

Porus lactiferous - contains many adipocytes

Nipple -

Thin type of skin

Convoluted epidermis

Gets the color since it contains more melanocytes

Sebaceous glands without hair follicles are presented – Montgomery’s glands

On the side of the areola mammae could be small apocrine glands

Smooth muscle cells for lifting nipples when cold

Ductus lactiferous

Sinus lactiferous

Openings on the surface - porus lactiferous