Integumentary System Flashcards
What percentage of body mass does skin account for?
15-20%
Where is epidermis derived from?
Ectoderm
Where is dermis derived from?
Mesoderm
What is thick stratum corneum?
No hairs, abundant sweat glands, found in palms and soles of feet
Thin stratum corneum contains?
Hairs, sweat glands, sebaceous glands
Describe statum basale
Small cuboidal to low columnar, basophilic cells that rest on basal lamina, mitotically active stem cells, abundance of ribosomes that synthesize cytokeratin, contains cytokeratin intermediate filaments called tonofilaments
What are stratum basale cells attached to each other by?
Desmosomes
What are stratum basal cells attached to basal lamina by?
Hemidesmosomes
What are tonofilaments?
Cytokeratin intermediate filaments that strengthen hemidesmosomal attachment
What does basophilic cytoplasm of stratum basale cells indicate?
They are actively synthesizing keratin protein in form of tonofilaments
What are white cells that can be found in stratum basale that are not basophilc?
Melanocytes
Describe stratum spinosum
Prickle cell layer, cuboidal or polygonal cells, numerous short cytoplasmic processes known as spines, Nodes of Bizzozero, contains keratin filaments, and melanin granules
What are Nodes of Bizzozero?
Desmosomal attachments of spine processes in stratum spinosum
How are cytoplasmic processes attached to other processes in stratum spinosum?
Desmosomes
What is cytoplasm of stratum spinosum filled with?
Melanin granules, and tonofilaments that extend into cytoplasmic processes and attach to desmosomes
What happens to cells in stratum spinosum as they mature and move towards granulosum layer?
Polygonal shape cells at base start to flatten and become squamous shaped towards surface
What are the pale staining cells located in stratum spinosum that are not prickle cells?
Langerhans cells, come from monocytes which is part of MPS system
What do the tonofilamets in stratum spinosum cytoplasm attach to?
Extend through cytoplasmic processes and attach to desmosomes
Describe stratum granulosum
1-3 cell layers thick, basophilic cells due to active synthesis and contains many keratohyalin granules
What do keratohyalin granules contain in stratum granulosum?
Filaggrin, and Trichohyalin
What happens when Filaggrin and Trichohyalin are released into cytoplasm of granulosum cell?
Promote aggregation of keratin filaments into tonofibrils, leading to conversion of granular cells into cornified cells; called keratinization
Where is stratum lucidum found?
Only thick skin
Describe stratum lucidum
Eosinophilic cells, well advanced keratinization, nucleus and organelles become disrupted and disappear as cell fills with keratin
What happens to pH as cells rise from stratum granulosum to stratum corneum?
pH rises to more acidic range;
7.1 in granulosum
6.5 in lucidum
4.5 in corneum
Describe stratum corneum
Anucleated cells, filled with keratin filaments, thickness allows for identification of thick or thin skin
Describe stratum corneum
Anucleated cells, filled with keratin filaments, thickness allows for identification of thick or thin skin
What layer creates the water barrier?
Stratum corneum
What is the water barrier?
Cells of deeper portion are coated with an extracellular layer of lipids
What are dermal papillae?
Finger like protrusions of CT, project into undersurface of epidermis
What are epidermal ridges or Rete ridges?
Epidermal protrusions into dermis
What happens to rete ridges at sites of increased mechanical stress?
They are much deeper, and dermal papillae are longer and closely spread; increasing interface between epidermis and dermis
Where are dermal ridges found?
Thick skin, fingertips
What is arrangement of dermal ridges?
Parallel arrangement, with dermal papillae located in between
What do dermal ridges form?
Distinctive pattern that is genetically unique and forms basis of Dermatoglyphics
How is epidermis connected to underlying dermis?
Hemidesmosomes
Proteins of hemidesmosomes link?
Intermediate filaments (tonofilaments) of cytoskeleton into basal lamina
How are tonofilaments attached to plaque?
BP230
How is plaque attached to laminin in basal lamina?
BP180 or Type 17 collagen
What regulates the function of laminin in basal lamina?
BP180 or Type 17 collagen
What is Bullous Pemphigoid?
Rare autoimmune condition where high levels of antibodies are formed against BP230 and BP180, absence of BP230 causes blistering of the skin due to build up of fluid between epidermis and dermis, sores typically heal without scarring
What are two layers of dermis?
Papillary layer and reticular layer
What is papillary layer of dermis?
Most superficial layer below epidermis, consists of loose CT, includes dermal papillae and rete ridges
What does papillary layer of dermis contain?
Type 1 and 3 collagen, elastic fibers form irregular threads, blood vessels and sensory nerve endings
What is reticular layer of dermis?
Deep to papillary layer, thicker and less cellular, creates langers lines
What does reticular layer of dermis contain?
Thick irregular bundles of type 1 collagen and coarse elastic fibers
What are Langers Lines?
Collagen and elastin form regular lines of tension in skin
What do langers lines provide involving skin incisions?
Least scarring when lines are followed during incisions
What two vascular plexuses are present in reticular layer of dermis?
Subpapillary and Deep Plexus
Where is subpapillary reticular layer located in dermis?
Below papillary layer
Where is deep plexus reticular layer located in dermis?
Interphase between dermis and subcutaneous layer
What is found between the two vascular plexuses in reticular layer of dermis?
Numerous AV arterio-venous anastomoses called Glomus bodies
What are glomus bodies surrounded by?
Connective tissue capsule
What are glomus bodies involved in?
Body temperature regulation, numerous in fingers toes and lips
In glomus bodies, arteriolar smooth muscle cells are modified to?
Glomus cells, serve as sphincters
Deepest part of reticular layer contains smooth muscle plexuses in what sites?
Areola, penis, scrotum, perineum, account for puckering of skin
What are the three features in the hypodermis?
Panniculus adiposus, arrector pili muscle, and panniculus carnosus
What is panniculus adiposus?
Thick layer of adipose tissue, major energy storage site, also considered as insulation layer
What is arrector pili muscle?
Individual or bundles of smooth muscle cells that originate in hypodermis, connects base of hair follicles to superficial dermis
What does contraction of arrector pili muscle in hypodermis cause?
Erection of hair and puckering of skin (goosebumps)
What is panniculus carnosus?
Thin striated muscular layer located deep to subcutaneous fascia, well defined in human platysma of neck, facial expression muscles, and scalp
Keratinocytes originate in?
Stratum basale
What is function of keratinocyte?
Produce keratin filaments called tonofilaments, and form epidermal water barrier
What does EM of keratinocytes show?
Many secretory cells, and many free ribosomes
Why does keratinocytes need lots of ribosomes?
For synthesis of keratins which forms tonofilaments
What happens when synthesis of keratin filaments continues in stratum spinosum?
The filaments become grouped and form tonofibrils
Keratinocytes in UPPER part of stratum spinosum begin to produce what?
Keratohyalin granules, and lamellar bodies
What happens to production of keratohyalin granules in stratum granulosum?
Keratohyalin granules production increases in stratum granulosum
What do keratohyalin granules contain?
Filaggrin and Trichohyalin
What happens with Filaggrin and Trichohyalin is released?
They convert tonofilaments into tonofibril bundles, this leads to conversion of granular cells into cornified cells called keratinization
What is formed keratin known as in keratinization process?
Soft keratin
What does transformation of granular cells into cornified cells during keratinization include?
Breakdown of nucleus and organelles, thickening of plasma membrane, decrease in pH from 7.1 in granulosum to 4.5 in corneum
How long does keratinization take?
2-6 hours
What is desquamation process in keratinization regulated by?
Proteolytic degradation of desmosomes
What becomes active in keratinocytes in acidic pH?
Kallikreins
What do kallikreins do?
Degrade desmosomes and cause keratinocyte release
What is epidermal water barrier established by?
Deposition of substances on outer and inner surfaces in terminally differentiating keratinocytes
What happens to outer surface in epidermal water barrier?
Formation of lipid layer that is attached to outer layer of plasma membrane, called LIPID ENVELOPE
What happens to inner surface in epidermal water barrier?
Deposition of insoluble proteins on inner surface of plasma membrane, called CELL ENVELOPE
How is lipid envelope made?
Keratinocyte lamellar bodies contain ceramides, cholesterol and fatty acids, lamellar bodies are discharge by cells in granular layer, when secreted out, ceramides provide a teflon like coating on underside cell surface of plasma membrane
As cells move towards the surface, how is barrier constantly maintained?
Keratinocytes reaching terminal differentiation
How is cell envelope made?
Insoluble proteins deposited on inner surface of plasma membrane formed by Small proline rich proteins and large structural proteins
What are some of the large structural proteins used in cell envelope?
Keratin chains, desmosomal proteins, loricrin, elafin, filaggrin, involucrin
Melanocytes originate from where?
Neural crest
What are melanocytes?
Pigment producing dendritic cells scattered among basal keratinocytes of stratum basale
Where do melanocyte processes reach to?
Stratum spinosum layer
One melanocyte is associated to how many keratinocytes?
36
What is ratio of melanocyte to keratinocyte in stratum basale?
1:4 to 1:40 depending on area of body, ratio is constant to all races
Do melanocytes form desmosomal attachments to keratinocytes?
NO
What is function of melanocyte?
Produce and distribute melanin into keratinocytes
How is melanin produced in melanocyte?
By oxidation of tyrosine to DOPA and transformation of DOPA into melanin
Where is melanin produced in?
Membrane bound premelanosomes
What is formed with increased production of melanin?
A mature melanin granule called Melanosome
Where can mature melanosomes be found?
At the ends of melanocyte processes
Describe pigment donation in melanocytes?
Keratinocytes phagocytose tips of melanocyte processes through cytocrine secretion
Why does light skin occur?
Melanosomes are more concentrated in keratinocytes near basal layer, melanin is degraded faster because of lysosomal activity in keratinocytes of stratum spinosum, therefore melanin doesnt reach the upper layers of epidermis
What are two forms of melanin that are genetically determined?
Eumelanin: brownish - black
Pheomelanin: red - yellow
What is albinism?
Hereditary lack of pigmentation
What is Leukoderma?
White patches on the skin, due to partial or total loss of skin pigmentation, many causes for this
What are langerhans cells?
Antigen presenting cells in epidermis, part of MPS system
What happens to antigens caught by langerhans cells?
After antigen processing in the skin, the cells go to regional lymph nodes and interact with T lymphocytes
Does langerhans cells form desmosomal attachments with keratinocytes?
NO
What do langerhans cells closely resemble?
Dendritic antigen presenting cells in lymph node, spleen and thymus
What does langerhans cells look like in TEM?
Nucleus is indented in many places, show characteristic granules called BIRBECK GRANULES
What does rod shaped Birbeck granules indicate?
Active cell against pathogens or antigens
How are Birbeck granules formed?
Proteins langerin and CD1a are present as receptors on plasma membrane, takes in antigens through langerhans cell, when cell is activated then Birbeck granules are formed
Where are merkel cells found?
Stratum basale
What is function of merkel cell?
Cutaneous sensation, tachtile sensation or 2 point discrimination
Where are merkel cells abundant?
Where sensory perception is acute; fingertips
How are merkel cells bound to adjacent keratinocytes?
Desmosomes
What filaments do merkel cells have in the cytoplasm?
Keratin filaments
Why does merkel cell bulge into dermis?
Merkels disc: myelinated afferent nerve looses its myelin when reaches merkel cell, cell puts out process and takes up merkel disc into cytoplasm
What is considered the merkel corpuscle?
Combination of afferent nerve terminal and merkel cell
What does cytoplasm of merkel cell consist of?
Dense cytoplasm, may contain some melanosomes, but best characterized by presence of dense cored neurosecretory granules
What is merkel cell considered to be?
Sensitive mechanoreceptor, found in relation to hair follicles
What are the most numerous nerve supply receptors in the skin?
Free nerve endings
Where do free nerve endings terminate?
Stratum granulosum
What do free nerve endings lack?
CT cover or schwann cell sheath
What do free nerve endings function in?
Fine touch, heat, cold, pain
Where are free nerve endings usually found?
Papillary layer of dermis
What is the hair root plexus?
Network of free nerve endings surrounding hair follicles, sensitive to hair movement and serve as mechanoreceptors
Encapsulated nerve endings are enclosed by what?
CT capsule
What are the four types of encapsulated nerve endings?
Pacinian corpuscle
Meissners corpuscle
Ruffinis corpuscle
Krauses end bulbs
Pacinian corpuscles are what kind of pressure receptors?
Deep pressure receptors for vibratory and mechanical pressure
Where are pacinian corpuscles located in epithelium?
Deep dermis, hypodermis
Where can pacinian corpuscles be found?
CT, joints, periosteum, internal organs
How is pacinian corpuscle composed?
Composed of myelinated nerve ending surrounded by capsule, nerve enters capsule at one end with myelin intact, then myelin is lost and unmyelinated portion extends to opposite end
What is considered the inner core of pacinian corpuscle?
Unmyelinated portion of nerve surrounded by a series of tightly packed flattened schwann cell lamellae
What is considered the outer core of pacinian corpuscle?
The bulk of the capsule, formed of a series of concentric lamellae, composed of flattened cells that correspond to perinerial cells
What are the lamellae separated by in the pacinian corpuscle?
Filled with lymph like fluid, collagen fibrils, occasional capillaries
What are meissners corpuscles considered to be?
Fine touch receptors, senses very little pressure
Where are meissners corpuscle located in epithelium?
Dermal papilla just beneath epidermal basal lamina
Where are meissners corpuscles abundant in?
Lips, palm and sole of foot, particularly in fingertips and toes
Describe structure of meissners corpuscle
CT capsule, cylindrical structure, perpendicular to skin surface, consists of 1 to 2 unmyelinated endings of myelinated nerves, unmyelinated endings take a spiral path; surrounded by flattened schwann cells that form irregular lamellae
What is function of ruffinis corpuscles?
Respond to mechanical displacement of adjacent collagen fibers during stretch and torque
Describe structure of ruffinis coupuscle
Thin CT capsule encloses fluid filled space, afferent myelinated nerve enters capsule, loses its myelin and forms an arborization of axonal endings each ending in a bulb
What is function of Krauses end bulbs?
Sense cold temperatures
Describe structure of Krauses end bulbs
Oval bodies, capsule, contain soft semifluid core in which nerve terminates in a bulbous extremity or in a coiled up plexiform mass
What is a hair follicle?
Invagination of epidermis in which a hair is formed
What are 4 regions in growing hair follicle?
Infundibulum, Isthmus, Follicular Bulge, Inferior Segment
What is the follicular bulge contain?
Epidermal stem cells
What does inferior segment of hair follicle contain?
Bulb which holds matrix cells, and dermal papilla which is tuft of vascularized loose CT
What are matrix cells in hair follicle?
Stem cells from follicular bulge collected in inferior segment and populate hair bulb
What do matrix cells differentiate into?
Keratin producing cells of hair and form internal root sheath
Division and proliferation of matrix cells account for what?
Hair growth
External root sheath is formed by?
Epidermal downgrowth
What is basal lamina of hair follicle epidermis called?
Glassy membrane
What happens when matrix cells divide?
Produce a set of cells that move upwards towards surface, form internal root sheath and then modify themselves to form hair shaft, then undergo keratinization with soft keratin being formed, hair follicle has hard keratin
What do epithelial cells covering apex of dermal papilla give rise to?
Medulla of the hair
What do epithelial cells of lateral dermal papilla give rise to?
Hair cortex
What do epithelial cells at the margin of dermal papilla give rise to?
Follicular cuticle
What is the keratogenous zone in a hair follicle?
Where maturing cells of hair follicle accumulate hard keratin through keratinization
What does matrix cells contain that produce melanin in hair?
Melanocytes
What does the hair shaft consist of?
Medulla, cortex, and cuticle
What is Griscelli syndrome?
Mutation in Myosin Va gene involved in the transport of melanin containing melanosomes and causes silvery hair
Keratin on hair shaft is ?
Hard Keratin
Keratin on internal root sheath is?
Soft keratin
What do sebaceous glands secrete?
Sebum that coats the hair and skin
How do sebaceous glands develop?
Develop as outgrowth of external root sheath of hair follicle
Basal lamina of sebaceous gland is ______ with epidermis and hair follicle
Continuous
Sebaceous gland cells are attached by what?
Desmosomes
Cells at the periphery of sebaceous glands are known as?
Basal cells, produce new cells by mitosis
Why are basal cells in sebaceous gland darkly staining?
Have many sER and rER
What do the basal cells in sebaceous glands produce as they move away from basal layer?
Produce lipids and sER content increases
Where is sebum secreted in sebaceous gland?
Secreted into the infundibulum of hair follicle by holocrine secretion
Eccrine sweat glands consists of 2 segments?
Secretory segment, and duct segment
Where is secretory segment of eccrine sweat gland located?
Deep dermis or upper part of hypodermis
Where is duct segment of eccrine sweat gland located?
Leading to epidermal surface
What is function of eccrine sweat glands?
Regulation of body temperature
Describe structure of secretory component of eccrine sweat gland
Double layer of cuboidal epithelial cells, and within the basal lamina, is a layer of myoepithelial cells
Describe structure of duct component of eccrine sweat gland
Narrowed outside diameter, consists of double layer of small cuboidal cells without myoepithelial cells
What 3 cell types does the secretory component of eccrine sweat gland contain?
Clear cells, Dark cells, and myoepithelial contractile cells
What do clear cells in eccrine sweat gland have abundantly?
Glycogen, mitochondria, plasma membrane folds laterally and apically
How do clear cells in eccrine sweat gland secrete since they dont reach the lumen?
Secrete water and electrolytes through lateral folds of cell into intercellular canaliculi
What do clear cells of eccrine sweat gland produce?
Watery component of sweat
What are abundant in dark cells of eccrine sweat gland?
Abundant in rER and granules, apical cytoplasm has mature secretory granules and occupies most of luminal surface
How do dark cells of eccrine sweat gland secrete?
Secrete glycoproteins through lumen of cell by exocytosis (merocrine secretion), mixes with clear cell secretion in lumen
Where are myoepithelial cells located in eccrine sweat glands?
Basal aspect of secretory segment and lies between secretory cells
What does cytoplasm of myoepithelial cells in eccrine sweat gland contain?
Numerous actin filaments
What does contraction of myoepithelial cells in eccrine sweat gland cause?
Causes expression of sweat from the gland
What are apocrine sweat glands associated with?
Hair follicles
Where is secretory portion of apocrine sweat gland located?
Dermis or hypodermis
Where does duct of apocrine sweat gland open into?
Into the hair follicle just above where sebaceous gland duct enters
Where are apocrine sweat glands located?
Axilla, areola, circumanal glands, external genitalia, ceruminous glands of external ear, glands of Moll of eyelid, mammary glands are modified apocrine sweat glands
How do apocrine sweat glands differ from eccrine sweat glands?
Wider lumen, stores secretions in lumen, secretory portion composed of simple epithelium, only one cell type is present, eosinophilic cytoplasm
When does secretory activity of apocrine sweat gland start?
At puberty
Describe structure of apocrine sweat gland
Apical surface has bleb like protrusion, apical granules are discharged by exocytosis, therefore secretory mode is merocrine secretion (not apocrine)
What cells are present in secretory portion of apocrine sweat gland that facilitate expulsion of secretion?
Myoepithelial cells
What is duct of apocrine sweat gland lined with?
Stratified cuboidal epithelium with no myoepithelial cells
Where are circumanal apocrine sweat glands located?
Lower part of ano-rectal junction, at the anal verge where there is stratified squamous epithelial cover with hair follicles
What are nails classified as?
Plates of keratinized cells containing hard keratin
What do nail plates rest on?
Nail bed consisting of epithelial cells
What is proximal part of nail called?
Nail root, buried in a fold of epidermis
What is the edge of the epidermal fold in nails called?
Eponychium or cuticle
What does the epidermal fold in nails cover?
Cells of the germinative zone or matrix
The cuticle is composed of what kind of keratin?
Hard keratin, therefore does not desquamate
The free edge of the nail is secured by thickened epidermal layer called?
Hyponychium
What does nail matrix contain?
Stem cells that regularly divide
Where do stem cells in nail matrix migrate to?
Towards the nail root, differentiate to produce hard keratin of nail
What does constant addition of new cells at root and their keratinization account for?
Nail growth
