23 - Integument Flashcards
Where do humans have extra skin folds? Why?
We have extra skin folds over certain joints to prevent skin from breaking upon flexion
- Elbow
- Knuckles
- Knee joint
- Achilles tendon
What does the integument include?
Integument
- Skin
- Its appendages
- Sweat glands
- Sebaceous glands
- Hair
- Nails
What are the functions of the skin?
Functions:
- Protection
- Regulation of body temperature
- Reception
- Absorption
- Excretion
How does the skin protect?
Protection
- The skin covers almost the entire body
- The only exception is the nails
- The skin protects from invasion from microorganisms and dehydration
How does the skin regulate body temperature?
Regulation
- Sweat glands relsease sweat
- This cools down the body when the sweat is evaporated
How does the skin function in reception?
Reception
- Neuroreceptors may relay pain, touch, pressure and/or position to the central nervous system (CNS)
- Thermoreceptors on our skin sense temperature
- The skin allows us to form an image of the environment around us
How does the skin fucntion in absorption?
Absorption
- Absorbs ultraviolet radiation for vitamin D production
How does the skin function in excretion?
Excretion
- Eliminates waste products through sweat
What is the largest organ of the body?
The skin!
How do we classify skin?
There are two classifications:
- Thin skin
- Thick skin
Thin skin
- Covers most of the body’s surfaces
- Contains hair follicles, sebaceous glands, sweat glands, erector pilae muscles
Thick skin
Thick skin…
- Covers the palms and soles of the feet
- No hair follicles are found on these surfaces
- No sebaceous glands
- Sebaceous glands are oil-producing glands that are found in hair follicles
- No erector pilae muscles
- Erector pilae muscles are smooth muscles that anchor the root of the hair follicle
- This erects hair when contracted in order to keep the body warmer
- Sweat glands ARE present
What are the layers of the skin?
Two layers:
- Epidermis
- Dermis
Epidermis
Epidermis
- Contains stratified squamous keratinaized epithelium
- Divided into sub-layers called “strata”
Dermis
Dermis…
- Composed of two layers of connective tissue that is found under the epidermis
- Loose connective tissue that is more superficial
- Dense irregular collagenous connective tissue that is deeper
What types of cells ar found in the epidermis?
Keratinocytes
- Cells that accumulate keratin
- This is the most common cell type found in the epidermis
Non-keratinocytes are also found in the epidermis
Ridges and papilla
Ridges (epidermis) and papilla (dermis)
- The epidermis has folds that extend down into the dermis, known as epidermal ridges
- The dermis sends projections into the epidermis known as dermal papilla
- The two structure interdigitate
- Function
- Increase the surface area of the dermis and epidermis
- Ensure the two layers stay together and don’t slip apart
Basal cells
Basal cells
- Basal cells are a layer of epidermal cells that are found where the epidermis meets the dermis
- Also called stratum basale
- This is an area of intense mitotic activity
Basal cell migration
Migration
- Cell from the stratum basale (basal cells) migrate to the surface of the skin
- As they migrate, they acquire more keratin, become keratinized, then die and “slough off”
- It takes 20-30 days for the cells to migrate from the strata basale to the superficial layer of the skin
- This migration takes place mostly at night, so a good night sleep DOES make your skin look better (think beauty rest)
Non-keratinocytes
Non-keratinocytes are also found in the epidermis, but not as commonly as keratinocytes are
- There are three types of non-kerantinocyes
- Langerhans cells - defense cells, protect against invading antigens
- Merkel cells - mechanoreceptors
- Melanocytes - act as umbrellas to provide UV protection
Langerhan cells
Langerhan cells (dendritic cells, antigen-presenting cells)
- Langerhan cells are derived from precurors in bone marrow
- These precurosr cells enter the blood stream and travel to the epidermis
- Once in the epidermis, they differentiate into Langerhan cells, which are
Cytoplasmic processes of Langerhans cells
Cytoplasmic processes
- Extensions of the Langerhan cells into the extracellular space of neighboring cells are known as cytoplasmic processes
Function of Langerhans cells
Function
- Foreign bodies which invade the skin are phagocytosed by the Langerhans cells
- The LCs move a piece of what they ate (an antigen) to their cell surface
- Then they travel to a nearby lymph node, and present that antigen to immune cells (lymphocytes)
Membrane-bound birbeck granules of Langerhans cells
Birbeck granules
- Have a unique, tennis racket structure
- Composed of a rod which is attached to a vesicle
- The function of birbeck granules is not well understood, but it is thought that they are a part of the defense mechanism for the skin (protection from antigens)
Merkel cells
Merkel cells are found in the base of hair follicles and fingertips
- Merkel cells are mechanoreceptors (tactile receptors)
- Responsible for fine/discriminating touch
- Allow our fingertips to feel detailed textures
- Merkel cells attach to keratinocytes by desmosomes
- Neurite complexes form from merkel cells, which contain unmyelinated nerve terminals
- Merkel cells are found in the stratum basale
Melanocytes
Melanocytes arise from the neural crest
- Melanocytes synthesize the pigment, melanin
- Melanocytes are located in the stratum basale and the superficial dermis
- Note that the spots and stripes on animals (leopard/zebra) are not only on the fur, but on the skin as well and are produced by concentrations of melanocytes
How do melanocytes convert tyrosine into melanin?
Melanocytes synthesize tyrosinase
- Tyrosinase is an enzyme that turns tyrosine into malanin
- Tyrosinase is synthesized at the rER then processed/packaged in the Golgi
- The Golgi relseases tyrosinase in membrane vesicles called melanosomes
- Melanosomes take up tyrosine from the cytoplasm
- Tyrosinase inside the melanosomes turns the tyrosine into melanin
- The melanosome because dark (now known as a melanin granules)
- The melanin granules make their way into the cytoplasmic processes of melanocytes
Release of melanin granules
Melanin granules can be found in the cell processes of melanocytes
- Melanocytes lie in the stratum basale (bottom layer of the epidermis)
- The cytoplasmic processes extend up into the stratum spinosum (some even enter nearby cells)
- Melanocytes release their melanin granules into nearby cells via vesicles
- The granules will surround the nucleus of neighboring cells - this covers and protects the DNA from UV radiation
Number of melanocytes
This number varies in different areas of the skin
- Dependent on the amound of sunlight the skin is exposed to
- For example, there are fewer melanocytes in the axillary fossa than on the front of the arm
- The TOTAL number of melanocytes in the body is about the same in all races
- The pigmentation of skin is not due to the number of melanocytes present
Pigmentation of the skin (differences between races)
Pigmentation is dependent upon…
- Tyrosinase activity
- Darker skin has increased activity
- Number of melanin granules
- Size of melanin granules
- Darker skin has larger
- Distribution of melanin granules
- Lighter skin are located more in the nucleus
- Darker skin is more scattered around the cell
- Rate of breakdown
- Dark skin break down slower
Vitiligo
Vitiligo is an autoimmune disease
- The body self-destructs melanocytes
- The patchy skin pigmentation is due to a decrease or a complete loss of melanocytes in certain areas
- All races and all ages can be affected
Albinism
In albinos…
- Melanocytes are present
- However, melanocytes do not synthesize melanin due to a defect or absence of tyrosinase
Malignant melanoma
Remember the ABCDEs…
- A = Appearance (general appearance, is it itchy?)
- B = Border (irregular, contour, notches, dimples)
- C = Color (irregular, red/black/brown, pigmentation)
- D = Diameter (larger than a pencil eraser needs removal)
- E = Evolution (any recent changes)
Risk factors include heriditary, light skin, excessive sun exposure
Strata of the epidermis
Strata = layers
- The epidermis is the epithelial (most superficial) layer of the skin
- The epidermis is avascular
- No blood vessesls
- The epidermis get nutrients from the capillaries from the underlying layer (the dermis)
5 strata of thick skin
Strata of thick skin, from the bottom (innermost) layer out
-
Stratum basale
- Bottommost layer, a lot of mitosis going on here
- As the cells migrate upward, they aquire different morphological characteristics and accumulate more keratin
-
Stratum spinosum
- Thickest layer
- Stratum granulosum
-
Stratum lucidum
- Actually a sub-layer of the stratum corneum
-
Stratum coreum
- Most superficial layer
Stratum Basale (Germinativum)
Stratum basale
- Single layer of columnar cells
- Basement membrane is found underneath them between the basal cells and the dermis
- Anchors the dermis to the epidermis
How are individual cells attached to each other and to the basement membrane within the stratum basale?
Attachments
- Attached to each other, and more superficial epidermal cells, via desmosomes
- Attached at the basal aspect to the basement membrane via hemidesmosomes
What are the functions of the stratum basale?
Functions
- Cell renewal (regermination of the epidermis)
- Anchoring the epidermis to the underlying dermis
Basal cell carcinoma
Caused by chronic sun exposure
- Develops on the top of the head and in places where the skin is exposed to sunlight all the time
Pearly papule
- Arises from cells found in the stratum basale
- Slow growing and rarely metastasis
- Can be excised without issue
Subepidermal blood vessels
- These lesions contain their own blood vessels
Stratum spinosum function
Function
- Has numerous cell adhesions to give the skin its strength
- Allows the skin to resist abrasions
- This provides protection from outside microorganisms
Stratum spinosum appearance
Appearance
- Called “spinosum” because the cells appear to have spines sticking out from their cytoplasm
- Look like “railroad tracks”
- They are actually intercellular bridges between neighboring cells
Desmosomal junctions between interdigitating processes of two adjacent keratinocytes
Adjacent cells
- Two adjacent cells will project cytoplasmic processes towards each other
- Attach via desmosomes (macula adherens)
- If there were no desmosomal attachments…
- Fissures in the skin would form due to injury
- This would cause the body to be vulnerable to microorganisms (bacteria, viruses)
Stratum granulosum
Stratum granulosum
- In thick skin, granulosum contains 3 or 4 layers
- Cells here have nuclei but they are fragmented
- DNA is breaking down
- Cells appear apoptotic
- Cells have many granules
- Keratohyalin granules (protein, contain keratohalin)
- Membrane coating granules (lipid)
Membrane-coating granules of the stratum granulosum
Membrane-coating granules
- Relsease lipid into the extracellular space
- Lipid forms sheet of waterproof material
- Good for sheilding the body from water gain/loss
- But the lipids also impede diffusion of nutrients and oxygen, causing cell death beyond this layer
Stratum lucidum
Stratum lucidum
- Allows light to pass through - it is the light staining layer
- Not very visible in micrographs of thin skin
- It is a sublayer of the stratum coreum
- Contains ONLY dead cellular material
- There are NO cytoplasms or organelles present
Stratum Corneum
Stratum corneum
- Very thick in the thick skin
- Recall that the thickest skin is found in the soles of our feet and also to a lesser extend in the palms of our hands
- This is a lyer of DEAD cellular material
- Lots of keratin is found here (protective material)
Strata of thin skin
Thin skin contains…
-
Stratum corneum (thin)
- There is an absence of a definitive stratum lucidum, however individual cells are present
- There is also an absense of a definitive stratum granulosum, hoever individual cells are present
- Stratum spinosum
- Stratum basale
Ichthyosis
Dermis
Dermis
- Connective tissue layer of the skin
- Contains two layers
- Papillary layer
- Reticular layer
Papillary layer of the dermis
Papillary layer
- Most superficial layer of the dermis that extends into dermal papilla
- Composed of loose connective tissue
- Has fibroblasts, macrophages, mast cells, plasma cells
- Functions to protect the body from invasion by microorganisms
Papillary layer of the dermis in THICK skin
Thick skin
- In areas subject to “mechanical stress” (palms and soles), you will see…
- Prominant epidermal ridges (dermal papilla)
- True dermal ridges
Reticular layer of the dermis
Reticular layer
- Provides tensile strength
- Thickest layer of the dermsi
- Contains collagen bundles
- Many bundles will run in different directions (look like pink ribbons)
- Prevent the skin from breaking apart
- Also contains some elastic fibers
What do the dome-shaped ridges of thick skin form?
Finger prints!
Dermis vs. Hypodermis
The hypodermis is NOT part of the skin
- Dermis contains…
- Ducts of sweat glands
- Portions of hair follicles
- Sebaceous glands
- Hypodermis: the layer underneath the dermis
- Also known as the superficial fascia
- Contains some adipose tissue
- Again, NOT part of the skin
Four types of receptors found in the skin
There are four types:
-
Free nerve endings
- Pain and temperature receptors
-
Pacinian corpuscle
- Detects pressure and vibrations
-
Meissner’s corpuscle
- Mechanoreceptors for discriminatory, fine touch
- Found in dermal papilla
-
Krause end bulbs
- Function is unclear
What are the two types of sweat glands in our body?
- Eccrine
- Apocrine
Which of the two sweat glands is the “ordinary” sweat gland found throughout the body?
Eccrine sweat glands
- Found in most of the skin
- Activated in heat and exercise
- They squirt out their products onto the skin
- Also function in the excretion or expulsion of waste product
What kind of cells help with expuslion in eccrine sweat glands?
- These glands have myoepithelial cells which assist in the “expulsion” of the secretory product (sweat) from the secretory unit
What type of secretory method is used in eccrine sweat glands?
- Sweat glands utilize the merocrine secretory method (they only secrete the product)
What is the innervation of eccrine sweat glands?
Innervation
- Postganglionic - sympathetic fibers
What type of duct does the eccrine sweat gland have?
Simple coiled tubular gland
- You will see the secretory portions lined with simple/stratified, columnar/cuboidal epithelium
- Some ducts will be made up of two layers of cuboidal epithelium
- You will see a long coiled tube
What type of sweat gland is specialized to have a huge lumen and is found in areas producing large amounts of sweat?
Apocrine sweat glands
- Found in the axilla, areola of the nipple, anal region
- Merocrine secretion (secretory product only)
- Innervated by the sympathetic NS
- Produce large amounts of sweat
- Sweat itself is odorless
- Bacteria on our skin breakdown products of sweat - this produces the odor
What do sebaceous glands produce?
Sebaceous glands are the oil producing glands of the body
- Sebaceous glands are induced by hormones and holocrine secretions
- The secretory product is know as sebum
- Empties into the hair follicle
- Cells themselves are part of the sebum
- Mature cells of the sebum become part of the secretion
What are the parts of a hair follicle?
Hair follicle
- Hair bulb (at base of hair) - encloses the dermal papilla
- Medulla - moderate keritinization
- Cortex - keritiniaed
- Cuticle - keritinized
- Internal root sheath - some keritinization
- External root sheat - not part of the hair (cells outside of the internal root sheath)
- Glassy membrane (like a bsement membrane)
- Connective tissue
Arrector pili muscle
Smooth muscle
- Attaches to the hair follicle midway and obliquely
- Functions to rais the hair
- “Cradles” the sebaceous gland
Nail plate
Nail plate
- The nail plate is a dense keratinized plate
- Rests on the nail bed (stratified squamous epithelium)
Nail matrix
Nail matrix
- Epithelium under nail root
- Growth occurs here
