Integumentum Flashcards
What constitutes to the integumentary system?
the skin (cutis) and its derivatives
How many layers does the skin consist of?
2 layers
What are the two main layers of the skin?
1) the epidermis
- keratinized stratified squamous epithelium
- grows continuously
- maintains normal thickness by desquamation
2) the dermis
- dense connective tissue
- imparts mechanical support, strength and thickness
- derived from the mesoderm
What is the dermis also called?
true skin
What is the epidermis composed of?
keratenized stratified squamous epithelium
What is the dermis composed of?
dense connective tissue
How does the epidermis maintain its thickness?
- grows continuously
- process: desquamation
What is the dermis derived from?
the mesoderm
What does the dermis contain?
- hair follicles
- glands
- sweat glands
- etc.
What lies below the dermis?
the hypodermis
What are the different epidermal derivatives of the skin?
- hair follicles
- hair
- sweat (sudoriferous) glands
- sebaceous glands
- mammary glands
What is the epidermis composed of? What are the distinct layers?
composed of: keratinized stratified squamous epithelium
4 distinct layers:
thick skin= 5 distinct layers (outside to inside):
- stratum corneum (keritinized cells)
- stratum lucidum (limited to thick skin!) (subdivision of stratum corneum)
- stratum granulosum (numeous intensely staining granules)
- stratum spinosum (light microscopic appearance of short process extending from cell to cell)
- stratum basale/stratum germinativum (mitotically active cells= stem cells))
What is the easiest way to indentify the different layers of the epidermis?
Look for stratum granulosum: darkest, deepest colour.
What epidermis layer is distinct to thick skin only?
stratum lucidum (part of stratum corneum)
State the 4 skin layers from the outside to the inside.
stratum corneum
stratum granulosum
stratum spinosum
stratum basale
What is the stratum basale? What is represented by? What does it contain?
stratum basale: most deepest layer of the dermis
represented by a single layer of cells laying on the basal lamina
contains:
- stem cells from which new cells (keratinocytes) arise by mitotic division.
- melanocytes in cytoplasm (produce melanin) (5% of cells in spidermis)
Where do all the epidermis layers come from?
Stratum basale stem cells divide mitotically generating new cells.
What cells arise from the stratum basale stem cells? how?
kerinocytes
by mitotic division
What else, except of stem cells, is present in the stratum basale?
melanin:
- transferred from neighbouring melanocytes
- intersperced in statum basale
Where are melanocytes located? What is their structure? What percentage do they make up of the epidermis?
location: stratum basale; stratum spinosum (processes)
structure: long processes that extend between keratinocytes into the stratum spinosum
5% of cells in the epidermis
What cells reside in the stratum basale?
melanocytes
What is the connection of skin colour to melanin?
The greater the melanin number the darker the skin colour.
What does melanin do?
Keeps all dividing cells protected (shields their nucleus= shielfing their genetic material).
What do the long processes of melanocytes extend into?
into stratum spinosum through the keratinocytes
What do melanocytes synthesize? Where?
synthesize melanin pigment in melanosomes
What happens during the process of pigment donation?
melanocytes transfer melanin in melanosomes into adjacent keratinocytes.
What is the process called when melanin is transferred? In what is it transferred? From what cells? To what cells?
process name: pigment donation
from: melanocytes
in: melanosomes
to: keratinocytes
How does melanin enter epidermis cells?
1) Melanocyte processes (containing melanin pigment) fit between different keratinocytes.
2) Melanin donation occurs: some cytoplasm parts of the membrane detach from the melanocyte and enters the keratinocyte.
3) The melanin cell part moved throughout the epiermis cell.
4) The melanin cell membrane ruptures, releasing melanin granules into the keratinocyte.
5) Melanin granules create a c-shape/moon shape circle around the keratinocyte nucleus, protecting the nucleus from UV light.
How does melanin protect keratinocytes from UV?
- absorbs UV light
- refracts UV light
What does UV light also influence?
the genetic material of viruses and bacteria
Why can’t viruses and bacteria survive in the outside environment for a long time?
They are not protected from UV light by melanin granules. UV light damages their genetic material, causing them to degrade.
What is the function of melanin? What happens with it after pigment donation?
- accumulates above nuclei of keratinocytes
- function: protects nuclear DNA from UV radiation and damage
What is the thickness of stratum spinosum?
at least several cells thick
State the differences in keratinocyte shape of the different epidermal layers.
Stratum basale cells are cuboidal in shape, and then all otehr layers progressively get more flat.
What is the reason for the name ‘stratum spinosum’?
keratinocytes in stratum spinosum have spine-like cytoplasmic processes.
What is stratum spinosum composed of? State the structure of these cells.
keratinocytes
- larger than stratum basale keratinocytes
- have cytoplasmic processes (spines)
not flat, not round, much flatter!
What happens as cells mature in the stratum spinosum?
- mature and move to the surface
- increase in size
- become flattened in a parallel plane to the surface
Where is the maturing of spinous cells most distinctably seen? Why?
most superficial spinous cells
- nuclei elongate (instead of ovoid they match the squamous shape of the cell)
What is the stratum granulosum? What is its thickness?
- most superficial layer of the non-karatinized epidermis
- 1-3 cells thick
Why is the stratum granulosum epidermal layer much darker than the other layers.
Most of the cells inner volume in occupied by keratohyalin granules.
Where do keratohyalin granules begin to form?
stratum spinosum
What do keratohyalin granules do?
Bind together all of the keratin fillaments (present in all cells), later accumulating them through the protein filaggrin.
- important for stratum corneum (cells mostly filled by keratin)
What cells is the startum granulosum made up of? What is special about them?
keratinocytes
- contain numerous keratohyalin granules
What do keratohyalin granules contain? What contains these granules?
keratinocytes in the stratum granulosum contain keratohyalin granules.
keratohyalin granules contain precursor proteins of filaggrin (aggregates keratin filaments)
What does the precursor protein of fillagrin do? What contains the presursor?
- aggregate with keratin fillaments (presnt in the startum corneum cornified cells),
- keratinocytes in the stratum granulosum contain keratohyalin granules
State the shape and size of keratohyalin granules. Where are they located?
in keratinocytes of stratum granulosum
- irregular shape and size
Where are there more epidermis layers present? Why?
Parts of the skin which are exposed to more mechanical stress, eg. hands, feet.
- epidermis must resist the additional strain
How many layers can the epidermis reach in thick skin which is subjected to great mechanical stress?
500+ layers
What does skin thickness depend on?
- species
- individual (eg. occupation)
occupation- farmer, teacher, etc.
What are the distinguishable characteristics of thick skin?
- contains 5 epidermis layers
- has more individual layers (lines)
- does not have hair!
What are the distinguishable characteristics of thin skin?
- contains 4 epidermis layers (does not contain stratum lucidum)
- has less individual layers (100-200 cell lines)
- has hair!
What is stratum lucidum? What is it a subdivision of? Where is it seen?
- subdivision of stratum corneum
- seen in thick skin
What is the structure of stratum lucidum in the light microscope?
refractile appearance
stains poorly
What does the refractile layer of stratum lucidum contain? What process is advanced in such cells? How is it advanced?
- eosinophilic cells
- advanced keratinization process (nucleus and cytoplasmic organelles become disrupted and dissapear as the cell fills with keratin)
What is hairless skin referred to as?
thick skin
Where does skin posses a thinner epidermis?
thin skin (with hair)
What cells make up stratum corneum? What are they filled with?
- most differenciated cells in the skin
- loose nucleus and cytoplasmic organelles
- filled almost entirely with keratin fillaments
- dead cells!
What epidermis cell layers are made up of dead cells?
2 layers:
- stratum lucidum (thick skin only)
- stratum corneum
What is the thick plasma membrane of the keratinized stratum corneum cells coated in? From which side? What does it form?
layer of lipids
coated from the outside
forms the water barrier in the epidermis
What is the function of keratin?
- water resistant
- protects from pathogens (thickness and pH)
- changes physical environemnt (acidic)
What system is the skin a part of? Why?
immune system:
- barrier
- skin and mucosa protects from 98% of pathogen invasions
What is the desquamation process? How rapidly does it occur?
The most outside cells (final cells in the stratum corneum) are constantly detatching.
- very rapid: 1000 cells are detatched every centimeter, every hour
Why is skin thickness always constant?
amount of cells produced = amount of cells lost (desquamation)
balance!
Approximately how long does total epidermal turnover take?
47 days
What other cells are present in the epidermis? What are their functions? What percentage of the epidermis do they make up?
Langerhans’ Cells (dendritic cells):
- 2% - 5%
- antigen presenting cells
- involved in the signaling of the immune system
Merkel’s Cells:
- 6% - 10%
- mechanoreceptor
What are Langerhans’ cells? Another name?
Dendritic Cells:
- antigen-presenting cells
- involved in the signaling of the immune system
What function do Merkell’s cells have?
mechanoreceptor function
Where are Merkel’s cells abundant?
- highly sensitive skin
- eg. human fingertips
What do Merkel’s cells do?
make synaptic contacts with sensory nerve nerve fibers.
What type of light damages genetic material?
UV light
How do Merkell cells develop?
unknown
What is the function of Merkells cells?
- unknown
- mechanoreceptors (making nervous impulses from mechanical impact and vibrations)
- gets most impact such as fingerprints, vibrations etc.
- transfers signals into sensory neuron dendrites
Are Langerhans cells macrophages? What do they do?
NO! They do not digest everything.
- they act as antigen presenting cells
- if small injuries occur in skin, Langerhans cells protect it from pathogens
- catch and digest some pathogens
- move into the nearest lymph node (ability to migrate)
- antigens in lymph nodes activate B-lymphocytes and T-lymphocytes
- lymphocytes travel to the infected area, fighting the infection.
What is the dermis composed of?
2 layers:
- papillary layer
- reticular layer
What is the papillary layer of the dermis composed of? Where is it located?
- superficial layer
composition:
- loose connective tissue
- extensive plexus of blood
- lymphatic vessels
- sensory never endings
What does the epidermal-dermal junction contain?
dermal papillae:
- numerous finger-like connective tissue protrusions corresponding to similar epidermal protrusions (epidermal ridges)
What do dermal papillae contain?
- nerve endings
- network of blood capillaries
- network of lymphatic capillaries
What is the effect of location on the epidermal-dermal junction?
increased mechanical stress:
- deeper epidermal ridges (thicker epithelium)
- longer and denser dermal papillae
more extensive interfereance between the epidermis and dermis.
What does the papillary layer have direct contact with?
the epidermis
In easy words, state the epidermal-dermal junction.
epidermis- infoldings
dermis- outfoldings
What is the reticular layer composed of? What is its location?
- deeper
composition:
- dense irregular connective tissue
- collagen
- elastic fibers
- larger blood vessels
How does the reticular and papillary layer compare?
reticular layer:
- thicker
- less cellular
papillary layer:
- thinner
- more cellular
What layer lays deeper to the dermis? What is it composed of?
hypodermis
composition:
- loose connective tissue
- adipose tissue (special connective tissue: large cell with large lipid droplet and border nucleus)
- highly vascular
What is the hypodermis a route for? Why?
drug administration
- highly vascular
- absorbs drugs quickly
drugs in muscle (deeper) = slower absorption (low vascularisation)
What is the ‘hypodermis’?
connector layer between:
- skin (dermis)
- muscles
Where is hair situated?
in hair follicles (inner skin infolding)
What is a hair follicle?
- inner infolding of the skin
- invagination of the epidermis in which a hair is formed
What is a hair follicle responsible for?
The production and growth of a hair.
How many regions are hair follicles divided into? What are they?
4 regions:
- infundibulum
- isthmus
- suprabulb part
- hair bulb
What region is the infundibulum? Where is it located? What is it part of?
location:
- from the surface opening of the follicle
- to the level of the opening of the sebaceous gland
part of:
- pilosebaceous canal (route of sebum discharge)
What is the name of the canal present within a hair follicle?
pilosebaceous canal
What is the pilosebaceous canal?
route for the discharge of sebum, an oily substance
Where is the isthmus positioned?
from: infundibulum
to: level of the insertion of the arrector pilli muscle
What does the sebaceous gland open into?
the hair follicle.
not the skin directly!
Why does hair stand when scared or in cold temperatures?
mechanism to keep body warm
- heater air is trapped between the ‘standing’ hair
What is the end part of the hair follicle called?
hair bulb
What is the part of the hair called located between the isthmus and the hair bulb?
the suprabulb part
What is the follicular bulge? Where is it located? What does it contain?
- protrudes hair follicle near the insertion of the arrector pilli muscle
- contains epidermal stem cells
What is the diameter of the hair follicle like?
inferior segment: nearly uniform
base: forms bulb
What is the base of the hair bulb invaginated by?
dermal papilla
What cells form the hair bulb?
‘hair matrix’ = matrix cells
- surrounding the dermal papilla connective tissue
- fused, all layers from the epidermis and dermis layers = matrix
What accounts for the growth of hair?
the division and proliferation of matrix cells
What is the hair matrix? What layer is most important?
a mixture of layers of the epidermis and dermis located at the end of the hair bulb.
most important: stratum basale (stem cells)
What is the hair shaft surrounded by?
the epidermal and dermal root sheath
What is hair?
Elongated filamentous structures projecting from hair follicles.
What is hair composed of?
- heavily cross-linked hard keratins
- consist of 3 layers
What are the layers of the hair?
1) cuticle
2) cortex
3) medulla
What is the hair medulla? What does it consist of? Where is it present?
- central part of the shaft
- column of large, loosely connected keratinized cells containing SOFT keratin
- only present in thick hair
highly keratinized cells = non living (similar to stratum corneum)
What is made up of soft keratin? What does that mean?
soft keratin= hair medulla
- not as well protected as cortex or stratum corneum of the skin
What is the hair cortex? What does it consist of? What are their properties? Where is it present?
- largest layer (80% of total hair mass)
- located outside the medulla (all hair)
- cortical cells filled with HARD keratin
HARD KERATIN: highly concentrated, more protective properties, more resistant to environmental factors
Shortly, state the composition and part function of hair.
1) Cuticle: outermost layer protecting the cortex. Hard shingle like layer of overlapping cells, like scales.
2) Cortex: provides strength, moisture, colour and texture.
3) Medulla: innermost layer, can be absent in fine/blonde hair.
What is the hair cuticle? What is it composed of?
- outermost layer of hair
- contains several layers of overlapping, semitransparent, keratinized squamous cells
What is the function of the cuticle?
- protects hair from physical and chemical damage
- determines hair porosity
What is the function of the sinus located within the hair follicle? Where is it present?
transport of oxygen and blood to the hair follicle
- present only in tactile hair!
What are tactile hairs?
receptor hairs responsible for certain actions eg. whiskers to measure distance.
What glands are associated with skin? (What do they produce?)
- sebaceous glands (sebum)
- apocrine glands
- merocrine glands
- mammary glands
What are sebaceous glands associated with? What do they moisturize?
- hair follicles in the skin
- mosturize hair and sometimes skin partially
What are apocrine glands? Where are they most active?
- principal animal sweat glands
- coiled tubular glands
- very active in the horse!
What are merocrine glands? Where are they located?
- sweat glands
- coiled tubular glands
located in:
- footpad of carnivores
- frog of the horse
- nasolabial region of ruminants and swine
What do secretions of sebaceous and sweat glands do?
- lubricate
- moisture
- cool
the integument
What is the difference in the sweat produced by the different glands?
apocrine gland: more solid sweat (includes parts of cells: proteins)
merocrine gland: small vesicles in final product, more watery
Compare the structure of the different sweat glands.
Both:
- coiled tubular organs
- secrete sweat
Merocrine gland:
- opens directly to the skin surface
- most common in apes!
Apocrine gland:
- opens into the infundibulum of the hair follicle
- most common in all animals (but humans)
apocrine glands open into infundibulum like the sebaceous gland
What is a mammary gland? What does it produce? What is it lined by?
type: compound tubuloalveolar gland
produces: milk
- secretory alveoli are lined by *myoepithelial cells
- myoepithelial cells are lined by *simple cuboidal epithelium
What are the secretory alveoli of mammary glands lined by?
- secretory alveoli are lined by myoepithelial cells which are lined by simple cuboidal epithelium
What cells produce milk in the mammary gland?
simple cuboidal epithelium cells
What cells push out the secrete from the mammary glands?
myoepithelial cells
How does milk flow in the mammary gland?
alveolus
intralobular duct
lobular duct
lactiferous lobar duct
lactiferous sinus (gland sinus)
teat sinus
papillary duct (teat canal)
Where is milk collected in the mammary gland?
lactiferous sinus
State the epithelium lining the duct passages of the mammary gland.
transitions from simple cuboidal epithelium (simple columnar –> stratified columnar) to stratified squamous epithelium.
cannot be stratified cuboidal as it would take too much effort and time for milk to be squeezed through thick layers.
stratified squamous- skin like (it has direct contact with the environment (teat))
State the types of secretions occuring in the mammary gland. What do they secrete?
merocrine secretion: protein component of milk
apocrine secretion: lipid component of milk
What are glands classified into? What are they made up of? What are mammary glands exceptions?
active or inactive
- made up of the same components (stroma and parenchyma), yet at different ratios.
most galnds are active all the time
mammary gland: only active when an animal has young
What is an active gland? What features does it have?
- parenchyma takes up most of its volume
- open alveoli
What is an inactive gland? What features does it have?
- stroma (loose connective tissue and adipose tissue) takes up most of the volume
- alveoli collapse
parenchyma is exchanged for stroma
