I n t e g u m e n t a r y S y s t e m
What is integument ?
The integument as an organ, and is an alternative name for skin.
The integumentary system includes the skin and the skin derivatives hair, nails, and glands.
The integument can also be thought of as a
cutaneous membrane that covers the outer
surface of the body.
Introduction
The Integument
o Is the largest system of the body o 16% of body weight
o The integument is made up of two parts:
1. Cutaneous membrane
a. Epidermis– Superficial epithelium
b. Dermis – underlying CT with blood supply c. Hypodermis
2. Accessory structures a. Hair
b. Nails
c. Exocrine Glands
We lose
almost a kg
of skin
epithelium a year that becomes a major part of household
“dust”.
Functions
Protection
o First line of defense against
• Bacteria
• Viruses
o Protects underlying structures from
• Ultraviolet (UV) radiation
• Dehydration
Vitamin D production
o Needed for calcium absorption
Sensation
o Sensory receptors
Funcitons
Body temperature regulation
o If too hot
• Dermal blood vessels dilate
• Vessels carry more blood to surface so heat can escape
o If too cold
• Dermal blood vessels constrict
• Prevents heat from escaping
Excretion
o Small amounts of waste products are lost through perspiration
Structure
Understanding how the skin can function in these many ways starts with understanding the structure of the 3 layers of skin
The Epidermis
o Epithelial tissue
Dermis
o Dense connective tissue proper – irregular
Hypodermis
o Subcutaneous tissue- loose connective
tissue proper and adipose tissue
Structure
/subcutaneous layer
Structure/Epidermis
The Epidermis is
•A stratified squamous epithelia, composed of four to five layers (depending on body region) of epithelial cells.
•Nutrients and oxygen diffuse from
capillaries in the dermis
Structure/Cells of Epidermis
The epidermis is composed of
five types of cells
Structure/Cells of Epidermis
• Stem cells are undifferentiated cells that divide and give rise to the keratinocytes described next. They are found only in the deepest layer of the epidermis, called the stratum basale. Basal cells are an example of tissue-specific stem cells, meaning they can turn into a variety of cell types found in that tissue. Under normal conditions, daughter basal cells most commonly replace lost keratinocytes.
Structure/Cells of Epidermis
• Keratinocytes are the great majority of epidermal cells. They are named for their role in synthesizing keratin. In ordinary histological specimens, nearly all of the epidermal cells you see are keratinocytes.
• The keratinocytes on the most superficial layer of the epidermis are dead, and periodically slough away, being replaced by cells from the deeper layers. As keratinocytes move superficially from the deeper layers, they lose cytoplasm and become flattened, allowing for many layers in a relatively small space.
Structure/Cells of Epidermis
• Melanocytes also occur only in the stratum basale, amid the stem cells and deepest keratinocytes. They synthesize the brown to black pigment melanin. They have branching processes that spread among the keratinocytes and continually shed melanin- containing fragments from their tips.
• The keratinocytes phagocytize these fragments and accumulate melanin granules on the “sunny side” of the nucleus. Like a parasol, the pigment shields the DNA from ultraviolet radiation.
Structure/Cells of Epidermis
• Tactile (Merkel) cells, relatively few in number, are receptors for the sense of touch.
They, too, are found in the basal layer of the epidermis and are associated with an underlying dermal nerve fiber. The tactile cell and its nerve fiber are collectively called a tactile (Merkel) disc.
Structure/Cells of Epidermis
• Dendritic (Langerhans) cells are found in two layers of the epidermis called the stratum spinosum and stratum granulosum. They are macrophages that originate in the bone marrow but migrate to the epidermis and epithelia of the oral cavity, esophagus, and vagina.
• The epidermis has as many as 800 dendritic cells per square millimeter. They stand guard against toxins, microbes, and other pathogens that penetrate into the skin. When they detect such invaders, they alert the immune system so the body can defend itself.
Stucture/Epidermal Strata
• Cells of the epidermis are arranged in four to five zones, or strata (five in thick skin).
• Thin Skin (A)
Covers most of the body
Has four layers of keratinocytes
• Thick Skin (B)
Covers the palms of the hands and soles of the feet Has five layers of keratinocytes
• The following description progresses from deep to superficial, and from the youngest to the oldest keratinocytes.
Stucture/Epidermal Strata
• The stratum basale consists mainly of a single layer of cuboidal to low columnar stem cells and keratinocytes resting on the basement membrane.
• Scattered among these are the melanocytes and tactile cells. As stem cells of the stratum basale divide, they give rise to keratinocytes that migrate toward the skin surface and replace lost epidermal cells.
• The stratum basale is attached to basement membrane by hemidesmosomes.
• Forms a strong bond between epidermis and dermis.
• Dermal papillae (tiny mounds)
Increase the area of basement membrane Strengthen attachment between epidermis and dermis
Stucture/Epidermal Strata
• The stratum
spinosum consists of several layers of keratinocytes. In most skin, this is the thickest stratum, but in the thick skin it is usually exceeded by
the stratum
corneum. Eight to ten layers.
• The deepest cells of
the stratum
spinosum remain capable of mitosis, but as they are pushed farther upward, they cease dividing. Instead,
they produce more and more keratin filaments, which cause the cells to flatten. Therefore, the higher up you look in the stratum spinosum, the flatter the cells appear.
• Dendritic cells are
also found
throughout the stratum spinosum but are not usually visible in tissue sections.
Stucture/Epidermal Strata
• The stratum spinosum is named for an artificial appearance (artifact) created by the histological fixation of tissue specimens.
• Keratinocytes are firmly attached to each other by numerous desmosomes, which partly account for the toughness of the epidermis.
• Histological fixatives shrink the keratinocytes so they pull away from each other, but they remain attached by the desmosomes—like two people holding hands while they step farther apart.
• The desmosomes thus create bridges from cell to cell, giving each cell a spiny appearance from which we derive the word spinosum.
«spiny layer»
Stucture/Epidermal Strata
• The stratum granulosum consists of three to five layers of flat keratinocytes—more in the thick skin than in the thin skin. The keratinocytes of this layer contain coarse, dark-staining keratohyalin granules that give the layer its name.
• Epidermal keratinocytes are also bound to each other by tight junctions, which make an essential contribution to water retention by the skin.
• Stops dividing, starts producing Keratin
A tough, fibrous protein Makes up hair and nails Keratohyalin
Dense granules
Cross-link keratin fibers
«grainy layer»
Stucture/Epidermal Strata
• The stratum lucidum is a thin zone superficial to the stratum granulosum, seen only in the thick skin. Here, the keratinocytes are densely packed with a clear protein named eleidin. The cells have no nuclei or other organelles. This zone has a pale, featureless appearance with indistinct cell boundaries
«clear layer»
Stucture/Epidermal Strata
• The stratum corneum consists of up to 30 layers of dead, scaly, keratinized cells that form a durable surface layer.
This layer is especially resistant to abrasion, penetration, and water loss.
• Shed and replaced every 2 weeks.
«horn layer»
Stucture/Epidermis/Skin Pigments
• Skin Pigments
• Melanin is produced by melanocytes in the stratum basale
• Eumelanin (brown to black)
• Pheomelanin (yellow to red)
•Freckles are clusters of concentrated
melanin triggered by exposure to sunlight.
Stucture/Epidermis/Skin Pigments
• Vitiligo is a chronic disorder that causes depigmentation patches in the skin. The precise pathogenesis, or cause, is not known, but is most likely a combination of genetic factors coupled with a disorder of the immune system (autoimmune disease).
• Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair, and eyes due to a defect of an enzyme involved in the production of melanin.
Stucture/Dermis
The Dermis
Located between epidermis and subcutaneous layer
Anchors epidermal accessory
structures (hair follicles, sweat glands)
Two components
1. Outer papillary layer
2. Deep reticular layer
Stucture/Dermis
The Papillary Layer
Consists of areolar connective tissue
Contains smaller capillaries, lymphatics, and sensory neurons Has dermal papillae projecting between epidermal ridges
The Reticular Layer
Consists of dense irregular connective tissue
Contains larger blood vessels, lymphatic vessels, and nerve fibers
Contains collagen and elastic fibers Contains connective tissue proper
Stucture/Dermis/Dermatitis
An inflammation of the papillary layer Caused by
infection, radiation, mechanical irritation, or chemicals
Characterized by
itch or pain
Characteristics
Strong, due to collagen fibers
Elastic, due to elastic fibers
Flexible
Stucture/HypoDermis
• The subcutaneous layer is also called the hypodermis, and it attaches the skin to underlying tissues and organs.
• It contains blood vessels and nerves in transit to the more superficial layers.
• It also contains lamellated (pacinian) corpuscles that detect external pressure applied to the skin.
• Deposits of Subcutaneous Fat.
Benefits of Multiple Layers
Multiple layers in the skin allow for specialization.
o Adapted to fast turn-over, the epidermis resists damage and offers protection to underlying
tissues.
o The dermis provides temperature stability and prevents dehydration, and yet is capable of
limited healing.
o The subcutaneous tissues insulate, store fat,
and anchor the skin.
Sensory Receptors
The skin contains different types of sensory receptors to differentiate between the different tactile (“touch”) sensations.
• Light touch, pressure, vibration, itch and tickle
These sensory receptors are found in different layers:
• Superficially
Merkel discs, free nerve endings (detect many stimuli), Meissner corpuscles, and hair root plexuses
• Deep
Pacinian corpuscles
Accessory Structures of
the Skin
Hair/Wool/Mohair
Hair is associated with the word “pili”.
• It is present on most surfaces except the palms,
anterior surfaces of fingers, and the soles of the feet.
•It is composed of dead, keratinized epidermal cells.
•Genetics determines thickness and distribution.
Hair helps with touch sensations and protects the body against the harmful effects of the sun and against heat loss.
Stucture/Hair
The Hair Follicle
Hair follicles are the organs that form the hairs.
Located deep in dermis.
Produces nonliving hairs.
Wrapped in a dense connective tissue sheath.
Base is surrounded by sensory nerves (root
hair plexus).
Stucture/Hair
Stucture/Hair
Skin Glands
Sebaceous (oil) glands are connected to hair follicles.
o They secrete an oily substance called sebum which does 2 important things:
• Prevents dehydration of hair and skin
• Inhibits growth of certain bacteria
Skin Glands
In addition to oil glands, there are 2 types of skin sweat glands (also called sudoriferous glands).
Both are simple,coiled tubular glands.
Eccrine sweat glands are the most numerous. They secrete a watery solution that helps to cool the body and eliminates small amounts of waste.
Apocrine sweat glands are located mainly in the skin of the axilla, groin, areolae, and facial regions of adult males. They secrete a slightly viscous sweat. Located mostly in the subcutaneous layer, and the excretory duct opens into hair follicles
Skin Glands/Mammary Gland
Knowledge of the microscopic anatomy of the mammary gland is important to the understanding of mastitis in large animals and mammary tumors in small animals. Mastitis is inflammation of this gland and is one of the most common and economically significant
clinical diseases in the cow. In response to bacterial infection, inflammatory changes occur in the gland with influx of many
bloodborne neutrophils.
Skin Glands/Mammary Gland
• They are modified skin glands takes form as united tubulo-alveoler structure. This connective tissues’ penatration of the mammary glands which is surrendered by rich subcutaneous tissue with collagens and elastic fibres are creates the lob and lobule concept.
• Alveoli
• Secretory alveoli of the mammary gland are spherical to ovoid inshape with a large lumen
• The eluent channel of mammary glands:
• intralobuler duktus laktiferus
• İnterlobuler duktus laktiferus
• İnterlober duktus laktiferus
Skin Glands/Mammary Gland
400 liters of blood is get through from mammary glands for 1 liter of milk
Clusters of alveoli form lobules within the gland. All the lobules are not in the same secretory phase at the same time. Some lobules may complete their secretory cycle and be filled with milk before others begin. Therefore, a single histologic section may contain lobules in various stages of activity. Usually, all of thesecretory alveoli within a lobule are in approximately the same secretory phase.
OXYTOCIN hormone which is secrated from of pituitary are ensures the contraction of myoepitel cells and causes the
milk’s getting down
The protein(especially casein) carbonhydrates(lactoses), minerals and vitamins are in a molten state in milk.
Nails/Claws/Hoof
Nails/claws/hoofs are composed of hard,
keratinized epidermal cells located over the
dorsal surfaces of the ends of foots.
Nails/Claws/Hoof-WALL
• The wall of the hoof is composed of three layers .
• From the outside inward, they are the stratum externum (tectorium), the stratum medium, and the stratum internum (lamellatum).
Nails/Claws/Hoof-WALL
Stratum externum
•This is a thin layer is situated on the outside of the nail. It’s also called glazed layer because it’s bright. It’s composed by the flat cells in epidermis.
Stratum medium
•The thickest and the strongest part which situated in the middle of nail. It’s in a complete horny structure. This horn mass gets shape by the epitel cell messes that stayed between the cylinderic formations (cylinderical cornea) which parallelly reaches the nails surface
Stratum internum (lamellatum).
•The inner layer which part the epidermis faces the dermis. (chorium) The hornified epitel cell messes creates lamellas here (capsula lamella) This main lamellas reaches to the dermis as a shape of finger. Every main lamellas devides to the more little and not-hornified seconder lamellas and geary image The connective tissues that is under this formations are gets between them and they gets a finger shaped structure. This lamellas that formed by connective tissues are named chorium lamella
CLINICAL SIGNIFICANC
Dermatologic problems are among the most commonly seen disorders in veterinary hospitals.
It is important for the veterinarian to know and understand about the physiology of the skin about the most common dermatolohic disorders that affects animals.
Since the skin is the largest organ of the animal's body and cover the animal's exterior , it is subjected to many types of injurious agents.
Dermatology is the study of the the skin and its associated disease.
The skin must protect the animal from becoming over hydrated during immersion in water, from becoming dehydrated during exposure to heat or sun and from the a variety of bacterial, viral, fungal,and parasitic agents
