lab practical #2

Major Divisions of the Skin

• Epidermis
• Dermis

• Hypodermis (or subcutaneous layer)-is not a part of the Integumentary system; is located below the dermis; is a major storage site for adipose tissue

Epidermis

• The outer layer of the skin
• Is composed of epithelial tissue
• Is keratinized stratified squamous epithelial
• Four types of cells are found here
• Keratinocytes
• Melanocytes
• Langerhans cells
• Merkel cells

Keratinocytes

• Comprise 90 % of the cells of the epidermis
• Produce keratin, a tough fibrous protein that protects the skin and deeper tissues from chemicals, microbes, and heat
• Also produce granules which secrete a lipid-rich product that helps waterproof the skin

Melanocytes

• Comprise 8% of the epidermal cells
• Produce and secrete the pigment melanin

Langerhans Cells

• Are immune system cells that attack pathogens that enter the skin

Merkel Cells

• Are the least abundant cell type and are found only in the deepest layer of the epidermis
• These cells function as touch receptors and are associated with sensory neurons

Layers of the Epidermis (Deep to Superficial)

• Stratum Basale (or Stratum Germinativum)
• Stratum Spinosum
• Stratum Granulosum
• Stratum Lucidum
• Stratum Corneum

Stratum Basale (or Stratum Germinativum)

• A single row of cells attached to the basement membrane
• Contains stem cells that divide to form new keratinocytes
• Melanocytes, Langerhans cells, and Merkel cells are also found within this layer

Stratum Spinosum

• Contains 8 to 10 rows of cells, mainly keratinocytes

Stratum Granulosum

• Granules are observed within keratinocytes
• Contains 3 to 5 rows of flattened keratinocytes that are beginning to die
• No dividing cells are present in this layer or more superficial layers

Stratum Lucidum

• Contains 3 to 5 rows of flat, dead keratinocytes
• Is not found in thin skin

Stratum Corneum

• Is a very thick layer containing 25 to 30 or more rows of dead, squamous-shaped keratinocytes
• This layer is tough and water repellent
• These cells continually slough off and are replaced by cells in the adjacent layer

Thick Skin

• Found in the palms and soles of the feet
• Has all five strata

Thin Skin

• Covers the majority of the body
• Does not have visible stratum Lucidum and has a thinner stratum corneum

Dermis

• Is the connective tissue layer that is firmly attached to the epidermis by a basement membrane
• Provides the avascular epidermis with nutrients
• Connects the epidermis to the underlying hypodermis
• Consists of two regions:
• Papillary Region
• Reticular Region
• Is highly vascularized

Papillary Region

• Is a thin layer or areolar connective tissue that is deep to the stratum basale of the epidermis and basement membrane
• Dermal Papillae are finger-like projections of this region that extend into the epidermis

Dermal Papillae

• Are finger-like projections of the papillary region that extend into the epidermis
• In the palms, fingers, soles, and toes, these cause genetically determined whorls in the epidermis called epidermal ridges that increase surface area. Sweat glands deposit their secretions onto these ridges, resulting in fingerprints

Reticular Layer

• Is the deeper and much thicker region of the dermis
• Is composed mainly of dense, irregular connective tissue whose collagen fibers provide the skin with strength and whose elastic fibers provide elasticity
• Some adipose tissue can be found in this layer

Accessory Structures of the Skin

• Hairs
• Hair Follicles
• Nails
• Sweat Glands (Sudoriferous Glands)
• Sebaceous Glands
• Ceruminous Glands
• Mammary Glands
• All of these are derived from epidermal tissue and extend into the dermis

Sweat Glands (or Sudoriferous Glands)

• Secrete a watery substance that is important in excretion and body temperature regulation
• Two types:
• Eccrine Glands
• Apocrine Glands

Eccrine Glands

• Are the most common type of sudoriferous gland
• Are found on most areas of the body
• Ducts from these glands deposit their secretions, called sweat, on the epithelial surface

Apocrine Glands

• Are found only in the axilla, genital area, and pigmented area around the nipples
• Produce a secretion similar to sweat but more viscous
• This secretion is deposited on the distal end of the hair root
• Is odorless until broke down by bacteria

Ceruminous Glands

• Are found in the ear canal and secrete a waxy substance called Cerumen that prevents foreign substances from entering the auditory canal

Mammary Glands

• Are found in the breasts and synthesize and secrete milk after appropriate hormonal stimulation

Sebaceous Glands

• Or oil glands
• Are found surrounding hair follicles and deposit sebum, an oily substance that lubricates the skin and hair, into the neck of the follicle

Hair

• Found all over the body with the exception of the palms, soles, lips, and parts of the external genitalia
• Consists of dead, keratinized epithelial cells
• Had two main sections
• Shaft
• Root

Shaft

• Projects from the skin surface

Root

• Extends into the dermis of the skin and sometimes the hypodermis

Hair Follicle

• Surrounds the hair root
• Is sometimes formed from epidermal layers that project into the dermis
• A connective tissue sheath comprised of dermal tissue surrounds this accessory

Hair Bulb

• The expanded base of the hair follicle
• Contains the papilla of the hair and the matrix

Papilla

• Is a projection of connective tissue into the hair follicle and contains blood vessels that provide nutrients to the dividing cells of the matrix

Matrix

• IS derived from the stratum basale of the epidermis
• Forms new hair cells that are added to the base of the hair root

Arrector Pili

• Is a bundle of smooth muscle cells attached to the connective tissue sheath around the hair follicle
• Contraction moves the hair from its normal angle to a 90° with the skins surface
• Contracts in response to stress (including cold temperature)

Cuticle (Outer Layer)

• The layer of hair that we see
• A thin layer of dead, flattened, keratinized cells that overlap each other

Cortex and Medulla

• Cells in these areas contain pigments granules that give hair its color

Nails

• Are found on the distal ends of the digits
• Assist in grabbing and manipulating objects
• Protect the digits

Nails Consist of:

• Nail Body
• Free Edge
• Root

Nail body

Is the part of the nail that is visible

Free edge

• Extend beyond the digit

Root

• Is within the fold of the skin at the proximal end of the nail body

Epiphyses

• The enlarges proximal and distal ends of the long bones
• Spongy bone forms the interior

Diaphysis

• The middle shaft area of the long bones
• Compact bones forms the exterior (or cortex) of long bones and most of _____
• A small layer of spongy bone lines the interior

Metaphyses

• Are areas in an adult bone where the epiphyses and diaphysis join
• In a growing bone, contains a layer of hyaline cartilage called the epiphyseal plate

Epiphyseal Line

• Bone growth stops when the epiphyseal plate cartilage becomes ossified and forms a bony structure called the _____ _____

Articular Cartilage

• Composed of hyaline cartilage
• Covers both epiphyses

Periosteum

• Covers the bone, excluding the epiphyses
• A tough, connective tissue membrane

Medullary Cavity

• The hollow center of the bony diaphysis
• A small amount of spongy bone is found in this area
• Is lined with a connective tissue membrane called endosteum

Endosteum

• A connective tissue membrane
• Lines the medullary cavity
• Also lines the cavities within the spongy bone of the epiphyses

Both the periosteum and endosteum contain _____ and _____

Osteoclasts and Osteoblasts

Assists with bone formation, bone tissue repair, and bone remodeling

Osteoclasts and Osteoblasts

Yellow Marrow

Is a fatty substance found within the medullary cavity

Red Marrow

Is found within the cavities of spongy bone and produces blood cells

Nutrient Artery

• Is a large artery that enters compact bone near the middle of the diaphysis
• Immediately branches into proximal and distal portions which supply blood to the inner layer of compact bone, spongy bone, and red marrow

Nutrient Foramen

• Is the foramen through which the nutrient artery enters

Compact (cortical) Bone

• Is composed of repeating units of osteons, with each unit having a central canal running longitudinally

Central (Haversian) Canal

• Contains blood vessels, lymphatic vessels, and nerves that serve compact bone tissue

Periosteum

• Dense, regular connective tissue covering the bone surface

Perforating (Volkmann) Canals

• These run horizontally in compact bone and connect with the central canal

Concentric Lamellae

• The main feature of each osteon
• Concentric rings

Osteocytes reside in the _____

Lacunae

Lacunae

Are found between concentric lamellae

Canaliculi

• The thin lines (small channels) that connect the lacunae
• Allow nutrients from the blood vessels in the central canal to diffuse to the osteocytes embedded in the solid bone material
• The route by which waste materials are removed from the cells

Osteocytes

• Are mature bone cells that reside in the lacunae
• The process extend through the canaliculi

Interstitial Lamellae

• Fill in the spaces between the osteons

Spongy (Cancellous or Trabecular) Bone

• Does not contain osteons but instead has trabeculae
• Has many spaces filled with red marrow
• Needs the protection of an outer layer of compact bone
• Is found in the epiphyses of long bones and in the interior of short, flat, and irregular bones
• Blood vessels within the red marrow provide the osteocytes with nutrients

Trabeculae

• Flat plates with a lattice-like network of thin, bony columns lined with endosteum
• Have lamellae, lacunae, osteocytes, and Canaliculi