Catalyst Questions

• 1. What are the primary cells of the Integumentary System? Briefly describe each of their functions.

• 2. What are the organs of the Integumentary System?

• 3. What are your long term goals after high school?

What’s Going On In Science?

Let’s Review…

• 1. Stem Cells, keratinocytes, melanocytes, tactile cells, dendritic cells.

Stem Cells

• These are undifferentiated cells that undergo mitosis and give rise to the keratinocytes described next

• They are found only in the deepest layer of the epidermis, the stratum basale (we will discuss this later next week)

Keratinocytes

• The great majority of epidermal cells.

• They are named for their role in synthesizing keratin.

• In most epidermal pictures, keratinocytes are the only epidermal cells you see.

Melanocytes

• These cells synthesize, or make, melanin, a brown to black pigment in the skin.

• They have long branching processes that spread among the keratinocytes and continually shed melanin-containing fragments from their tips.

• Melanin in the skin helps protect the DNA in the nucleus from harmful UV Rays.

Tactile (Merkel) Cells

• These are relatively few in number and are receptors for the sense of touch.

• They are found in the stratum basale and are associated with the underlying nerve fibers.

• You can remember this cell’s function because of Tactile = Touch.

– A tactile learner is one that needs to touch something to learn it.

Dendritic (Langerhans) Cells

• These are found in two layers of the epidermis called the stratum spinosum and the stratum granulosum.

• These cells “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.

Long Term Goals?

• How/why is this class important to me or my long term goals?

• Self-reflection for 8 minutes

Hair and Nails

Mr. Zeilik

Objectives

• You will be able to list the organs of the Integumentary System.

• You will be able to describe the histology and function of a hair and its follicle.

• You will be able to describe the structure and function of the nails.

Hair and Nails

• Composed of mostly dead, keratinized cells

• Made mostly of hard keratin, whereas your skin contains soft keratin – Hard keratin is more compact than soft keratin

Hair

• A hair is also known as a pilus (plural, pili).

• It is a slender filament of keratinized cells that grows from an oblique tube in the skin called a hair follicle.

• Hair is found almost everywhere on the body except the lips, nipples, parts of the genitals, palms and soles, ventral and lateral surfaces of the fingers and toes, and distal segment of the fingers.

• There are about 100,000 hairs on the average person’s scalp.

Hair Zones• A hair is divisible into

three zones along its length: 1) The bulb- a swelling at the base where the hair originates in the dermis2) The root- which is the remainder of hair within the follicle3) The shaft- the portion of the hair that lies above the skin surface.

Hair Growth

• Except near the bulb, all the tissue is dead.

• Hair grows at the bulb because it receives nourishment from the dermal papilla.

• Immediately above the dermal papilla is a region of mitotically active cells, the hair matrix, which is the hair’s growth center.

• All the cells above this area are dead.

Layers of Hair

• When we look at a transverse section of the hair, it has three layers:

1)The medulla- a core of loosely arranged cells and air spaces found in thick hairs, but absent from thin ones

2) The cortex- a layer of keratinized cuboidal cells

3) The cuticle- a surface layer of scaly cells that overlap one another like roof shingles.

Sections of Hair

Cuticle

Cortex

Medulla

Hair Follicle and Associated Strucutres

• The follicle is a diagonal tube that dips deeply into the dermis and sometimes extends as far as the hypodermis.

• Nerve fibers called hair receptors entwine each follicle and respond to hair movements.

• Piloerector muscle, a bundle of smooth muscle cells that responds to cold, fear, or other stimuli. – When these things are sensed by

the hair receptors the piloerector muscle contracts and makes the hair stand on end

Function of Hair

• In most mammals, hair serves to retain the body heat.

• While some hair, like beard, pubic, and axillary hair advertise sexual maturity, most hair serves to keep us warm.

Nail Composition

• Fingernails and toenails are clear, hard derivatives of the stratum Corneum.

• They are composed of very thin, dead, scaly cells that are densely packed together and filled with parallel fibers of hard keratin.

Nail Function

• Most mammals have claws, but we have flat nails.

• These allow for more fleshy and sensitive fingertips, and can also be used as tools for digging, grooming, picking apart food, and other manipulations.

Nail Parts• Nail groove- the groove

where the nail fold meets the nail plate

• Lunule (or lunula)- the region at the base of the nail that appears as a small white crescent

• Cuticle- dead epidermis that covers the proximal end of the nail

• Free Edge- portion of the nail plate that extends beyond the digit

• Nail Body- major portion of the nail plate

• Nail Fold- the fold to the skin around the margins of the nail plate

Free EdgeNail Groove

Sketches

• Sketch and then label the stated structures of the following on the even page of your science notebook:

1. A hair originating in the dermis and extending from the epidermis- label the dermal papilla, bulb, root, shaft, follicle, piloerector muscle

2. A frontal section of a pilus- label cortex, medulla, cuticle3. A transverse section of a pilus- label cortex, medulla,

cuticle4. The tip of a finger, with its nail- label the nail groove,

lunula, cuticle, free edge, nail body, and nail fold