Name______Date ______Hour ______

A&P—Ch. 4—Structure of the Skin & Skin Appendages (pages 95-101)

1.  Structure of the Skin

Layer of the Integument (skin) / Describe each layer
Epidermis / Made up of Stratified Squamous Epithelium and is capable of keratinization (becomes hard and tough) to create a physical barrier between our bodies and the external environment. This part of the skin is 5 layers.
Dermis / Made up of dense connective tissue. Is firmly connected with the overlying epidermis. This part of the skin is two layers. If significant friction or abrasion happens, they can separate the layers and form a blister.
Subcutaneous Tissue or Hypodermis / This layer is not actually part of the skin. It is the layer beneath the dermis (hence the name hypodermis). It is comprised mostly of adipose tissue. It anchors the skin to underlying organs and acts as a shock absorber and insulator against extreme temperature changes.

2.  Epidermis

The epidermis is composed of five zones or layers called _Strata___ and is _____Avascular_____ which means it lacks blood supply.

This layer is composed mostly of cells called _____Keratinocytes______which produce ___Keratin___ that makes the epidermis a tough protective layer.

Layer of the Epidermis
(Deep to Superficial) / Describe each layer (cell type; function; and major details)
Stratum Basale / The deepest layer of the epidermis (on top of the dermis); the only layer of the epidermis to receive adequate nutrients from the dermis. These cells are constantly dividing (mitosis) to produce over a million new cells every day. Also called the stratum germinativum. Once the new cells are formed, they are pushed superficially toward the surface of the skin and become part of the other epidermal layers and eventually die.
Stratum Spinosum / Contains cells with spiny appearance (hence the name spinosum); forms one of the middle layers
Stratum Granulosum / Contains diamond shaped cells which contain granules (hence the name granulosum); forms the middle layer above the stratum spinosum
Stratum Lucidum / This layer is only found in hairless areas where thick skin is present such as on the palms of the hands and soles of feet. The cells move farther away from the nutrients and eventually die. They are also keratinized (accumulate keratin) for water-proofing.
Stratum Corneum / This is the outermost layer of the skin (most superficial). It is often 20 to 30 cell layers thick (what we saw under the microscopes during Unit 2). This layer accounts for ¾ of the thickness of the epidermis and all shingle-like cells are dead and heavily keratinized or cornified (aka horny cells). Provides a durable overcoat for the body which offers significant protection against biological, chemical, and physical assaults. This layer is rubbed off and replaced frequently.

Describe the role(s) of melanin and melanocytes in human skin.

Melanin is a pigment that is produced in specialized cells called melanocytes which are primarily found in the stratum basale which mitosis is regularly occurring. It is responsible for the yellow, brown, and black hues of various skin colors. Melanin traps UV radiation from the sun to protect against damage to the skin. When our skin gets exposed to sunlight, the melanocytes produced more melanin to help absorb the harmful UV rays (this is how we tan). Melanin is phagocytized (or eaten) by the other cells in the stratum basale and forms an “umbrella” of protection around the nuclei of the cells to shield their DNA from the UV rays that might cause can mutations and then cancer.

In which layer of the epidermis can we find melanocytes? ____Stratum basale______

What are the negative effect(s) of excessive exposure to sunlight (UV rays)?

Excessive sunlight causes the elastic fibers in the dense connective tissue to clump up forming a leathery skin appearance. It also depresses our immune system and has been linked to Herpes simplex or cold sore outbreaks post-sunning. Finally, over-exposure to certain UV rays can cause damage of the DNA in cells (mutation) and could lead to cancer. For this reason, African American people have a low occurrence of skin cancer because they possess more of the pigment melanin to help them avoid the damaging effects of sunlight.

3.  Dermis

The dermis is your “__Hide___.” It is a strong stretchy envelope that helps to hold the body together. Your leather bag, belt, and shoes are really made of ____Treated Dermis of Animals______.

The Two Major Regions of the Dermis

Layer of the Epidermis
(Superficial to Deep) / Describe each layer (cell/tissue type; function; and major details)
Papillary Layer / This layer is the upper or most superficial dermal layer. This layer has an uneven edge full of finger-like projections on its superior surface called dermal papillae which indent or raise the overlying epidermis. The results are the whorled epidermal ridges that cause fingerprints. Inside the dermal papillae there are capillary loops to deliver nutrients to the epidermis and specialized pain and touch receptors called Meissner’s corpuscles. These papillary patterns are genetically determined and are unique to every individual. They also have special pores where sweat can exit and leave a film that characterizes our fingerprints on a surface.
Reticular Layer / This is the deeper of the two dermal layers (deepest of all skin layers). It contains the blood vessels, sweat and oil glands, as well as deep pressure receptors called Pacinian corpuscles. There are lots of phagocytes (white blood cells) to fight off bacterial invaders that may have made their way through the epidermis. Collagen and elastic fibers are prevalent which give the dermis its toughness. The collagen fibers attract water to keep skin hydrated and the elastic fibers provide elasticity to the skin.

What happens to the skin’s dermis as we age?

The number of collagen and elastic fibers decrease. The underlying hypodermis also loses adipose. The result is less elastic skin that appears to sag or wrinkle.

Explain how the blood vessels within the dermis play a role in maintaining body temperature (thermal homeostasis).

The dermis is loaded with blood vessels that play a huge role in thermoregulation (maintaining body temperature homeostasis). When an individual gets hot or temperature rises, the blood vessels swell or dilate (called vasodilation) with heated blood. This moves the heated blood closer to the skin’s surface (giving us a reddish hue) where heat can be lost through radiation.

When an individual gets cold or is exposed to cooler temperatures, the blood vessels constrict or shrink in size (called vasoconstriction). The blood also bypasses these blood vessels thus keeping the warm blood closer to the interior. The result is often whitish skin or in some extreme cases, blue or purple coloration.

Explain how and why decubitus ulcers (bedsores) occur in bedridden, hospitalized, or paralyzed patients.

Decubitus ulcers, also known as bedsores, can occur if the blood supply to the skin is restricted such as when the body is compressed against a surface, such as a bed, for extended periods of time. The weight of the body puts pressure on the skin (especially over bony projections of the skeleton), restricting the blood supply and causing the skin to become pale or blanched. Over time the cells begin to die, cracks and breaks in the skin can appear, permanent damage to the tissue results, and ulcers appear.

4.  Skin Color

Pigment Name / How it contributes to skin color
Melanin / Yellow, reddish brown, or black pigment in the epidermis
More melanin leads to a darker skin color, and vice versa
Major determinant of skin color
Carotene / Yellow orange pigment
Eating large amounts of carrots and other orange, yellow, and green vegetables gives skin a yellow-orange cast
Hemoglobin (bound to oxygen) / Oxygen rich hemoglobin protein has a crimson red color
Gives skin a rosy glow (in lighter skin)

Abnormal Skin Colorations (Indicators of Disease or Impaired Homeostasis)

Skin Condition / Description including Causes of Condition
Cyanosis / Skin appears blue due to poorly oxygenated hemoglobin protein
Common during heart failure and breathing disorders
Redness or Erythema / Skin appears red, flushed
Common during embarrassment (blushing), fever, hypertension (high blood pressure), inflammation, and allergy
Pallor or Blanching / Skin appears pale and lighter than usual
Common during strong emotions (fear, anger), anemia, low blood pressure, or impaired blood flow
Jaundice / Skin appears abnormally yellow
Commonly indicates a liver disorder (bile pigments are absorbed into blood and deposited into body tissues)
Bruises / Skin appears black and blue
Areas where blood has escaped from circulation and has clotted in the tissue spaces (called a hematoma)
Common in hemophiliacs (have bleeder’s disease) or if deficient in Vitamin C

5.  Appendages of the Skin

The skin appendages include ____cutaneous glands______, __hairs & hair follicles_____, & ___nails______. Each of the appendages arise from the __epidermis_____ and plays a unique role in maintaining __body______homeostasis_____.

Cutaneous Glands

What is an exocrine gland again? (Hint: you learned this in Unit 2)

Exocrine glands are glands that release their secretions to a particular site via ducts.

The cutaneous glands are exocrine glands that release their secretions (sweat and oil) to the skin surface via ducts.

Cutaneous Gland / Description (Anatomy/Structure and Physiology/Functions)
Sebaceous (Oil) Glands / Found all over the skin (except palms of hands and soles of feet)
Ducts usually empty into a hair follicle, some open on skin surface directly
Sebum = product of sebaceous gland
·  Mixture of oily substances and fragmented cells
·  Acts as lubricant to keep skin soft and moist, keeps hair from becoming brittle
·  Contains chemicals that kill bacteria
Glands very active during adolescence = oily skin
Acne = active infection of sebaceous glands, pimples form
Sudoriferous (Sweat) Glands
Sudoriferous Glands Cont. / Eccrine
Numerous and found all over the body
Sweat = product of eccrine gland
·  Released to the skin surface via a duct that opens into a funnel-shaped pore
·  Clear secretion that is mostly water + salts (NaCl), vitamin C, traces of metabolic waste (ammonia, urea, and uric acid) and lactic acid
·  Acidic in pH (pH = 4-6), helps to inhibit overgrowth of bacteria
Body temperature homeostasis is regulated through sweating when body temp is high
When sweat evaporates, it carries body heat with it, cooling down the body
A human can sweat out 7 liters of body water a day!
Apocrine
Found in the axillary and genital regions of the body
Larger than eccrine glands, ducts empty into hair follicles
Sweat = product of apocrine gland
·  Contains products of eccrine sweat + fatty acids & proteins
·  May have milky or yellowish color
·  Odorless until bacteria use it as a food source, leads to musky, unpleasant odor (body odor)
Begin to function during puberty
Minimal role in thermoregulation (body temp homeostasis), can be activated by pain, stress, sexual foreplay

Hair and Hair Structures

Hair Structure / Brief Description
Hair Root / The part of the hair enclosed in the follicle (at base of hair)
Hair Shaft / The part of the hair projecting from the surface of the scalp or skin
Hair Bulb Matrix / The growth zone that forms the hair through cell division of stratum basale cells at the inferior end of the follicle
As cells are pushed upward from this region, they become keratinized, harden, and die. The bulk of the hair shaft is dead and made of mostly protein.
Hair is one of the fastest growing tissues in the body
Hair Follicle / Area that encloses the hair root (base of hair), made of two layers: inner epidermal sheath (forms the hair) and outer dermal sheath (supplies blood and give structure to the follicle)
Arrector pili (muscle) / Small bands of smooth muscle that connect the hair follicle to the dermal tissue
When muscle contracts, the hair is pulled upright, giving the skin “goose bumps” (such as when we are cold or scared)

Nails

A nail is a ___scalelike______modification of the __epidermis_____ that corresponds to the hoof or claw of other animals.

Explain why hair and nails are mostly non-living material. (You may have to go back and re-read the hair section)

As hair and nail cells are produced by the hair bulb matrix and nail matrix, respectively, they become heavily keratinized and die. Therefore, hair and nails consist mostly of protein that is non-living material.