Chapter 5 Flashcards
Integumentary system
System composed of the skin, hair, oil and sweat glands, nails, and sensory receptors.
Skin
AKA cutaneous membrane; covers the external surface of the body and is the largest organ of the body in weight.
What are the two main parts that skin consists of?
Epidermis and dermis
Epidermis
The superficial, thinner portion, which is composed of epithelial tissue; is avascular (therefore, if you cut the epidermis, there is no bleeding); composed of keratinized stratified squamous epithelium.
What are the four principle types of cells found in the epidermis?
Keratinocytes, melanocytes, intraepidermal macrophages, and tactile epithelium
Keratinocytes
~90% of epidermal cells; arranged in four or five layers and produce the protein keratin and lamellar granules.
Keratin
A tough fibrous protein that helps protect the skin and underlying tissues from abrasions, heat, microbes, and chemicals.
Lamellar granules
Release a water-repellent sealant that decreases water entry and loss and inhibits the entry of foreign materials
Melanocytes
~8% of epidermal cells; develop from the ectoderm of a developing embryo and produce the pigment melanin. Their long, slender projections extend between the keratinocytes and transfer melanin granules to them. Once inside the keratinocytes, the melanin granules cluster to form a protective veil over the nucleus, on the side towards the skin surface. They do this to shield the nuclear DNA from damage by UV light. Although their melanin granules effectively protect keratinocytes, melanocytes themselves are particularly susceptible to damage by UV light.
Melanin
A yellow-red, or brown-black pigment that contributes to skin color and absorbs damaging ultraviolet (UV) light.
Intraepidermal macrophages
AKA Langerhans cells; arise from red bone marrow and migrate to the epidermis, where they constitute a small fraction of the epidermal cells; they participate in immune responses mounted against microbes that invade the skin and are easily damaged by UV light; their role in the immune response is to help other cells of the immune system recognize an invading microbe and destroy it.
Tactile epithelium
AKA Merkel cells; are the least numerous of the epidermal cells; they are located in the deepest layer of the epidermal cells, where they contact the tactile discs (AKA Merkel’s disks); tactile epithelial cells and tactile disks detect touch sensations.
Subcutaneous layer
AKA the hypodermis; deep to the dermis, but not part of the skin; this layer consists of areolar and adipose tissues. Fibers that extend from the dermis anchor the skin to the subcutaneous layer, which in turn attaches to underlying fascia, the connective tissue around muscles and bones; the subcutaneous layer serves as a storage depot for fat and contains large blood vessels that supply the skin.
Lamellated corpuscles
AKA Pacinian corpuscles; nerve endings that are sensitive to pressure; the subcutaneous layer, and sometimes the dermis, contain these.
What are the layers of the epidermis?
Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
Stratum basale
Deepest layer, composed of single row of cuboidal or columnar keratinocytes that contain scattered keratin intermediate filaments (tonofilaments); stem cells undergo cell division to produce new keratinocytes; melanocytes and tactile epithelial cells associated with tactile discs are scattered among keratinocytes.
Stratum spinosum
Eight to ten rows of many-sided keratinocytes with bundles of keratin intermediate filaments; contains projections of melanocytes and intraepidermal macrophages.
Stratum granulosum
Three to five rows of flattened keratinocytes, in
which organelles are beginning to degenerate; cells contain the protein keratohyalin (converts keratin intermediate filaments into keratin) and lamellar granules (release lipid-rich, water-repellent secretion).
Stratum lucidum
Present only in skin of fingertips, palms, and soles; consists of four to six rows of clear, flat, dead keratinocytes with large amounts of keratin.
Stratum corneum
Few to 50 or more rows of dead, flat keratinocytes that contain mostly keratin.
Callus
An abnormal thickening of the stratum corneum.
Keratinization
A process in which newly formed cells in the stratum basale are slowly pushed to the surface. As the cells move from one epidermal layer to the next, they accumulate more and more keratin. Then they undergo apoptosis. Eventually the keratinized cells slough off and are replaced by underlying cells that in turn become keratinized; process takes between four to six weeks.
Epidermal growth factor (EGF)
Hormonelike proteins that play a role in regulating growth of the epidermis.
Dermis
The deeper, thicker connective tissue portion; is vascular (therefore, if a cut penetrates to the dermis, there is bleeding); is composed of dense irregular connective tissue containing collagen and elastic fibers. This network of fibers has great tensile strength (resists pulling or stretching forces); the dermis also has the ability to stretch and recoil easily; it is much thicker than the epidermis.
What are the two regions that the dermis can be divided into?
Papillary region and reticular region
Papillary region
Superficial portion of dermis (about one-fifth); consists of areolar connective tissue with thin collagen and fine elastic fibers; contains dermal ridges that house blood capillaries, corpuscles of touch, and free nerve endings.
Dermal papillae
Small, nipple-shaped structures that project into the undersurface of the epidermis and increase the surface area of the papillary region.
Capillary loops
Blood vessels; all dermal papillae contain them.
Corpuscles of touch
AKA Meissner corpuscles; nerve endings that are sensitive to touch; some dermal papillae contain them.
Free nerve endings
Dendrites that lack any apparent structural specialization; different free nerve endings initiate signals that give rise to sensations of warmth, coolness, pain, tickling, and itching; some dermal papillae contain them.
Reticular region
Deeper portion of dermis (about four-fifths); consists of dense irregular connective tissue with bundles of thick collagen and some coarse elastic fibers. Spaces between fibers contain some adipose cells, hair follicles, nerves, sebaceous glands, and sudoriferous glands.
Extensibility
The ability to stretch; the combination of collagen and elastic fibers in the reticular region allows for this.
Elasticity
The ability to return to original shape after stretching; the combination of collagen and elastic fibers in the reticular region allows for this. (Eg. Seen around joints and in pregnancy and obesity).
Epidermal ridges
Found on the palms, fingers, soles, and toes, and appear either as either as straight lines or as a pattern of loops and whorls; epidermal ridges create a strong bond between the epidermis and dermis in a region of high mechanical stress; the epidermal ridges also increase the surface area of the epidermis and thus increase the grip of the hand or foot by increasing friction; finally, the epidermal ridges greatly increase surface area. Which increases the number of corpuscles of touch and thus increase tactile sensitivity; because the ducts of sweat glands open on the top of epidermal ridges as sweat pores, the sweat and ridges form fingerprints (or footprints) on touching a smooth object.
Explain the basis for different skin colors
Melanin, hemoglobin, and carotene are three pigments that impact a wide variety of colors of skin. The amount of melanin causes the skin’s color to vary from pale yellow to reddish-brown to black. The number of melanocytes, the melanin-producing cells, is about the same in all people, so differences in skin color are due mainly to the amount of pigment the melanocytes produce and transfer to keratinocytes
Hairs
Genetic and hormonal influences largely determine the thickness and the pattern of the hair distribution; hair on the head guards the scalp from injury in the sun’s rays. It also decreases heat loss from the scalp; eyebrows/eyelashes protect the eyes from foreign particles, similar to the way hair in the nostrils and in the external ear canal defends those structures; touch receptors (hair root plexuses) associated with hair follicles are activated whenever a hair is moved even slightly. Thus, hairs also function in sensing light touch.
Hair shaft
Superficial portion of the hair, which projects above the surface of the skin.
Hair root
Portion of the hair deep to the shaft the penetrates into the dermis, and sometimes into the subcutaneous layer.
What three layers do the shaft and root of the hair consist of?
Medulla, cortex, and cuticle of the hair
Medulla (of the shaft and root of the hair)
Inner layer; may be lacking in thinner hair; composed of two or three rows of irregular shaped cells that contain large amounts of pigment granules in dark hair, small amounts of pigment granules in gray hair, and lack pigment granules and the presence of air bubbles in white hair.
Cortex (of the shaft and root of the hair)
Middle layer; forms the major part of the shaft and consists of elongated cells.
Cuticle of the hair
Outermost layer; consists of a single layer of thin, flat cells that are most heavily keratinized. Cuticle cells on the shaft are arranged like shingles on the side of a house, with their free edges pointing toward the end of the hair.
Hair follicle
Made up of an external root sheath and an internal root sheath; external root sheath is a downward continuation of the epidermis; the internal root sheath is produced by a matrix and forms cellular tubular sheath of epithelium between the external root sheath and the hair.
Together, the external and internal root sheath are referred to as the ______.
Epithelial root sheath
Dermal root sheath
Dense dermis surrounding hair follicle.
Hair bulb
Onion-shaped structure that are at the base of each hair follicle and its surrounding dermal root sheath.
Papilla of the hair
Nipple-shaped indentation which contains areolar connective tissue and many blood vessels that nourish the growing hair follicle.
Hair matrix
A germinal layer of cells in the hair bulb; the hair matrix cells arise from the stratum basale, the site of cell division; hence, hair matrix cells are responsible for the growth of existing hairs, and they produce new hairs when old hairs are shed; this replacement process occurs within the same follicle; hair matrix cells also give rise to the cells of the internal root sheath.
Arrector pilli
Smooth muscle cells associated with hairs; extends from the superficial dermis in the skin to the dermal root sheath around the side of the hair follicle; in it’s normal position, hair emerges at a less than 90-degree angle to the surface of the skin. Under physiological or emotional stress, such as cold or fright, autonomic nerve endings stimulate the arrector pili muscles to contract, which pulls the hair shafts perpendicular to the skin surface. This action causes “goose bumps” or “gooseflesh” because the skin around the shaft forms slight elevations.
Hair root plexus
Dendrites of neurons surrounding each hair follicle; are sensitive to touch. Generate nerve impulses if their hair shafts are moved.
Sebaceous glands are also known as ______.
Oil glands
Describe the distribution of sebaceous (oil) glands
Largely in lips, glans penis, labia minora, and tarsal glands; small in trunk and limbs; absent in palms and soles.
Describe the location of the secretory portion of sebaceous (oil) glands
Dermis
Where is the termination of excretory ducts of sebaceous (oil) glands?
Mostly connected to hair follicle.
What do sebaceous (oil) glands secrete?
Sebum (mixture of triglycerides, cholesterol, proteins, and inorganic salts).
Describe the functions of sebaceous (oil) glands
Prevent hairs from drying out, prevent water loss from skin, keep skin soft, inhibit growth of some bacteria.
What is the onset of function for sebaceous (oil) glands?
Relatively inactive during childhood; activated during puberty.
Sudoriferous glands are also known as ______.
Sweat glands
Describe the distribution of eccrine sweat glands
Throughout skin of most regions of body, especially skin of forehead, palms, and soles.
Describe the location of the secretory portion of eccrine sweat glands
Mostly in deep dermis (sometimes in upper subcutaneous layer).
Where is the termination of excretory ducts of eccrine sweat glands?
Surface of epidermis.
What do eccrine sweat glands secrete?
Perspiration, which consists of water, ions (Na+, Cl−), urea, uric acid, ammonia, amino acids, glucose, and lactic acid.
Describe the functions of eccrine sweat glands
Regulation of body temperature, waste removal, stimulated during emotional stress.
What is the onset of function for eccrine sweat glands?
Soon after birth.
Thermoregulation
The homeostatic regulation of body temperature.
Thermoregulatory sweating
Helping the body achieve thermoregulation; during thermoregulatory sweating, sweat first forms on the forehead and scalp and then extends to the rest of the body, forming last on the palms and soles.
Insensible perspiration
Sweat the evaporates from the skin before it is perceived as moisture.
Sensible perspiration
Sweat that is excreted in large amounts and is seen as moisture on the skin.
Emotional sweating
AKA cold sweating; sweat in response to an emotional stress such as fear or embarrassment; in contrast to thermoregulatory sweating, emotional sweating first occurs on the palms, soles, and axillae, and then spreads to other areas of the body.
Describe the distribution of apocrine sweat glands
Skin of axillae, groin, areolae, bearded regions of face, clitoris, and labia minora.
Describe the location of the secretory portion of apocrine sweat glands
Mostly in deep dermis and upper subcutaneous layer.
Where is the termination of excretory ducts of apocrine sweat glands?
Hair follicles.
What do apocrine sweat glands secrete?
Perspiration, which consists of same components as eccrine sweat glands plus lipids and proteins.
Describe the functions of apocrine sweat glands
Stimulated during emotional stress and sexual excitement.
What is the onset of function for apocrine sweat glands?
Puberty.
Describe the distribution of ceruminous glands
External auditory canal.
Describe the location of the secretory portion of ceruminous glands
Subcutaneous layer.
Where is the termination of excretory ducts of ceruminous glands?
Surface of external auditory canal or into ducts of sebaceous glands.
What do ceruminous glands secrete?
Cerumen, a waxy material. AKA earwax
Describe the functions of ceruminous glands
Impede entrance of foreign bodies and insects into external ear canal, waterproof canal, prevent microbes from entering cells.
What is the onset of function for ceruminous glands?
Soon after birth
What three things do nails consist of?
Nail body, free edge, and nail root
Nail body
AKA plate; is the visible portion of the nail; comparable to the stratum corneum of the epidermis of the skin, with the exception that its flattened, keratinized cells fill with a harder type of keratin and the cells are not shed; below the nail body is a region of epithelium and a deeper layer of dermis; most of the nail body appears pink because of blood flowing through the capillaries in the underlying dermis.
Free edge
Part of the nail body that may extend past the distal end of the digit; the free edge is white because there are no underlying capillaries.
Nail root
Portion of the nail that is buried in a fold of skin; the whitish crescent-shaped area of the proximal end of the nail body is called the lunula. It appears whitish because the vascular tissue underneath does not show through due to a thickened region of epithelium in the area.
Hyponychium
Thickened region of the stratum corneum that is just beneath the free edge; junction between the free edge and skin of the fingertip and secures the nail to the fingertip.
Nail bed
Skin below the nail plate that extends from the lunula to the hyponychium; the epidermis of the nail bed lacks a stratum granulosum.
Eponychium
AKA cuticle; narrow band of epidermis that extends from and adheres to the margin (lateral border) of the nail wall; it occupies the proximal border of the nail and consists of stratum corneum. A hangnail has nothing to do with the nail itself, it is a small torn piece if skin at the side or base of a fingernail or toenail, usually caused by the dryness of the eponychium.
Nail matrix
The portion of the epithelium proximal to the nail root. The superficial nail matrix cells divide mitotically to produce new nail cells. The growth of nails is determined by the rate of mitosis in matrix cells, which is influenced by factors such as a person’s age, health, and nutritional status. Nail growth also varies according to the season, the time of day, and environmental temperature. The growth rate is somewhat slower in toenails. The longer the digit the faster the nail grows.
What are the three functions of nails?
- They protect the distal end of the digits.
- They provide support and counterpressure to the palmar surface of the fingers to enhance touch perception and manipulation.
- They allow us to grasp and manipulate small objects, and they can be used to scratch and groom the body in various ways.
Describe the distribution of thin skin
All parts of body except areas such as palms, palmar surface of digits, and soles.
Describe the epidermal thickness for thin skin?
0.10–0.15 mm (0.004–0.006 in.).
Are epidermal strata present in thin skin?
Stratum lucidum essentially lacking; thinner strata spinosum and corneum.
Are epidermal ridges present in thin skin?
Lacking due to poorly developed, fewer, and less well-organized dermal papillae.
Are hair follicles and arrector pili muscles present in thin skin?
Present
Are sebaceous glands present in thin skin?
Present
Are sudoriferous glands present in thin skin?
Fewer.
Are sensory receptors present in thin skin?
Sparser.
Describe the distribution of thick skin
Areas such as palms, palmar surface of digits, and soles.
Describe the epidermal thickness for thick skin?
0.6–4.5 mm (0.024–0.18 in.), due mostly to a thicker stratum corneum.
Are epidermal strata present in thick skin?
Stratum lucidum present; thicker stratum spinosum and corneum.
Are epidermal ridges present in thick skin?
Present due to well-developed and more numerous dermal papillae organized in parallel rows.
Are hair follicles and arrector pili muscles present in thick skin?
Absent.
Are sebaceous glands present in thick skin?
Absent.
Are sudoriferous glands present in thick skin?
More numerous.
Are sensory receptors present in thick skin?
Denser.
How does the skin contribute to regulation of body temperature?
Contributes to thermoregulation in two ways: 1.) by liberating sweat at its surface and 2.) by adjusting the flow of blood in the dermis.
How does the skin contribute to the storage of blood?
Skin acts as a blood reservoir as the dermis houses an extensive network of blood vessels that carry 8-10% of the totally blood flow in a resting adult.
How does the skin contribute to protection?
The skin provides protection to the body in various ways; keratin protects underlying tissues from microbes, abrasion, heat, and chemicals, and the tightly interlocked keratinocytes resist invasion by microbes; lipids released by lamellar granules inhibit evaporation of water from the skin surface, thus guarding against dehydration. They also retard entry of water across the skin surface during showers and swims; the oily sebum from the sebaceous glands keeps skin and hairs from drying out and contains bactericidal chemicals (substances that kill bacteria); the acidic pH of perspiration retards the growth of some microbes; the pigment melanin helps shield against the damaging effects of ultraviolet light.
Cutaneous sensations
Sensations that arise in the skin, including tactile sensations – touch, pressure, vibration, and tickling – as well as thermal sensations such as warmth and coolness. Another cutaneous sensation, pain, usually is an indication of impending or actual tissue damage. There is a wide variety of nerve endings and receptors distributed throughout the skin, including the tactile discs of the epidermis, the corpuscles of touch in the dermis, and hair root plexuses around each hair follicle.
How does the skin contribute to excretion and absorption?
The skin normally has a small role in excretion, the elimination of substances from the body, and absorption, the passage of materials from the external environment into body cells. Despite the almost waterproof nature of the stratum corneum, about 400 mL of water evaporates through it daily. Besides removing water and heat from the body, sweat also is the vehicle for excretion of small amounts of salts, carbon dioxide, and two organic molecules that result from the breakdown of proteins – ammonia and urea. The absorption of water-soluble substances through the skin is negligible, but certain lipid-soluble materials do penetrate the skin. These include fat-soluble vitamins (A, D, E, and K), certain drugs, and the gases oxygen and carbon dioxide. Toxic materials that can be absorbed through the skin; certain drugs that are absorbed by the skin may be administered by applying adhesive patches to the skin.
How does the skin contribute to synthesis of vitamin D?
Requires activation of a precursor molecule in the skin by ultraviolet (UV) rays in sunlight. Enzymes in the liver and kidneys then modify the activated molecule, finally producing calcitriol, the most active form of vitamin D. Calcitriol is a hormone that aids in the absorption of calcium from foods in the gastrointestinal tract into the blood. Most cells of the immune system have vitamin D receptors, and the cells activate vitamin D in response to an infection, especially a respiratory infection, such as influenza. Vitamin D is believed to enhance phagocytic activity, increase the production of antimicrobial substances in phagocytes, regulate immune functions, and help reduce inflammation.
