13: Integumentary System - Biology

13: Integumentary System - Biology

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This chapter describes the structure and functions of the epidermis and dermis, hair, and nails. In addition, the chapter outlines types of skin cancer and risk factors for skin cancer.

  • 13.1: Case Study - Skin Cancer
    Summer sun may feel good on your body, but its invisible UV rays wreak havoc on your skin. Exposing the skin to UV light causes photo-aging: premature wrinkling, brown discolorations, and other unattractive signs of sun exposure. Even worse, UV light increases your risk of skin cancer.
  • 13.2: Introduction to the Integumentary System
    This is Maud Stevens Wagner, a tattoo artist who is pictured above in 1907. Clearly, tattoos are not just a late 20th and early 21st century trend. They have been popular in many eras and cultures.
  • 13.3: Skin
    The epidermis is the outer of the two main layers of the skin, the inner layer being the dermis. It averages about 0.10 mm thick and is much thinner than the dermis. The epidermis is thinnest on the eyelids (0.05 mm) and thickest on the palms of the hands and soles of the feet (1.50 mm). The epidermis covers almost the entire body surface. It is continuous with, but structurally distinct from, the mucous membranes that line the mouth, anus, urethra, and vagina.
  • 13.4: Hair and Nails
    This blue and green spiky hairstyle makes quite a fashion statement. Many people spend a lot of time and money on their hair, even if they don’t have such an exceptional hairstyle as this one. Besides its display value, hair actually has important physiological functions.
  • 13.5: Case Study Skin Cancer Conclusion and Chapter Summary
    Skin cancer begins in the outer layer of skin, the epidermis. There are three common types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma.

Skin and its layers. Shown is a drawing of the layers of skin and associated glands and vessels (epidermis, dermis, fatty tissue, blood vessels, follicle, oil gland, sweat gland).Image used with permission (Public Domain; National Cancer Institute; NIH).

The Structure of the Integumentary System

The integumentary system consists of the largest organ in the body: the skin. This extraordinary organ system protects the internal structures of the body from damage, prevents dehydration, stores fat, and produces vitamins and hormones. It also helps maintain homeostasis within the body by assisting with the regulation of body temperature and water balance.

The integumentary system is the body's first line of defense against bacteria, viruses, and other pathogens. It also helps provide protection from harmful ultraviolet radiation. The skin is a sensory organ, too, with receptors for detecting heat and cold, touch, pressure, and pain. Components of the skin include hair, nails, sweat glands, oil glands, blood vessels, lymph vessels, nerves, and muscles.

The skin is composed of three layers:

  • Epidermis: The outermost layer of the skin, which is composed of squamous cells. This layer includes two distinct types: thick skin and thin skin.
  • Dermis: The thickest layer of the skin, which lies beneath and supports the epidermis.
  • Hypodermis (subcutis): The innermost layer of the skin, which helps insulate the body and cushion internal organs.


Figure 2. The parts of a finger nail

The fingernail is an important structure made of keratin. The fingernail generally serve two purposes. It serves as a protective plate and enhances sensation of the fingertip. The protection function of the fingernail is commonly known, but the sensation function is equally important. The fingertip has many nerve endings in it allowing us to receive volumes of information about objects we touch. The nail acts as a counterforce to the fingertip providing even more sensory input when an object is touched.

Nail Structure

The structure we know of as the nail is divided into six specific parts: the root, nail bed, nail plate, eponychium (cuticle), perionychium, and hyponychium.

Root The root of the fingernail is also known as the germinal matrix. This portion of the nail is actually beneath the skin behind the fingernail and extends several millimeters into the finger. The fingernail root produces most of the volume of the nail and the nail bed. This portion of the nail does not have any melanocytes, or melanin producing cells. The edge of the germinal matrix is seen as a white, crescent shaped structure called the lunula.

Nail Bed The nail bed is part of the nail matrix called the sterile matrix. It extends from the edge of the germinal matrix, or lunula, to the hyponychium. The nail bed contains the blood vessels, nerves, and melanocytes, or melanin-producing cells. As the nail is produced by the root, it streams down along the nail bed, which adds material to the undersurface of the nail making it thicker. It is important for normal nail growth that the nail bed be smooth. If it is not, the nail may split or develop grooves that can be cosmetically unappealing.

Nail Plate The nail plate is the actual fingernail, made of translucent keratin. The pink appearance of the nail comes from the blood vessels underneath the nail. The underneath surface of the nail plate has grooves along the length of the nail that help anchor it to the nail bed.

Eponychium The cuticle of the fingernail is also called the eponychium. The cuticle is situated between the skin of the finger and the nail plate fusing these structures together and providing a waterproof barrier.

Perionychium The perioncyhium is the skin that overlies the nail plate on its sides. It is also known as the paronychial edge. The perionychium is the site of hangnails, ingrown nails, and an infection of the skin called paronychia.

Hyponychium The hyponychium is the area between the nail plate and the fingertip. It is the junction between the free edge of the nail and the skin of the fingertip, also providing a waterproof barrier.

Integument of Mammals

The integument of mammals is the basic reason to conform to the structure of the organism. The epidermal layers are normally thick in places that need protection such as palms and soles of the feet.

Hair forms a protective layer on mammals from heat and foreign matter. Hair grows from follicles but has its roots in the dermis. When the mitosis in the roots stops, the hair growth also stops which results in baldness. These are normally the characteristics of the human integument.

Glands of the Skin

Glands of the skin are responsible for protection, heat regulation, and giving off a scent. The eccrine and apocrine are the sweat glands responsible for heat regulation. The mammary glands are the secretory glands often found in females.

Antlers, Horns, Hoofs, Claws, Nails

All these are integumental derivatives that grow at specific organisms on the specific parts of the body.

13: Integumentary System - Biology

acne: skin condition due to infected sebaceous glands

albinism: genetic disorder that affects the skin, in which there is no melanin production

anagen: active phase of the hair growth cycle

apocrine sweat gland: type of sweat gland that is associated with hair follicles in the armpits and genital regions

arrector pili: smooth muscle that is activated in response to external stimuli that pull on hair follicles and make the hair “stand up”

basal cell carcinoma: cancer that originates from basal cells in the epidermis of the skin

basal cell: type of stem cell found in the stratum basale and in the hair matrix that continually undergoes cell division, producing the keratinocytes of the epidermis

bedsore: sore on the skin that develops when regions of the body start necrotizing due to constant pressure and lack of blood supply also called decubitis ulcers

callus: thickened area of skin that arises due to constant abrasion

catagen: transitional phase marking the end of the anagen phase of the hair growth cycle

corn: type of callus that is named for its shape and the elliptical motion of the abrasive force

cortex: in hair, the second or middle layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb

cuticle: in hair, the outermost layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb

dermal papilla: (plural = dermal papillae) extension of the papillary layer of the dermis that increases surface contact between the epidermis and dermis

dermis: layer of skin between the epidermis and hypodermis, composed mainly of connective tissue and containing blood vessels, hair follicles, sweat glands, and other structures

desmosome: structure that forms an impermeable junction between cells

eccrine sweat gland: type of sweat gland that is common throughout the skin surface it produces a hypotonic sweat for thermoregulation

eczema: skin condition due to an allergic reaction, which resembles a rash

elastin fibers: fibers made of the protein elastin that increase the elasticity of the dermis

eleiden: clear protein-bound lipid found in the stratum lucidum that is derived from keratohyalin and helps to prevent water loss

epidermis: outermost tissue layer of the skin

eponychium: nail fold that meets the proximal end of the nail body, also called the cuticle

external root sheath: outer layer of the hair follicle that is an extension of the epidermis, which encloses the hair root

first-degree burn: superficial burn that injures only the epidermis

fourth-degree burn: burn in which full thickness of the skin and underlying muscle and bone is damaged

glassy membrane: layer of connective tissue that surrounds the base of the hair follicle, connecting it to the dermis

hair bulb: structure at the base of the hair root that surrounds the dermal papilla

hair follicle: cavity or sac from which hair originates

hair matrix: layer of basal cells from which a strand of hair grows

hair papilla: mass of connective tissue, blood capillaries, and nerve endings at the base of the hair follicle

hair root: part of hair that is below the epidermis anchored to the follicle

hair shaft: part of hair that is above the epidermis but is not anchored to the follicle

hair: keratinous filament growing out of the epidermis

hypodermis: connective tissue connecting the integument to the underlying bone and muscle

hyponychium: thickened layer of stratum corneum that lies below the free edge of the nail

integumentary system: skin and its accessory structures

internal root sheath: innermost layer of keratinocytes in the hair follicle that surround the hair root up to the hair shaft

keloid: type of scar that has layers raised above the skin surface

keratin: type of structural protein that gives skin, hair, and nails its hard, water-resistant properties

keratinocyte: cell that produces keratin and is the most predominant type of cell found in the epidermis

keratohyalin: granulated protein found in the stratum granulosum

Langerhans cell: specialized dendritic cell found in the stratum spinosum that functions as a macrophage

lunula: basal part of the nail body that consists of a crescent-shaped layer of thick epithelium

Meissner corpuscle: (also, tactile corpuscle) receptor in the skin that responds to light touch

Merkel cell: receptor cell in the stratum basale of the epidermis that responds to the sense of touch

medulla: in hair, the innermost layer of keratinocytes originating from the hair matrix

melanin: pigment that determines the color of hair and skin

melanocyte: cell found in the stratum basale of the epidermis that produces the pigment melanin

melanoma: type of skin cancer that originates from the melanocytes of the skin

melanosome: intercellular vesicle that transfers melanin from melanocytes into keratinocytes of the epidermis

metastasis: spread of cancer cells from a source to other parts of the body

nail bed: layer of epidermis upon which the nail body forms

nail body: main keratinous plate that forms the nail

nail cuticle: fold of epithelium that extends over the nail bed, also called the eponychium

nail fold: fold of epithelium at that extend over the sides of the nail body, holding it in place

nail root: part of the nail that is lodged deep in the epidermis from which the nail grows

Pacinian corpuscle: (also, lamellated corpuscle) receptor in the skin that responds to vibration

papillary layer: superficial layer of the dermis, made of loose, areolar connective tissue

reticular layer: deeper layer of the dermis it has a reticulated appearance due to the presence of abundant collagen and elastin fibers

rickets: disease in children caused by vitamin D deficiency, which leads to the weakening of bones

scar: collagen-rich skin formed after the process of wound healing that is different from normal skin

sebaceous gland: type of oil gland found in the dermis all over the body and helps to lubricate and waterproof the skin and hair by secreting sebum

sebum: oily substance that is composed of a mixture of lipids that lubricates the skin and hair

second-degree burn: partial-thickness burn that injures the epidermis and a portion of the dermis

squamous cell carcinoma: type of skin cancer that originates from the stratum spinosum of the epidermis

stratum basale: deepest layer of the epidermis, made of epidermal stem cells

stratum corneum: most superficial layer of the epidermis

stratum granulosum: layer of the epidermis superficial to the stratum spinosum

stratum lucidum: layer of the epidermis between the stratum granulosum and stratum corneum, found only in thick skin covering the palms, soles of the feet, and digits

stratum spinosum: layer of the epidermis superficial to the stratum basale, characterized by the presence of desmosomes

stretch mark: mark formed on the skin due to a sudden growth spurt and expansion of the dermis beyond its elastic limits

sudoriferous gland: sweat gland

telogen: resting phase of the hair growth cycle initiated with catagen and terminated by the beginning of a new anagen phase of hair growth

third-degree burn: burn that penetrates and destroys the full thickness of the skin (epidermis and dermis)

vitamin D: compound that aids absorption of calcium and phosphates in the intestine to improve bone health

vitiligo: skin condition in which melanocytes in certain areas lose the ability to produce melanin, possibly due an autoimmune reaction that leads to loss of color in patches

13: Integumentary System - Biology

We all have skin. It covers our entire body and keeps the good stuff in and the bad stuff out. But what exactly is skin? We'll get into the details below, but for starters the skin is an organ. Just like the heart or the brain. It's an important organ that performs many functions to enable us to live.

The skin is part of an important organ system called the integumentary system. The integumentary system consists of the skin, hair, nails, and exocrine glands.

Functions of the skin

  • Protection - One of the basic functions of the skin is protection. Over the majority of your body the skin is around 2mm thick. In some areas, like your eyelids, it's thinner, while in other areas, like the soles of your feet, it's much thicker. The skin helps to keep bad stuff out of our body, like germs and dirt that can cause infection. It also keeps good stuff in, like fluids such as water and blood.
  • Sense of Touch - The skin also houses one of our five senses: touch. In our skin are thousands and thousands of sensors or receptor cells. These sensors send information to the brain about things we touch. They can tell the brain if it's hot, cold, rough, smooth, or painful. Different areas of our body have more receptor cells than others. Our hands, feet, and lips all have extra receptors making those areas even more sensitive. There are actually different types of receptor cells for each type of sensation.
  • Temperature Control - The skin plays a large role in regulating our body's temperature. When we get too hot it sweats to help cool us off. It can also widen the skin's blood vessels to get more blood near the skin where it can cool off. At the same time the skin can narrow the blood vessels to help us warm up. By controlling blood flow and sweat, the skin regulates our body's temperature.
  • Epidermis - The epidermis is the outer layer of skin. Its main function is protection. The cells on the very outer layer of the epidermis are constantly dying and getting replaced by new cells.
  • Dermis - The dermis is thicker than the epidermis. The dermis houses blood cells, hair follicles, and sweat glands.
  • Hypodermis - The hypodermis lies under the dermis and connects the skin to muscles and bone.

A. Epidermis
B. Dermis
C. Hypodermis
D. Blood Vessels
E. Stratum Germinativum
1.Hair Shaft
2.Stratum Corneum
3.Pigment Layer
4.Stratum Spinosum
5.Stratum Basale
6.Arrector Pili Muscle
7.Sebaceous Gland
8.Hair Follicle
9.Papilla of Hair
10.Nerve Fiber
11.Sweat Gland
12.Pacinian Corpuscle
15.Sensory Nerve ending (for touch)
16.Dermal Papillary
17.Sweat Pore

Skin Temperature - How does our skin lower or raise our temperature?

Watch the video: Immunology in the skin (August 2022).