The integumentary system
Definition:
The integumentary system is the largest and heaviest of the body's organ systems.
In humans, this system accounts for about 12 to 15 percent of total body weight
and covers 1.5-2m2 of surface area. It distinguishes, separates, protects and informs
the regard to its surroundings. The integumentary system is consists of the skin and
its derivatives—(hair, nails, and cutaneous glands).
Origin:
Some parts originate from the ectoderm while others are mesodermal in origin.
Function:
1. Protect the body’s internal living tissues and organs.
2. Protect against invasion by infectious organisms (contains immune system
cells).
3. Protect the body from dehydration (barrier to water).
4. Protect the body against sudden change in temperature, and sunburns by
secreting melanin.
5. Synthesis vitamin D through exposure to ultraviolet (UV) light and act as a
barrier to its radiation.
6. Thermoregulator and Osmoregulator.
7. Help excrete wastes (water, fat and metabolic).
8. Act as a receptor for touch, pressure, pain, heat, and cold.
9. Very sensitive to changes in the outer environment.
10. Allows movement in all directions.
11. Store water, fat and glucose.
12. Synthesizes chemicals.
13. Maintenance of the body form.
14. Formation of new cells from stratum germinativum to repair minor injuries.
15. Aid in physical examination as color of the skin may indicate many
conditions e.g.it becomes yellowish in jaundice.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
1
Divisions:
Human Integument
Skin
Thick skin
Derivatives
Thin skin
Glands
Hair
nails
Layers of the skin:
Whether the skin is thick or thin, it is composed of two major layers of tissue in the
human:
• Epidermis
• Dermis
• Hypodermis or subcutaneous layer; it is another connective tissue layer
below the skin.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
2
Figure 1: Structure of the Skin and Subcutaneous Tissue.
1- Epidermis
The epidermis originates from the ectoderm; it forms the outermost layer, it is
made up of a keratinized stratified squamous epithelium. It does not contain blood
vessels. Its main function is protection, absorption of nutrients, and homeostasis. It
consists of four types of cells:
1.
2.
3.
4.
Keratinocytes - (Synthesizing keratin).
Melanocytes - (Synthesize melanin).
Merkel (Tactile) cells - (Touch receptors).
Langerhans (Dendritic) cells - (Stand against microbes & toxins
(phagocytic)).
The major cell of the epidermis is the keratinocyte, which produces keratin.
Keratin is a fibrous protein, which consists of dead cells packed with the rough
protein that aids in protection. The cells undergo mitosis and produce new
epidermal cells to replace the dead ones. Keratin is also a water-proofing
protein. Millions of dead keratinocytes rub off daily. The only skin on the body
that is non-keratinized is the lining of skin on the inside of the mouth. Nonkeratinized cells allow water to "stay" atop the structure.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
3
The epidermis usually consists of four layers (five in thick skin), described from
deep to superficial and from youngest to oldest keratinocytes:
1. Stratum Basale or Stratum germinativum
It consists of a single layer of cuboidal to low columnar
Cells (rests on the basement membrane) and Keratinocytes
(give rise to most new epidermal cells that are pushed
outward during cell division) with scattered melanocytes
and tactile cells.
2. Stratum Spinosum
It consists of several layers of keratinocytes. Dendritic cells
are also found. It is the thickest stratum.
3. Stratum Granulosum
It consists of 3-5 layers of keratinocytes, which contain
Dark staining keratohyalin granules.
4. Stratum Lucidum
It ia a thin layer, only in thick skin, such as the soles of the
feet. Keratinocytes are densely with a clear protein eleidin.
The cells have no nuclei or other organelles.
5. Stratum Corneum
It consists of up to 30 layers of dead, scaly, keratinized
cells that form a surface layer. It is resistant to scratch, penetration,
and water loss.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
4
Figure 2: Different layers and cell types of the Epidermis.
Epidermis
Skin varies in thickness due to variations in the stratum corneum.
Thick skin:
Thin skin:
a- Found on few areas of the body.
b- Palms of hands
Soles of feet.
c- Very tough stratum
um corneum.
aa Found on majority of body surface
b Sensitive areas such as lips, eyelids,
bear drums and some parts of the genitals.
c- Very thin stratum corneum.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
5
2- Dermis
The dermis originates from the mesoderm; it is composed of two layers:
1. The Papillary Layer: (Contains areolar connective tissue).
t
2. The Reticular Layer: (Contains
(
dense irregular connective
onnective).
The dermis lies underneath the epidermis layer; it is composed of dense
irregular connective tissues rich in collagen and elastic fibers.
fibers These layers serve
to give elasticity to the integument, allowing stretching
stretching and conferring
flexibility, while also resisting distortions, wrinkling, and sagging. The dermal
layer provides a site for the endings of blood vessels and nerves. Many
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
6
chromatophores are also stored in this layer, as are the bases of integumental
structures such as hair, feathers, and glands. Also it contains muscular tissue.
3- Hypodermis
Also called subcutaneous tissue, or superficial fascia, it means beneath the skin.
It is derived from the mesoderm. It is the deepest layer, which is primarily made up
of adipose cells, also fibroblasts and macrophages are found. It attaches the skin to
the underlying organs, such as bones or muscles. Pacinian corpuscles, which are
nerve endings sensitive to pressure, are usually distributed in the subcutaneous
layer. Hypodermis is 8% thicker in females.
Integumentary Derivatives:
Hair and nails are accessory organs to the skin, and are made of protein keratin
hardens epidermal tissue (compared to the soft keratin of skin). These are
structures derived from dermis and epidermis layers.
1. Nail:
The nails are hardest derivatives of the stratum corneum; they composed of very
thin, scale like dead cells (cornified cells). They grow from thin area called the nail
matrix, which is the growth zone at the proximal end of the nail; growth of nails is
1 mm per week on average. The nail plate is the nail itself. The nail arises from the
nail bed, which is thickened to form a lunula (or little moon). The lunula is the
semi-circular shape area at the base of the nail; this is a lighter colour as it mixes
with the matrix cells.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
7
Figure 3: Anatomy of Fingernail.
2. Hair:
Hair is considered as the distinguishing characteristic of mammals.
Almost all areas of the skin have hair, except lips, nipples, palms and
soles, and portions of the fingers and genitals. This kind of hair is known
as lanugo hair, which is a very thin, somewhat long hair, shortly before
birth, it will fall off from allover the body except for the scalp, eyelids
and eye brows.
• Villus hair on the other hand is a strong, thick, coarse hair replacing
lanugo hair especially after puberty.
• Genetics controls several features of hair: baldness, color, texture. The
color of hair is due to the relative abundance of keratin.
•
The hair is divided into three zones: the shaft, the portion above the skin surface;
the hair root extends from the surface to the base or hair bulb; and the bulb, a
swelling at the base where the hair originates in the dermis. The only living cells of
a hair are in and near the bulb. In cross section, the core of the hair (the medulla)
is made up of loosely arranged cells and air spaces; the cortex is densely packed
keratinized cells; and the cuticle is a layer of overlapping scaly cells.
The hair follicle dips into the dermis and has two layers. The epithelial root sheath
is an extension of the epidermis (inner). The connective tissue root sheath, derived
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
8
from the dermis, surrounds the epidermal sheath (outer). Also associated with the
follicle are hair receptors, and an arrector pili muscle. The growth of hair is due
to mitosis in cells in the stratum basale of the epidermal root sheath.
Figure 4: Anatomy of hair follicle.
3. Glands:
Cutaneous Glands
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
9
A. Sweat Glands:
Sudoriferous (sweat) glands are the most numerous cutaneous glands. They
produce watery sweat composed of water, sodium chloride and very small
quantities of urea. They are two kinds: Merocrine (eccrine) sweat glands produce
watery perspiration to cool the body. Apocrine sweat glands occur in the groin,
axilla, and areola as well as on the faces of males. Some population differences in
their distribution can be found. These are scent glands that respond to stress and
sexual stimulation.
These glands can be distinguished functionally and histologically, the secretory
part of an apocrine gland has much larger lumen than that of merocrine gland;
apocrine sweat is thicker and more milky than merocrine sweat because it has more
fatty acids in it.
B. Sebaceous Glands:
Sebaceous glands produce an oily sebum to moisturize the skin and hair. They are
flask-shaped with short ducts that usually open into a hair follicle. These are
holocrine glands with little visible lumen.
C. Ceruminous Glands:
Ceruminous glands are found only in the external ear canal where they produce
cerumen (earwax). Cerumen keeps the eardrum pliable, kill bacteria, and coat the
guard hairs of the ear, making them sticky and more effective in blocking foreign
particles from entering the auditory canal.
D. Breasts and Mammary Glands:
1. Both men and women have breasts; it is only during pregnancy and lactation
that women develop mammary gland tissue within the breasts capable of
producing and secreting milk.
2. Mammary glands are modified apocrine sweat glands.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
10
C
Figure 5:: A. Sebaceous gland B. Merocrine sweat gland C. Apocrine sweat gland.
Figure 6: Sweat glands & Sebaceous gland
Figure 7: Mammary gland
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
11
Skin Color:
1. Skin color is due to the presence of blood vesseles close to the surface, and
the presence of melanin.
2. Melanin is produced by melanocytes in response to exposure to UV light.
Heredity determines the extent of melanin production.
3. The skin can take on other colors: carotene imparts a yellowish caste; the
skin can appear bluish during cyanosis; stress or shock can cause pallor;
those that lack the ability to produce melanin are albinos; erythema is
abnormal redness of the skin; jaundice makes the skin appear yellow; and a
hematoma (bruise) gives a purplish caste.
‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
12