Integumentary System First Year B. Pharm Semester 1

The integumentary system is the body's outermost layer of protection, serving as a vital barrier between the internal organs and the external environment. It is a complex network that includes the skin, hair, nails, glands, and sensory receptors. Together, these components work to safeguard the body against various environmental threats, regulate temperature, and perform a variety of other essential functions.

Key Components of the Integumentary System
Skin: The skin is the largest organ in the body and is made up of three primary layers:

Epidermis: The outermost layer, composed mostly of keratinocytes, which produce keratin, a tough protein that provides strength and protection. It also contains melanocytes, which produce melanin, the pigment responsible for skin color and protection against UV radiation.
Dermis: Beneath the epidermis, the dermis contains connective tissue, blood vessels, nerve endings, hair follicles, and various glands. It supports the skin's structure and provides nutrients to the epidermis. The dermis is also involved in regulating body temperature through the contraction and dilation of blood vessels.
Hypodermis (Subcutaneous Layer): This deeper layer consists of fat and connective tissue, which insulates the body, absorbs shock, and provides energy storage.
Hair:
Hair is produced by follicles located in the dermis. It grows from the base of the follicle and extends through the epidermis. Hair serves a variety of functions, including insulation, protection from UV radiation, and acting as a sensory receptor. Scalp hair, for example, helps to protect the head from sunburn, while body hair serves as a sensory tool, alerting the body to touch or changes in the environment.

Nails:
Nails are hard, keratinized structures that protect the tips of the fingers and toes from injury. They also assist in fine motor tasks, such as picking up small objects, and help increase tactile sensation in the fingertips.

Glands: Several types of glands are found in the skin, each serving different functions:

Sweat Glands: There are two main types of sweat glands—eccrine and apocrine. Eccrine glands produce a watery sweat to regulate body temperature through evaporation, while apocrine glands, located in areas like the armpits, secrete a thicker sweat that, when broken down by bacteria, can produce body odor.
Sebaceous Glands: These glands secrete an oily substance called sebum, which lubricates the skin and hair, preventing them from becoming dry or cracked. Sebum also has antimicrobial properties that protect the skin from harmful microorganisms.
Sensory Receptors:
The skin is rich in sensory receptors that allow the body to detect changes in temperature, pressure, pain, and touch. These receptors help the body respond to stimuli and maintain a constant internal environment (homeostasis). For example, when you touch something hot, pain receptors in the skin trigger a reflex to pull away quickly, preventing injury.

1. The Integumentary System
Prof. Amol B. Deore
Assistant Professor
Department of Pharmacology
MVP Samaj College of Pharmacy, Nashik
BP101T: Human Anatomy and Physiology-I (Theory)
First Year B. Pharm

2. Introduction
•The integumentary system is the organ system that forms the external
covering of the body and protects it from external harm.
•The organs of the integumentary system include the skin and its
accessory structures including hair, nails, and glands, as well as blood
vessels, muscles and nerves.
•Dermatology is the branch of medicine that deals with structure,
functions, diagnosis, treatment, and prevention of diseases and
conditions affecting the integumentary system.

3. Structure of the Skin
•The skin covers the body and is the largest organ of the body by
surface area and weight.
•Its area is about 2 square meters (22 square feet) and weighs 4.5-5 kg,
about 16% of body weight.
•It is 0.5 – 4 mm thick, thinnest on the eyelids, thickest on the heels;
•The average thickness of skin is 1 – 2 mm.

4. Structure of the Skin
•The epidermisis the outer, thinner layer of the skin made of epithelial
tissue. It is avascular (has no blood vessels), so a cut to the epidermis does
not bleed.
•Below it is the dermis, a thicker layer of connective tissue that is vascular
(has blood vessels), so a deeper cut that reaches the dermis causes
bleeding.
•Beneath the dermis is the subcutaneous layer(also called the hypodermis),
which is not part of the skin. It consists of areolarand adiposetissues,
stores fat, and contains large blood vessels that supply the skin.
•This layer connects the skin to underlying tissues like muscles and bones via
fibers from the dermis. It also contains lamellated corpuscles(Pacinian
corpuscles), which are nerve endings sensitive to pressure.

6. EPIDERMIS

7. Structure of Epidermis
The epidermis is made of keratinized stratified squamous epithelium
and contains four main types of cells:
•Keratinocytes
•Melanocytes
•Intraepidermal Macrophages (Langerhans cells)
•Tactile Epithelial Cells (Merkel cells)

8. Types of Cells in
the Epidermis

9. Keratinocytes:
•Make up about 90% of
epidermal cells.
•Arranged in 4-5 layers and
produce keratin, a tough
protein that protects the skin
from abrasion, heat, microbes,
and chemicals.
•Produce lamellar granules,
which release a water-repellent
seal to reduce water loss and
block foreign materials.
Melanocytes:
•Comprise about 8% of
epidermal cells and produce
melanin, a pigment that gives
skin its color and absorbs
harmful UV light.
•Melanin granules protect
keratinocyte nuclei from UV
damage but melanocytes
themselves are vulnerable to
UV light.

10. Intraepidermal Macrophages
(Langerhans cells):
•Derived from red bone marrow,
these immune cells help identify
and fight invading microbes.
•They are sensitive to UV light.
Tactile Epithelial Cells (Merkel
cells):
•The least common epidermal
cells, found in the deepest layer.
•Work with sensory neurons to
detect touch through structures
called Merkel discs.

11. Epidermis
•The epidermis typically has four layers:
1.Stratum basale
2.Stratum spinosum
3.Stratum granulosum
4.Stratum corneum (thin layer).
•This is referred to as thin skin and is found on most parts of the body.
•In areas exposed to high friction, like the fingertips, palms, and soles, the
epidermis has an additional layer called the stratum lucidum and a thicker
stratum corneum. This is known as thick skin.

12. •The stratum basale is the deepest layer of the epidermis, made up
of a single row of cuboidal or columnar keratinocytes.
•Some of these cells are stem cellsthat divide to produce new
keratinocytes.
•The keratin intermediate filamentsin these cells form the protein
keratin, which helps protect deeper skin layers. These filaments
attach to desmosomes(which bind cells to each other) and
hemidesmosomes(which attach keratinocytes to the basement
membrane between the epidermis and dermis).
•The stratum basalealso contains melanocytes(which produce
pigment) and tactile epithelial cells(which help detect touch). This
layer is also called the stratum germinativumbecause it is
responsible for creating new skin cells.
Stratum basale

14. •The stratum spinosum is the layer above the stratum basale, consisting
of 8–10 layers of keratinocytes. The keratinocytes, produced by stem
cells in the basal layer, begin to flatten as they move upward.
•These cells contain organelles similar to those in the basal layer, and
some can still divide. In this layer, keratinocytes form thicker bundles of
keratin intermediate filamentsthan in the stratum basale.
•They remain connected by desmosomes. These desmosomes, along
with the keratin filaments, provide strength and flexibility to the skin.
•The stratum spinosumalso contains intraepidermal macrophages
(immune cells) and melanocytes(melanin pigment-producing cells).
Stratum spinosum

16. •The stratum granulosum is located in the middle of the epidermis and
consists of 3–5 layers of flattened keratinocytes undergoing apoptosis
(programmed cell death).
•As the cells move away from the dermal blood supply, their nuclei and
organelles break down, and they lose the ability to perform metabolic
functions.
•Key features of this layer:
•Keratohyalin granules: These dark-staining granules help convert keratin
filaments into keratin.
•Lamellar granules: These release a lipid-rich secretion that forms a water-
repellent seal between cells, preventing water loss and blocking foreign
materials.
•The stratum granulosumserves as a transition zone between the
metabolically active cells in the deeper layers and the dead cells in the
upper layers.
Stratum granulosum

17. •The stratum lucidum is found only in thick skin, like the
fingertips, palms, and soles.
•It consists of 4–6 layers of flattened, dead keratinocytes that are
full of keratinand have thickened plasma membranes. This
helps provide extra toughness to these areas of thick skin.
Stratum lucidum

18. Stratum corneum
•The stratum corneum is the outermost layer of the epidermis,
made up of 25 to 30 layers of flattened, dead keratinocytes.
•These cells are thin, flat, and packed with keratin, but no
longer contain a nucleus or organelles.
•The stratum corneum constantly sheds and replaces cells from
deeper layers.
•This layer helps protect the skin from injury and infection.
•When the skin is exposed to frequent friction, the stratum
corneum thickens, forming a callus.

19. DERMIS

20. Dermis
•The dermis, the deeper layer of the skin, is made of dense irregular connective
tissue with collagen and elastic fibers.
•This structure provides strength, flexibility, and the ability to stretch and recoil.
•The dermis is thicker than the epidermis, especially on the palms and soles, and
includes various structures like blood vessels, nerves, glands, and hair follicles.
•Dermal blood vessels supply nutrients to all skin cells. These vessels help
regulate body temperature.
•The dermis contains different sensory receptors. Lamellated (Pacinian)
corpuscles, located in the deeper dermis, detect heavy pressure, while tactile
(Meissner’s) corpuscles, found in the upper dermis, respond to light touch and
texture.
•The dermis has two regions: Papillary Region and Reticular Region

22. Papillary Region
•The papillary layer is composed of areolar connective tissue that
includes tough collagen fibers and elastic fibers in a gel-like ground
substance.
•Networks of these fibers give the skin toughness and elasticity.
•Features dermal papillae, small projections into the epidermis that
increase surface area.
•These may contain:
•Capillary loops(blood vessels).
•Meissner corpuscles(touch-sensitive receptors).
•Free nerve endings, which detect sensations like warmth, coolness,
pain, tickling, and itching.

23. Reticular Region
•The reticular layer is made up of dense irregular connective tissue
located deeper, attached to the subcutaneous layer.
•The reticular layer is rich in collagen fibers (providing strength), elastic
fibers (offering flexibility), and reticular fibers (forming a supportive
network for dermal structures).
•Additionally, lamellated(Pacinian) corpuscles are found in the reticular
layer to detect pressure and vibrations.
•The spaces between fibers hold blood vessels, nerves, hair follicles,
andsebaceous (oil) and sweat glands.
•The dermis is essential for the survival of the epidermis and provides
structural support and sensation.

24. •The dermis is rich in blood vessels that help regulate body temperature.
•When the body is hot, dermal capillaries fill with heated blood, causing
the skin to appear red and warm, allowing heat to escape.
•In cooler conditions, blood flow to these capillaries is reduced to
conserve heat and maintain internal body temperature.

26. EPIDERMAL RIDGES
•The palms, fingers, soles, and toes have ridges and grooves that form patterns of
loops and whorls, such as fingerprints. These epidermal ridges develop in the
third month of fetal development when the epidermis pushes down into the
dermis.
•Functions of Epidermal Ridges:
•Strength: They create a strong bond between the epidermis and dermis,
especially in areas under mechanical stress.
•Grip: The ridges increase surface area and friction, improving grip in hands and
feet.
•Tactile Sensitivity: More surface area allows for more touch receptors,
enhancing sensitivity.
•Fingerprints: Sweat pores open on top of the ridges, creating unique fingerprints
or footprints when touching surfaces.

27. •Stretch marks are a type of internal scarring
that occurs when the skin is stretched too
much.
•When the skin is overstretched, the collagen
fibers in the dermis are damaged, and small
blood vessels may rupture. This causes
reddishstreaksto appear.
•Stretch marks commonly appear on the
abdomen during pregnancy, on bodybuilders
who rapidly gain muscle mass, and in people
with obesitywhere the skin is stretched.
Stretch
Marks

28. Skin Color and Its Basis
•Skin color is determined by three pigments: melanin, hemoglobin, and carotene.
•Melanin:
•Range of Colors: Varies from pale yellow to reddish-brown to black.
•Types:
•Pheomelanin: Yellow to red.
•Eumelanin: Brown to black (especially noticeable in hair).
•Location: Melanocytes, the cells that produce melanin, are found in areas like
the penis, face, limbs etc.
•Skin Color Differences:
•All humans have a similar number of melanocytes.
•Variations in skin color depend on how much pigment melanocytes produce
and transfer to keratinocytes.

29. Freckles and Age Spots:
•Freckles: Patches of melanin that darken in the summer.
•Age Spots: Darker than freckles, caused by melanin buildup from sun
exposure, common after age 40, and do not fade in winter.
•Moles (Nevus): Benign overgrowths of melanocytes that develop in
childhood or adolescence.
Melanin Production:
Melanin is made from the amino acid tyrosine with the help of the
enzyme tyrosinase, inside organelles called melanosomes.
UV Light:
•Increases melanin production, leading to tanning.
•Melanin absorbs UV radiation, protects DNA from damage, and
neutralizes harmful free radicals.
•Tanning fades as keratinocytes containing melanin are shed.

30. Subcutaneous Layer
•Subcutaneous (subQ) layer (also called hypodermis) is not part of
the skin but, among its functions, it attaches the skin to the
underlying tissues and organs; this layer (and sometimes the dermis)
contains lamellated (pacinian) corpuscles which detect external
pressure applied to the skin.

31. Accessory structures of the skin
•Hairs, skin glands, and nails—originate
from the embryonic epidermis.
•Hair and nails protect the body, while
sweat glands regulate body temperature.

32. HAIR
•Hair is found on most skin surfaces except the palms,
soles, and some areas. It’s denser on the scalp,
eyebrows, armpits, and around the genitals.
•Hair helps protect the body, such as shielding the scalp
from injury and sun, and eyebrows and eyelashes protect
the eyes. Hair also aids in sensing light touch.
Hair
Structure
•A hair consists of keratinized cells and has two parts: the
shaft, visible above the skin, and the root, below the
skin. The hair is made up of three layers:
•Medulla(inner layer) –contains pigment granules or
air bubbles
•Cortex(middle layer) –forms most of the hair shaft &
consists of elongated cells.
•Cuticle(outer layer) –flat, keratinized cells that overlap
like shingles on the roof of a house.

35. Hair Follicle
The hair follicle surrounds the root and
has two sheaths:
•External root sheath – a continuation of
the epidermis
•Internal root sheath–formed by the
hair matrix and is closer to the hair
These sheaths are collectively known as
the epithelial root sheath. The
surrounding dermal tissue is the dermal
root sheath.
•At the base of the follicle is the hair bulb,
which contains the papillawith blood
vessels that nourish the hair. The hair
matrixin the bulb produces new hair
and replaces old hair.
Additional Structures
•Sebaceous glands secrete oil to lubricate
the hair.
•Arrector pilimuscles cause hair to stand
up when cold or scared, leading to
goosebumps.
•Hair root plexus–nerve endings around
the follicle that detect hair movement.

36. •Several kinds of exocrine glands are
associated with the skin:
•Sebaceous (oil) glands,
•Sudoriferous (sweat) glands
Skin Glands

37. Sebaceous Glands
•Sebaceous glands, also known as oil glands, are small, branched, rounded (acinar)
glands located in the skin. Their main function is to produce and secrete an oily
substance called sebum. These glands are typically connected to hair follicles, with
their secreting portions lying within the dermis layer of the skin.
Distribution and Location:
•Connected to Hair Follicles: Most sebaceous glands open into the neck of hair
follicles.
•Directly on Skin Surface: In certain areas like the lips, glans penis, labia minora, and
tarsal glandsof the eyelids, sebaceous glands open directly onto the skin.
•Absent Areas: They are absent in the palmsand solesof the feet.
•Size Variations: These glands are small on most areas of the trunk and limbs but are
relatively large on the breasts, face, neck, and upper chest

38. Sebaceous glands secrete sebum, a mixture of:
•Triglycerides: Fats that help maintain hydration and skin softness.
•Cholesterol: Assists in skin barrier function.
•Proteins and Salts: Provide additional structural and protective support.
Role of Sebum:
•Protects Hair: Coats the surface of hair to prevent drying and brittleness.
•Moisturizes Skin: Helps the skin retain moisture by reducing water loss.
•Softens: Keeps the skin soft and flexible.
•Antibacterial Properties: Inhibits the growth of certain bacteria on the
skin, contributing to a protective barrier.

40. •Sweat glands, also known as sudoriferous glands, are structures
found throughout the skin that help regulate body temperature and
perform excretory functions.
•Each sweat gland consists of a small tube that originates from a
coiled, ball-shaped structure located in the deeper dermis or
superficial subcutaneous layer.
•The coiled portion is lined with sweat-secreting epithelial cells.
•Types of Sweat Glands: Eccrine Sweat Glandsand Apocrine Sweat
Glands
•Both types of sweat glands play essential roles in maintaining
homeostasis, managing stress responses, and, in the case of
apocrine glands, signaling through scent.
Sweat Glands

41. Eccrine Sweat Glands
•Structure and Function: Eccrine glands are simple, coiled tubular glands located
in most areas of the skin, especially on the forehead, palms, and soles, but absent
from the lips, nail beds, and certain genital areas. Their secretory portion lies in
the deep dermis or upper subcutaneous layer, and the ducts open directly onto
the skin's surface.
•Sweat Composition: Eccrine sweat is primarily water with small amounts of ions,
urea, uric acid, ammonia, amino acids, glucose, and lactic acid.
•Role in Thermoregulation: These glands help regulate body temperature by
producing sweat that cools the skin through evaporation, a process called
thermoregulatory sweating. This begins on the forehead and scalp and spreads
across the body, appearing last on the palms and soles.
•Other Functions: Eccrine glands also assist in waste elimination, although the
kidneys play a larger role. Additionally, they produce sweat during emotional
stress, known as emotional sweating or a cold sweat, which starts on the palms,
soles, and armpits before spreading elsewhere.

42. •Structure and Location: Apocrine glands are larger than eccrine
glands, with bigger ducts and lumens. They are located mainly in the
armpits, groin, areolae, and bearded areas of the face in adult
males.
•Their secretory portion is found in the lower dermis or upper
subcutaneous layer, and their ducts open into hair follicles.
•Sweat Composition: Apocrine sweat is thicker and milky or
yellowish due to the presence of lipids and proteins. While odorless
initially, it produces a musky body odor when bacteria on the skin
metabolize its components.
•Activation and Function: Apocrine glands become active at puberty
and respond to emotional stress, sexual activity, or other stimuli.
Unlike eccrine glands, they do not participate in thermoregulation.
Apocrine Sweat Glands:

43. Nails
•Nails are hard coverings made of dead, keratinized cells on the tips
of fingers and toes. They have several parts:
•Nail Body: The visible part of the nail. It’s similar to the outer skin
layer but with harder keratin. The pink color comes from blood
vessels beneath it.
•Free Edge: The white part of the nail that extends beyond the
fingertip. It appears white because there are no blood vessels
underneath.
•Nail Root: The hidden part of the nail under the skin.

44. Nails

45. Other features of nails include:
•Lunula: The white, crescent-shaped area at the base of the
nail, where the tissue underneath is thicker, hiding the blood
vessels.
•Hyponychium: The thickened skin under the free edge,
securing the nail to the fingertip.
•Nail Bed: The skin under the nail from the lunula to the
hyponychium. It lacks a specific skin layer called the stratum
granulosum.
•Cuticle (Eponychium): A thin strip of skin at the nail’s base,
helping to protect the nail.

46. Nail Growth:
•New nail cells are produced in the nail matrix near the root.
•Fingernails grow about 1 mm per week, faster than toenails.
Growth rates depend on factors like age, health, and
environment.
Functions of Nails:
•Protect the tips of fingers and toes.
•Support touch and improve manipulation of objects.
•Help in grasping, scratching, and grooming.

47. Skin Functions

48. Regulation of Body Temperature
•Maintaining body temperature is crucial, as even small changes can
disrupt metabolic processes. The internal body temperature is typically
around 37°C (98.6°F).
•Thermoregulationis the body’s process of maintaining a stable internal
temperature. The skin plays a key role in regulating temperature by
adjusting sweat production and blood flow based on the environment

49. In Hot Weather
•Increased Sweat Production:
•When the body heats up due to high external temperatures or exercise, eccrine
sweat glandsin the skin produce more sweat.
•Sweat evaporates from the skin's surface, carrying heat away and helping to cool
the body down.
•Blood Vessel Dilation (Vasodilation):
•The blood vesselsin the dermis(middle layer of the skin) dilate(widen). This
increases blood flow through the skin, allowing more heat to be transferred from
the blood to the skin's surface.
•As a result, heat can be released from the body more effectively into the
surrounding environment.
•These mechanisms help lower the body’s core temperature and prevent overheating.

50. In Cold Weather:
•Decreased Sweat Production:
•In response to cold temperatures, sweat productionfrom eccrine sweat glands
slows down or stops. This helps the body conserve heat rather than lose it
through evaporation.
•Blood Vessel Constriction (Vasoconstriction):
•To retain heat, the blood vesselsin the dermis constrict(narrow). This reduces
blood flow to the skin, minimizing heat loss.
•Less blood flow to the skin means less heat is transferred to the surface and lost
to the environment, helping maintain the body's core temperature.
•Shivering:
•If the temperature drops significantly, the body can also generate heat by
inducing shivering, where muscles contract rapidly to produce heat.
•These responses help the body retain warmth and prevent hypothermia in cold
environments.

51. •The skin protects the body in several ways. Keratin helps shield
underlying tissues from microbes, abrasion, heat, and chemicals.
•The tightly packed keratinocytes also resist microbial invasion.
•Lipids from lamellar granules prevent water loss and protect against
dehydration, while also reducing water entry during activities like
swimming or showering.
•Sebum, an oily substance from sebaceous glands, keeps skin and hair
moist and contains chemicals that kill bacteria.
•The acidic pH of sweat inhibits the growth of some microbes.
•Melanin helps protect against the harmful effects of ultraviolet light.
•Two types of immune cells in the skin provide further protection:
intraepidermal macrophages detect and alert the immune system to
harmful microbes, while dermal macrophages consume bacteria and
viruses that bypass the epidermis.
Protection

52. •The skin plays a small role in both excretion (removing
substances from the body) and absorption (allowing
materials to enter the body). About 400 mL of water
evaporates through the skin daily.
•A sedentary person loses an additional 200 mL as sweat,
while active individuals lose more. Sweat also helps excrete
small amounts of salts, carbon dioxide, and waste products
like ammonia and urea from protein breakdown.
•Water-soluble substances do not easily pass through the
skin, but lipid-soluble materials like fat-soluble vitamins (A,
D, E, and K), certain drugs can.
Excretion and Absorption

53. Excretion and
Absorption
•Toxic substances, such as organic solvents
(acetone, carbon tetrachloride), heavy metals
(lead, mercury, arsenic), and poison compounds,
can also be absorbed through the skin.
•Topical steroids, such as cortisone, are lipid-
soluble and easily penetrate the skin to reduce
inflammation by inhibiting histamine production.
•Some drugs are delivered through the skin using
adhesive patches.

54. •Vitamin D synthesis begins in the skin when it is exposed to
sunlight. The process involves:
•Sunlight Activation: UV rays convert a molecule in the skin, 7-
dehydrocholesterol, into cholecalciferol, a precursor of vitamin
D.
•Liver and Kidneys: Enzymes in the liverand kidneysfurther
process cholecalciferol into calcitriol, the active form of vitamin
D.
•Role of Calcitriol: Calcitriol helps the body absorb calciumfrom
food, which is essential for strong bones and other functions.
Synthesis of Vitamin D

55. Most immune cells have vitamin D
receptors and can activate vitamin D
during infections (e.g., flu).
Immune
System
Benefits:
•Vitamin D boosts the immune response by:
•Enhancing the activity of cells that engulf harmful microbes
(phagocytes).
•Reducing inflammation.
•In short, vitamin D is essential for bone health, immune
function, and reducing inflammation.

56. References
Tortora, G. J., & Derrickson, B. H. (2021). Principles of
Anatomy and Physiology (15th ed.). Wiley.
Shier, D., Butler, J., & Lewis, R. (2022). Hole's human
anatomy & physiology (15th ed.). McGraw-Hill Education.
Marieb, E. N., & Keller, S. (2020). Essentials of human
anatomy & physiology (12th ed.). Pearson.