Lecture Three Assit.Lect.

Maha Mustafa

Integumentary system
It is our primary means of identifying the organism, and is what
defines the boundary of its body. Skin is also the primary means through
which an organism interacts with its environment.

Because of its importance as the primary interface between an organism and

its environment, the skin is designed to perform many functions.

These functions include:

 It forms part of the exoskeleton and thickens to resist mechanical

injury.

 The barrier it establishes prevents the entrance of pathogens.

 Osmotic regulation and movement of gases and ions to and from the
circulation are aided by the integument conjunction with other system.

 Heat regulation.

 Respiration.

 It hold feathers for locomotion, hair for insulation, horn for defense

 Skin pigment block the harmful sunlight and bright colors during
courtship, cryptic or display.

Skin

The skin of all vertebrates is built in accordance with the basic

blueprint. It consists of a multilayered epidermis derived from ectoderm and
dermis derives from mesoderm. Between the integument and deep body
musculature is transitional subcutaneous region made up of very loose
connective and adipose tissue called hypodermis.

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Lecture Three Assit.Lect.Maha Mustafa

Modification of the epidermis and dermis involve:

1. The relative number and complexity of skin glands.

2. Differentiation and specialization of the most superficial layer

(Stratum corneum) of the epidermis.

3. The extent to which bone develops in the dermis.

General Features of the integument:

1- Epidermis

This skin is further divided into five, separate layers. In order from most
superficial to deepest, they are the:

 Stratum Corneum:- this layer is composed of the many dead skin

cells that you shed into the environment—as a result; these cells are
found in dust throughout your home. This layer helps to repel water.
 Stratum Lucidum: - this layer is found only on the palms of the
hands, fingertips, and the soles of the feet.
 Stratum Granulosum: - this is the layer where part of keratin
production occurs. Keratin is a protein that is the main component of
skin.
 Stratum Spinosum: - this layer gives the skin strength as well as
flexibility.
 Stratum Basale (germinativum):- this is where the skin’s most
important cells, called keratinocytes, are formed before moving up to
the surface of the epidermis and being shed into the environment as
dead skin cells.

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Lecture Three Assit.Lect.Maha Mustafa

The epidermis made up of 4 cell types:

 Keratinocytes: - Produce keratin protein a fibrous protein

that helps protect the epidermis.
 Melanocytes: - produces the brown pigment melanin these
are cells located in the bottom layer of the skins epidermis
and in the middle layer of the eye, the uvea. Through a
process called melanogenesis, these cells produce melanin,
a pigment in the skin, eyes, and hair.
 Langerhans Cells: - participate in immune response -
Formed in bone marrow. -Move to the skin.
 Merkel cells: - participates in the sense of touch
Connected to nerve cells from dermis.

The Dermis

Underneath the epidermis lies the dermis. The dermis contains:

 Blood vessels that nourish the skin with oxygen and nutrients. The
blood vessels also allow immune system cells to come to the skin to
fight an infection. These vessels also help carry away waste products.
 Nerves that help us relay signals coming from the skin. These signals
include touch, temperature, pressure, pain, and itching.
 Various glands.
 Hair follicles.
 Collagen, a protein that is responsible for giving skin strength and a
bit of elasticity.

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Lecture Three Assit.Lect.Maha Mustafa

Integument of Tetrapods:

Amphibians
The integumentary system of frog is very different from that of fishes,
reflective the partially terrestrial mode of life of the animals:

Frog skin is composed of epidermal and dermal layers; frog

epidermis is relatively thin and thus often limited to the stratum
corneum (outermost layer), central stratum spinosum, and stratum
germinativum (basal layer).

 The stratum corneum is composed of a very thin layer

of keratinized cells.

 The stratum spinosum is composed of terminally

differentiating cells, acting as an intermediate layer
between the stratum corneum and the regenerative
stratum germinativum layer.

 The stratum germinativum, which directly connects to

the dermis, contains a mixture of cell types including
epithelial cells, immune cells and chromatophores that
provide frogs with dynamic pigmentation patterns.

The dermal layer can be divided into two distinct layers: the
upper spongious dermis and lower compact dermis. Capillary beds
restricted to the dermis in most vertebrates reach in to lower part of
epidermis in amphibians serving cutaneous respirations.

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Lecture Three Assit.Lect.Maha Mustafa

Reptiles
The skin of reptile reflects their greater commitment to terrestrial existence:

1. The skin is rough, thick, dry and scaly. Skin is suited to the terrestrial
environment which prevents any loss of water.

2. The epidermis is generally delineated into three regions

 Stratum corneum: heavily keratinized outer layer,

 Intermediate zone: composed of stratum germinativum cells in
various stages of development,
 Stratum germinativum: the deepest layer, consisting of cuboidal
cells. Undergoes mitosis to form the intermediate zone.

3. The skin of reptiles has a thick stratum corneum that gives rise to a
variety of cornified appendages.

4. Skin glands are fewer than in amphibians.

5. Dermis of reptilian skin composed of fibrous connective tissue.

Birds

1. Epidermis comprise the (stratum corneum and the stratum basal) and
between them is transitional layer.

2. The thin skin of birds is characterized by feathers (contour, down and

flioplumes) derived from stratum corneum.

3. The dermis especially near the feather follicle is richly supplied with
blood vessel, sensory nerve ending and smooth muscle.

4. Bird skin has few glands.

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Lecture Three Assit.Lect.Maha Mustafa

Mammals
1. In mammals skin (stratum corneum) is thick, elastic and water proof.

2. The epidermal cells form into five layers stratum corneum, stratum
lucidium, stratum granulosm, stratum spinosum, stratum
germinativum (also called stratum basale).

3. The epidermis has multicellular glands (Sebaceous and sweat glands.

The mucous glands are absent). And Presence of mammary glands is
the characteristic of mammals

4. Dermis is very thick. It has intricate system of connective tissue fibers

extending in all directions, it consist of two layers (papillary and
reticular layers).

Figure (1) cross section of mammalian skin

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Lecture Three Assit.Lect.Maha Mustafa

Glands
 Epidermal glands of terrestrial vertebrates

Skin glands in terrestrial vertebrates are fewer but more diverse than in
aquatic species:

Amphibians
 It is usually includes two types of multicellular glands: mucous and
poison glands both are located in the dermis and open to the surface
through connecting ducts.

 Mucous glands secrete mucus to maintain the moisture, permeability

and elasticity of the skin, all of which are necessary for amphibian
homeostasis.

 Granular glands these glands have the potential to secrete serous

fluid, or toxic substances, and are therefore also known as serous or
parotoid/poison glands.

Figure (2) cross section of frog skin

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Lecture Three Assit.Lect.Maha Mustafa

 Chromatophores are cells that contain or produce pigments or reflect

light in order to display a certain colors. Amphibians benefit from the
colors that they display in a number of ways, ranging from
maintaining body temperature to avoiding predators.

Reptiles
 Integument glands of reptiles are thought to play role in reproductive
behavior; most of the secretions are holocrine. that is the cell of the
glands constitute the secretion and many of them are pheromones
(substance secreted into the environment by an organism that have an
effect on the behavior or physiology of other members of the
population)

 The glands usually restricted to certain area of the body. Many lizards
possess rows of femoral glands along the underside of the hind limb
in the thigh region, some turtles have scent glands.

Birds
 Uropygial gland (oily secretion) located at the base of the tail
secretes lipid and protein product that bird collected on the sides of
their beak and then smear on their feathers. Preening coats the feathers
with the secretion make them water repellent.

 Salt gland which is well developed in marine birds. Salt glands

excrete excess salt obtained when these bird ingest marine food and
sea water.

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Lecture Three Assit.Lect.Maha Mustafa

Mammals
Mammals have two main types of gland (sweat and sebaceous glands)
scent and mammary glands derived from them.

 Sebaceous glands: produce an oily secretion, sebum, that is released

into hair follicles and the oil lubricates the skin. Several lands open in
association with one follicle but in some areas the open directly onto
the surface of the skin .Marine mammals are practically devoid of hair
and do not have Sebaceous glands.

 In outer ear canal of mammals modified sebaceous glands

(Ceremonious glands) secrete cerumen, a waxy grease

 Meibomian glands of the eyelid secret oil onto the conjunctiva

of the eyeball.

 Sweat glands: are long, slender, coiled tubes of epidermal cells

extending deep into the dermis. That produces a watery product called
perspiration or sweat. Two types are usually recognized based on the
viscosity of their sweat (viscous or thin), their associations (with or
without hair follicles)

 One type produce thin sweat is not associated with hair

follicle and it is products function in regulation of body
temperature.

 the other produces viscous sweat is associated with hair

follicles

Sweat glands are not found in all mammals and their

distribution varies. In human have the greatest numbers of
sweat glands including some on the palms and soles.

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Lecture Three Assit.Lect.Maha Mustafa

In mice, rates and cats they are present on the paws and in
rabbits they appear around the lips, in elephants sweat and
sebaceous gland are absent

 The scent glands:

Are derived from sweat glands and produce secretions that play apart in
social communications. These glands may be located almost anywhere on
the body as:

On the chin (rabbits), face (deer), chest and arms (in some carnivores).
Secretion of these glands are used to indicate information such as status,
territorial marking, mood, and sexual power

 Mammary glands:

Produce milk a watery mixture of fats, carbohydrates and proteins the

number of mammary glands varies among species. Release milk to suckling
is lactations.

Mammary glands consist of numerous lobules. Each lobule is a cluster of

secretory alveoli in which milk produce. The alveoli can open in to a
common duct that in turn can open directly to the surface through a raised
epidermal papilla or nipple. The nipple surrounded by a circular pigmented
area of skin called the areola.

Alveolar ducts also can open into common champers or cistern with along
collar of epidermis called teat. The teat forms secondary duct carrying milk
from the cistern to the surface. Adipose tissues can build up beneath the
mammary glands to produce breast.

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