Integumentary System | Biology for Grade 11 PDF Download

INTEGUMENTARY SYSTEM

INTRODUCTION

1. Skin together with its derivative constitutes the integumentary system of the body.
2. Skin is largest, functional organ of the body having 16-18% of the body weight.
3. Skin is called Jack of all trades.
4. Skin is ecto-mesodermal in origin.
5. Skin of mammals possess spy lines, which is very distinct on palm and fingers. Every human has particular spy lines. No, two human, can have similar, finger print. (Quetlets rule)
6. Total surfce area of skin in an adult person is about 1.6 m².
7. Furrow (sulci cutis) and ridges (cristae cutis) are also present on the skin of Palm and Soles.

Note :

1. Study of finger prints is called Dactyloscopy.
2. The skin of rabbit is adopted for complete exposure to air due to terrestrial mode of life it is soft, but thick and dry completely covered with a thin blanket of hair called palage. Palage prevent excessive loss of heat. Presence of dense palage on rabbit shows that its native place is Europe.
3. Skin in mammals are attached with underlying skeletal muscle layer by tela subcutanea.

Note :
In human female after delivery, clear and permanent lines appears on the skin of abdomen these lines are called linea gravidarum after each delivery number of these lines becomes more and more dense.

GENERAL HISTOLOGY OF SKIN

Histologically, the skin is formed of two distinct layer, outer epidermis (ectodermal) and inner dermis. (mesodermal)

EPIDERMIS

General character Epidermis develops from ectoderm.

1. It has no blood capillary and is nourished by dermis which contain blood capillary.
2. It is composed of keratinized stratified squamous epithelium and is extremely thick in palm and sole. It is thinnest in conjuctiva of eyes.
3. Epidermis is composed of five layers which are as follows : (from inside to outside)

1. Stratum malphighi

1. It is innermost living layer and composed of single layer of columnar cells. When these cells spread outside the skin their shape changes from columnar to cuboidal.
2. At many places on this layer elevation and depression are found. The elevation is called (Rete pegs).
3. The cells of the layer remain in touch with dermis, hence get, nutrition from it.
4. This layer, undergoes, massive, mitotic divisions throughout the life and produce new cells which moves upward and forms new layer consistently.

INTEGUMENTARY SYSTEM

1. At numerous places, in between the cells pigmented dendritic cells are found, these cells are called melanophores or melanocytes.
2. Melanocyte arise from melanoblasts which are present at the junction of epidermis with dermis.
3. In cytoplasm of melanocytes numerous granules are found called melanosomes.
4. In this granules melanin is synthesized. Melanin is a pigment of black colour.
5. Melanin get synthesized from amino acid tyrosine. Enzyme tyrosinase induces melanin synthesis.
6. In an organism (man in particular) inability of synthesis of an enzyme tyrosinase leads to a genetical disease albinism. In albinism a person lacks pigment completely.

Note :

Melanin prevents skin cancer and mutation which leads to cancer, It absorbs harmful radiation (U.V.radiation).

In lower vertebrate like amphibian and reptilian pigmented cells are found in dermis, these cells are called chromatophores. These pigmented cells of lower vertebrates have capacity to change colour of the pigment, this unique capacity is called metachrosis. Mammals, birds lacks this quality and capacity. On basis of pigment, chromatophores are of numerous types

(a) Melanophores
In it melanin pigment is found.
It is of brown and black colour.

(b) Guanophores
In it crystal of guanine is found.
It is bright white in colour.

(c) Lipophore
Yellow coloured pigment lipids are found, called chromolipids. eg. Carotene.

Note :
In fishes, amphibians, and reptilians, capacity of colour changing is controlled by MSH which is secreted by middle lobe of pituitary.

2. Stratum spinosum

This is a stratum of six or seven sub layers of cell next to the stratum malpighi Cell of these layers are polyhedral.
It provides rigidity to the epidermis.
In cytoplasm of the cells of this layer numerous Golgi complex and mitochondria are found.

3. Stratum granulosum

The cells of this layer are flattened or diamond shaped.
Their nuclei are denser and cytoplasm contain the basophilic and keratohyaline protein.

4 Stratum lucidium

This is the fourth layer which is not always seen.
In these the keratohyaline, granule first dissolve and then transform into a protein, eleidin. Which is semi transparent and water proof and acts as a barrier layer.

5 Stratum corneum

1. It is thickest and outermost layers of epidermis with 99% dead cells. The cells dies because of keratinisation and cornification.
2. Composed of 8 to 10 layers
3. It lack nucleus.
4. Cells of this layer are scale like Eleidin present in cytoplasm get transformed into nonliving keratin which is sceloprotein.
5. Majority of cells of this layer are non-living.
6. It is thick at palm and sole.
7. In this layer some living cells are found, which secretes hormones, these hormones controls the cell division of malphighi layer.
8. Stratum corneum undergoes periodic shedding in pieces. This is called as Ecdysis. Complete shedding called sloughing occurs in snakes.

Note :
Exoskeleton is formed from this layer in mammals and other vertebrates.
eg. Hair, Nails, Wings beak etc.

DERMIS

General character

1. Dermis originates from mesoderm.
2. It is 2-3 times thick in comparison to epidermis.
3. It is composed of connective tissue. In it white collagen fibres, white elastic fibres and unstriated muscle fibres are found.
4. Elastin fibre provides flexibility whereas, collagen provides strength which makes dermis strong.
5. Dermis is thick in male in comparison to female. From dermis leather is obtained, to obtain leather epidermis is dissolved, and this process is called Tanning.

Note :
Preservation of complete skin along with hairs are called Taxidermy.

Layers of Dermis

Dermis is composed of two layers :
Papillary layer
Reticular layer

1. Papillary layer (Pars Papillaris)

1. It is outer layer
2. This layer at many places remains embedded in epidermis called dermal papilla.
3. Collagen fibres are less in this layer.
4. Its lines are called (lines of langerhans)
5. In this layer tactile corpuscles or meisners granules are found. It is found in large number at the tips of fingers.

2. Reticular layer (Pars Reticularis)

1. It is thick in comparision to papillary layer.
2. It this layer at numerous places mast cells, macrophages and melanin pigment are found.
3. Large number of collagen fibres are found in this layer. These fibre is responsible for stretching of skin.

STRATUM ADIPOSUM (PANNICULUS ADIPOSUS)

1. This layer is composed of adipose tissues and lies just below dermis.
2. This layer is extremely thick in whale, elephant, rhino, and called blubber.

Functions of stratum adiposum

(i) It acts as shock absorber.
(ii) It is site of food storage.
(iii) It acts as heat insulator.
(iv) It helps in attaining shape to the body.

DERIVATIVES OF SKIN

Derivatives of skin includes
Epidermal gland
Exoskeleton structure
Integumentary receptor

EPIDERMAL GLAND
Epidermal gland of skin includes Sweat gland Sebaceous gland
Meibomian gland Lacrymal gland
Mammary gland Tyson gland

Sweat gland

1. Sweat gland is also called sudoriferous gland.
2. Sweat glands are simple coiled or simple branched tubular glands located in deeper zone of dermis.
3. It is at most places merocrine gland but in some parts of body it is apocrine gland.
4. In man over 2.5 million sweat glands is found, maximum on palm and sole, and is absent on glanspenis and lips.
5. It is absent in dog, whale, shrew,, moles, cetacean, spinyanteater, sirenia.
6. Red coloured sweat is produced in Kangaroo, Hippopotamus and Rhesus monkey.
7. In rabbit maximum sweat glands found on lips.

Functions of Sweat gland

The chief function of sweat gland is as follows :

(i) Thermoregulation
(ii) Excretion
(iii) Water balance

2. Sebaceous gland

1. Sebaceous gland is also called oil gland.
2. Sebaceous gland generally remain associated with hair follicle but it may exist without hair follicle like in glans penis.
3. It is branched alveolar gland, holocrine in nature.
4. It secrets sebum which makes the skin and hair water proof.
5. In sebum cholesterol is found which synthesizes vitamin D in presence of sunlight.
6. In human being sebaceous gland is not found on palm, sole, forehead & face (maximum)

3. Meibomian gland

1. Meibomian gland is modified sebaceous gland.
2. It is found in the dense connective tissue plate (tarssus) that support the free edges of each eyelid.
3. It opens into follicle of eye lashes
4. It produces oily secretion which keeps the cornea moist and prevent from getting dried, moreover only secretion forms a thin film over the layer of lacrimal fluid.

4. Lacrimal gland

1. Lacrimal gland is tear gland found beneath upper eyelids and produce watery secretion (tears) to keep eyes moist.

5. Mammary gland

1. Mammary gland is modified sweat gland. It is compound tubulo alveolar, apocrine gland.
2. It is characteristic feature of mammals, present in both sex, in human male it is vestigeal.
3. In rabbit 4-5 pairs of mammary glands are found on abdomen; whereas in human it is one pair.

Note :

1. Study of mammary gland is called Mastology.
2. Early milk which comes out after child birth is called colostrum.

6. Perineal gland or Inguinal gland

1. These glands are found around the anus of rabbit and releases certain thin liquid of typical smell which attract animal of opposite sex. Pheromones are found in secretion of these gland.
2. Except human it is found in all mammals.

7. Tyson gland

1. It is modified sweat gland, apocrine glands, present in skin of prepuce of glans penis.
2. It produces smegma which lubricates the glans penis, during copulation.

8. Zeis gland & Moll gland

1. Zeis gland is modified sebaceous gland found in skin of eye lashes, while moll gland is modified sweat gland.
2. It opens into hair follicles of eyelashes.
3. Its secretion keeps eyelashes smooth and supple.

9. Ceruminous gland

1. Ceruminous gland is modified sebaceous gland, Holocrine
2. It is found in skin of external auditory canal.
3. It secrets cerumin which is called ear wax.
4. It protects ear drum.

EXOSKELETON STRUCTURE

1. Exoskeleton of skin is composed of keratin.
2. Exoskeleton of skin includes, hairs scales, nail, horn claws, feather.

Hair

Hairs are characteristic feature of mammals. It develops as a thickening of the stratum germinativum of the epidermis.Each hair lies in a tubular pit called hair follicle.

Hair follicle

Hair follicle is composed of 2 layers outer layer and inner layer.
Outer layers is composed of stratum spinosum like cells whereas inner layers is composed of 3 sub layer, which are as follows.
(a) Cuticle (b) Huxley layer (c) Henley layer

Cuticle - It is innermost layer and is composed of dead, flat cells.

Huxley layer - Nucleus of this part of cells is horney.

Henley layers - Within cells of this layers cuboidal nucleus is found.

At the base of the hair, hair follicle invaginates inward to form hair papilla. Within hair papilla bunch of blood capillaries and nerve fibres are found.

Structure of hair

Hair shaft - Part of hair which comes out of epidermis called hair shaft.

Hair root - Hair root is slightly bulged called hair bulb. The cells of hair bulb just above hair papilla are live and divisible and is called germinal matrix of hair. Due to division of these cells, hair increases in size.

Note :
Except germinal matrix of hair rest part of hair is composed of dead & keratinized cells.

Arrector Pilli
An arrector pilli muscles connect each hair with basement membrane of epidermis. When arrector pilli contracts it squeezes the oil out from the sebaceous gland, it results in errection of the hair. This process is called Goose flesh. The contraction of arrector pilli muscle takes place due to adrenalin and sympathetic stimulation.

In T.S. of hair possess 3 regions :

Medulla- It is large, vacuolated moderately keratinized cells is found.
Cortex - It is middle layer heavily keratinized cells are found.
Cuticle - It is outer most layer. It is Heavily keratinized overlapping cells are found having their free ends directed upward. Melanocyte present in hair bulb produces and transfer melanin to the corticalb cells of the hair.

Note :
In old age hair turns grey because air spaces between the cells of the medulla increases in number and pigment formation decreases.
In old age hair loss becomes more because of reduction of blood supply.

Hair on human body is vestigeal organ.

Functions

Eyelashes, hairs in the nostril and ear canal, Keep out dust particles.

Hair follicle helps in repairing the epidermis injured by burns and because it is deeply seated and retain stratum germinitavum.

INTEGUMENTARY RECEPTOR

1. Algesireceptor
It is pain receptor.
It is composed of naked nerve fibre.
In human body 40 lakhs algesi receptor are found.
It is maximum in all cutaneous receptor

2. Tangoreceptor
It provides sense of touch.
In human body 5 lakhs tangoreceptor is found it is of numerous type which are as follows :
(a) Meissener’s corpuscles
It is found mainly and in maximum numbers on nipple, glanspenis, lips, end of finger tips, on palm, clitoris etc.

Note : Those meissners corpuscles which are found on external genital organ are called genital corpuscles.
(b) Merkel’s discs
Merkel’s discs are found in epidermis are their junction with dermis of human and other mammals.

These are absent in Rabbit.

3. Pacinian corpuscles (Proprioreceptors)

Pacinian corpuscles are pressure receptors or baroreceptor.
It is found deep in dermis.

4. End bulb of Krause or end organs of Ruffini

Both are thermoreceptor.
Bulb of Krause is sensitive to Cold. (frigidoreceptors)
End organ of Ruffini is sensitive to Hot. (Caloreceptors)

FUNCTIONS OF SKIN

(a) Protection - Skin forms cover on organs and protects the body from mechanical injury.
(b) Safety against sunburn - Melanin of epidermis gives protection against ultravoilet rays of sun, these rays causes sunburn.
(c) Excretion - The skin removes the excess of water, lactic acid, traces of urea and some salt (chiefly NaCl) from the blood as sweat. As a result of keratinization, horny dead cells are produced constantly, sheeding of corneal layer is a kind of excretion.
(d) Secretion - Skin secrets numerous important substances which is very important for survival of an animal. Preen gland in bird produces oil for water proofing their feather.
(e) Chemical defence - The sweat, oil and wax from skin gland contain lactic acid and fatty acid. These acids make the pH acidic enough to kill or retard the growth of many bacteria and fungi.
(f) Nourishment - The skin is capable of forming vitamin D from a cholesterol derivative in the presence of sunlight.
(g) Barrier to germs and poison - The outer hard and horney layer of insect checks the entry of microrganisms in the body.
(h) Heat conservation - Hair tend to trap a layers of air which insulates the body, reducing heat exchange with the environment. In some mammals such as sheep and rabbit, air retaining capacity is increased by the hairs sticking together to make a belt, subdermal fat also prevents body heat.
(i) Regulation of body temperature - The normal body temperature of man is 98.4 ºF. (37ºC). The temperature is maintained in all seasons. The sweat cools the skin if it get overheated. In winter, blood capillaries which lead to skin undergo constriction called vasoconstriction, as a result heat not get lost from the body. In contrast, in summer dilation takes place in blood capillaries which is called vasodilation, as a result heat get lost from the body.

Note :
In summer rabbit erect their ears as a result heat is lost through blood capillaries of ear.
In summer dogs loses their body temperature through tongue by excessive salivation and panting .

SPECIAL POINTS

• During embryonic conditions, soft hair is called lanugo.
• In leucoderma skin pigment is not found at some places.
• Brown fat found in neonates, it prevents neonates from cold.
• During sweating PH of skin becomes 3 to 5.
• Sweat, saliva, tears possess lysozyme, which destroys microorganism.
• About 80 to 100 hairs are lost per day.
• Thinnest skin occurs over the eyelids. Thinnest epideris is of conjuctiva.
• Bradykinin- When body temperature rises the sweat gland release potent vasodilator peptide bradykinin,
• which dilates blood vessel to lose heat quickly.
• Vibrissae - These are special long, stiff sensory hair on the side of the mouth of certain mammals,
• such as rabbit and lion.(Vibrioreceptors)
• Seborrhoea - Oversecretion of sebaceous glands is called seborrhoea.
• The skin of older people becomes loose and wrinkled because elasticity of dermis decreases.
• During life time 23 kg of skin is shed.
• Goose flesh is also called cutis anserina (Erection of Hairs on skin).
• Colour variation in human being depends upon amount and colour of melanin rather than the number of melanocytes.
• Hippoptamus have sweat glands only on pinna.