Hard Derivatives . Dr. Vidhin Kamble Department of Zoology. Sangola College, Sangola

Hard Derivatives of Epidermis.

B. Sc- III Zoology. Dr. Kamble V. S.

1. Following types of horns are known:
2. 1.     Hollow Horns
3. 2.     Pronghorn
4. 3.     Antlers
5. 4.     Hair Horn
6. 5.     Giraffe Horns
7. Hollow Horns

Horns are found in ungulate (even-toed hoofed) mammals only. True horns of the hollow type are found in pronghorn, cattle, antelope, sheep and goats consist of an inner core of bone which is an outgrowth from the frontal bone. It is encased in a keratinised, epidermal covering. True horns continuously grow throughout life and are not shed.

Pronghorn

Pronghorn is a true horn, consists of a permanent projection of the frontal bone covered by a hard, horny epidermal sheath. The sheath is forked bearing one to three prongs made only of horny sheath. The horny sheath is shed annually and is replaced by another which grows from the skin that surrounds the core. It is found in Russian antelope Antilocapra.

Antlers

Antlers are found in the males of deer family, but they are present in both sexes in reindeer and caribou. An antler consists of a branching solid outgrowth of the frontal bone formed of dense connective tissue. It is covered during growth by hairy, vascular skin called ‘velvet’. The velvet is shed exposing the antler naked when the antler reaches full growth.

Thus, the antler consists only of dermal bone. The bony antler is also shed annually after the breeding season, and a new antler develops. Antlers are solid mesodermal bone, but they are formed under the influence of the integument. Formation of antlers is controlled by the hormones of testes and anterior lobe of the pituitary.

Rhinoceros or Hair Horn 

horn has no skeletal element. It is made by keratinised cells of the epidermis and consists of matted keratin fibres bound together, but its fibres are not true hair. It is a permanent epidermal structure and if broken it grows again. There is one horn in the Indian rhinoceros and two in the African species.

 

Giraffe Horns:

They develop from cartilaginous protrusions which are present at birth. They ossify and fuse at the top of the skull, where they appear as knobs permanently covered with living skin and hair. Giraffe possesses three of these knobs, one is median and anterior to the other two. These horns are short, unbranched and are permanent, and are present in both sexes.

 

Digital tips

In amniota the distal ends of digits have claws, nails or hoofs formed from the horny layer of the epidermis. They grow parallel to the surface of the skin and are built on the same plan.

Claws:

Claws made their appearance first in the reptiles. A claw is made of a hard horny dorsal scale-like plate called unguis and a relatively soft ventral subunguis, both converge terminally and cover the terminal part of the last phalanx. Claws of reptiles and birds are similar but in mammals the subunguis is much reduced and is continuous with a pad at the end of a digit. In cat family claws are retractile.

ii. Nails:

They are found in primates. The dorsal unguis is large and flat and subunguis is soft and much reduced. Tip of the digit forms a sensitive and vascular pad over which the nail groove is present. It is formed by the invagination of epidermis. Growth of the unguis takes place from the nail root lying below the skin in the nail groove.

iii. Hoofs:

They are found in ungulates. The horny unguis is thick and around the end of the digit, and encloses the thickened subunguis which touches the ground. Subunguis surrounds the soft, horny cuneus. Tip of digit, thus, forms a pad containing a blunt phalanx. Nails and hoofs of mammals are modified claws. Whalebone plates of toothless whales are also the modification of stratum corneum.

 Hair:

Hair is found only in mammals. It projects at an acute angle from the skin. Hair covers the entire integument in most (furred mammals), but in others only traces are left, such as whales have only a few core hairs on the snout.

But during development the body of the embryos of all mammals is covered with a coating of fine hair called lanugo which is usually shed before birth and replaced by a new one. Hair is entirely epidermal in origin.

Hairs are not modified scales but are new outgrowths of the epidermis only. A hair has an upper projecting shaft and a lower root lying in a hair follicle which is a sunken pit in the dermis. The shaft is made of only dead, keratinised cells. The part of the hair protruding above the skin is dead.

The hair shaft has an external cuticle of transparent overlapping cells which have lost their nuclei, inside the cuticle is a cortex (middle part of hair) containing shrivelled cells and pigments, and a central core or medulla having air spaces.

Feathers in Bird

Feathers are found only in birds and are formed from the epidermis in which the stratum corneum is highly specialised. Feathers are light, strong, elastic, waterproof and show many colours due to pigments and structural arrangement. The pigments are carotenoids and melanins. Carotenoids are frequently called lipochromes which are soluble in fat solvents like methanol, ether or carbon disulphide, and insoluble in water.

A typical feather consists of following parts.

1.     Central axis or Scapus

2.     Vexillum or vane.

3.       Scapus (Axis): The scapus is divided into

1. 1.     Basal calamus
2. 2.     Upper shaft or rachis.                     

Soft Derivatives of Integument By. Dr. Vidhin Kamble

 

Derivatives of Integument: Soft Derivatives 

Both layers of integument have given rise to various types of derivatives. The epidermis gives rise to integumentary glands, epidermal scales, horns, digital structures, different corneal structures, feathers, and hairs. The dermis forms dermal scales of fishes and of some reptiles, plates or scutes in reptiles, fin rays in fishes and antlers in mammals.

I. Epidermal Derivatives:

Epidermal derivatives are epidermal glands (unicellular and multicellular), epidermal scales and scutes, horns, digital structures (claws, nails and hoofs), feathers and hairs.

 1. Epidermal Glands

 Epidermal glands are formed from the Malpighian layer of the epidermis. They arise from the epidermis and often penetrate the dermis.

According to their structure they are

1. 1.     Unicellular 
2. 2.     Multicellular,
3. 3.     Tubular
4. 4.     Alveolar
5. 5.     Simple Or Compound (branched) glands.
6. These are lined by cuboidal or columnar cells.

 (a) Unicellular glands are single modified cells found among other epithelial cells, they are present in amphioxus, cyclostomes, fishes, and larvae of amphibians. Unicellular glands are known as mucous cells or goblet cells. They secrete protein mucin which combines with water to form the mucus which lubricates the surface of the body. Other unicellular glands are granular cells and large beaker cells of cyclostomes and fishes, they also secrete mucus.

 

(b) Multicellular glands are of two types:

 (i) Tubular glands:

These are multicellular tubes of uniform diameter formed as ingrowths of the Malpighian layer into the dermis, e.g., glands of Moll on the margin of the human eyelids. Tubular glands may become coiled at the base deep in the dermis, e.g., sweat or sudoriferous glands of mammals, or they may divide into many tubules which are then called compound tubular glands, e.g., mammary glands of females and of males in monotremes and primates, etc., and gastric glands in stomach.

 (ii) Alveolar or saccular glands:

 These are multicellular down growths of the Malpighian layer into the dermis, having a tubular duct whose terminal parts form a rounded expansion to become flask-shaped, e.g., mucous and poison glands of amphibians. Alveolar glands may branch into many lobules which finally open into a common duct, they are then called compound alveolar glands, e.g., mammary glands of eutherians, and salivary glands.

 

Different Types of Epidermal Glands

 Kinds of Epidermal Glands:

According to function, the epidermal glands of vertebrates are of the following types:

  i. Mucous Glands:

They may be unicellular or multicellular. The unicellular glands are mucous gland cells, granular cells and beaker cells of amphioxus, cyclostomes and fishes. They secrete mucus which keeps the skin moist and slippery, and also affords protection against bacteria and fungi. Mucous cells and granular cells lie near the surface, but the beaker cells lie more deeply and extend from the Malpighian layer to the surface.   

Multicelluar mucous glands are alveolar found in some fishes and amphibians. They occur all over the surface of the body and produce mucus for lubricating the skin and in amphibians they keep the skin moist to aid in respiration.

 

ii. Poison Glands:

Amphibians also have alveolar poison glands which are larger but less numerous than mucous glands. In toads masses of poison, glands from parotoid glands behind the head. The secretion of poison glands has a burning taste and is used as a defense. Caecilians have giant poison glands.

Some tubular glands are found on the feet and suctorial discs of tree frogs which aid in climbing. Tubular glands are also found on the swollen glandular thumb parts of male frogs and toads during the breeding season. They aid in clasping the female during amplexus.

 iii. Luminescent Organs or Photophores:

They are found in longitudinal rows near the ventral side of the body in those fishes which live in the deep sea where no light penetrates. Each photophore is a group of epidermal cells lying in the dermis.

Each photophore has a lower layer of luminous cells below which is a layer of reflecting pigment cells, and the upper layer of mucous cells forms a lens. The glandular cells produce phosphorescent light which is transmitted to the outside by other cells. The light helps to attract the prey of deep sea fishes.

 

iv. Femoral Glands:

Femoral glands are found in male lizards (e.g., Uromastix) below the thighs in a row from the knee to the cloaca. They secrete a sticky substance which hardens into short spines that are used for holding the female during copulation.

 v. Uropygial Glands:

These are the only glands in birds, and they are best developed in aquatic birds. Uropygial glands are branched alveolar glands located on the dorsal side at the base of the tail or uropygium in the form of swelling. They secrete an oil which is odoriferous and attracts the opposite sex. The oil contains pomatum which is picked up with the beak and used for preening and water­proofing the feathers.

 

vi. Sweat Glands:

The largest number and variety of epidermal glands are found in the skin of mammals. They are tubular or alveolar and multicellular. Sudorific or sweat glands are long, coiled tubular glands embedded deep in the dermis. Their upper part forms a duct which opens on the surface by a pore and the lower coiled part lies in the dermis surrounded by a network of blood capillaries.

Sweat glands are not uniformly distributed. In man they are more numerous on palms, soles, and arm pits. In cats, rats, and mice they are confined to the soles of the feet. In rabbit they are around the lips; in bats on the sides of head; in ruminants on the muzzle and the skin between the digits and in hippopotamus they are found only on the pinnae.

 Modified sudorific glands form glands of Moll in the margins of the human eye in connection with eye-lashes.

 

Ceruminous glands:

in the external ear passages of mammals are modified sweat glands and secrete a waxy substance which combines with the secretion of sebaceous glands to form earwax which catches dust. Oil glands form ceruminous glands in the external ears of some gallinaceous birds.

 

vii. Sebaceous Glands:

Sebaceous glands are alveolar glands opening in hair follicles containing hairs. They also independently open at the skin surface around the genital organs, tip of the nose, and edges of the lips. Sebaceous glands secrete an oil (sebum) to lubricate the hairs and also cover the skin with a film of oily coating. The oily secretion of sebaceous glands contains waxes, fatty acids, and cholesterol, which makes the skin pliable.

Sebaceous glands are absent in Manis (pangolin), and Sirenia, and Cetacea which practically have no hairs.

Meibomian glands

Modified sebaceous glands form Meibomian glands in the eyelids, each has a long straight duct into which separate alveoli open.

They produce an oily secretion which forms a film over the lacrimal fluid or tears holding them evenly on the surface of the eyeball for keeping the eye moist, in weeping the oily film are broken and tears flow out.

Ceruminous glands:

Ceruminous glands of external auditory meatus are modified sebaceous glands. Their greasy or waxy secretion, called the cerumen traps the insects and dust particles.

viii. Scent Glands:

Scent glands are modified sebaceous glands or sweat glands. Their secretion is an allurement to the opposite sex. Scent glands are located in the deer family on the head near the eyes. Skunks and carnivores have scent glands around the anus, and pigs and goats have scent glands between their toes.

x. Mammary Glands:

These are characteristic of mammals. They secrete milk generally in the females for nourishment of the young. In monotremes both sexes may secrete milk, this condition is called gynaecomastism which is not a normal condition. Mammary glands of monotremes are compound tubular glands, while in other mammals they are compound alveolar.  Mammary glands of monotremes have no nipples, they open into pits on the surface of the skin, and the young ones obtain milk by licking tufts of hairs. In others, the mammary glands open by their ducts separately into a nipple.

Mammary glands along with fat form integumentary swellings called mammae or breasts. The number and location of mammae varies in different mammals. The number ranges from two in many mammals to 25 in the opossum. Mammae may run along two ventral milk lines from the armpits to the groin, or they may be axillary, thoracic, abdominal or inguinal in position.

MCQ- 2 Physiology

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MCQ No- 1 Physiology

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MCQ with answer - Physiology - By Dr. Vidhin Kamble

 1. Which one of the following is a pentose sugar? – Ribose.

2. The polysaccharide found in liver and muscles is – Glycogen.

3. For a human being 25-30% of total calories should come from – Fat.

4. Which one of the following is a disaccharide? – Maltose.

5. The process of clotting of blood is aided by – Vitamin K.

6. Dry, wrinkled and Keratinised cornea may be due to – Xeropthalmia.

7. The process of maturation of erythrocytes is due to – Vitamin B12.

8. Identify the mineral necessary for O2 transport in our body – Iron.

9. The only enzyme present in salivary juice is – Ptyalin.

10. In the stomach HCl is secreted by – Oxyntic cells.

11. The ulcer causing bacterium is called – Helicobacter pylori

12. Woman who had several pregnancies may be affected by – Femoral Hernia.

13. Excessive alcohol consumption may cause – Hepatitis.

14. How many bones are present in our body skeletal system? – 206.

15. Pathological fracture may be due to – Hyperparathyroidism.

16. The blood clot at the place of fracture form a – Haematoma.

17. Metabolic arthritis is due to the error of – Purine metabolism.

18. In adults Vit-D and calcium deficiency lead to? – Osteomalacia.

19. The constitution of skeletal muscles in our body is – 40%

20. Each muscle fibre is made up of thread like structure called – Myofibrils.

21. The thin filament of a band is – Actin.

22. The energy for muscle action is provided by – ATP molecules.

23. A few hours after death all the muscles of the body attain a state of contracture.

It is called as – Rigor mortis.

24. Which one of the following disease is considered as auto immune disease?

– Myasthenia Gravis.

25. The rate of diffusion of O2 and Co2 are in the ratio of – 1:10

26. The nerve that controls the respiratory process is – Vagus nerve.

27. Herring – Brueur reflex controls – Respiration.

28. Collection of fluids between the lungs and the chest wall is called – Pleural effusion.

29. The concept established by yoga is – Mind over Body.

30. The disease preumonia can be controlled by – Paracetamol

31. Which blood vessel begins the systemic circulation? – Aorta

32. The Sinu Atrial mode is situated in the wall of – Right atrium.

33. The dimensions of S.A. Node is – 1.5cm x 3mm

34. The blood flow between the right atrium and right ventricle is regulated by

– Tricuspid valve.

35. Increase in RBC leads to – Polycythemia.

36. Lack of blood supply to brain leads to – Stroke.

37. The normal blood pressure of a healthy man is – 120/80mm Hg

What is a cardiac cycle:The sequential events occurring from the initiation of one heart beat to the commencement of the next is called as one cardiac cycle.

1. The basic units of Nervous system are - Neurons.

2. Synapsis is – Junction between two neurons.

3. The diameter of synaptic cleft is – 10 – 20nm.

4. The ions involved in nerve conduction are – Na+ions, K+ions.

5. The transmitter substance at the synapse is – acetylcholine.

6. At the junction of two nerves lies a gap called – Synaptic cleft.

7. The electrical activity of the brain is recorded by – EEG.

8. The principal organ of urea biosynthesis is – liver

9. The structural and functional unit of kidney is – Nephron.

10. The biological filter is – Malpighian body.

11. The Kidneys normally receive an abundant blood supply of about – 1200ml / min.

12. During ornithine cycle – NH3 is converted into urea.

13. The total Volume of glomerular filtrate in 24 hours is – 170 to 180 lit.

14. The high threshold substance in excretion is – Urea.

15. The low threshold substance in excretion is – Glucose

16. Reabsorption takes place in – Uriniferous tubules.

17. The amount of water excreted in each day is – 1-2Lit.

18. The amount of water filtered by kidney is – 180 lit / day.

19. What is malpighian organ?

20. Malpighian body comprises Bowman’s capsule and glomeruli. Ultra filtration of blood takes place in the malpighian body which act as a biological filter.

21. What are the components of Urine?

In Urine there are 96% water, 2% Urea and 2% Metabolic products.

22.  What is renal failure?

The reduction in the ability of the Kidney to filter waste product from blood to excrete them in the urine is called renal failure.

23.  What is dialysis?

Dialysis involves a technique used for removing waste products from the blood and excess fluid from the body as a treatment for kidney failure. It is also called as artificial kidney.

B.Sc-III Zoology MCQ Integument and its derivatives by Dr. Vidhin Kamble

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Comparative study of Vertebrate brain - MCQ By. Dr. Vidhin Kamble

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