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Integument System
The outer covering of the animal and comprises of the skin, fur and claws
| Question | Answer |
|---|---|
| Describe the epidermis layer of the skin (7 points) | - The superficial (outer) layer - Made up of stratified (layered) squamous (multiple) epithelium - This makes it tough and protective - This layer is avascular, and instead gets its supply of nutrients from blood vessels within the dermis - Contains NO nerves - Consists of layers that are continually renewed - Last cells are seen as scurf of the top of the animal’s coat |
| Describe the dermis layer of the skin (6 points) | - The underlying layer of the skin - Epidermis sits on top - Consists of dense (tightly packed) connective tissue, with irregularly arranged elastic fibres and collagen - This layer is vascular with a good blood supply - Well supplied with nerves - Glands and hair follicles of the skin are found within the dermis |
| What are the 5 layers of the epidermis - in order from surface? | 1. Stratum corneum 2. Stratum lucidum 3. Stratum granulosum 4. Stratum spinosum 5. Stratum basale |
| Describe the stratum corneum layer of the epidermis? (2 points) | - This is the outermost layer of the epidermis - It is composed of many layers of dead cells called Corneocytes |
| What is a corneocyte? (2 points) | - Consist of keratin and provide a waterproof covering to the skin - The outer corneocytes are continuously sloughed and replaced by cells from the lower layers |
| Describe the stratum lucidum layer of the epidermis? (4 points) | - This is Latin for ‘clear layer’ - The cells lose their nuclei and become clearer - This layer is ONLY found on the nose and footpads - It consists of dead cells that contain lipid, which give the nose and foot pads a glassy appearance |
| Describe the stratum granules layer of the epidermis? (3 points) | - In this layer cells begin to die and are filled with keratin which gives them their granular appearance under the microscope - The cells are flattened and keratinisation begins in this layer (infiltration of the cells by keratin) - Keratin makes the cells more hard wearing |
| Describe the stratum basal layer of the epidermis? (3 points) | - This is the lowest layer of the epidermis and consists of a single layer of cells. - New cells are formed by mitotic division, as new cells are produced they push previously produced cells up to the next layer - Melanocytes, which give the skin its pigment and are present in this layer |
| Describe the stratum spinoism layer of the epidermis? (2 points) | - The cells in this layer have a spiky appearance and are still alive and nucleated. - This layer is 1-2 cells thick in areas where hair is present and up to 20 cells thick in areas where hair is absent |
| Describe the hypodermic layer (3 points) | - The hypodermis (or subcutis) is not actually part of the skin but is a layer of loose connective tissue and fat lying beneath the dermis - It contains elastic fibres which give the skin its flexibility (This is evident when we lift the fold of skin on the back of dog or cats neck to give injections - It is into the hypodermis into which subcutaneous injections are given |
| Why is hair important to animals? (2 points) | - Maintaining body temperature by providing both insulation and if dark in colour can also absorb light - Protection as provides a barrier to injury and also in some species camoflauge |
| Describe the structure of a hair? (5 points) | - Hair is a keratinised structure which grows from follicles found in the dermis - The hair follicle originates from a peg of epidermal cells that grows down into the underlying dermis, where it forms a hair cone over a piece of dermis called the dermal pailla -The dermal papilla provides the blood and nerve supply for the growing hair - The visible part of the hair, above the skin’s surface, is called the hair shaft - The part of the hair that lies within the follicle is called the hair root |
| What are the three phases of hair growth? | 1. Anagen – rapid growth phase 2. Catagen – transitional phase 3. Telogen – resting phase when no growth takes place |
| What are arrestor pills muscles and how do they benefit the animal? ( 3 points) | - When frightened or cold animals can make their hair stand up due to the presence of a small, smooth muscle called the arrector pili muscle - When the muscle contracts it pulls the hair to an erect position - Hair that stands erect can better trap insulating layers of air than nonerect hair |
| What are the three hair types? | 1. Guard hairs (primary) 2. Wool hairs (secondary) 3. Tactile hairs |
| What is the purpose of guard hairs? (1 point) | Guard hairs give the coat its waterproof quality, water will ‘run off’ the coat unless the animal is submerged in water for a long time. |
| What is the purpose of wool hairs? 1 (point) | These form the innermost, soft undercoat and are more numerous than guard hairs |
| What is the purpose of tactile hairs and where are they found on the body? (2 points) | - Include sinus hairs which are known as whiskers or vibrissae. They are very thick, stiff and have a profuse blood supply - Found on the muzzle, eyelids, lips and face and also on the palmar aspect of the carpus in cats - Act as SLOW- adapting mechoreceptors |
| What are mechanoreceptors? (1 point) | A sense organ that responds to mechanical stimuli |
| What are tylotrich hairs and where are they found on the body? (3 points) | - Found scattered throughout the skin amongst primary and secondary hairs - They are strong and thick and present as a single hair within a large follicle - They act as FAST-acting mechanorecpetors |
| What are compound hair follicles? (3 points) | - Animals with fur often have compound follicles in which multiple hair strands emerge from a single pore, although each strand has its own follicle and bulb - As many as 15 hairs may be associated with one pore - In compound follicles a single, long primary hair, also known as a guard hair, is usually surrounded by shorter secondary hairs, also called wool hairs |
| What are the 3 functions of sebum? | - Forms a waterproof layer on the skin and coat, giving the coat a ‘sheen’ appearance and making the skin more supple - Antiseptic quality which controls bacterial growth on the skin surface - Plays an important role in the production of vitamin D |
| Where does sebum come from in the body? (1 point) | Sebaceous glands (have a single duct which empties into a hair follicle) |
| What is the description and function of the tail gland (2 points) | - Found on the dorsal surface of the base of the tail - Function is individual recognition and identification between individuals |
| What is the description and function of the circumanual gland (3 points) | - Located on the entire circumference of the anus - Drain into specialised sweat glands - Function is that their secretion is to contribute to the overall smell of the dog (again identification purposes) |
| What is the description and function of the anal glands (3 points) | - Lie within the walls of the paired spherical anal sacs on either side just below the anus - Produce a foul-smelling secretion that is expressed during defecation - This coating on the faeces and has the function of serving as a territorial marker |
| What is the description and function of the circumoral glands (3 points) | - Found on the lips of cats ONLY - The secretion has the function of territorial marking - This can be observed when a cat rubs its face on objects such as furniture or owner’s legs |
| What is the description and function of the cerminous glands (2 points) | - Found on the external ear canal - Has the function of secreting cerumen (ear wax) |
| What is the description and function of the meibomian / tarsal glands (2 points) | - Open onto the eyelids - Produce the fatty component of the tear film that has the function of moistening the eye |
| What are the two types of sweat glands and where do they empty? | - Apocrine - empty into hair follicles - Eccrine - empty onto the surface of the skin(in dogs only found in the foot pads and nasal planum |
| What is the function of sweat glands? (1point) | Produce a watery, transparent liquid that helps to cool the body by evaporation |
| What are mammary glands? (2 points) | - Greatly modified, enlarged sweat glands - Secrete milk for nourishment of the young |
| What is the function of the foot pads? (2 points) | - Protect the underlying joints -Act as shock absorbers as the animal walks or runs |
| What is the foot pad also referred to as? | Digital cushion |
| Describe the structure of claws (2 points) | - made from modified keratinised epidermis - Form the horny outer covering of the distal (third) phalanx of each digit |
| How do cats retract their claws? (2 points) | - Retracted by elastic ligaments that run from the 2nd and 3rd phalanx - Contraction of the digital flexor muscle overcomes the pull of these ligaments and the claws are extended |
| What is the quick of a nail? (1 point) | - Avascular dermis which lies at the base of the claw (bleeds if you cut the claws too short) |
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