Integumentary System Colville & Bassert Chapter 6: p122-141 Mammals Chapter 17: p344-349 Birds

Skin Functions Protects deeper tissues from: Aids in: Makes Vitamin D Mechanical damage Chemical damage Damage from micro-organisms Damage from heat and Ultra violet radiation Drying out Aids in: Heat regulation Excretion (of metabolic wastes) Makes Vitamin D Storage organ – whales & blubber (Fat = insulation) Sexual attraction – scent, colour

Skin Structure Three layers: Epidermis – outer layer Stratified squamous epithelium Often keratinized (Hardened by keratin) Dermis – middle layer Dense irregular connective tissue Hypodermis, Subcutaneous layer – innermost layer Anchors the skin to underlying organs Mainly adipose tissue

Skin Structure Outside the body Epidermis Dermis Hypodermis Deeper tissues

Epidermis – 3 layers Made of keratinised stratified squamous epithelium Outer waterproof layer Thickness varies between animals & parts of body Keratinocytes thin layer along basement membrane continually dividing and push older layers up Inner layer (next to the dermis) Stratum basale Keratin deposits increase & without nutrients cells rarely divide & cytosol, nuclei and organelles gradually disappear from cells. Cells begin to die Middle layer – 3 sublayers can be present Up to ¾ of the total thickness of epidermis – lifeless sheets of keratin Dead cells on surface separate and rub off These are replaced from below Outer layer Stratum corneum Keratinocytes located along basement membrane – plenty of blood supply from dermis) secrete keratin (tough, fibrous, waterproof protein)

Specialised cells found in the epidermis Keratinocytes (covered above) Produce keratin Melanocytes Produce melanin Langerhans cells epidermal macrophages Engulf foreign material Merkel cells (Mechanical receptors) Surround nerve endings at the junction with the dermis to form Merkel discs

Skin Structure: Epidermis/Dermis

Dermis – 2 layers Papillary Layer - next to epidermis, is loose connective tissue, contains: Pain receptors Capillaries Projections called dermal papillae Reticular layer (dense connective tissue) contains: Blood vessels Glands Nerves Fibres in both layers provide strength, support, cushioning and flexibility

Hypodermis – Subcutaneous layer Layer under the dermis Rich in adipose tissue (fat), blood & lymph vessels, touch receptors Attaches the dermis to underlying structures Allows skin to move freely over the underlying structures Insulation Shock absorption

Name the structures and layers

Associated structures of the skin Keratin structures Hair/ fur/ wool/ spines Hooves, claws, pads Horny scales, snake skin, bird’s legs, rat’s tails Horns, Antlers Bills or beaks Feathers

Hair Most hairy skin has relatively thin epidermis Epidermis of ‘hairy skin’ is covered in scale-like folds Hair comes from under the scales and points away from the opening Dogs have 3 hairs emerging from each follicle Hair – provides warmth and protection. Eyelashes and nose hairs have a protective function Hair pigment is produced by melanocytes at the base of the hair follicle. Grey or white hair results from a decrease in melanin production.

Dogs have 3 hairs emerging from each follicle Hair – provides warmth and protection. Eyelashes and nose hairs have a protective function Hair pigment is produced by melanocytes at the base of the hair follicle. Grey or white hair results from a decrease in melanin production.

Hair follicle Extends down into dermis layer and the deep end is a bulb. As new hair cells are produced by the base, the older part of the hair is pushed upward, and fused cells die off. Each follicle is supplied with sebum from a sebaceous (oil) gland, this often: Softens and lubricates the skin. Kills bacteria

Appendages of the Skin - Hair Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Hair follicle bulb

Skin Structure Figure 4.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cortex surrounds medulla Cuticle on outside of cortex Hair Anatomy Central medulla Cortex surrounds medulla Cuticle on outside of cortex Most heavily keratinized Figure 4.7b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Associated Hair Structures Hair follicle Dermal & epidermal sheath surrounds hair root Arrector pilli Smooth muscles –pulls hair (fur) erect Sebaceous gland Lubricates hair Sweat gland Secretes waste products & moisture

Guard Hairs longer forming the top coat these have a smooth muscle which allow the hairs to stand up

shorter, softer, many hairs per follicle providing a dense look Wool Hairs shorter, softer, many hairs per follicle providing a dense look

Whiskers, these are specialised and aid direction. Vibrissae Whiskers, these are specialised and aid direction.

Nails, Claws & Hooves Scale like modification of the epidermis. Grows from the bottom where the white crescent is a thickened area of skin.

Pads Modifications of the skin on the feet to provide protection for those areas that come in contact with the ground. They are covered by a hairless, densely keratinized epidermis area. Pads are mainly made up from thickened hypodermis containing many collagenous and elastic fibres interspersed with adipose tissue. Both cats and dogs have sweat glands on nose and pads.

Horns are paired and protrude from the front of the skull Horns & Antlers Horns are paired and protrude from the front of the skull They are unbranched and epidermal in origin Made up of a bony core and a keratinized sheath. Mature horns are hollow and composed of keratin In most animals they grow throughout life – not shed Antlers are also paired structures that protrude from the front They are branched and dermal in origin Primarily in males They are shed annually; American proghorn sheds its horns anually Antlers grow from pedicels, which are bony supporting structures that develop in the lateral region of the frontal bones. Secretions from the pituitary initiate the growth in April or May. In the northern hemisphere increasing day length also plays a role. Early in their development, antlers have high water and protein content. As they grow, antlers are covered with skin and soft hair called velvet, which carries blood vessels and nerves. As antlers near the end of the growing process, spongy bone in their outer edges is replaced by compact bone, while their centers become filled with coarse, spongy, lamellar bone and marrow spaces. The velvet dies and is removed in part by the animals rubbing and thrashing their antlers against vegetation. The antlers also are stained during this action, giving them the brown, polished, wooden look.

Other types of horns Giraffe horns are paired, short, unbranched, permanent, bony processes that are covered with skin and hair. They differ from other horns in that they do not project from the frontal bones, but lie over the sutures between the frontal and parietal bones. Giraffe horns begin as cartilaginous structures in the fetus and may not fuse to the cranium until the animal is 4 years old. Horns are present in both sexes of giraffes and even on newborns.

Other types of horns Rhino horns have no core or sheath. They are made up of multitude of epidermal cells and bundles of dermal papillae, Cells from each papilla form a horny fibre These are held together by the mass of epidermal cells, are not true hairs. Rhino horns grow from dermal papillae which extend up into the horn. The rhino horn is situated over the nasal bones. In species that have two horns, the second horn lies over the frontal bones.

Skin Colouration Colour is due to pigments that either reflect or refract light. Often found within the epidermis layer, feathers or hair. Cuttlefish have special cells called chromatophores. Some animals chromatophores produce a range of different colours

http://www. youtube. com/watch http://www.youtube.com/watch?feature=player_detailpage&v=dF-jHp-5XfU&list=PL78925FA46CFDFD45 Pigment cells have sphincter muscles and can squeeze the pigment up into disc near the surface. When muscles relax the colour runs down into the cell Cuttlefish with this ability can generate a wide range of colors and many interesting patterns. By perceiving the color of a backdrop and constricting the right combination of chromatophores, the animal can blend in with all sorts of surroundings. Cuttlefish may also use this ability to communicate with each other.

Colour Colour is used for: Concealment In most cases, either changing amounts of daylight or shifts in temperature trigger a hormonal reaction in the animal that causes it to produce different biochromes.

Where is the frog?

A leafy sea dragon, photographed off the coast of Australia A leafy sea dragon, photographed off the coast of Australia. Leafy sea dragons have developed flowing appendages and vivid coloration that lets them blend in with the undersea plant life in their environment. Leafy Sea Dragon flowing appendages and vivid coloration that lets them blend in with the undersea plant life

Communication Colour often serves as social communication, help members of the same species identify individuals, their gender, reproductive status, social rank etc.. bright yellow color of the male American goldfinch. Many male bird's, like the northern cardinal, www.nhptv.org/NatureWorks/nwep3a.htm

Often changes colour Depending on environmental and social cues - temperature Not always to blend in with the environment the chameleon, alters its skin color using a similar mechanism, but not usually for camouflaging purposes. Chameleons tend to change their skin color when their mood changes, not when they move into different surroundings. http://animals.howstuffworks.com/animal-facts/animal-camouflage2.htm

Melanin Pigment (melanin) is produced by Melanocytes found in deepest epidermal layers (only type of chromoatophore in mammals) Cells have long projections from which melanin is released and absorbed by keratinocytes. Colour is yellow to brown to black Most melanocytes are in the innermost layer of the epidermis The amount of melanin depends on the inheritance of the animal and the exposure to sunlight

Structures of the Skin - Glands Located in dermis but really invaginations of epithelium from epidermis Sebaceous glands Produce oil Lubricant for skin Kills bacteria Most with ducts that empty into hair follicles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structures of the Skin - Glands Sweat glands Widely distributed in skin Two types Eccrine Open via duct to pore on skin surface Apocrine Ducts empty into hair follicles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Sweat and Its Function Composition Function Mostly water Some metabolic waste Fatty acids and proteins (apocrine only) Function Helps dissipate excess heat Excretes waste products Acidic nature inhibits bacteria growth Odour is from associated bacteria Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Circumoral glands: in lips of cats – secretion to mark territory. Other Skin Glands Circumoral glands: in lips of cats – secretion to mark territory. Tail glands: gland found on the dorsal side of the tail in some carnivores Circumanal glands: in the skin of dogs Glands of the anal sacs: scent glands- secreted after faeces Mammary glands: covered in reproductive system