Skin Anatomy and Functions

Skin Colour

• Melanin: A pigment in the epidermis that comes in various shades (yellow, reddish-brown, black). The amount and type of melanin determine skin colour.
• Carotene: A pigment deposited in the stratum corneum and subcutaneous tissue.
• Haemoglobin: Oxygen-rich haemoglobin in dermal blood vessels also contributes to skin tone.

Skin Appendages

• Structures that arise from the epidermis, including cutaneous glands (sweat and sebaceous), hair and hair follicles, and nails.

Cutaneous Glands

• All exocrine glands: They secrete substances onto the surface of the skin.
• Formed from the stratum basale: These glands originate in the deepest layer of the epidermis and push into deeper skin regions.
• Two types of cutaneous glands:
  • Sebaceous glands: Produce sebum, an oily substance that lubricates the skin, keeps it soft and moist, and helps prevent hair from becoming brittle.
  • Sweat glands: Produce sweat, a key component in temperature regulation.

Sebaceous Glands

• Location: Found everywhere on the skin except the palms of the hands and soles of the feet.
• Ducts: Usually empty into hair follicles, but some open directly onto the skin surface.
• Sebum: A complex mix of oily substances and fragmented cells.
• Whitehead: A blocked sebaceous gland duct filled with sebum.
• Blackhead: A whitehead that oxidizes and darkens.

Sweat Glands

• Location: Widely distributed in the skin.
• Two main types:
  • Eccrine glands: More numerous than apocrine glands, found all over the body, essential for temperature regulation. They produce sweat.
  • Apocrine glands: Concentrated in the axillary and genital areas. Larger than eccrine glands, activated by nerves during pain, stress, and sexual arousal. They secrete sweat, fatty acids, and proteins.

Eccrine Glands

• Sweat: Acidic (pH 4 to 6), clear secretion that inhibits bacterial growth. Composed of water, salts (sodium chloride), vitamin C, trace metabolic wastes (ammonia, urea, uric acid), and lactic acid.

Apocrine Glands

• Secretion: Milky or yellowish, odorless initially, but acquires a musky odour when broken down by bacteria on the skin.
• Activation: Start functioning during puberty under the influence of androgens.

Hair

• Structure: A flexible epithelial structure formed by stratum basale cells in the matrix of the hair bulb. The majority of the hair shaft is dead material, primarily protein.
• Two parts:
  • Root: The portion of the hair enclosed within the follicle.
  • Shaft: The visible part of the hair extending from the scalp or skin.

Hair Structure

• Medulla: The central core of the hair.
• Cortex: The bulky outer layer of the hair.
• Cuticle: An outermost single-layer cell covering that provides strength, prevents matting, and is prone to wear and tear.

Hair Follicles

• Inner epidermal sheath: Composed of epithelial tissue and forms the hair.
• Outer dermal sheath: Made of connective tissue and supplies blood vessels to the epidermal portion.
• Arrector pili: Small bands of smooth muscle that connect each side of the hair follicle to the dermis. When they contract, the hair stands on end, causing 'goose bumps'.

Nails

• Structure: A modification of the epidermis, consisting of a free edge, body, and root.
• Nail folds: Skin folds that overlap the borders of the nail.

Skin Colour

• Melanin is the pigment that gives the skin its colour.
• Melanin comes in three forms: yellow, reddish-brown, or black.
• Carotene is another pigment found in the skin, deposited in the stratum corneum and subcutaneous tissue.
• Oxygen-rich haemoglobin in dermal blood vessels contributes to the skin's colour.

Skin Appendages

• Skin appendages are structures that arise from the epidermis.
• They include cutaneous glands, hair and hair follicles, and nails.

Cutaneous Glands

• They are all exocrine glands, meaning they secrete substances onto the surface of the skin.
• They're formed by the cells of the stratum basale and push into deeper skin regions, residing mostly in the dermis.
• There are two types: sebaceous glands and sweat glands.

Sebaceous Glands

• Found everywhere except on the palms of the hands and soles of the feet.
• Their ducts usually empty into a hair follicle, but some open directly onto the skin surface.
• They produce sebum, which is a mixture of oily substances and fragmented cells.
• Sebum lubricates the skin, keeps it soft and moist, prevents hair from becoming brittle, and kills bacteria.
• Blockage of the duct by sebum can lead to whiteheads or blackheads.

Sweat Glands

• Widely distributed in the skin.
• There are two types: eccrine glands and apocrine glands.

Eccrine Glands

• More numerous than apocrine glands.
• Found all over the body.
• Important for heat regulation.
• Produce sweat.
• Sweat is acidic (pH 4 to 6) and inhibits bacterial growth.
• Sweat is composed of water, salts (especially sodium chloride), vitamin C, traces of metabolic waste (ammonia, urea, and uric acid), and lactic acid.

Apocrine Glands

• Primarily found in the axillary and genital areas.
• Larger than eccrine glands.
• Not involved in heat regulation.
• Activated by nerve fibres during pain, stress, and sexual foreplay.
• Their ducts empty onto hair follicles.
• They secrete sweat, fatty acids, and proteins.
• Apocrine sweat has a milky or yellowish colour and is odorless initially. It acquires a musky smell when bacteria on the skin use its proteins and fats.
• These glands begin functioning at puberty under the influence of androgens.

Hair

• Hair is a flexible epithelial structure made by cells in the matrix of the hair bulb at the base of the follicle.
• Most of the hair shaft is made of dead protein.

Hair Structure

• Hair is divided into two parts: the root (enclosed within the follicle) and the shaft (projecting from the skin surface).
• Each hair consists of a medulla, a cortex layer, and a cuticle (single layer of overlapping cells).

Cuticle

• The cuticle helps keep the hairs apart and prevent matting.
• It strengthens the inner hair layers, keeping them compact.
• It is exposed to wear and tear.

Hair Follicles

• Surrounded by an inner epidermal sheath made of epithelial tissue, which forms the hair.
• Also surrounded by an outer dermal sheath, comprised of dermal connective tissue, that supplies blood vessels to the epidermal portion and reinforces it.

Arrector Pili

• Small bands of smooth muscle connect each side of the hair follicle to dermal tissue.
• Contraction causes the hair to stand upright, leading to "goose bumps".

Nails

• A modification of the epidermis.
• Consist of a free edge, a body, and a root.
• The borders of the nail overlap with skin folds called nail folds.

This quiz explores the key components of skin anatomy including skin color, appendages, and cutaneous glands. Learn about the roles of melanin, carotene, and haemoglobin in determining skin tone, as well as the functions of sebaceous and sweat glands. Test your knowledge on the intricacies of human skin.