BIOL122 the integumentary system

What are the four key functions of the skin?

1. Protecting: Against injury, infection, and UV radiation.

2. Regulating: Temperature, water balance, and waste excretion.

3. Producing: Vitamin D and nitric oxide.

4. Sensing: Touch, pressure, vibration, pain, heat, cold, and light.

What type of epithelium makes up the epidermis?

Stratified squamous epithelium.

Where is "thick skin" located, and what unique epidermal layer does it contain?

It is located on the palms of the hands and soles of the feet. It uniquely contains the Stratum Lucidum.

Name the four major cell types found in the epidermis and their rough abundance/function.

Keratinocytes (90%): Form the main structural barrier; undergo turnover.

Melanocytes (8%): Produce pigment (melanin).

Langerhans Cells: Recognise and process microbial invaders (immune function).

Merkel Cells: Attached to sensory nerve endings to detect touch.

Briefly describe the process of keratinisation and how long epidermal turnover takes.

• Epidermal keratinocytes are produced by stem cells in the deepest layer (stratum basale) and migrate upward, pushing older cells up.

• As they move up, upper layers secrete lamellar granules to form a water-barrier membrane.

• The cells eventually become dead, dry, scale-like cells at the surface.

• The entire turnover takes about 4 weeks.

How do melanocytes protect surrounding skin cells, and what is their typical ratio to basal cells?

• Melanocytes transfer pigment-containing packages called melanosomes to surrounding keratinocytes via their dendrites.

• The ratio of melanocytes to basal cells ranges from 1:4 to 1:20.

What type of tissue makes up the dermis, what are its main fibres, and what are its primary cell types?

• Connective tissue containing mostly collagen fibres (which limit flexibility/provide strength) and

• Elastic fibres (which provide flexibility).

• Main cell types are fibroblasts, alongside mast cells, phagocytes, blood vessels, and adipocytes.

What are the structural benefits of dermal papillae (ridges)?

They create a wavy boundary that provides a larger surface area for attachment between the epidermis and the dermis, preventing them from separating.

Describe the Papillary Dermis (thickness, tissue type, and key structures).

Thickness: Comprises about 20% of the dermis.

Tissue Type: Areolar connective tissue with fine collagen and elastic fibers.

Key Structures: Contains capillary loops, free nerve endings, and Meissner corpuscles (receptors sensitive to light touch).

Describe the Reticular Dermis (thickness, tissue type, and key structures).

Thickness: Comprises about 85% (approximate remaining bulk) of the dermis.

Tissue Type: Irregular dense connective tissue with thicker collagen and elastin fibers providing strength and flexibility.

Key Structures: Contains epidermal appendages (hair follicles, sweat and sebaceous glands) and Pacinian corpuscles (receptors that detect vibration and pressure).

From outer to inner, what are the three structural layers of a hair shaft?

1. Cuticle: Outer protective layer.

2. Cortex: Main bulk containing pigment.

3. Medulla: The soft inner core.

What are the functions of the hair bulge and the dermal papilla at the base of a hair follicle?

Hair Bulge: Contains the stem cell population for hair regeneration.

Dermal Papilla: Contains specialized mesenchymal cells, blood vessels, and melanocytes to support and pigment growing hair.

What type of gland is a sebaceous gland, and what is its function?

• Simple branched acinar gland typically connected to hair follicles.

• Secretes oily sebum to moisturise and protect skin/hair and provides antibacterial properties.

• Too much sebum/inflammation causes acne.

Differentiate between Eccrine and Apocrine sweat glands.

Eccrine Glands: Secreted directly onto the body surface; produce watery sweat (water, ions, urea, glucose, etc.) to regulate body temperature. Can produce up to 600ml per day.

Apocrine Glands: Secreted into hair follicle ducts; produce a 'thick' sweat that causes body odour. (Note: They actually use merocrine secretion methods despite the name) .

What is a nail anatomically made of, and where does it grow from?

• A nail consists of dead, tightly compressed cells packed with keratin.

• It grows out of the nail root, which is an epidermal fold hidden beneath the surface of the skin.