The skin, which is otherwise referred to as the cutaneous membrane or the integument, is a pliable (can stretch) yet adaptable external body covering. It is a dry membrane (when intact) that acts as a barrier for water – it keeps water and important molecules within the body, whilst keeping water from outside sources out of it.
Functions of the Integument
The integument acts as protection against:
Mechanical Damage
- Through Keratin, which is a protein, the skin offers protection from mechanical damage which includes direct hits;
- Pressure receptors act as sensors that sense extra pressure on the skin (eg. a patient who is immobile cannot automatically retract when pressure receptors sense prolonged pressure on the skin, and this results in bed sores);
Chemical Damage
- Impermeability to chemical substances that can cause damage to deeper tissues is caused by the keratinized cells within the integument;
- Water-diluted chemicals trigger pain receptors when in contact with the skin;
Bacterial Damage
- In normal circumstances, skin secretions, which are acidic, inhibit bacteria;
- Intact skin provides an ‘unbroken surface‘;
- Phagocytes within the dermis ingest foreign pathogens (fights off bacteria), stopping them from damaging structures within the integument;
UV Radiation
- In normal circumstances, Melanin, which is produced by melanocytes, offers protection from UV radiation, but if amount of UV damage is higher than the produced amount of Melanin, damage is caused;
Thermal Damage
- Changes within the environment trigger a response by heat or cold pain receptors to avoid thermal damage to be caused to the skin
Desiccation
- Desiccation (extreme dryness of the skin) is prevented through Keratin and Glycolipids, both of which are hydrophobic i.e. waterproof
Heat Loss or Heat Retention
- In the case of heat retention, sweat glands activate, causing blood to rush to the skin capillary beds so heat is lost. The process occurs in reverse in the case of heat loss;
Urea and Uric Acid
- Sweat glands secrete urea and uric acid, both of which are broken down protein, through perspiration;
Modified Cholesterol Molecules
- Vitamin D is important for the body’s wellbeing. Sunlight causes modified cholesterol molecules to convert to Vitamin D;
Structure of the Integument
The EPIDERMIS contains no blood vessels. It gets its needed nutrients and blood supply from the dermis.
The DERMIS contains larger vasculature structures within its lower part.
The HYPODERMIS, which is mostly adipose tissue, connects the skin to underlying organs, acts as a shock absorber, and provides insulation of the deeper tissues from extreme thermal changes coming from the body’s outside environment.
Histology
The Epidermis consists of the following layers:
- Stratum Corneum – 20 -30 layers of anucleated cells thick, impregnated with Keratin; allows top layer loss and is subject to wear and tear; cells are replaced by those produced through division of the deeper Stratum Basale cells.
- Stratum Lucidum – flatter cells that start to fill up with Keratin, which end up dying and forming the clear Stratum Lucidum in the process.
- Stratum Granulosum & Stratum Spinosum – daughter cells of the Stratum Basale push themselves upwards towards the skin surface, i.e. within these two layers.
- Stratum Basale – deepest layer of the epidermis; contain Keratinocytes (which undergo continuous cell division), Melanocytes (containing Melanin) and Tactile cells.
The Dermis consists of the following layers:
- Papillary Layer – the upper dermal region which is made up of areolar connective tissue; contains dermal papillae (finger-like projections) which indent the epidermis above it.
- Dermal Papillae – contain Capillary Loops which provide nutrients to the epidermis, Pain Receptors which are free nerve endings, and Touch Receptors (a.k.a. Meissner’s Corpuscles).
- Reticular Layer – deepest, thickest layer of the skin which contains irregularly arranged dense fibrous connective tissue, sweat and oil glands, Phagocytes, blood vessels (at the base, just above the Hypodermis), and Pacinian Corpuscles (deep pressure receptors which react to different pressures on the skin).
Skin Colour
The major contributor to the colour of the skin is Melanin – to be exact, the amount and kind of Melanin (yellow, reddish, brown or black) found within the Epidermis. Additionally, Melanin protects the skin from UV radiation.
Other contributors to skin colour include Carotene (deposited in the Stratum Corneum and subcutaneous tissue) and Oxygen-rich Haemoglobin within the blood vessels in the Dermis (contribute to pinkish/reddish colour in the skin).
Skin Appendages
Skin appendages are structures associated with the skin that carry out particular functions such as sensations, heat loss, contractility and lubrication. These structures, which include cutaneous glands, hair and hair follicles, and nails, rise from the epidermis but originate from the dermis.
Cutaneous Glands:
- are all exocrine glands
- are formed by cells within the stratum basale, pushing into deeper skin regions, but mostly reside within the dermis
- can be divided into 2 types: Sebaceous Glands (related to hair and hair follicles that exert sebum) and Sweat Glands
SEBACEOUS GLANDS
- are found everywhere on the skin except on the palms of the hands and the soles of the feet
- produce sebum – a combination of oily substances and fragmented cells which lubricates the skin, keeping it soft and moist, prevents hair from becoming brittle and also kills bacteria through chemicals contained within (note: blocked sebaceous gland duct results in a whitehead; oxidised and dried accumulated material forms into a blackhead)
- usually empty into hair follicles, but at times may open directly onto the surface of the skin
SWEAT GLANDS
- are found everywhere within the skin
- include 2 types: Eccrine Glands (widely spread throughout the body – produce sweat and contribute towards the body’s heat-regulating system) and Apocrine Glands (larger than eccrine glands – found in the axillary and genital area – are activated during puberty through androgen hormones – produce odor)
- sweat produced is a clear acidic (pH4-6) secretion that inhibits bacterial growth – sweat is a combination of water, salts (especially sodium chloride), vitamin C, traces of metabolic wastes (ammonia urea and uric acid) and lactic acid (causes a decrease in BP through excessive sweating)
Hair and Nails
Hair:
- is a flexible epithelial structure
- is formed by the stratum basale epithelial cells within the hair bulb matrix
- shaft is made of dead material, almost entirely protein
- structure includes the ROOT (the part enclosed in the follicle) and the SHAFT (the part projecting out of the scalp or skin surface)
- consists of the medulla, cortex layer, and cuticle (keeps each hair apart from another, provides strength to the inner hair layers to keep them compacted, but is exposed to wear and tear)
- include the Arrector Pili, which are small bands of smooth muscle cells that connect each side of the hair follicle to the dermal tissue – when these muscles contract, hair is pulled upright, resulting in goose bumps on the skin surface
Nails:
- can be seen as a modification of the epidermis
- have a free edge, a body and a root
- have borders which are overlapped by skin folds known as nail folds
- have cuticles which aim to offer protection from pathogens (removal of the cuticle exposes the skin to pathogens, which makes the skin susceptible to fungal infections
NOTE: Creams don’t penetrate into the nail bed easily, which is why the best treatment for nail fungus is oral therapy.
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Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing.
Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.
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