Integumentary System & Skin

What does the integumentary system consist of?

Skin, hair, nails, sweat & sebaceous glands, & sensory receptors

State 6 functions of the integumentary system

1. Regulation of body temperature

2. Blood storage

3. Protection from external environment

4. Excretion & absorption of substances

5. Vitamin D synthesis (in the skin)

6. Detection of cutaneous sensations

What are the two layers of skin?

• Epidermis: outermost, thinner layer composed of epithelial cells

• Dermis: deeper, thicker layer composed of dense connective tissue

Are the epidermis & dermis vascularised? Explain

• Only the dermis is vascularised; the epidermis is not

  • The dermis & hypodermis develop from the mesoderm along with blood vessels, but the epidermis is derived from ectoderm

• The epidermis receives its nutrients via diffusion through interstitial fluid from vessels in the dermis

What is the hypodermis (superficial fascia)?

Subcutaneous tissue deep to the skin

Does the epidermis have a high or low degree of functional capacity?

Low degree of functional capacity

• The epidermis does have pores for sweat glands, however;

• Many functional organs for sweat glands are located in the dermal layer, not the epidermal layer

Label the following diagram of an embryo in relation to the integumentary system

List the 5 layers of epidermis from superficial → deep

1. Stratum corneum (h0rny layer) - thickest of epidermal layers, comprised of dead cells

2. Stratum lucidum (clear layer)

3. Stratum granulosum (granular layer) - 1-5 layers of flattened cells

4. Stratum spinosum (prickly layer) - same thickness as stratum granulosum, several layers of keratinocytes unified by desmosomes

5. Stratum basale (basal layer) - 1 layer of newly formed stem cells which push their way upwards superiorly

Where are melanocytes produced & how do they contribute to skin pigmentation?

• Produced in the stratum basale (deepest layer) of the epidermis

• Produce melanin pigment → transferred to overlying keratinocytes

• Skin pigmentation depends on the amount of pigment produced by melanocytes, not the number of melanocytes (same for all people

How does the structure of skin vary over the body?

Variability in the epidermal thickness

• Dermis is mainly static

• Basal layer of epidermal tissue has cells which push their way upward → epidermis is a changing tissue

What are the 2 types of epidermis, in terms of epidermal thickness?

• Thin skin (hairy): absent stratum lucidum (2nd most superficial layer) + other strata are thinner

• Thick skin (hairless): covers area subject to abrasions + thicker stratum corneum (most superficial layer) in response to greater mechanical stress

Describe the physical & mechanical properties of the dermis

Physical properties:

• Composed of dense irregular connective tissue (collagen + elastic fibres)

• Much thicker than epidermis

• Rich supply of nerve fibres, blood vessels & lymphatic vessels

Mechanical properties:

• High tensile strength

• Easily stretches & recoils

State the 2 layers of the dermis

1. Papillary

2. Reticular

Label the following diagram

Describe the papillary layer of the dermis

• More superficial

• Makes up ~ 1/5 of the thickness of dermis

• Contains blood vessels (capillaries) & sensory receptors

• Forms dermal ridges in regions of thick skin (→ fingerprints & footprints)

  • In place by the 4th month of embryonic development

Describe the reticular layer of the dermis

• Deepest layer of dermis, attached to the subcutaneous tissue/hypodermis/superficial fascia

• Majority of the thickness of the dermis

• Consists of collagen fibres running in specific planes → cleavage/tension lines

• Contains blood vessels, nerves, hair follicles, sebaceous glands & sweat glands

How is blood transmitted to the skin?

Via subcutaneous tissue; projections of blood vessels are sent into the dermis

What are cleavage/tension lines?

Separations/less dense regions of collagen fibre bundles in the reticular dermis due to natural tension in the region

Describe the appearance of tension lines in the skin of the:

• Head & limbs

• Neck & trunk

• Head & limbs - longitudinal tension lines

• Neck & trunk - circular tension lines

How are tension lines clinically significant for surgeons?

• Incisions parallel to tension lines gape less → reduce scarring

• Incisions perpendicular to tension lines → more gaping → more bleeding + ^ scarring → harder to heal

What are septa?

Fibrous strands which bind subcutaneous tissue to underlying dense connective tissue, especially at the palms, soles & scalp

What regions of the body contain muscle in their subcutaneous tissue?

• Face

• Neck

• Palm

• Scrotum

Describe the structure of hair

Dead, keratinised cells organised into 3 concentric layers, bound together by extracellular proteins

• Medulla (deepest): 2-3 rows of irregularly shaped cells

• Middle cortex: major part of shaft of hair, consisting of elongated cells

• Cuticle (most superficial): just deep to the epithelial root shaft, consisting of a single layer of thin, flat cells

Hair follicle/root sheath: a continuation of the epidermis, surrounding the 3 layers of keratinized cells

Label the following diagram

What are nails made of?

Tightly packed, hard, dead keratinized epidermal cells

• Nail root + lunule + nail plate

What is the nail bed?

Skin beneath the nail plate

What is the subungual dermis?

Thick, highly vascular underlay of the nail bed

What is the lunule?

The half-moon crescent @ the inferior aspect of the nail body

What is the free-edge of a nail?

The other white edge at the surface (the ‘fingernail’)

Label the following diagram

What is the follicle of a hair?

The downward continuation of the epidermis which surrounds the hair root

What are arrector pili?

Muscles which pull the hair shaft perpendicular to the skin surface (goose bumps)

Label the following diagram

What are sebaceous glands?

Glands which secrete oily substances (sebum) & are connected to hair follicles

What are sweat glands?

Exocrine glands which release sweat into hair follicles or the skin surface via pores

What are ceruminous glands?

Modified sweat glands which produce ear wax in the ear canal

How do somatic sensations arise in the skin?

From the stimulation of sensory receptors in the dermis of the skin

What are the 4 modalities of cutaneous nerves & sensory receptors?

• Tactile: touch, pressure, vibration, itch, tickle

• Thermal: warm, hot, cold

• Pain

• Proprioceptive: sensory organs located mainly in muscle & joints

What receptors are located superficially vs deep in the skin?

• Superficially: discs which mediate tactile modalities

  • fine touch, pressure, & vibration

• Deep: crude touch & stretching of the skin

• Deepest: pressure & fast vibration

Describe the embryological development of dermatomes

• Relationship b/w nerves & skin is established during development

• Tissue which gives rise to muscle, bone & dermis are organised segmentally into somites

• Somites → limb buds → drag segmental innervation w/ them during growth

Describe the difference b/w somatic & visceral pain

• Somatic pain: pain from the skin

  • Sharp & well-localised

• Visceral pain: dull & poorly localised

  • Accompanied by referred pain

  • Referred to somatic area by the same dermatome

What is referred pain?

When you feel pain in one area of the body, but the actual source of the pain is located elsewhere

Provide an example of referred pain?

Radiation of chest pain down the arms during a heart attack b/c of these somatic areas supplied by the same dermatome which supplies the pericardium of the heart

How are stretch marks formed?

• Overstretching of skin → disruption of lateral bonding b/w collagen fibres in the dermis + rupturing of small blood vessels

• Rupturing of small blood vessels → leaked blood in the dermal layer → reddish streaks → turn silver when (poorly vascularised) scar tissue appears

  • Scar tissue replaces where collagen fibres were located @ the epidermal layer

Why are burns life-threatening?

One of the roles of the skin is to maintain hydration, so severe damage to the skin → catastrophic loss of body fluids → dehydration

How can the % of fluid loss when a person is burned be determined?

By evaluating the % of the body surface burned

What are first, second & third degree burns?

• 1st: injured epidermis only

• 2nd: injured epidermis & 1st layer of dermis

• 3rd: injury to full thickness of skin