Integumentary System

Question 1

Thick and thin skin

Answer 1

Thick skin
- Epidermis (thick)
- Dermis
- Appendages: no hair
Thin skin
- Epidermis (thin layer)
- Dermis
- Appendages: hair folicle

Question 2

Functions of integumentary system

Answer 2

• Barrier: physical, chemical and biological agents
• Immunologic: antigen processing to the appropriate effector cells in the lymphatic system
• Homeostasis: body temperature and water loss
• Conveys sensory info about the external environment to the nervous system
• Endocrine: secreting hormones, cytokines and growth factors + converting precursor molecules into hormonally active molecules vitamin D
  • Excretion: sweat

Question 3

Epidermis

Answer 3

• consists of stratified squamous keratinised epithelium
• Several layers (stratum)
• Melanin pigment – colour of skin

Question 4

Dermis

Answer 4

• Blood/lymph vessels, appendages, nerves, sensory nerve endings

Question 5

Hypodermis

Answer 5

• (not considered part of the skin)
• Layer of subcutaneous loose connective tissue
• Presence of adipose tissue

Question 6

5 epidermis layers

Answer 6

• Stratum Corneum; dead keratinized cells
• Stratum Lucidum; (Thick skin only)
• Stratum Granulosum; Cells that are about to die
• Stratum Spinosum; Maturing and slowly dying cells, Keratinocytes produce keratin filaments
• Stratum Basale; Stem cells , capable of differentiation

Question 7

Cells of the epidermis

Answer 7

• keratinocytes (aka stratified squamous keratinized epithelium)
• melanocytes
• langerhans
• merkel
• its in a state of dynamic equilibrium in which exfoliated keratinized cells are constantly replaced by a steady flow of terminally differentiated cells

Question 8

Keratinocytes

Answer 8

• they account for 85% of the cells in the epidermis.
• Originate in the stratum basale.
• Keratinocytes has two essential activities: produce keratins (cytokeratins) + participate in formation of the epidermal water barrier.

Question 9

Life cycle of epidermis

Answer 9

• basal cell layer originate new cells with keratin filaments
• As cells mature, they move upwards.
• In upper part of the spinous layer, the cells begin to produce keratohyalin granules and glycolipid-containing lamellar bodies to form the water barrier
• pH is low enough to digest desmosomal proteins promoting detachment of the most superficial layer of keratinocytes.

Question 10

Epidermal cell differentiation and replacement

Answer 10

- Division of stem cells in the 
stratum basale (1-2 days)
- Newly formed cells move 
upward as they differentiate 
into keratinized cells.
- Keratinized cell are lost by 
exfoliation on skin surface.
- process takes 47 days and is maintained in equilibrium (cell divisions vs cell loss)

Question 11

Psoriasis

Answer 11

• Normal epidermal turnover time takes ∼47 days

- In psoriasis the epidermal turnover time is faster, taking approximately 8 to 10 days.

Question 12

Merkel’s cells

Answer 12

• Detect touch sensations
• Least numerous
• Most abundant in skin where sensory perception is acute (fingertips)
• Have desmosomes and contain keratin filaments
• Nucleus is lobed
• Cytoplasm contains neurosecretory granules
• Closely associated with the expanded terminal bulb of afferent myelinated nerve fibres = merkel’s corpuscle

Question 13

Melanocytes

Answer 13

• Melanocyte to keratinocyte ratio 1:4 to 1:10
• Constant throughout all races
• Skin colour = Amount of melanin present
• Darker skin individuals have slower melanin degradation
• Once produced, melanin granules migrate from melanocytes to keratinocytes

Question 14

Albinism

Answer 14

• inability of melanocytes to synthesise melanin

Question 15

Vitiligo

Answer 15

• degeneration and disappearance of entire melanocyte

Question 16

Melanoma

Answer 16

• Tumour formed by proliferation of melanocytes

- darker colour; Increased number of melanocytes in a small area leads to increased production in melanin in the area

Question 17

Langerhans cells

Answer 17

• Originate from Common lymphoid progenitor (CLP)
• Immunological function: encounter, process and express antigens, antigen presenting cells (APCs), migrates to the lymph node to present the antigen to T-lymphocytes

Question 18

Skin - Dermis

Answer 18

• below epidermis

- It is the connective tissue that supports the epidermis and bind to the hypodermis

Question 19

What does the dermis contain?

Answer 19

• blood/lymph vessels
• appendages
• nerves
• sensory nerve endings

Question 20

Epithelial appendages

Answer 20

• All are outgrowths of the epidermis in one way or another
• All extend into the dermis
• Hair follicle and hair
• Nails
• Glands; sebaceous, eccrine (sweat), apocrine (sweat) glands

Question 21

Hair follicle and hair

Answer 21

• Invagination of the epithelium that extends into the hypodermis
• Associated with a sebaceous gland and smooth muscle = pilosebaceous organ
• Not found in thick skin
• Bulb contains the matrix cells for hair formation; melanocyte stem cells are found in the bulb, shaft and root

Question 22

Hair

Answer 22

• Consists of hard keratin

- Colour is determined by the amount of melanin produced by the melanocytes in the bulb

Question 23

Three layers of hair

Answer 23

- Medulla - central part 
contains large vacuolated cells and only present in thick hairs
- Cortex - peripherally to the 
medulla and contains cuboidal 
cells undergo differentiation 
into keratin-filled cells
- Cuticle - squamous cells that 
form the outermost layer

Question 24

Three types of glands in skin

Answer 24

• Sebaceous
• Eccrine (sweat)
• Apocrine (sweat) glands

Question 25

Eccrine sweat glands

Answer 25

• distributed over the entire body surface
• they are especially numerous in thick skin of hands and feet
• Evaporation of the secreted sweat on the skin surface cools the body
• Simple coiled tubular glands
• Secretory portion is in the deep dermis

Question 26

Apocrine sweat glands

Answer 26

• localized in the axilla, areolae, perineal and perianal area, prepuce, scrotum, mons pubis, and labia majora
• Coiled tubular glands
• Secretory portion is located in dermis or even hypodermis
• Secretory lumen larger than eccrine sweat glands
• Secrete pheromones
• Ducts are straight and lined by stratified cuboidal epithelium has a narrow lumen

Question 27

Sebaceous glands

Answer 27

• discharge their secretion into the follicle, from where it reaches the skin surface
• sebaceous secretion is rich in lipid.
• Simple branched acinar
• Secretory portion is located in the deeper dermis
• Opens into hair follicle
• Secretion is holocrine
• Product is sebum, clear with H&E staining
• Helps prevent the hairs from becoming dry + brittle

Question 28

What do eccrine glands contain?

Answer 28

• Clear cells - abundant glycogen stains well with PAS
• Dark cells - rER and secretory granules are abundant
• Myoepithelial cells - basal aspect of the secretory
  segment
• The duct passes through the dermis and epidermis to
  open onto the surface

Question 29

Nails

Answer 29

• Hard plates of epidermal keratinized cells
• Help with grip, gives protection
• Resting on a nailbed; nail matrix, hyponychium
  • Grow 1mm/week

Question 30

Skin sensorial receptors

Answer 30

• skin is endowed with sensory receptors of various types that are peripheral terminals of sensory nerves
• also well supplied with motor nerve endings to the blood vessels, arrector pili
  muscles, and sweat glands.

Question 31

Free nerve endings

Answer 31

• the endings are “free” in that they lack a connective tissue or Schwann cell investment

Question 32

Merkel’s corpuscle

Answer 32

• a dendritic cell for cutaneous sensation, such as the fingertips

Question 33

What do encapsulated nerve endings include?

Answer 33

• Pacinian corpuscles (pressure changes and vibrations)
• Meissner’s corpuscles (light touch)
• Ruffini’s (stretch and torque) corpuscles
• Krause’s end bulb (cold)