Unit 8 - Skin

Question 1

what are the 3 layers of the skin?

Answer 1

1. epidermis
2. dermis
3. hypodermis

Question 2

basic structure and function of the epidermis

Answer 2

• Epithelial layer
• Composed of stratified squamous epithelium
• Avascular
• Average thickness = 0.1 mm
• Thick skin average = 1-2 mm

• Primary barrier to:

• Mechanical damage
• Desiccation
• Microbial invasion

Question 3

basic structure and function of the hypodermis

Answer 3

• Aka superficial fascia or subcutaneous layer
• Loose, irregular connective tissue with varying proportions of fat.
• Fatty layer- acts as shock absorber.
• It anchors skin with the underlying structures

Question 4

what are the 5 layers of the epidermis (from deepest > superficial)

Answer 4

1. Stratum basale /germinativum
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum (present only in thick skin)
5. Stratum corneum

Come Lets Get Sunburnt

Question 5

Structure and function of Stratum basale

Answer 5

Structure: Composed of single layer of cuboidal or columnar stem cells

Function:
• Germinating layer from which all the keratinocytes are formed.
• capable of continual cell division and production of all the keratinocytes in the epidermis.
• Also contains melanocytes & merkel discs

Question 6

Structure and function of Stratum spinosum

Answer 6

Structure:
• Contains 8 – 10 rows of many-sided cells that fit closely together.
• The keratinocytes have spine-like projections which holds the cells together.

Function:
• These cells obtain melanin from long processes of melanocytes.
• Langerhans’s cells are scattered among the keratinocytes

Question 7

Structure and function of Stratum granulosum

Answer 7

Structure:
• Composed of 3 – 5 rows of flattened keratinocytes.

Function:
• Cells contain darkly stained granules of keratohyalin, a precursor of keratin.
• Nuclei are in various stages of degeneration
• Cells can no longer carry on vital metabolic reactions, and they die.

Question 8

Structure and function of Stratum lucidum

Answer 8

• Normally only found in the thick skin of the palms and soles

Structure:
• Composed of 3 – 5 rows of clear, flat, dead keratinocytes

Function:
Contains droplets of an intermediate substance that will become Keratin.

Question 9

Structure and function of Stratum corneum

Answer 9

Structure:
• Consists of 25 – 30 rows of flat, dead keratinocytes filled with keratin.

Function:
• Cells are continually being shed and replaced by cells from the deeper layers.
• Serves as an effective barrier against light, heat, bacteria, and chemicals.

Question 10

what are the 4 types of cells found in the epidermis?

Answer 10

1. Keratinocytes
2. Melanocytes
3. Langerhans’s cells
4. Merkel cells

Question 11

Function of keratinocytes

Answer 11

• Comprise 90% of cells in epidermis
• Produce keratin - fibrous, waterproof protein that gives the epidermis its protective properties, strength, and toughness
• Keratinocytes divide and increase in number and keep moving to the superficial layers

Question 12

Function of melanocytes

Answer 12

• Make up about 8% of cells
• Produce melanin which they transfer to keratinocytes
• Melanin absorbs UV radiation and contributes to skin colour

Question 13

function of Langerhans’s cells/dendritic cells

Answer 13

• Arise from bone marrow and migrate to epidermis.
• Involved in the immune response
- Ingest foreign substances
- Present antigens and stimulate production of T cells.
• Damaged by UV radiation

Question 14

Function of Merkel cells/tactile cells

Answer 14

• Located in the deepest layers of epidermis
• Sensory reception for touch
• Connected to sensory nerve fibres which carries message to brain

Question 15

what gives rise to fingerprints?

Answer 15

Friction ridges in the palms and soles along with sweat

Question 16

structure of dermis

Answer 16

• Composed of connective tissue containing thick bundles of collagen and elastin fibres
• The blood supply to the skin is all in the dermis.
• The nerve supply serves the dermis and epidermis.
• Contains glands and hair follicles.

Question 17

what structures are located in the dermis?

Answer 17

• abundant nerve fibres
• blood vessels
• lymphatic vessels
• Hair follicles
• Sweat glands
• Sebaceous glands

Question 18

what are the 2 layers of the dermis

Answer 18

1. Papillary region

2. Reticular region

Question 19

describe the papillary region of the dermis

Answer 19

• Outer portion of the dermis
• Approx. 1/5th of the total thickness of the dermis
• Composed of areolar connective tissue with interlacing collagen and elastic fibres
• Surface is covered in papilla/ dermal papilla which indent the epidermis above

Question 20

describe the reticular region of the dermis

Answer 20

• Inner portion of the dermis

* Coarse, dense, irregular connective tissue with interlacing bundles of collagen and elastin.

Question 21

what are the 4 cell types of the dermis?

Answer 21

1. Fibroblasts
2. Mast cells
3. Macrophages
4. Adipocytes

Question 22

describe fibroblasts

Answer 22

Undifferentiated cells in connective tissue that give rise to various precursor cells such as collagenoblasts.

Question 23

describe mast cells

Answer 23

• Found in areolar connective tissue

* Release histamine, which causes dilation of small blood vessels during inflammation.

Question 24

describe macrophages

Answer 24

• Derived from monocytes.

* They phagocytose foreign materials.

Question 25

describe adipocytes

Answer 25

Fat cells that contain a large fat vacuole which potentially can contain triglycerides.

Question 26

describe the role of sebaceous glands

Answer 26

* Secrete oily substance called sebum on to skin and hair. * Most open into hair follicles * Arrector pili muscle contractions force sebum out of the hair follicles to the skin. * Sebum aids in heat retention, softens skin and makes hair supple. * Fatty acids in sebum make skin slightly acidic which controls bacterial growth.

Question 27

what are the 2 types of Sudoriferous glands?

Answer 27

* Eccrine and Apocrine * Each type consists of a coiled tube that straightens and opens out on the surface of the skin via a duct and a pore. * There are about 3 million sweat glands per person.

Question 28

describe Eccrine (Merocrine) glands

Answer 28

* Most numerous type * abundant on the palms, soles of the feet and forehead * Its secretion is clear sweat containing water, NaCl, urea, lactic acid and breakdown products of food substances such as garlic. * Function is to cool the body by evaporation of the sweat.

Question 29

describe Apocrine glands

Answer 29

* Approximately 2000 glands- located in axillary, anal, genital areas. * Become functional only at puberty. * Their sweat is thicker due to presence of fatty substances and proteins which is consumed by bacteria. * Characteristic odour is caused by bacterial waste.

Question 30

describe Ceruminous glands

Answer 30

* Type of modified sweat gland | * Found in lining of the external ear canal which produce a waxy secretion.

Question 31

What is the structure and function of the hypodermis

Answer 31

Structure • It is composed of a mixture of adipose tissue and loose areolar tissue. • Interlaced with blood vessels and nerves Function • Main structural support for the skin • Insulation • Shock absorption

Question 32

what are the 4 types of protection offered by the skin

Answer 32

1. Physical 2. Osmotic 3. Bacterial 4. Ultraviolet Radiation

Question 33

describe the physical protection provided by skin

Answer 33

Skin forms the major interface between internal & external environments and protects from physical abrasion.

Question 34

describe Osmotic protection provided by skin

Answer 34

Sebum & keratin waterproof skin and restricts flow of water in either direction.

Question 35

describe bacterial protection provided by skin

Answer 35

* Intact skin forms first line of defence against infection. | * Fatty acids in sebum create an acid environment = barrier to invasion by microorganisms.

Question 36

describe UV protection provided by skin

Answer 36

• Melanin absorbs U.V. light as it forms a protective veil over the nucleus preventing damage to genetic material.

Question 37

what are the 3 ways the skin controls the regulation of body temperature?

Answer 37

1. Evaporation 2. Changes in blood flow 3. Erection of hair

Question 38

what are the 3 ways the skin in involved in sensation

Answer 38

1. Temperature 2. Touch 3. Pressure and Pain

Question 39

what are 7 other functions the skin has?

Answer 39

1. Endocrine function: vitamin D 2. Blood reservoir: 8-10% of blood in dermis at rest 3. Absorption: drug admin 4. Excretion: sweat 5. Immunity: Langerhans’ cells are ‘Antigen presenting cells’ 6. Social communication: vascular and muscular responses 7. Locomotion: friction, grip, movement

Question 40

what are the 3 main structures of the nail?

Answer 40

1. Free edge of nail 2. Body of nail/nail plate: made of a plate of dead tightly compressed cells packed with hard keratin 3. Root of nail: Proximal part covered by skin fold.

Question 41

Function of hair

Answer 41

* Hair on the scalp protects head from physical injury, from ultraviolet radiation, reduces heat loss. * Eyebrows, eyelashes, nasal hairs and hairs of external ear canal prevent entry by foreign particles. * Hair on the skin sense insects before they bite or sting

Question 42

Structure of hair

Answer 42

• Composed of dead, keratinised (hard keratin) cells. • Shaft: Part that emerges above the surface of the skin. • Root: Embedded in the skin, generally in the dermis. • Both made of 3 concentric layers Inner medulla Middle cortex Outer cuticle

Question 43

what is the hair papilla?

Answer 43

* A small connective tissue peg that protrudes into the hair bulb. * Contains blood capillaries and nerves.

Question 44

what is the hair matrix

Answer 44

* Actively dividing cells that produces hair. | * New cells are formed at the base, older cells and parts are pushed upwards.

Question 45

structure and function of hair follicles

Answer 45

• Hairs develop in follicles. • Follicle surrounds the root of the hair (under skin) • Function: - support, nourish and protect hair. • Structure: - A root hair plexus of sensory nerves surrounds the base of each follicle. - Each hair follicle is associated with arrector pili muscles.