the skin

Question 1

What are the functions of the skin? (7)

Answer 1

Barrier, protection, thermoregulation, senses, synthesis of vitamins, storage, fluid maintenance

Question 2

What are the 3 main layers of the skin?

Answer 2

Epidermis, Dermis, Subcutaneous Tissue

Question 3

What is the Epidermis composed of?

Answer 3

stratified keratinised squamous epithelium.
No blood vessels or nerve endings.
The deeper layers are bathed in interstitial fluid from the dermis, which provides oxygen and nutrients, and drains away as lymph.

Question 4

What is the basal layer of the epidermis?

Answer 4

The first layer, made of cuboidal, nucleated, highly active epithelial cells which are constantly dividing.

Question 5

how is the skin protected from dehydration?

Answer 5

Lipids released by lamellar granules inhibit evaporation of water from skin surface. Also providing a water-resistant barrier.

Question 6

what does sebum do?

Answer 6

Sebum protects skin and hair from drying out and contains chemicals that kill surface bacteria

Question 7

How does perspiration act as protection?

Answer 7

The acidic pH of perspiration retards growth of some microbes

Question 8

How does melanin act as protection?

Answer 8

Provides some protection against UV

Question 9

what do epidermal Langerhans do?

Answer 9

Epidermal langerhans cells alert the immune system to presence of possible harmful microbe invaders. Macrophages in dermis phagocytise bacteria and viruses that penetrate skin surface

Question 10

How does the skin synthesise vitamin D?

Answer 10

Sunlight converts de-hydrocholesterol (lipid-based substance) in the skin into Vitamin D.
Vitamin D is involved (with other substances) in the growth and repair of bones

Question 11

Which areas of the skin are particularly sensitive and why?

Answer 11

The lips and the fingers because they have more receptors than other areas.

Question 12

The skin as a barrier

Answer 12

Although the skin forms a physical barrier, some drugs and chemicals can still be absorbed through it, such as mercury.

Question 13

What does skin excrete?

Answer 13

Around 400ml of water evaporates through it daily
Sedentary person loses an extra 200ml per day/active lose much more
Sweat is the mode of transport for excretion releasing water, salts, CO2, amino acids and urea

Question 14

How does the outer layer of the epidermis protect the body?

Answer 14

Outer fibrous layer of keratin cells protects from heat damage and microbes
Prevent water entry and loss.

Question 15

What is in the dermis layer of skin?

Answer 15

Elastic and connective tissue providing strength and pliability. The matrix is collagen fibres interlaced with elastic fibres.
Contains blood vessels, nerve fibres and hair follicles, lymphatic vessels and sweat glands.

Question 16

What happens when elastic fibres are ruptured or overstretched?

Answer 16

Result is stretch marks. Typically found in pregnancy and obesity.

Question 17

what do collagen fibres do?

Answer 17

Bind water and give the skin its tensile strength. This ability declines with age and so wrinkles develop

Question 18

What are the main cells found in the dermis?

Answer 18

fibroblasts, macrophages and mast cells.

Question 19

What does the dermal papillae do?

Answer 19

anchors the dermis securely to the epidermis. Allows passage and exchange of nutrients and wastes to the lower part of the epidermis. This arrangement stabilises the two layers, preventing damage to shearing forces. Blisters develop when trauma separates the dermis and epidermis, serious fluid collects between the two layers

Question 20

Where is the epidermis thickest?

Answer 20

In the areas where wear-and-tear is greatest. This is the palms and the soles of the feet. They don’t have hair on. In these areas the dermal papillae are arranged in parallel lines, giving the skin a surface a ridged appearance.

Question 21

what affects skins colour?

Answer 21

Melanin- a dark pigment derived by the ammo acid tyrosine and secreted by melanocytes in the deep germinative layer, is absorbed by surrounding epithelial cells.
The amount of melanin is genetically determined and varies between ethnic groups. The number of melanocytes is constant; differences depend on the amount of melanin secreted. Exposure of the skin to sunlight promotes synthesis of melanin.
Normal saturation of haemoglobin and the amount of blood circulating in the dermis gives white skin its pink colour. When oxygen is very low, the skin in white people may appear bluish (cyanosis). Excessive level of bile pigments in blood and carotenes in subcutaneous fat give the skin a yellowish colour.

Question 22

What is found in the subcutaneous layer?

Answer 22

areolar (loose) tissue, varying amounts of adipose tissue

Question 23

What are the two types of sweat glands, and which is more common?

Answer 23

Eccrine and Apocrine. Eccrine are more common.

Question 24

Eccrine sweat glands

Answer 24

Open on the skin surface through tiny pores. The sweat produced here is clear, watery fluid, important in temperature regulation.

Question 25

Apocrine sweat glands

Answer 25

Open in the hair follicles and become active at puberty. They may play a role in sexual arousal. These glands are found in the axilla and genital area. Secrete a milky substance rich in protein which smells after bacterial decomposition. A specialised example of this type of gland is the ceruminous gland of the out ear, which secretes earwax

Question 26

Where in the body are sweat glands?

Answer 26

They are widely distributed throughout the skin, most numerous in the palms of the hands, the soles of the feet, axillae and groin.

Question 27

what's the name of the muscles which erect hairs on the skin?

Answer 27

arrector pili muscles erect hairs in response to fear or low temperature.

Question 28

What is hair made of?

Answer 28

Hair is dead keratinized epithelial cells Consisting of a central axis of cells with soft keratin. The medulla surrounded by cortex of cells with hard keratin The cortex is covered by a single layer of cells filled with hard keratin Hair has 2 parts: Shaft- projects from the skin surface Root- is deeper penetrating into the dermis

Question 29

How does the root of hair work?

Answer 29

The root is surrounded by hair follicle. The base is the bulb, holstering blood vessels called papilla. The germinal layer of dividing cells is the hair matrix. Arrector and root plexuses are associated with hair follicles going through growth stages and resting stages.

Question 30

What are nails made out of?

Answer 30

Epidermis and hair. Hard keratin plates. The root of the nail is embedded in the skin and covered by the cuticle, which forms the hemispherical plae area called luna. The nail plate is exposed part that has grown out from the nail bed, basal layer of epidermis.

Question 31

What is the process of keratinisation

Answer 31

Keratinisation New cells are formed Old cells pushed to surface Apoptosis (slough off) The outer cells protect the underlying layers The cells undergo shape and chemical changes The cells are filled with keratin These cells die and produce outer layer to resist abrasions and formers a permeability barrier It’s a continual process Around a 4-week cycle

Question 32

What are the four stages of wound healing?

Answer 32

Haemostasis and coagulation, Inflammation, Proliferation and Migration, Remodelling

Question 33

What is the objective of haemostasis and how does it work?

Answer 33

The objective is to stop the bleeding. During this process, platelets come into contact with collagen, resulting in activation and aggregation. The thrombin enzyme initiates the formation of a fibrin mesh, which strengthens the platelet clumps into a stable clot

Question 34

What happens in the inflammation stage of wound healing?

Answer 34

A type of white blood cell called neutrophils enter the wound to destroy bacteria and remove debris. These cells often reach their peak population between 24 and 48 hours after injury (reducing in a few days) As the white blood cells leave, specialised cells called macrophages arrive to continue clearing debris. These cells also secrete growth factors and proteins that attract immune system cells to the wound to facilitate tissue repair. This phase often lasts four to six days and is often associated with oedema, erythema, heat and pain.

Question 35

What happens in the proliferation and migration phase of wound healing?

Answer 35

The wound bed is filled with connective tissue, and new blood vessels are formed. The extensive growth of epithelial cells beneath the scab, random deposit of fibroblasts and continued growth of blood vessels. The clot dries to scab Epithelial cells migrate beneath scab to bridge wound Deeper fibroblasts migrate through the clot and begin to synthesis collagen fibres and glycoprotein in dermis Damaged blood vessels begin to regrow The connective tissue filling wound here is called granulation tissue, will become scar tissue

Question 36

What happens during the remodelling stage of wound healing?

Answer 36

During the Maturation/remodelling phase, the new tissue slowly gains strength and flexibility. Collagen fibres reorganise, the tissue remodels and matures and there is an overall increase in tensile strength. The Maturation phase varies greatly from wound to wound, often lasting anywhere from 21 days to 2 years.  Formation of scar tissue is called fibrosis Scar tissue that remains in the boundaries of the wound is called a hypertrophic scar If it extends beyond boundaries, it is called a keloid scar Scar tissue is different from normal skin, it had less elasticity, fewer blood vessels, denser arrangement of collegan fibres. It may not have same number of hairs, skin glans, sensory structures Due to arrangement of fibres and vessels the skin is usually lighter in colour