Session 5.3 - Group Work Flashcards
30th October 2017 - 10:15 - 11:15
1) Skin is the body’s largest organ, weighing around 9kg in an adult male, but what are its functions?
Function of the skin
- The skin, which is the largest organ of the body both by mass and by size, is a multi-functional organ that serves several important purposes.
1) Protection
- Perhaps the most evident function of the skin is that in protection.
- The skin consists of strong and elastic protein fibers (collagen, keratin and elastin) that protect the body from physical and mechanical forces. This ensures that the internal organs are not damaged.
- Aside from protecting from physical damage, the skin also protects from (1) excessive UV radiation (2) bacterial and viral micro-organisms (3) dehydration (4) dangerous chemicals.
2) Sensation
- The skin contains somatic sensory receptors that aid in sensation. It also contains cells called Merkel cells that are believe to be involved in sensation. The skin contains pressure receptors, light receptors, pain receptors, thermal receptors, among others.
3) Thermal Regulation and Insulation
- Every exothermic process in the body produces excessive energy (heat) that must be dissipated by the body to prevent overheating. The blood vessels that run in the dermis of the skin can expel this heat via radiation. The skin can also expel heat via the endothermic process of evaporation. The skin can also prevent heat loss by redirecting the blood away from the skin.
4) Excretion and Secretion
- The skin is an excretion organ. It can excrete water to the skin’s surface via diffusion. Waste products such as urea, salts such as sodium & water can also be excreted via sweating.
5) Immunity
- Langerhans cells of the epidermis can interact with T-cells to help protect the body from bacterial agents. Phagocytic cells in the hypodermis can engulf bacterial cells.
6) Endocrine
- Cells in the epidermis can produce vitamin D3 (cholecalciferol) by using the energy stored in UV radiation. This can be ultimately activated to the hormone calcitriol in the kidneys.
7) Growth
- The skin can expand due to the elastin fibres. Therefore, as the organism grows, so does the skin.
2) What colour was the first human? Why?
“The earliest humans evolved in high-UV environments, in equatorial Africa. The earliest members of our lineage, the genus Homo, were darkly pigmented. And we all share this incredible heritage of having originally been darkly pigmented, two million to one and half million years ago.”
The first human was darkly pigmented, bc they evolved from equatorial Africa, where there is a high concentration of UVB radiation from the sun. This meant humans produced a lot of melanin, produced by our melanocytes, as a natural sunscreen.
2)
a) What disease do dark skinned individuals suffer from in temperate climates?
Vitamin D deficiency
UVB radiation from the sun is essential to make vitamin D in our bodies.
The higher production of melanin in dark-skinned individuals, whilst at the equator, is sufficient to protect them from the sunlight, and thus is optimised to allow sufficient UVB radiation to produce vitamin D in the skin … in temperate climates, there is much less UVB radiation, thus, alongside the higher level of protection with increased melanin, so less vitamin D is made, reducing these individuals to a risk of vitamin D deficiency.
[Textbook p294: As well as being obtained from the diet, vitamin D is also made in the skin using sunlight. UVB rays passing through the epidermis convert 7-cholesterol into cholecalciferol, a relatively inactive form of vitamin D. This is carried by the blood to the kidneys, where it is converted into calcitriol, or active vitamin D3. Since melanin filters UV light, people with darker skin need more UV radiation to make the same amount of vitamin D. UV radiation can be measured using an index.
This map indicates the different amounts of UV radiation from the sun around the globe each day. A dark-skinned person with a poor diet in a low UV area could suffer from vitamin D deficiency.]
Vitamin D deficiency can cause rickets (children) or osteomalacia (adults).
[Textbook p441: Osteomalacia - In this painful condition, known as rickets in children, the bones become softened and may bend and crack.
Osteomalacia is due to a deficiency in vitamin D, which the body needs to absorb calcium and phosphate. These minerals give bone strength and density. In healthy people, vitamin D is made in the skin. Small amounts come from oily fish, eggs, vegetables, fortified low-fat spreads, and milk. Deficiency commonly occurs in people who follow a restricted diet or cover their skin, and absorption is reduced in darkly pigmented skin. Symptoms include painful, tender bones, fractures after minor injuries, and difficulty in climbing stairs. Treatment depends on the underlying cause and may include calcium and vitamin D supplements.
Rickets - This child has rickets, which is caused by vitamin D deficiency. This causes the bones to become softer and weaker, leading to pain and deformity.]
2)
b) What diseases do light skinned individuals risk in equatorial climates?
[Textbook, p438: Skin cancer - Skin cancers are the most often diagnosed cancers worldwide. The most common forms are basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.
Basal cell and squamous cell carcinoma are both usually caused by cumulative ultraviolet (UV) light exposure (often from sunshine and tanning beds). They are most common in people with light skins in countries with high levels of UV light. They affect males more often, perhaps due to differing lifetime sunlight exposures.
Basal cell carcinoma (BCC) arises from the basal cell layer and is rare before the age of 40. It accounts for around 80 per cent of skin cancers. The lesion appears as a raised, smooth, pink, or browny-grey bump with a pearly border, which may have visible blood vessels on it. It is not painful or itchy. The centre may be pigmented or ulcerate. It grows slowly and only very rarely metastasises (spreads to other organs or parts of the body). Diagnosis of BCC is by skin biopsy, and it can usually be cured by surgical excision.
- has a typical smooth pink bump; the centre may crust and bleed and is often described as a sore that does not heal.
Squamous cell carcinoma (SCC) arises from the squamous cell layer. It may rarely also be due to exposure to chemical carcinogens (such as tar) or ionising radiation as well as UV light. It usually occurs from the age of 60 onwards, but this varies. SCC accounts for around 16 per cent of skin cancers. The lesion is a raised, hard, pinkish, and scaling patch that may ulcerate, bleed, and crust. It slowly enlarges, sometimes developing into a large mass, and it rarely metastasises. It is diagnosed by skin biopsy, and treatment is by surgical excision, which is usually curative.
Malignant melanoma arises from the melanocytes (pigment-producing cells) in the skin. Sunlight exposure especially in childhood, episodes of blistering sunburn, using sunbeds and a family history increase the risk. It is most common in light-skinned people and those with many moles. Melanoma may arise from a pre-existing mole or appear as a new, enlarging black or brown mole (see below) and treated by complete surgical excision. The prognosis depends on the depth and spread of the tumour. Melanomas often metastasise and are fatal in around 1 in 5 cases. For all people with skin cancer, regular screening for developing cancers and future sun avoidance (protective clothing, sunglasses, sunblock, avoiding sun exposure during the middle of the day) is recommended.
- Warning signs of malignant change in a mole include a change in size, shape, colour, or height; bleeding; itching; ulceration; irregular shape; variable colour, and asymmetric border.]
[NHS: The term non-melanoma distinguishes these more common types of skin cancer from the less common skin cancer known as melanoma, which can be more serious.
The two most common types of non-melanoma skin cancer are:
- basal cell carcinoma (BCC) – also known as a rodent ulcer, BCC starts in the cells lining the bottom of the epidermis (outermost layer of skin) and accounts for about 75% of skin cancers
- squamous cell carcinoma (SCC) – starts in the cells lining the top of the epidermis and accounts for about 20% of skin cancers
Basal cell carcinoma
Basal cell carcinoma (BCC) usually appears as a small, shiny pink or pearly-white lump with a translucent or waxy appearance. It can also look like a red, scaly patch.
There’s sometimes some brown or black pigment within the patch.
The lump slowly gets bigger and may become crusty, bleed or develop into a painless ulcer.
Squamous cell carcinoma
Squamous cell carcinoma (SCC) appears as a firm pink lump with a rough or crusted surface. There can be a lot of surface scale and sometimes even a spiky horn sticking up from the surface.
The lump is often tender to touch, bleeds easily and may develop into an ulcer.]
UVB light is thought to cause DNA damage and folate destruction?
3) Explore albinism and the risk of skin cancer in this disease
[Textbook p431: Albinism - This name is used for a group of genetic disorders causing a lack of the pigment that gives colour to skin, eyes, and hair.
Albinism is a recessive disorder, meaning that both parents need to have affected genes in order to pass on the condition. If both parents are carriers (carry the genes for albinism but do not have the disorder), a child has a 25 per cent (1 in 4) chance of inheriting the condition (both faulty genes) and a 50 per cent chance of being a carrier. No prenatal test is possible unless parents have previously had a child with albinism so that the particular genetic abnormality can be identified. Usually the genes instructing the body to make pigment are abnormal. Individuals with albinism have poor vision and little or no pigment in eyes, skin, or hair, resulting in pale skin, fair hair (which can be white) and eyes that are usually blue or violet but with a thin iris that tends to give back a red reflection in bright light. There is no cure, but those with the condition are advised to stay out of the sun. Problems with vision can be corrected to some degree.]
The lack of melanin in Albinos increases the risk of developing skin cancer by 1,000 fold as compared with the general African population.(? source for figures, but the lack of melanin in Albinos greatly increases the risk of skin cancer)
[Cancer Research UK: Melanoma skin cancer risk is more than twice as high in people with skin phototype I compared with people with skin phototype IV, and around twice as high for all skin phototype II, and 35% higher for skin phototype III compared with skin phototype IV, a meta-analysis showed.
Skin Phototype Typical Features Tanning Ability
Type I Tends to have freckles, red or fair hair, and blue or green eyes. Often burns, rarely tans.
Type II Tends to have light hair, and blue or brown eyes. Usually burns, sometimes tans.
Type III Tends to have brown hair and eyes. Sometimes burns, usually tans.
Type IV Tends to have dark brown eyes and hair. Rarely burns, often tans.
Type V Naturally black-brown skin. Often has dark brown eyes and hair.
Type VI Naturally black-brown skin. Usually has black-brown eyes and hair.]
Albinism links to: MCBG: autosomal recessive BL: this module Neuropsychiatry: visual defects* (see NHS) Integrated: dermatology
[*Visual defects (NHS):
The reduced amount of melanin can also cause other eye problems. This is because melanin is involved in the development of the retina, the thin layer of cells at the back of the eye.
Possible eye problems linked to albinism include:
poor eyesight – either short-sightedness or long-sightedness, and low vision (sight loss that can’t be corrected)
astigmatism – where the cornea (clear layer at the front of the eye) isn’t perfectly curved or the lens is an abnormal shape, causing blurred vision
photophobia – where the eyes are sensitive to light
nystagmus – where the eyes move involuntarily from side to side, causing reduced vision; you don’t see the world as “wobbling” because your brain adapts to your eye movement
squint – where the eyes point in different directions
Some young children with albinism may appear clumsy because problems with their eyesight can make it difficult for them to perform certain movements, such as picking up an object. This should improve as they get older.]
4) Globally, dead skin accounts for about a billion tons of dust in the atmosphere. Your skin sheds 50,000 cells every minute. Can you relate this to the disease state of psoriasis?
[Textbook, p436: Psoriasis - Psoriasis is a long-term skin disorder in which the skin cells reproduce too rapidly, causing itchy, flaky patches.
Psoriasis affects around 1 in 50 people. Men and women are affected equally, and it runs in families. It begins between the ages of 10 and 45 and can be triggered by a throat infection, skin injury, drugs, and physical or emotional stress. Around 80 per cent of those with the disorder have plaque psoriasis, where red, flaky patches (plaques) covered in silver scales appear usually on the elbows, knees, and scalp, which are itchy and sore. In flexural psoriasis, less scaly patches occur in skin folds such as the groin and armpit. In guttate psoriasis, smaller scaly red patches occur all over the body in a young person, following a throat infection. Guttate psoriasis usually clears up completely. Psoriasis may affect only the scalp. The condition is diagnosed on its appearance. Psoriasis responds well to phototherapy (UV light) but is usually a long-term condition. Topical (external) treatments include emollients, coal tar-based preparations, corticosteroids, dithranol, and vitamin D and A analogues*.
Plaque psoriasis
Patches (plaques) of the skin are thickened, red, flaky, and covered in silvery-white scales, and have a sharp border. They usually itch and may burn.]
*thought to help the immune system
[NHS: People with psoriasis have an increased production of skin cells.
Skin cells are normally made and replaced every 3 to 4 weeks, but in psoriasis this process only takes about 3 to 7 days. The resulting build-up of skin cells is what creates the patches associated with psoriasis.]
[Integration: https://www.clinicalkey.com/#!/content/clinical_overview/67-s2.0-5c047fba-f19f-4a81-9c8e-ece9a4bf04b8?scrollTo=%23synopsis-heading-1
Psoriasis is a chronic skin disorder characterized by excessive proliferation of keratinocytes, resulting in the formation of thickened scaly plaques, itching, and inflammatory changes of the epidermis and dermis; multisystem inflammatory disorder with multiple comorbidities, not solely a cutaneous disorder]
People with psoriasis have the same rate of skin cell shedding, but the replacement rate of keratinocytes is increased - therefore more cells move up, eventually resulting in increased numbers of dead cells in the stratum corneum.
