Archive for the ‘Uncategorized’ Category

United Nations Special Committee on Decolonisation pamphlet collection in SearchWorks

April 13, 2017

https://searchworks.stanford.edu/view/10559707

Holocrine secretion

April 13, 2017

Holocrine is a term used to classify the mode of secretion in exocrine glands in the study of histology. Holocrine secretions are produced in the cytoplasm of the cell and released by the rupture of the plasma membrane, which destroys the cell and results in the secretion of the product into the lumen.

Holocrine secretion is the most damaging (to the cell itself and not to the host of which begot the cell) type of secretion, with merocrine secretion being the least damaging and apocrine secretion falling in between.

Examples of holocrine glands include the sebaceous glands of the skin and the meibomian glands of the eyelid. The sebaceous gland is an example of a holocrine gland because its product of secretion (sebum) is released with remnants of dead cells.

Holocrine, apocrine and merocrine glands are sebaceous

March 31, 2017

https://en.m.wikipedia.org/wiki/Holocrine

WordCamp Kyoto 2017 is Looking for Speakers! — WordCamp Central

March 31, 2017

The WordCamp Kyoto 2017 team has announced call for speakers for a day conference in Kyoto University on June 24. Date Saturday, June 24, 2017 (No sessions are planned for the Contributor Day on Sunday, June 25) Venue Kyoto University – Main Campus, International Science Innovation Building (Access) Session Format 15 mins or 30 mins,…

via WordCamp Kyoto 2017 is Looking for Speakers! — WordCamp Central

English Grammar | LearnEnglish | British Council | irregular verbs – learnenglish.britishcouncil.org

March 26, 2017

https://learnenglish.britishcouncil.org/en/english-grammar/verbs/irregular-verbs

SKIN FUNCTIONS

July 10, 2015

The three major components of the skin are firstly the hypodermic subcutaneous fat just beneath the skin that functions as insulation and padding for the body. Next the dermis provides structure and support and lastly the epidermis acts as protection for the body.

As the deepest section of the skin, the hypodermic fat tissue below the dermis insulates the body from cold temperatures and provides shock absorption. Fat cells also store nourishment and energy. Buttocks, palms of the hands and soles of the feet provide the thickest part. Contributing to the thinness of ageing skin, the hypodermic tissues begin to atrophy with age. Located between the hypodermic fat and the epidermis is the dermis, a fibrous network of tissue, providing structure and resilience to the skin. Major components of the dermis work together in a mesh like endothelial network composed of structural proteins collagen and elastin, blood and lymph vessels, special cells and fibroblasts. A jelly like ground substance plays a crucial role in the hydration and moisture balance in the skin.

SKIN CARE AND PRESERVATION

July 10, 2015

Blood and lymph vessels, nerves and specialised cells play a vital role in triggering the skin’s inflammatory response to invading bacteria, allergies and physical injury. Blood vessels in the dermis help to regulate heat by constricting or dilating to conserve or release the body’s heat. They also aid immunity and give oxygen and nutrients to the epidermal layers. Nutrients diffuse only into the very bottom layers as blood vessels do not extend into the epidermis. Dead cells in the upper layers do not receive oxygen and nourishment.

A wave like border at the junction between the dermis and the epidermis provides an increased surface for this exchange of food and oxygen between the two sections. Along this junction are projections called dermal papillae. They tend to flatten with ageing as the flow of oxygen and nutrients decreases.

Stratified into five horizontal layers the epidermis as the topmost layer actually consists of between fifty cell layers in the thin areas to one hundred cells in thickness, on average 0.1 millimetres, similar in fineness to a leaf. Complete renewal of the cells occurs monthly in the epidermis which acts as a protection for the body. A single layer of cubed cells sits directly on top of the dermis in the deepest or first epidermal layer, the stratum basale. New skin cells called keratinocytes are formed in this layer through cell division to replace those shed continuously from the upper layers. The rate of this regenerative skin cell renewal decreases with ageing.

Melanocytes in the basement membrane produce the skin pigment melanin, which is photo protective against the skin’s exposure to ultraviolet rays in the sun. From the melanocytes, melanin transfers to nearby keratinocytes that will eventually migrate to the skin’s surface.

The second epidermal spinous or prickle-cell layer, the stratum spinosum, has polygonal, many sided keratinocytes. These lie in about eight to ten layers which begin to become rather flattened.

Keratin, a tough fibrous protein giving skin its protective property comprises the third or granular layer, the stratum granulosum. Flattened cells in these three to five layers begin to die as they are too far from the dermis to receive nourishment by diffusion. Making up the outer layer of skin, keratin is the key structural material of hair and nails and it provides the necessary strength and toughness for masticatory organs, such as the tongue, gums and hard palate.

A fourth epidermal layer of extremely flattened cells in three to five layers is called the stratum lucidum. This clear layer makes up only fingertips, palms and soles of the feet.

Dead keratinocytes are flattened in twenty five to thirty rows in the top outermost horny layer. This fifth layer, the stratum corneum is the real protective part of the skin, shedding keratinocytes continuously by friction and replacing them by cells from deeper epidermal sections.

Lipids, ceramides and fatty acids in between the keratinocytes in the horny layer act as cement around the skin cells. A combination of keratinocytes interspersed with epidermal lipids forms a waterproof barrier to keep moisture in the skin. Loss of the balance of oil and moisture in the skin to protect against bacteria causes dryness, itching, redness, stinging and skin problems.

Acidity helps maintain the hardness of keratin proteins keeping them tightly bound together. If the skin’s surface is alkaline, keratin fibres loosen and soften, losing its protective acidity. Skin becomes dehydrated, and infection, roughness, scaliness and other irritations appear. Slightly acidic moisture layers are derived from the combined secretions of sebaceous and sweat glands, inhibiting the growth of harmful bacteria and skin blemishes.

Hair, sebaceous and sweat glands are common components of both the dermis and epidermis. Pores are formed by a folding in of the epidermis into the dermis.

Dead keratinocytes, the skin cells that line the pore are constantly being shed like the epidermal cells at the top of the skin. The lining of the pore loses keratinocytes which, mixed with the sebum, clog the pore forming eruptions on the skin surface. Oil builds up inside the pores, disrupting surrounding tissue and pores begin to enlarge. When the skin loses its protective balance of oil and moisture or becomes alkaline, skin eruption results. Hair growth out of the pores is composed of dead cells filled with keratin proteins. A bulbous follicle at the base of each hair divides to produce new cells. The follicles are nourished by tiny blood vessels and glands. Hair prevents heat loss and helps protect the epidermis from exposure to the sun’s rays.

Sebaceous glands connected to hair follicles secrete sebum to help lubricate the follicle as it grows. Sebum, the oily liquid produced within the sebaceous glands is regulated by hormones and contributes to the lipids and fatty acids in the moisture balance.

Perspiration excreted by sweat glands is acted upon by bacteria producing a characteristic odour and helps cool the body temperature, hydrate the skin, eliminate some toxins, mainly salt. Long coiled hollow tubes of cells produce sweat either by ductless glands below the epithelial surface or by long portions of a duct on apocrine and exocrine glands secreting directly to the pore opening on the skin surface and by eccrine external secretion regulating body heat.

Understanding how the skin functions and is constructed can help you better care for a healthy skin.

EPIDERMIS AND DERMIS

July 10, 2015
Five layers of the epidermis

Epidermal layers

DERMIS AND EPIDERMIS

July 10, 2015

Fibroblasts are cells located in the upper edge of the dermis bordering the epidermis and are specialised in producing the skin’s collagen and elastin. Collagen proteins found in the skin, as well as in cartilage and bone, form a mesh like framework in the dermis to give the skin strength and elasticity. Moisture binding molecules called glycoproteins enable collagen fibres rich in glycine, to retain water and give moisture to the epidermis. Another coil like connective tissue protein, elastin, which has a high percentage of both glycine and alanine, is found in the dermis giving the skin its ability to return to the original shape, or its elasticity.

Keratins, which have larger amounts of the sulphur-containing amino acid cysteine, assemble into bundles to form intermediate keratin proteins capable of annealing end-to-end into long filaments. These are tough and form unmineralised tissues. Derived from the Greek root kerato meaning “horn like”, filaments called keratin abound in keratinocytes in the cornified layer of the epidermis and are present in epithelial cells in general. These are cells which have undergone keratinisation. For example, thymic epithelial cells are known to react with antibodies for keratin in the thymus.

Combined into “hard” or “soft” cytokeratins, proteins are understood to occur as either neutral basic or acidic keratin in the skin’s stratum corneum of the stratified epithelial layers, cornea of the eye, squamous epithelia and ducts as well as the simple epithelium. More flexible and elastic keratins of the hair are harder and consist of coiled single protein strands which are then twisted helically into ropes that may be further coiled.

SKIN AS INTEGUMENT

July 10, 2015
Ageing skin

Skin’s collagen and elastin