The Dermis

Layers of dermis:

(Superficial) papilary layer=20% (superficial layer adjacent to epidermis) (Deep) reticular layer (adjacent to subcutaneous layer)

Sensory nerves-messages to brain

-Receive information from external stimuli and relay it back to brain. -Found near skins surface and respond to: Heat cold touch pain pressure

Lymph vessels of the dermis:

-Run alongside the circulatory system -Responsible for filtering waste out of body. -Defense system that contains white blood cells which fight off foreign invaders e.e. bacteria and viruses Lymph vessels begin as blind finger like vessels in papillae and drain lymph away from the stratum germinativum into lymph capillaries in dermis, then into superficial lymph vessels in hypodermis.

Tactile corpuscles ( touch)

A low threshold of sensitivity and fine with the faintest touch. In the dermis they reach into the papillae of papillary layer. Called meissners corpuscles they are located in area's sensitive to touch -lips, genitals, nipples, fingertips,eyelids.

Arteries-arterioles

Arteries carry blood from the heart. gradually reduce in size to form arterioles which form a fine network of capillaries which supply the dermis, swear glads, sebaceous glads and hair follicles with oxygen and nutrients. Arterioles run a fairly straight course through dermis forming capillary beds,- branch in tree like fashion underneath epidermis.

Papilary layer=20%

Composed of a matrix of collagen, elastin and reticulin fibres -Reticulin fibres under the epidermis form th ebasal lamina (membrane that anchors epidermis to dermis) -Dermal papillae protrude into the lover laywer of the epidermis -some papillae contain nerve endings,loops of cappilaries, or lie atop dermal ridges to form epidermal ridges. -Blind end lymph vessels start here

Reticular layer =80%

Composed of dense irregular tissue, mainly collagen with reticulin and elastin fibres -80% if the dermis is the reticular layer -collagen lies in wavy bundles, most run parallel to skins surface-Seperations between these bundles from tension lines (langer lines)-natural cleavage lines in the skin -Contains fine veins and arteries which link up to blood cappilaries -Contains hair follicles, sweat and oil glands, nerve arise from this layer

Vasoconstriction:

Constiction of the dermal blood vessels in response to a drop in temperature- body is then out of normal temperature range. Causes warm blood to temporarily bypass skin to slow passive heat loss from body -Skin may become paler in colour due to this.

Mast cells

Contains granules which secrete histamine and heparin in response to allergic reaction or tissue damage.

Vasodilation:

Dilation of the dermal blood vessels in response to rise in body temperature in which blood flow to the skin increases to allow heat to escape. Skin may become redder due to this.

Hyaluronic acid

Forms part of the matrix which surrounds collagen and elastin fibres. A natural moisturising ingredient responsible for the skin moisture content (hydration) and aids in trransport of nutrients from blood to skin. Also a natural humectant with the ability to atteact and capture water.

Mechano receptors (pressure)

Found in the deep reticular layer off dermis and the subcutaneous layer of skin.Consist of nerve endings surrounded by many layers of flattened cells. Sensitive to deep pressure and vibration-called pacinian corpusules

Different sensory nerves-classified under four main groups:

Free nerve endings (pain) tactile corpuscles (touch) mechano receptors (pressure) thermo-receptors (temperature)

Blood vessels of dermis-the root traveled by blood.

Heart-arteries-aterioles-capilaries-venules-veins.

Blood vessels

Help in temperature control of body through vasoconstiction and vasodilation

Veins-venules

In close association with meshwork of arterioles is a series of venuels that drain blood from capillaries to the to the veins which in turn carry blood to the heart.

Histiocytes

Ingest and remove cell debris and bacteria and form reticulin fibres

Langers lines

Lines define the direction within the human skin along which the skin has the least flexibility and correspond to the alignment of collagen fibres. Helpful during surgical operations in which incisions are carried out in the direction of the langers lines for better healing and less scaring.

Capillaries

Link between arterioles and venuels. Nutrients and oxygen are diffused to the cells of skin from capillaries. Networks of capillaries are most numerous around structures that need nutrients for growth,repair and regeneration. e.g. hair follicle. Capillaries form capillary loops which supply the epidermis with oxygen and nutrients through papillae in the dermis and make up part of the superficial vertical plexus.

Thermo-receptors ( temperature)

Located in dermis are 2 temperature receptors, both can respond to changes in tempreture but predominately Ruffini's end organs sense heat, and krause corpuscles or bulbs sense cold.

Fibroblasts

Located in the reticular layer and crear collagen and elastin fibres-are easily damaged by UV light.

Elasin

Made up of yellow elastic tussue forming elastic fibres. Gives skin its elastic (stretch and recoil) properties. Over extension (rapid weight gain/loss, pregnancy) can occur leading to rupture of the elastic fibres, allowing the collagen to become overstretched or even tear, a stretch mark occurs.

Cells of dermis

More cells in papliary layer than in deeper reticular layer. Listed from most abundant to least

macrophages (form of leucocyte)

Move around and absorb foreign material such as bacteria or dead debris-to fight infection and disease.

Epidermal ridges

On the palms of hands and soles of feet dermal papilae lie atop mound called dermal ridges which elevate the overlying epidermis to form epidermal ridges-these ridges enhance the fripping ability of fingers and feet, these epidermal ridge patterns are genetically unique to each person and form fingerprints

Discription of the dermis

Provides strength, flexibility and smoothness to the skin -made of dense, strong connective tussue -binds entire body together -provides nourishment to epidermis -has a high water content -is supplied with dermal structures: nerve fibres, blood vessels, lymphatic vessels, hair follicles, oil and sweat glands, papillary muscles (erector pili) - contains specialised cells -comprised of 2 layers -provides the base for epidermis

Motor nerves-messages from brain:

Situated in muscle tissue (erector pili sweat and sebaceous glads and blood vessels. -Respond to i.e. muscle movement, increase in sweat, dialation of blood vessels, increase in secretion.

Fibres and matrix of dermis:

Skins fibres are contained in a firm jelly called the matrix which is rich in nutrients. Three main fibres in the dermis: collagen elastic reticulin fibres

Superficial nerve supply:

Two main types of nerves found in body -Sensory nerves- Messages to brain -Motor nerves- messages from brain

Collagen:

White fibrous tissue made up of proteins. gives strength, reselience and a plump youthful apperance. Collagen synthesis starts in dermal fibroblasts cells where pro-collagen molecules pass out of fibroblasts into matrix of the dermal connective tissue-these groups of pro-collagen arrange lengthways and become collagen fibres

Free nerve endings (pain)

Widely spread in the dermis and branch into epidermis. Fire in response to strong and painful stimulation which is felts as pain, and sensitive to changes in temperature and pressure.

Reticulin fibres

not as strong as collagen and elastin, and run through and between other fibres and structures in dermis, helping to support them and keep them in place. also joins connective tissue to other tissues.