Skin – largest organ in our body PDF

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Summary

Skin – largest organ in our body.  Epidermis (0 millimetres thickness) – composed of keratinising stratified squamous epithelium. o Well suited for areas in the body subject to constant abrasion - protection. o Outer, acellular layer of the epithelium is composed of dead cells – composed of 15-20 l...

Description

Skin – largest organ in our body.  Epidermis (0.1 millimetres thickness) – composed of keratinising stratified squamous epithelium. o Well suited for areas in the body subject to constant abrasion - protection. o Outer, acellular layer of the epithelium is composed of dead cells – composed of 15-20 layers of flattened cells with no nuclei and cell organelles. o The epithelium is made up of 5 layers of cells. o The epidermis is composed of keratinized, stratified squamous epithelium. It is made of four or five layers of epithelial cells, depending on its location in the body. It does not have any blood vessels within it (i.e., it is avascular). Skin that has four layers of cells is referred to as “thin skin.” From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Most of the skin can be classified as thin skin. “Thick skin” is found only on the palms of the hands and the soles of the feet. It has a fifth layer, called the stratum lucidum, located between the stratum corneum and the stratum granulosum. 

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Dermis (ranges in thickness from anout 0.5mm to 3.0 mm) – composed of largely irregular dense connective tissue – it provides strength, making the skin resistant to tearing as consequence of stretching forces from different directions. Cushions the body from stress and strain. o Blood vessel – provide nourishment and waste removal for both dermal and epidermal cells. o Sebaceous glands – found all over body except palm and sole – secretes sebum. Sebum lubricates hair, waterproofs our skin and defence against pathogens.  Microscopic exocrine glands in the skin that secrete sebum.  In colder conditions, the nature of sebum becomes more lipid and in coating the hair and skin, rain is effectively repelled.  In hot conditions, the secretions emulsify the sweat produced by the eccrine glands and this produces a sheet of sweat that is not readily lost in drops of sweat. This is of importance in delaying dehydration.  Sebaceous glands are usually attached to hair follicles and release a fatty substance, sebum, into the follicular duct and thence to the surface of the skin. o Hair follicles – tiny hair producing organs that extend deep into the dermis. Hair is a non-living keratinized structure – insulate skull, keep out foreign particles and sensory receptors.  The lowest part of the follicle is called the dermal papilla, this is the living part of the hair. Tiny indentations in the skin.  Hair follicles made up of epithelial cells derived from the outer layers of the skin that produce hair – hair matrix (dividing cells pushed towards the surface to produce hair), hair papilla (lump of CT that surrounds blood vessels and nerves at base of follicle) and hair bulb (epithelial cells surrounding the papilla).

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Hair are made from keratin.

o Sweat glands – simple tubular glands found almost everywhere on our body. Help regulate body temperature.  The two main types of sweat glands are eccrine sweat glands and apocrine sweat glands. 

Each gland made up of a secretory section and excretory duct.

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Secretory portion is a twisted and coiled tube that has an opening at its very top – sweat produced in the coiled portion.

Subcutaneous (hypodermis) – provides for most of the body’s fat storage and participates in thermoregulation. o Adipose connective tissue – main role is to store energy in the form of fat, also cushions and insulates the body. Protective function – providing mechanical protection and support around major organs. o 0.1 mm in diameter. o The lipid droplets in adipose tissue can be unilocular and or multilocular. Unilocular cells contain a single large lipid droplet which pushes the cell nucleus against the plasma membrane4, giving the cell a signet-ring shape. Goblet cells:  Lumen is 12um wide.  Secrete mucus – to protect the mucous membranes.  Conjunctiva contain goblet cells that secrete mucins to protect the eye. ...