Changes

One or more sebaceous glands surround each '''hair follicle''' at a point about 1/3 of its length beneath the skin's surface.  Each gland is composed of numerous ''acini'' attached to a common '''excretory duct''' through which they discharge their secretions ('''sebum''') onto the hair shaft and epidermis.  In the skin and eyelids such glands release the cell contents together with secretory products with holocrine secretion.  This secretion involves [[General Pathology - Necrosis#Apoptosis|apoptosis]] in which the secretory products and cell debris are released into the gland lumen.  The secretory products vary from species to species and include various fatty acids, diglycerides, cholesterol, diesters, wax esters and giant-ring lactones.

One or more sebaceous glands surround each '''hair follicle''' at a point about 1/3 of its length beneath the skin's surface.  Each gland is composed of numerous ''acini'' attached to a common '''excretory duct''' through which they discharge their secretions ('''sebum''') onto the hair shaft and epidermis.  In the skin and eyelids such glands release the cell contents together with secretory products with holocrine secretion.  This secretion involves [[General Pathology - Necrosis#Apoptosis|apoptosis]] in which the secretory products and cell debris are released into the gland lumen.  The secretory products vary from species to species and include various fatty acids, diglycerides, cholesterol, diesters, wax esters and giant-ring lactones.

The function of sebum is that of an emolient of the hair and skin, preventing excessive dryness.  It may combine with '''sweat''' to form an emulsion within the stratum corneum and a form of cement around the hair pores preventing bacterial invasion of the epidermis.  Sebum is also released from the glands during piloerection, as the action of the ''arrector pili'' muscle squeezes the gland as it raises the hair.

The function of sebum is that of an emolient of the hair and skin, preventing excessive dryness.  It may combine with '''sweat''' to form an emulsion within the stratum corneum and a form of cement around the hair pores preventing bacterial invasion of the epidermis.  Sebum is also released from the glands during piloerection, as the action of the [[Hair - Anatomy & Physiology#Hair Types|arrector pili]] muscle squeezes the gland as it raises the hair.

In sheep, sebum is often referred to as "'''lanolin'''".  This is the cause of many skin allergies in humans.

In sheep, sebum is often referred to as "'''lanolin'''".  This is the cause of many skin allergies in humans.