1.1.4.2　Sebaceous glands

The sebaceous glands produce sebum and belong to the alveolar glands，which are composed of acinus and shorter ducts.The acinus has no glandular cavity，and the outer layer is flat or cuboid cells，surrounded by a basement membrane band and connective tissue.After rupture of the glandular cells，intracellular components including lipid droplets are released and discharged through the catheter.The catheter is composed of a stratified squamous epithelium，which is opened in the upper part of the hair follicle and is located in the angle between the hairy muscle and the hair follicle.The sebaceous glands are widely distributed on the whole body skin except the palms，soles and flexor side of the digit.There are many sebaceous glands in the head and face and the upper part of the chest and back，which is called the sebum overflow site.In areas of hairless skin such as buccal mucosa，lips，women's areola，labia majora，eyelids，and inner foreskin，the glandular duct directly opens to the skin surface.The sebaceous glands also have a growth cycle，but it has nothing to do with the hair follicle growth cycle，which is mainly controlled by androgen levels.(https://www.daowen.com)