B140.Histology_ Epithelium and Glands - Mammary Gland.pptx

Histology of the Mammary Gland Michael Hortsch, Ph.D. Department of Cell and Developmental Biology University of Michigan [email protected] Industry Relationship Disclosures: No Industry Supported Research...

Histology of the Mammary Gland Michael Hortsch, Ph.D. Department of Cell and Developmental Biology University of Michigan [email protected] Industry Relationship Disclosures: No Industry Supported Research and Outside Relationships © 2023 Michael Hortsch (unless obtained from other sources as marked on the slide information window)  Learning Objectives : Be able to identify the histological components of the mammary gland, specifically the structures associated with the nipple and the areola, the overall organization into lobes and lobules, as well as secretory alveoli (acini), lactiferous ducts and sinuses and the intralobular and interlobular connective tissue. Identify and describe the histological differences between the mammary gland in adult females prior to pregnancy (inactive), during pregnancy and during lactation (active). Understand the multiple, cellular mechanisms involved in the formation and release of milk.  The mammary gland is one of the major secretory organs in mammals. Its major function is the production of milk for newborn infants: The smaller secretory lobules are surrounded by a collagenous connective tissue layer and spaces between lobules are filled by adipose tissue. Multiple lobules form larger lobes.  The mammary gland is a compound tubulo-acinar gland The secretory portions of the gland are connected to the nipple by a branched ductal system. The final larger ducts are called lactiferous ducts that end in lactiferous sinuses, which can store some milk between nursing sessions. Ink-injected duct system of a mammary gland  Inactive mammary gland The endings of the ductal tree are terminal tubules (TD) that connect to intralobular ducts (ID), which connect to larger extralobular ducts. The secretory TD ID lobules are surrounded by a collagenous connective tissue layer and spaces between lobules contain adipose tissue. The terminal ductules have two layers, the inner layer consisting of a simple columnar epithelium (C) and the outer layer of myoepithelial cells (M). (S) indicates a small amount of secretion product, which results from menstrual cycle hormone secretion. Evolutionary, the mammary gland is considered a modified apocrine sweat gland. Before puberty there is no detectable difference between the mammary gland anlagen of males and females. Its development is mainly controlled by estrogen, which is lacking in males, and is also inhibited by testosterone. The brown staining represent estrogen receptors in the nuclei of mammary gland epithelial cells  Especially during pregnancy and afterwards during breast feeding, the secretory activity of the mammary gland is under the control of pituitary and ovarian hormones (e.g. prolactin). In an inactive/resting mammary gland, the glandular tissue within the lobules is not well developed and is mainly composed primarily of duct elements.  Especially during pregnancy and afterwards during breast feeding, the secretory activity of the mammary gland is under the control of pituitary and ovarian hormones (e.g. prolactin). In an active but non-lactating mammary gland of pregnancy, the glandular elements of the lobules are much more developed with a marked reduction of the interlobular dense irregular connective tissue.  Especially during pregnancy and afterwards during breast feeding, the secretory activity of the mammary gland is under the control of pituitary and ovarian hormones (e.g. prolactin). In a lactating mammary gland, little interlobular connective tissue is left. After breast feeding ceases the tissue returns to its normal or resting state over several months, a process called involution. Secretion from the mammary gland involves both apocrine (for the lipid component of milk) and merocrine (for proteinaceous component of milk) secretion mechanisms. Near the nipple the large mammary gland ducts merge to form lactiferous sinuses, which are lined by a two layered epithelium (the outer layer consisting of myepithelial cells). The pigmented area of the nipple is referred to as the areola. Note the presence of abundant smooth muscle (regulated by oxytocin) and of sebaceous glands (protecting the skin of the nipple).  Due to a decrease in the levels of estrogen, the breast undergoes normal changes in older individuals. The lobular tissue regresses and the adipose tissue is replaced by fibro-collagenous tissue. Normal breast tissue from a 23-year-old woman versus normal breast tissue from a 43-year-old woman.  Mammary carcinoma is still a prevalent and deadly form of cancer in women (in rare instances also in men). Breast cancer usually develops from the terminal ductules or the epithelium of the larger ducts, including the lactiferous ducts. Mammary carcinoma derived from mammary ducts  Summary Mammary Gland The mammary gland is a compound acinar gland organized in larger lobes that are subdivided into smaller lobules. Supposedly, it is has evolved from an ancestral apocrine-type sweat gland. It is surrounded by dense irregular connective and adipose tissue. In its inactive state it only consists of remnant ducts. During pregnancy hormonal control initiates the formation of secretory acini (active gland). After birth, it becomes a lactating gland using both merocrine and apocrine secretion mechanisms to produce milk that is temporarily stored in lactiferous ducts and expelled during nursing by smooth muscle in the nipple tissue. Also note the abundance of sebaceous glands in the nipple area. When the infant is no longer nursed the gland returns to its inactive state. Also note the normal changes of the gland with age (adipose tissue is replaced by dense irregular CT) and remember the pathological formation of mammary carcinomas.  Learning Objectives: 1. Be able to identify the histological components of the mammary gland, including the structures associated with the nipple and the areola, the overall organization into lobes and lobules, as well as secretory alveoli (acini), lactiferous ducts and sinuses and the intralobular and interlobular connective tissue. 2. Identify and describe the histological differences between the mammary gland in adult females prior to pregnancy (inactive), during pregnancy and during lactation (active). 3. Understand the cellular mechanisms involved in the formation and release of milk.