Anatomy and Cell Biology 3309 Lecture Notes - Lecture 41: Apocrine Sweat Gland, Lactiferous Duct, Eccrine Sweat Gland
2 May 2018
School
Department
Professor
Mammary Glands
Learning Objectives
1. Describe the connective tissue component and organization of a resting mammary gland.
2. Explain the histological components of the nipple.
3. Describe the lactiferous duct and the role of lactiferous sinuses.
4. List the changes that occur in the mammary gland during puberty pregnancy and lactation.
5. List the steps involved in the production and release of protein and lipid in milk.
6. Explain the milk ejection reflex.
- Hormones are important in regulated function and development of the mammary gland
- Mammary glands: compound tubuloalveolar gland with 15-20 lobes, derived from modified apocrine
sweat glands
- Nipple is surrounded by a highly pigmented area = Areola
o Under hormonal influences during pregnancy, the pigmentation changes
- Nipple is designed as the exit point of the mammary gland
o Mammary gland collectively is made up of 15-20 lobes
▪ IMPORTANT: Each lobe opens up separately on the surface of the nipple. It carries
the secretory product (milk) all the way to the surface through ducts (lactiferous
duct)
▪ Each lobe is drained by one main lactiferous duct, which branches into lobules
▪ At the end of each lobule, we have acini that form a grape like arrangement of
secretory cells. The cells function under the influence of various hormones
o Tubuloacinar compound glands
▪ Compound = branching duct system
- The entire gland is a modified apocrine sweat gland
o Eccrine sweat gland: all over the place, underneath the skin
o Apocrine sweat gland: produce pheromones in certain animals
▪ Axilla, groin regions
o MODIFIED because it produces milk rather than the general sweat substance
- The gland secretes only partially by an apocrine mechanism
o Apocrine sweat gland secretes by merocine mechanism!! BUT the milk secreting mammary
gland is an example of an apocrine gland because part of the milk produce is released via an
apocrine mechanism
- The mammary gland is embedded in dense connective tissue (reticular layer of dermis) and adipose
o The size of the breast is NOT determined by how much glandular tissue is present, but rather
how much adipose tissue is present
o Even a lady with small breasts
produces as much milk as a lady with
larger breasts – HAS NO IMAPCT ON
MILK PRODUCTION!
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- Since the mammary gland undergoes changes during development, puberty and pregnancy, you have
to distinguish different views
- Islands of ducts cut in cross section, is surrounded by dense connective tissue that forms the basis of
the tissue, where the mammary gland is embedded
- The lobules develop principally only during and after puberty under the influence of hormones
o Before puberty, the male and female mammary gland looks identical
▪ Composed of rudimentary duct system (branching duct system)
▪ Nothing much happened at the end = blind ending duct system
▪ There are small buds of cells that will later on (in females) under the influence of
hormones, proliferate and form acini (secretory structures)
- During lactation, in an active mammary gland, the milk is being delivered to the nipple
o Underneath the nipple there is a region that is covered by the alveoli, where the lactiferous
ducts enlarge to form lactiferous sinus
▪ The sinus is an expansion of the lumen of a lactiferous duct
o The lactiferous sinus is a reservoir that is able to hold relatively large amount of milk
▪ Purpose: when a baby latches on and suckling, it immediately gets food and
continues to suckle
- In order for the baby to grab a hold of the nipple, there are smooth muscle bundles within the
connective tissue right underneath the nipple in the areola, that forms a ring like structure and also
runs radially
o NOTE: this is the same in males and females. The smooth muscle reacts to all sorts of stimuli
▪ Experience it when it gets cold, you touch the skin, the nipple gets erect
▪ Purpose is to provide a large surface area for the baby to latch on to
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Development of the Mammary Gland
- Early on, in the first or second trimester of pregnancy in the embryo, there are groups of epithelial
cells located from the axilla region to the groin = milk line
o The cells in the epithelium are prone to stimulation from mesenchymal cells underneath
o Usually, in mammals, there are many mammary glands developing along the milk line BUT in
humans there are only two
o During development, these epithelial cells under the influence of signals from the adipose
issue and mesenchyme, form cords. As a bud that starts to develop into the mammary gland
- Later on, the cords become hollow
o The cells differentiate into two main cell types:
▪ 1. Luminal cells – form the duct
• Secretory cells that are there after puberty and during lactation
• Depending on their location;
o If they are at the end of the duct – secretory cells
o Further down – duct cells
▪ 2. Myoepithelial cells that are of epithelial origin, that help in squeezing the
product out to the duct system
1. Dermal mesenchymal cells induce formation of epithelial bud
2. Adipose cells stimulate branching of epithelial mammary cords
3. Mammary cords become hollow and some luminal epithelial cells differentiate into myoepithelial
cells
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Hormones are important in regulated function and development of the mammary gland. Mammary glands: compound tubuloalveolar gland with 15-20 lobes, derived from modified apocrine sweat glands. Nipple is surrounded by a highly pigmented area = areola: under hormonal influences during pregnancy, the pigmentation changes. Nipple is designed as the exit point of the mammary gland: mammary gland collectively is made up of 15-20 lobes. Important: each lobe opens up separately on the surface of the nipple. The cells function under the influence of various hormones: tubuloacinar compound glands, compound = branching duct system. The gland secretes only partially by an apocrine mechanism: apocrine sweat gland secretes by merocine mechanism!! But the milk secreting mammary gland is an example of an apocrine gland because part of the milk produce is released via an apocrine mechanism. Since the mammary gland undergoes changes during development, puberty and pregnancy, you have to distinguish different views.
