Anatomy and Cell Biology 3309 Lecture Notes - Lecture 20: Apocrine Sweat Gland, Lactiferous Duct, Eccrine Sweat Gland
15 May 2018
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Lecture 20 – Mammary Gland
- Areola: highly pigmented area surrounding the nipple
o Under hormonal influences during pregnany, the pigmentation changes
- Nipple is designed as the exit point of the mammary gland
- Mammary gland is collectively made up of 15-20 lobes
o Lobes: tubuloalveolar/tubuloacinar compound glands
▪ Compound: branching duct system
o Each lobe opens up separately on the surface of the nipple
o Lobes carry the milk (secretory product) to the surface through lactiferous ducts
o Each lobe is drained by one main lacteriferous duct which branches into lobules
o At the end of each lobule, there are acini that form grape-like arrangement of
secretory cells
o Acini cells function under the influence of hormones
- Entire gland is a modified apocrine sweat gland
o Eccrine sweat glands are underneath skin vs. apocrine sweat glands produce
pheromones
o MODIFIED because it produces milk rather than general sweat substance
- Gland secretes only partially by an apocrine mechanism
o Apocrine sweat glands secrete by merocrine
- Milk secreting mammary gland is an example of an apocrine gland
o Part of the milk product is released in an apocrine mechanism
- Mammary gland is embedded in dense CT (reticular layer of the dermis) and adipose tissue
- Size of the breast is not determined by how much glandular tissue is present
- Size is determined by how much adipose tissue is present
o No impact on production of milk
o E.g. small breasts can produce same amount of milk as large breasts
- Mammary gland undergoes changes during development, puberty and pregnancy
- There are islands of ducts surrounded by dense CT that forms the basis of the tissue that the
mammary gland is embedded
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- Lobules develop only during and after puberty under the influence of hormones
- Before puberty, male and female mammary gland looks identical
o Composed of rudimentary duct system
o Branching duct system with nothing happen
o Blind ending duct system where there are only small buds of cells that will later on
in females (under influence of hormones) proliferate and form secretory
structure/acini
- During lactation, in an active mammary gland, milk is delivered to the nipple
o Under the nipple, there is a region covered by the areola where lactiferous ducts
enlarge and form a lactiferous sinus
- Lactiferous sinus is a reservoir that can hold a large amount of milk
o Purpose of lacteriferous gland: when baby latches on and starts suckling, it
immediately gets food and does not stop suckling and continues to suckle
o Lactiferous sinus is an expansion of the lumen of a lactiferous duct
- For the baby to grab hold of the nipple, there are smooth muscle bundles within the CT
under the nipple in the areola that form a ring like structure and also runs radially
o This is the same in males and females
o Smooth muscle reacts to stimuli
o Nipple gets erect when touched or when cold
o This is to provide a large SA for the baby to latch on
Development of the mammary gland
- 1. Dermal mesenchymal cells induce formation of epithelial bug
o Early on in the embryo, there are groups of epithelial cells that are located from the
axilla region to the groin (called milk lines)
o Cells in the epithelium are prone to stimulation from mesenchymal cells underneath
o In humans only two mammary glands develop along milk lines
o Epithelial cells (under influence of signals from adipose tissue and mesenchyme)
form chords
- 2. Adipose stimulate branching of epithelial mammary cords
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find more resources at oneclass.com
o Bud starts to develop into mammary gland
- 3. Mammary cords become hollow and some luminal epithelial cells differentiate into
myoepithelial cells
o Cells differentiate into two main cell types
o Luminal cells form the ducts and secretory cells (after puberty and during lactation)
▪ These are the cells that secrete product
▪ Luminal cells (depending on location), if they are at the end of the duct
system, form secretory cells and if they are further down they form duct
cells
o Myoepithelial cells are of epithelial origin and help in squeezing the product out into
the duct system
- Image is of developing mammary gland
- There are two distinct cell types present in the developing mammary gland
- Chords invades the CT and there are cells at the tip that can differentiate to become outside
myoepithelial cells or they proliferate to become luminal cells
- For the structure to become hollow, the inner most cells undergo apoptosis
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Areola: highly pigmented area surrounding the nipple: under hormonal influences during pregnany, the pigmentation changes. Nipple is designed as the exit point of the mammary gland. Entire gland is a modified apocrine sweat gland: eccrine sweat glands are underneath skin vs. apocrine sweat glands produce pheromones, modified because it produces milk rather than general sweat substance. Gland secretes only partially by an apocrine mechanism: apocrine sweat glands secrete by merocrine. Milk secreting mammary gland is an example of an apocrine gland: part of the milk product is released in an apocrine mechanism. Mammary gland is embedded in dense ct (reticular layer of the dermis) and adipose tissue. Size of the breast is not determined by how much glandular tissue is present. Size is determined by how much adipose tissue is present: no impact on production of milk, e. g. small breasts can produce same amount of milk as large breasts. Mammary gland undergoes changes during development, puberty and pregnancy.
