(05) Mammary Gland & Lactation Flashcards
(1)
(intro)
As the name implies, mammary glands are a distinctive feature of the class Mammalia and are found in all members of its subclasses: the monotremes, marsupials and eutherians. Almost without exception, successful reproduction in the mammals requires lactation from functional mammary glands for its completion. Their development has allowed intense maternal investment in offspring to continue beyond the time of parturition, permitting birth of young at a stage of development where they would otherwise not survive.
(2)
- Monotremes (prototherians: platypus and echidna), lay eggs and have very altricial young.
do they have nipples?
mammary glands discharge into specialized area of skin called what?
- have a short gestation period (usually just the length of the luteal phase of the estrous cycle) and the young are born at an immature, almost embryonic, stage. Following birth they climb unaided to the pouch and attach to a nipple (located in the pouch). This subsequently swells and they are fixed to it, unable to detach until they have achieved sufficient growth. It has been said that marsupials “have exchanged the placenta for the teat”.
- Within the eutherians (true placental mammals) neonatal development varies from what to what?
all dependent on milk?
- no
areola (from where the young lick it up)
- altricial to precocious
yes - for the early part of post-uterine life
(3)
(Comparative Mammary Gland Anatomy)
(External Anatomy)
- what animals can have non-paried nipples sometimes?
- what have two?
what have 18?
- (positioning)
thorax?
abdominal
inguinal
all along ventral thorax, abdomen and inguinal region
almost dorsal
determined when?
- (shape)
flattened sheets
flat circular
prominent
dependent
- In all species each mammary gland has nipple/teat - except what?
- in what species is the nipple absent in males?
- marsupials (can fuse into single gland during development –> odd numbers)
- humans, sheep, goats
sow
- primates, elephants, bats
whales
cow, goat, sheep
sow, rat, rabbit
coypu
embryonic development
- rat
rabbit
human
ruminants
- monotremes
6 mouse and rat
(4)
(Internal anatomy)
- mammary gland consists of what 2 basic types of tissue?
- structure of milk secreting tissue similar across species
what is basic milk secreting structure?
what is it?
- outside this layer is what?
which have important properities for what?
- beyond this is what?
- outside this?
- each alveolus discharges its secretion through what?
- parenchyma (secretory) and supporting tissue (stroma)
- alveolus
sack lined by single layer of secretory epi cells (cont w/ those lining ducts)
- myoepithelial layer (aka basket cells)
contractile properties for milk-let down
- basement membrane
- network of capillaries that brings in raw materials for milk synthesis
- a capillary milk duct
(5)
(Internal anatomy cont)
- alveoli arranged how?
2 the individual capillary milk ducts empty into what?
- These enter into progressively larger ducs to provide what?
- Each lobule is surrounded by what?
groups of lobules further arranged into what?
- groups or clusters termed lobules (like grapes)
- the intralobular ducts
- route for milk removal
4 CT
lobes
(6)
(Diff in int anatomy)
- While the secretory tissue is identical across species, differences are manifested in the anatomy and arrangement of the duct system.
- In monotremes, major ducts discharge where?
- In dogs and humans?
- In cow, goat, sheep?
- In the mare and sow, 2 gland systems, with their relatively small (compared to ruminants) gland and teat cisterns are drained by a single teat - the teat has what?
- ducts discharging at the nipple (or skin in monotremes) are called what?
- directly onto skin of alveolus or mammary patch
- 12-20 major ducts have openings on each nipple
- major duct empty into large cistern (cont with teat cistern) –> drained via single streak canal
- 2 openings or streak canals. one for each gland system
- galactophores
(7)
(Anatomy cont)
- Outside the glandular tissue is what?
functions as what?
The mammary epi cells (which create the duct and alveolar systems) will not grow unless what?
- stroma (mix of CT and fat) - termed fat pad
supporting tissue (essential for normal development of parenchyma)
placed in an environment of adipose tissue
(8)
(Supporting Structures are best descrbed in cow)
- udder is divideded into distinct left and right by what?
composed of what?
elastin acts as what in lactating cows?
what are two other supporting structures?
- udder skin provides little support but is barrier to infection
- median suspensory ligament
elastin and collagen
shock absorber
lateral suspensory ligaments, and lamellar plates (both project into/are interspersed w/ parenchyma)
(9)
(Mammary Development in the Embryo and Fetus)
(Embryonic development)
- mammary glands derived from what?
- development of the glands begins as bilateral thickening of ectoderm on what?
- This then develops through a defined series of changes, during which they become discontinuous, to finish as what?
- What are these?
- embryonic ectoderm
- ventrolateral aspect of developing embryo
- the mammary buds
- spheres of ectodermal cells that have grown into the underlying mesoderm in loactions of future mammary glands (spec spef)
(10)
(Mammary Development in the Embryo and Fetus)
(Fetal Development)
(Primary Cord)
- As soon as the bud attains its spherical shape the next stage commences. Groups of cells proliferate out of the sphere and form cords of cells that elongate deeper into the dermal tissue to form the what?
base of which remains attached to what?
number of primary cords that grow out of each bud will determine what?
(secondary cords)
- Once the primary cord attains a certain size, its distal end branches to form what?
These in turn elongate into cords which will eventually form what?
(Canalization of the cords)
- While they are elongating, the cords also increase in diameter. The result of this is what?
(Supporting Tissue)
- Connective tissue supporting structures for the mammary gland also form during fetal life. In the fetal heifer, with further growth of the 4 glands and their fat pads, the median suspensory ligament becomes more prominent and four distinct quarters are palpable by the time of birth.
- primary mammary cord (aka primary spout)
epidermis ((it is growing down into deeper tissues so its base is at the surface)
number of ducts that will open into nipple
- 2 or more secondary buds
large milk ducts (in ruminants will discharge into gland cistern)
- cells in the center of the cord get further away from their nutrient source, supplied by small capillaries, and they die
(Thus the cords become hollow (canalization) and form the mammary ducts.)
(11)
(Control of Embyronic and Fetal Mammary Development)
- While the mammary gland is derived from ectoderm (=epithelium = embryonic skin), its development is controlled by factors from what?
- To this end, early in development a layer of adipose tissue cells surround the mammary bud. Subsequently other epithelial structures that form during mammary differentiation are also surrounded by adipose tissue.
What is a prerequisite for successful mammary growth?
- Is there any requirement for ovarian factors (steroid hormones) in the development of mammary glands in fetal life?
- In species such as mice and rats, the influence of testosterone in male fetus causes primary mammary cord to do what?
this results in what?
- local mesenchyme
(Mesenchyme, which arises from the mesoderm or middle layer of the embryo (ectoderm-mesoderm-endoderm) forms connective tissues, fat (adipose tissue) and blood among other things)
(Removal of mammary mesenchyme prevents formation of the mammary gland.)
- adequately formed mammary fat pad
(From early fetal life the female develops a more extensive fat pad than her male counterpart.)
- NO!!
- lost its attachement to surface epi during later fetal life
male mice and rats have no nipples (same with horse/beaver)
(12)
(Mammary Development: From Birth To puberty)
- At birth the mammary gland consists of a rudimentary duct system that opens at a small nipple. The gland shows general growth at an what rate?
- Several weeks prior to puberty, depending on species, the growth of the mammary gland becomes what rate?
this is due to what?
- isometric (same rate as rest of body)
(There is also some maturation of parts not clearly defined at birth such as the teat sphincter.)
- allometric (faster than rest)
increased secretion of ovarian hormones (estrogen) from developing follicles during this period (mammary gland growth in males and ovariectomized females continues at an isometric rate)
(13)
(Mammary Development Following Puberty)
Which component of the mammary tissue grows, how quickly and to what extent following puberty (in a nonpregnant animal) depends on the species examined and on the type of estrous cycle they have.
- Animals with ultra short cycles and virtually non-existent luteal phases (mouse, rat) have what kind of growth?
- Primates have a longer cycle and full luteal phase, and here duct development is what?
- In the bitch, with a long luteal phase that can be considered a pseudopregnancy, this duct growth is accompanied by what?
- mostly duct growth and alveoli are rarely formed
- almost full, to the extent of formation of the fine ductules that indicate the future lobules, which also contain a few alveol
(This also applies to most of our domestic species that have short cycles)
- considerable lobulo-alveolar development
(This degree of development is only seen during pregnancy in other species.)
(14)
(Attainment of Full Alveolar Development)
The time when mammary development reaches the anatomic stage that it would be competent to secrete milk for offspring (full alveolar development) if appropriately stimulated depends on species:
- Full alveolar development in monotremes occurs in response to what?
- In marsupials the development in pregnant and non-pregnant females is what?
Full development is
dependent on the suckling stimulus of what?
- In the eutherian mammals, full development of the mammary gland is only completed when?
he growth of the gland during pregnancy in nearly all eutherian species fits an exponential curve, where the overall rate of growth is inversely proportional to what?
Usually it is not until when that lobulo-alveolar development really takes off?
- egg incubation
- identical (Pregnancy generally being the same length or even slightly shorter than an estrous cycle.)
the permanently attached pouch young.
- during pregnancy or even early lactation
gestation length for that species
the second half of gestation
(15)
(Attainment of Full Alveolar Development cont)
- During pregnancy, the mammary fat pad is slowly infiltrated and the adipose cells replaced by what?
- Developing alveoli arranged in lobules take over much of the gland volume previously occupied by stroma. By the last third of pregnancy the stroma is represented by thin bands of connective tissue that divide the lobules and, at a higher level, regions of lobules into lobes.
- In some species, such as ruminants, the alveolar cells will begin to secrete when?
In other species secretion doesn’t commence until when?
- n all species there is burst of secretory activity when?
- Prior to this, full secretory activity is held in check by what?
- duct tissue, alveoli, blood and lymphatic vessels, and connective tissue supporting structures.
2 in the last third of pregnancy, and the alveolar lumen becomes distended
just before parturition
- just prior to, or just after, parturition
5 the high circulating progesterone levels.