Slide Set 3: Mammogenesis Flashcards
What are the phases of the mammary gland?
- mammogenesis (development of the mammary gland)
- lactogenesis (initiation of lactation)
- galactopoiesis (maintenance of lactation)
- involution (regression of mammary gland)
Define mammogenesis
The development of the mammary gland
☛ Starts in early embryonic stages
☛ Ceases after initiation of lactation (lactogenesis)
What are the stages of mammogenesis?
☛ Development before birth
☛ Development after birth to pregnancy
☛ Development during pregnancy (the most important part for milk production)
☛ Development during lactation
What are the steps of the mammary growth during lactation cycle?
prepuberty –> postpuberty –> conception –> pregnancy –> parturition –> secretory phase –> weaning –> involution
What type of growth do we observe in terms of mammogenesis and DNA?
during mam,ogenesis the DNA has exponential growth - increase in increasing rates
What is the relationship between mammogenesis (DNA) and length of the pregnancy?
there is an inverse relationship between the gestational period and mammogenesis
meaning the shorter the gestational period the faster the mammogenesis
What is the reason that mammogenesis continues even after birth?
mammogenesis cannot stop after brith bc it is going really fast it will continue to develop for these animals (guinea pig, goat, cow)
What are the 3 cell layers of an embryo?
ectoderm
mesoderm
endoderm
Which cell layers of an embryo give rise to the mammary gland?
ectoderm
mesoderm
What are the embryonic stages of mammogenesis?
ectoderm –> mammary band –> mammary streak –> mammary line (ridge)–> mammary crest –> mamary hillock –> mammary bud
What is a third nipple called?
polythelia
What is the first sign of mammogenesis?
mammary band
What determines the amount of mammary glands?
2 mammary buds = 2 mammary glands
What is polymastia?
Polymastia, supernumerary breasts, is the condition of having an additional breast. Extra breasts may appear with or without nipples or areolae. Can happen in both sexes
How does mammogenesis proceed in the fetal stage?
- Mature mammary bud sinks into the mesoderm giving rise to a primary sprout
- Primary sprout gives rise to galactophores (fore-runner of teat & gland cistern) Maximum growth @13 wk of age
- More cell multiplication gives rise to secondary sprout which gives rise to mammary duct and canalization
How is the number of teat openings determined?
the number of primary sprouts equals to the amount of teat opening and humans have around 15
What is canalization?
removal of cells making a hole
What are the steps of mammogenesis before birth?
☛ The gland cistern is formed by a continual growth of the lumen (15 weeks)
☛ The formation of the teat cistern occurs with the progressive canalization of the primary sprouts towards the distal end (16 weeks)
☛ Streak canal is formed after the narrowing of the teat cistern
☛ Most of mammogenesis takes place during the first 6 months
How are the gland cisterns formed?
The gland cistern is formed by a continual growth of the lumen (15 weeks)
How are the teat cistern formed?
The formation of the teat cistern occurs with the progressive canalization of the primary sprouts towards the distal end (16 weeks)
How is the streak canal formed?
Streak canal is formed after the narrowing of the teat cistern
When does the most of mammogenesis take place?
Most of mammogenesis takes place during the first 6 months
Connective tissue and fatty pad (stroma) arise from _____
the mesoderm
Connective tissue and fatty pad (stroma) provide _____
support and regulatory control of
mammogenesis
Why doesn’t males form mammary glands?
- testosterone
- The proximity of fatty pad to scrotum in male fetus terminates mammogenesis in early stages
Most mammary growth before birth is complete during the ______ of fetal growth
first 6 month
What happens to mammogenesis at birth?
☛ Teats are well developed
☛ Non-secretory tissues (stroma) are well developed
☛ Gland and teat cisterns are well developed
☛ Vascular and lymphatic systems comparable with those of adults
☛ Skin and hair covering the udder are comparable with those of adults
☛ Mammary glands are distinct entities but not yet formed into an udder
Three stages in mammogenesis after birth in bovine
1- Isometric growth (A growth rate similar to the body’s)
2- Allometric growth (3.5 times higher than the body’s)
3- Isometric growth
Explain isometric growth 1:
☛ During 2- 3 months after birth
☛ Growth mostly fat pad and connective tissues
☛ No development of the secretory tissues
Explain Allometric growth (during recurring estrus cycles):
☛ Begins just prior to onset of estrous cycle
☛ Continues for 2-3 months after puberty (7-9 months
of age)
☛ Will not occur in the absence of the fat pad
☛ Mostly ductular growth (duct thickening, lengthening & branching)
Allometric growth is under the influence of:
☛ Estrogen (follicular phase) –> Elongation & branching of ducts
☛ Progesterone (luteal phase) –> Widening and enlargement of ducts
What are the steps of ductular growth?
1- Duct growth from a single duct 2- Branching 3- Complex branching 4- Compound branching 5- end buds form on ends of ducts 6&7- Enlargement in response to hormonal stimuli
Explain isometric growth 2:
☛ 12-15 months (until conception)
☛ Some ductular growth and branching
☛ Udder quarters continue to grow (mainly adipose tissue), and fore and rear quarters approach each other, until become joined at the base
The major portion of mammary growth occurs during ______
pregnancy
Explain mammogenesis during pregnancy
☛ Growth is controlled by estrogen and progesterone
☛ Growth is mainly ductule-lobular during the first
1/2 of gestation (mostly ductular growth)
☛ During the second 1/2, growth is mostly lobule- alveolar (mostly alveolar growth)
What happens during the first 3 months of mammogenesis in pregnancy?
Duct proliferation (progesterone inhibits lactation)
What happens during the 4th-7th months of mammogenesis in pregnancy?
Development of secretory tissue (alveolar development)
What happens during the 9th months of mammogenesis in pregnancy?
Secretory activity
What happens when someone gets ovariectomy?
when you remove the ovaries the mammogenesis stops
What are the roles of progesterone and estrogen in mammogenesis during pregnancy?
☛ Accelerate the rate of cell division in the mammary gland (terminal end buds)
☛ Estrogen alone stimulates mammary duct growth
☛ Progesterone alone stimulates formation of alveoli
☛ Synergistically, progesterone and estrogen induces lobule-alveolar development
How does mammogenesis proceed in lactation? Give examples such as rats and mice and guinea pigs.
☛ Continue to increase in early lactation (up to peak of lactation)
☛ Increases in DNA from parturition to day 2-5 of lactation are rapid in rats , guinea pigs and rabbits
☛ Rats and mice: max at day 10
☛ guinea pigs and goats: max at day 5
☛ If suckling by the young is not permitted, the increase in DNA after parturition will not occur
What happens in the first month of gestation in terms of mammogenesis of the baby?
two primitive mammary streaks
What happens by week 5 in terms of mammogenesis of the baby?
Streaks become milk lines by week 5
What happens by week 7&8 in terms of mammogenesis of the baby?
Milk lines grow inward into the chest wall (week 7&8)
What happens by week 12 to 16 in terms of mammogenesis of the baby?
- Some cells differentiate into smooth cells of the nipples and areola
- Development and branching of mammary buds
- Placental sex hormones enter fetal circulation to stimulate canalization of branched epithelial cells (continue to week 32)
What happens by week 32 to 40 in terms of mammogenesis of the baby?
- Ductal development
- Fetal mammary tissue mass increases 4-time its original mass
- Further development and pigmentation of nipples and areola
- Growth during childhood is limited to general growth
What happens at puberty (10-12 years) in terms of mammogenesis?
- Primary and secondary ducts grow from terminal end bud under influence of estrogen (follicular phase), progesterone (luteal phase) and growth hormone
- Estrogen and growth hormone (pituitary factor) become the major factors influencing mammogenesis
- Growth of primary and secondary ducts to form terminal end-bud (TEB)
- TED develops into new branches and ductules (give rise to alveoli or acini
- moderate mammogenesis, branching and widening of the ducts.
Which hormones are involved in mammogenesis at puberty?
estrogen and growth hormone (pituitary factor)
What happens in term of mammogenesis at the beginning of each menstrual cycle?
- Proliferation and active growth of duct tissue occur during follicular luteal phase (maximum at late luteal phase)
- Enlargement occurs due to deposition of fat & connective tissue
- Nipple becomes enlarged and pigmented
- Progesterone fosters further mammogenesis
- Mammogenesis continues until about the age of 35 years
- Prolactin (human placental lactogen) is involved in late stages of mammogenesis
Explain mammogenesis during pregnancy
- Complete development occurs only during pregnancy (mostly due to progesterone) Other hormones: prolactin
- More intense growth and branching of mammary ducts into ductal, alveolar and myoepethilial tissues in preparation for lactation
- Ductal growth is predominantly controlled by estrogen, whereas alveolar growth is a progesterone effect facilitated by estrogen
- Estrogen also stimulates the release of prolactin (from 20 to 200 ng/ml during pregnancy)
- Prolactin & estrogen act together to stimulate lobulo-alveolar tissues
- Prolactin also induces the enzymes necessary for aleveolar secretory activity after parturition
- In the presence of estrogen and prolactin, progesterone stimulates alveolar growth and inhibits lactose synthesis
- High concentrations of estrogen and progesterone during late pregnancy inhibit the secretory effects (lactation) of prolactin
- Other hormones involved in mammogenesis my include GH & glucocorticoids
Ductual growth during pregnancy during pregnancy is predominantly controlled by _____, where as alveolar growth is a ______ effect facilitated by ______
estrogen
progesterone
estrogen
What inhibits lactation during pregnancy?
High concentrations of estrogen and progesterone during late pregnancy inhibit the secretory effects (lactation) of prolactin
What is the function of progesterone in terms mammogenesis in pregnancy?
In the presence of estrogen and prolactin, progesterone stimulates alveolar growth and inhibits lactose synthesis
What are the other hormones that are involved in mammogenesis in pregnancy?
GH and glucocorticoids
What are the types of lobules?
Type 1 to 4
What is a type 1 lobule?
(at birth) Simple branching of ductular buds around a terminal end bud (TEB)
What is a type 2 lobule?
(after puberty) Changing levels of estrogen and progesterone during menstrual cycles stimulate type 1 to branch new alveolar ducts
What is a type 3 lobule?
(during pregnancy) A marked increase in ductular branching and lobular formation is initiated by luteal and placental hormones
What is a type 4 lobule?
(late pregnancy) Functional secretory tissues with breast milk
What happens during the second trimester in terms of milk appearance?
In the 2nd trimester, colostrum (first milk) appears in the alveoli in small quantities, reflecting the beginning of protein synthesis under the influence of prolactin
What happens during the third trimester in terms of milk appearance?
In the 3rd trimester, the alveoli contain significant amounts of colostrum and the adipose tissues replaced by secretory tissues
TRUE/FALSE
Rats have progesterone
FALSE
progesterone is absent during pregnancy bc rats have a short cycle they cannot produce progesterone unless they are mated/conceived
Explain the mammogenesis in a newborn mice
- Newborn: During the first 3 weeks of life, the mammary ducts elongate and branch slowly. Blood vessels in the fat pad are well visible. The primary duct can also be seen and end buds are faintly visible.
Explain the mammogenesis in a 4 wk virgin mice
Starting at about the 4th week, growth of the mammary ducts increase significantly. The system of ducts begin to
elongate around the lymph node. The end buds are now more visible.
Explain the mammogenesis in a 6 wk virgin mice
Here the gland has just about reached the periphery of the mammary fat pad. There is significant branching and the end buds are quite prominent.
Explain the mammogenesis in a 10 wk virgin mice
The ducts have completely reached the periphery of the mammary fat pad. At this point the terminal end buds form terminal ductal structures with. Ductal development will decrease with the acquirement of sexual maturity.
Explain the mammogenesis in a day 9 pregnancy in mice
At this stage there is extensive and rapid proliferation of the mammary ducts. During pregnancy the mammary gland comes under the influences of estrogen, progesterone, and other placental hormones.
Explain the mammogenesis in a day 16 pregnancy in mice
About 50% of the total growth of the mammary gland occurs during pregnancy from day 12 until term. The mammary epithelium expands vastly. Pregnancy is usually 18-21 days in the mouse.
What is dry period?
☛ Secretory cells degenerate (involution) to prepare for the next lactation
