Reproductive Physio 5 Flashcards
What happens during late pregnancy? Towards the end of the last trimester?
Irregular uterine contractions increase in frequency in the last month of pregnancy.
The difference between the body of the uterus and the cervix becomes evident at the time of delivery.
The cervix, which is firm in the nonpregnant state and throughout pregnancy until near the time of delivery, softens and dilates, while the body of the uterus contracts and expels the foetus.
Towards term rising oestrogen levels increase the ratio of oestrogen to progesterone.
Makes the myometrium more sensitive to stimuli that promote contractions.
Oestrogen secretion is also increased by rising foetal cortisol levels.
Overpowers the uterine-calming effects of progesterone
Describe the process of parturition
The process of giving birth to offspring, characterised by uterine contractions to expel the foetus from the mothers body.
Mainly facilitated by oestrogen, oxytocin and prostaglandins.
Oxytocin stimulates the contractions of labour.
Oestrogens increase the number of oxytocin receptors in the myometrium and the decidua (the endometrium of pregnancy).
Uterine distention late in pregnancy may also increase their formation.
These receptors increase more than 100-fold during pregnancy and reach a peak during early labour.
The posterior pituitary progressively boosts its secretion of oxytocin in late gestation, towards delivery.
Once labour starts, the uterine contractions dilate the cervix, and this dilation in turn sets up signals in afferent nerves that increase oxytocin secretion.
The plasma oxytocin level rises and more oxytocin becomes available to act on the uterus.
Thus, a positive feedback loop is established that aids delivery and terminates on expulsion of the products of conception.
Explain the positive feedback of oxytocin secretion during childbirth
What is the role of oxytocin in parturition?
Oxytocin increases uterine contractions in two ways:
It acts directly on uterine smooth muscle cells to make them contract.
It stimulates the formation of prostaglandins in the decidua, which enhance the oxytocin-induced contractions.
The foetal pituitary also secretes oxytocin, which increases prostaglandins even further.
As labour nears, oxytocin begins to stimulate stronger, more painful uterine contractions.
KEEP IN MIND THAT: During labour, spinal reflexes and voluntary contractions of the abdominal muscles (“bearing down”) also aid in delivery. However, delivery can occur without bearing down since paraplegic women can go into labour and deliver.
What is lactation?
The process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to an infant sucking at the nipple
What are the functions of breast milk?
Breast milk:
1. provides ideal nutrition and passive immunity for the infant,
2. encourages mild uterine contractions to return the uterus to its pre-pregnancy size (i.e., involution)
3. induces a substantial metabolic increase in the postpartum person, consuming the fat reserves stored during pregnancy.
Describe the structure of a lactating breast
Mammary glands are modified sweat glands.
The non-pregnant and non-lactating female breast is composed primarily of adipose and collagenous tissue, with mammary glands making up a very minor proportion of breast volume.
The mammary gland is composed of milk-transporting lactiferous ducts, which expand and branch extensively during pregnancy in response to oestrogen, growth hormone, cortisol, and prolactin.
Progesterone causes clusters of breast alveoli (lined with milk-secreting cuboidal cells, or lactocytes) to bud from the ducts and expand outward toward the chest wall.
Breast alveoli are balloon-like structures lined with milk-secreting cuboidal cells, or lactocytes, that are surrounded by a net of contractile myoepithelial cells.
Milk is secreted from the lactocytes, fills the alveoli, and is squeezed into the ducts.
Clusters of alveoli that drain to a common duct are called lobules; the lactating female has 12–20 lobules organized radially around the nipple.
Milk drains from lactiferous ducts into lactiferous sinuses that meet at 4 to 18 perforations in the nipple, called nipple pores.
The small bumps of the areola (the darkened skin around the nipple) are called Montgomery glands.
They secrete oil to cleanse the nipple opening and prevent chapping and cracking of the nipple during breastfeeding.
How do the breasts develop in pregnancy?
Many hormones are necessary for full mammary development.
In general, oestrogens are primarily responsible for proliferation of the mammary ducts and progesterone for the development of the lobules.
During pregnancy, prolactin levels increase steadily until term, and levels of oestrogens and progesterone are elevated as well, producing full lobuloalveolar development.
However, oestrogen, progesterone, and other placental hormones inhibit prolactin-mediated milk synthesis during pregnancy
What is the let-down reflex?
When the infant suckles, sensory nerve fibres in the areola trigger a neuroendocrine reflex that results in milk secretion from lactocytes into the alveoli.
The posterior pituitary releases oxytocin, which stimulates myoepithelial cells to squeeze milk from the alveoli so it can drain into the lactiferous ducts, collect in the lactiferous sinuses, and discharge through the nipple pores.
It takes less than 1 minute from the time when an infant begins suckling (the latent period) until milk is secreted (the let-down)
How does the composition of breast milk change in pregnancy?
In the final weeks of pregnancy, the alveoli swell withcolostrum, a thick, yellowish substance that is high in protein but contains less fat and glucose than mature breast milk.
It is secreted during the first 48–72 hours postpartum and is rich in immunoglobulins, which confer gastrointestinal, and also likely systemic, immunity as the newborn adjusts to a nonsterile environment.
As the infant goes through growth spurts, the milk supply constantly adjusts to accommodate changes in demand.
Mature milk changes from the beginning to the end of a feeding.
The early milk, calledforemilk, is watery, translucent, and rich in lactose and protein.
Its purpose is to quench the infant’s thirst.
Hindmilkis delivered toward the end of a feeding.
It is opaque, creamy, and rich in fat, and serves to satisfy the infant’s appetite.
