Physiology of pregnancy and lactation Flashcards by Youssef El Soussi

How does the oocyte enter the fallopian tube?

The rupture of the graffin follicle releases a secondary oocyte arrested in meiosis 2 with 23 chromosomes that is surrounded by the zona pellucida and corona radiata
The fimbriated ends are lined by ciliated columnar cells, stimulated by estrogen, which beat towards the opening in order to get the ovulated egg to the uterus with a success rate of 98%
Even if one fibria is missing the other fallopian tube can pick up the egg

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What guides the secondary oocyte to the uterine cavity?

Chemoattractants
Chemical stimuli
Estrogen is secreted (which increases the beating of the fallopian tube cells)

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How is the sperm transported towards the ovum?

Once ejaculation occurs, few sperms are transported upwards from the vagina through the uterus and then fallopian tube and then the ampulla
The sperm transport is mediated by the uterus and fallopian tube contraction, prostaglandins in the seminal fluid, and the oxytocin from the post.pituitary

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What is meant by sperm capacitation?

It is a process that takes 1-10 hours, which is the collective changes that occur in the sperm after meeting the female genital tract, enabling their fertilization capacity, it occurs as:

1) The fluid of the uterus and the fallopian tube washes away the inhibitory factors in the semen

2) The sperm swims away from the cholesterol vesicles (allowing the entry of calcium)

3) Calcium influx, which makes the sperm very motile and changes the cellular membrane to release the acrosomal enzymes (once in contact with the oocyte)

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Summarize the capacitation process

1) Washing of inhibitory factors

2) Removing the cholesterol covering

3) Entry of calcium

4) Weakening the membrane of the acrosomal head

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What is the acrosomal reaction?

It is the process by which the secondary oocyte loses the granulosa cells that cover it

As the sperm nears the ovum, it must first navigate through the surrounding granulosa cells. During this journey, the acrosomal cap continues to weaken, though the full acrosomal reaction has not yet occurred. Some hydrolytic enzymes are gradually released, helping the sperm penetrate this outer layer. Once it reaches the zona pellucida, the sperm binds to specific receptors—primarily ZP3—triggering the full acrosomal reaction needed to penetrate the glycoprotein layer and reach the oocyte membrane

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Describe the acrosomal reaction

1) Oriteolytic enzymes in the female tract strip off the glycolytic coat on the acrosomal cap (allowing the release of more hyaluronidase)

2) Hyaluronidase will depolarize the hyaluronic acid polymers that hold the granulosa cells

3) Proteolytic enzymes will digest the proteins in the structural elements of tissue cells that adhere to the ovum

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What happens next during the acrosomal reaction?

Triggered by the binding of the sperm to the ZP3 receptor in the zona pellucida
In this reaction, the acrosome will rapidly dissolve the zona pellucida for the sperm head to enter, allowing the cell membrane of the sperm head and the oocyte to fuse, forming a new cell

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What prevents the entry of more than one sperm into the oocyte (cortical reaction)?

1) Fast block (massive Na influx)

2) Slow block

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What is the fast block?

Occurs as soon as the first sperm head penetrates the ovum

1) Massive influx of sodium is triggered

This influx of sodium depolarizes the ovum, making it positive inside, repelling the positively charged sperm (and thus inhibiting their penetration)

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What is the slow block?

Depolarization created by the massive influx of sodium triggers the influx of calcium

1) The calcium will facilitate the exocytosis of several secretory cortical vesicles

2) These secretory vesicles inactivate the ZP3 receptors and harden the zona pellucida

3) Initiates the release of zinc ions, which helps reinforce the block of polyspermy by further hardening the zona pellucida, Zinc also activates the oocyte, supporting the completion of meiosis 2

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Where does fertilization occur?

Ampulla of the fallopian tube

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How do a sperm and an egg cell unite to form a zygote?

1) Sperm enters the oocyte:

This triggers the egg to complete meiosis 2
A second polar body is removed to remove the extra chromosomes
The egg becomes a mature ovum

2) The sperm head becomes a male pronucleus:

Once inside the egg, the sperm loses its tail
The head will then swell and form a pronucleus

3) Ovum forms a female pronucleus:

4) Fusion of the pronuclei:

The membranes of the two pronuclei break down
The chromosomes align and pair up, resulting in 46 chromosomes in the zygote

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What happens after fertilization occurs?

3-5 days are required for the transport of the zygote to reach the uterine cavity
The zygote undergoes several cell divisions (becomes a blastocyst), and gets its nutrition from the secretion of the fallopian tube

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From where does the zygote get its nutrition before implantation occurs?

From the secretions of the fallopian tube, stimulated by progesterone

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What facilitates the transport of the zygote along the fallopian tube?

1) Fluid current (due to the epithelial secretions)

2) The action of the ciliated epithelium

3) The contractions of the fallopian tube

How does the implantation of the blastocyst occur?

It remains in the uterine cavity for 1-3 more days, where implantation occurs 5-7th day post-ovulation
Before implantation, the blastocyst obtains its nutrients from the uterine secretions called the (uterine milk)
Trophoblast cells will then develop over the surface of the blastocyst and secrete proteolytic enzymes to digest the cells of the uterine endometrium (allowing the blastocyst to obtain nutrients from the digested endometrial tissue and the blood vessels)
After implantation occurs, the trophoblast cells, together with the cells from the blastocyst and endometrium, proliferate to form the placenta and other membranes of pregnancy
After the trophoblast has sufficiently invaded the endometrium, progesterone stimulates the decidual reaction. This leads to the transformation of endometrial cells into decidual cells, which provide a more stable and continuous source of nutrition for the embryo. This shift to relying on decidual cells typically occurs a few days after implantation, as the decidual reaction becomes fully established

Before implantation, from where does the blastocyst obtain its nutrients?

Uterine secretions (uterine milk)

What are the important hormones in pregnancy?

1) Estrogen

2) Progesterone

3) Human chorionic gonadotropic

4) Human chorionic somatomammotropin (human placental lactogen)

What secretes the hCG?

The syncytotrophoblast (trophoblastic cells)

It can be measured 8-9 days after ovulation, and it reaches its maximum concentrations at weeks 10-12, and decreases by the 16-20th week

What are the functions of the human chorionic gonadotropin?

1) Prevents the involution of the corpus luteum (and thus maintains progesterone and estrogen)

Progesterone and estrogen are important (as they continue the endometrial growth and accumulation of nutrients)

2) It stimulates the interstitial cells of the testes of males (testosterone production, crucial for the formation of male sexual organs and the descent of the testes. By the end of pregnancy, testosterone levels play a key role in the final descent of the testes into the scrotum)

If the corpus luteum is removed before the 7th week, abortion would occur (as normally it should involute slowly after 13-17 weeks of pregnancy

What are the structures that secrete estrogen during pregnancy?

It is secreted by the ovarian follicles, then by the corpus luteum (stimulated by LH), and finally by the placenta
Placenta does not synthesize estrogen de novo; rather, it converts it from its precursor provided by the adrenal glands of both the mother and the fetus
98% of estrogen is bound to SHBG (sex-hormone binding globulin), which binds to testosterone

What is the function of estrogen during pregnancy?

1) Enlarges the mother’s uterus

2) Enlarges the mother’s breasts

3) Stimulates the growth of the mother’s breast ductal structure

4) Enlarges the mother’s external genitalia

5) Relaxes the pelvic ligament of the mother, and the symphysis pubis becomes elastic (allowing an easier passage of the fetus through the birth canal)

Estrogen = proliferation

What are the functions of progesterone during pregnancy?

Moderate quantities are secreted by the corpus luteum, and then tremendous quantities are secreted by the placenta

1) Develops the decidual cells in the endometrium to provide nutrition to the early embryo

2) Decreases the contractility of the uterus (preventing abortion)

3) Increases the secretion of the mother’s fallopian tubes and uterus to provide nutrition to the developing blastocyst

4) Helps prepare the mother’s breast for lactation

Progesterone = secretions

What are the functions of the human chorionic somatommamotropin?

- Secreted by the placenta at the 5th week of pregnancy (its concentration rises steadily through pregnancy, directly proportional to the weight of the placenta) 1) Prolactin-like function 2) Weak GH action 3) Decreases insulin sensitivity and utilization of glucose by the mother (more glucose for the baby) 4) Releases free fatty acids from the mother stores (providing an alternative energy source for the mother's metabolism)

What is relaxin?

- It is a hormone secreted by the corpus luteum under the stimulation of hCG and the placental tissue (peaks in the first trimester) 1) Relaxes the mother's pelvis outlet 2) Inhibits uterine muscle contractions 3) Maintains the uterine rest and prevents abortion 4) Later, it facilitates the easier passage of the fetus into the birth canal once labor begins

What are the stages of a baby's birth?

1) Stage 1: period from the onset of the uterine contraction until dilation is complete 2) Stage two: Period from the time of maximal cervical dilation until the baby exits 3) Stage three: the process of expulsion of the placenta through the vagina

What increases the excitability of the uterine musculature?

1) Hormones 2) Mechanical factors

How do the hormonal factors increase the excitability of the uterine contractions?

1) Increased ratio of estrogen to progesterone - From the 7th month, estrogen secretion continues to increase while progesterone secretion remains constant - Estrogen increases the contractions (while progesterone decreases them) 2) Oxytocin - Its secretion increases during labor - Uterine contractions increase due to the increasing number of oxytocin receptors on the uterine muscle 3) Fetal hormones: 1) Oxytocin by the fetal pituitary 2) Cortisol by the fetal adrenal glands 3) PGs by the fetal membrane

What are the mechanical factors that increase the excitability of the uterine musculature?

1) Strech of the uterine musculature 2) Strech of the cervix

How does labor start?

1) Baby moves deeper into the canal 2) The receptor in the uterus senses the increased pressure 3) Nerve impulses are sent to the brain 4) The hypothalamus receives impulses and stimulates the posterior pituitary gland 5) Oxytocin is released from the posterior pituitary, stimulating the contraction of the uterus - CYCLE KEEPS ON REPEATING STRONGER AND IN A SHORTER INTERVAL

Describe the structure of the mammary gland

1) It consists of lobes: - Each lobe contains several secretory lobules, which are separated by dense connective tissue 2) The nipple on each breast contains ducts from the mammary gland to the surface

What stimulates the development of the breasts?

1) Estrogen (stimulates the growth of the ductal system) 2) Progesterone (it is responsible for the final development of the breasts into a milk-secreting organ) 3) Prolactin for milk 4) Oxytocin for the milk to get out

What are the changes that occur in the best during pregnancy?

1) Increased size 2) Increase in the size and darkening of the nipples 3) Production of colostrum (yellowish precursor to the breast milk)

What is the hormonal control of the mammary gland during pregnancy?

1) Estrogen: stimulates the growth and branching of the ductal system 2) Progesterone: stimulates the development of the alveolar gland 3) Placental lactogen: promotes the development of the breast - The action of prolactin is inhibited by the placental hormones

What is the hormonal control of the mammary gland following childbirth?

1) Prolactin actions are not inhibited anymor,e and thus the breast begins to produce milk 2) Mechanical stimulation of the breast = secretion of milk 3) Oxytocin stimulates the release of milk from the ducts 4) Prolactin is released as the breastfeeding continues

FYI

- Prolactin levels increase throughout pregnancy, but its action is inhibited by high levels of estrogen and progesterone produced by the placenta. After childbirth and the delivery of the placenta, estrogen and progesterone levels drop, relieving the inhibition on prolactin. Although prolactin levels naturally begin to fall, breastfeeding provides a mechanical stimulus that triggers a positive feedback loop, maintaining prolactin secretion for milk production. This is why early initiation of breastfeeding is recommended—delaying it may allow prolactin levels to drop too low, potentially affecting milk supply - Prolactin stimulates the cuboidal alveolar epithelial cells in the mammary glands to produce milk. In contrast, oxytocin acts on the myoepithelial cells surrounding the alveoli, causing them to contract and eject the milk through the ducts during breastfeeding