Physiology of Pregnancy, Parturition and Lactation Flashcards
1
Q
Fertilization steps
A
1) sperm goes through follicular cells and binds zona pellucida (3 glycoproteins)
2) Acrosomal reaction which is Ca dependent- fuse acrosome with the sperm cell plasma membrane
3) Hydrolytic enzymes released to penetrate zona pellucida, the sperm also rapidly oscillates/rocks to aid in penetration process
4) Cell membranes of sperm and oocyte fuse. Cytoplasmic portion of the sperm head and tail enter the oocyte
5) Oocyte undergoes cortical reaction, preventing entry of other sperm (Ca dep)
6) Oocyte completes 2nd meiotic divison, and 2nd polar body expelled
7) Sperm head condenses and becomes Male pronucleus
8) Male and female pronuclei fuse forming zygote.
2
Q
Menstrual Cycle
A
- follicular phase- follicles undergo further development in response to FSH and synthesize androgens which are converted to estradiol under the influence of LH
- ultimately one follicle matures
- uterine endometrium proliferates in response to estradiol
- near midcycle, estradiol rises to a level that initiates positive feedback and thus a surge in LH and FSH release by anterior pituitary which results in ovulation
- during luteal phase the mature follicle becomes the corpus luteum, which secretes progesterone and estradiol
- the uterus undergoes further proliferative and secretory changes
- unless pregnancy occurs, endometrial sloughing and menstruation eventually occur, marking the beginning of a new cycle
3
Q
Fertilization and implantation
A
- fertilization occurs in fallopian tube, and 3-5 days pass as the blastocyst slow makes its way to uterus and another 1-2 days pass before implantation
- of the almost half billion of sperm deposited in the vagina, less than a hundred make their way to the ampulla of the fallopian tube
- in addition to flagella motility, sperm transport is facilitated by contractions of the uterus, cervix, and fallopian tubes in response to oxytocin released during the female orgasm, and prostaglandins in the male seminal fluid
- at this early stage of pregnancy, the corpus luteum continues to produce steroid hormones to maintain pregnancy as the placenta develops from trophoblasts and adjacent cells
4
Q
Human chorionic gonadotropin (hCG)
A
- produced in the syncytiotrophoblasts by the blastocyst
- closely related to LH and sustains the corpus luteum in the face of declining levels of maternal LH. In this manner, sex steroid production increases
- also immunosuppressive agent, growth promoting activity, and promotes placental development
- measured in urine home pregnancy tests
- also stimulates the testes of the male fetus to produce testosterone, leading to male sex organ development
5
Q
Fetal nutrition
A
- early weeks is due to trophoblastic digestion and absorption of nutrients from the endometrial decidua
- later nutrition is provided by diffusion through the placenta
6
Q
Key hormones supplied by placenta
A
- amines, polypetides, proteins, and glycoproteins
- hCG is the most important placental peptide hormone
- steroid hormone synthesis
- also important are somatomammotrpin- coordinate fuel economy by contributing to the conversion of glucose to fatty acids and ketones; they also promote mammary gland development in the pregnant mom
7
Q
Steroid hormones in pregnancy
A
- steroid hormones rise rapidly and remain elevated during pregnancy
- after 8 weeks of gestation the coordinated activity of the maternal placental fetal unit maintains high levels of estrogens and progesterone
8
Q
Maternal fetal placental unit
A
- placenta requires the assistance of both mother and fetus to produce steroid hormones
- unlike the corpus luteum, the placenta itself cannot manufacture adequate amounts of cholesterol, the precursor for steroid hormone synthesis
- the placenta lacks two key enzymes needed for synthesis of estrone and estradiol, and a third enzyme needed for synthesis of estriol- 17 alpha hydroxylase, 17,20 desomlase and 16 alpha hydroxylase
- fetus lacks 3 beta hydrocysteroid dehydrogenase and aromatase
- mother supplies LDL particles
9
Q
Maternal Response to Pregnancy
A
- increased blood volume
- MAP decreases during midpregnancy (vasodilating effects of steroid hormones) and then rises during 3rd trimester, it usually remains lower than normal
- increased cardiac output (increase in stroke volume)
- increases alveolar ventilation (increased tidal volume)
- increased demand for dietary protein as well as iron and folic acid
- the uterus increases fomr 50 gms to 1100, the breasts double in size
- average weight gain 25-35 lbs
- BMR increases -15%
10
Q
Parturition
A
- combination of endocrine, mechanical stretching and paracrine factors are involved
- the uterus is quiescent throughout most of pregnancy due to presence of progestogens and relaxin
- during last month Braxton Hicks
- prostaglandins inititate contractions and they are sustained by oxytoxin and more prostaglandins (PGE2 and PGF2a) produced by a paracrine mechanism to stimulate uterine smooth muscle cells, promote formation of gap junctions between uterine smooth muscle cells which potentiates their response to oxytocin which causes thinning (effacement of cervix)
11
Q
Hormoens and parturition
A
- may be triggered by an increase in fetal production of cortisol near term which increases the ratio of estrogen/progesterone, and thus the sensitivity of the uterus to contractile stimuli
- during pregnancy, estrogen increases the number of oxytocin receptors on the myometrial tissue in the uterus. Maternal oxytocin is released in bursts with increasing frequency during labor. This occurs in response to distension of the cervix
- positive feedback loops sustain production of prostaglandins and oxytocin as labor progresses
- relaxin is produced by the corpus luteum, placenta and decidua. Increased production during labor may helop to soften/dilate the cervis
- involution of the uterus occurs after delivery in response to the changed endocrine milieu
12
Q
Oxytocin and prolactin
A
- promotes milk let down and uterine contractility
- prolactin promotes milk synthesis
- both hormones are released in response to suckling
13
Q
Lactaction
A
- the breast responds to multiple hormones both during and after pregnancy
- mammogenic- promote cell proliferation (add progesterone)
- lactogenic- promote initiation of milk production
- galactokinetic- promote milk ejection or let down
- galactopoietic- maintain milk production
14
Q
Progesterone
A
- an important mammogenic hormone
- once the ductal system has developed, progesterone acts synergistically with estroen and other hormones to cause additional growth of breast lobules with alveoli budding and secretory characteristics
15
Q
Alveolus
A
- functional secretory unit of the breast
- organized into lobules, which drain into a ductule
- groups of 15-20 ductules drain into a duct leading to the outside
- contractile myoepithelial cells surround each alveolus and adipose cells and promote milk let down in response to oxytocin
- secretory epithelail cells comprise the alveolus and secrete milk in response to prolactin and permissive hormones, especially cortisol
