Reproductive Physio 4 Flashcards
Where does fertilization occur?
In humans, fertilization of the ovum by the sperm usually occurs in the ampulla of the uterine tube because of the short life span of the unfertilized egg, as it is very slowly driven towards the uterine cavity
Outline sperm transport and capacitation
Within a minute or so after intercourse, some sperm can be detected in the uterus.
The fluid pressure of the ejaculate and the pumping action of the penis in the vagina during ejaculation propels sperm out of vagina, through cervix and into the uterus.
The mortality rate of sperm during the trip is huge.
Acidic vaginal environment
Length and energy requirements of the trip.
Of the several hundred million sperm deposited in the vagina, only a few hundred reach the uterine tube
This is one of the major reasons there must be so many sperm in the ejaculate for fertilization to occur.
Sperm are not able to fertilize the egg until they have resided in the female tract for several hours and been acted upon by secretions of the tract.
This process is termed capacitation and it causes:
A more whiplike action of the sperm’s tail that propels it forward in strong lurches.
Alteration of the sperm’s plasma membrane so that it will be capable of fusing with the surface membrane of the egg.
Explain the process of fertilization
Following fusion of the sperm and egg, development is initiated.
Fusion also reduces the membrane potential of the ovum that prevents polyspermy (fertilization of the ovum by more than one sperm).
Upon fertilization the oocyte completes meiosis to become the haploid female gamete.
The genetic material from the two haploid nuclei intermingle, completing the process of fertilization resulting in a single-celled diploid zygote with all the genetic instructions it needs to develop into a human.
This conceptus is referred to as ablastocyst (moves down the tube into the uterus).
Within this structure, a group of cells forms into aninner cell mass, which is fated to become the embryo
Outline the embryonic development of a fertilized egg
The genetic material from the two haploid nuclei intermingle, completing the process of fertilization resulting in a single-celled diploid zygote with all the genetic instructions it needs to develop into a human.
This conceptus is referred to as ablastocyst (moves down the tube into the uterus).
Within this structure, a group of cells forms into aninner cell mass, which is fated to become the embryo
The cells that form the outer shell are called trophoblasts (trophe = “to feed” or “to nourish”).
These cells will develop into the chorionic sac and the foetal portion of theplacenta(the organ of nutrient, waste, and gas exchange between a pregnant person and the developing offspring).
What is gestation?
Gestation: the period of time required for full development of a foetus in utero(gestare = “to carry” or “to bear”).
A developing human is referred to as anembryoduring weeks 3–8, and afoetusfrom the ninth week of gestation until birth
Describe the placenta with reference to the umbilical cord
The mature placenta is composed of tissues derived from the embryo, and maternal tissues of the endometrium.
It connects to the conceptus via theumbilical cord.
This cord carries deoxygenated blood and wastes from the foetus through two umbilical arteries; while nutrients and oxygen are carried to the foetus through the single umbilical vein.
The umbilical cord is surrounded by the amnion, and the spaces within the cord around the blood vessels are filled with Wharton’s jelly, a mucous connective tissue.
Describe the endocrine (hormonal) changes during pregnancy
In all mammals, the corpus luteum, at the time of fertilization, fails to regress and instead enlarges in response to stimulation by gonadotropic hormones secreted by the placenta.
The placental gonadotropin in humans is called human chorionic gonadotropin (hCG).
Structurally similar to LH (as well as TSH and FSH)
hCG is detected in the blood as early as 6 – 14 days after conception.
Its presence in the urine in early pregnancy is the basis of the various laboratory tests for pregnancy.
hCG released from syncytio-trophoblasts of embryo → maintains the corpus luteum of pregnancy ( for 8-10 weeks) → secretes oestradiol, progesterone, and relaxin.
Relaxin helps maintain pregnancy by inhibiting myometrial contractions.
The function of the corpus luteum begins to decline after 8 wk of pregnancy, but it persists throughout pregnancy
After 8-10 weeks the placenta will release:
Progesterone
Oestradiol
Human placental lactogen (hPL), also known as human chorionic somatomammotropin (hCS).
Relaxin
Prolactin
What are the effects of progesterone in pregnancy?
Endometrial gland and spiral artery development (maintains endometrium)
Breast development
Decreases oestrogen receptor stimulation (prevents uterine contractility)
Decreases myometrial excitability (contractions)
Causes vasodilation (↓ BP and ↓ PVR) → slightly increased heart rate
Acts centrally on the brainstem to increase respiratory rate
What are the effects of oestrogen in pregnancy?
Oestrogens cause endometrial proliferation and increase myometrial excitability (inhibited by progesterone)
What are the effects of hPL in pregnancy?
hPL decreases maternal insulin sensitivity and increases maternal lipolysis → increased nutrients for foetus.
What are the effects of prolactin in pregnancy?
Prolactin prepares mammary glands for milk production
What are the effects of relaxin in pregnancy?
Relaxin relaxes the pubic symphysis and pelvic ligaments → easier passage of foetus; aids cervical dilation during labour.
