anat lab 18: pregnancy and development

Question 1

describe the uterine (menstrual cycle)

Answer 1

The term uterine (menstrual) cycle refers to a series of changes that occur in the
endometrium of a non-pregnant female. Each month the endometrium is prepared to receive
a blastocyst (the early form of embryo which implants in the wall of the uterus). If no
fertilization and implantation occur, a portion of the endometrium is shed. The ovarian cycle
is a monthly series of events associated with the formation and release of the female gamete.

Question 2

what hormones are involved in the menstrual cycle and what do they do?

Answer 2

Gonadotropic hormones of the anterior pituitary gland initiate the uterine cycle, ovarian cycle,
and other changes associated with puberty in the female. Follicle-stimulating hormone
(FSH) stimulates the initial development of the ovarian follicles and the secretion of estrogens
by the follicles. Another anterior pituitary hormone, luteinizing hormone (LH), stimulates
the further development of ovarian follicles, brings about ovulation, stimulates progesterone
production by the corpus luteum, and readies the mammary glands for milk secretion.

Question 3

What are the functions of these hormones in the human male?
Follicle stimulating hormone -
Luteinizing hormone

Answer 3

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) play essential roles in regulating male reproductive function. These hormones are produced by the anterior pituitary gland in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. Here’s how each functions in males:

Follicle-Stimulating Hormone (FSH):
1. Spermatogenesis Support:
- FSH acts on the Sertoli cells in the seminiferous tubules of the testes.
- Sertoli cells provide nourishment and structural support for developing sperm (spermatogenesis).
- FSH stimulates the production of androgen-binding protein (ABP), which binds testosterone, ensuring high local concentrations necessary for sperm production.

2. Inhibin Regulation:
   
   • Sertoli cells produce inhibin in response to FSH.
   • Inhibin regulates FSH secretion through negative feedback to the anterior pituitary.

Luteinizing Hormone (LH):
1. Testosterone Production:
- LH targets the Leydig cells in the interstitial space of the testes.
- Leydig cells produce testosterone in response to LH stimulation.
- Testosterone is essential for the development and maintenance of male secondary sexual characteristics, libido, and spermatogenesis (via its action on Sertoli cells).

2. Feedback Regulation:
   
   • Elevated testosterone levels inhibit LH (and GnRH) secretion through negative feedback to the hypothalamus and pituitary, maintaining hormonal balance.
     FSH and LH Together:
     - These hormones work synergistically to ensure the proper development, maturation, and function of sperm and the male reproductive system. Without FSH, spermatogenesis would be impaired, and without LH, testosterone production would decline, leading to further reproductive and systemic effects.

Question 4

what are the 5 functions of estrogen

Answer 4

1) They promote development and maintenance of
female reproductive organs, the secondary sex characteristics, and the breasts. 2) They
control fluid and electrolyte balance. 3) They increase protein anabolism. 4) They are believed
to contribute to the female sex drive. 5) Moderate levels of estrogens in the blood inhibit the
secretion of FSH by the anterior pituitary gland. This inhibition provides the basis for the
action of one kind of contraceptive pill.

Question 5

function of progesterone

Answer 5

Progesterone works with estrogens to prepare the endometrium for implantation and to
prepare the breasts for milk secretion.

Question 6

what happens during menstruations (period)

Answer 6

is the periodic discharge
of blood, tissue fluid, mucus, and epithelial cells from the endometrium of the uterus. It lasts
for approximately the first five days of the cycle. The discharge is associated with endometrial
changes in which the functional layer (stratum functionalis) degenerates, resulting in patchy areas of bleeding and uterine glands discharging their contents. Eventually the
entire functional layer is shed, and the endometrium is very thin because only the basal
layer (stratum basalis) remains

Question 7

what happens in the ovary during the menstrual phase

Answer 7

During the menstrual phase, the ovarian cycle is also in operation. Several primordial ovarian
follicles in each ovary begin to develop into primary and then secondary ovarian follicles due
to FSH from the anterior pituitary. It may take several months for them to reach maturity and
be ovulated. Although a number of ovarian follicles begin development each cycle, usually
only one will attain maturity.

Question 8

What happens to the secondary ovarian follicles that don’t finish maturation?

Answer 8

Estrogens and inhibin secretion by the dominant follicle inhibit FSH, causing others to stop growing and undergo atresia

Question 9

What happens if more than one mature ovarian follicle is ovulated?

Answer 9

Results in fraternal twins or triplets

Question 10

what happens in the ovarian follicles during the menstrual phase?

Answer 10

The granulosa cells of the secondary ovarian follicles begin to secrete follicular fluid, which
accumulates in a space called the antrum, forcing the oocyte to the edge of the follicle. The
granulosa cells are also producing estrogens and inhibin.
At this point, the first meiotic division is completing, creating the secondary oocyte within the
secondary follicle.

Question 11

what is this

Answer 11

Ovary slide showing primordial ovarian follicles (primary oocytes with
follicle cells), and a primary follicle (primary oocyte with surrounding granulosa
cells)

Question 12

Answer 12

Question 13

what is the preovulatory phase

Answer 13

The preovulatory phase is the period between the end of menstruation and ovulation. It
lasts from day 6 to 13 in a 28-day cycle. During the preovulatory phase, a secondary follicle
in the ovary matures into the tertiary (mature) ovarian follicle, ready for ovulation. During
the maturation process, the granulosa cells increase their production of estrogens.

Question 14

what hormones are involved in the preovulatory phase

Answer 14

Early in the preovulatory phase, FSH is the dominant hormone, but close to the time of
ovulation, LH is secreted in increasing quantities. FSH and LH stimulate the ovarian follicle to
produce estrogens, and this increase in estrogens stimulates the repair of the endometrium in
the uterus. During the process of repair, basilar cells (stratum basale) undergo mitosis and
produce a new functionalis layer.

Question 15

what are pther names for the preovulatory phase

Answer 15

Because the proliferation of endometrial cells occurs during the preovulatory phase, the phase
is also referred to as the proliferative phase. Still another name for this phase is the
follicular phase because of increasing secretion of estrogens by the developing follicle.
Functionally, estrogens are the dominant hormones during the pre-ovulatory phase of the
uterine cycle.

Question 16

Question 17

describe ovulation

Answer 17

Ovulation, the rupture of the mature follicle with the release of the secondary oocyte
(surrounded by the corona radiata and zona pellucida) into the pelvic cavity, occurs on
day 14 in a 28-day cycle. Just prior to ovulation, the high estrogens level that developed
during the preovulatory phase inhibits FSH secretion by the anterior pituitary. Concurrently,
LH secretion by the anterior pituitary is greatly increased. As LH and estrogens secretion
increase and FSH secretion is inhibited, ovulation occurs.

Question 18

Answer 18

Question 19

What happens if the secondary oocyte is not swept into the uterine tube as it usually is?

Answer 19

The cells degenerate unless the secondary oocyte is penetrated by sperm then meiosis II resumes in which the secondary oocyte is split into two haploid cells, the ovum and the second polar body

Question 20

how long is the postovulatory phase and what does it represent

Answer 20

The postovulatory phase lasts from days 15 to 28 in a 28-day cycle. It represents the period
of time between ovulation and the onset of the next menses.

Question 21

explain the luteal phase

Answer 21

the mature follicle collapses,
and the blood within it forms a clot. The ruptured follicle is called the corpus
hemorrhagicum. The clot is eventually reabsorbed by the remaining follicular cells. LH
stimulates the follicular cells of the corpus hemorrhagicum to enlarge, change character, and
form the corpus luteum. The corpus luteum then produces increasing quantities of estrogens
and progesterone, which are responsible for the changes in the endometrium

Question 22

phases of the menstrual cycle in order

Answer 22

Question 23

phases of the ovarian cycle in order

Answer 23

Question 24

ovarian cycle vs menstrual cycle

Answer 24

Both cycles are synchronized and regulated by hormones.
The ovarian cycle drives ovulation, while the menstrual cycle prepares the uterus for pregnancy

Question 25

the secretory phase of the unterine cycle

Answer 25

prepares the endometrium for implantation of the
blastocyst: the filling of the endometrial glands with secretions that cause the glands to
appear highly coiled, vascularization of the superficial endometrium, thickening of the
endometrium, and an increase in the amount of tissue fluid. These preparatory changes are
maximal about one week after ovulation, and they correspond to the anticipated arrival of the
blastocyst. During the postovulatory phase, FSH secretion gradually increases and LH
secretion decreases. The functionally dominant hormone during this phase is progesterone.

Question 26

what happens if fertilization and implantation do not occur

Answer 26

the corpus luteum’s secretory activity declines
and it degenerates into the corpus albicans. Without the estrogens, progesterone and
inhibin produced by the corpus luteum, the pituitary hormones increase, leading to a new
ovarian cycle and the resumption of follicular growth.

Question 27

what happens if fertilization and implantation do occur

Answer 27

the corpus luteum is “rescued” from degeneration
by the human chorionic gonadotropin produced by the chorion of the newly implanted
embryo. The estrogens and progesterone secreted by the corpus luteum maintain the uterine
lining, preventing menstruation

Question 28

menarche vs menopause

Answer 28

The uterine cycle normally occurs once each month from menarche (the first uterine cycle)
until menopause, when there is the complete cessation of menstruation. Menopause typically
occurs between 45 and 50 years of age and results from the ovaries ceasing to respond to
the stimulation of gonadotropic hormones from the anterior pituitary.

Question 29

graph of events of uterine and ovarian cycle

Answer 29

Question 30

Question 31

define pregnancy

Answer 31

is a sequence of events including fertilization, implantation, embryonic growth,
and fetal growth

Question 32

how to pregnancy

Answer 32

Fertilization (the union of the genetic material from a sperm and an ovum)
normally occurs about one-third of the way down the uterine (fallopian) tube, usually within
24 hours of ovulation. Sperm must remain in the female genital tract for about 7 hours before
they are capable of fertilizing an oocyte. Sperm undergo capacitation, whereby the tail beats
more vigorously and the plasma membrane of the head can respond to chemicals released by
the oocyte.

Question 33

how does the spermatozoa cross plasma membrane of oocyte

Answer 33

In order to reach the plasma membrane of the oocyte the spermatozoa must pass through
the corona radiata and the zona pellucida. The acrosome, a helmet-like structure that covers
the head of the spermatozoa, contains acrosomal enzymes such as hyaluronidase, acrosin
and other proteases. One glycoprotein in the zona pellucida, called ZP3, binds to receptors on
the sperm head and triggers the acrosomal reaction, which releases the contents of the
acrosome; hyaluronidase digests the cells of the corona radiata while the beating tail forces
the spermatozoa into contact with the zona pellucida; acrosin digests the acellular zona
pellucida beneath the corona radiata and the membrane of the oocyte. The first spermatozoa
to penetrate past the zona pellucida and enter the plasma membrane of the oocyte achieves
fertilization

Question 34

what happens once penetration is achieved by the spermatozoa

Answer 34

Once penetration is achieved, the oocyte develops a fertilization membrane that is
impermeable to the entrance of other spermatozoa. When the spermatozoan has entered the
oocyte, the flagellum is shed, the oocyte completes the second meiotic division, and the nuclei
of the ovum and sperm fuse to form a zygote. The nucleus of the zygote contains 23
chromosomes from the female and 23 chromosomes from the male

Question 35

what happens immediately after fertilization

Answer 35

Immediately after fertilization, rapid cell division (by mitosis) of the zygote takes place. This
early division of the zygote is called cleavage. See models 6 – 9. The progressively smaller
cells produced are called blastomeres. Successive cleavages produce a solid mass of cells,
the morula, which is only slightly larger than the original zygote

Question 36

what happens during morula stage

Answer 36

As the morula descends through the uterine tube, it continues to divide and eventually forms
a hollow ball of cells. At this stage of development, the mass is referred to as a blastocyst.
See model 9b. The blastocyst is differentiated into an outer covering of cells called the
trophoblast, an inner cell mass or embryoblast, and an internal space called the blastocyst
cavity.

Question 37

what happens to the trophoblast

Answer 37

Question 38

what is implantation

Answer 38

The attachment of the blastocyst to the endometrium typically occurs 6 to 8 days following
fertilization and is called implantation. At this time, the endometrium is in its postovulatory
phase. The blastocyst adheres and implants itself in the functionalis layer of the endometrium,
and eventually becomes completely surrounded by the endometrium. Implantation enables
the blastocyst to absorb nutrients from the glands and blood vessels of the endometrium for
subsequent embryonic growth and development.

Question 39

what happens following implantation

Answer 39

Following implantation, the inner cell mass (or embryoblast) of the blastocyst begins to
differentiate and eventually forms the three primary germ layers: the ectoderm,
mesoderm and endoderm. The primary germ layers are the embryonic tissues from which
all tissues and organs of the body will develop.

Question 40

describe the trophoblast and what it develops into

Answer 40

The trophoblast is the outer layer of cells in a blastocyst (an early stage of embryonic development). It plays a critical role in implantation and the formation of structures that support the embryo.

Key Features of the Trophoblast:
- Surrounds the inner cell mass and the fluid-filled cavity of the blastocyst.
- Functions as a protective and nourishing layer for the developing embryo.
- Secretes enzymes and hormones (like human chorionic gonadotropin, hCG) to aid implantation into the uterine lining.

What the Trophoblast Develops Into:
The trophoblast differentiates into two main layers:
1. Cytotrophoblast
- The inner layer of the trophoblast.
- Maintains cellular structure and continues to divide to produce more cells.

2. Syncytiotrophoblast
   
   • The outer layer of the trophoblast.
   • Multinucleated and invades the uterine lining to establish a connection with the maternal blood supply.

End Results:
- Placenta: The trophoblast forms the fetal portion of the placenta, which is essential for nutrient exchange, waste removal, and hormone production throughout pregnancy.
- Chorion: The trophoblast contributes to the formation of the chorion, an extra-embryonic membrane that surrounds the embryo and helps form the placenta.

Thus, the trophoblast is vital for embryo implantation, nourishment, and the establishment of a successful pregnancy.

Question 41

describe the embryoblast / inner cell mass and what it develops into

Answer 41

The embryoblast, also known as the inner cell mass (ICM), is a cluster of cells within the blastocyst. It is the part of the blastocyst that will give rise to the embryo itself, as well as some extra-embryonic structures.

Key Features of the Embryoblast:
- Located at one pole of the blastocyst.
- Composed of pluripotent stem cells, meaning these cells have the ability to differentiate into most cell types of the body.

What the Embryoblast Develops Into:
The embryoblast differentiates into two primary layers during the bilaminar embryonic disc stage:
1. Epiblast
- Forms the amniotic cavity.
- Gives rise to all the tissues of the embryo through the process of gastrulation, leading to the three germ layers:
- Ectoderm: Develops into the skin, nervous system, and sensory organs.
- Mesoderm: Forms muscles, bones, blood vessels, and internal organs.
- Endoderm: Creates the lining of the digestive and respiratory systems, and associated organs.

2. Hypoblast
   
   • Forms part of the yolk sac, an extra-embryonic structure that supports early development.

End Results:
- The epiblast is the source of all the embryo’s tissues and organs.
- The embryoblast contributes to both the embryo and extra-embryonic structures (like the amniotic sac and yolk sac), which are essential for early growth and survival.

Question 42

describe the first 8 weeks of development

Answer 42

The first eight weeks of development are considered the embryonic period. During this
period, the developing human is called an embryo. After the second month, it will be called
a fetus.

Question 43

what happens during the embryonic period

Answer 43

During the embryonic period, the four extraembryonic membranes form. These
membranes lie outside the embryo and will protect and nourish the fetus. Three of these
membranes, the umbilical vesicle (yolk sac), amnion, and allantois, develop from the
embryoblast. The chorion develops from the trophoblast.

Question 44

what is the umbilical vesicle (yolk sac)

Answer 44

seen on model 13.
The umbilical vesicle (yolk sac) is an endoderm-lined membrane that provides the embryo
with nutrients during the second and third weeks of development, after which this function is
taken over by the developing placenta. As a result, the umbilical vesicle remains small and
decreases in size during development. It eventually forms part of the digestive canal.

Question 45

What are four other important functions of the umbilical vesicle (yolk sac)?

Answer 45

The umbilical vesicle (yolk sac) has several important functions during early embryonic development, beyond its role in nutrient transfer. Here are four key functions:

1. Hematopoiesis
   
   • It is the primary site of blood cell formation during early development (weeks 3–6 of gestation) before the liver takes over this role.
2. Primordial Germ Cell Development
   
   • The yolk sac produces and harbors primordial germ cells, which later migrate to the developing gonads to form the sperm or eggs.
3. Development of the Digestive System
   
   • It contributes to the formation of the primitive gut. Part of the yolk sac is incorporated into the embryo during folding, forming the foregut, midgut, and hindgut.
4. Nutrient and Gas Exchange
   
   • Before the placenta is fully functional, the yolk sac assists in the exchange of nutrients and gases between the embryo and maternal tissues.

These functions are critical in supporting the embryo during the earliest stages of development until the placenta becomes the primary organ for nourishment and waste exchange.

Question 46

what is the amnion and amniotic fluid?

Answer 46

The amnion is a thin protective membrane that surrounds the embryo, covers the fetal
portion of the placenta and the umbilical cord. Amniotic fluid fills the space between the
embryo/fetus and the amnion. The amnion ruptures just before birth and its fluid constitute
the so-called “bag of waters”.

Question 47

What is amniotic fluid formed from? and what are the function of amniotic fluid

Answer 47

Amniotic fluid is initially formed from several sources during early pregnancy and evolves as the pregnancy progresses. Here’s an overview:

Sources of Amniotic Fluid:

1. Maternal Plasma
   
   • Early in pregnancy, amniotic fluid is primarily derived from maternal blood plasma. It passes through the amniotic sac and surrounding tissues into the amniotic cavity.
2. Fetal Urine
   
   • By the second trimester, the fetus begins to contribute significantly to amniotic fluid through urine production. Fetal urine becomes a major component of amniotic fluid as the fetal kidneys mature.
3. Fetal Lung Secretions
   
   • The fetus secretes fluid from its lungs into the amniotic sac. This contributes to the composition of the amniotic fluid and plays a role in lung development.
4. Fetal Skin Transudate
   
   • Before the fetal skin keratinizes (around weeks 20–25), fluid passes through the skin into the amniotic cavity.
5. Amniotic Membrane Secretions
   
   • The cells of the amniotic sac itself secrete fluid that contributes to the volume and composition of the amniotic fluid.

Functions of Amniotic Fluid:
- Protects the fetus by cushioning it from external forces.
- Facilitates movement for proper musculoskeletal development.
- Maintains a stable temperature.
- Supports fetal lung development through inhalation and exhalation of the fluid.
- Serves as a medium for nutrient and waste exchange during early development.

The dynamic composition of amniotic fluid reflects the ongoing interaction between maternal and fetal systems.

Question 48

what happens during the second week of development?

Answer 48

During the second week of development, part of the chorion forms the connecting stalk, the
future umbilical cord. Review the material on the fetal circulation from Lab 7 in Biol 1190.
Development of a functioning placenta is the next major event of the embryonic period,
accomplished by the third month of pregnancy. The placenta is formed by the chorion of the
embryo and the functional layer of the mother’s endometrium. It provides an exchange of
nutrients and wastes between the fetus and mother and secretes the hormones necessary to
maintain pregnancy.

Question 49

How does the chorion protect the embryo and fetus from the mother’s immune response?

Answer 49

The chorion plays a crucial role in protecting the embryo and fetus from the mother’s immune response through several mechanisms:

1. Physical Barrier
   
   • The chorion forms the outermost fetal membrane and acts as a physical barrier between the maternal tissues and the embryo. This minimizes direct contact between maternal immune cells and fetal cells.
2. Immune Modulation
   
   • The trophoblast cells of the chorion (particularly the syncytiotrophoblast) secrete molecules that suppress maternal immune responses locally. These include:
     
     • Human Chorionic Gonadotropin (hCG): Helps maintain immune tolerance.
     • Immunosuppressive cytokines: Such as interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β), which dampen maternal immune activation.
3. HLA-G Expression
   
   • Trophoblast cells express a special form of human leukocyte antigen (HLA-G), which is not recognized as foreign by the maternal immune system. This helps prevent the maternal immune cells from attacking the fetal tissues.
4. Lack of Direct Blood Contact
   
   • The syncytiotrophoblast layer lacks direct connections to maternal blood vessels, reducing exposure of fetal antigens to the maternal immune system. Instead, nutrient and waste exchange occurs via diffusion across this layer, limiting immune recognition.
5. Regulation of Natural Killer (NK) Cells
   
   • NK cells are abundant in the maternal decidua (uterine lining). The chorion’s trophoblast cells interact with these NK cells in a way that promotes a supportive, non-cytotoxic response, ensuring the pregnancy is not rejected.
6. Secretion of Decidual Prostaglandins
   
   • The chorion helps modulate prostaglandin production in the maternal decidua, creating an environment that supports implantation and prevents inflammatory immune responses.

By employing these strategies, the chorion ensures that the fetus, which contains paternal antigens foreign to the mother, is not rejected by the maternal immune system.

Question 50

what is chorionic villi

Answer 50

d chorionic villi, grow
into the functional layer of the endometrium. The villi contain fetal blood vessels and continue
growing until they are bathed in the maternal blood in the sinuses of the functional layer of
the endometrium.
Thus, maternal and fetal blood vessels are brought into close proximity, but do not mix.
Oxygen and nutrients from the mother’s blood diffuse across the walls and into the umbilical
vein. Wastes leave the fetus through the umbilical arteries, pass into the capillaries of the
villi, and diffuse into the maternal blood.

Question 51

Besides oxygen, carbon dioxide, nutrients and wastes, list at least three other substances or
types of substances that can cross the barrier of the placenta:

Answer 51

In addition to oxygen, carbon dioxide, nutrients, and wastes, the placenta allows the transfer of several other substances. Here are three types:

1. Hormones
   
   • Some maternal hormones, like thyroid hormones (T3 and T4), cross the placenta and are essential for fetal development, especially for the brain and metabolic regulation.
2. Antibodies (Immunoglobulin G, IgG)
   
   • Maternal IgG antibodies pass through the placenta, providing the fetus with passive immunity. This helps protect the newborn against infections during the first months of life.
3. Drugs and Chemicals
   
   • Many medications and substances, such as alcohol, caffeine, and certain prescription or recreational drugs, can cross the placental barrier. These may impact fetal development depending on the substance and timing of exposure.

Other examples include viruses (e.g., rubella, Zika), some bacteria, and environmental toxins. The placenta is selective, but it does not block all substances, making maternal health and lifestyle crucial during pregnancy.

Question 52

what does the placenta store?

Answer 52

The placenta also stores carbohydrates, proteins, calcium and iron that can be released into
the fetal circulation as needed.

Question 53

what is the allantois

Answer 53

The allantois is a small, vascularized membrane that forms from the wall of the umbilical
vesicle (yolk sac). It functions in the early formation of blood and blood vessels and is
associated with development of the urinary bladder. Later its blood vessels extend into the
connecting stalk.

Question 54

Answer 54

Question 55

what happens during the fetal period

Answer 55

During the fetal period, rapid growth of organs established by the primary germ layers occurs.
No new structures are formed, but there is accelerated growth and maturation of structures
that were laid down during the embryonic period. At the beginning of the fetal period, the
organism takes on a human appearance.

Question 56

what happens to the corpus luteum after fertilization

Answer 56

Following fertilization, the corpus luteum continues to secrete estrogens and progesterone
until about the fourth month of pregnancy. Both these hormones maintain the lining of the
uterus during pregnancy and prepare the mammary glands to secrete milk.
The amounts of estrogens and progesterone secreted by the corpus luteum, however, are
only slightly higher than those produced after ovulation in a normal ovarian cycle and are
suited to maintain the pregnancy only during the first 3 - 4 months. The higher levels of
hormones needed to maintain pregnancy during the later stages, and to initiate lactation, are
provided by the placenta, beginning at about the 3rd month.

Question 57

wat hormones does the chorion of the placenta secrete during pregnancy)

Answer 57

During pregnancy, the chorion of the placenta secretes a hormone called human chorionic
gonadotropin (hCG). This hormone is secreted from about the first week of pregnancy,
reaching its peak during the third month. The primary role of hCG seems to be to maintain
the activity of the corpus luteum, especially with regard to continuous progesterone secretion - an activity necessary for the continued attachment of the embryo/fetus to the lining of the
uterus. hCG is excreted in the urine, which serves as the basis for some pregnancy tests.

Question 58

Question 59

when does the placenta secrete estrogen and progesterone

Answer 59

As noted earlier, the placenta provides the high levels of estrogens and progesterone needed
for the maintenance of pregnancy. The placenta begins to secrete these hormones no later
than the sixtieth day of pregnancy. They are secreted in increasing quantities until they reach
their maximum levels at the time of birth.

Question 60

what happens to the secretion of hCG once placenta is established

Answer 60

Once the placenta is established, the secretion of hCG is cut back drastically at about the
fourth month. This decrease results in disintegration of the corpus luteum, which is no longer
needed because the placenta supplies the levels of estrogens and progesterone needed to
maintain the pregnancy. Following delivery, the levels of estrogens and progesterone in the
blood decrease to their non-pregnant values.

Question 61

gestation, labor, parturition

Answer 61

The time that the embryo or fetus is carried in the uterus is called gestation. It is assumed
that the total human gestation period is 280 days from the beginning of the last menstrual
period. The term labor refers to the process of giving birth; the expulsion the fetus from the
uterus through the vagina. Another term for labor is parturition. The onset of labor stems
from complex interactions involving several hormones.

Question 62

what happens just prior to birth

Answer 62

Just prior to birth, the muscles of the uterus contract rhythmically and forcefully. Both
placental and ovarian hormones play a dominant role in these contractions. You may recall
that progesterone and relaxin inhibits contractions of the myometrium. Until the effects of
progesterone are effectively diminished, labor cannot take place. At the end of gestation,
however, there are sufficient estrogens in the mother’s blood to overcome the inhibiting
effects of progesterone, and labor commences. Coupled with this, oxytocin from the posterior
pituitary gland stimulates uterine contractions.

Question 63

describe uterine contractions

Answer 63

Uterine contractions occur in waves which travel from the fundus of the uterus towards the
cervix. True labor is recognizable by the regular but gradually shortening intervals between
contractions. As the intervals shorten, the strength of the contractions increases. The cervical
canal dilates and blood and mucus from the cervix is discharged (called the “show”). In false
labor, these signs are absent and the pains occur at irregular intervals.

Question 64

Labor can be divided into three stages. Describe what is occurring during each of the three
stages of labor seen in the models:
Stage of dilation -
Stage of expulsion -
Placental stage -

Answer 64

Stage of dilation. The time from the onset of labor to the complete dilation of the cervix is the stage of dilation. This stage, which typically lasts 6–12 hours, features regular contractions of the uterus, usually a rupturing of the amniotic sac, and complete dilation (to 10 cm) of the cervix. If the amniotic sac does not rupture spontaneously, it is ruptured intentionally.
Stage of expulsion. The time (10 minutes to several hours) from complete cervical dilation to delivery of the baby is the stage of expulsion.
Placental stage. The time (3–5 minutes or up to an hour or more) after delivery until the placenta or “afterbirth” is expelled by powerful uterine contractions is the placental stage. These contractions also constrict blood vessels that were torn during delivery, reducing the likelihood of hemorrhage.

Question 65

lactation

Answer 65

. The term lactation refers to the secretion of milk by the mammary glands. During
pregnancy, the mammary glands are prepared for lactation by estrogens, progesterone,
and by prolactin during the 3rd trimester. With the delivery of the placenta at birth,
the levels of estrogens and progesterone in the mother’s blood decrease. Once the
inhibiting effect of progesterone ceases, prolactin can stimulate the secretory cells of the
mammary glands to produce milk. Lactation starts three to four days after delivery.
In order to provide the newborn with sufficient nutrients until the milk is ready,
colostrum is secreted by the mammary glands. Although not as nutritious as milk,
colostrum is adequate until the arrival of true milk.

Question 66

what is the milk ejection reflex

Answer 66

Milk ejection reflex: Once initiated by prolactin, lactation is stimulated and maintained by
the suckling action of the infant. Suckling initiates afferent nerve impulses to the
hypothalamus, which then stimulates the anterior pituitary to continue prolactin secretion,
and the posterior pituitary to release oxytocin, causing the ejection of milk (let-down).
Oxytocin causes the contraction of the myoepithelial cells surrounding the acini and ducts of
the mammary glands, producing milk ejection to assist infant feeding. Lactation usually
prevents the occurrence of the female reproductive cycles for the first few months following
delivery.

Question 67

What important components do you find in human milk?

Answer 67

Human milk is a complex and dynamic fluid that provides essential nutrients, immune protection, and bioactive compounds to support infant growth and development. Key components of human milk include:

1. Nutrients
- Macronutrients:
- Carbohydrates: Primarily lactose, which provides energy and supports brain development.
- Proteins: Such as casein and whey proteins (e.g., alpha-lactalbumin) for growth and digestion.
- Fats: Rich in long-chain polyunsaturated fatty acids (LCPUFAs) like DHA for brain and eye development.

• Micronutrients:
  
  • Vitamins: Includes vitamin A, D, E, and K, as well as water-soluble vitamins like B-complex and C.
  • Minerals: Calcium, phosphorus, magnesium, iron, zinc, and trace elements.

2. Immune Factors
- Antibodies (Immunoglobulins):
- Primarily IgA, which protects the infant’s gut and immune system from pathogens.
- Leukocytes: White blood cells that provide direct immune defense.
- Cytokines: Molecules that help regulate the infant’s immune response.
- Lactoferrin: Binds iron to inhibit bacterial growth and has immune-boosting properties.

3. Bioactive Compounds
- Human Milk Oligosaccharides (HMOs):
- Complex sugars that feed beneficial gut bacteria and protect against harmful microbes.
- Growth Factors:
- Promote the development of the gut, immune system, and other tissues.
- Hormones:
- Includes leptin and adiponectin, which regulate energy balance and metabolism.

4. Beneficial Microbes
- Probiotics:
- Human milk contains beneficial bacteria like Lactobacillus and Bifidobacterium, which support a healthy gut microbiome.

5. Enzymes
- Lipase: Aids in fat digestion.
- Amylase: Helps in carbohydrate digestion.

6. Water
- Constitutes about 87% of human milk, ensuring proper hydration for the infant.

These components make human milk uniquely suited to meet the nutritional, developmental, and immune needs of infants, adapting over time to support the changing needs of the growing baby.

Question 68

inactive vs active mammary glands

Answer 68

Question 69

when does a woman’s body produce a small quantity of luteinizing hormone. how does the amount of it change

Answer 69

during ovulation

However, the LH level
greatly increases for a short time in the middle of the uterine and ovarian cycles. About 9
hours after the LH surge, ovulation occurs. There is a urine test kit available which can be
used as an aid in predicting the time of ovulation.

Question 70

What is the advantage of knowing the time of the LH surge?

Answer 70

helps you get pregnant

Question 71

when does human chorionic gonadotropic hormone appear.

Answer 71

Another hormone, human chorionic gonadotropin (hCG) appears in the urine and serum
of pregnant women in large concentrations. The hormone is a glycoprotein produced by
placental trophoblastic cells and plays a major role in developing and maintaining the
corpus luteum. The corpus luteum maintains the state of pregnancy by the production of the
hormones progesterone and estrogens until the placenta takes over.

Question 72

what happens to hCG levels following implantation

Answer 72

Following implantation of a fertilized ovum, hCG levels increase rapidly in urine and may reach
detectable levels shortly after conception. Laboratory test demonstration of the hormone’s
presence is generally indicative of pregnancy.

Question 73

when does a false pregnancy positive test occur

Answer 73

False positive results may be obtained if the urine and serum contain high levels of LH, if the
individual is menopausal, or if some specific cancerous states exist, such as chorioepithelioma
or choriocarcinoma, or in situations of a miscarriage (spontaneous abortion). Following
miscarriage, the results remain positive for approximately a week.
The tests for pregnancy used in the lab are accurate, rapid and simple. It clearly replaces the
various tests that require specialized equipment, radioactive agents, or the use of animals
such as frogs, rats or rabbits.

Question 74

what is the importance of colostrum

Answer 74

It’s highly concentrated with nutrients and antibodies to fight infection and protect your baby. It provides a powerful, unique immunity that only it can provide