Ch. 29: Development and Inheritance Flashcards
1
Q
Embryonic period.
A
Fertilization to the 8th week of development.
2
Q
Fetal period.
A
9th week of development to birth.
3
Q
Prenatal development.
A
Fertilization to birth. Includes embryonic and fetal periods. Divided into trimesters.
4
Q
First trimester.
A
Most critical stage of development. All of the major organ systems begin to form. The developing organism is most vulnerable to drugs, radiation and microbes.
5
Q
Second trimester.
A
Nearly complete development of organ systems. By the end of this phase, the fetus assumes distinct human features.
6
Q
Third trimester.
A
Rapid fetal growth. The weight of the fetus doubles. Organs systems are fully functional (not all).
7
Q
What occurs in the first week of development?
A
Fertilization, cleavage of zygote, blastocyst formation, implantation.
8
Q
What occurs in the second week of development?
A
Trophoblast, bilaminar embryonic disc, amnion, yolk sac, sinusoids, extra embryonic coelom, and chorion development.
9
Q
What occurs in the third week of development?
A
Gastrulation, neurulation, development of chorionic villi and placenta.
10
Q
Fertilization.
A
Genetic material of haploid sperm and haploid secondary oocyte merge into a single diploid nucleus. Occurs in the uterine tube within 12-24 hours after ovulation.
11
Q
Pregnancy is most likely to occur if intercourse takes place during a _____ window.
A
3 day. From 2 days before ovulation to 1 day after ovulation.
12
Q
Sperm swims from the vagina into the ________ by the whip-like movements of their flagella. The passage of sperm through the rest of the uterus and then into the uterine tubes results mainly from _________ .
A
Cervical canal. Contractions of these organs.
Prostaglandins in semen stimulate uterine motility at the time of intercourse and aid in the movement of sperm through the uterus and uterine tube.
13
Q
Sperm that reach the vicinity of the oocyte within minutes after ejaculation are not capable of fertilizing it until ______.
A
7 hours later.
14
Q
Capacitation.
A
Secretions of female reproductive tract remove cholesterol, glycoproteins and proteins from the PM around the head of the sperm. This allows the sperm to be attracted to and respond to the chemicals released by the cells surrounding the secondary oocyte.
15
Q
In order for a sperm cell to fertilize a secondary oocyte, it must first penetrate the ______ and ______ .
A
Corona radiata: layer of granulosa cells surrounding the secondary oocyte.
Zona pellucida: layer of glycoproteins between corona radiata and plasma membrane.
16
Q
In order for a sperm cell to fertilize a secondary oocyte, it must first penetrate the ______ and ______ .
A
Corona radiata: layer of granulosa cells surrounding the secondary oocyte.
Zona pellucida: layer of glycoproteins between corona radiata and plasma membrane.
17
Q
Acrosome.
A
Structure that covers the head of the sperm and contains enzymes.
18
Q
______ and ______ help the sperm penetrate the cells of the corona radiata and come into contact with the zona pellucida.
A
Acrosomal enzymes. Strong tail movements.
19
Q
ZP3.
A
Glycoprotein in zona pellucida that acts as a sperm receptor. Its binding to specific membrane proteins in the sperm head triggers the acrosomal reaction, which is the release of the contents of the acrosome. The acrosomal enzymes then digest a path through the zona pellucida as the sperm tail pushes the sperm cell onward.
20
Q
Although many sperm bind to ZP3 molecules and undergo acrosomal reactions, only the _______________ fuses with the oocyte.
A
First sperm cell to penetrate the entire zona pellucida and reach the oocyte’s plasma membrane.
21
Q
What initiates the blocks of polyspermy?
A
Fusion of sperm with oocyte.
22
Q
Fast block to polyspermy.
A
Initiated seconds after fusion. Cell membrane of the oocyte depolarizes.
23
Q
Slow block to polyspermy.
A
Depolarization of the oocyte’s cell membrane triggers the intracellular release of Ca2+ ions, which stimulate exocytosis of secretory vesicles from the oocyte. The molecules released by exocytosis inactivate ZP3 and harden the zona pellucida.
24
Q
What happens after the sperm cell enters the secondary oocyte?
A
The oocyte completes meiosis II. It divides into a larger ovum and a smaller second polar body that disintegrates. The nucleus in the head of the sperm develops into the male pronucleus, and the nucleus of the ovum develops into the female pronucleus. Both of these nuclei fuse to produce a single diploid nucleus. The fertilized ovum is now a zygote.
25
Dizygotic twins.
Fraternal. Release and fertilization of two separate secondary oocytes.
26
Monozygotic twins.
Identical. Develop from a single fertilized ovum that has separated into two embyros before the 8th day of development.
27
What would most likely happen if a fertilized ovum were to separate after the 8th day of development?
Conjoined twins.
28
Cleavage of zygote.
Zygote undergoes rapid mitotic cell division. The progressively smaller cells produced are called blastomeres. Successive cleavages eventually produce a solid sphere of cells, called a morula.
29
By the second day after fertilization, the second zygote cleavage cleaves _____ cells.
4
30
By the third day after fertilization, the third zygote cleavage cleaves _____ cells.
16
31
Blastocyst formation.
Morula enters the uterine cavity on day 4 or 5 after fertilization. A glycogen-rich secretion from the glands of the endometrium enters the morula through the zone pellucida. This uterine milk and nutrients in the blastomeres provide nourishment for the developing morula. At the 32-cell stage, the uterine milk enters the morula, collects between blastomeres, and reorganizes them around the blastocyst cavity / blastocoel. Once the blastocyst cavity is formed, the developing mass is the blastocyst.
32
Which 2 cell populations arise during the formation of the blastocyst?
Embryoblast: inner cell mass, eventually develops into the embryo.
Trophoblast: outer superficial layer of cells, forms sphere-like wall of the blastocyst, eventually develops into outer chorionic sac that surrounds the fetus and fetal part of placenta.
33
What happens on the 5th day after fertilization?
The blastocyst hatches from the zona pellucida by digesting a hole in it with an enzyme and then squeezing through.
34
Implantation.
Blastocyst loosely attaches to the endometrium 6 days after fertilization. It then firmly attaches to the endometrium 7 days after fertilization while endometrial glands enlarge, and the endometrium becomes more vascularized. The blastocyst eventually secretes enzymes and burrows into the endometrium and becomes surrounded by it.
35
Blastocyst remains free within the uterine cavity for _____ before it attaches to the uterine wall.
2 days
36
After implantation, the endometrium is known as the ____ .
Decidua. This separates from the endometrium after the fetus is delivered.
37
Decidua basalis.
Part of the endometrium between the embryo and the stratum basal of the uterus. Provides glycogen and lipids for developing embryo and fetus. Eventually becomes the maternal part of the placenta.
38
Decidua capsularis.
Part of the endometrium between the embryo and uterine cavity. As the emrbyo/fetus enlarges, this area bulges into the uterine cavity and fuses with the decidua parietalis, obliterating the uterine cavity. By 27 weeks, the the decidua capsular degenerates and disappears.
39
Decidua parietalis.
Remaining modified endometrium that lines the non-involved areas of the rest of the uterus.
40
Trophoblast development.
8 days after fertilization, the trophoblast develops into two layers in the region of contact between the blastocyst and endometrium. These layers become part of the chorion as they undergo further growth.
41
What happens to the trophoblast during implantation?
The syncytiotrophoblast secretes enzymes that enable the blastocyst to penetrate the uterine lining by digesting and liquifying the endometrial cells.
42
Trophoblast and hCG.
Trophoblast also secretes hCG, which rescues the corpus luteum from degeneration and sustains its secretion of progesterone and estrogens.
43
9th week of development.
hCG secretion is peaked. Placenta is fully developed, and continues to produce progesterone and estrogens.
44
Development of the bilaminar embryonic disc.
Cells of the embryoblast differentiate into two layers around the 8th day after fertilization. A small cavity appears within the epiblast, which enlarges to form the amniotic cavity.
45
Amnion development.
As the amniotic cavity enlarges, a single layer of squamous cells forms a dome roof above the epiblast cells, which is the amnion. The amnion increases in size to cover the entire embryo, creating the amniotic cavity that becomes filled with amniotic fluid.
46
The ____ forms the roof of the amniotic cavity, and the ____ forms the floor.
Amnion, epiblast.
47
Amniotic fluid.
Most of the fluid is initially derived from maternal blood. Then, the fetus contributes urine to the fluid.
Serves as a shock absorber for the fetus, helps regulate fetal body temperature, helps prevent fetus from drying out, and prevents adhesions between the skin of the fetus and surrounding tissues.
48
Yolk sac development.
On the 8th day after fertilization, cells at the edge of the hypoblast migrate and cover the inner surface of the blastocyst wall. The migrating columnar cells become squamous and then form the exocoelomic membrane. The hypoblast and the exocoelomic membrane form the wall of the yolk sac. The bilaminar embryonic disc is now positioned between the amniotic cavity and yolk sac.
49
Yolk sac functions.
Supplies nutrients to embryo during 2nd and 3rd weeks of development. Source of blood cells from the 3rd to 6th weeks. Contains the first cells that will migrate into the developing gonads, differentiate into primitive germ cells, and form gametes. Forms part of the gut. Shock absorber. Prevents the embryo from drying out.
50
Sinusoids development.
As the syncytiotrophoblast expands, small lacunae develop within it. On the 12th day after fertilization, these lacunae fuse to form larger lacunar networks. Endometrial capillaries around the embryo become dilated and are now called maternal sinusoids. As the syncytiotrophoblast erodes some of the maternal sinusoids and endometrial glands, maternal blood and gland secretions enter the lacunar networks and flow through them.
51
Maternal blood.
Rich source of materials for embryonic nutrition. Disposal site for the embryo's wastes.
52
Development of the extraembryonic coelom.
The extraembryonic mesoderm develops on the 12th day after fertilization. These mesodermal cells are derived from the yolk sac and form a mesenchyme around the amnion and yolk sac. Large cavities develop in the extraembryonic mesoderm, which fuse to form the extraembryonic coelom.
53
Chorion development.
The chorion is formed by the extraembryonic mesoderm, and the two layers of the trophoblast. It surrounds the embryo/fetus, and eventually becomes the principal embryonic part of the placenta. It produces hCG. The inner layer of the chorion fuses with the amnion. The extraembryonic coelom is now called the chorionic cavity.
54
How does the chorion protect the embryo/fetus from immune responses of the mother?
1) It secretes proteins that block antibody production by the mother.
2) It promotes the production of T-lymphocytes that suppress the normal immune response in the uterus.
55
By the end of the 2nd week of development, the bilaminar embryonic disc becomes connected to the trophoblast by....
A band of extraembryonic mesoderm. Called the connecting stalk, which is the future umbilical cord.
56
Gastrulation.
15 days after fertilization. The bilaminar embryonic disc transforms into a trilaminar embryonic disc consisting of 3 primary germ layers (ectoderm, mesoderm, endoderm). Involves the rearrangement and migration of cells from the epiblast.
57
What is the first evidence of gastrulation?
The formation of the primitive streak, which is a faint groove on the dorsal surface of the epiblast that elongates from the posterior to the anterior part of the embryo. It clearly establishes the head and tail of the embryo, and its right and left sides.
58
Primitive node.
A small group of epiblastic cells at the head of the primitive streak.
59
Invagination.
Cells of the epiblast move inward below the primitive streak and detach from the epiblast. Once the cells have invaginated, some of them displace the hypoblast, forming the endoderm. Other cells remain between the epiblast and newly formed endoderm to form the mesoderm. Cells remaining in the epiblast then form the ectoderm.
60
Ectoderm and endoderm.
Epithelia of tightly packed cells.
Ectoderm: develops into epidermis of skin and nervous system.
Endoderm: becomes epithelial lining of GI tract, respiratory tract, and other organs.
61
Mesoderm.
Loose connective tissue.
Gives rise to muscles, bones, peritoneum, other connective tissues.
62
Notochordal process.
16 days after fertilization, mesodermal cells from the primitive node migrate toward the head of the embryo and form a hollow tube of cells in the midline.
63
Notochord.
22-24 days after fertilization, the notochordal process becomes a solid cylinder of cells. This structure plays an important role in induction, which is the process by which one tissue stimulates the development of an adjacent unspecialized tissue into a specialized one. An inducing tissue produces a chemical substance that influences the responding tissue. The notochord induces mesodermal cells to develop into vertebral bodies. It also forms the nucleus pulposus of the intervertebral discs. It also induces ectodermal cells to form the neural plate.
64
Neurulation.
By the end of the 3rd week of development, the lateral edges of the neural plate become more elevated and form the neural fold. The neural groove is the depressed mid-region. The neural folds fuse together, and convert the neural plate into a neural tube. Neural tube cells develop into the brain and spinal cord.
65
Neural crest.
As the neural tube forms, some of the ectodermal cells migrate to form the neural crest. Neural crest cells give rise to all sensory neurons and postganglionic neurons of the peripheral nerves, the adrenal medullae, melanocytes of skin, arachnoid mater, pia mater, and almost all of the skeletal and connective tissue components of the head.
66
Chorionic villi development.
These fingerlike projections begin to develop by the end of the 2nd week. They consist of chorion, and project into the endometrial wall of the uterus. By the end of the 3rd week, blood capillaries develop in the chorionic villi. These blood vessels connect to the embryonic heart by way of the umbilical arteries and umbilical vein through the connecting stalk. The fetal blood capillaries within the chorionic villi project into the lacunae, which unite to form the intervillous spaces that bathe the chorionic villi with maternal blood. Maternal blood bathes the chorion-covered fetal blood vessels.
67
Placentation.
Placental development. The placenta develops from the mother and fetus, and produces hormones. The placenta allows oxygen and nutrients to diffuse from maternal blood into fetal blood, while CO2 and wastes diffuse from fetal blood into maternal blood. Forms a protective barrier because most microorganisms cannot pass through it. Stores CHO, proteins, Ca2+, Fe.
68
By the 12th week of development, the placenta has 2 parts.
1) Fetal portion: formed by chorionic villi.
2) Maternal portion: formed by decidua basalis.
69
Umbilical cord.
Actual connection between placenta and embryo/fetus. Develops from connecting stalk. Consists of 2 umbilical arteries that carry deoxygenated fetal blood to the placenta, 1 umbilical vein that carries oxygen and nutrients from the mother's intervillous spaces into the fetus, and supporting mucous connective tissue. A layer of amnion surrounds the umbilical cord.
70
Fetal period.
Tissues and organs that developed during the embryonic period grow and differentiate. Very few new structures appear during this time. The fetus is less vulnerable to the damaging effects of drugs, radiation, and microbes than it was as an embryo.
71
Hormones during pregnancy.
Progesterone and estrogens: During the first 3-4 months of pregnancy, the corpus luteum secretes progesterone and estrogens. From the 3rd month through the remainder of the pregnancy, the placenta then secretes progesterone and estrogens. These hormones are secreted in increasing quantities until labor.
hCG: The chorion of the placenta secretes hCG, stimulating the corpus luteum to continue production of progesterone and estrogens. During the 4th and 5th months of pregnancy, the hCG levels decrease, and then level off until childbirth.
Relaxin: Produced by the corpus luteum and later by the placenta. Increases the flexibility of pubic symphysis, and ligaments of sacroiliac and sacrococcygeal joints. Dilates uterine cervix during labor.
hCS: Also known as hPL. The rate of secretion of this hormone increases in proportion to placental mass. Maximum levels are reached at 32 weeks. Helps prepare mammary glands for lactation. Enhances maternal growth by increasing protein synthesis. Regulates metabolism in mother and fetus.
CRH: Produced by placenta. Establishes timing of birth. Secretion begins at 12 weeks, and increases a lot toward the end of pregnancy. Increases cortisol secretion, which is needed for maturation of fetal lungs and surfactant production.
72
A high level of progesterone ensures that...
The uterine myometrium is relaxed, and that the cervix is tightly closed.
73
Near the end of pregnancy, the uterus pushes the ____ , ____ , and ____ superiorly, elevates the ______ , and widens the _________ .
Intestines, liver, stomach.
Diaphragm.
Thoracic cavity.
74
Pregnancy changes in cardiovascular system.
Increased maternal blood flow to placenta, and increased metabolism.
Stroke volume increases by 30%.
CO increases by 20-30%.
HR increases by 10-15%.
Blood volume increases by 30-50%.
75
Why is not a good idea for a pregnant woman to lie on her back?
The enlarged uterus may compress the aorta, resulting in diminished blood flow to the uterus.
76
Compresses of ____ decreases venous return, which leads to edema in lower limbs and varicose veins.
Inferior vena cava.
77
Compression of the _____ can lead to renal hypertension.
Renal artery.
78
Pregnancy changes in respiratory system.
Tidal volume increases by 30-40%.
Expiratory reserve volume reduces by 40%.
Functional residual capacity reduces by 25%.
Minute ventilation increases by 40%.
Airway resistance in bronchial tree reduces by 30-40%.
Total body oxygen consumption increases by 10-20%.
79
During pregnancy, the uterus increases from _____ to _____.
60-80g, 900-1200g.
80
The onset of labor is determined by interactions of...
Placental and fetal hormones.
81
Labor cannot take place until the effects of ____ are diminished because....
Progesterone, it inhibits uterine contractions.
82
How are the effects of progesterone diminished before labor?
Estrogen levels rise sharply, which results from increased secretion of CRH from the placenta, which stimulates the anterior pituitary of the fetus to secrete ACTH. ACTH stimulates fetal adrenal glands to secrete cortisol and DHEA. The placenta then converts DHEA into estrogen. High levels of estrogens cause the number of oxytocin receptors on uterine muscle fibres to increase. High levels of estrogens also cause uterine muscle fibres to form gap junctions with one another. Oxytocin release by posterior pituitary stimulates uterine contractions. Relaxin from placenta assists by increasing flexibility and dilation. Estrogens also stimulate the placenta to release prostaglandins, which induce the production of enzymes that digest collagen fibres in the cervix, causing it to soften.
83
Labor contractions.
Contractions of the uterine myometrium force the baby's head or body into the cervix, distending the cervix. Stretch receptors in the cervix send nerve impulses to neurosecretory cells in the hypothalamus, causing them to release oxytocin into the posterior pituitary for release. Oxytocin travels to the uterus, where it stimulates the myometrium to contract more forcefully. The baby moves deeper into the cervix, stretching it more, and causing more oxytocin to be released (positive feedback).
84
True labor.
Begins when uterine contractions occur at regular intervals. Back pain is intensified by walking. Cervix is dilating. There is a discharge of blood-containing mucus into the cervical canal.
85
False labor.
Pain is felt in the abdomen at irregular intervals. Pain does not intensify with time or by walking. No cervical dilation or discharge of blood-containing mucus.
86
What are the 3 stages of true labor?
1) Stage of dilation: The time from the onset of labor to the complete dilation of the cervix. 6-12 hours. Regulation contractions. Rupturing of amniotic sac.
2) Stage of expulsion: The time from complete cervical dilation to delivery. 10 minutes to several hours.
3) Placental stage: The time after delivery until the afterbirth is expelled by uterine contractions. These contractions also constrict blood vessels that were torn during delivery, reducing the likelihood of hemorrhage. 5-30 minutes.
87
Why would the fetal adrenal medulla secrete EP and NE during labor?
Because the fetus undergoes a great amount of stress. The head is compressed, and it may undergo intermittent hypoxia due to compression of the umbilical cord and placenta. EP and NE provide protection against this stress. They clear the lungs, prepare the lungs to breathe air, mobilize nutrients for cellular metabolism, and promote increased blood flow to brain and heart.
88
Puerperium phase.
6-week period following delivery where the maternal reproductive organs and physiology return to pre-pregnancy state.
89
Involution.
Uterus undergoes a reduction in size after delivery, through a process of tissue catabolism.
90
Why does the fetus depend entirely on the mother for obtaining O2 and eliminating CO2?
The fetal lungs are either collapsed or partially filled with amniotic fluid. After birth, this fluid is absorbed.
91
The production of surfactant begins by the end of the ____ month of development.
6th
92
What happens to the fetal respiratory system right after birth?
CO2 builds up in the baby's blood because it is no longer being removed by the mother. Rising CO2 levels stimulates the respiratory center in medulla oblongata, causing the respiratory muscles to contract, and the baby to draw their first breath.
93
What happens to the fetal cardiovascular system right after birth?
Closure of the foramen ovale between the atria of the fetal heart. This diverts deoxygenated blood to the lungs for the first time. The foramen ovale is closed by 2 flaps of septal heart tissue that fold together and permanently fuse. The remnant of the foramen ovale is the fossa ovalis.
94
Once the fetal lungs begin to function, the ______ shuts off due to _______ , and it becomes the _______ .
Ductus arteriosus.
Contractions of smooth muscle in its wall.
Ligamentum arteriosum.
The muscle contraction is mediated by bradykinin, which is released from the lungs during initial inflation.
95
In the fetus, the ductus venosus connects the ______ directly with the ______ .
Umbilical vein.
Inferior vena cava.
This allows blood from the placenta to bypass the fetal liver.
96
When the umbilical cord is severed, the ______ collapses, and venous blood from the viscera of the fetus flows into the ______ to the liver and then via the hepatic vein to the ________ .
Ductus venosus.
Hepatic portal vein.
Inferior vena cava.
97
The remnant of the ductus venosus becomes the ______ .
Ligamentum venosum.
98
Prolactin.
Anterior pituitary. Principal hormone in lactation. Maintains lactation, once oxytocin initiates it. Provides milk for the next nursing period.
99
Even though prolactin levels increase as pregnancy progresses, why does no milk production occur?
Progesterone inhibits the effects of prolactin.
100
Suckling.
Main stimulator of oxytocin and prolactin release. Initiates nerve impulses from stretch receptors in nipples release oxytocin. Oxytocin then decreases hypothalamic release of prolactin-inhibiting hormone and increase release of prolactin-releasing hormone.
101
_____ causes release of milk into the mammary ducts via the milk ejection reflex.
Oxytocin.
102
Milk ejection reflex.
Stimulation of touch receptors in nipple initiates sensory nerve impulses to hypothalamus. Oxytocin release from posterior pituitary increases. Oxytocin travels to mammary glands and stimulates contraction of myo-epithelial cells surrounding glandular cells and ducts. This moves the milk from the alveoli of the mammary glands into the mammary ducts, where it can be suckled.
103
Even though the actual ejection of milk does not occur until 30-60 seconds after nursing begins...
Some milk stored in lactiferous sinuses near the nipple is available during this latent period.
104
Colostrum.
Cloudy fluid secreted from mammary glands around birth. Contains less lactose and no fat compared to milk.
105
Lactation often blocks ovarian cycles for the first few months following delivery if the frequency of suckling is ______ .
8-10 times a day. This effect is inconsistent.
106
The suppression of ovulation during lactation is believed to occur as follows....
During breastfeeding, neural input from the nipple reaches the hypothalamus and cases it to produce neurotransmitters that suppress the release of GnRH. Production of LH and FSH then decreases, and ovulation is inhibited.
