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Anatomy and Physiology 2 > Chapter 28- Pregnancy and human development > Flashcards

Chapter 28- Pregnancy and human development Flashcards

1
Q

Zygote

A

A diploid cell resulting from the fusion of two haploid gametes. Sometimes called a single celled embryo

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2
Q

Embryo

A

Stage of development from soon after the fertilization of the ovum to week 8 of development. No longer single celled at this point

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3
Q

Fetus

A

week 8 to birth, called an infant after birth

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4
Q

Fertilization definition

A

The process in sexual reproduction that involves the union of a sperm and an egg to form a diploid zygote

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5
Q

What is the time window for fertilization?

A

An oocyte is only viable for 24 hours at most after ovulation, and sperm are most viable 24-48 hours in the female reproductive system. General rule- in order for fertilization to occur- intercourse must occur no more than 2 days before ovulation and no more than 1 day after ovulation. Y chromosome sperm swim faster but are smaller, so they break down more quickly, but there’s not a large difference between Y and X in terms of lifespan

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6
Q

Why do only a fraction of sperm that enter the vagina reach the uterus? (2)

A
  1. Millions lost immediately by leaking from the vagina

2. Millions more lost by acidic environment of vagina- glycogen fermenting bacteria

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7
Q

How can sperm be lost in the uterus?

A

Phagocytes kill off many more sperm. Only a few thousand “survivors”- reverse peristaltic waves push these sperm toward the uterine tubes as the uterus contracts toward the fundus.

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8
Q

How do sperm travel in the right direction?

A

Sperm have various receptors (chemical, temperature, fluid flow) to ensure they travel in the correct direction

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9
Q

Sperm capacitation

A

Sperm are incapable of fertilizing the oocyte immediately after entering the vagina- want digestive enzymes to be weakened in the female anatomy but strong in the male anatomy. Before fertilization occurs- sperm must be “capacitated”- motility is enhanced and there is a weakening of membranes- allows easier release of enzymes that help with penetrating the egg. Can take hours after ejaculation

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10
Q

2 protective structures that surround the oocyte

A
  1. Zona pellucida- innermost layer

2. Corona radiata- outer layer

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11
Q

Zona pellucida

A

Innermost layer produced by primary oocyte and follicle. Protects secondary oocyte, is necessary for fertilization to occur

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12
Q

Corona radiata

A

Outer layer, contains cells that allows communication between cells and oocyte. Protects egg after it has been ovulated

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13
Q

Which structures must the sperm cross for fertilization to occur?

A

For fertilization to occur, sperm must be able to cross both structures in the egg. Sperm burrow through cells of the corona radiata

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14
Q

Acrosomal reaction

A

Sperm bind zona pellucida- calcium levels in sperm rise. Acrosomal enzymes released from the acrosome of the sperm- digest holes through the zona pellucida to the plasma membrane of the oocyte. One sperm’s enzymes are never going to be enough to allow fertilization to occur- to get one sperm through, the other sperm have to release all of their enzymes. The first sperm won’t fertilize the egg- neither will the first thousand.

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15
Q

What happens once the acrosomal reaction is initiated and the sperm gets through the layers? (2)

A
  1. The plasma membrane of the sperm binds to the sperm binding receptors on the plasma membrane of the oocyte
  2. Once bound, the two membranes fuse together- sperm contents enter the oocyte
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16
Q

Polyspermy

A

The entry of more than one sperm cell into the oocyte- results in incorrect chromosome number. Resulting embryo cannot mitotically divide- dies

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17
Q

2 ways the oocyte can block polyspermy

A
  1. Oocyte membrane blocks- sperm binding receptors are shed from oocyte surface. Sperm unable to bind oocyte surface and fertilize eggs with those receptors
  2. Cortical reaction
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18
Q

Cortical reaction

A

Endoplasmic reticulum of oocyte releases calcium in response to binding of single sperm cell. Granules release enzymes to destroy binding receptors and causes the zona pellucida to harden

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19
Q

How many fertilizing events spontaneously abort?

A

About 70% of fertilizing events spontaneously abort- unclear why, but likely due to chromosomal mismatch. People often spontaneously abort without knowing that they’re pregnant

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20
Q

Completion of meiosis 2 and fertilization (4 steps)

A
  1. Sperm nucleus must travel to the oocyte nucleus. As it travels, sperm nucleus swells in size to form male pronucleus
  2. Surge in calcium from cortical reaction causes release of zinc from oocyte. Meiosis 2 is completed as zinc leaves cell- forms 2nd polar body and mature ovum
  3. After meiosis 2- female pronucleus forms
  4. Pronuclei membranes rupture
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21
Q

What happens when the male pronuclei membranes rupture?

A

Chromosomes are released together, and maternal and paternal chromosomes combine to form a diploid zygote- this is fertilization. This is also the first appearance of the zygote

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22
Q

When does development begin?

A

Development begins at fertilization. Diploid cell (zygote) quickly begins to divide mitotically

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23
Q

Cleavage

A

Rapid mitotic divisions of the zygote. About 36 hours after fertilization- zygote has completed first division, contains 2 identical blastomere cells. 72 hours after fertilization- morula is formed- 16 cells

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24
Q

What is the benefit of cleavage?

A

Genetically identical cells are clumped together, which increases the surface area of the embryo- allows for better gas exchange, waste removal, and uptake of nutrients. A lot easier to build a functional person from many cells than from one single large cell- easier to start with many pieces you can put together however you want than with one large piece of stone that you have to carve to make the house

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25
Q

The morula divides to form

A

Morula continues to divide- forms blastocyst with 100+ cells

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26
Q

2 layers of the blastocyst

A
  1. External trophoblast

2. Internal embryoblast

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27
Q

External trophoblast

A

Single layer of flattened cells. Aids in embryo implantation, contributes to chorion formation/function, has immunosuppressive effects

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28
Q

Internal embryoblast

A

Cluster of 20-30 rounded cells. Will eventually form the embryo proper (and organs) and extraembryonic membranes

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29
Q

How is the blastocyst implanted in the endometrium?

A

Endometrium is receptive to implanting embryo due to high estrogen and progesterone levels. Cell adhesion molecules on endometrium bind the trophoblast when it makes contact with the lining, this usually occurs high in the uterus.

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30
Q

Once bound, what happens to the blastocyst?

A

Now called a trophoblast. Once bound, trophoblast releases digestive enzymes and growth factors on epithelium of endometrium

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31
Q

Trophoblast growth factors

A

Endometrium thickens as blood vessels enlarge and become leaky. Trophoblast proliferates, forms 2 layers- cytotrophoblast and syncytiotrophoblast.

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32
Q

Cytotrophoblast

A

Innermost layer. Mass of cells that anchors growing embryo to uterine tissue and release enzymes to facilitate implantation

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33
Q

Syncytiotrophoblast

A

Outermost layer. Mass of fused cells that produce and release enzymes to facilitate implantation

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34
Q

Trophoblast digestive enzymes

A

Responsible for erosion of endometrium around blastocyst. Blastocyst buries itself in the blood rich lining, and surrounding endometrial cells proliferate- covers the blastocyst

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35
Q

Human chorionic gonadotropin (hCG)

A

Released by embryo once implantation is complete. hCG is a hormone that prevents breakdown of the corpus luteum and suppresses female immune system. hCG drops at 4 months, corpus luteum breaks down. By this time, the placenta has formed and is making estrogen and progesterone

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36
Q

The placenta

A

A temporary organ originating from embryonic and maternal tissues. Functions- maintain pregnancy, exchange respiratory gasses, provide nutrients to embryo/fetus, dispose of waste, etc

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37
Q

When does the placenta become a fully functional organ?

A

The placenta is a fully functional organ by the 4th month of pregnancy. Will allow oxygen, nutrient, and waste exchange before this time, maternal and fetal blood do not mix

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38
Q

Embryonic contribution to placenta formation

A

Formation of the chorion membrane that surrounds embryo/fetus. Blood vessels extend from chorionic villi, form umbilical vein and arteries

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39
Q

Parental contribution to placenta formation (3)

A
  1. Functional layer of endometrium develops blood filled lacunae, which chorionic villi are immersed in
  2. Endometrium that lies underneath embryo becomes decidua basalis
  3. Endometrium that surrounds uterine cavity face of embryo forms decidua capsularis
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40
Q

Lacunae

A

Chorionic villi has bloods of blood (lacuna) from the parent, where exchange occurs between parent and fetus

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41
Q

Decidua basalis function

A

Forms the true placenta with the lacuna and chorionic villi immersed in it. Function- forms placenta with chorionic villi

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42
Q

Decidua capsularis

A

Endometrium that surrounds uterine cavity face of embryo forms decidua capsularis. Function- expands to accommodate the growing fetus. Chorionic villi here degenerate as pregnancy progresses

43
Q

Vasculature of the placenta

A

Umbilical vein and 2 umbilical arteries

44
Q

When do extraembryonic membranes form?

A

Membranes formed during the first few weeks of development. Embryoblast divides into epiblast and hypoblast to form the embryonic disc. Extraembryonic membranes and primary germ layers form from the disc and the divisions

45
Q

Extraembryonic membranes include (4)

A
  1. Amnion
  2. Yolk sac
  3. Allantois
  4. Chorion
46
Q

Amnion

A

Thin, transparent layer that extends completely around the embryo, except where umbilical vein and arteries enter. Filled with amniotic fluid- amniotic fluid is derived from fetal urine later in pregnancy

47
Q

Functions of amniotic fluid (4)

A
  1. Provides buoyancy and protection- protects embryo from being crushed by its own body and acts as a shock absorber
  2. Maintains consistent temperature
  3. Prevents developing parts of embryo from sticking together/fusing
  4. Allows movement
48
Q

Yolk sac definition

A

Sac structure that hangs from ventral surface of the embryo

49
Q

Yolk sac functions (3)

A
  1. Eventually forms digestive tube
  2. Forms earliest blood cells
  3. Primordial germ cells move from here to gonads- forms sperm/ova
50
Q

Allantois

A

Structural basis for the umbilical cord, will eventually form part of the urinary bladder

51
Q

Chorion functions (2)

A

The chorion is the embryonic contribution to the placenta

  1. Contain chorionic villi- contact maternal blood and allow exchange of gasses, nutrients, and wastes
  2. Encloses all other extraembryonic membranes
52
Q

Gastrulation definition

A

Cellular rearrangements and migrations of cells from 2 layered embryonic disc into a 3 layered embryo

53
Q

3 primary germ layers

A
  1. Endoderm
  2. Ectoderm
  3. Mesoderm
54
Q

Gastrulation process (4 steps)

A
  1. Begins with formation of primitive streak in the embryonic disc
  2. Epiblast cells migrate and enter the primitive streak
  3. Other cells follow, push between cells of upper and lower layers
  4. Some cells remain at the dorsal surface
55
Q

Primitive streak

A

Primitive streak is a groove with raised edges that will form the long axis of the embryo

56
Q

Notochord

A

Mesodermal cells immediately beneath primitive streak form the notochord. The notochord is the first axial support of the embryo

57
Q

Organogenesis

A

Formation of body organs and organ systems, begins with gastrulation. Early process- all organ systems are recognizable by week 8

58
Q

How does organogenesis occur?

A

When plates of gastrulation begin to form, they fold laterally soon after, like folding paper. Anterior and posterior ends will eventually fold over and close the tube, resulting in an embryo (looks kind of like a tadpole at first). The endoderm is the layer that is enclosed inside, and these cells fuse to seal off the embryo. The yolk sac hangs from the ventral portion of the embryo

59
Q

What does the endoderm specialize into?

A

Folding process forms the primitive gut, endoderm becomes epithelial lining of GI tract. The respiratory tract forms from outpocketing of the foregut. Other glands formed from endothelial outpocketings along the tract. Oral and anal ends of the gut will open

60
Q

What does the ectoderm specialize into?

A

Undergoes neurulation, remaining portion becomes the epidermis

61
Q

Neurulation

A

Formation of the brain and spinal cord, induced by chemicals released by notochord. Results in formation of a neural tube that sits over the notochord. Anterior portion becomes the brain, remaining becomes the spinal cord

62
Q

How long does it take the preliminary structures of the nervous system to form?

A

By week 4- forebrain, midbrain, and hindbrain evident. By week 8- cerebral hemispheres evident, brain waves can be recorded. There is some electrical activity in the cells

63
Q

What structures does the mesoderm develop into?

A

Forms mesodermal blocks called somites that hug the notochord on either side. Remaining mesoderm forms kidneys and gonads, connective tissue of limbs, heart and blood vessels, dermis of ventral body, etc. If it’s not formed by the endoderm or ectoderm, it’s formed by the mesoderm

64
Q

3 functional parts of somites

A
  1. Sclerotome- produce vertebrae and rib at each associated levels
  2. Dermatome- forms dermis in dorsal part of the body
  3. Myotome- forms skeletal muscle of neck, body trunk, and limbs
65
Q

Cardiovascular modifications seen only during development, not maintained after birth (2)

A
  1. Umbilical arteries and vein

2. Vascular shunts

66
Q

Umbilical arteries and vein function

A

Although blood is transported via these structures, gas exchange (oxygen and carbon dioxide), waste elimination, and various other processes occur in the placenta. Vein carries oxygenated blood to the fetus, arteries carry oxygen poor blood away from the fetus.

67
Q

Vascular shunts function

A

Redistributes blood to parts of the body that need it most, mostly bypasses organs not yet used by developing fetus

68
Q

Vascular shunts (3)

A
  1. Ductus venosus
  2. Foramen ovale
  3. Ductus arteriosus
69
Q

Ductus venosus

A

Shunt that bypasses the liver. This is because the parent’s liver does all the work for the fetus

70
Q

Foramen ovale

A

Shunts blood from the right atrium to the left atrium, causes blood to bypass lungs

71
Q

Ductus arteriosus

A

Shunts blood from pulmonary trunk to aorta, causes blood to bypass lungs

72
Q

After birth, what happens to the umbilical blood vessels?

A

Umbilical blood vessels constrict and fibrose. Umbilical artery gives rise to- portion of artery supplies the bladder and one portion of artery also becomes median umbilical ligaments. Umbilical vein remnant become the round ligament of the liver

73
Q

What happens to the ductus venosus after birth?

A

Ductus venosus collapses and is converted to ligamentum venosum

74
Q

What happens to the foramen ovale after birth?

A

Foramen ovale closes as pulmonary circulation becomes functional. Edges fuse to septal wall of heart- forms the fossa ovalis

75
Q

What happens to the ductus arteriosus after birth?

A

Ductus arteriosus constricts and closes off- forms the ligamentum arteriosum. Helps support the pulmonary artery and the aorta

76
Q

What happens to the size of the uterus during pregnancy?

A

At beginning of pregnancy, the uterus is about the size of a pear, at the end of pregnancy, the top of the uterus is even with the xiphoid process. Uterus and fetus push all other organs up and out. Pelvis widens from release of relaxin- eventually makes it difficult to walk normally

77
Q

How long does pregnancy last?

A

Pregnancy lasts 38-40 weeks so all organs can develop enough. The lungs are the last to develop and are usually formed by week 38

78
Q

How much weight is gained during pregnancy?

A

About 28 pounds- depends on weight at beginning of pregnancy. This is due to fat, extra weight of the fetus, placenta, and uterus. About 300 extra calories per day necessary to maintain a healthy pregnancy- not a huge amount necessary

79
Q

Which hormones affect the metabolism of the pregnant person? (3)

A
  1. Placental growth hormone
  2. Human placental lactogen (hPL)
  3. Corticotropin-releasing hormone (CRH)
80
Q

Placental growth hormone

A

Replaces growth hormone in pregnant women. Stimulates lipolysis and glucose production for growing fetus

81
Q

Human placental lactogen (hPL)

A

Stimulates maturation of breasts for lactation, promotes fetal growth, and is glucose sparing. Glucose sparing- mother’s cells metabolize more fatty acids to save glucose for fetus. Side effect- reduction in insulin sensitivity (gestational diabetes)

82
Q

Corticotropin-releasing hormone (CRH)

A

Rises only toward end of pregnancy. As CRH rises, mother’s ACTH and cortisol levels rise- helps during birth

83
Q

Cortisol functions (2)

A
  1. Cortisol leads to maturation of fetal organs- especially the lungs
  2. Cortisol increases blood glucose which is delivered to the fetus
84
Q

How can pregnancy affect the GI system?

A

Surge in HCG, estrogen, and progesterone can result in nausea/vomiting- called “morning” sickness, but can occur at any time of day. Protective measure in an evolutionary sense- often occurs when smelling meat. This is because spoiled meat is very threatening to the pregnancy. Also, the uterus invades the abdomen, pressing on other organs- heartburn and constipation

85
Q

How can pregnancy affect the urinary system?

A

Increased metabolic rate, higher blood volume and need to dispose of extra waste from fetus= more urine produced. Uterus pushes on bladder- increases frequency of urination

86
Q

How can pregnancy affect the respiratory system?

A

The uterus does not enter the thoracic cavity, but it eventually pushes on the bottom part of the diaphragm- diaphragm can’t flatten out like it should and breathing is difficult by end of pregnancy. Respiratory rate is unaffected, but there is an increase in tidal volume and a decrease in residual volume. Increased carbon dioxide, medullary respiratory centers become more sensitive to carbon dioxide

87
Q

How does blood volume change during pregnancy?

A

Total blood volume increases by at least 25%, may be as high as 40% by the end of the 32nd week. Accommodates needs of fetus, protects mother from blood loss during childbirth. Blood pressure remains the same

88
Q

How does pregnancy affect the cardiovascular system?

A

Cardiac output increases 35-40%. Uterus pushes on blood vessels as it grows- blocks blood flow, forming varicose veins and edema, especially in the legs. Blood tends to pool in the legs if the person stands for too long

89
Q

How is labor initiated?

A

The fetus determines its own birth date. Increases in fetal cortisol levels leads to maturation of lung tissue (and increase in surfactant) and surge in estrogen from the placenta

90
Q

Affects of the surge of estrogen from the placenta to initiate labor (3)

A
  1. Increased synthesis of prostaglandins- soften/thin the cervical mucus
  2. Addition of more actin, myosin, and other contractile elements. Allows uterus to contract more forcefully during labor and as a single unit.
  3. Increase in oxytocin and prostaglandin receptors in myometrium. Both chemicals lead to strong, rhythmic contractions associated with labor
91
Q

Why is oxytocin released during labor?

A

Released by the posterior pituitary gland of mother to stimulate uterine contractions- uterine contractions push head of fetus into the cervix. Stretching of cervix by head stimulates more oxytocin release by the posterior pituitary- positive feedback mechanism. When fetus exits, the mechanism turns off

92
Q

Stages of labor (3)

A
  1. Dilation stage- occurs from onset of labor until cervix is fully dilated
  2. Expulsion- occurs from full dilation to delivery
  3. Placental- occurs after delivery of infant
93
Q

Dilation stage of labor

A

Highly variable duration of time- dilation caused by force of baby’s head against cervix. Full dilation is about 10 cm in diameter. Contractions begin as weak/short, becomes progressively stronger. Push of head against the cervix will physically break the amnion- “water” breaks

94
Q

Expulsion stage of pregnancy

A

Contractions occur every 2-3 minutes, last about 1 minute, urge to push becomes strong. Crowning occurs when the largest portion of infant’s head distends vulva. Ideally, the infant is in a vertex position

95
Q

What are the advantages of the baby being in the vertex position?

A

Dilates the cervix for rest of body to pass easier, can suction mucus from oral/nasal passage for breathing to occur sooner

96
Q

Breech position

A

Butt first- dangerous for infant and difficult to stretch the cervix enough for the infant to pass through in that position

97
Q

Placental stage of labor

A

Occurs about 30 minutes after birth. Mother must also deliver placenta and all of its structures (afterbirth). Uterine contractions compress blood vessels and tear placenta from uterine wall. If not completely removed, can result in infection

98
Q

Which major adjustments occur in the baby immediately after birth? (2)

A
  1. Taking the first breath

2. Closing shunts and fetal blood vessels

99
Q

What happens for the baby to take their first breath?

A

Umbilical blood vessels constrict- prevents removal of carbon dioxide from infant. Respiratory acidosis results- stimulation of respiratory centers occurs and is normally followed by the first breath. Also, the lungs must be completely inflated and not collapse. Surfactant prevents lung collapse

100
Q

Structure of mammary glands

A

Each gland consists of 15-20 lobes. Lobules contain glandular alveoli- produce milk during lactation, but not before. The glands aren’t functional when a person isn’t pregnant.

101
Q

Prolactin

A

During late pregnancy and after birth, rising levels of progesterone, hPl, and estrogens leads to release of prolactin. Glandular alveoli to become active- produce and release milk. Prolactin only produced for a few weeks after birth- milk production stimulated by feeding infant after this

102
Q

Colostrum

A

There is a delay in milk production, and during this time, colostrum is secreted by the mammary glands. Contains less lactose than milk, very little fat, but contains much more protein, minerals, vitamin A and certain antibodies (IgA). IgA is resistant to being destroyed by gastric juices, provides a starter immune defense

103
Q

Benefits of breast milk for the infant (4)

A
  1. Various components of breast milk are more easily metabolized by the infant (fat, certain minerals, some amino acids)
  2. Various protective molecules- IgA, complement, lysozymes, interferon (protect from viruses), interleukins
  3. Helps build healthy bacterial flora of infant
  4. Serves as a natural laxative
104
Q

Why is it beneficial for breast milk to act as a laxative?

A

Cleanses infant bowels of meconium- contains epithelial cells, bile, other substances. Failure to clear it leads to jaundice- increased absorption of bilirubin from the intestine if there is a large amount in the intestine. Infant’s skin and eyes will turn yellowish orange

Anatomy and Physiology 2 (20 decks)

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