A&PII Ch.29 Pregnancy Selections of Female Reproductive System

Question 1

Three Trimesters of pregnancy

Answer 1

• 1st Trimester is the first 3 months (0-13 wks.) of pregnancy where the zygote becomes an embryo and then an early fetus
• 2nd Trimester is 4-6 months (14-27 wks.) of pregnancy includes the growth of fetus and expansion of maternal tissues
• 3rd Trimester is 7-9 months (28-42 wks.) of pregnancy where the fetus is growing most rapidly and the mother’s body is preparing for labor and delivery

Question 2

Prenatal Period

Answer 2

• Begins with fertilization
• Secondary oocyte and sperm unite
• Ends 38 weeks later with birth
• Composed of three shorter periods
  -Pre-embryonic period
  -Embryonic period
  -Fetal period

Question 3

Pre-embryonic Period, Embryonic Period, and Fetal Period

Answer 3

*Pre-embryonic period is the first 2 weeks after fertilization where the zygote cell is produced by fertilization, becomes spherical multicellular structure (blastocyst), ends when the blastocyst implants in uterine lining
* Embryonic Period is week 3-8 of development, rudimentary versions of major organs appear, baby is now called an embryo
* Fetal Period is the remaining 30 weeks prior to birth (week 9-38), organism is now called a fetus, continues to grow and increase in complexity

Question 4

Fertilization

Answer 4

• Sperm are attracted to the ovulated oocyte via chemoattractants (Progesterone and Allurin)
• Sperm acrosome pierces zona pellucida
• After penetration of secondary oocyte
  -immediate hardening of zona pellucida prevents other sperm from entering this layer
  -ensures only one sperm fertilizes the oocyte
• Polyspermy: two or more sperm enter simultaneously
  -is immediate fatal with 23 triplets of chromosomes (69 chromosomes)

Question 5

Chemoattractants

Answer 5

• Progesterone: certain chemokines from oocyte
  *Allurin: from fallopian tubes

Question 6

Fertilization Fusion

Answer 6

• After the sperm penetrates, Fusion of sperm and oocyte plasma membranes and fusion of sperm and ovum pronuclei occurs
• Contact of sperm and oocyte plasma membranes
  -immediately fuse; only sperm nucleus enters oocyte
• Secondary oocyte completing second meiotic division
  -forms an ovum
  *Nucleus of sperm and ovum
  -Each have haploid number of chromosomes
• They fuse together to become diploid nucleus
• Zygote, the single diploid cell is formed

Question 7

Phases of Fertilization

Answer 7

• Phase 1) Sperm penetrates corona radiata
• Phase 2) Sperm undergoes acrosome reaction (digesting the proteins of the zona pellucida to break it down) and penetrates zona pellucida
• Phase 3) Sperm and oocyte plasma membranes fuse; pronuclei of ovum and sperm fuse

Question 8

Cleavage

Answer 8

• Series of mitotic divisions of zygote
• Increases cell number but not overall size of structure
  -size only increases after implantation in uterine wall
• Zygote divisions start to be named at the 16-cell stage, known as morula
  -cells of morula continue to divide
  -develops fluid-filled cavity, blastocyst cavity
• At this stage, pre-embryo is a blastocyst
  -Trophoblast, outer ring of cells surrounding cavity will form the chorion
  -Embryoblast, packed cells within one side of blastocyst which will form the embryo proper and cells pluripotent are able to develop into any tissue

Question 9

Implantation

Answer 9

• Blastocyst enters the lumen of the uterus by the end of the first week
• Zona pellucida around blastocyst breaks down
• Balstocyst burrows into the endometrium, implantation
• Begins about day 7
• By day 9, blastocyst completely burrowed into the uterine wall
  -Contains nutrients in uterine glands

Question 10

Implantation and Positive Pregnancy Tests

Answer 10

• Blastocysts produce Human Chorionic Gonadotropin (hCG)
• Signals the reproductive system that implantation has occurred
• Promotes maintenance of corpus luteum which then produces estrogen and progesterone to build uterine lining
• Detected in urine by the 2nd week
  -basis of most pregnancy tests
• Levels are high for the first 3 months of pregnancy
  -then decline, causing corpus luteum degeneration
  -by then the placenta is producing its own estrogen to maintain pregnancy

Question 11

Embryo Membranes

Answer 11

• By day 8, membranes start to develop to protect/ nourish embryo
• Yolk Sac is the first extraembryonic membrane to develop, it does not store the yolk (as birds and reptiles do), instead it is the important site for early blood cell and blood vessel formation outside
• Amnion eventually encloses the entire embryo in fluid-filled sac (amniotic cavity), it protects the membrane from drying out and is specialized to secrete amniotic fluid bathing the embryo

Question 12

Extraembryonic Membranes (continued)

Answer 12

• Chorion
  -outermost extraembryonic membrane
  -cells blend with functional layer of endometrium
  -eventually form placentawhich is the cite of nutrient exchange between the embryo and the mother

Question 13

The Placenta

Answer 13

• Highly Vascular Tissue
• Functions to be the site of exchange of nutrients, wastes, and respiratory gases between maternal and fetal blood
  -transmits maternal antibodies to developing embryo or fetus
  -produces estrogen and progesterone which maintains and builds the uterine lining
  *Begins to form during 2nd week, not fully developed until after 3 months

Question 14

Chorionic Villi

Answer 14

• Finger-like structures formed from chorion
• Contain branches of umbilical vessels
• Site for Gas and nutrient exchange
  -maternal blood does not mix with fetal blood
  -bloodstreams so close that nutrients and gases mix
  -O2 diffusing from maternal blood to fetal blood
  -CO2 diffusing from fetal to maternal blood

Question 15

Gastrulation

Answer 15

• Critical period of development; occurs during third week
• Epiblast forms three primary germ layers
  -cells from which all body tissues develop
  -ectoderm, mesoderm, endoderm
• Three-layered structure called an embryo

Question 16

Cells of the Embryo (1st Layer)

Answer 16

• Ectoderm is the epidermis layer of skin and epidermal derivatives (hair, nails, sweat glands, mammary glands)
• Nervous tissue and sense organs
• Pituitary Gland
• Adrenal Medulla
• Enamel of teeth
• Lens

Question 17

Cells of Embryo (2nd Layer)

Answer 17

• Dermis of skin
• Epithelial lining of blood vessels, lymph vessels, serous membranes
• Muscle tissue
• Connective tissue
• Adrenal cortex
• Heart
• Kidneys and Ureters
• Internal reproductive organs
• Spleen

Question 18

Endoderm

Answer 18

• Epithelial lining of respiratory tract, GI tract, urinary tract, reproductive tract, tympanic cavity, auditory tube
• Liver (most of)
• Gallbladder
• Pancreas
• Palantine Tonsils (portion of)
• Thyroid gland
• Parathyroid glands
• Thymus

Question 19

Organogenesis

Answer 19

• Organ development
• Begins once layers have formed and cell folding complete
• By week 8:
  -upper/lower limbs have adult shape and most organ systems have a rudimentary form
• Particularly Sensitive to teratogens during this time
  -Substances causing birth defects or death
  -Include: alcohol, tobacco, drugs, and some viruses

Question 20

Fetal Period

Answer 20

• From beginning of 3rd month to birth
• Maturation of tissues and organs
• Rapid growth of body
• 2.5cm embryo grows to average 53cm at birth
• Weight increase most striking during last two months

Question 21

Factors that Lead to Labor

Answer 21

• Labor is the physical expulsion of fetus and placenta from the uterus
  -typically at 38 weeks for full-term pregnancy
  -not all uterine contractions lead to true labor
• Contractions are weak and irregular at first they become more intense and frequent with increasing estrogen and oxytocin
• Premature labor is prior to 38 weeks which is undesirable because the infant’s body system is not fully developed

Question 22

False Labor

Answer 22

• uterine contractions not resulting in 3 stages of labor
• Braxton-Hicks contractions are irregularly spaced and do not become more frequent
  -relatively weak and do not increase in intensity
  -pain is limited to the lower abdomen and pelvic region
  -pain sometimes stops with movement
  -do not lead to cervical changes

Question 23

Initiation of true Labor

Answer 23

• True Labor is uterine contractions that increase in intensity and regularity, result in changes to the cervix
• Mother’s hypothalamus secretes increasing levels of oxytocin
• Fetus’s hypothalamus is also secreting oxytocin
• Both sources stimulate placenta to secrete prostaglandins
  -stimulate uterine muscle contraction
  -soften and dilate the cervix
• Combined maternal and fetal oxytocin initiates true labor

Question 24

Positive Feedback Mechanisms of True Labor

Answer 24

*Control Center is Fetus’s hypothalamus and mother’s hypothalamus both secrete oxytocin
-Stimulus is oxytocin from the fetus’s and mother’s hypothalamus
-Effector is that it stimulates the placenta to make prostaglandins
-stimulates the uterus to contract
*Stimulus is then the prostaglandins stimulate more frequent and intense contractions of the uterus
-effector is uterine contractions that cause the fetal head to push against the cervix, making the cervix stretch and dialate
*Stimulus then becomes the dialating cervix which initiates nerve signals to the hypothalamus which cause it to secrete more oxytocin (positive feedback)
* Positive Feedback mechanism ends when fetus is no longer in the uterus, therefore, no fetal pressure is felt

Question 25

Dialation Stage

Answer 25

• 1st stage of labor it begins with onset of regular uterine contractions
• ends when the cervix is effaced (thinned) and dilated to 10cm
• longest of 3 stages
• greatest variability especially between nulliparous and parous women
  -Nulliparous women (have not given birth before) and experience a longer dilation stage, 8-24 hours
• Parous women have given birth before and may be in the stage of dialation for 4-12 hours

Question 26

Dilation Stage Continued

Answer 26

• Begins with regularly spaced uterine contractions that increase with intensity and frequency
• Baby’s head against the cervix causes effacing and dilation
  *Amniotic sac ruptures and releases amniotic fluid
  -“water breaking”
  -manually ruptured if necessary

Question 27

Expulsion Stage

Answer 27

• Begins with complete dilation of cervix
• Ends with expulsion of fetus
• Usually 30 min to several hours
• Nulliparous women with longer stage
• Uterine contractions help push fetus through vagina
  -facilitated if woman “bears down”

Question 28

Expulsion Stage (continued)

Answer 28

• Crowning
  -when first part of baby’s calvarium distends vagina
  -head followed by rest of the body
• Episiotomy sometimes necessary
  -perineal muscles surgically incised
  -creates wider opening for body
• Umbilical cord clamped and tied off

Question 29

Placental Stage

Answer 29

• occurs after baby is expelled
• uterus continuing to contract
  -compresses uterine blood vessels; displaces placenta from uterine wall

Question 30

Afterbirth

Answer 30

• Placenta and remaining fetal membranes
• Expulsion completed within 30 minutes
• Carefully examined to make sure all expelled
  -complications may occur if fragments are left

Question 31

Newborn Breathing

Answer 31

• Respiratory changes in neonate
• Fetus after being expelled from uterus
• Fetal lungs not fully inflated prior to birth
  -takes breath within 10 seconds of birth
  -caused by central nervous system reactions to change in environment
  -lungs inflated with first breath
  -surfactant keeping alveoli open
  -if born earlier than 28 weeks, surfactant is insufficient (may need ventilator until lungs mature)

Question 32

Lactation and Prolactin

Answer 32

• production and release of breast milk from mammary glands
• produced by anterior pituitary
• responsible for milk production
• secretion inhibited by dopamine in nonpregnant individuals
• increased by high levels of estrogen
  -both cause acini proliferation/branching of lactiferous ducts

Question 33

Colostrum

Answer 33

• produced by mammary glands
  -during late pregnancy and first few days after birth
• watery, milk-like substance
• lower concentration of fat than true breast milk
• rich in immunoglobulins, especially IgA
  -infant acquiring passive immunity from the mother
• laxative effect, facilitating infants first bowel movement

Question 34

Breast Milk

Answer 34

• Starts to be produced few days postpartum
• Higher fat content than colostrum
• Has essential fatty acids, enzymes for digestion, and immunoglobulins
• More easily digestible than breast milk substitutes

Question 35

Milk Letdown

Answer 35

• Release of breast milk
• Involves positive feedback mechanism
  -w/ suckling, mechanoreceptors in breast are stimulated
  -sends signals to the hypothalamus
  -hypothalamus is stimulated to produce oxytocin, released into blood by posterior pituitary
• Targets myoepithelial cells in mammary acini
  -cells contract, releasing breast milk from acini
• As milk is released, infant continues to nurse, which facilitates further milk release

Question 36

Milk Letdown Reflex

Answer 36

draw it