Development & Inheritance Concepts

Question 1

Describe the % of typically ejaculated sperm that reach the oocyte.

Answer 1

200 of 200 million sperm (0.01%) reach the secondary oocyte

Question 2

Describe fertilization as a series of steps, including capacitation, acrosomal reaction, and fast & slow blocks to polyspermy

Answer 2

ONLY ONE SPERM CAN PENETRATE THE OOCYTE

Capacitation:
- The hydrolytic and proteolytic enzymes that were used to take the sperm through the female reproductive tract are stripped off the head of the sperm

Acromsomal reaction:
- When the sperm binds to a receptor on the zonal pellucida, the head is dissolved, releasing Acrosmal enzymes that digest the zonal pellucida to allow the sperm access to the cell membrane of the secondary oocyte

Fast block to polyspermy:
- First sperm contact with the membrane depolarizes it within seconds (Na ions rush into oocytes)
- Other sperm cant enter a depolarized oocyte

Slow block to polyspermy:
- Depolarization of the oocyte membrane (by inward Na surge) also releases Ca ions from intracellular stores, which cause vascular fusion with the oocyte membrane. Chemicals released from the vesicles “harden” what’s left of the Zona pellucida (closing the door on other sperm)

Question 3

Describe fertilization in terms of pronuclei and ploidy.

Answer 3

• Sperm entry triggers the secondary oocyte to finish meiosis, leaving two fully formed haploid, “pronuclei,” each with n= 23 chromosomes
• The two pronuclei fuse and you have a fertilized (2n = 46) Zygote - the genetic blueprint for a human being

Question 4

Contrast the 3 types of maternal decidua based on location.

Answer 4

Basal decidua:
- Within the endometrium, so it functions as the “border” between the fetus and the mother

Capsular decidua:
- Surrounds the growing fetus and gradually pushes into the uterine cavity as the fetus grows
- Eventually moves across the entire uterine cavity to fuse with parietal decidua

Parietal decidua:
- Essentially the entire lining of the uterine cavity

Question 5

Describe the two layers of the split trophoblast and the location & function of each in implantation & placentation.

Answer 5

Cytotrophoblast:
- Remains a complete cell layer covering the part of the embryo burrowing into the maternal Decidua (formerly known as the endometrium)

Synctiotrophoblast:
- The “tip of the spear”
- It’s more of a mass without definitive cell membranes
- “Digests” the decidua to make room for the invading embryo

Question 6

Relate the two layers of the trophoblast to the eventual chorion & placenta

Answer 6

• Cytotrophoblast and Syncytiotrophoblast are going to become the chorion, the most superficial membrane surrounding the growing fetus
• The part of the chorion attached to the umbilical cord is the placenta

Question 7

Describe the bilaminar disc that will become the embryo, relating the epiblast to the amnion, & amniotic cavity, and the hypoblast to the extraembryonic endoblast (or extracoelemic membrane) and the yolk sac

Answer 7

• The bilaminar embryonic disc is made up of epiblasts & hypoblasts
• The disc separates the amniotic cavity and yolk sac (umbilical vesicle)
• The epiblasts are closer to the amniotic cavity, and the hypoblasts are closer to the extraembryonic endoblast

Question 8

Describe the “fusing” of fetal chorionic tissue and maternal decidual tissue, and the diffusion path it creates

Answer 8

• The spreading syncytiotrophoblasts are digesting the tissue around structures of the maternal decidua (sinusoid capillaries and endometrial glands)
• This builds lacunae (little lakes) to collect blood and exocrine secretions from Mom
• Diffusing oxygen and nutrients from the maternal blood, inside lacunae, inside the decidua, into fingers of cytotrophoblasts of the fetal tissue
• The fetus diffuses its waste out into the maternal blood

Question 9

Describe the formation of the extracoelemic (& chorionic cavity) by extraembryonic mesoderm, and the formation of the connecting stalk & eventual umbilical cord

Answer 9

• Extraembryonic mesoderm squeezes into the space between the amniotic cavity and the cytotrophoblast and starts spreading around the whole embryo, edging itself between the amniotic cavity and the cytotrophoblast or the yolk sac and the rest of the trophoblast
• This wedging will form the extracoelemic cavity, which becomes the chorionic cavity
• Extraembyronic mesoderm, cytotrophoblast, and syncytiotrophoblast make the full chorion, which will surround the entire fetus
• It’s connected to the bilaminar discs by a band of extraembryonic mesoderm that will form a stalk that will become the umbilical cord

Question 10

Contrast gastrulation & neurulation, focusing on the location, cells involved & structures produced

Answer 10

Gastrulation
- Making bilaminar disc into trilaminar
- The Epiblast of the bilaminar disc starts gastrulation by forming a central thickened region called a primitive streak, and at the head end is the primitive node.
- The epiblasts around the primitive streak migrate medially and inferiorly to become endoderm and replace hypoblast. They migrate down to pack mesoderm superiorly to endoderm and migrate laterally to rearrange themselves into ectoderm
- Some epiblast become specialized mesoderm that becomes the notochordal process which induces ectoderm to form a neural plate to start neurulation

Neurulation
- The first major step to molding a human body out of the trilaminar disc
- Making the neural tube that will become the brain

Question 11

Contrast the 3 layers of the trilaminar disc, in terms of the type of tissue, and which part of the bilaminar disc gives rise to all 3.

Answer 11

• Epiblast becomes ectoderm, endothelial tissue
• Hypoblas becomes endoderm, epithelial tissue
• Mesoderm fills in between the two, loose connective tissue

Question 12

Name one tissue of the adult body that derives from each of the 3 layers of the trilaminar disc

Answer 12

Ectoderm = tightly packed endothelial cells, epidermis of the integument

Endoderm= tightly packed epithelium, the internal lining of the GI tract

Mesoderm= loose connective tissue, muscle

Question 13

Name the 3 common “views” that we use to look at the developing embryo & associated amniotic cavity & yolk sac

Answer 13

Dorsal
Partial
Transverse

Question 14

Discuss the structure, and eventual fate, of the oropharyngeal & cloacal membranes

Answer 14

• At the head and tail end, the mesoderm doesn’t expand to the edges of the trilaminar disc, so there are two areas left where endoderm and ectoderm fuse together without mesoderm between
• Oropharyngeal and cloacal membrane
• Future mouth and anus

Question 15

Describe the notochordal process, in terms of the process that developed it, its structure, location & role in neurulation

Answer 15

• Some epiblast become highly specialized (and mission-critical) mesoderm that forms a hollow tube projecting anteriorly, along the midline, from the primitive node (pit)
• This mesoderm is called the notochordal process
• The notochordal process becomes the “taskmaster” that induces other mesoderm (& ecto- & endoderm) to differentiate into structures as embryonic development processes
• It induces the ectoderm to form the neural plate along the midline between the primitive node and oropharyngeal membrane. Neurulation will start with this neural plate.

Question 16

Describe the formation of neural crest cells, and give one example of a type of tissue that develops from neural crest cells.

Answer 16

• The neural plate pushes towards the midline and forces some ectoderm on the midline to dip down to form the neural groove
• The two leading edges of the neural fold moving medially will fuse over the neural groove to form the neural tube
• Neural crest cells form, too, which go on to become major portions of the peripheral NS

Question 17

Trace the progression of the 3 primary vesicles of the neural tube, through to the various parts of the adult brain.

Answer 17

Prosencephalon -> Telencephalon -> Cerebrum
Diencephalon -> Thalamus, hypothalamus, and epithalamus

Mesencephalon -> Mesencephalon -> Midbrain

Rhombencephalon-> Metencephalon -> Pons, Cerebellum
Myelencephalon > Medulla oblongata

Question 18

Describe a chorionic villus, and an intervillus space, structurally, and functionally & based on who it belongs to – Mom or embryo/fetus.

Answer 18

Chorionic villi (fingers) were just formed from syncytiotrophoblasts.
- Belongs to the fetal placenta
- Interlocks intervillous spaces

Intervillus space
- Maternal part of the placenta
- Maternal blood leaks out of sinusoids into these spaces

Question 19

Trace the diffusion path of oxygen and nutrients from maternal sinusoids to fetal blood, across the chorion.

Answer 19

Oxygen and nutrients from maternal sinusoids empty into intervillous space and diffuse into capillaries that enter the umbilical cord of the fetus.

Fetal waste is emptied from the capillaries, into the intervillous space, and out into the maternal sinusoids to be processed by Mom

Question 20

Contrast lateral & head-tail folding, based on key structures formed by each

Answer 20

Lateral folding:
- Medially fuse and make a cylinder with ectoderm most superficially, mesoderm deep to that, and endoderm most deep
- Creates the gut tube from part of the yolk sac

Head-tail folding:
- Bring developing mouth and heart into their final adult positions and developing anus at the “tail” region of the embryo

Question 21

Track the development of the 3 parts of the gut, by head-tail folding, and give a BRIEF description of GI structures formed by each of the 3

Answer 21

• Foregut at the head end = pharynx, esophagus, stomach, proximal duodenum
• Midgut between the two = distal duodenum, jejunum, ileum, ascending colon and proximal transverse colon
• Hindgut at the tail end = distal transverse colon, descending, sigmoid, and rectum

Question 22

Identify ONE embryonic structure prominent at the 4th, 6th, 7th & 8th weeks of embryonic development.

Answer 22

Week 4= limb buds
Week 6= tail
Week 7= Short and webbed digits formed on limbs
Week 8= distinct digits

Question 23

Name two things that happen during fetal growth.

Answer 23

Continuous growth and development of previously formed structures
Growth in mass

Question 24

Name a handful of sources of maternal weight gain during pregnancy, focusing on which are fetally based, and which are maternally-based

Answer 24

Fetally based:
- Fetal growth
- Amniotic fluid
- Placenta growth

Maternally based:
- Placenta growth
- Uterine enlargement
- Body water increase
- Increased metabolite storage
- Breast enlargement

Question 25

Name ONE respiratory, ONE cardiovascular, ONE digestive, and ONE urinary change in maternal physiology during pregnancy

Answer 25

Respiratory
Difficulty breathing

Cardiovascular
Heart rate increases

Digestive
Increased calorie demand

Urinary
Increased frequency and urgency to urinate

Question 26

Describe uterine changes during pregnancy, contrasting the roles of hyperplasia & hypertrophy

Answer 26

• Increase from 70 to 1100g
• Muscle growth in the myometrium is huge

Hyperplasia:
- More smooth muscle cells
- Early on

Hypertrophy:
- Cell enlargement
- Later on in pregnancy

Question 27

Describe the source & function of 6 key hormones of pregnancy.

Answer 27

2 Ovarian Hormones: Progesterone and estrogen
- Prepare the mother’s body for the birth of the baby

3 Chorionic (placental) Hormones: Human chorionic gonadotrophin, human chorionic somatomammotropin, and CRH
- Human chorionic gonadotrophin rescues the corpus luteum from degeneration until the third or fourth month of pregnancy
- Human chorionic somatomammotropin helps prepare mammary glands for lactation
- CRH increases the secretion of cortisol

Relaxin starts as ovarian, then becomes chorionic (placental)
- Increases flexibility of pubic symphysis

Question 28

Where appropriate, trace the profile of the hormone across the 39 weeks of pregnancy (i.e. hCG, estrogen & progesterone)

Answer 28

• hCG rescues the corpus lutem, which releases progesterone and estrogen, in the ovaries from degeneration
• hCG released from the placenta drives an ovarian hormone, progesterone, to maintain pregnancy for the first trimester (prevent decidual sloughing), until the placenta kicks in and supplies much higher levels of progesterone and estrogen through the 2nd and 3rd trimesters
• Progesterone keeps the uterine myometrium calm and keeps the cervix closed tightly during pregnancy

Question 29

Discuss the onset of true labor and the role of progesterone in triggering true labor.

Answer 29

The onset of labor starts with uterine contractions, but those cant start if progesterone is high

Contractions are timed and cervical dilation (opening) that can be measured

Progesterone has to come down at the very end of gestation, and estrogen has to spike

Question 30

Contrast the 3 phases of labor/delivery, in terms of length, and key events

Answer 30

Dilation:
- Regular uterine contractions start and end when the cervix is fully dilated (10cm)
- 6-12 hours
- Amniotic sac ruptures

Expulsion:
- 10 minutes to several hours
- Difficult for mom and fetus
- Hypoxia during delivery is common and blood levels of epinephrine and NE of the fetus are off the charts

Placental:
- 5-30 minutes after delivery
- Continued powerful uterine contractions expel the placenta as it’s torn from the uterine wall
- Those contractions also constrict blood vessels ruptured during delivery, reducing maternal hemorrhaging

Question 31

Describe the positive feedback loop driven by oxytocin to stimulate uterine contractions

Answer 31

Increased stretching of the cervix causes the release of more oxytocin, which results in more stretching of the cervix

Question 32

Describe two physiological processes seen during the Puerperium phase

Answer 32

Massive catabolism consumes the uterus and brings it back to pre-pregnancy size

Maternal organs & physiology return to pre-pregnancy states

Question 33

Describe the respiratory adjustments by baby within the first couple of seconds of post-natal life, focusing on the importance of CO2 buildup, and the structural changes needed to form fully functional post-natal lungs & respiratory function

Answer 33

• Drive to breathe is triggered by CO2
• Build up of CO2 is what triggers hypercapnia, which triggers the respiratory center of the medulla oblongata to contract the respiratory muscles violently
• Surfactant has been building up by cortisol and immediately supports the alveolar shape once they’re inflated at first breath

Question 34

Describe ONE cardiovascular adjustment, focusing on the fetal circuit, and the post-natal change needed to transform the fetal circuit into the “adult” circuit

Answer 34

• In the fetal circuit, the foramen ovale allows blood to pass from the right atrium to the left atrium.
• Post-natally, the foramen ovale closes almost instantly at birth and blood takes the “adult” pulmonary route for the first time

Fetal: Inferior vena cava - right atrium - (foramen ovale) - left atrium - left ventricle - ascending aorta

Adult: Inferior vena cava - right atrium - right ventricle - pulmonary trunk - lungs - left atrium - left ventricle - ascending aorta

Question 35

Describe the process by which prolactin drives milk production in the mammary glands, focusing on progesterone inhibition, then the standard sense, integrate, respond

Answer 35

• Prolactin increases as pregnancy progresses, but as long as progesterone is high it inhibits the ability of prolactin to produce milk
• Suckling on the breast riggers nerve impulses from the nipple to the hypothalamus
• The hypothalamus decreases the release of PIH and increases the release of PRH
• PRH travels to the anterior pituitary
• Prolactin is secreted from the anterior pituitary and travels to the mammary glands
• In the mammary glands, prolactin production increases 10-fold for about an hour

Question 36

Contrast colostrum & breast milk in terms of timing of release & content

Answer 36

Colostrum:
- Takes a couple of days to get breast milk, so for the first few days colostrum is ejected
- Less lactose than breast milk and no fats, but lots of other great things including antibodies

Breast Milk:
- Takes a couple of days
- More lactose and more fats

Question 37

Describe the positive feedback loop driven by oxytocin to stimulate the ejection of breast milk, and the role of lactiferous sinuses in this loop.

Answer 37

• Suckling on the breast triggers nerve impulses sent to the hypothalamus
• Neruosecretory cells of the hypothalamus release oxytocin from the posterior pituitary
• Oxytocin travels from the posterior pituitary to the mammary glands
• In the mammary glands, oxytocin stimulates the contraction of myoepithelial cells, which eject milk from the mammary glands
• Rewarded with milk, the baby continues to suckle

Question 38

Name several benefits of breast milk to infant health & development

Answer 38

• Fats, sugar, and proteins in abundance to fuel anabolic growth, as well as lysozymes, inference, and maternal IgA antibodies to help the baby’s immune system
• Neutrophils, macrophages, and plasma cells that can help the baby’s immune system
• Increased bonding between Mom and baby
• Breastfeeding is correlated with better growth, intellectual, and neurological development, and immune system function, and reduces chances of all kinds of pathologies

Question 39

Contrast phenotype & genotype and contrast dominant & recessive alleles.

Answer 39

Genotype is a trait, and phenotype is the physical expression of these traits

Dominant (P) means if it matches with a recessive allele (p), in the heterozygote (Pp), then the dominant allele shows in the phenotype, and the recessive allele is masked.

Question 40

Contrast autosomal & sex-linked inheritance patterns, focusing on how to write genotypes.

Answer 40

• Autosomal is written with standard dominant P and recessive p

Sex-linked is written as:
- XX is female
- XY is male

X is always carrying a superscript C or c and Y never carries a superscript

Question 41

Contrast “Normal” Mendelian genetics with human genetics, according to multiple alleles per trait, co-dominance, incomplete dominance, polygenic inheritance, and complex inheritance.

Answer 41

• Written the same way with the dominant P and recessive p
• Co-dominance: red rose + white rose = half red half white rose
• Incomplete dominance (hybrid): red rose + white rose = pink rose
• Polygenic inheritance means that multiple genes control one phenotype trait
• Environmental factors will also affect the phenotype (complex inheritance). Tanning booths?