Human Development Flashcards
Where does fertilization occur?
in the ampulla of the oviduct
- ~0.001% of sperm (2,000 – 3,000) in ejaculate reach the ovum
How do sperm get there within 5 – 10 minutes of release?
flagellar action of sperm
mucous strands in cervical canal
uterine contractions
What is capacitation?
Ascension of sperm cells through the female genital tract (in contact with its secretions).
- sperm cell membranes mature
requires ~10 hours
female fluids remove cholesterol from sperm membranes
sperm membrane becomes more fragile
How long do sperm remain viable?
6 days in female reproductive tract
“window of opportunity” = a few days before ovulation to 14 hr after
What is the acrosomal reaction?
Allows spermatozoa to penetrate the zona pellucida and fuse with the oocyte membrane
hyaluronidase and acrosin (a protease)
- released from sperm that allows penetration of zona pellucida
What are the barriers to penetration for sperm?
corona radiata
zona pellucida
ovum cell membrane
What genetic events take place upon sperm entry/fertilization?
2º oöcyte completes meiosis, becomes oötid
male pronucleus joins female pronucleus
chromosomes line up for first mitosis (now a zygote)
What prevents polyspermy?
fast block = depolarization of oötid membrane
slow block = cortical reaction = formation of impenetrable fertilization membrane
What is cleavage?
Mitosis during first 3 days of development
- each individual cell called a blastomere
When a sperm fertilizes an egg and both pronuclei fuse, finish meiosis and becomes a zygote
zygote continues mitosis and become a 16 cell morula and enters uterine cavity
- lies free in uterus 4 – 5 days
mitosis continues → ~100 cells
Morula becomes Blastocyst
- Hollow sphere
- trophoblast = outer layer becomes embryonic membrane
- inner cell mass = embryoblast become the baby
- blastocoel - filled w/ fluid
Blastocyst implants in uterus
What occurs during implantation?
implantation in the fundus of the uterus
Trophoblast forms providing nourishment and eventually forming the placenta
- begins secreting human chorionic gonadotropin (HcG)
What are the stages of development?
Predifferentiation stage (0-2 weeks) - ball of cells
Embryonic Stage (3-8 weeks)
- formation of new structures (gastrulation+ extraembryonic membranes)
- extremely important
Fetal Stage (9-38 weeks) - growth of existing structures
What occurs during the embryonic stage?
Gastrulation
- Formation of 1st of 3 germinal tissues (endoderm, mesoderm, ectoderm)
Differentiation of the inner cell mass into germ layers + extraembryonic membranes
This process is called gastrulation (forming a gastrula)
No longer a blastocyst
What is the ectoderm?
Forms epidermis + nervous system
Skin has alot of receptors so makes sense that it develops w/ nervous system
External apperance + brain (nervous tissue) = “attractoderm”
What is the mesoderm?
Mesoderm - in between ectoderm+endoderm
Muscle cells, bone, connective tissue (ligaments, tendons), cardiovascular system (heart, blood vessels)
Meso derm = “meansoderm” = means of getting around
What is the endoderm?
Endoderm - inside/internal
Epithelial lining of digestive tract, reprodcutive system etc (lining for all internal systems)
“Endernal”
What extraembryonic membranes are formed during the embryonic stage?
Amnion (amniotic sac) and amniotic fluid - surrounds the embryo
- Shock absorption, thermal regulation, prevents tissue from sticking together as they develop
Yolk sac - first blood cells come from yolk sac and first germ cells (cells that’ll become oogonia+spermatogonia)
- Eventually other cells take over the job of making cells
Allantois - collects waste until placenta is formed and eventually gives rise to umbilical cord blood vessels
Chorion and chorionic villi - fetal side of the placenta
What are congenital malformations? What are the causes? When are you most susceptible during development?
defects you’re born with
10% genetic
10% environmental (teratogens)
80% unknown
Embryonic phase most susceptible
What are the hormones of pregnancy?
Human chorionic gonadotropin (hCG)
Estrogens + Progesterone
Human chorionic somatomammotropin (hCS)
Relaxin
What is Human chorionic gonadotropin (hCG)?
hCG keeps the corpus luteum alive = continuing secretion of estrogen + progesterone from corpus luteum
As hCG levels taper off the corpus luteum dies but after week 10, the placenta takes over for estrogen+progesterone secretion
What do estrogen + progesterone do during pregnancy?
Estrogens + Progesterone keep stratum functionalis (endometrium) alive
Progesterone keeps uterine glands alive and secreting glycogen
What does Human chorionic somatomammotropin (hCS) do during pregnancy?
Leads to proper development of female mammary glands
Changes mother’s metabolism to be using fats/proteins for cellular respiration (mainly fats)
Making glucose readily available for baby development and mother uses fats/proteins
What does Relaxin do during pregnancy?
Relaxes pubic symphysis and makes the bony pelvis wider to accomodate baby being born
What are the phases of pregnancy?
Ovarian phase - when corpus luteum is responsible for secreting estrogen+progesterone
Placental phase - when placenta is responsible for secreting estrogen+progesterone
Overlap between ovarian/placental phase IOT maintain high levels of estrogen+progesterone
If levels are not high enough then stratum functionalis will suffer and it will affect embryo
What is true labor called? False Labor?
PARTURITION = true labor
braxton hicks = false labor
What are the stages of labor?
dilation
expulsion
placental
Go over the positive feedback theory of labor.
begin ~30 minutes apart → progress to every 1 – 3 minutes
cervical stretch → neuroendocrine reflex → oxytocin secretion → uterine contraction → more stretch → repeat
How is lactation controlled before/after pregnancy?
Mammary glands develop during pregnancy
High levels of progesterone+estrogen prevent production of milk
After birth you get placenta removed so no source of estrogen+progesterone
What is secreted for the first 3 days after birth?
colostrum not milk
What is the let down reflex?
Controlled by oxytocin
tactile/audio stimulation causes posterior pituitary gland to secrete oxytocin which causes milk to be ejected
