Human Development

Question 1

Where does fertilization occur?

Answer 1

in the ampulla of the oviduct

- ~0.001% of sperm (2,000 – 3,000) in ejaculate reach the ovum

Question 2

How do sperm get there within 5 – 10 minutes of release?

Answer 2

flagellar action of sperm
mucous strands in cervical canal
uterine contractions

Question 3

What is capacitation?

Answer 3

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

Question 4

How long do sperm remain viable?

Answer 4

6 days in female reproductive tract

“window of opportunity” = a few days before ovulation to 14 hr after

Question 5

What is the acrosomal reaction?

Answer 5

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

Question 6

What are the barriers to penetration for sperm?

Answer 6

corona radiata
zona pellucida
ovum cell membrane

Question 7

What genetic events take place upon sperm entry/fertilization?

Answer 7

2º oöcyte completes meiosis, becomes oötid

male pronucleus joins female pronucleus

chromosomes line up for first mitosis (now a zygote)

Question 8

What prevents polyspermy?

Answer 8

fast block = depolarization of oötid membrane

slow block = cortical reaction = formation of impenetrable fertilization membrane

Question 9

What is cleavage?

Answer 9

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

Question 10

What occurs during implantation?

Answer 10

implantation in the fundus of the uterus

Trophoblast forms providing nourishment and eventually forming the placenta
- begins secreting human chorionic gonadotropin (HcG)

Question 11

What are the stages of development?

Answer 11

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

Question 12

What occurs during the embryonic stage?

Answer 12

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

Question 13

What is the ectoderm?

Answer 13

Forms epidermis + nervous system

Skin has alot of receptors so makes sense that it develops w/ nervous system

External apperance + brain (nervous tissue) = “attractoderm”

Question 14

What is the mesoderm?

Answer 14

Mesoderm - in between ectoderm+endoderm

Muscle cells, bone, connective tissue (ligaments, tendons), cardiovascular system (heart, blood vessels)

Meso derm = “meansoderm” = means of getting around

Question 15

What is the endoderm?

Answer 15

Endoderm - inside/internal

Epithelial lining of digestive tract, reprodcutive system etc (lining for all internal systems)

“Endernal”

Question 16

What extraembryonic membranes are formed during the embryonic stage?

Answer 16

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

Question 17

What are congenital malformations? What are the causes? When are you most susceptible during development?

Answer 17

defects you’re born with

10% genetic
10% environmental (teratogens)
80% unknown

Embryonic phase most susceptible

Question 18

What are the hormones of pregnancy?

Answer 18

Human chorionic gonadotropin (hCG)
Estrogens + Progesterone
Human chorionic somatomammotropin (hCS)
Relaxin

Question 19

What is Human chorionic gonadotropin (hCG)?

Answer 19

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

Question 20

What do estrogen + progesterone do during pregnancy?

Answer 20

Estrogens + Progesterone keep stratum functionalis (endometrium) alive

Progesterone keeps uterine glands alive and secreting glycogen

Question 21

What does Human chorionic somatomammotropin (hCS) do during pregnancy?

Answer 21

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

Question 22

What does Relaxin do during pregnancy?

Answer 22

Relaxes pubic symphysis and makes the bony pelvis wider to accomodate baby being born

Question 23

What are the phases of pregnancy?

Answer 23

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

Question 24

What is true labor called? False Labor?

Answer 24

PARTURITION = true labor

braxton hicks = false labor

Question 25

What are the stages of labor?

Answer 25

dilation
expulsion
placental

Question 26

Go over the positive feedback theory of labor.

Answer 26

begin ~30 minutes apart → progress to every 1 – 3 minutes

cervical stretch → neuroendocrine reflex → oxytocin secretion → uterine contraction → more stretch → repeat

Question 27

How is lactation controlled before/after pregnancy?

Answer 27

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

Question 28

What is secreted for the first 3 days after birth?

Answer 28

colostrum not milk

Question 29

What is the let down reflex?

Answer 29

Controlled by oxytocin

tactile/audio stimulation causes posterior pituitary gland to secrete oxytocin which causes milk to be ejected