Unit 3: Human Development Flashcards
Human development:
(1. First trimester):
•weeks 1-12.
•neurulation.
-neural tube formed: becomes CNS.
•organs are formed, cartilage skeleton formed.
•body grows in length.
•by end of trimester, can determine sex.
Human development:
(2. Second trimester):
•weeks 13-24.
•can detect heartbeat; bones begin to form.
•nervous system starts functioning: brain grows.
•limbs grow (movement).
Human development:
(3. Third trimester):
•weeks 25-38.
•brain grows rapidly; testes descend; fat layer grows.
•digestive and respiratory systems mature last.
Sex determination:
•prior to the 7th week of development, the gonads are identical in both male and female fetuses.
•if the Y chromosome is present in the embryos cells, a gene called the SRY gene will turn on.
•SRY = sex-determining region of the Y-chromosome.
•in the presence of the SRY gene, the developing gonads become testes and the testes synthesize hormones that directs the development of male characteristics.
•the absence of the SRY gene will cause the development of female characteristics.
Teratogen:
•means “monster forming”.
•substance that disrupts normal fetal development.
•most harmful during the first 9 weeks of development.
•examples:
-cigarette smoke: low birth weight, still births, miscarriages.
-alcohol: fetal alcohol spectrum disorder.
•thalidomide:
-a sedative used to help with morning sickness.
-used by pregnant women in Europe in the 1960s; was banned in the USA.
-when taken during the limb bud differentiation (days 26-56), it sometimes resulted in deformed infants with flipped like arms and legs.
Mom’s pregnancy changes:
•estrogen and progesterone:
-produced first by corpus luteum then placenta.
-breast enlargement, morning sickness.
•relaxin:
-produced by placenta prior to labor causes softening of cervix and ligaments within the pelvis to loosen providing a flexible passage way for the baby during delivery. Triggered when baby “drops” so that head is on the cervix.
•as well:
-increased urination, difficulty breathing, blood volume/pressure increase.
Parturition (birth):
-onset:
•estrogen levels increase. Uterus becomes irritable.
-progesterone has been “calming” the uterus.
•fetal cells produce oxytocin; placenta produces prostaglandins.
-both cause contractions: Braxton-Hicks (false labor).
•estrogen and progesterone both drop after birth.
Positive feedback:
- Head pushes on cervix causes it to stretch.
- Nerve impulses to hypothalamus.
- Stimulates posterior pituitary to release oxytocin.
- Oxytocin stimulates uterus to contract:
- Pushes fetus downwards causing cervix to stretch even more—> +ve feedback because a small effect gets amplified.
Stages of labour:
- Dilation:
-amnion breaks (“water breaks”).
-cervix opens (10cm).
-can take 2-20 hours. - Expulsion:
-pushing phase; baby through cervix to vagina (birth canal).
-can take 0.5-2 hours. - Placental:
-placenta and umbilical cord expelled.
-10-15 min after.
Lactation:
•formation and secretion of breast milk.
•anterior pituitary: releases prolactin—> milk production after baby is born.
•colostrum (first 3-5 days):
-beginning milk, thin yellowish fluid, high protein.
•suckling reflex:
-positive feedback.
-stimulates nerves in nipple and areola.
-nerve impulses to hypothalamus.
-stimulates posterior pituitary to release oxytocin:
-causes weak contractions of smooth muscle within the breast forcing milk into the ducts.
-mammary lobules contract—> milk let down.
Breast feeding feedback loop:
•suckling of baby stimulates nerves in areola of breast.
•nerves stimulates pituitary to release prolactin and oxytocin.
•prolactin initiates milk production and moves milk into ducts.
•oxytocin causes weak contractions in the breast to move the milk down to nipple.
•oxytocin also causes weak contractions in the uterus to return the uterus to its normal size and shape.
