BIOL1040 Module 2 L4: Placental Mammal Fertilization, Implantation & Development

Key features of a sperm cell

Acrosome cap filled with enzymes, nucleus (haploid DNA), midpiece (mitochondraia for ATP), tail (flagellum fo rmotor)

Which layers surround a mammalian oocyte before fertilisation?

Plasma memnbrane of egg, vitelling (zona) layer, the zona pellucida glycoprotein shell, and the outer corona radiata of follicle cells.

How do internal and external fertilisation differ in animals?

External fertilisation releases eggs and sperm into an aquatic environment (required moisture). Internal fertilisation deposits sperm within or near the female tract, protecting ther gametes and embryo

WHat is the first contact event in the acrosomal process

rthe sperm acrosome adheres to and binds receptors on the zona pellucida

What enzumes are released from the acrosome and what is their function

hydrolutic enzymes digest a pathway through the zona pellucida into the perivitelline space

what occurs when sperm and egg plasma fuse

the sperm nucleus enters the egg cytoplasm and cortical grandules exocutose to harden the zona, preventing polyspermy

 List the five chronological steps from ovulation to blastocyst implantation.

1) Ovulation releases secondary oocyte into oviduct. 2) Sperm entry completes oocyte meiosis II and forms zygote. 3) Cleavage in oviduct; 4) Blastocyst forms and floats in uterine cavity; 5) Blastocyst implants into endometrium ~7 days post‐fertilisation.

What development stages occur between day 0 and Day 5 poost fertilisation

Zygote (Day 0) → 2‐cell (Day 1) → 4‐cell (Day 2) → 8‐cell (Day 3) → morula → blastocyst (Day 5).

What are the two main cell lineages in the mammalian blastocyst?

 Inner cell mass (embryoblast), which gives rise to embryo proper, and the outer trophoblast, which forms placenta.

WHat is the role and clinical use of hCG

it maintains the corpus luteim progesterone/estrogen until placenta takes over

Hormone trends across trimesters?

hCG peaks ~Week 10 then falls; estrogen & progesterone rise (placental takeover after 1st trimester).

Early vs later embryonic nutrition?

Early → uterine secretions via diffusion. Later → placental villi exchange with maternal blood.

What are the placenta’s functions?

Exchange of gases, nutrients, wastes between mother & foetus.

How do maternal and foetal blood flow in the placenta?

Maternal blood → intervillous spaces via arteries, leaves via veins. Foetal blood → villus capillaries, returns via umbilical vein.

Name 3 exchange mechanisms across the placenta.

Diffusion, active transport, selective absorption.

When does organogenesis begin & what is the first organ to function?

In 1st trimester; heart is first to beat.

When is the embryo termed a foetus?

After organogenesis begins and heart starts beating.

What hormonal shift happens in the 2nd trimester?

hCG declines, corpus luteum degenerates, placenta takes over progesterone production.

Which hormones drive labour and how does the positive feedback loop work?

Rising oestradiol increases uterine oxytocin receptors. The foetal head pressing on the cervix triggers stretch receptors → hypothalamus → posterior pituitary releases oxytocin. Oxytocin stimulates uterine contractions and prostaglandin release from the placenta, both of which intensify contractions. Stronger contractions cause more cervical stretch, feeding back to increase oxytocin — a positive feedback cycle until birth.

What are 2 main contraceptive strategies?

Steroid-based (hormonal) & immunocontraception.

What is a wildlife example of contraception?

Pigeons in Brussels fed contraceptive corn daily.