Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Spermatogenesis occurs in the seminiferous tubules of the testes and involves mitosis, cell growth, two divisions of meiosis, and differentiation to produce four haploid () spermatozoa from one diploid () spermatogonium.
Oogenesis begins during fetal development where oogonia undergo mitosis and begin meiosis, pausing at Prophase I. Meiosis II is only completed if fertilization occurs, resulting in one functional ovum () and three non-functional polar bodies.
The Acrosome Reaction is a crucial step in fertilization where enzymes are released from the sperm's acrosome to digest the , allowing the sperm to reach the egg membrane.
The Cortical Reaction prevents polyspermy; upon sperm entry, cortical granules release enzymes that harden the , making it impermeable to further sperm.
Implantation of the blastocyst into the endometrium is essential for the continuation of pregnancy. The blastocyst secretes Human Chorionic Gonadotropin (), which maintains the corpus luteum.
The placenta facilitates the exchange of materials between maternal and fetal blood. Nutrients, , and antibodies move to the fetus, while and urea move to the mother. It also takes over the secretion of estrogen and progesterone.
Birth is mediated by a positive feedback loop: Estrogen induces oxytocin receptors on the uterus; Oxytocin stimulates uterine contractions, which causes more Oxytocin release from the posterior pituitary, increasing the intensity of the contractions.
📐Formulae
💡Examples
Problem 1:
Explain the role of in early pregnancy and why its concentration eventually plateaus and declines.
Solution:
(Human Chorionic Gonadotropin) is secreted by the developing blastocyst and later the chorion. Its primary role is to maintain the corpus luteum so that it continues to produce progesterone and estrogen, preventing the degradation of the endometrium. By the second trimester, the placenta becomes fully functional and produces sufficient levels of these hormones independently, leading to a decrease in the requirement for and a subsequent decline in its levels.
Explanation:
This involves understanding the transition of endocrine control from the ovary (corpus luteum) to the placenta.
Problem 2:
Compare the number of gametes produced from one primary spermatocyte versus one primary oocyte.
Solution:
One primary spermatocyte () yields four functional haploid () sperm cells. In contrast, one primary oocyte () yields only one functional haploid () ovum and up to three polar bodies, which eventually degenerate.
Explanation:
This difference is due to the unequal distribution of cytoplasm during cytokinesis in oogenesis, ensuring the zygote receives the maximum amount of nutrients and organelles.