Q1. What is placenta. Mention the functions of placenta.
Ans: A structural and functional unit present between developing embryo (foetus) and maternal body is called placenta.
Functions of placenta as follows;
Provides nutrients and oxygen to the developing embryo.
Removes C02 and waste materials from the embryo.
Acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), oestrogens, progesterone that are essential to maintain pregnancy.
Q2. What is foetal ejection reflex? How it helps in parturition?
The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.
This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions. This leads to expulsion of the baby out of the uterus through the birth canal – parturition.
Q3. Mention the different phases of menstrual cycle and the hormones which regulate the menstrual cycle.
Menstrual phase: last for 3-5 days
Proliferative/Follicular phase: last for 10-17 days
Ovulatory phase: last for 48 hours
Luteal phase: last for 12-14 days
The menstrual cycle is regulated by the complex interaction of hormones: luteinizing hormone, follicle-stimulating hormone, and the female sex hormones oestrogen and progesterone.
Q4. Explain the process of spermatogenesis with a labelled schematic representation.
Spermatogenesis is a process in which diploid spermatogonia undergo meiosis to produce haploid spermatids.
Spermatogenesis begins at puberty.
The spermatogonia (2n) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers.
Each spermatogonium is diploid and contains 46 chromosomes.
Resultant cells are called primary spermatocytes (2n).
These primary spermatocytes periodically undergo meiosis and produce two equal, haploid cells called secondary spermatocytes (n), which have only 23 chromosomes each.
The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids (n).
The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis.
Q5. Explain the process of oogenesis with a labelled schematic representation.
The process of formation of a mature haploid female gamete from the diploid oogonium is called oogenesis.
Oogenesis is initiated during the embryonic development stage, couple million of oogonia are formed within each foetal ovary.
Oogonia undergo meiosis and enters prophase-I, and get temporarily arrested at the stage called primary oocytes.
Each primary oocyte then gets surrounded by a layer of granulosa cells and then called the primary follicle.
The primary follicles get surrounded by more layers of granulosa cells and a new theca and called secondary follicles.
The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum.
The primary oocyte within the tertiary follicle undergoes first meiotic division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.
Secondary oocyte undergoes second meiotic division to produce a haploid ovum (n) with a second polar body.
Q6. Name the two layers of blastocyst.
Outer trophoblast and
Inner cell mass (embryoblast)
Q7. During which period of pregnancy, the foetal heart is formed?
Ans: The foetal heart is formed after one month of pregnancy.
Q8. Describe the hormonal regulation of spermatogenesis.
Ans: Spermatogenesis is initiated at the age of puberty by the gonadotropin releasing hormone (GnRH) secreted by the hypothalamus.
The increased levels of GnRH stimulate the anterior pituitary which then secretes the FSH (follicle stimulating hormone) and LH (luteinising hormone). FSH stimulates Sertoli cells to secrete some factors which help in spermiogenesis. LH acts on the Leydig cells and stimulates synthesis and secretion of androgen.
Q9. Explain the structure of human sperm with a neat labelled diagram.
A mature sperm composes of a head, neck, a middle piece and a tail.
A plasma membrane envelops the whole body of sperm.
The sperm head contains an elongated haploid nucleus and a cap-like structure, acrosome.
The acrosome is filled with enzymes that help fertilisation of the ovum.
The middle piece possesses numerous mitochondria, which produce energy for the movement of tail that facilitate sperm motility.
Centriole present in the neck region helps in cleavage after fertilization.