Human Reproduction Test 11

• Gametes are formed by meiosis of germ cells. Hence, they are haploid.
• Gametes are produced through the process of meiosis.
• In males, gametes are produced in testes and in females, gametes are produced in ovaries.
• Since gametes are formed through meiosis, they undergo two set of divisions: meiosis I and meiosis II. 
• During meiosis, recombination occurs in which homologous pairs of chromosomes exchange their segments. Since gametes are formed through meiosis, therefore they have chromosomes that have undergone recombination.

After the age of 45, the number of ovarian follicles decreases and the ovaries become less responsive to luteinizing hormone and follicle-stimulating hormone. Hence the ovaries stop producing estrogen and progesterone. So the menstrual cycle stops and reproductive capacity is arrested. Menopause marks the end of the reproductive phase. Thus the correct answer is option A.

Meroblastic cleavage is seen in centrolecithal eggs in which yolk is located in the centre of the egg.

Polar body is a small degenerate cell that forms after during oogenesis. During meiosis, the first polar body is formed when the secondary oocyte is formed. The polar bodies do not take part in fertilization.

Thymus epithelial cells, the lining of the follicles of the thyroid gland liver and pancreas are developed from endoderm.

So the correct answer is 'Liver, pancreas and thymus/thyroid.'

Karl Ernst von Baer was the first to discover the egg of the mammal in the ovary. Regner de Graaf discovered follicles in the human ovary in 1671 and considered them to be eggs. Since Graaf discovered follicles, they are also called as Graafian follicles. Robert Brown named the cell nucleus in 1827. Spallanzani was the first to disprove spontaneous generation theory. Thus, the correct answer is option B.

The placenta is an organ that connects the developing foetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply, fight against internal infection and produce hormones to support pregnancy. In humans, the placenta usually has a disc shape and it is formed by allantois, chorion and uterine wall.

Parturition is the process in which a mother gives birth to its young one. It initiates when the message initiating parturition starts with the fetal brain, its control of ACTH release from the pituitary, and increased cortisol production by the fetal adrenal. The cortisol stimulates placental enzymes which cause placental progesterone to be made into estrogen. Oxytocin leads to the contraction of smooth muscles of myometrium of the uterus, which directs the full-term foetus towards the birth canal.

So the correct option is 'ACTH, corticosteroid, oxytocin'.

Testosterone is produced by the gonads (by the Leydig cells in testes in men and by the ovaries in women), although small quantities are also produced by the adrenal glands in both sexes. It is an androgen, meaning that it stimulates the development of male characteristics.

• Fertilization takes place in the oviduct. Oviduct is also called a Fallopian tube.
• Oviduct is where most fertilization happens for humans. It can occur in the upper portion of the uterus or it could even happen on the outside of the reproductive tract in the event of inflammatory disease in the pelvic region. This would create an ectopic pregnancy which is a serious occurrence.
• The menstrual cycle gets the woman's body ready and about halfway through human fertilization begins. The egg reaches ovulation and is released into the oviduct where fertilization will take place.
• If the egg becomes fertilized no other sperm is able to penetrate the egg. The genes of the baby are determined the moment the egg is fertilized. Sperm with a Y chromosome means it's a boy and an X chromosome it's a girl.
• While the egg remains in the oviduct for up to 4 days it starts to divide into cells just 24 hours once it has been fertilized. The main focus of the egg is to implant itself into the side of the uterus. After about 3 weeks the first nerve cells of the baby have been formed.
   

Seminal plasma is the fluid part of semen and is contributed by seminal vesicles, prostate gland and bulbourethral glands. Seminal vesicles contribute fructose, citric acid and other nutrients as well as fibrinogen and prostaglandin. Secretions from prostate gland contain calcium ions, phosphate Ion, etc. and are alkaline in nature. Bubo urethral glands secrete alkaline mucus which is important for the lubrication of penis.

Oestrogens regulate growth and development of female accessory reproductive organs, secondary sexual character and sexual behaviour.

The fixing of the blastocyst in the wall of the uterus is known as implantation. The implantation takes place after seven days of fertilization.

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Parturition is the process of giving birth or delivery. The signals for parturition originate from the placenta as well as the fully developed foetus. Both these induce uterine contractions. These uterine contractions are called as foetal ejection reflex. This then stimulates the release of oxytocin hormone from the maternal pituitary gland.

In general eggs of mammals have a little yolk. The human egg is alecithal meaning it is totally devoid of yolk. Hence, the human zygote gets implanted in the uterus of female and the egg or zygote is not laid. Humans are viviparous and females give birth to young ones.

Oogenesis occurs in the outermost layers of the ovaries. Oogenesis starts with a germ cell called oogonium and undergoes mitosis to increase in number. The process of oogenesis takes place in the following three stages: Pre-natal.

Ovulation occurs about midway through the menstrual cycle, after the follicular phase, and is followed by the luteal phase.

During ovulatory phase, LH induces rupturing of Graafian follicle and during secretory phase, empty Graafian follicle changes into corpus luteum.

Immediately after ovulation, the layer that forms around the ovum is called corona radiata.

If mammalian ovum fails to get fertilized, the oestrogen secretion does not decrease further, while corpus luteum will disintegrate. Primary follicle starts developing and progesterone secretion rapidly declines.