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Reproduction - Human Reproduction

Grade 12ICSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

The male reproductive system includes testes, which are extra-abdominal located in the scrotum to maintain a temperature 22.5C2-2.5^{\circ}C lower than the internal body temperature for spermatogenesisspermatogenesis.

Spermatogenesis is the process of forming haploid (n)(n) sperm from diploid (2n)(2n) spermatogonia. This involves SertoliSertoli cells for nutrition and LeydigLeydig cells for the secretion of testosteronetestosterone.

Oogenesis is the formation of a haploid (n)(n) ovum. It initiates during the fetal stage, remains arrested at Prophase IProphase\ I until puberty, and completes Meiosis IIMeiosis\ II only upon fertilization by a sperm.

The Menstrual Cycle consists of the Menstrual phase, Follicular phase (proliferative), Ovulatory phase (LHLH surge on day 1414), and Luteal phase (secretory).

Fertilization occurs at the ampullary-isthmic junctionampullary\text{-}isthmic\ junction of the Fallopian tube. The acrosome of the sperm releases enzymes like hyaluronidasehyaluronidase to penetrate the zona pellucidazona\ pellucida.

The BlastocystBlastocyst stage is responsible for implantation in the endometriumendometrium. It consists of an outer trophoblasttrophoblast and an inner cell massinner\ cell\ mass.

The PlacentaPlacenta acts as an endocrine tissue, secreting hCGhCG (human Chorionic Gonadotropin), hPLhPL (human Placental Lactogen), estrogensestrogens, and progesteroneprogesterone.

Parturition is a neuroendocrine mechanism triggered by the fetal ejection reflexfetal\ ejection\ reflex, leading to the release of oxytocinoxytocin from the maternal posterior pituitary.

📐Formulae

Spermatogenesis: 1×Primary Spermatocyte (2n)Meiosis4×Spermatozoa (n)\text{Spermatogenesis: } 1 \times \text{Primary Spermatocyte } (2n) \xrightarrow{Meiosis} 4 \times \text{Spermatozoa } (n) patterns

Oogenesis: 1×Primary Oocyte (2n)Meiosis1×Ovum (n)+Polar Bodies\text{Oogenesis: } 1 \times \text{Primary Oocyte } (2n) \xrightarrow{Meiosis} 1 \times \text{Ovum } (n) + \text{Polar Bodies}

Zygote Formation: n (Sperm)+n (Ovum)2n (Zygote)\text{Zygote Formation: } n \text{ (Sperm)} + n \text{ (Ovum)} \rightarrow 2n \text{ (Zygote)}

Diploid Number (Human): 2n=46\text{Diploid Number (Human): } 2n = 46

Haploid Number (Human): n=23\text{Haploid Number (Human): } n = 23

💡Examples

Problem 1:

Calculate the number of primary oocytes and primary spermatocytes required to produce 200200 eggs and 200200 sperm cells respectively.

Solution:

200200 primary oocytes and 5050 primary spermatocytes.

Explanation:

In oogenesis, one primary oocyte (2n)(2n) undergoes meiosis to produce only 11 functional ovum (n)(n) and polar bodies. Thus, 200200 oocytes produce 200200 eggs. In spermatogenesis, one primary spermatocyte (2n)(2n) undergoes meiosis to produce 44 functional spermatozoa (n)(n). Therefore, 2004=50\frac{200}{4} = 50 spermatocytes are required.

Problem 2:

Explain the significance of the LHLH surge in the menstrual cycle.

Solution:

The LHLH surge triggers ovulationovulation.

Explanation:

Rapid secretion of Luteinizing Hormone (LHLH) leading to its maximum concentration during the mid-cycle (around day 1414) is called the LHLH surge. It induces the rupture of the Graafian follicleGraafian\ follicle and the release of the secondary oocyte into the pelvic cavity.

Problem 3:

A zygote is found to have 46,XX46, XX chromosomes. Determine the sex of the child and the contribution from the parents.

Solution:

The sex is Female. Both parents contributed an XX chromosome.

Explanation:

The sex determination in humans is XYXY type. A zygote with XXXX develops into a female. Since the mother always contributes an XX chromosome in the ovum (22+X)(22+X), the sperm must have also carried an XX chromosome (22+X)(22+X) to result in 46,XX46, XX.

Human Reproduction - Revision Notes & Key Diagrams | ICSE Class 12 Biology