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SOLAR ECLIPSE 2025

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   Introduction to Solar Eclipses Solar eclipses are one of the most fascinating celestial events, capturing the curiosity of scientists, astronomers, and the general public alike. These occur when the Moon passes between the Earth and the Sun, either partially or completely obscuring the Sun's light. There are different types of solar eclipses: Total Solar Eclipse : The Moon completely covers the Sun. Partial Solar Eclipse : The Moon partially blocks the Sun, creating a crescent shape. Annular Solar Eclipse : The Moon covers the center of the Sun, leaving a ring-like appearance. Hybrid Solar Eclipse : A rare eclipse that transitions between total and annular phases. The Solar Eclipse of 2025 In 2025, two significant solar eclipses will occur: March 29, 2025 – A partial solar eclipse , visible in several parts of the world but not visible from India . September 21, 2025 – Another partial solar eclipse , with possible limited visibility in India. Key Details of the March 29, ...
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Human Reproduction Summary Notes

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 Male Reproductive System

  • Primary sex organs: A pair of testes suspended in the scrotum
  • Secondary sex organs: A pair of ducts each differentiated into rete testis, vasa efferentia, epididymis and vas deferens, ejaculatory duct and the associated glands
  • External genitalia: Penis

Gametogenesis (Spermatogenesis)

  • The process of formation of male gametes (sperms) in the testes
  • Spermatogonia (immature male germ cells) undergo mitotic division to increase in number
  • Spermatogonia differentiate into primary spermatocytes
  • Primary spermatocytes undergo meiotic division to produce secondary spermatocytes
  • Secondary spermatocytes undergo meiotic division to produce spermatids
  • Spermatids are transformed into spermatozoa by the process of spermiogenesis

Hormonal Control of Spermatogenesis

  • Gonadotropin releasing hormone (GnRH) is secreted by the hypothalamus
  • GnRH stimulates the anterior pituitary to secrete luteinizing hormone (LH) and follicle stimulating hormone (FSH)
  • LH acts on Leydig cells in the testes to stimulate the secretion of androgens
  • FSH acts on Sertoli cells in the testes to support spermatogenesis

Structure of Sperm

  • Sperm is a microscopic structure composed of a head, neck, middle piece, and tail
  • The sperm head contains the elongated haploid nucleus, which is covered by an acrosome
  • The acrosome contains enzymes that help the sperm penetrate the egg

Female Reproductive System

  • Primary sex organs: A pair of ovaries
  • Secondary sex organs: A pair of fallopian tubes, uterus, cervix, and vagina
  • External genitalia: Mons pubis, labia majora, labia minora, clitoris
  • Mammary glands: A pair of glands that produce milk

Gametogenesis (Oogenesis)

  • The process of formation of female gametes (ova) in the ovaries
  • Oogonia (gamete mother cells) are formed during embryonic development
  • Oogonia divide by mitosis to produce primary oocytes
  • Primary oocytes undergo meiotic division I and arrest in prophase I until puberty
  • At puberty, a few primary oocytes begin to complete meiotic division I to produce secondary oocytes
  • Secondary oocytes are ovulated from the ovaries and undergo meiotic division II only if they are fertilized by a sperm

Menstrual Cycle

  • The menstrual cycle is a series of hormonal changes that occur in the female reproductive system each month
  • The cycle begins with the menstrual phase, which is the shedding of the endometrium (lining of the uterus)
  • The follicular phase follows, during which a follicle in the ovary develops and produces estrogen
  • Estrogen stimulates the proliferation of the endometrium
  • The ovulatory phase occurs when the follicle ruptures and releases an ovum (egg)
  • The luteal phase follows, during which the corpus luteum (ruptured follicle) produces progesterone
  • Progesterone maintains the endometrium in preparation for implantation of a fertilized egg
  • If the egg is not fertilized, the corpus luteum degenerates and progesterone levels drop
  • This drop in progesterone triggers menstruation

Fertilization

  • Fertilization is the fusion of a sperm with an ovum
  • Fertilization occurs in the ampullary-isthmic junction of the fallopian tube
  • After fertilization, the zygote (fertilized egg) travels down the fallopian tube and implants in the endometrium of the uterus

Implantation

  • Implantation is the process by which the zygote attaches to the endometrium of the uterus
  • Implantation occurs 5-6 days after fertilization
  • After implantation, the zygote begins to develop into an embryo

Embryonic Development

  • The embryo undergoes cleavage to form a blastocyst.
  • The blastocyst implants in the endometrium of the uterus.
  • The inner cell mass of the blastocyst develops into the embryo.
  • The ectoderm, endoderm, and mesoderm develop from the inner cell mass.
  • The major organs and external genital organs develop by the end of 12 months.

Parturition and Lactation

  • Parturition is the process of delivery of a fully developed fetus.
  • Signals for parturition originate from the fully developed fetus and placenta.
  • Oxytocin is released from the maternal pituitary to induce uterine contractions.
  • The mammary glands of the female start producing milk at the end of pregnancy.
  • The milk produced during the initial few days of lactation is called colostrum.

Polyspermy

  • Polyspermy is the fertilization of an egg by more than one sperm.
  • If polyspermy occurs, the resulting cell has too much genetic material to develop normally.

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