HL Bio - Unit #4.4: Reproduction Growth/Development

Puberty

Sequence of developmental changes for individuals going from childhood to sexual maturity

Puberty is controleld by which hormone?

Gonadotropin releasing hormones (GnRH)

Gonadotropin releasing hormones (GnRH)

secreted from a fetus from 4-6 months to kick start its growth and then it stops until the child reaches puberty and then stops once more when adulthood has been reached

• GnRH helps promote the secretion of FSH and LH from the pituitary gland

FSH: Secreted from lower frequency pulses

• Male: Stimulate the growth of the testis and production of sperm

• Female: Stimulates the development of the follicles

LH: Secreted from higher frequency pulses

• Male: Help with sperm production 

• Female: Stimulates the development of the follicles wall 

  • Which then turns into corpus luteum

Gametogenesis

Process of diploids cells undergoing meiotic division to produce haploid gametes

Spermatogenesis: For male gametes - Spermatozoa (Sperm)

Occurs in the testes - Composed of seminiferous tubules with gaps 

• The gaps are filled testosterone secreting Leydig cells

• The outer layer of the tubule is the germinal epithelium

  • This layer produces cells through mitosis which travel within the tubule where they divide through meiosis (Produces 4 sperms)

Spermatogenesis Phases

1. Primary Spermatocyte: The diploid cell that enters into the seminiferous tubule from the germinal epithelium

2. Secondary Spermatocyte: Diploid cell enters first phase of meiosis and splits into two daughter cells with half the amount of DNA

3. Spermatid: Haploid cells enter the second phase of meiosis and split once more but maintain the same half amount of chromosomes

4. Sperm: Spermatid matures to form sperm through differentiation

Oogenesis: For female gametes - Oocytes (Egg)

Begins during the foetal development where the female gets all of her germ cells (~400,000) 

• It grows until it reaches its first meiosis and then it remains suspended in prophase I until puberty

• Once puberty hits once a menstruation cycle FSH stimulates some of the germ cells to continue the meiosis process (produces one ovum and 3 polar bodies)

Phases of Oogenesis

1. Primary Oocyte: Reaches this point as foetus and remains here until puberty

2. Secondary Oocyte: Diploid oocyte divided into one haploid oocytes and creates one polar body (uneven cytoplasm distribution)

   • Released during ovulation

3. Ovum: Haploid oocyte enters the second phase of meiosis and splits into another polar body and the ovum, while the original polar body divides into two more polar bodies

Polyspermy

Process of multiple sperms fertilising the same egg

• little bro dies

Acrosome Reaction:

The acrosome is a large enzyme sac in the head of the sperm that is released onto the eggs zona Pellucidas glycoprotein layer to digest through it and enter the egg

Cortical Reaction:

Cortical Granules: Thousands of enzyme-containing vesicles located near the eggs cell plasma membrane

• Once fertilisation occurs these vesicles release their contents via exocytosis and causes a general toughening of the zona pellucida 

  • Makes it hard for other sperm to enter 

  • Also changes specific glycoproteins to which sperm binds so that can no longer occur