Summary: Reproduction

Read the summary and the most important questions on reproduction

• 1 Male and female embryonic morphology and anatomy

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• What is the resaon that the ovaries develop?

  In a female embryo, the XX sex chromosomes are present. As there is no Y chromosome, there is no SRY gene to influence development. Without it, the primitive sex cords degenerate and do not form the testis cords.
  
  Instead, the epithelium of the gonad continues to proliferate, producing cortical cords. In the third month, these cords break up into clusters, surrounding each oogonium (germ cell) with a layer of epithelial follicular cells, forming a primordial follicle.

• 1.1 The Internal Genitalia

• The indifferent stage van the internal genitalia?

  In the first weeks of urogenital development, all embryos have two pairs of ducts, both ending at the cloaca. These are the:
  

  • - Mesonephric (Wolffian)
  • - Paramesonephric (Mullerian) ducts 

• The internal genitalia male

  In the presence of testosterone (produced by the Leydig cells), the mesonephric ducts develop to form the primary male genital ducts. They give rise to the efferent ductules, epididymis, vas deferens and seminal vesicles. Meanwhile, the paramesonephric ducts degenerate in the presence of anti-Mullerian hormone – produced by Sertoli cells in the testes. Its developmental remnant is the appendix testis; a small portion of tissue located on the upper pole of each testicle, which has no physiological function.
  

  • - AMH hormone leads to regression of the ductus paramesonephricus

• The internal genitalia female?

  In the female, there are no Leydig cells to produce testosterone. In the absence of this hormone, the mesonephric ducts degenerate, leaving behind only a vestigial remnant – Gartner’s duct. Equally, the absence of anti-Mullerian hormone also allows for development of the paramesonephric ducts. Initially, these ducts can be described as having three parts:
  

  • - Cranial – becomes the Fallopian tubes
  • - Horizontal – becomes the Fallopian tubes
  • - Caudal – fuses to form the uterus, cervix and upper portion of the vagina.

  
  The lower portion of the vagina is formed by sinovaginal bulbs (derived from the pelvic part of the urogenital sinus).

• 1.2 External Genitalia

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• The indifferent stage of the external genitalia?

  The development of the external genitalia begins in the third week. Mesenchymal cells from the primitive streak migrate to the cloacal membrane to form a pair of cloacal folds. Cranially, these folds fuse to form the genital tubercle. Caudally, they divide into the urethral folds (anterior) and anal folds (posterior). Genital swellings develop either side of the urethral folds.

• The external genitalia of the female

  Oestrogens in the female embryo are responsible for external genital development. The genital tubercle only elongates slightly to form the clitoris. The urethral folds and genital swellings do not fuse, but instead form the labia minora and labia majora respectively. The urogenital groove therefore remains open, forming the vestibule into which the urethra and vagina open.

• 2 spermatogenesis

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• Leydig cells and there function?

  Leydig cells (LC) are present in the testicular interstitial tissue, and their main function is to produce testosterone (T) for the maintenance of spermatogenesis and extra testicular androgenic and anabolic functions. The cells can be found between seminiferous tubules. 

• Sertoli cells and there function?

  • - The monolayer of sterol cells and the basement membrane lead to a barrier --> the blood testis barrier --> function is that no Ig get in to the testis. Because sperm cells are 1N they are attacked by the immune system through immunoglobulins.  formation of blood-testis barrier by tight-junctions
  • - nourishment of sperm forming cells
  • - cleaning up the cell remnants and defective cells
  • - production of paracrine and endocrine growth factors and hormones.
  • - provide structural support and secrete fluids to nourish and support developing sperm cells

• 2.2.1 the differentiation phase and elongation of spermatids

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• The 5 steps in differentiation and elongation phase of spermatids

  1. Golgi phase
     
  2. cap phase
  3. acrosomal phase
  4. muturation phase
  5. elongation phase

• 2.3 condensation of sperm DNA

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• How is the sperm DNA condensated and in which steps

  In a spermatid there is condensation of the DNA. The nucleosomes are replaced with protaminated proteins to form dense DNA toroids. The DNA is protected from oxygen and toxins.
  

  • Protamine binding to DNA induces coiling of DNA into donuts like structures (toroids) and then sandwich wrapping
  • DNA binds together in the major groove
  • It is possible that not all histons are removed therfore you see in the embryo, histons form the father and the mother.