MENSTRUATION AND THE DEVELOPMENT OF THE EMBRYO

MENSTRUATION
Monthly discharge of blood from the vagina. The blood is normally referred to as MENSES and it contains blood, broken uterine lining and unfertilized egg. Normally menstruation takes about five days.

SUMMARY: ROLES OF HORMONES IN MENSTRUATION

• Onset of menstruation (starting from day one): The pituitary gland secretes follicle stimulating hormone (FSH) into the bloodstream and from here it is then transported to the Target organ (Ovary)
• In the ovary FSH stimulates one primary follicle to ripen (mature) into Graafian follicle
• FSH also stimulates the follicles in the ovary to secrete oestrogen
• Oestrogen causes the repair and growth of the uterine lining (after menstruation)
• Oestrogen (in high concentration) also inhibits FSH production (therefore preventing ripening of more follicles)
• Oestrogen also stimulates the pituitary gland to secrete luteinising hormone (LH)
• LH causes ovulation
• LH also causes the formation of corpus luteum
• Corpus luteum secretes progesterone
• Progesterone keeps the uterine lining thick to prepare itself for implantation if there is fertilization
• Progesterone inhibits both FSH and LH production
• If there is no fertilization, the corpus luteum breaks; Progesterone production stops; Uterine lining breaks; MENSTRUATION occurs

DEVELOPMENT OF THE EMBRYO

• After fertilization, the zygote passes along the oviduct to the uterus and as it does so, it begins to divide (by mitosis) to form a ball of cells which later develops into an embryo
• It takes about five days for the embryo to reach the uterus and upon reaching the uterus, it will eventually sinks in or embeds itself in the uterine lining, hence IMPLANTATION takes place
• The embedded embryo will then develop into a foetus
• Function of amniotic fluid: to enclose the foetus in a fluid-filled space known as the amniotic cavity
• The amnion/amniotic cavity functions in supporting and cushioning the foetus, thus preventing it from mechanical damage
• The amniotic fluid also acts as a shock absorber
• During birth, the amniotic fluid lubricates and reduces friction in the vagina
• The amniotic fluid also buoys the foetus and allows it to move freely during growth
• Generally the umbilical cord functions in supplying the foetus with oxygen and dissolved food nutrients as well as removing waste products (carbon dioxide and urea) from the foetus
• Inside the umbilical cord, there are three blood vessels. Two of these blood vessels are the umbilical arteries whereas one is an umbilical vein
• The umbilical arteries function in carrying deoxygenated blood from the foetus to the placenta
• The umbilical vein functions in carrying oxygenated blood (rich in oxygen and food substances as well as antibodies) from the placenta to the foetus

FUNCTIONS OF PLACENTA

• Allows dissolved food substances (e.g. glucose, amino acids, mineral salts) and oxygen to diffuse from the mother’s blood into that of the embryo
• Allows metabolic waste products (e.g. urea and carbon dioxide) to diffuse from the foetus’ blood into the mother’s blood
• Allows antibodies to diffuse from the mother’s blood into the foetus’ blood (antibodies protect the foetus against diseases)
• Produces progesterone which maintains uterine lining in healthy state during pregnancy
  

NOTE: MOTHER'S BLOOD AND FOETUS' BLOOD DO NOT MIX AND MOTHER'S BLOOD DO NOT DIFFUSE INTO THE PLACENTA NOR DOES FOETUS' BLOOD DIFFUSE OUT OF THE PLACENTA INTO THE MOTHER'S BLOOD