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MCAT Biology > Reproduction and Development > Flashcards

Reproduction and Development Flashcards

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1
Q

Gonadotropin Releasing Hormone

Leutinizing Hormone

Follicle Stimulating Hormone

A
  • Gonadotropin releasing hormone (GnRH) is made in the hypothalamus
  • GnRH stimulates the anterior pituitary to release leutinizing hormone (LH), and follicle stimulating hormone (FSH)
    • LH and FSH travel to the gonads
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2
Q

Spermatogenesis and Where it Occurs

A
  • Spermatogenesis is the formation of sperm
  • Occurs in the seminiferous tubules in the testes
  • Sperm is genereated from spermatogenic cells__​
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3
Q

Sperm Production

A
  • Primary spermatocytes become secondary__ spermatoyctes after meiosis 1
  • After meiosis 2, four spermatids are generated, which then transform into spermatozoa
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4
Q

Leydig Cells

A
  • Leydig cells lie in the interstitial space between adjacent seminiferous tubules
  • Are responsible for the production of testosterone from cholesterol
    • LH acts in a secondary manner to increase the conversion of cholesterol to testosterone
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5
Q

Sertoli Cells

A
  • Sertoli cells are located in the seminiferous tubules
  • Responsible for converting testosterone to dihydrotestosterone (dHT)
  • FSH binds to sertoli cells; this helps convert testosterone to dHT
  • dHT leads to the upregulation of enzymes/proteins that aide in spermatogenesis
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6
Q

Male Hormone Feedback Mechanisms

A
  • Testosterone has negative feedback on the hypothalamus and anterior pituitary, inhibiting the production of GnRH and LH
  • Inhibin, which is produced by sertoli cells also has a negative feedback on the anterior pituitary
  • Males have constant LH and FSH levels because there is constant spermatogenesis
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7
Q

What is Oogenesis?

A
  • Oogenesis is the production of female germ cells
  • All oogonia a female has are produced in her first three months of fetal development
    • Oogonia then mitotically divide to form primary oocytes
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8
Q

Ova Production

A
  • Primary oocytes undergo their first meiotic division after the LH-surge/ovulation to produce secondary oocytes
  • Secondary oocytes will not undergo their second meiotic divison until fertilization
  • Once the secondary oocyte leaves the ovary, it leaves behind the corpus luteum, the leftover follicle that nourished the primary oocyte until ovulation
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9
Q

Theca Cells

A
  • Theca cells are analagous to leydig cells
  • Theca cells are stimualted by LH to produce testosterone from cholesterol
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10
Q

Granulosa/Follicular Cells

A
  • Granulosa__/follicular cells convert testosterone into estrogen
  • FSH stimulates granulosa cells to do the above process
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11
Q

Female Hormone Feedback Mechanisms

A
  • LH surges at ovulation; this is caused by the increase in estrogen levels before ovulation
  • Estrogen and progesterone will surge after ovulation
  • Estrogen at low concentrations have a negative feedback on FSH production
  • Estrogen at high concentrations have a positive feedback on LH production
  • Corpus luteum produces estrogen and progesterone, which in combination, have negative feed bck on LH and FSH production
    • Primary follicle is prevented from developing at this point
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12
Q

Fertilization

Maintaining Estrogen and Progesterone Levels

Chorionic Gonadotropin and Placenta

A
  • Once the oovum (secondary oocyte) comes into contact with the spermatozoan, the oovum undergoes its secondary meiotic divison
  • The 23 chromosomes of each nucleus come together to result in 46 chromosomes, forming the zygote
  • Estrogen and progesterone levels are maintained to prevent the development of another primary follicle
  • Corionic gonadotropin (CG) is made by the placenta and tells the corpus luteum to continue making estrogen and progesterone
  • Placenta will start making estrogen and progesterone after 3 months
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13
Q

Developmental Stages

A
  1. Fertilization
  2. Cleavage
  3. Gastrulation
  4. Neurulation
  5. Neural crest formation
  6. Oranogenesis
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14
Q

Fertilization

A
  • Grey crescent forms on the opposite side of where sperm penetrates the egg; grey crescent is located on the dorsal aspect (future back)
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15
Q

Cleavage

A
  • Zygote undergoes special divisons to increase mass but not overall size
  • Cleavages can be meridional and equatorial
  • Individual cells are called blastomeres
  • Small “ball” of cells is known as a morula
  • Turns into the blastula, which is hollow and contains a fluid-filled cavity known as the blastocoel
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16
Q

Gastrulation

A
  • Gastrulation defines the time where cells rearrange
  • Cells will invaginate through the blastopore; this forms a new internal cavity known as the archenteron, and the embryo becomes a gastrula
17
Q

Germ Layers of Gastrula and Their Fates

A
  • Ectoderm is the most outside cell line of the gastrula
    • Forms the skin, lens of the eye, brain, and nervous system
  • Mesoderm is the middle cell line of the gastrula; forms latest
    • Forms the notochord, heart, skeleton, muscles, reproductive organs, and outer coverings of internal organs
  • Endoderm is the most inside cell line of the gastrula
    • Forms the digestive tract, respiratory tract, major glands (liver/pancreas)
18
Q

Neurulation

A
  • During neurulation, the formation of the notochord takes place along the body midline
  • The neural plate, deriving from the ectoderm, will eventually curl and fuse together, fortming the neural tube (which eventually becomes the spinal cord)
19
Q

Neural Crest Formation

A
  • During the formation of the neural tube, some specialized ectodermal cells form the neural crest
  • These will lead to the formation of sense organs in the head
    • Olfaction, touch
    • Adrenal medulla - adrenaline
20
Q

Oranogenesis

A
  • Interation between mesoderm and ectoderm
  • Organs form
21
Q

Hormones and Pregnancy

A
  • At some specific ratio of [estrogen] : [progesterone], contrations begin
    • Progesterone production eventually plateaus near the end of pregnancy
  • Contraction of uterus stimulates oxytocin release by the anterior pituitary
    • Hypothalamus receives signal and tells anterior pituitary to release
    • Positive feedback mechanism

MCAT Biology (5 decks)

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