Gametogenesis And Fertilization (Exam II)

Question 1

How are indifferent gonads (not yet differentiated) formed?

Answer 1

The primordial germ cells from the yolk sac endoderm migrate to the genital ridge.

Question 2

What part of the genital organs are created from which types of germ layers?

Answer 2

Intermediate mesoderm gives rise to the majority of the urogenital organs (leydig cells, sertoli cells, follicular cells, ovary, testis, ducts, uterus).
Urogenital sinus endoderm gives rise to terminal internal parts of urogenital organs (vesicular, port state and bulbourethral glands)

Question 3

What do Mullerian/Paramesonephric Ducts develop into in the female? Why do males not have the same development?

Answer 3

Develops into the Fallopian tubes, uterus and cervix (tubular structures in female genitals)
Males they disappear under the influence of anti-paramesonephric hormone.

Question 4

What do prepuberal testis consist of?

Answer 4

Seminiferous cords (no lumen): Contain sertoli cells (secrete estrogen) and primordial germ cells (stem cells for spermatogenesis - stay dormant until puberty).
Inactive interstitial cells of Leydig (secrete testosterone)

Question 5

What grows/widens and causes the testis to be pulled down during their descent?

Answer 5

The gubernaculum.

Question 6

What is cryptorchidism? What are the 2 types and their consequences? What causes it?

Answer 6

Testes fail to descend into scrotum.
Unilateral (fertile) or Bilateral (sterile, but normal sexual behavior)
Caused by an inherited sex-limited autosomal recessive trait.

Question 7

What are the 2 primitive sex cells called? Do they have a complete DNA complement?

Answer 7

Spermatogonia and Oogonia

Yes, they have a complete DNA complement.

Question 8

Define Mitosis and Meisosis

Answer 8

Mitosis - results in formation of 2 daughter cells each with diploid set of chromosomes - same # and identical chromosomes as mother cell
Meiosis - results in daughter cells with half the parental # of chromosomes (haploid).

Question 9

What are the goals of meiosis?

Answer 9

Reduction of diploid set of chromosomes into haploid in gametes.
Exchange of genetic material between male and female chromatids in prophase I of meiosis I (crossing over) - allows for 4 daughter cells with 4 different genetic makeups.

Question 10

List important characteristics of Spermatocytes

Answer 10

Sperm supply is continually renewed.
One primary spermatocyte produces 4 sperm.
Initial large cell results in small cells.
Motile.
X or Y sex chromosome.

Question 11

List important characteristics of Oocytes.

Answer 11

All oocytes are present at birth.
One primary oocyte gives rise to 1 ovum and 2-3 polar bodies.
Initial small cells grows to a large cell.
Immotile.
X chromosome only.

Question 12

Describe the stages of Oogenesis.

Answer 12

Oogonia (2N) (prenatal mitosis and differentiation) –> primary oocytes (4N) at birth and are arrested in Meiosis I until puberty (folliculogenesis) –> At ovulation, Meiosis I is completed (except for dogs and mares) –> In uterine tube, secondary oocyte (2N) awaits fertilization (1st polar body is present) –> Meiosis II is completed upon sperm contact –> Ovum (1N) and 2nd polar body.

Question 13

Describe Folliculogenesis

Answer 13

Primordial Follicles (resting follicles) - oocyte I and single layer of squamous follicular cells 
Primary Follicles (activated/growing follicles) - zona pellucida forms
Secondary Follicles (secretory, antral follicles) - fluid filled spaces are formed among the granulosa cells. 
Tertiary/Mature/Graafian Follicles - antrum containing liquor follicular, have eccentric cumulus oophorus, corona radiata, contains primary oocyte

Question 14

Where does the zona pellucida form? What does it do?

Answer 14

Primary follicles

Acts as immunologic protective barrier for developing egg and early embryo.

Question 15

What happens after ovulation to the follicular space? Describe all steps.

Answer 15

Follicular space fills with blood and clots - Corpus Hemorrhagicum.
Replaced by infiltrating luteal cells to becomes the Corpus Luteum (yellow body)
Corpus Luteum regresses during diestrus and forms the Corpus Albicans.

Question 16

What is the Corpus Luteum? What does it do?

Answer 16

Aka Yellow Body
Produces progesterone and some estrogen (done by 2 cell populations that infiltrate the space left by the ruptured follicle: Granulosa Luteal Cells (large luteal cells) & Theca Luteal Cells (small luteal cells)

Question 17

What does progesterone do? Where is it produced?

Answer 17

Progesterone helps to maintain pregnancy stimulate mammary development and locally down regulate the immune system.
Released from corpus luteum.

Question 18

What it’s the corpus albicans?

Answer 18

AKA White Body

Leftover after corpus luteum regresses in diestrus. The connective tissue scar that remains.

Question 19

What is an atretic follicle?

Answer 19

A follicle not selected to complete maturation. It will undergo programmed destruction, this is the fate of many follicles.

Question 20

Describe the steps of Spermatogenesis.

Answer 20

Spermatogonium (2N) (undergoes mitosis and differentiates) –> Primary Spermatocyte (4N) (meiosis I ) –> Secondary Spermatocyte (2N) (meiosis II) –> Spermatids (Do not divide but undergo spermatogenesis (morphological changes)) –> Spermatozoa (Sperm, Sperm cells)

Question 21

List the functions of Sertoli Cells

Answer 21

Secrete AMH (Anti-Mullerian Hormone) during fetal development to inhibit uterus formation
Secrete inhibit and activins after puberty to regulate FSH secretion from pituitary
Secrete ABP (Androgen Binding Protein) to bind testosterone and increase concentrations in the seminiferous tubules and stimulate spermatogenesis.
Provide support, protection and possibly nutrition to spermatids.

Question 22

What activates sertoli cells?

Answer 22

FSH - Follicle Stimulating Hormone

Question 23

What makes up the head of a sperm?

Answer 23

The nucleus and the acrosomal cap which is surrounded by an acrosomal membrane.

Question 24

Describe the structure of an axonema (eg sperm flagellum)

Answer 24

9 pairs of central microtubules and outer ring of 9 doublets of dynein arms.
Each pair of microtubules has a complete microtubule A with dynein arms and an incomplete microtubule B

Question 25

How often does spermatogenesis happen?

Answer 25

Continual process (throughout the year) except in seasonal breeders. It’s a highly organized process with a fixed length of time for each species.

Question 26

How much sperm does an animal typically produce?

Answer 26

About 25 million sperm per gram of testicular tissue per day. Except humans which are 4 million sperm per gram per day.

Question 27

Where is meiosis completed in spermatogenesis? When do spermatogonia start to proliferate by mitotic division?

Answer 27

Within the testis.

Spermatogonia start to proliferate by mitotic division at puberty.

Question 28

Where is meiosis completed in oogenesis?

Answer 28

In the Fallopian Tube ( Salpinx)

Question 29

What are the steps of Fertilization for the Sperm?

Answer 29

Capacitation - occurs in uterine environment. Gain ability to fertilize oocyte. The plasma membrane over the acrosomal is destabilized and breaks down together with the acrosomal membrane.
Acrosome Reaction - Release of acrosomal enzymes that digest through zona pellucida
Fusion - of sperm plasma membrane with plasma membrane of oocyte

Question 30

Describe the steps of Fertilization for the ovum (oocyte II)

Answer 30

Cortex of oocyte below oolemma contains cortical granules. When the sperm contact the oocyte plasma membrane there are proteases that are released from the cortical granules that modify the zona pellucida (becomes a barrier for other/further sperm penetration). Ca2+ wave causes oocyte to complete meiosis II (now 1N).

Question 31

What is syngamy?

Answer 31

The union of female and male pronuclei. They merge restoring the diploid set of chromosomes and enter the first mitotic division. Becomes a zygote!