Hy Embryology 01

Front 1

Describe Gametes

Back 1

1. Are descendants of primordial germ cells that originate in the wall of the yolk sac of the embryo and migrate into the gonad region
2. Are produced in the adult by either oogenesis or spermatogenesis, processes that involve meiosis

Front 2

Describe Meiosis

Back 2

1. Occurs only during the production of gametes
2. Consists of two cell divisions (meiosis I and meiosis II) and results in the formation of gamets containing 23 chromosomes and 1N amount of DNA (23,1 N)
3. Promotes the exchange of small amounts of maternal and paternal DNA via crossover during meiosis I

Front 3

Describe Female gametogenesis

Back 3

1. Primordial germ cells (46,2N) from the wall of the yolk sac arrive in the ovary at week 4 of embryonic development and differentiate into oogonia
2. Oogonia enter meiosis I and undergo DNA replication to form primary oocytes (46,4N). All primary oocytes are formed by the fifth month of fetal life and remain dormant in prophase (diplotene) of meiosis I until puberty
3. During a woman’s ovarian cycle, a primary oocyte completes meiosis I to form a secondary oocyte (23,2N) and a first polar body, which probably degenerates
4. The secondary oocyte enters meiosis II, and ovulation occurs when the chromosomes align at metaphase. The secondary oocyte remain arrested in metaphase of meiosis II until fertilization occurs
5. At fertilization, the secondary oocyte completes meiosis II to form a mature oocyte (23,1N) and a second polar body

Front 4

Describe the formation of oogonia

Back 4

Primordial germ cells (46,2N) from the wall of the yolk sac arrive in the ovary at week 4 of embryonic development and differentiate into oogonia

Front 5

What type of cell enters meiosis I in oogenesis?

Back 5

Oogonia

Front 6

When do all primary oocytes form?

Back 6

The fifth month of fetal life and they remain dormant in prophase (diplotene) of meiosis I until puberty

Front 7

In what stage are oocytes arrested in until puberty?

Back 7

Prophase

Front 8

Describe what occurs in a woman’s ovarian cycle to the oocyte

Back 8

1. During a woman’s ovarian cycle, a primary oocyte completes meiosis I to form a secondary oocyte (23,2N) and a first polar body, which probably degenerates
2. The secondary oocyte enters meiosis II, and ovulation occurs when the chromosomes align at metaphase. The secondary oocyte remain arrested in metaphase of meiosis II until fertilization occurs

Front 9

Describe hormone control of the female reproductive cycle

Back 9

1. The hypothalamus secretes gonadotropic-releasing hormone (GnRH)
2. In response to GnRH, the adenohypophysis secretes the gonadotropins, follicle-stimulating hormone (FSH) and leuteinizing hormone (LH)
3. FSH stimulates the development of the a secondary follicle to a Graafian follicle within the ovary
4. Granulosa cells of the secondary Graafian follicle secrete estrogen
5. Estrogen stimulates the endometrium of the uterus to enter the proliferative phase
6. LH stimulates ovulation
7. Following ovulation, granulose lutein cells of the corpus luteum secrete progesterone
8. Progesterone stimulates the endometrium of the uterus to enter the secretory phase

Front 10

What organ secretes GnRH?

Back 10

Hypothalamus

Front 11

What is the response to GnRH in the female?

Back 11

The adenohypophysis secretes FSH and LH

Front 12

What is the role of FSH in the hormonal control of the female reproductive cycle?

Back 12

1. The adenohypophysis secretes LH and FSH in response to GnRH
2. FSH stimulates the development of the secondary follicle to a Graafian follicle within the ovary
3. Granulosa cells of the secondary and Graafian follicle secrete estrogen

Front 13

What is the role of estrogen in the hormonal control of the female reproductive cycle?

Back 13

1. Granulosa cells of the secondary and Graafian follicle secrete estrogen
2. Estrogen stimulates the endometrium of the uterus to enter the proliferative phase

Front 14

What is the role of LH in the hormonal control of the female reproductive cycle?

Back 14

Stimulates ovulation

Front 15

Which cells secrete progesterone following ovulation?

Back 15

Granulosa lutein cells

Front 16

Describe the role of progesterone in the hormonal control of the female reproductive cycle

Back 16

1. Following ovulation, granulose lutein cells of the corpus luteum secrete progesterone
2. Progesterone stimulates the endometrium of the uterus to enter the secretory phase

Front 17

Describe the events of the menstrual cycle

Back 17

1. Menstrual phase (days 1-4)
-Characterized by the necrosis and shedding of the functional layer of the endometrium
2. The proliferative phase (days 4-15)
-Characterized by the regeneration of the functional layer of the endometrium and a low basal body temperature (97.5F)
3. Ovulatory phase (Days 14-16)
-Characterized by ovulation of the secondary oocyte and coincides with the LH surge
4. Secretory phase (15-25)
-Characterized by secretory activity of the endometrial glands and an elevated basal body temperature (>98F)
-Implantation occurs in this phase
5. Premenstrual phase (Days 25-28)
-Characterized by ischemia due to reduced blood flow to the endometrium

Front 18

What are the three phases of male gemetogenesis?

Back 18

1. Spermatocytogenesis
2. Meiosis
3. Spermiogenesis

Front 19

Describe Spermatocytogenesis

Back 19

1. Primordial germ cells (46,2N) from the wall of the yolk sac arrive in the testes at week 4 of embryonic development and remain dormant until puberty

2. At puberty, primordial germ cells differentiate into type A spermatogonia (46,2N)

3. Type A spermatogonia undergo mitosis to provide a continuus supply of stem cells throughout the reproductive life of the male (called spermatocytogenesis).

4. Some type A spermatogonia differentiate into type B spermatogonia (46,2N)

Front 20

Describe what occurs in Male gametogenesis before puberty

Back 20

Primordial germ cells (46,2N) from the wall of the yolk sac arrive in the testes at week 4 of embryonic development and remain dormant until puberty

Front 21

What type of cell is responsible for providing a continuous supply of stem cells for sperm throughout the reproductive life of the male

Back 21

Type A spermatogonia (46,2N)

Front 22

Describe Type A spermatogonia

Back 22

-From primordial germ cells
-The cell responsible for providing a continuous supply of stem cells for sperm throughout the reproductive life of the male

Front 23

Describe Meiosis in make gametogenesis

Back 23

1. Type B spermatogonia enter meiosis I and undergo DNA replication to form primary spermatocytes (46, 4N)

2. Primary spermatocytes complete meiosis I to form two secondary spermatocytes (23,2N)

3. Secondary spermatocytes complete meiosis II to form four spermatids (23,1N)

Front 24

What type of cell enters meiosis in male gametogenesis?

Back 24

Type B spermatogonia

Front 25

Describe Spermiogenesis

Back 25

1. Spermatids undergo a postmeiotic series of morphological changes (called spermiogenesis) to form sperm (23,1N)

2. Newly ejaculated sperm are incapable of fertilization until they undergo capacitation, which occurs in the female reproductive tract and involves the unmasking of sperm glycosyltransferases and removal of proteins coating the surface of the sperm

Front 26

Where does capacitation of sperm occur? What does it involve?

Back 26

-Female reproductive tract
-Unmasking of sperm glycosyltransferases

Front 27

Describe problems with the offspring of older women

Back 27

-Prolonged dormancy of primary oocytes may be the reason for the high incidence of chromosomal abnormalities in offspring of older women. Since all primary oocytes are formed by month 5 of fetal life, a female infant is born with her entire supply of gametes. Primary oocytes remain dormant until ovulation; those ovulated late in the woman's reproductive life may have been dormant for as long as 40 years

-The incidence of trisomy 21 (Down syndrome) increases with advanced age of the mother

Front 28

What are the symptoms of trisomy 21?

Back 28

1. Severe mental retardation
2. Epicanthal folds
3. Brushfield spots
4. Simian creases
5. Association with a decrease in α-fetoprotien

Front 29

What is the primary cause of Down syndrome?

Back 29

Maternal meiotic nondisjuction

Front 30

Describe issues with the offspring of older men

Back 30

An increased incidence of achondroplasia (an autosomal dominant congenital skeletal anomaly characterized by retarded bone growth in the limbs with normal-sized head and trunk) and Marfan syndrome are associated with advanced paternal age

Front 31

Describe achondroplasia

Back 31

An autosomal dominant congenital skeletal anomaly characterized by retarded bone growth in the limbs with normal-sized head and trunk

Front 32

Describe Male Fertility

Back 32

1. Depends on the number and motility of sperm

2. Fertile males produce from 20 to more than 100 million sperm/mL of semen. Sterile males produce less than 10 million sperm/mL of semen

3. Normally up to 10% fo sperm in an ejaculate may be grossly deformed (two heads or two tails), but these sperm probably do not fertilize an oocyte owing to their lack of motility

Front 33

What is Anovulation?

Back 33

The absence of ovulation in some women due to inadequate secretion of FSH and LH

Front 34

Describe the treatment for Anovulation

Back 34

-Clomiphene citrate (a fertility drug)

-Clomiphene citrate competes with estrogen for binding sites in the adenohypophysis, thereby suppressing the normal negative feedback loop of estrogen on the adenohypophysis. This stimulates FSH and LH secretion and induced ovulation.