Fertilization, Oogenesis and Spermatogenesis Flashcards
What is Patau’s syndrome (Trisomy 13)? What are its symptoms. (at least 4)
What are three functions of the zona pellucida.
- Prevents polyspermy
- Prevents ectopic pregnancy; for implantation to take place, hatching of the blastocyst from zona pellucida must take place.
- It ensures species specificity
- Facilitates compaction
In which part of the fallopian tube does fertilization take place?
Ampulla
What is Down’s syndrome? What are its symptoms? (at least 4)
A genetic disorder caused by the presence of a third copy of chromosome 21, hence it is also called Trisomy 21.
Symptoms: short neck, excess skin on the back of the neck, hyperkeratosis, small ears, low-set ears, flattened face, cognitive deficit, brachycephaly, relatively large tongue [Diagram]
Extra notes:
* Brachycephaly, or flat head syndrome is a head shape condition where the head is wide in proportion to the length. Babies sometimes develop brachycephaly when they’re a few months old, usually as a result of them spending a lot of time lying on their back.
** Hyperkeratosis is thickening of the stratum corneum (the outermost layer of the epidermis, or skin) due to the presence of an abnormal amount of keratin.
Identify the developmental anomaly and state its basis: [Image].
Hydatidiform mole/molar pregnancy
Basis: It occurs when the set of paternal genome is more than that of the set of the maternal genome. It manifests as cystic swellings as a result of vesicular proliferation of the placental tissues. The moles are of trophoblastic origin and produce excessive amounts of HCG.
Additional image(s): [Image 1]
Outline the phases of gametogenesis.
- Origin of stem cells - Precursor cells invade developing gonads (prenatally)
- Multiplication phase - Series of mitotic divisions, hence exponential numerical increase
- Haploidy phase - Meiotic cell division, reducing the chromosomal number by half
- Differentiation phase - Both morphological and functional maturation events
State the following regarding spermatogenesis:
(a )Site
(b) Start time
(c) Duration
(d) End time
(e) Temperature
(f) Supporting cells
(a) Site: Seminiferous tubules
(b) Start time: Puberty
(c) Duration: 64 - 74 days
(d) End time: At death
(e) Temperature: 34° C
(f) Supporting cells: Sertoli cells
Fill in the blanks in the following flowchart showing the process of spermatogenesis:
primordial germ cells ➔ Commitment ➔ (a) ➔ (b) ➔ Primary spermatocytes ➔ (c) ➔ (d) ➔ (e) ➔ Spermatids ➔ (f) ➔ Spermatozoa ➔ Spermiation ➔ Free spermatozoa
[Hint: (b), (c), (e) and (f) are processes]
(a) Spermatogonia
(b) Spermatocytogenesis
(c) Meiosis I
(d) Secondary spermatocytes
(e) Meiosis II
(f) Spermiogenesis
Further notes:
Spermiation is the process by which mature spermatids are released from the supporting somatic Sertoli cells into the lumen of the seminiferous tubule. This process is a critical determinant of the number of sperm entering th epididymis, and thus the sperm content of the ejaculate.
During spermiation, the remaining unnecessary cytoplasm and organelles are removed. The resulting spermatozoa are now mature but lack motility, rendering them sterile. The non-motile spermatozoa are transported to the epididymis in testicular fluid secreted by the Sertoli cells, with the aid of peristaltic contraction. Whilst in the epididymis, they acquire motility.
State the following regarding oogenesis:
Site
Start time
Duration
End time
Pattern
Supporting cells
Site: Ovarian cortex
Start time: Prenatally
Duration: Several years
End time: Menopause
Pattern: Cyclic maturation (monthly)
Supporting cells: Follicular cells
Outline the process of oogenesis.
☛ maturation process begins during the fetal period; however it is not completed until after puberty
☛ during early fetal life, oogonia proliferate by mitosis and enlarge to form primary oocytes
☛ at birth, all primary oocytes have completed prophase of the first meiotic division. The oocytes remain in prophase until puberty. [i.e. 1st meiotic arrest at P1]
☛ Shortly before ovulation, a primary oocyte completes the first meiotic division; division of cytoplasm is unequal.
☛ The secondary oocyte receives almost all the cytoplasm, whereas the first polar body receives very little.
☛ At ovulation, the nucleus of the secondary oocyte begins the second meiotic division but progresses only to metaphase [i.e. 2nd meiotic arrest at M2].
☛ If fertilization occurs, the second meiotic division is completed, and a second polar body formed.
☛ The secondary oocyte released at ovulation is surrounded by the zona pellucida and a layer of follicular cells, the corona radiata.
☛ [7-minute video] [Diagram]
Click on Diagram and label parts 1 to 8.
- Secondary oocyte
- Zona pellucida
- Corona radiata
- Granulosa cells
- Cumulus oophorus
- Basement membrane
- Theca folliculi [an envelope of connective tissue surrounding the granulosa cells]
- Antrum
Anovulation?
- failure of ovulation to occur
- physiologic adolescent anovulation is abnormal
- may be associated with polycystic ovaries
What would happen if PCGs do not migrate into the developing gonad?
- Gonadal dysgenesis (streak gonads):
- embryonic gonad lacks the PCGs
- the gonad is underdeveloped and dysfunctional (infertile), composed largely of fibrous tissue - Teratomas:
- if PCGs migrate to an ectopic site, they may develop into a tutor
State the mechanisms of ovum transport.
- Sweeping movements of the fimbrial end of the Fallopian tube (during ovulation)
- Ciliary activity of the Fallopian tubes
- Secretions within the Fallopian tube
- Contractions of the Fallopian tube
