Fertilization, Oogenesis and Spermatogenesis Flashcards
The human endometrium is stratified into two zones namely: ________.
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 the most common site for development of an ectopic pregnancy?
The ampulla of the fallopian tube.
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:
(a) Site
(b) Start time
(c) Duration
(d) End time
(e) Pattern
(f) Supporting cells
(a) Site: Ovarian cortex
(b) Start time: Prenatally
(c) Duration: Several years
(d) End time: Menopause
(e) Pattern: Cyclic maturation (monthly)
(f) 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 primordial germ cells do not migrate into the developing gonad?
(a) Gonadal dysgenesis (streak gonads):
⚚ embryonic gonad lacks the PCGs
⚚ the gonad is underdeveloped and dysfunctional (infertile), composed largely of fibrous tissue
(b) Teratomas:
⚚ If PCGs migrate to an ectopic site, they may develop into a tumor.
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
State the mechanisms of sperm transport in the male system.
- Secretions of the Sertoli cells
- Contractions of the myoid cells
- Sperm motility
- Contractions of the vas deferens
State the mechanisms of sperm transport in the female system.
- Increased sperm motility
- Contractions of the female tract
Briefly outline the process of fertilization.
☑ Capacitation of the sperms
☑ Penetration of the corona radiata
☑ Contact with the zona pellucida
☑ Acrosome reaction
☑ Only the head enters
☑ Cortical (zona) reaction
☑ The male pronucleus forms
☑ The oocyte completes its 2nd meiotic division, forms female pronucleus – hence the ootid stage is established
☑ Fusion of the male & female pronuclei
State the outcomes of fertilisation.
✓ Completion of the 2nd meiotic division of the oocyte and formation of the 2nd polar body
✓ Formation of zygote
✓ Restoration of diploidy
✓ Initiation of cleavage (metabolic activation and restoration of the capacity for cell division)
✓ Determination of embryonic sex (XX or XY genotype)
✓ Genetic variation (variation of species)
Highlight common clinical correlations of the science of fertilisation.
- Invitro fertilization
- Contraception
- Aneuploidy
- Hydatidiform mole
Contraception: The deliberate use of artificial methods or other techniques to prevent pregnancy as a consequence of sexual intercourse. List the various methods of contraception.
- Coitus interruptus
- Barrier methods
- Sterilization - BTL (Bilateral Tubal Ligation), vasectomy
- Fertility awareness-based (natural) methods
- Emergency/postcoital contraception
- Hormonal methods
- Intrauterine contraceptive devices (IUCD)
- Lactation
What is Patau’s syndrome (Trisomy 13)? What are its symptoms? (at least 4)
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]
Further 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.
