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Questions and Answers
What process do sperm undergo after ejaculation to prepare for fertilization?
What process do sperm undergo after ejaculation to prepare for fertilization?
At what stage does oogenesis begin?
At what stage does oogenesis begin?
How many primary oocytes approximately remain at puberty after further cell death?
How many primary oocytes approximately remain at puberty after further cell death?
Which structure forms around the primary oocyte during the Pre-Antral Stage?
Which structure forms around the primary oocyte during the Pre-Antral Stage?
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What distinguishes the Antral Stage from the Pre-Antral Stage in follicle development?
What distinguishes the Antral Stage from the Pre-Antral Stage in follicle development?
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What triggers the Pre-Ovulatory Stage in oogenesis?
What triggers the Pre-Ovulatory Stage in oogenesis?
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What is formed during meiosis I in the Pre-Ovulatory Stage?
What is formed during meiosis I in the Pre-Ovulatory Stage?
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What role do theca folliculi cells play during follicle development?
What role do theca folliculi cells play during follicle development?
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What is the primary role of Sertoli cells in the testes?
What is the primary role of Sertoli cells in the testes?
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What is the sequence of cells in spermatogenesis starting from diploid cells?
What is the sequence of cells in spermatogenesis starting from diploid cells?
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How many haploid cells are produced after meiosis II in spermatogenesis?
How many haploid cells are produced after meiosis II in spermatogenesis?
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What is the significance of the blood testis barrier?
What is the significance of the blood testis barrier?
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Which process results in the release of spermatids into the lumen of the seminiferous tubule?
Which process results in the release of spermatids into the lumen of the seminiferous tubule?
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At what stage does a spermatogonium become a primary spermatocyte?
At what stage does a spermatogonium become a primary spermatocyte?
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How long does the entire process of spermatogenesis approximately take?
How long does the entire process of spermatogenesis approximately take?
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How often do new groups of spermatogonia arise during the spermatogenic cycle?
How often do new groups of spermatogonia arise during the spermatogenic cycle?
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What happens to the secondary oocyte before ovulation?
What happens to the secondary oocyte before ovulation?
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What role does the LH surge play in ovulation?
What role does the LH surge play in ovulation?
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What is produced when the secondary oocyte completes meiosis II after fertilization?
What is produced when the secondary oocyte completes meiosis II after fertilization?
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What occurs to the oocyte if fertilization does not happen within 24 hours after ovulation?
What occurs to the oocyte if fertilization does not happen within 24 hours after ovulation?
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During which trimester do most organs finish their development?
During which trimester do most organs finish their development?
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What is the role of the extra embryonic mesoderm (EEM) during early development?
What is the role of the extra embryonic mesoderm (EEM) during early development?
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Which layer is involved in forming the amniotic cavity?
Which layer is involved in forming the amniotic cavity?
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What happens during the cleavage stage of prenatal development?
What happens during the cleavage stage of prenatal development?
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What is the role of the yolk sac during early embryonic development?
What is the role of the yolk sac during early embryonic development?
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Which layers contribute to the formation of the chorion?
Which layers contribute to the formation of the chorion?
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Which structure forms from the somatopleuric layer of extraembryonic mesoderm?
Which structure forms from the somatopleuric layer of extraembryonic mesoderm?
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During which week does a significant portion of the yolk sac get integrated into the primordial gut?
During which week does a significant portion of the yolk sac get integrated into the primordial gut?
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What separates the visceral/splanchnopleuric extra-embryonic mesoderm from the parietal/somatopleuric mesoderm?
What separates the visceral/splanchnopleuric extra-embryonic mesoderm from the parietal/somatopleuric mesoderm?
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What type of cells line the primary yolk sac?
What type of cells line the primary yolk sac?
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Which component of the placenta is derived from maternal tissue?
Which component of the placenta is derived from maternal tissue?
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What becomes of the connecting stalks as embryonic development progresses?
What becomes of the connecting stalks as embryonic development progresses?
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Study Notes
Spermatogenesis
- Males begin producing sperm at puberty (typically ages 10-16).
- Continuous sperm production occurs at a high rate (~200 million per day).
- Sperm production takes place in the seminiferous tubules within the testes.
- A blood-testis barrier (formed by Sertoli cells) isolates the seminiferous tubules from the systemic circulation.
- This barrier prevents blood-borne substances (hormones/waste products) from affecting developing sperm.
- It also prevents the male's immune system from recognizing sperm as foreign (sperm has different surface antigens).
Forming Functional Sperm
- Spermatogonia are the initial diploid cells that divide by mitosis to create new spermatogonia and primary spermatocytes.
- Type B spermatogonia divide by mitosis to create primary spermatocytes.
- Primary spermatocytes undergo meiosis I to produce secondary spermatocytes, which are haploid and linked by cytoplasm bridges.
- Secondary spermatocytes undergo meiosis II, creating four haploid spermatids per primary spermatocyte.
Maturation
- Cytoplasmic bridges between spermatids break down.
- Spermatids are released into the seminiferous tubules, undergoing spermiogenesis to transform into sperm.
- Spermatids travel to the rete testis for sperm concentration by removing excess fluid.
- Sperm then move to the epididymis where final maturation stages occur.
- For continuous sperm production, multiple spermatogenic cycles happen simultaneously within the same seminiferous tubule; every 16 days a new spermatogenic cycle begins.
Following Ejaculation
- Sperm undergoes capacitation in the female reproductive tract.
- Capacitation involves removing cholesterol and glycoproteins from the sperm head, enabling it to bind to the zona pellucida of the egg.
Oogenesis
- Oogenesis begins in the fetus before birth, in contrast to spermatogenesis.
- Primordial germ cells migrate to the primordial gonad.
- Replication by mitosis peaks around 7 million by mid-gestation (~20 weeks).
- Significant cell death occurs after this peak, leaving roughly 2 million cells.
- Primary oocytes are formed and arranged in clusters in the gonads, surrounded by flattened epithelial cells (primary follicle).
- Atypical atresia (cell death) occurs during childhood, decreasing the number of oocytes to approximately 40,000 at puberty.
- Several primary oocytes begin to mature each month, but only one reaches full maturation to become an oocyte.
- Primary oocytes undergo three stages: pre-antral, and antral.
Pre-antral Stage
- The primary oocyte remains in meiosis I.
- Follicular cells proliferate, forming a stratified cuboidal epithelium.
- Granulosa cells are formed, secreting glycoproteins that form the zona pellucida around the oocyte.
- Theca folliculi cells differentiate from surrounding connective tissue.
Antral Stage
- Fluid-filled spaces form between granulosa cells and combine to form antrum.
- Follicles are now called secondary follicles.
- One secondary follicle becomes dominant each month, developing under influence of FSH, LH, and oestrogen.
Pre-Ovulatory Stage
- LH surge triggers the completion of meiosis I.
- Two unequally sized haploid cells are created: a secondary oocyte and a first polar body.
- The secondary oocyte then undergoes meiosis II, but is arrested in metaphase II until fertilization.
- The follicle grows larger becoming a mature Graafian follicle.
- LH surge also increases collagenase activity.
- Collagen breakdown results in weakening of the follicular wall.
- Muscular contractions of the ovarian wall cause ovulation (release of the ovum)
- The fimbriae in the fallopian tube captures the ovum and transports it into the fallopian tube.
Fertilization
- Meiosis II is completed only with fertilization, releasing a third polar body.
- Fertilization results in a fertilized egg.
- If no fertilization occurs, the oocyte degenerates after 24 hours.
- Peristaltic movements of the fallopian tube transport the fertilized ovum to the uterus for implantation.
Prenatal Development
- Gestation is divided into three trimesters, each lasting 3 months.
- The first trimester involves cleavage, implantation, placentation, and embryogenesis.
- The second trimester is characterized by organ development completion.
- The third trimester shows rapid growth.
Blastocyst Formation
- Stages of cleavage and blastocyst formation occur during the first week after fertilization.
- Development culminates in implantation (7-10 days).
Stages of Implantation
- Stages in the implantation process (Days 6-9).
Blastodisc Organization & Gastrulation
- Blastodisc becomes two layers (epiblast and hypoblast).
- Epiblast migration leads to amnion formation.
- Hypoblast formation prepares for yolk sac development.
- Gastrulation (week 3): Formation of three germ layers (ectoderm, mesoderm and endoderm)
Fates of Germ Layers
Embryonic Membranes & Placenta
Extra Embryonic Mesoderm
Chorionic Villi
Placental Components
Uterus & Placenta
- Maternal placenta and fetal placenta components.
Chorionic Villi (details)
- Chorionic villi development and differences between primary, secondary and tertiary villus.
Primary, Secondary, and Tertiary Villi (details)
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Description
This quiz covers the process of spermatogenesis, detailing the stages of sperm production that occur in males from puberty onward. It explains the role of the seminiferous tubules and the importance of the blood-testis barrier in protecting developing sperm cells. Test your knowledge on the formation of functional sperm and the cellular mechanisms involved.
