Questions and Answers
What is the term for the production of spermatozoa in males?
At what age does spermatogenesis typically begin in males?
What is the ideal temperature for spermatogenesis?
Where do the testes produce spermatozoa?
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What is the approximate number of spermatozoa produced per testis per day at peak?
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How long does it take for spermatogenesis to complete from spermatogonium to spermatozoon?
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What is the term for the production of gametes in females?
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What is the term for the female gametes?
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What is the ball of blastomeres at the 16-cell stage called?
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What is one of the obstacles that sperm encounter in the female genital tract?
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What is a requirement for fertilization to occur?
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How long can a sperm survive in the female genital tract?
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What is the third step in the fertilization process?
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What surrounds the primary oocyte inside a mature follicle?
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What occurs as a result of the release of cortical granules from the oocyte?
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What is the result of the sperm head releasing paternal chromosomes into the oocyte?
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What is the function of the second polar body?
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What event determines the genetic sex of the zygote?
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What is the result of the combination of maternal and paternal chromosomes?
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What is the immediate event of fertilization that involves the fusion of two pronuclei?
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What is the role of cross-over and independent assortment of chromosomes?
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What is the immediate event of fertilization that involves the completion of the second meiotic division of the oocyte?
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What is the term for the fluid-filled cavity in the blastocyst?
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What is the process by which the blastocyst hatches out of the zona pellucida?
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What is the term for the week during which two cavities develop in relation to the two layers of the embryoblast?
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What is the process by which the bilaminar embryonic disc is replaced with a trilaminar disc?
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From which layer do all cell layers of the trilaminar disc originate?
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What is the term for the structure that forms from the epiblast during gastrulation?
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What forms at the cephalic end of the primitive streak?
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What is the term for the single layer of outer cells that surround the blastocoel?
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During gastrulation, which layer of cells forms the notochord?
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What is the resulting structure formed after gastrulation?
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Which tissue type arises exclusively from the mesoderm?
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What is the origin of nerve tissue?
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Which of the following tissue types arises from all three primary germ layers?
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What is the origin of muscle tissue?
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Study Notes
Gametogenesis in the Male (Spermatogenesis)
- Gametogenesis in the male is known as spermatogenesis, which occurs in the testes after puberty (12-14 years) under the influence of follicle-stimulating hormone (FSH) and testosterone.
- Spermatogenesis is optimal at 2-3°C below body temperature (37°C), which is why the testes are located in the scrotum below the pelvis.
- This process is continuous throughout post-pubertal life and peaks at around 25 years of age, producing approximately 150,000 spermatozoa per testis per day at peak.
Spermatogenesis - Summary
- The entire process of spermatogenesis takes 64 days, broken down into:
- 16 days from spermatogonium to primary spermatocytes
- 24 days from primary spermatocytes to spermatids
- 24 days from spermatids to spermatozoa
Gametogenesis in the Female (Oogenesis)
- Gametogenesis in the female produces secondary oocytes (commonly called ova).
- The ball of blastomeres at the 16-cell stage is called the morula.
Obstacles that Sperm Encounter in the Female Genital Tract
- Sperm face obstacles such as:
- Acidity of vaginal fluid, which kills many spermatozoa
- Viscosity and acidity of cervical mucus, which weakens and traps many spermatozoa
- Distance from the vagina through the uterine cervix and cavity to the ampulla of the oviduct
- Must survive for 30 minutes to 12 hours and wait up to 72 hours for ovum
Fertilization
- Fertilization requires a healthy secondary oocyte (ovum) with:
- No structural abnormalities
- The correct number of chromosomes (22 autosomes + X)
- Completion of the first meiotic division prior to ovulation
- Encountering competent sperm within 24 hours of ovulation
- Fertilization is a multistep process involving:
- Penetration of corona radiata
- Penetration of the zona pellucida
- Binding and fusion of the oocyte and sperm cell membranes
- A slow block to polyspermy or zonal reaction is triggered by the release of cortical granules from the oocyte.
Immediate Events of Fertilization
- Immediate events of fertilization include:
- Completion of the second meiotic division of the oocyte and formation of the female pronucleus
- Formation of the zygote by fusion of the male and female pronuclei
- Determination of the genetic sex of the zygote (XX = female; XY = male)
- Restoration of the diploid number of chromosomes (23 + 23 = 46)
- Introduction of genetic variation via cross-over and independent assortment of chromosomes
- Differentiation of cells during the formation of the blastocyst
Review - Implantation
- Implantation is the process by which the blastocyst hatches out of the zona pellucida, and its trophoblast adheres, attaches, and burrows into the endometrium, where further development continues.
The Second Week of Human Development
- The second week of human development is characterized by the formation of two cavities in relation to the two layers of the embryoblast (the bilaminar embryonic disc).
Week 3 of Human Development
- Week 3 is characterized by the replacement of the bilaminar embryonic disc with a trilaminar disc, a process called gastrulation.
- All cell layers of the trilaminar disc originate from the epiblast via a primitive streak.
Gastrulation - Summary
- Gastrulation involves:
- Formation of the primitive streak from epiblast
- Formation of a primitive node at the cephalic end of the primitive streak
- One wave of cells migrating to form the notochord
- A second wave of cells migrating to form a layer beneath the epiblast to form mesoderm
- Thus, the trilaminar embryonic disc results from gastrulation, comprising ectoderm, mesoderm, and endoderm.
Embryonic Origin of Basic Tissues
- The four basic tissues arise from the trilaminar embryonic disc:
- Epithelia - arise from all primary germ layers
- Connective tissues - arise exclusively from mesoderm
- Nerve tissue - arise exclusively from ectoderm
- Muscle tissue - arise exclusively from mesoderm
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Description
Learn about gametogenesis in males, also known as spermatogenesis, which occurs in the testes after puberty. Understand the optimal conditions and hormones involved in this process.
