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Questions and Answers
Which germ layer gives rise to the skin and nervous system?
Which germ layer gives rise to the skin and nervous system?
The yolk sac in humans provides essential nutrients to the embryo.
The yolk sac in humans provides essential nutrients to the embryo.
False
What is the function of the trophoblast during early embryonic development?
What is the function of the trophoblast during early embryonic development?
It forms the outer layer of the blastocyst and contributes to the formation of the placenta.
Gastrulation is the phase of embryonic development where the __________ germ disc acquires a third germ layer.
Gastrulation is the phase of embryonic development where the __________ germ disc acquires a third germ layer.
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Match the following structures to their primary functions:
Match the following structures to their primary functions:
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The endoderm is associated with which of the following organs?
The endoderm is associated with which of the following organs?
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The hypoblast forms on Day 8 from the inner cell mass and is responsible for forming the embryonic structure.
The hypoblast forms on Day 8 from the inner cell mass and is responsible for forming the embryonic structure.
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What does the term 'trilaminar' refer to in embryonic development?
What does the term 'trilaminar' refer to in embryonic development?
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The _______ is formed from epiblast cells and serves as a protective cavity for the embryo.
The _______ is formed from epiblast cells and serves as a protective cavity for the embryo.
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What is the main purpose of the acrosome in the head of a spermatozoon?
What is the main purpose of the acrosome in the head of a spermatozoon?
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The middle piece of a spermatozoon contains a large amount of cytoplasm.
The middle piece of a spermatozoon contains a large amount of cytoplasm.
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What are the two major parts of a mature sperm formed during spermiogenesis?
What are the two major parts of a mature sperm formed during spermiogenesis?
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During spermiogenesis, the nucleus of the spermatid becomes _______ and acquires an oval shape.
During spermiogenesis, the nucleus of the spermatid becomes _______ and acquires an oval shape.
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Match the following parts of a spermatozoon with their functions:
Match the following parts of a spermatozoon with their functions:
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What happens to the cytoplasm during the tail formation of spermatozoa?
What happens to the cytoplasm during the tail formation of spermatozoa?
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Which part of the alimentary canal is considered the hindgut?
Which part of the alimentary canal is considered the hindgut?
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Spermatogenesis occurs in females.
Spermatogenesis occurs in females.
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What is the primary follicle in oogenesis?
What is the primary follicle in oogenesis?
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The ________ is the stage where the ovum is released from the tertiary follicle.
The ________ is the stage where the ovum is released from the tertiary follicle.
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Match the following stages of oogenesis with their descriptions:
Match the following stages of oogenesis with their descriptions:
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What triggers the release of a secondary oocyte from the ovary?
What triggers the release of a secondary oocyte from the ovary?
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At what stage do females have a lifetime supply of developing oocytes?
At what stage do females have a lifetime supply of developing oocytes?
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The secondary oocyte completes the second meiotic division prior to fertilization.
The secondary oocyte completes the second meiotic division prior to fertilization.
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What structure forms a protective layer around the ovum during oogenesis?
What structure forms a protective layer around the ovum during oogenesis?
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Gametogenesis includes the differentiation of immature cells into mature gametes.
Gametogenesis includes the differentiation of immature cells into mature gametes.
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What is the difference between spermatogenesis and oogenesis?
What is the difference between spermatogenesis and oogenesis?
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The menstrual cycle begins at puberty and typically ends with _____ in women.
The menstrual cycle begins at puberty and typically ends with _____ in women.
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The ________ is produced in the testes and is essential for male reproduction.
The ________ is produced in the testes and is essential for male reproduction.
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Match the phase of the menstrual cycle with its description:
Match the phase of the menstrual cycle with its description:
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During which phase does the ovum travel through the fallopian tube?
During which phase does the ovum travel through the fallopian tube?
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Which of the following is the correct order of stages in oogenesis?
Which of the following is the correct order of stages in oogenesis?
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Only one secondary oocyte is typically released during each ovarian cycle.
Only one secondary oocyte is typically released during each ovarian cycle.
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What happens to the secondary oocyte if fertilization does not occur?
What happens to the secondary oocyte if fertilization does not occur?
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The _____ phase occurs approximately 14 days before the expected menstrual period when the ovum is released.
The _____ phase occurs approximately 14 days before the expected menstrual period when the ovum is released.
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What hormonal change occurs in response to the maturation of follicles?
What hormonal change occurs in response to the maturation of follicles?
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What triggers the LH surge during ovulation?
What triggers the LH surge during ovulation?
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The zona pellucida is the layer that surrounds the nucleus of a mature ovum.
The zona pellucida is the layer that surrounds the nucleus of a mature ovum.
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What is the time required for a spermatogonium to develop into a mature spermatozoon in humans?
What is the time required for a spermatogonium to develop into a mature spermatozoon in humans?
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The __________ is released by the hypothalamus and stimulates the pituitary gland to release LH and FSH.
The __________ is released by the hypothalamus and stimulates the pituitary gland to release LH and FSH.
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Match the following phases of spermatocytogenesis with their descriptions:
Match the following phases of spermatocytogenesis with their descriptions:
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What is the primary function of Luteinizing Hormone (LH)?
What is the primary function of Luteinizing Hormone (LH)?
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The perivitelline space is where polar bodies are found after ovulation.
The perivitelline space is where polar bodies are found after ovulation.
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Name the three phases of spermatocytogenesis.
Name the three phases of spermatocytogenesis.
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The largest cell in the body is the __________.
The largest cell in the body is the __________.
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Which hormone is NOT involved in the hormonal feedback loop regulating the ovulatory process?
Which hormone is NOT involved in the hormonal feedback loop regulating the ovulatory process?
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Study Notes
Early Embryo Stages and Development
- Blastocyst: Forms on Day 4, made up of trophoblast, blastocoele, and embryoblast.
- Trophoblast: Outer layer of the blastocyst, important for placenta formation.
- Blastocoele: Cavity within the blastocyst.
- Hypoblast: Forms on Day 8 from inner cell mass, precursor to extra-embryonic tissues like the yolk sac, chorion, amnion, and allantois.
- Epiblast: Forms on Day 8 from inner cell mass, lies above the hypoblast, pluripotent (capable of becoming any cell type).
- Amniotic cavity: Formed by the end of Week 2 from epiblast cells.
- Yolk sac: Formed by the end of Week 2 from hypoblast cells, vestigial in humans, likely offered early nutrition.
- Chorion: Forms part of the placenta.
- Amnion: Surrounds the embryo, creating a protective cavity.
- Allantois: Contributes to umbilical cord formation.
Gastrulation and Germ Layers
- Gastrulation: Phase where the bilaminar germ disc gains a third layer, becoming trilaminar.
- Trilaminar germ disc: Composed of ectoderm, endoderm, and mesoderm, formed during gastrulation.
- Ectoderm (outer layer): Develops into skin, nervous system, hair, and sensory organs.
- Mesoderm (middle layer): Develops into muscles, bones, connective tissue, and the circulatory system.
- Endoderm (inner layer): Gives rise to internal organs like lungs, liver, and pancreas.
Alimentary Canal Development
- Foregut (anterior part): Extends from the mouth to the duodenum, forms the esophagus, stomach, duodenum, liver, gallbladder, pancreas, and spleen.
- Midgut (middle part): Forms the intestines, connecting the foregut at the bile duct opening to the hindgut.
- Hindgut (posterior part): Consists of the distal 1/3 of the transverse colon, splenic flexure, descending colon, sigmoid colon, and rectum.
Gametogenesis: The Formation of Gametes
- Gametogenesis: Process of creating gametes (sperm and egg cells) for sexual reproduction.
- Spermatogenesis: Production of sperm cells in the testes of males.
- Oogenesis: Production of egg cells in the ovaries of females.
Oogenesis: Development of the Ovum
- Oogonium: The immature cell that develops into an ovum.
- Primary follicle: An oogonium surrounded by a layer of cells, forming a follicle.
- Growing follicle: Follicle increases in size, the ovum grows.
- Primary oocyte: Ovum within the growing follicle undergoes meiosis but arrests in prophase I.
- Secondary follicle: Follicle continues to grow, the ovum remains in meiosis.
- Tertiary follicle: Largest follicle, containing a mature ovum.
- Ovulation: Mature ovum is released from the tertiary follicle into the oviduct.
- Mature ovum: Released ovum ready for fertilization.
Oogenesis: Important Points
- Females are born with a lifetime supply of developing oocytes, each in prophase I.
- One secondary oocyte is released each month from puberty to menopause (around 400-500 eggs).
- Primary oocytes don't complete the first meiotic division until puberty.
- The secondary oocyte completes the 2nd meiotic division after fertilization by sperm in the fallopian tube, resulting in the ovum and a second polar body.
- Without fertilization, the secondary oocyte degenerates without completing the second meiotic division.
Oogenesis: Significant Ovum Changes
- Growth and maturation.
- Meiosis (reduction of chromosome number).
- Development of the zona pellucida (protective layer).
- Formation of the corona radiata (cell layer surrounding the ovum).
Ovulation: Release of the Secondary Oocyte
- Process where the secondary oocyte is released from the ovary after the mature Graafian follicle ruptures.
- Only one secondary oocyte is likely to rupture per ovarian cycle, starting at puberty and ending at menopause.
- Occurs around 14 days before the expected menstrual period.
Ovarian Cycle: Phases
- Menstrual Phase (Days 1-5): Uterine lining sheds, resulting in bleeding. The body prepares for a new cycle, and hormone levels drop.
- Follicular Phase (Days 6-12): Ovaries produce follicles containing eggs. Estrogen levels rise, causing the uterine lining to thicken, cervical mucus to increase, and a slight rise in body temperature.
- Ovulation (Day 14): Mature egg is released from the dominant follicle, travels through the fallopian tube, fertilization is possible.
- Luteal Phase (Days 15-28): Empty follicle produces progesterone, which prepares the uterus for a fertilized egg. Uterine lining thickens further, and body temperature rises slightly.
- Premenstrual Phase (Days 26-30): If the egg is not fertilized, hormone levels drop, the uterine lining sheds, and menstruation occurs.
Changes in the Follicle Before Ovulation
- Graafian follicle: Enlarges to 20 mm.
- Follicular wall: Becomes thinner near the ovarian surface.
- Cytoplasmic volume: Increases.
- Mitochondria and Golgi: Changes in number and distribution.
- First meiotic division: Completes, forming the secondary oocyte and first polar body, each with a haploid number of chromosomes (23X).
Hormones and Ovulation
- FSH/LH mid-cycle surge: Responsible for follicle maturation, rupture, and oocyte expulsion.
- Follicle-Stimulating Hormone (FSH): Stimulates follicle growth and maturation in the ovary.
- Estrogen peak: Rapid increase in estrogen from growing follicles triggers the LH surge.
- Luteinizing Hormone (LH) surge: Pituitary gland releases a sudden surge of LH, triggering egg release from the dominant follicle.
- Gonadotropin-Releasing Hormone (GnRH): Released by the hypothalamus, stimulates the pituitary gland to release LH and FSH.
- Hormonal feedback loop: Delicate balance of estrogen, progesterone, and inhibin regulates ovulation.
Structure of a Mature Ovum
- Largest cell in the body.
- Composed of cytoplasm and a nucleus with an eccentric nucleolus.
- Contains 23 chromosomes (23X).
- Surrounded by a cell membrane called the vitelline membrane.
- Outer transparent mucoprotein envelope called the zona pellucida.
- Tiny channels in the zona pellucida allow transport from granulosa cells to the oocyte.
- Perivitelline space between the vitelline membrane and zona pellucida accommodates polar bodies.
- After leaving the follicle, the oocyte retains granulosa cells called the corona radiata, derived from the cumulus oophorus.
Spermatogenesis: Formation of Sperm Cells
- Development of spermatids from primordial male germ cells and differentiation into spermatozoa.
- Takes approximately 61 days for a spermatogonium to become a mature spermatozoon.
- Two phases: Spermatocytogenesis (formation of spermatids) and Spermiogenesis.
Spermatocytogenesis: Three Stages
- Multiplication Phase (Proliferation): Diploid spermatogonia multiply mitotically to form spermatocytes. New spermatogonia are generated and enter the growth phase.
- Growth Phase: Limited growth of spermatogonium, volume doubles, becoming primary spermatocytes (still diploid), and entering the maturation phase.
- Maturation Phase: Primary spermatocytes enter meiotic prophase (a complex process involving chromosome rearrangements, DNA duplication, and migration of homologous pairs toward opposite poles).
Spermiogenesis: Morphological Changes
- Final stage of spermatogenesis, transforming round spermatids into mature spermatozoa.
- Head and tail formation.
- Most of the cytoplasm is eliminated, forming a cytoplasmic drop at the end of the flagellum, which is later removed in the epididymis.
- Sperm with cytoplasmic droplets indicate immaturity.
Spermiogenesis: Head Formation
- Nuclear changes: Nucleus shrinks, chromosomes pack tightly, and becomes elongated and narrow.
- Acrosome formation: Cap-like structure covering the apical area of the head, contains hydrolytic enzymes for penetrating the zona pellucida during fertilization.
Spermiogenesis: Tail Formation
- Cytoplasm reduction: Most cytoplasm is eliminated, displaced towards the flagellum's end piece, forming the cytoplasmic drop.
- Middle piece formation: Contains many mitochondria providing energy for locomotion and centrioles.
- Tail is responsible for sperm motility.
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Description
Explore the critical stages of early embryo development, including the formation of the blastocyst, trophoblast, and the important structures emerging by the end of Week 2. Learn about gastrulation and how the three germ layers are established in this fascinating journey of growth and transformation.
