Gametogenesis and Fertilization Overview : lecture 9

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Questions and Answers

What are somatic cells responsible for?

Halving DNA content for fertilization

Forming gametes in the ovaries and testes

Undergoing mitosis to produce identical cells for growth (correct)

Producing non-identical cells for reproduction

What occurs to the primary oocyte during the menstrual cycle?

It completes meiosis I and resumes division

It grows but remains arrested in metaphase I until ovulation (correct)

It develops into a primary follicle

It pauses in prophase II until fertilization

Which phase of the menstrual cycle involves the shedding of the uterine lining?

Secretory phase

Luteal phase

Proliferative phase

Menstrual phase (correct)

What triggers the prevention of polyspermy?

Cortical granule release following oocyte activation Signup and view all the answers

What is the primary function of the corpus luteum?

To prepare the uterus for potential implantation Signup and view all the answers

What happens during spermiogenesis?

Spermatids mature into capable spermatozoa Signup and view all the answers

What is the function of enzymes released from the acrosome?

To digest the zona pellucida for sperm entry Signup and view all the answers

What is amphimixis?

The mixing of genetic materials during the first cell division of the zygote Signup and view all the answers

What is the initial stage of prenatal development referred to?

Pre-embryo Signup and view all the answers

What organ system primarily arises from the endoderm?

Gastrointestinal tract Signup and view all the answers

How are fraternal twins formed during development?

From two separate fertilized eggs Signup and view all the answers

Which structure forms from the ectoderm during development?

Skin Signup and view all the answers

What is the primary function of the placenta during pregnancy?

To support fetal development and exchange nutrients Signup and view all the answers

What happens to the ductus arteriosus after birth?

It closes Signup and view all the answers

Which congenital heart defect increases pulmonary blood flow?

Increasing pulmonary blood flow lesion Signup and view all the answers

What condition is commonly associated with spina bifida?

Hydrocephalus Signup and view all the answers

Study Notes

Gametogenesis and Fertilization

Somatic cells divide by mitosis to create identical copies for tissue growth and repair
Gametes are produced by meiosis, which creates non-identical cells with half the DNA content
Meiosis halves the DNA content to ensure a zygote with the correct chromosome number (46) after fertilization

Oogenesis

Germinal epithelium becomes inactive after birth and no longer divides
Primary oocyte grows in size after puberty but remains arrested in metaphase I until ovulation
Menstrual cycle:
- A secondary follicle develops, and one primary oocyte completes meiosis I to become a secondary oocyte
- The secondary oocyte pauses in prophase II of meiosis

Ovarian and Menstrual Cycles

Ovarian cycle:
- Follicular phase (days 1-14)
- Luteal phase (days 15-28)
Corpus luteum secretes progesterone to prepare the uterus for implantation
Menstrual cycle:
- Menstrual phase (days 1-5): Uterine lining is shed
- Proliferative phase (days 6-14): Lining regrows and glands proliferate
- Secretory phase (days 15-28): Uterine glands secrete compounds for implantation

Spermatogenesis

Occurs in seminiferous tubules of the testes
Primary spermatocytes undergo meiosis I to produce haploid secondary spermatocytes
Spermatids mature into spermatozoa during spermiogenesis

Events Leading to Fertilization

Corona radiata: a layer of granulosa cells surrounding the oocyte
Sperm penetrates the zona pellucida using enzymes from the acrosome
Polyspermy is prevented by oocyte activation, which triggers cortical granule release, hardening the zona pellucida and digesting remaining sperm receptors

Fertilization and Early Development

Amphimixis: mixing of paternal and maternal DNA during the first mitotic division of the zygote
Cleavage: division of the zygote into smaller cells called blastomeres
Implantation: the blastocyst embeds into the uterine lining

Development Stages and Twins

Prenatal development stages: pre-embryo, embryo, and fetus
Identical twins form from splitting a single zygote into two inner cell masses
Fraternal twins form from the fertilization of two separate oocytes by two different sperm

Germ Layers and Organ Formation

Ectoderm:
- Brain
- Spinal cord
- Nerves
- Skin
Mesoderm:
- Muscles
- Bones
- Heart
- Kidneys
- Connective tissue
Endoderm:
- Gastrointestinal tract
- Lungs
- Various glands

Placental Circulation and Fetal Development

Placenta: supports fetal development by exchanging nutrients and waste between fetus and mother
Umbilical arteries: carry deoxygenated blood
Umbilical vein: carries oxygenated blood to the fetus

Neural Tube and Congenital Disorders

Spina bifida: neural tube defect where spinal cord content protrudes outside the vertebrae
Hydrocephalus: excess cerebrospinal fluid accumulates, often causing mental deficits and nerve dysfunction

Congenital Heart Defects and Risks

Leading cause of neonatal death after prematurity
Maternal factors increasing risk: rubella, diabetes, medication use during pregnancy
Types of congenital heart defects:
- Lesions increasing pulmonary blood flow
- Lesions decreasing pulmonary blood flow
- Obstructive lesions
- Mixed lesions

Lung Development and Premature Births

Canalicular phase: (weeks 17-27) immature alveoli form and lung vascularization increases
Insufficient surfactant causes infant respiratory distress syndrome (IRDS) due to alveolar collapse

Postnatal Changes and Transition to Neonatal Circulation

Ductus arteriosus and foramen ovale close after birth to separate pulmonary and systemic circulations
IRDS symptoms: rapid breathing, cyanosis, nasal flaring, fatigue
IRDS treatment: artificial surfactants, mechanical ventilation, oxygen therapy

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Description

This quiz focuses on the processes of gametogenesis and fertilization, detailing how somatic cells and gametes are formed. It explains oogenesis and the ovarian and menstrual cycles, highlighting the key phases and hormonal influences involved in these reproductive processes.