29 Questions
During which period does the transformation from embryo to fetus occur?
9th week to birth
At the beginning of the 3rd month, what fraction of the crown-rump length (CRL) does the head constitute?
1/2
When does the rapid growth of the body occur during the fetal period?
During the last two months of gestation
What is the length of pregnancy from the last normal menstrual period (LNMP)?
280 days or 40 weeks
At what point does the size of the head become approximately 1/4th of crown-heel length (CHL)?
Beginning of 5th month
What happens at the end of the 12th week during fetal development?
Head becomes less than 1/2 CRL
At what week does the transfer of erythropoiesis site from liver to spleen occur?
9th to 12th week
What occurs during the 14th week of fetal development?
Rapid growth and coordinated limb movement
What marks the end of the first half of intrauterine life?
Fetal movements felt by mother (quickening)
At what week does the spleen become an important site of hematopoiesis?
26th week
What occurs during the 22nd to 23rd weeks of fetal development?
Responds to noise (blink-startle responses)
What is the approximate fetal length and weight at the end of the first half of intrauterine life?
$15cm$, about ½ the total length of newborn, and less than $500$ gm
When do intestinal loops withdraw into the abdominal cavity during fetal development?
12th week
What occurs by the end of the 28th week of fetal development?
$1100gms$ weight and bone marrow hematopoiesis
At what week does the fetus begin to respond to noise with blink-startle responses?
$22nd$ week
What stimulates the ovarian primary follicles to develop and become mature?
Follicle-stimulating hormone (FSH)
Which hormone is responsible for the production of Estrogen by the follicular cells?
Follicle-stimulating hormone (FSH)
Under normal conditions, how many of the primary-stage follicles reach full maturity in each ovarian cycle?
Only one follicle
Which gland controls the sexual cycles in females?
Pituitary gland
During which phase of the ovarian cycle is luteinizing hormone (LH) active?
Ovulatory phase
Which hormone acts on cells of the pituitary gland to stimulate and control cyclic changes in the ovary?
Gonadotropin-releasing hormone (GnRH)
What is the role of FSH in the early development of the ovarian follicle?
Induces early development of the ovarian follicle
What is the function of LH in the final stages of maturation of the ovarian follicle?
Triggers ovulation
How does estrogen production by the granulosa and thecal cells affect the uterine endometrium?
Enters the proliferative phase
What is the role of LH at mid-cycle?
Triggers ovulation
What occurs under the influence of FSH and LH immediately preceding ovulation?
Development of vesicular follicle
What is thought to carry the oocyte into the uterine tube just before ovulation?
Sweeping movements of the fimbriae
How long does it take for a fertilized oocyte to reach the uterine lumen in humans?
3-4 days
Where does fertilization occur in humans?
Ampullary region of fallopian tube
Study Notes
Fetal Development Stages
- Transformation from embryo to fetus occurs around the end of the 8th week of gestation.
- At the beginning of the 3rd month, the head constitutes approximately one-half of the crown-rump length (CRL).
- Rapid growth of the body during the fetal period occurs predominantly between weeks 9 and 16.
- Length of pregnancy from the last normal menstrual period (LNMP) is typically around 40 weeks.
Key Developmental Milestones
- The size of the head becomes about one-quarter of the crown-heel length (CHL) around week 12.
- By the end of the 12th week, all major organs and systems have formed, marking significant fetal development.
- The transfer of the site of erythropoiesis from the liver to the spleen occurs around week 28.
Mid to Late Fetal Development
- During the 14th week, the developing fetus experiences muscle movements and begins to show reflexes.
- The end of the first half of intrauterine life is marked at the end of week 20.
- The spleen becomes an essential site of hematopoiesis by week 12.
Growth and Responses
- Between weeks 22 and 23, significant accumulation of adipose tissue occurs.
- At the end of the first half of intrauterine life, the approximate fetal length is around 25 cm, and weight is about 250 grams.
- Intestinal loops withdraw into the abdominal cavity by the end of week 12.
- By the end of the 28th week, the fetus is approximately 37 cm long and can respond to stimuli.
Hormonal Regulation in Ovarian Cycle
- The process of ovarian primary follicles developing into mature follicles is stimulated by FSH (Follicle Stimulating Hormone).
- Estrogen production by follicular cells is influenced by LH (Luteinizing Hormone).
- Under normal conditions, about 1 to 2 of the primary-stage follicles reach full maturity in each ovarian cycle.
- The anterior pituitary gland controls the sexual cycles in females.
Ovarian Cycle Phases
- Luteinizing hormone (LH) is particularly active during the ovulatory phase of the ovarian cycle.
- FSH stimulates early development of the ovarian follicles, encouraging growth and maturation.
- LH promotes the final maturation of the ovarian follicle, leading to ovulation.
Ovulation and Fertilization
- Estrogen produced by granulosa and thecal cells helps to thicken the uterine endometrium in preparation for potential implantation.
- Mid-cycle, LH surges trigger ovulation.
- Just before ovulation, fluids generated by the follicle help carry the oocyte into the uterine tube.
- It takes approximately 3 to 4 days for a fertilized oocyte to reach the uterine lumen in humans.
- Fertilization typically occurs in the ampulla region of the uterine tubes.
Learn about the fetal period, from the 9th week to birth, and the rapid growth and maturation of tissues and organs. Understand the transformation from embryo to fetus and the patterns of growth in length and weight during pregnancy.
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