Human Reproduction and Development Flashcards
What are primary sex organs called?
- gonads
Primary sex organs (gonads) in male and female
- testes in males
- ovaries in females
What do gonads produce?
- sex cells or gametes
- steroid hormones called sex hormones
Accessory reproductive organs
- ducts, glands and external genitalia
What do testes produce?
- sperm
- seminiferous tubules produce them in fact
Location of testes
- within the scrotum – sac of skin and superficial fascia that hungs outside the abdominal cavity at the root of penis
Midline that divides the scrotum
- septum
- provides the compartment for each testes
Male duct system in order
- epididymis, ductus deferens, ejaculatory duct, urethra
Male accessory glands
- paired seminal glands and a single prostate
Spermatogenesis
- process in which seminiferous tubules of the testes produce male gametes called sperm or spermatozoa
normal chromosomal number in most body cells
- diploid 2n
- in humans, diploid chromosomal number is 46, containing 23 pairs of chromosomes called homologous chromosomes
chromosomes in humans
- 23 pairs
- homologous chromosomes or homologues
Number of chromosomes in human gametes
- 23
- haploid chromosomal number
What is hormonal control in reproductive system called?
- hypothalamus-pituitary-gonadal axis
Define pregnancy
- events that occur from the time of fertilization (conception) until the infant is born
Conceptus
Developing offspring in the womb
Gestation period
- from last menstrual period until birth
- approximately 280 days
Embryonic period
- from fertilization through week 8
When is conceptus called an embryo?
- during embryonic period
- fertilization to week 8
When is conceptus called a fetus?
- during fetal period
- from week 9 through birth
Fetal period
- from week 9 to birth
When does ovum complete meiosis II?
- only when sperm penetrates the oocyte and is finding its way to the nucleus
When does fertilization occur?
- when sperm’s chromosomes combine with those of egg (secondary oocyte) to form a fertilized egg (zygote)
What happens when the sperm enters the oocyte?
- sperm’s plasma membrane is gone
- sperm uses microtubules to locomote its nucleus towards oocyte nucleus
- meanwhile, nucleus grows bigger into a male pronucleus
- secondary oocyte completes meiosis II forming ovum nucleus and second polar body
Male pronucleus + female pronucleus
- mitotic spindle develops between them
- nuclei membranes rupture and chromosomes are released
When is the “true” moment of fertilization?
- when maternal and paternal chromosomes combine and produce diploid zygote (fertilized egg)
Explain “cleavage” period in embryonic development
- mitotic divisions of zygote without intervening growth to increase surface-to-volume ratio for nutrient uptake and waste disposal
Cleavage division 36 hours after fertilization
- first division
- 2 identical daughter cells called blastomeres
Cleavage division 72 divisions after fertilization
- cluster of 16 or more cells called morula
How many cells does the embryo have after 4 or 5 days of fertilization?
- about 100 cells that accumulate fluid within internal cavity
How many days does the blastocyst float in the uterine cavity?
- two to three days
How is the blastocyst nourished while floating in the uterine cavity?
- glycoprotein-rich uterine secretions
- steroid and nutrients like iron and fat-soluble vitamins
When does implantation begin?
- six to seven days after ovulation when the endometrium is properly prepared
What does the sperm use to approach, bind and enter the oocyte?
- acrosomal enzymes and receptors
- receptors in oocyte cause the Ca2+ levels within sperm to rise triggering acrosomal reaction
- enzymes digest holes through zona pellucida of the oocyte
How can polyspermy be blocked?
- entry of sperm causes oocyte cytoplasm Ca2+ to rise
- it triggers cortical reaction that hardens zona pellucida and sperm receptors are clipped off
How long does implantation take?
- about 5 days, usually completed 12 days after ovulation
How is the viability of corpus luteum maintained?
- hCG secreted by trophoblast cells
- prompts corpus luteum to continue secreting progesterone and esterogen
When is hCG detectable?
- one week after fertilization until end of second month
- after that, the level falls and reaches a low by 4 months
Placenta between 2 and 3 months
- takes over to produce estrogen and progesterone until the end of pregnancy (corpus luteum degenerates)
How does the embryo get nutrients before placenta?
- by digesting endometrial cells
Function of trophoblast cells
- secret hCG
- give embryo nutrients
- develop into placenta
Placentation
- formation of placenta
- cells from original inner cell mass give rise to extraembryonic mesoderm layer that lines the inner surface of trophoblast
What is the chorion?
- double-layered membrane formed by the trophoblast and the extra-embryonic mesoderm
- helps in the exchange of nutrients, gases, and wastes between the embryo and the mother’s body.
What is the gastrula?
- blastocyst is being converted into 3 primary germ layers (during week 3)
- endoderm, ectoderm, mesoderm
What happens to inner cell mass before becoming three-layered?
- it subdivides into 2 layers
- upper epiblast and lower hypoblast
- subdivided inner cell mass is embryonic disc
What is the embryonic disc?
- subdivided inner cell mass before becoming three-layered
- with upper epiblast and lower hypoblast
What do the extraembryonic membranes include?
- amnion, yolk sac, allantois, chorion
- form during first 2 to 3 weeks of development
The amnion
- develops when cells of epiblast fashion themselves into a transparent membranous sac
What does the amnion contain?
- amnionic fluid
What is the amnion’s function?
- buoyant environment: protects the developing embryo against physical trauma
- helps maintain homeostatic temperature
- prevents growing embryo parts from fusing together –> freedom of movement
Where does amniotic fluid come from?
- initially from maternal blood
- after that, fetal urine
What is yolk sac formed from?
- cells of primitive gut which arrange themselves into a sac that hangs from the ventral surface of embryo
How is yolk sac important for humans?
- forms part of gut (digestive juice)
- source of earliest blood cells and blood vessels
Allantois
- small outpocketing embryonic tissue at the caudal end of yolk sac
Function of allantois
- structural base for umbilical cord that links embryo to placenta
- becomes a part of urinary bladder
What does a fully formed umbilical cord contain?
- embryonic connective tissue, umbilical arteries and veins
- covered by amniotic membrane
Organogenesis
- formation of organs and organ systems
Mean duration of pregnancy in weeks
- 38 weeks
Effect of pregnancy into female reproductive organs
- become increasingly vascular and engorged with blood
- increases vaginal sensitivity and sexual intensity
Why do breasts enlarge and engorge with blood during pregnancy?
- rising levels of estrogen and progesterone
What does the hormone relaxin do?
- produced by the placenta
- causes pelvic ligaments and pubic symphysis to relax, widen and become more flexible
How do multivitamins like folic acid help?
- reduce the risk of having a baby with neurological problems
Metabolic changes in the mother during pregnancy
- placenta secretes human placental lactogen (hPL) also known as human chorionic somatomammotropin (hCS)
- hPL works with estrogens and progesterones to prep breasts for lactation
- promote fetus growth and exerts glucose-sparing effect on mother
- maternal cells metabolize more fatty acids and less glucose
Pregnancy effect on GI system
- nausea and vomitting due to hCG, esterogen, progesterone
- heartburn due to reflux of stomach acid into esophagus
- constipation
Pregnancy effect on urinary system
- more urine produced
- increased metabolic rate and uterus pressing against bladder
Pregnancy effect on respiratory system
- nasal mucosa become edematous and congested due to estrogens
Pregnancy effect on cardiovascular system
- total body water rises and BV increase as much as 40% by 32 weeks
- safeguard blood loss
Parturition
- giving birth to the baby
Rise in estrogen in the last weeks of pregnancy
- stimulate myometrial cells of uterus to form oxytocin receptors
- promote gap junction formation between uterine smooth muscle cells
- antagonizes progesterone;s quieting influence on uterine muscles
What does oxytocin do?
- causes placenta to release prostaglandins that stimulate more uterine smooth muscle gap junctions
- more contractions
Stages of labour
- dilation, expulsion, placental stage
What is the neonatal period?
- four-week period immediately after birth
Lactation
- production of milk by mammary glands
Hormonal control of lactation
- rising levels of estrogen, progesterone, hPL stimulate hypothalamus to release prolactin-releasing factors
- ant. pit. responds by secreting prolactin
Advantages of breast milk
- fats and ions r better absorbed and amino acids are better metabolized
- beneficial chemicals like IgA protect infant from infections
ulcer causing bacteria
- helicobacter pylori
