Reproductive System Flashcards
Which type of cells are involved in spermatogenesis? Where are they located?
- Sertoli cells
- Basement membrane of seminiferous tubule (form continuous layer connected by tight junctions)
Describe the blood-testis barrier?
- Molecules from blood must be allowed through Sertoli cells to reach developing spermatozoa
Where are spermatogonia located?
- Located on the basement membrane of seminiferous tubules
Where do spermatogonia travel towards?
- Move towards lumen as they develop into spermatozoa
Describe the 5 steps of spermatogenesis?
1 - Spermatogonia are DIPLOID cells that give rise to 2 daughter cells via MITOSIS
2 - One remains at the basement membrane as a stem cell
3 - Another (primary spermatocyte) develops into spermatozoa as it moves toward the tubule lumen
4 - 1st meiosis: DNA duplicates, then homologous chromosomes separate into 2 HAPLOID daughter cells
5 - 2nd meiosis: Duplicate chromatids separate into 4 HAPLOID daughter cells
How many spermatogonia are present in embryonic testes?
- 1000-2000
- So mitosis is crucial
How many sperm does the median ejaculation contain?
- About 255 million sperm in 1.5-5 mL fluid
What is considered oligospermia?
- Less than 20 million/mL
- Leads to decreased fertility
How are the seminiferous tubules protected from immune attack?
- By Sertoli cells
- Blood-testis barrier
- Production of FAS ligand which binds to FAS receptor on T cell, triggering T cell apoptosis and preventing immune system attack on developing sperm
What is the life span of sperm once ejaculation has occurred?
- About 80 hrs or 3 days
What helps in maintaining metabolic requirements of sperm?
- Cervical mucus
What happens to sperm when they migrate in the female reproductive tract?
- Sperm are rapidly separated from seminal fluid and resuspended in female reproductive fluid
- Undergo ‘capacitation’ (or maturation) during their passage through female reproductive tract
What is the acrosome of spermatozoa?
- Protein/enzyme layer at tip of sperm
Where is the nucleus located in spermatozoa?
- Head
Where is the mitochondria of spermatozoa located?
- Mid piece
What is capacitation?
- The process of physiological changes occurring in mammalian sperm during passage through the female reproductive tract that enables them to penetrate the egg membrane
- Alteration of glycoprotein surface of sperm under the influence of secretion of the tissues of the female reproductive tract
Which sperm does not require capacitation?
- Non-mammalian sperm
What does the surface of epididymal sperm contain?
- Glycoproteins
What happens to the glycoproteins when sperm is ejaculated?
- Surface glycoproteins are coated with seminal plasma proteins
What does capacitated sperm look like?
- Surface glycoproteins are removed
- Exposes molecules that can bind zona pellucida of the oocyte
How many sperm reach the site of fertilization?
- Only few
Where are most sperm eliminated? How?
- Cervix
- Uterotubal junction
- Female immune system attack
- Phagocytosis
What happens to damaged/immotile sperm?
- Carried back to cervix by ciliated cells
What is fertilization?
- Series of processes beginning with sperm penetrating corona radiata/zona pellucida surrounding the oocyte, entering the oocyte, and ending with intermingling of maternal/paternal chromosomes
Where does fertilization usually occur?
- Fallopian tube
About how many mature sperm reach the egg in the fallopian tube?
- About 100
How does fertilization occur?
- First sperm to successfully fuse with egg blocks polyspermy
- Electrical polyspermy blocks function in some animals (frogs, clams, marine worms)
- Mammals lack electrical block; polyspermy prevented by secreted chemical barrier
What is necessary to release egg?
- LH surge to promote follicle rupture
How do the LH/FSH levels change 2 days before ovulation?
- LH increases 6-10 fold
- FSH increases 2-3 fold
How does LH affect ovulation?
- Converts granulosa cells to estrogen/progesterone-secreting cells
When can fertilization occur?
- As early as 3 days prior to ovulation
- Up to 1 day after ovulation
When does the secondary oocyte disintegrate?
12-24 hours after ovulation if it isn’t fertilized
Describe the process of egg transport.
- Secondary oocyte enters fallopian tube
- Fertilization
- Becomes zygote
- Mitosis creates multi-celled zygote
- Morula (12-16 cells) formed when it enters the uterus
- Becomes a blastocyst after 5-6 days
- Implanted blastocyst contains inner (fetus) and outer (placenta) cell mass
How are dizygotic twins formed?
- Fraternal twins
- Develop from 2 separate oocytes fertilized at the same time
How are monozygotic twins formed?
- Identical twins
- Two individuals developed from one fertilized oocyte
- Identical genomes
What are conjoined twins?
- Monozygotic twins whose bodies are joined to a varying extent
How does implantation/nidation of the blastocyst occur?
- Trophoblasts produce enzymes that allow blastocyst to implant in endometrium of posterior wall of uterine cavity
- Trophoblasts secrete hCG to maintain corpus luteum (to make progesterone until placenta takes over)
Why do about 75% of lost pregnancies occur?
- Failed implantation
What is an ectopic pregnancy? How often does it happen?
- Implantation in different site than posterior wall of uterine cavity
- 0.25-1% of pregnancies
What is detected in pregnancy tests? Where is it made?
- hCG
- Trophoblasts in blastocyst
What hormones are secreted in pregnancy? By what?
- hCG (secreted by blastocyst)
- > High in early pregnancy, then drops after 2 months
- Estrogen/progesterone (secreted by corpus luteum then placenta)
- > gradually increases until delivery
Describe the mechanism of a pregnancy test?
- Immunoassay: tagged antibody specific to hCG (detected in blood/urine)
1 - 1st window
-> if hCG present = dye accumulates = visible line
2 - 2nd window
-> control to ensure proper function
What is the luteal-placental shift?
- Placenta takes over secreting estrogen/progesterone to maintain endometrial lining instead of corpus luteum
Why is the placenta required for pregnancy?
- ‘feeds’ fetus through umbilical cord
- Placental a2-adrenoceptors control vascular development at the interface b/n mother and embryo
- Substantial percentage of pregnancies are lost due to inadequately developed placenta
- Proper development of placental vascular system is essential to nutrient, gas, and waste exchange b/n mother and developing fetus
Which systems does the placenta perform the function of for the fetus?
- Digestive
- Respiratory
- Renal
What is the most preventable cause of illness and death among mothers and infants?
- Smoking during pregnancy
What necessary hormones does the placenta provide?
- Unique endocrine gland (transient, without extrinsic control)
- hCG: maintains corpus luteum
- Estrogen: Acts on uterine myometrium (growth, oxytocin receptors), breast ducts
- Progesterone: Suppresses uterine contractions, cervical plug, milk glands
- PTHrP: Mobilizes mother’s bone calcium
- CRH: Fetal lung maturation
What type of loop controls parturition?
- Positive feedback
Describe the endocrine control of parturition?
1 - Fetal adrenal gland secretes DHEAS and cortisol upon stimulation by CRH and ACTH
2 - Cortisol stimulates the placenta to secrete CRH, producing a positive feedback loop
3 - DHEAS is converted in placenta to Estriol, which together with placental prostaglandins and maternal oxytocin stimulate the maternal myometrium to undergo changes leading to labour
What are the only 2 anterior pituitary hormones whose secretion is regulated by both hypothalamic releasing and inhibiting hormones?
- Prolactin and GH
Describe the hypothalamus -anterior pituitary gland-mammary gland axis?
Hypothalamus -PIH/PRH-> Anterior pituitary -prolactin-> Mammary glands -> Milk production and growth/development of glands and ducts
How many lobes is the mammary gland composed of? What is it divided by?
- 7-10 lobes
- Divided by adipose tissue
How are the lobes of the mammary gland divided?
- Each lobe is subdivided into lobules
- Lobules contain alveoli
Which part of the mammary glands secretes milk?
- Alveoli secrete milk into secondary tubules, which form into mammary ducts, then lactiferous duct, then drain at nipple
What is the function of myoepithelial cells in lactation?
- Myoepithelial cells contract to propel milk through the duct system
Where does milk accumulate during nursing?
- Lumen of the lactiferous duct
Describe prolactin levels during pregnancy?
- High estrogen inhibits PIH, allowing prolactin to stimulate milk production
- However, high estrogen and progesterone levels inhibit milk secretion until after parturition when estrogen and progesterone levels decrease
How are high prolactin levels maintained?
- Act of nursing via neuroendocrine reflex
- Stimulus may be suckling or visual or auditory cue, or thought of child
Describe the milk-ejection reflex?
- Oxytocin stimulates myoepithelial cells surrounding lactiferous ducts to contract
What does human breast milk contain that can’t be replicated in formula?
- Immune cells
- Stem cells
- Immunoglobulins
- Cytokines
- Growth factors
- Other hormones
What is the trust/love potion?
- Oxytocin
What determine biological sex?
- SRY (Sex determining Region of the Y) induces the embryonic gonads to become testes
- Biological females lack a Y chromosome, and the absence of this gene causes the development of ovaries
Describe sex differentiation for females?
1 - Absence of SRY protein - gonadal tissue develops into ovaries
2 - Hence no Sertoli cells or testosterone, so no Mullerian inhibition factor (MIF) is made from Sertoli cells, so Wolffian duct degerates
3 - Absence of MIF allows the Mullerian duct to become the fallopian tube, uterus and vagina.
What is the sex of the fetus considered to be at 6 weeks?
- Bipotential primordium
- Gonadal tissue is indistinguishable between female and male
Describe sex differentiation in males?
1 - Presence of SRY protein - gonadal tissue develops into testes
2 - Presence of Sertoli cells and testosterone, so MIF is secreted from Sertoli cells, which maintains the Wolffian duct and causes the Mullerian duct to degerate
3 - Testosterone allows Wolffian duct to become seminal vesicle, vas deferens and epididymis
What is TDF?
Testis-determining factor
What are true hermaphrodites?
- An intersex condition where individuals have both ovary and testis tissue
- Abnormality in sex chromosomes
- Various degrees of mosaicism
What are pseudohermaphrodites?
- Congenital condition where a person has external genitalia of one sex, and internal sex organs of the other sex
- Born with external genitalia that appears female, at puberty, male genitalia and characteristics develop
- Endocrine disorder
- Genetically males with a defective gene for 5alpha-reductase (converts testosterone to 5-DHT)
Describe the mechanism of pseudohermaphroditism?
- Normal testosterone production
- Defective 5alpha-reductase
- Inadequate 5-DHT
- Inappropriate exposure to androgens early on
- At puberty, testes secrete testosterone again
In which sex does puberty occur more rapidly and earlier?
- Females
Describe puberty
- Activation of HPG axis resulting in gonad maturation
What is adolescence?
- Maturation of adult social and cognitive behaviours
What controls metamorphosis of the child into adult?
- Coupling of puberty and adolescence between endocrine system and nervous system
Describe the GnRH pathway?
Hypothalamus -GnRH-> Anterior pituitary -FSH/LH-> Endocrine cells of gonads -Androgen/estrogen/progesterone-> Germ cells of gonads
How does GnRH secretion occur?
- In pulses, NOT steadily
What happens to children with a deficiency in GnRH?
- Do not mature sexually
How do they treat a deficiency in GnRH? What is the result?
- Treat with GnRH pulses similar to those that occur naturally
- Children go through puberty
What affects puberty onset?
- Genetic variations
- Environmental factors
- Synthetic chemicals
- Nutrition
- Chronic illness
- Psychological factors
What has changed in puberty onset in developed countries?
- Girls are experiencing puberty earlier
What are some potential causes of early puberty?
- Obesity
- Premature birth
- Reduced altitude
- Exposure to light
- Endocrine-disrupting chemicals (flame retardants on fabric, bisphenol A in plastic, cigarette smoke)
- Family conflict/abuse
