BI513 Reproductive System Flashcards
What are the 2 main reasons why we have sex?
1) Accelerates evolution
2) Reshuffles the genetic composition
Name 3 short term losses from sex
Costly
Time consuming
Expends energy
What is sexual dimorphism?
Distinct differences in the size or appearance between the sexes of animals in addition to the sex organs themselves
Name 3 reasons we have sexual differentiation later in life
Avoids overpopulation
Individuals efficiently equipped to cope with child care
Evolutionary advantage of having grandmothers
On the human Y chromosome, what do PAR and SRY represent?
PAR - pseudo autosomal region
SRY - sex determining region
When does sexual differentiation occur?
Second month post fertilization
What do the Wolffian ducts become?
Develop in males, degenerate in females
Become epididymis, vas deferens, seminal vesicle
What do the Mullerian ducts become?
Develop in females
Becomes Fallopian tube, uterus, cervix, upper vagina
Do male gonads have more androgens or oestrogen’s?
Androgens
What series of events causes an embryo to become male?
- SRY gene produces testis determining factor (TDF)
- Leydig cells produce testosterone
- development of Wolffian ducts into accessory structures
- development of male genitalia
- Sertoli cells produce Mullerian inhibiting substance
- regression of Müllerian ducts
Describe the process of sperm development
1) Primordial germ cell in embryo |
2) Spermatogonial stem cell | develop in embryo
3) Spermatogonium develop during puberty
4) Primary spermatocyte
(Meiosis 1)
5) Secondary spermatocyte
(Meiosis 2)
6) Early spermatid
(Differentiation)
7) Sperm
What 2 things do the testes produce?
Sperm and testosterone
What structure make up around 80% of the testicular mass and contain developing sperm?
Seminiferous tubules (around 250-300)
How long does it take for a spermatogonia to become 4 sperm?
Around 64 days
Describe the structure of a sperm
Head: Nucleus and surrounding acrosome (acrosomal c)
Middle piece: Mitochondria
Tail: Axial filament and flagellum
What does the nucleus in the sperm head use to condense?
Protamines (not histones)
What are the main functions of the Sertoli cells?
- Regulate sperm development (provide nutrients)
- Manufacture and secrete proteins e.g inhibin, activin, enzymes and androgen binding protein (ABP)
- ABP binds to testosterone (concentrates it)
What are the main functions of the Leydig cells?
- Secrete testosterone
- First active in foetus as testosterone is needed to develop male phenotype
- Inactive after birth until puberty
Where is gonadotrophin produced, how often and what does it cause?
Produced in hypothalamus
Pulses every 90 minutes
Causes anterior pituitary to produce LH and FSH
What does FSH do in males?
- Targets Sertoli cells
- FSH stimulates paracrine factors needed for mitosis of spermatogonia
- FSH stimulates androgen binding protein (ABP)
What does LH do in males?
- Targets Leydig cells
- cells produce testosterone
- testosterone feeds back to inhibit LH
Describe the process in which hormones control reproduction in males
- Hypothalamus releases gonadotrophin releasing hormone (GnRH)
- GnRH causes anterior pituitary to produce LH and FSH
- LH causes Leydig cells to secrete testosterone
- FSH and testosterone cause Sertoli cells to produce proteins including ABP and inhibin
- Testosterone from Leydig and ABP from Sertoli bind (this stimulates sperm development from spermatogonia)
- Some testosterone goes to body for secondary effects
- Testosterone and Inhibin all have negative feedback on GnRH production from hypothalamus and LH production from anterior pituitary
What do the male accessory glands do?
Secrete fluid mixtures that meet with sperm upon ejaculation
- Fluid also protects reproductive tract against infection
What is the composition of semen?
Sperm -gametes Mucus - lubricant Water - provides liquid medium Buffers - neutralise acidic environment of vagina Nutrients (fructose, citric acid, vit C, carnitine) - nourish sperm Enzymes - clot semen in vagina Prostaglandins - smooth muscle contraction to aid sperm transport Zinc - unknown
What are the male primary sex characteristics?
Internal sex organs
External genitalia
What are some male secondary sex characteristics?
Body shape Beard/body hair Muscles Thickening of vocal cords Libido
What is capacitation?
- A step in the maturation of sperm
- confers sperms ability to swim rapidly to fertilise an egg
When does fertilisation usually occur and where does it occur?
- 12-24 hours after ovulation
- occurs in distal part of Fallopian tube
What occurs when a sperm reaches the egg?
- Must break through zona pellucida
- releases acrosome to dissolve zona pellucid
- fusion of membranes to release nucleus
- resumes female meiosis
- membrane fusion prevents polysermy
Name 3 pre testicular causes of male infertility?
conditions that impede adequate testicle support
- Obesity
- Drugs/alcohol
- Strenuous riding
- Medications eg chemo, anabolic steroids
- Tobacco smoking
Name 3 testicular factors that cause infertility
testicles producing inadequate/low quality sperm
- Age
- Genetic defects of Y chromosome
- Abnormal set of chromosomes eg Klinefelter syndrome (XXY)
- Mumps
- Malaria
- Testicular cancer
Name 3 post testicular factors that cause infertility
- Vas deferens obstruction
- Infection
- Retrograde ejaculation
- Ejaculatory duct obstruction
- Impotence
What are the definitions of the following: Oligospermia` Aspermia Hypospermia Azoospermia Teratospermia Asthenozoospermia
Decreased number of sperm in semen Complete lack of semen Reduced seminal volume Absense of sperm in semen Increase in sperm with abnormal morphology Reduced sperm motility
What are the 5 phases of the female reproductive system?
Early follicular phase Late follicular phase Ovulation Early to mid luteal phase Late luteal phase and menstruation ``1
Describe the structure of the ovary
- 2-4cm long
- Outer/inner connective tissue
- stroma
- Most of ovary
- thick cortex filled with follicles
- Small central medula
- nerves and blood vessels
- 500,000 primary oocytes
- Each oocyte contained in follicle
- outer layer of granulosa cells
- develops outer layer of cells known as the theca
How long is the menstrual cycle?
24 - 35 days
What are the 3 phases of the ovarian cycle?
Follicular phase (10 - 21 days) Ovulation (egg release) Luteal phase (follicular remnants become corpus luteum)
What are the phases of the uterine cycle?
Menses
Proliferative phase (thickening of endometrium)
Secretory phase
- After ovulation
- Endometrium converts to secretory structure
- Corresponds to luteal phase
Describe what happens in the early to mid follicular phase
- Hypothalamus produces GnRH
- Anterior pituitary produces LH and FSH
- FSH acts on granulosa cells of follicle
> Granulosa cells secrete oestrogen and enzymes int antrum to promote ovulation - LH acts on Thecal cells of follicle
> Thecal cells produce androgens that diffuse into granulosa cells where aromatase coverts them to oestrogens - Oestrogen causes negative feedback on hypothalamus and anterior pituitary to stop GnRH, LH and FSH production to prevent further follicles developing
> positive feedback on granulosa cells to produce more oestrogen
Describe late follicular phase
Granulosa cells secrete:
> Inhibin
> Progesterone
> Oestrogen
Oestrogen has positive feedback on GnRH secretion
Progesterone has positive feedback on GnRH and LH secretion
Inhibin has negative feedback on FSH secretion
LH surges
> FSH also surges but to lesser extent
> Polar body appears
> High levels of oestrogen prepare uterus for pregnancy
> Cervical glands produce mucus to facilitate sperm entry
When does ovulation occur and what happens
- occurs about 16 - 24 hours after LH peak
- artial fluid comes out of follicle with egg
> egg surrounded by granulosa cells
> eg swept into Fallopian tube - Mature follicle secretes collagenase
> holds follicle together
What happens in the early to mid luteal phase
- Corpus luteum is produced from follicular remnants
- Corpus luteum produces progesterone, oestrogen and inhibin
Progesterone:
> negative feedback on GnRH and LH secretion
> causes cervical mucus to thicken and plug the cervix to prevent further sperm entry
Oestrogen:
> negative feedback on GnRH secretion
Inhibin:
> negative feedback on FSH secretion
Endometrium continues to prepare for pregnancy - Glands coil
- More blood vessels
- More lipid and glycogen (nourishment for embryo)
What happens in the late luteal phase?
Corpus luteum lasts around 12 days
- if no pregnancy, undergoes apoptosis
- becomes corpus albicans
- reduces progesterone and oestrogen production
- removes negative feedback
- blood vessels on surface layer of endometrium contract and surface cells die
MENSTRUATION
What is produced during menstruation and how long does it typically last?
- ~40ml blood
- ~35ml serous fluid and cell debris
- 3 - 7 days
What sex characteristics do oestrogens and androgens control in females?
Oestrogens control:
> All primary sex characteristics
> Some secondary e.g hips, thighs, breasts
Androgens from adrenal cortex:
Other secondary e.g pubic and arm pit hair, libido
Name 3 acquired factors that contribute to female infertility
- Age
- Tobacco smoking
- STIs
- Body weight
- Chemotherapy
- Diabetes mellitus
- Coeliac disease
- Liver or kidney disease
- Can ibis smoking
What are the 3 phases of the human sexual response?
1) Excitation
- tactile and psychological stimuli
- penile and clitoral erection
2) Plateu
3) Orgasm
How does a psychological stimulus cause an erection?
Thought
Higher brain centres
Descending autonomic pathway increases parasympathetic input and inhibits sympathetic input by negative feedback
Parasympathetic pathway causes arterioles in penis to vasodilate and the corpus cavernosum fills with blood
How does a tactile stimulus cause an erection?
- Tactile stimulation
- Mechanoreceptors
- Sensory neurons
- Nerve cells in spinal cord
- Higher brain centers
- Nerve cells in SC and higher brain centres cause negative feedback on sympathetic input and postive feedback on parasympathetic input
- Arterioles in penis vasodilate and fill with blood as does corpus cavernosum
What is the corpus cavernosum?
Pair of sponge like regions of erectile tissue that contain most of blood during erection
What is emission?
Movement of sperm out of vas deferens in urethra
Joined by secretions from accessory glands to make semen
What occurs during ejaculation?
Muscle contractions causing semen to be expelled from urethra
Orgasm - pleasure sensation
Sphincter at base of bladder contracts to prevent mixing with urine
What is impotence and how is it tested for?
- Erectile dysfunction
- Can be physiological or psychological
- To establish which one is the cause - postage stamp test (during REM sleep)
What occurs on a molecular level to cause an erection?
- Neurotransmitter released from pelvic nerves
- Increase nitric oxide in smooth muscle
- Nitric oxide activates guaylyl cyclase
- Increase cGMP and causes vasodilation
How does viagra cause an big old erection?
- Blocks enzyme that degrades cGMP
- Prolonged effect of nitric oxide
What are some side effects of viagra?
- Headaches
- Indigestion
- Nasal congestion
- Impaired vision
What are the 3 main types of contraceptives and give examples
1) Prevent fertilisation
- Abstinence, barrier (condom), sterilisation (vasectomy)
2) Prevent embryos developing in uterus
- IUD (intrauterine device), morning after pill
3) Prevent developing gamete
- the pill
How does the pill work?
- combinations of oestrogen and progesterone to prevent GnRH secretion from anterior pituitary
- Suppresses LH and FSH production so no ovulation
What are the 2 main areas of a blastocyst (5-6 days) and explain what each is?
1) Outer cells (trophectoderm)
- becomes chorion
- Chorion develops into placenta
- Secretes enzymes that allows invasion of endometrium
- Finger like projections (chorionic villi) penetrate uterus
- Gas and nutrient exchange from mother to baby
2) Inner cell mass
- Develops into foetus
- Contains amnion that secretes amniotic fluid
- Contains Allantois that becomes part of the umbilical cord
How is the corpus luteam prevented from degenerating?
- Hormone signal from placenta (corpus luteum usually degenerates at day 12)
- Signal prevents degradation and thus prevents dropping of progesterone and oestrogen
- Therefore prevents menstruation
What 4 hormones prevent corpus luteum degradation?
1) Human chorionic gonadotrophin (hCG)
2) Human placental lactogen (hPL)
3) Oestrogen
4) Progesterone
What are the functions of human chorionic gonadotrophin (hCG)?
- Corpus luteum stays active in early pregnancy because placenta is secreting hCG (peaks at week 3)
- hCG structurally related to LH, binds to LH receptors
- Instructs corpus luteum to keep producing progesterone and keep endometrium intact
- By week 7 placenta takes over progesterone production so corpus luteum degenerates
- hCG also stimulates testosterone production in testes of male foetus
- Detection of hCG is basis of pregnancy tests
What is the function of human placental lactogen (hPL)
- Thought to be related to breast enlargement and milk production
> however not altered in women with mutated hPL
What are the functions of oestrogen and progesterone post fertilisation?
Produced continuously during pregnancy
- First by corpus luteum then by by placenta
- prevents further follicles from developing
- Oestrogen contributes to development of milk secreting ducts
- Progesterone helps maintain endometrium and prevent uterine contractions
What is parturition?
The process of giving birth
What is labour?
Rhythmic contractions of the uterus
What is the trigger of labour and what occurs after this?
- Foetus dropping head down
- Puts pressure on cervix (cervical stretch)
- Cervical stretch causes uterine contractions and oxytocin to be produced from posterior pituitary
- Oxytocin causes uterine contractions and production of prostoglandins
- Prostoglandins cause uterine contractions
- Uterine contractions cause more cervical stretch
ALL POSITIVE FEEDBACK
What is the definition of infertility?
Inability to conceive after 1 year of regular unprotected intercourse
How many couples are considered infertile in the UK?
1 in 6
What % of infertility in due to male factors, female and both?
40% male
40% female
20% both
What investigations can be done to detect infertility?
- Semen analysis
- Pelvic ultrasound scan
- Hycosy (ultrasound to detect any damage or blockage to fallopian tubes)
- Hormone tests
- Mandotory screening tests
- Karyotype
What are the male factors?
- Sperm problems (oligospermia, aspermia, teratospermia etc)
- Medical history
- Physical examination
- Blood sample (hormonal)
- Chromosomal
What are the main female factors?
- Blocked fallopian tube
- Premature ovarian failure
- Ovulation problems
- Polycystic ovarian syndrome (PCOS)
- Endometriosis
- Chromosomal
- Hormonal
- Sexual dysfunction
How can infertility be diagnosed?
Lab tests - hormone testing Examination and imaging - Endometrial biopsy - Fertiloscopy - Pap smear - Hiscosy
What are the male treatment options?
- Donor sperm
- IUI
- IVF
- ICSI
- PESA/MESA (percutaneous/microsurgical epididymal sperm aspiration)
- TESE (testicular sperm extraction)
- PGD/PGS (preimplantation genetic diagnosis/screening)
What are the female treatment options?
- Donor eggs
- Ovulation induction
- Timed sexual intercourse
- IUI
- IVF
- ICSI
- PGD/PGS
What are the HFEA (Human Fertilisation and Embryology Authority) Regulations for donor sperm?
Donors must be:
- Age 18 - 45
- Fit, healthy and free from infectious or hereditary disease
- Understand the implications of identifying info being released to potential offspring
- Help a max of 10 families
What are the HFEA (Human Fertilisation and Embryology Authority) Regulations for donor eggs?
- Same as for donor sperm but age 18 - 35
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