Component 2: Human Sexual Reproduction Flashcards
Name all the parts in the female reproductive system
Ovary, uterus, cervix, fallopian tube (oviduct), bladder, urethra and vagina
What are the 3 layers of the uterus?
- Perimetrium (outer layer)
- Myometrium (middle layer)
- Endometrium (inner layer)
What is the function of the ovary?
Produce female gametes (secondary oocytes) and secrete oestrogen & progesterone
What is the function of the uterus?
nourishes and protects a growing foetus
What is the function of the fallopian tubes (oviduct)?
connects ovary to uterus, finger like projection ends collect oocyte after ovulation and the ciliated epithelial cells move oocyte to uterus
What is the function of the endometrium?
embryo implants here and sheds every month if there is no embryo (menstruation)
What is the function of the cervix?
muscular ring that closes the entrance to the uterus and dilates during birth
What is the function of the vagina?
muscular tube that leads to the outside of the body
What is the function of the urethra in women?
allows passage of the urine
Name all the parts of the male reproductive system?
scrotum, testis, seminiferous tubule, epididymis, vas deferens, seminal vesicle, prostate gland, urethra, penis
What is the function of the scrotum?
the external sac that holds the testes outside the body to provide sperm production the optimum temperature of 35ºC
What is the function of the testes (testis)?
Produce the male gametes, spermatozoa
What is the function of the epididymis?
sperm collect and mature here
What is the function of the vas deferens?
tube that takes sperm from the testis to the urethra during ejaculation
What is the function of the seminal vesicle?
glands that secrete a mucus into the vas deferens that contains nutrients (e.g. fructose used for respiration to provide energy)
Whats is the function of the prostate gland?
(at the base of the bladder) produces an alkaline secretion that neutralises any urine left in the urethra and aids sperm in motility
What is the function of the urethra in men?
transfers semen and urine to the outside (not at the same time)
What is the function of the penis?
used to pass semen into female reproductive system, penetration of the vagina
What is the function of the tissue in the penis?
- allows penetration of vagina
- fills with blood
- makes penis erect
Draw and label the parts of a mature sperm?
Acrosome, Nucleus -> Head
Neck
Mitochondria -> Midpiece
Plasma membrane and flagellum -> Tail
What is spermatogenesis?
Occurs in the seminiferous tubules of testes
Sequence of events involving mitosis and meiosis to form male gametes (spermatozoa)
Haploid spermatozoa from diploid spermatogonia
What are the 4 stages of spermatogenesis (generally)?
- Multiplication
- Growth
- Maturation (meiosis)
- Differentiation
- these just give structure to the process, don’t learn them as stages
What happens in multiplication in spermatogenesis?
- Germinal epithelium cells (diploid) on the outer layer of the seminiferous tubule undergo mitosis to produce diploid spermatogonia
- spermatogonia undergo mitosis to make many of them (multiplication)
What happens in the growth stage of spermatogenesis?
- spermatogonia that have divided by mitosis grow into diploid primary spermatocytes
What happens in the maturation stage of spermatogenesis?
- diploid primary spermatocytes undergo meiosis I to produce haploid secondary spermatocytes
- secondary spermatocytes undergo meiosis II to produce haploid spermatids
What happens in the differentiation stage of spermatogenesis?
- haploid spermatids differentiate into spermatozoa, forming a midpiece and tails
- throughout they obtain nutrients from the sertoli cells
Draw the summary diagram of spermatogenesis?
(check in book)
Germinal epithelial cells (2n) <=Mitosis=> Spermatogonia (2n) -mitosis and growth-> Primary Spermatocytes (2n) -meiosis I-> Secondary Spermatocytes (n, n) -meiosis II-> spermatids (n,n,n,n) -differentiation-> Spermatozoa (mature sperm)
What is the job of the sertoli cells?
Nourish and protect the spermatozoa once they are formed
- protection from WBC/immune cells as meiosis changes the DNA (non identical cells = recognised as foreign)
Where are the sertoli cells found?
Inside the seminiferous tubule
What is the job of the leydig cells?
secrete testosterone (male sex hormone) which is involved in stimulating the process of spermatogenesis
Where are the leydig cells found?
Outside/between the seminiferous tubules
What is another name for the leydig cells?
Interstitial cells
What is oogenesis?
Occurs in the ovary and is a sequence of events involving mitosis and meiosis to form a secondary oocyte
What are the process of oogenesis before birth (1)?
- Germinal epithelial cells (2n) in the ovary divide to form more germinal epithelial cells and oogonia (2n) by mitosis
- Oogonia undergo mitosis and cytoplasm growth to form primary oocytes (2n)
- Primary oocytes start meiosis I but stop at prophase I
- Primary oocytes surrounded by follicles cells forming primary follicles
What is the process of oogenesis at puberty (2)?
- Monthly, FSH is released stimulating the primary follicles to develop into secondary follicles
- Just before ovulation a primary oocyte completes meiosis I to form a haploid secondary oocyte and the first polar body (both haploid)
- Secondary oocyte starts meiosis II but stops at metaphase II unless fertilisation takes place
What happens at ovulation (3)?
One of the follicles mature into a Graafian follicle, migrates to the surface of the ovary, bursts and projecting secondary oocyte into fallopian tube (ovulation)
What happens at formation of the zygote (4)?
- secondary oocyte completes meiosis II, becoming an ovum (n) and a second polar body (n) just before nuclei of ovum and spermatozoa combine and form a zygote
What happens after the zygote formation (5)?
- zygote divides by mitosis forming the blastocyst (hollow ball of cells)
- the repeated mitotic divisions is called cleavage
- after 3 days the blastocysts reaches the uterus and embeds itself into the endometrium wall in implantation
How is the corpus luteum formed?
After the Graafian follicle ejects the secondary oocyte in ovulation, it becomes the corpus luteum
What are the structures of the secondary oocyte after ovulation?
corona radiata, zona pellucida, first cell body, cell membrane, cortical granules and spindle apparatus/chromosomes suspended at metaphase II of meiosis
What are the structures of the Graafian follicle in the ovary?
- antrum (fluid filled space)
- granulosa cells (on the outside)
- secondary oocyte
- haploid nucleus (in the secondary oocyte)
When and where does fertilisation occur?
After sexual intercourse and at the beginning of the fallopian tube
What is capacitation?
- Changes in the sperm cell membrane that increases fluidity and allows the acrosome reaction to occur
- membrane becomes more permeable to Ca2+ ions which increases motility
What needs to happen first to the spermatozoa for fertilisation?
spermatozoa can only fertilise a secondary oocyte after capacitation process has taken place
What is the acrosome reaction?
- when the sperm reaches the secondary oocyte, acrosome ruptures and releases hydrolytic enzymes
- enzymes digest the corona radiata and zona pellucida
- this allows the sperm and oocyte cell membranes to fuse
What enzymes are released from the acrosome?
- Proteases released to digest corona radiata
- acrosin (proteases) hydrolyse zona pellucida
What happens at sperm head entry?
- cell membranes of sperm and secondary oocyte fuse
- head of sperm enters the cytoplasm
- secondary oocyte completes meiosis II and becomes an ovum and production of the second polar body
- the nucleus of the ovum fuses with that of the sperm to form a zygote
What is the cortical reaction?
- cortical granules fuse with the oocyte cell membrane and their contents modify the zona pellucida into the fertilisation membrane
- changes to the zona pellucida this prevents polyspermy
How is the fertilisation membrane created?
- when the sperm fuses, smooth ER releases Ca2+ ions into cytoplasm
- Ca2+ make cortical granules fuse with oocyte cell membrane & release enzymes
- enzymes chemically modify the zona pellucida to make it expand and harden forming fertilisation membrane
What happens to the endometrium after ovulation?
Endometrium thickens and increases blood supply to prepare to receive an embryo
What causes the degradation of the zona pellucida?
progesterone from the corpus luteum stimulates secretion in the uterus that degrades the zona pellucida
- this provides nutrients and enhances the blastocysts growth and ability to implant
What hormone does the embryo release?
Human Chorionic Gonadotrophin (hCG)
What is the role of hCG?
- maintains the corpus luteum which maintains the production of the hormones oestrogen and progesterone
- only for the first 16 weeks of pregnancy until the placenta is fully developed
What hormone is used for pregnancy test?
hCG
What is the role of both oestrogen and progesterone during pregnancy?
- inhibits FSH and LH release from anterior pituitary gland
- no more follicles will mature and ovulate
What is the role of progesterone during pregnancy?
Inhibits oxytocin which suppresses uterine wall’s ability to contact and milk duct contraction
What is the role of oestrogen during pregnancy?
- stimulates growth of the uterus to accommodate the foetus
- stimulates growth of mammary glands in the 3rd trimester
What is the placenta?
Connects the embryo and foetus to the uterus walls
22cm long
What are the 5 major roles of the placenta?
- An endocrine organ, secretion of progesterone and oestrogen
- Exchange of gases and nutrients (CO2, O2, nutrients and wastes)
- A barrier between the maternal and foetal circulation, barrier to blood pressures bloodborne pathogens and toxins in maternal blood
- Passive immunity, allows maternal antibodies to protect the foetus
- Protection against the mother’s immune system, prevents antibodies attacking the foetus
What are 4 problems of the placenta?
- Spontaneous abortions
- Pre-eclampsia
- Rhesus incompatibility
- Microbes and drugs cross the placenta
What happens with spontaneous abortions?
some spontaneous abortions seem to be equivalent to rejection of a transplant organ
What happens with pre-eclampsia?
In the 2nd trimester some women can develop extremely high blood pressure (pre-eclampsia)
- one cause being an abnormal immune response to the placenta
What happens with rhesus incompatibility?
- rhesus incompatibility between the mother and foetus can mean antibodies made by a rhesus negative mother attack blood cells of rhesus positive foetus
- this gets worse for each successive rhesus positive feedback
What happens with exceptions of crossing the placenta?
Some micro-organisms (e.g. rubella virus) and drugs (e.g. nicotine, heroin and alcohol) are able to cross the placenta
Describe the structure of the placenta?
2 umbilical arteries
1 umbilical vein
chorionic villi
intervillous spaces
Describe the difference between umbilical arteries and umbilical veins?
- umbilical arteries carry foetal blood to the placenta from foetus heart
- they are low in nutrients, low in oxygen, high in CO2 and high in waste
- umbilical vein carries blood back to the foetus from placenta
- is high in oxygen and nutrients, low in CO2 and waste
What type of circulation is in the placenta?
counter-current
What gives the placenta large surface area?
chorionic villi
What is the amniotic fluid?
fluid that is made up of 98% water, solution of urea, salts, little protein and a trace of sugar
What are the 2 roles of the amniotic fluid?
- Acting as a shock absorber (protection from injury from outside the uterus)
- Protecting the foetus during development
How does amniotic fluid protect the foetus?
- maintaining temperature
- providing lubrication
- contributing to lung protection
- allowing movement
What happens to hormone levels just before birth?
- oestrogen levels increase and progesterone levels decrease allowing the uterine wall to contract
- decrease in progesterone allows secretion of oxytocin and prolactin
- oxytocin stimulates contractions of the uterine wall which stimulates more oxytocin (positive feedback)
What is oxytocin?
- hormone secreted by the posterior pituitary gland
- causes contractions of the myometrium
- positive feedback leads to increasing oxytocin levels and stronger contractions
What is prolactin?
- hormone secreted by the anterior pituitary gland
- stimulates the mammary glands to synthesise milk
When is milk released?
When oxytocin causes the muscles around the milk ducts to contract
What are the 3 phases of the menstrual cycle?
Follicular phase (0-14 days) Ovulation (day 14) Luteal phase (14-28)
What is the menstrual cycle?
- occurs in the uterus to prepare for a fertilised egg
- repeating series of changes in the endometrium
- continues from menarche to menopause
What happens in the follicular phase?
- on day 0, concentration of all 4 hormones is low
- hypothalamus secretes GnRH stimulates the anterior pituitary gland to release FSH (and LH)
- FSH stimulates development of primary follicles and stimulates thecall cells on Graafian follicle to produce oestrogen
- oestrogen causes rebuilding of endometrium and inhibits FSH secretion but stimulates LH release
What is day 0?
The first day of a period
What is GnRH?
Gonadotrophic Releasing Hormone
What happens in ovulation in the menstrual cycle?
- LH induces ovulation
- highest concentration on day 14 causes Graafian follicle at the surface of the ovary to release secondary oocyte
What happens in the luteal phase?
- after ovulation, Graafian follicle is retained in the ovary as the corpus luteum, this produces progesterone and oestrogen
- these both inhibit production of FSH and LH reducing their concentration
- progesterone stimulates endometrium to thicken and remain in place
Describe the breakdown in menstrual cycle?
- if there is no menstrual cycle, the falling conc of FSH and LH cause the corpus luteum to break down
- breakdown occurs within 14 days if no embryo is present
- breakdown of corpus luteum means progesterone conc drops and causes the endometrium to shed
- as oestrogen is low so it will no longer inhibits FSH production, so the menstrual cycle will restart
What is FSH?
Follicle stimulating hormone
- secreted by the anterior pituitary gland
- stimulates development of the Graafian follicle (follicles to develop)
- increases oestrogen
What is LH?
Lutenising Hormone
- secreted by the anterior pituitary gland
- induces ovulates
- stimulates conversion of Graafian follicle into the corpus luteum
- increases progesterone, oestrogen and FSH
What is oestrogen?
- secreted by the corpus luteum and placenta
- rebuilds endometrium
- develops secondary sexual characteristics
- increases LH (decreases LH at the end of the cycle), decreases FSH and inhibits prolactin and oxytocin synthesis
What is progesterone?
- secreted by the corpus luteum and placenta
- maintains endometrium
- stops uterus from contracting in pregnancy
- decrease FSH and LH
