4.1 Sexual Reproduction (humans) Flashcards
Structure and function of ovary
- small oval shaped glands
- produce eggs and hormones, play a key role in the menstrual cycle, pregnancy, and fertility
Structure and function of fallopian tubes
- pair of ducts located between ovaries and uterus
- transport eggs and sperm and play key role in conception and pregnancy
Structure and function of uterus
- hollow, muscular organ in the pelvis
- plays key role in menstrual cycle, pregnancy and birth
Structure and function of endometrium
- lining of the uterus
- prepares uterus for implantation, maintains pregnancy and causes menstruation
Structure and function of the cervix
- cylindrical structure
- allows sperm to reach uterus, opens to allow blood to exit, closes during pregnancy
Structure and function of the vagina
- muscular, elastic tube that connects cervix to vulva
- menstruation, accommodate penis in sex, expand to birth baby
Structure and function of scrotum
- thick external sac of skin
- supports testicles and plays key role in sperm production
Structure and function of testes
- small, oval shaped organs
- produce sperm and hormones ie testosterone
Structure and function of epididymis
- coiled tube attached to back of each testicle
- store, mature, and transport sperm cells
Structure and function of vas deferens
- muscular tube
- transports sperm from the epididymis to the urethra
Structure and function of seminal vesicle
- a pair of glands in the male reproductive system
- produce fluids to contribute to semen
Structure and function of prostate gland
- gland below bladder and in front of rectum
- produces fluid for semen and helps to push semen out of body
Structure and function of urethra
- tube from bladder to outside of body
- allows urine and semen to leave body
Structure and function of penis
- male organ that surrounds urethra
- delivers sperm to female and plays role in sexual arousal
What cells undergo spermatozoa formation?
Cels of the seminiferous tubules
Features of secretions of the accessory glands (male)
- alkaline
- maintain sperm mobility
- provide nutrients for sperm
- neutralise acidity of any urine in urethra
- neutralise acidity of vaginal tract
What type of cell lies between developing spermatids?
- sertoli cells
—> columnar ad biochemically active
—> secrete a fluid which nourishes developing sperm and protects them from the immune system
Describe the 3 layers of the uterus
- perimetrium (thin layer)
- myometrium (muscle layer)
- endometrium (innermost layer) —> mucous membrane which is well supplied with blood and sheds in monthly cycle
Define gametogenesis
The production of gametes
Explain spermatogenesis
- Primordial germ cells divide several times by mitosis to form spermatogonia
- Spermatogonia grow, undergoing further division by mitosis to form primary spermatocytes
- Primary spermatocytes undergo the first meiotic division to form secondary spermatocytes
- Secondary spermatocytes undergo the second meiotic division to form spermatids (haploid, no flagellum or acrosome)
- Spermatids differentiate and grow to form spermatozoa
Briefly describe the structure of a sperm cell
- sperm head contains haploid nucleus covered at the anterior end by a lysosome called the acrosome, which contains the enzymes used at fertilisation
- packed with mitochondria to provide ATP for movement
- tail/flagellum makes lashing movements that move the sperm
Draw and label a sperm cell
Explain oogenesis
- Primordial germ cells divide several times by mitosis to form oogonia
- Only one oogonia continues to grow to form a primary oocyte
- First meiotic division forms one secondary oocyte and one polar body
- The second meiotic division of the secondary oocyte forms a haploid optic and polar body. Meiotic division of the polar body forms 2 more which degenerate and die as the optic develops
—> meiotic division starts in utero but halted at prophase and occurs only in response to fertilisation to form the mature ovum
Describe the structure of a secondary oocyte
- glycoproteins layer called zona pellucida surrounds cell membrane
- chromosomes are at metaphase II
- periphery of cytoplasm contains cortical granules
—> prevent entry of more than one sperm - corona radiata cells surround the secondary oocyte and provide nutrients
Briefly describe the acrosome reaction
- acrosome enzymes digest corona radiata and zona pellucida
- allows sperm and oocyte cell membrane to fuse
Briefly describe capacitation
- changes in the sperm cell membrane that increase its fluidity
—> removal of cholesterol and glycoproteins to make more permeable to calcium ions - allow acrosome reaction to occur
Briefly describe the cortical reaction
- fusion of cortical granule membranes with the oocyte cell membrane
- release contents
- convert zona pellucida into a fertilisation membrane
Explain fertilisation
- Several sperm cluster around the ovum. One penetrates the zona pellucida
- This triggers the acrosome reaction where the acrosome bursts and releases enzymes which digest the zona pellucida
- Membranes fuse and the haploid spermatozoa nucleus enters the egg cytoplasm
- This triggers the cortical reaction where cortical granules fuse with the cell membrane and release their contents into the zona pellucida which hardens and thickens. Ion channels open and close. Prevent polyspermy
- Meiosis II takes place and secondary oocyte matures into ootid and mature ovum
- Chromosomes combine to form diploid zygote
Describe implantation
- The zygote undergoes cleavage (mitosis without interphase) and divides to produce a hollow ball of cells called a blastocyst
- The blastocyst develops trophoblastic villi which grow into tissue of the uterus and implant the developing blastocyst into the uterine lining where it attaches and absorbs nutrients
Draw a blastocyst and an embedded blastocyst
Define implantation
The sinking of the blastocyst into the endometrium thickens ans
Describe the structure/formation of the placenta
- connects the embryo and the foetus to the uterus wall
- made of tissues derived from the embryo and the mother
- trophoblast develops into the chorion, an outer membrane surrounding the embryo
- cells of the chorion move into the trophoblastic villi and form chorion villi
- acquire blood vessels which are connected to the umbilical arteries and veins
Name the major roles of the placenta
- produce hormones to support the pregnancy
- exchange between mothers and foetus’ blood
- a physical barrier between foetal and maternal circulation
- provides passive immunity to foetus
- protection from mothers immune system
Describe how the placenta provides an exchange between the mothers and foetus’ blood
- inter-villus spaces called lacunae containing the mothers blood surround the chorionic villi which provide a large area of contact with the mothers blood
- embryo and mothers blood do not make actual contact
- concentration gradient is maintained by a counter current flow, enhancing the efficiency
Describe why the placenta acts a a physical barrier between foetal and maternal circulation
- protects fragile foetal capillaries from damage by the mothers higher blood pressure
- protects the developing foetus from changes in maternal blood pressure
How does the placenta provide passive immunity to the foetus?
- maternal antibodies cross the placenta and attack pathogens but do not attack foetal cells even though they carry the fathers foreign antigens
How does the placenta provide protection from the mother’s immune system?
- mother does not make immune response against foetus or placenta even though they contain foreign genes
- cells of the wall of the chorionic villi fuse so there are no spaces between them, making a syncitium
- migratory immune cells cannot get through to foetal blood
Describe some ways in which the placenta does not always provide immunological protection
- some spontaneous abortions are equivalent to rejection of a transplanted organ
- Rheusus disease in a foetus is the destruction of its blood cells by antibodies made by a Rheusus negative mother against a Rheusus positive foetus
- in 2nd trimester some women develop pre-eclampsia where they have very high blood pressure, caused by an abnormal immune response to the placenta
Draw the structure of the placenta
Describe the umbilical cord and it functions
- develops from the placenta
- transfers blood between foetus and mother
- blood comes out of foetus in two umbilical arteries
—> low in nutrients and deoxygenated - exchanges with mothers blood at the chorionic villi and returns to foetus in umbilical vein
—> high in nutrients and oxygenated
Briefly describe the oestrus cycle
- pigs and dogs
- short period where they’re fertile and sexually active
- in the absence of an implanted embryo the endometrium is resorbed and an anoestrus period follows
Describe the menstrual cycle
- hormonal and physiological changes
- in the absence of implantation, the endometrium is shed through menstruation by detaching
- appears as bleeding as it leaves the vagina
- system of positive and negative feedback, operating between the events involving the brain, ovaries and uterus
Name the significant menstrual hormones
- follicle stimulating hormone (FSH)
- luteinising hormone (LH)
- oestrogen
- progesterone
Steps in fertilisation
- capacitation
- acrosome reaction
- fusion of sperm and SO membrane
- cortical reaction
- meiosis to form ovum and second polar body
- fusion of nuclei forming zygote
Describe the role of GnRH in secreting FSH and LH
- Gonadotrophin releasing hormone secreted by hypothalamus to stimulate the anterior pituitary gland to release:
—> FSH which stimulates the development of primary follicle in the ovary. It forms a fibrous outer layer known as the theca which secretes fluid into the antrum. Thecal cells produce oestrogen
—> LH which reaches its maximum conc just before ovulation. The high conc causes the Graafian follicle to release a secondary oocyte and has a positive feedback effect on FSH - remains of Graafian follicle convert into corpus luteum which secretes oestrogen and progesterone, limiting FSH and LH secretion
Describe the secretion of oestrogen and progesterone
- increased FSH conc triggers oestrogen production
- corpus luteum secretes oestrogen and progesterone
- progesterone maintains newly built endometrium
- if no fertilisation, FSH and LH cause the corpus luteum to degenerate so oestrogen and progesterone production declines
Function of oestrogen and progesterone
- triggers rebuilding of endometrium
- inhibits FSH secretion by negative feedback
- stimulates LH by positive feedback
What is meant by the amnion?
A membrane that is derived from the inner cell mass of the blastocyst
What are the amniotic fluid components?
- water
- urea
- salts
- a little protein
- trace of sugar
- some foetal cells that have sloughed off the foetus
Functions of the amniotic fluid
- maintains foetus temp
- provides lubrication
- contributes to lung development
- allows movement so muscles and bones function before birth
- acts as a shock absorber to protect foetus from injury outside uterus
Briefly describe the 1st, 2nd and 3rd trimesters
1st = conception, implantation, embryogenesis, major organ development
2nd = all major structures complete, growth period
3rd = development
Describe and explain hCG
- human chorionic gonadotrophin is secreted by blastocysts
- glycoprotein that maintains corpus luteum in its secretion of progesterone which maintains the endometrium
Role of progesterone and oestrogen
- inhibit FSH (no more follicles mature), inhibit LH (ovulation not possible), inhibit prolactin (milk not produced)
- inhibit oxytocin so myometrium and milk ducts don’t contract
- oestrogen stimulates growth of uterus and mammary glands
Describe oxytocin
- secreted by posterior pituitary gland
- causes contraction of myometrium in uterus
- stimulates further oxytocin secretion by positive feedback
- stronger and more frequent contractions
Describe prolactin
- secreted by anterior pituitary gland
- stimulates glandular tissue in mammary glands to synthesis milk
- milk is released when oxytocin causes the muscles to contract
Role of FSH and LH in men
- secreted by anterior pituitary gland
- sperm development
- stimulate Leydig cells
Role and origin of testosterone
- Leydig cells
- sperm development and secondary sexual characteristics
What is meant by a polar body?
Small cells that bud off the oocyte, stick to it and do not develop into gametes
Name the hormone produced by the developing embryo which prevents the breakdown of the corpus luteum
HCG
Suggest why only one functional female gamete is produced as a result of meiosis
- reduction of genetic material at each stage of meiosis
- functional gamete retains cytoplasm which acts as a food store for the zygote
Why is there an increased risk of polyspermy in IVF?
- immature secondary oocyte has fewer developed cortical granules and so the zona pellucida doesn’t harden
Why is the developing embryo not transferred until 3 days after IVF?
- fertilisation typically happens in the fallopian tubes and cleavage occurs
- blastocyst embeds in the endometrium
- if embryo is put in the uterus instantly, the endometrium won’t be fully developed
- trophoblastic villi won’t develop
- embryo won’t survive
How does high arterial blood flow in the placenta aid its function?
Concentration gradient
How does high pressure in uterine arteries aid the placenta?
Pressure difference forces material through
How does the length of the capillaries in the placenta aid its function?
Large surface area for exchange
Explain hormones on day 1 of the menstrual cycle
- oestrogen and progesterone are low so the uterus sheds its lining
- FSH released by pituitary gland to stimulate follicle growth, secreting progesterone
- oestrogen levels increase which suppresses further follicle growth
Explain hormones during ovulation
- levels of LH increase rapidly, FSH also increases
- LH causes follicle to produce enzymes which rupture and therefore release the ovum
- ovum travels to fallopian tubes
Explain hormones during the luteal phase
- ovum travels along follopian tube
- corupus luteum stops secreting progesterone and oestrogen
—> lining of uterus thickens and fills with nutrients - FSH and LH decrease
Why is it important that the number of blood vessels in the ovary increase after ovulation?
Provides material for hormone transport
Why do the number of blood vessels in the ovary increase after ovulation?
Provide material for hormone transport
What is the role of the sperm head?
Carry genetic material
Why are ciliated epithelium important in the oviduct?
Cilia move the secondary oocyte along the oviduct toward the endometrium
Explain why hCG levels are used in pregnancy tests
- no hCG prior to pregnancy, but spikes after 4 weeks
- easy to detect the change
State the function of hCG in pregnancy and what happens if levels of hCG fall or are too
low at the start of the pregnancy.
- maintains corpus luteum
- if HCG levels decrease then corpus luteum degenerates
- endometrium shed (miscarriage)
Explain why mutations in the hCG genes
may or may not effect pregnancy
- small mutations will result in a functional protein
- major change (ie deletion) will alter protein and result in non-functional
explain the functions of the hormones oestrogen and progesterone during pregnancy.
- placenta secrete oestrogen and progesterone
- FSH and LH inhibited
- progesterone maintain endometrium
- oestrogen stimulate uterus and mammary gland growth
Describe the hormonal control of ovulation
- FSH stimulate development of follicles in ovary
- follicles produce oestrogen which inhibits FSH and stimulates LH
- LH further stimulate oestrogen which stimulates LH etc
- LH stimulate ovulation, aided by increase in FSH
- corpus luteum produce progesterone to develop endometrium
