chapter 18 reproduction in humans Flashcards
parts of male reproductive system + functions (6)
- Testis (plural: testes): produces sperms, male sex hormones such as testosterone
- Receives blood, oxygen, digested food substances from blood vessels in spermatic cord
- Epididymis stores inactive sperms from testis before they enter Vas deferens (before ejaculation) - Scrotum: pouch like sacs that contain the testes - place the testes outside main body cavity = provide a lower temp than body temp so as to let sperms develop properly
- Vas deferens (aka sperm duct): where sperms travel in to be released from testis into urethra to outside the body
- Respective glands (prostrate, Cowper’s, seminal vesicles): all 3 secrete sex fluid containing nutrients (such as simple sugars) and enzymes → mix with sperms to form semen = nourish sperms and stimulate them to swim actively
- Urethra: tube where semen and urine (not at same time) pass out of the body
- Penis: deposits semen in vagina during sexual intercourse
- Becomes erect (lengthened and wider) when aroused: spongy tissues are filled with incompressible blood
parts of female reproductive system + functions (6)
- Ovaries: produces the eggs, produces hormones such oestrogen and progesterone
- Oviduct: where ovaries release mature eggs into, where fertilisation takes place
- Ovum moves through oviduct through: - peristaltic movement in walls of oviduct/cilia present in oviduct that sweeps ovum AWAY from ovary
- Uterus: where the fetus develops during pregnancy
- Contains endometrium/uterine lining - (smooth, soft INNER lining of uterus): where embryo is implanted - Cervix: passageway between uterus and vagina, where menstrual blood flows out during menstruation
- Vagina (or birth canal): where semen is deposited into during sexual intercourse
parts of sperms + functions
Acrosome: vesicle that contains enzymes = digest and break down egg membrane = sperm is able to penetrate egg
Middle piece contains numerous mitochondria: releases energy as sperm has to travel a long distance in the body towards the egg
Flagellum: beating movement allows the sperm to move/swim on its own (sperms are motile)
Has a streamlined shape to swim faster
how are eggs developed in the ovary
- every woman is born with all the primary follicles in her lifetime (potential egg cells that have yet to mature, surrounded by follicle cells)
- Primary follicle goes through meiosis l to form tertiary follicle, then meiosis ll to form Graafian follicle (mature egg): contains a haploid egg cell surrounded by follicle cells and fluid filled space
- After meiosis, Graafian follicle will contain haploid chromosomes
- During menstrual cycle, Graafian follicle ruptures and releases haploid egg into oviduct from ovary = ovulation
- After ovulation, remnants of Graafian follicle (wall of follicle cells) develop into corpus luteum (endocrine gland): produce progesterone and little oestrogen = prepare body for pregnancy
- No fertilisation (no pregnancy): corpus luterum persists for some time before eventually breaking down, gets absorbed by ovary
describe stages of menstrual cycle
MENSTRUAL FLOW STAGE (day 1 to 5)
Uterine lining and unfertilised egg breaks down, sheds with some blood = flows from uterus out of body though vagina
AFTER MENSTURATION (day 6-13)
Follicles in ovaries secrete oestrogen (highest O concentration)= repair and thickens uterine lining, fills it with spongy blood vessels
High oestogen concentration leads to ovulation
OVULATION (day 14)
Release of mature egg from ovary -> the two ovaries take turns to release an egg
AFTER OVULATION (day 15 to 28)
Ovary (specifically corpus luteum) produces progesterone (highest P concentration):
Prevents ovulation and further development of eggs to become mature
Maintains uterine lining by causing it to thicken further and be richly supplied with blood capillaries = prepare for embryo implantation/pregnancy
Oestogen production reduces
If no fertilisation occurs:
Progesterone production decreases
Uterine lining breaks down and whole cycle repeats
fertile period of menstrual cycle
fertile period: from day 10 to 15
1. Egg is able to survive for up to 24 hours after being released from the ovary:
2. if ovulation occurs on day 14 of average menstrual cycle, egg survives and travels along oviduct from day 14 to day 15
3. Sperms can survive in female reproductive system for 3 to 5 days - able to survive throughout ovulation duration if sexual intercourse takes place on day 10
4. Fertilisation is very likely to take place
what if no fertilisation occurs
- Egg breaks down
- Blood progesterone level decreases (as corpus luteum breaks down)
- Body has no fertilised egg for pregnancy = body does not have to prepare for pregnancy (progesterone is the hormone that prepares you for pregnancy) = production of progesterone decreases - No progesterone on 28th day: uterine lining begins to break down, menstruation begins again
- Cycle repeats
- Since menstruation contains the shedding of uterine lining and unfertilised egg, it can only take place if you are not pregnant
- No fertilised egg = uterine lining does not have to remain thick and richly supplied with blood capillaries like for pregnancy = uterine lining sheds (menstrusation)
how does fertilisation take place
→ sexual intercourse has to take place first: semen is ejaculated into vagina - sperms swin to oviduct to meet egg - only one sperm out of millions will fertilise egg
→ fertilisation:
Breaking down: mature egg has layers of follicle cells - acrosome of sperm releases enzymes - disperses layers of cells - break down egg membrane and penetrate egg
Fusion: Only one sperm nucleus enters egg - haploid sperm nucleus fuses with haploid egg nucleus = fertilised egg/diploid zygote is formed
After entrance of sperm: membrane of egg hardens - no other sperm can enter - remaining sperms that did not fertilise egg die
what occurs right after fertilised egg is formed
- Implantation of embryo
- Sweeping by cilia lining inner surface of oviduct + peristaltic movement of oviduct wall = help to move zygote towards uterus
- Zygote undergoes mitosis = forms embryo - takes 5 days to reach uterus
Implantation: whole embryo becomes embedded in uterine lining (usually 7 days after fertilisation) - Development of placenta
- After implantation: villi will grown from embryo into uterine lining - contain blood capillaries of embryo
- Villi + uterine lining where the villi are embedded in = placenta (part embryonic tissue, part uterine lining)
- Umbilical cord attaches embryo to placenta - Development of amniotic sac to protect and support developing fetus with respective functions (below)
- Amniotic sac develops at same time as the placenta: encloses the embryo
- Amniotic sac filled with amniotic fluid = amniotic cavity
function of placenta
- (Placenta and umbilical cord) allows exchange between fetal blood and mother’s blood
- Allow oxygen and nutrients (eg glucose, amino acids, mineral salts) to diffuse from mothers blood to fetal blood
- Allows metabolic waste/excretory products (eg urea, carbon dioxide) to be removed by diffusing from fetus’ blood into mother’s blood
- Allows protective antibodies to diffuse from mother’s blood into fetal blood = antibodies protect fetus against certain diseases (Antibodies here refer to antibodies mother had in the past to fight against infections)
- Produces progesterone: maintains uterine lining to be thick and richly supplied with blood capillaries for healthy pregnancy
how does diffusion occur in placenta
Fetal blood capillaires are surrounded by maternal blood spaces (intervillous spaces) but separated from mother’s blood system with a thin tissue layer = diffusion occurs across this tissue
why are fetal and mother’s blood system separated
Mother’s heart is more muscular, pumps more blood at a higher rate = blood pressure of mother is much higher that of fetus = may kill fetus
Blood group of fetus and mother may be different = antibodies present in mother’s blood may cause fetal blood cells to agglutinate
Antibodies in this case are the antibodies that determine your blood group (a or b), not the protective antibodies that protect the fetus from diseases
adaptations of placenta
Numerous chorioric villi present on 1. surface layer of placenta = higher rate of exchange of oxygen, dissolved food substances, carbon dioxide and waste materials
- Contains maternal blood spaces → in direct contact with villi = reduces shorten diffusion distance = higher rate of exchange of substances between maternal and fetus blood
- Prevents maternal and fetal blood from mixing = prevent high BP in maternal blood from damaging fetal blood vessels
parts of umbilical cord + functions
- 2 umbilical arteries (transporting blood away from fetus’s heart): transport deoxygenated blood and metabolic waste substances from fetus to the placenta
- 1 umbilical vein (transporting blood towards fetus’s heart): transport oxygenated blood and food substances from placenta to fetus
- Fetal artery/vein do not join maternal artery/vein in maternal blood space = instead make a U-turn
functions of amniotic sac
Supports and cushions fetus before birth
Acts as a shock absorber
Fluid is incompressible = protects fetus against physical injury
Allows fetus a certain degree of movement = promotes muscular development
Lubricates and reduces friction in vagina during birth
