IB Biology HL: Human Reproduction - D3.1

sexual reproduction

two parents, and uses gametes

asexual reproduction

only one parents, mitosis. chromosomes are identical to parent

internal fertilisation

done in land aminals, as wet environment needed

external fertilisation

done by water animals, such as frogs or fish

animals doing asexual reproduction

• starfish

• sharks

• komodo dragons

• pythons

advantages of asexual reproduction

• very quick

• comparatively lower energy required (no looking for mates)

• more efficient

disadvantages of asexual reproduction

• sum of (negative) mutations

• less genetic variation

• can adapt less quickly

advantages of sexual reproduction

• variation in species is maintained

• best genes manage to reproduce

• better survival rates

Causes of genetic variation in sexual reproduction

• in meiosis 1, genetic material is exchanged between non sister chromatics (not the same) of homologous chromosomes: crossing over

• when members of homologous pairs separate during meiosis 1, maternal and paternal pairs split up: gametes have different variations of homologous chromosomes

adapations of sperm cells

• flagellum to propel cell to egg cells

• mitochondria to perform respiration, produce atp

• acrosome: has enzymes to break down egg cell membrane

• streamlined shape

• no waste of space in head; head mostly nucleus

parts of ovum

• haploid nucleus

• large stores of lipids in cytoplasm

• cortical granules

• layer of protective glycoproteins (zona pellicula)

• layer of follicle cells (corona radiata)

male reproductive system

• bladder: sack that store urine

• penis: used for internal fertilisation, to allow sperm to be as close as possible to egg cells

• prostate: produces fluid that helps in transport and nurishment of sperm

• sperm duct: transports sperm from testes to urethra

• epididymis: store sperm (right behind testicles)

• testis: outside the body to prevent overheating

• urethra: releases urine from bladder and sperm from seminal vesicle

• erectile tissue: part of penis, artery at the base of penis, which when needed will bring much blood, increasing tension

female reproductive system

• vagina; opening for penis, to allow internal fertilisation

• cervix: way from vagina to uterus

• fallopian tubes: site where fertilisation happens, attachment where ovary attaches to uterus

• ovaries: site of egg production and maturation

hermaphrodites

an organism with both female and male reproductive parts

example of hermaphrodite animals

• earthworms

• snails

• banana slugs

primordial follicle

bunch of small cells surrounding actual egg cell, before having matured.

the follicle doesn’t get released, and it breaks down into a corpus luteum

ovarian cycle

• follicular phase ( follicle maturation )

• ovulation phase ( mature follicle gets release )

• luteal phase ( corpus luteum gets broken down

uterine cycle

• menstruation: uterine lining breaks down and gets thinner

menbrane thickens, 14 days in ovulation occurs, 28 days if no fertilisation membrane breaks down as decrease in hormones

LH

luteinizing hormone: made by the pituitary gland. Promotes ovulation and the formation of the corpus luteum. stays relatively constant, when it peaks is ovulation

FSH

follicle stimulating hormone: made by pituitary gland. Promotes development of the follicles in the ovary. Peaks when ovulation occurs

estrogen

made by the developing follicle and corpus luteum in the ovary. promotes thickening of uterine lining. level of oestrogen is increasing as follicle develops. Peaks right before ovulation.

At low concentration, first 10 days, aestrogen inhibits LH production

after 10 days, aestrogen levels rise, and now has a positive effect on LH production

after ovulation, oestrogen inhibits progesterone

progesterone

made by corpus luteum. maintains thickened uterine lining. Increases right after ovulation

whole process of menstrual cycle

• drop in progesterone = menstruation

• FSH stimulates development off follicule in the ovary: follicle starts developing

• the follicle produces aestrogen which stimulates the thickening of uterine lining

• the peak of LH stimulates ovulation at day 14

• corpus luteum starts disintegrating but continues releasing progesterone

• progesterone increases, which maintains uterine lining

• eventually decreases

Outline the functioning of the hormones influencing menstrual cycle (7)

• decrease in progesterone leads to breakdown of uterine walls, and leads to menstruation

• FSH and LH are from the pituitary glands

• FSH gets released, stimulating the development of primary follicles

• development of Primary follicles secretes oestradiol

• oestradiol stimulates build up of uterine lining

• oestradiol concentration peaks, inhibits FSH, stimulates LH.

• no more FSH → prevents multiple follicles from developing

• LH peaks stimulates, ovulation, leads the follicle to turn into a corpus luteum

• corpus luteum secretes progesterone

• progesterone maintains uterine walls and inhibits FSH and LH secretion

• low FSH and LH lead to corpus luteum to degrade

• no more corpus luteum = no more progesterone = uterine walls break down, menstruation

• if egg is fertilised, releases a hormone which maintains corpus luteum until 16 weeks, after which placenta takes over. (human chorionic gonadotrophin)

why does fertilisation need to occur in a wet environment

sperm need to be able to swim

advantages and disadvantages of internal fertilisation

• more efficient: fertilisation more likely to happen

• parentage is more easy to determine

but

• mating rituals energy consuming

• require time in vulnerable state

advantages and disadvantages of external fertilisation

• already in wet environment

• less energy required, animals musn’t be immobile

but

• more vulnerable to environmental threats

• less certainty of fertilisation

• requires more gametes produced

how does the sperm cell get in the cell ?

• has a acrosome which contains digestine enzymes

• it allows it to get through the zona pellucida

• once one sperm gets in, cortical granules go towards cell wall, hardening the wall

In vitro fertlisation step

• downregulation of menstrual cycle

• superovulation: high levesl of FHS are injected over 10 days, to stimulate multiple follicles

• after that, an injection of human chorionic gonadotropin hormole is injected, to start egg maturation process

• after 36 hours, the egg cells are collected under general anesthesia

• eggs are prepared, removed from follicles, and combined with sperm

• fertilised eggs are incubated before implantation

• for 2 weeks after implantation, progesterone is given, keep getting given until pregancy is confirmed

• success rate is about 40%, so 1-2 blastocysts are added per attempt

what hormone is regulates FSH and LH ?

gonadotropin releasing hormone (GnRH) , from hypothalamus

anterior pituitary gland

next to Hypothalamus, produces LH and FSH

effect of LH and FSH on males

• carried to testes

• LH stimulates release of testosterone

  • testosterone increase leads to GnRH inhibition, which inhibits FSH and LH production

  • negative feedback mechanism

• FSH stimulates sperm production

hormonal feedback mechanism in females

 Which hormone(s) secreted by the anterior pituitary gland increase the sex hormone production in male and female reproductive systems? 

LH and FSH

What is the effect of estradiol (oestrogen) and testosterone on puberty? 

expression of secondary sexual characteristics

all secondary sexual characteristics

gametogenesis of egg cells

Oogenesis

featal phase

• oogonia, through mitotic division, turns into primary oocytes during faetal develpment

• girls are born with all of the ovocyte, which stopped at prophase of meiosis 1. Called mitotis arrest. Continues when/if that egg gets ovulated

ovulation

• meiosis 1 finished: First polar body + secondary oocyte → turns into n

• meiosis 2 starts and stops at metaphase

fertilisation

• meiosis 2 : second polar body + Ovym → n. Stops at metaphase of meiosis 2, unless fertilisation by a sperm occurs

Gametogenesis of sperm cells

spermatogenesis

• sperm mother cell 2n: spermatogoonia

• much mitosis: primary spermatocyte → 2n

• meiosis 1: 2 secondary spermatocytes → n

• meiosis 2: 2 spermatids → n

• spermatids turn into sperm (spermiogenesis)

one primary spermatocyte = 4 sperms

spermiogenesis

from spermatid (n) to sperm (not the whole process !)

changes during spermiogenesis

• flagellum gets formed

• acrosome caps get added

• shed extra cytoplasm

prevention of polyspermy

• plasma membrame becomes impermeable due to changes in membrane potential

• corticle reaction:

  • when sperm reaches the plasma membrane of the secondary ovocyte,

  • cortical granules fuse with plasma membrane

  • Release their contents (hydrolytic enzymes) by exocytosis so sperm get destroyed

  • and the zona pelucida hardens preventing the sperms from making any more progress

pre-implantation embryonic development stages

• rapid mitotic division (cleavage)

• Morula

• blastocyst

• trophoblast from blastocyst (outer layer) eventually differentiates into placenta

• zona pellucida is shed

• will eventually, after 7-8 days, implant into uterine endometrium

morula

• 16 cells

• day 4

• zona pellucida still surrounds it

• same size as zygote, as only division no growth

blastocyst

• 32 cells

• hollow

• two layers

  • outer: trophoblast (placenta)

  • inner cell mass (the actual body)

  • fluid filled cavity: blastocoel

• will eventually shed zona pellucida

hCG

human Chorionic Gonatropin

role of hCG in pregnancy

• trophoblast cells secrete hCG

• hCG maintain corpus luteum during pregnancy

• this causes it to continue secreting progesterone

• by month 3, not as necessary, placenta takes place of corpus luteum and secretes progesterone and oestradiol

how do pregnancy tests work

• test for presence of hCG in urine

• contains monoclonal antibodies

• will bind to hCG if positive, causing a colour change

role of placenta

exchange of resources from embryo to mother.

mother sends oxygen and nutrients

embryo sends waste and CO2

maternal portion of placenta

uterine endometrium

embryonic portion of placenta

chorionic villi

contains large surface area, to take in nutrients from material blood in the intervilious space

space between enbryomic and maternal section of placenta

intervillious space; mothers blood is present there, enters by endometrial arteries and comes back from endometrial veins. No direct contact between maternal blood and foetal blood

progesterone along pregnancy

• stays high until month 7

• starts to plateau, and eventually start declining when preparing for childbirth

effect of foetus pressure on uterus walls

• detectors on uterine walls detect stretch

• stimulates cortisol productions

• stimulates production of specific type of oestradiol: oestriol

• oestriol inhibits progesterone production by placenta

• and makes smooth uterine muscles more receptive to oxytocin

hormones during childbirth

• oxytocine is released by posterior pituitary gland

• vauses uterine contractions initiating parturition

• foetus responds, send prostaglandings, intensifying uterine contractions

• this causes posterior pitiutary gland to release more oxytocin

• this is a rare example of a positive feedback loop

hormone replacement therapy

• menopause marked by decrease of oestradiol and progesterone levels= bad side effects

• HRT is a treatment which relieves these symptoms

• oestradiol-progestin is given

• initially research suggested positive effects on CHD, but after controlling for income it was less conclusive