4.1 sexual reproduction in humans

label the side profile of the male reproducitive system

label the front profile of the male reproductive system

what is the function of the scrotum?

external sac of skin containing testes

what is the function of the testes?

produce gametes (sperm from spermatogenesis)

produces testosterone from Leydig cells

what is the function of the epididymis?

sperm stored here and mature to become fully motile

what is the function of the vas deferens?

carries sperm from the epididymis to the urethra during ejaculation

what is the function of the seminal vesicle?

secretes fluid into vas deferens (makes up 60% of semen)

what is in seminal fluid?

rich in mucus and nutrients for sperm

eg fructose for respiration and amino acids

what is the function of the prostate gland?

secretes fluid into vas deferens (makes up 30% of semen)

what is in prostate fluid?

Zn2+ needed by sperm

alkaline - neutralises acidity of urine in urethra and acidity of vaginal tract

what is the function of the urethra?

carries semen through penis and out of body

carries urine from bladder through penis and out of body

what is the function of the penis?

specialised organ adapted to transfer semen to vagina

organ of internal fertilisation

label the TS testis

why do the testis hang outside the body?

sperm production cannot occur at body temp (approx 2° lower)

label the TS seminiferous tubule in a testis

what is the function of a Sertoli cell?

provide nourishment for spermatids

protection against male immune system

label the seminiferous tubule

how many sperm cells are in each ejaculation?

400 million

label the sperm cell

what is the function of the head (sperm cell)?

haploid nulceus

restores diploid number of chromosomes after fertilisation of ovum

what is the function of the acrosome?

contains hydrolytic enzymes

needed for successful fertilisation

what is the function of the mid piece (sperm cell)?

many mitochondria - site of aerobic respiration

release energy/make ATP needed for movement of tail

what is the function of the tail/flagellum?

lashing movement

allows sperm to swim through female reproductive system

vagina → cervix → uterus → fallopian tube

what is the sequence of events during spermatogenesis?

primordial germ cell

spermatagonium (2n)

mitotic division

primary spermatocyte (2n)

meiosis I

secondary spermatocyte (n)

meiosis II

spermatids (n)

sperm cells (n)

why is the formation of haploid gametes important?

reforms diploid number of chromosomes after fertilisation of ovum

prevents double fertilisation of chromosomes each generation

what process in meiosis produces genetic variation in the daughter cells?

prophase I - crossing over of chiasmata between non-sister chromatids

metaphase I - independant assortment of homologous pairs

metaphase II - independant assortment of chromatids

label the side profile of the female reproductive system

label the front profile of the female reproductive system

what is the function of the ovary?

production of gametes (secondary oocytes formed during oogenesis)

produce oestrogen and progesterone

what is the function of the fallopian tube/oviduct?

lining of ciliated epithelial cells

move secondary oocyte from ovary to uterus

site of fertilisation

what is the function of the uterus?

during pregnancy it expands to accomodate growing fetus

what is the function of the endometrium?

inner most layer of uterus wall

good blood supply

site of embryo implantation

if implantation doesn’t occue then endometrium shed during menstruation

what is the function of the myometrium?

muscle layer that contracts during birth

what is the function of the perimetrium?

outer layer of uterus wall

what is the function of the cervix?

narrow ring of connective tissue and muscle

acts as barrier between uterus and outside environment during pregnancy

during pregnancy - mucus plug forms to seal uterus, preventing pathogen entry

what is the function of the vagina?

muscular walls

opens at vulva

semen deposited in it during sexual intercourse

fetus passes out it during birth

label the ovary structures over time

what process occurs in the ovary?

oogenesis

label the mature Graafian follicle

what is the sequence of events in oogenesis?

germinal epithelial cells (2n)

mitosis

oogonia (2n)

mitosis and enlarge

primary oocyte (2n) and follicle cells (2n)

meiosis I

secondary oocyte (n) and follicle cells (2n)

maturation

Graafian follicle

break down oogenesis before birth

germinal epithelium cells (2n) divide by mitosis

produce oogonia (2n)

divide many times by mitosis

form primary oocytes (2n) and follicle cells (2n)

follicle cells surround primary oocyte → primary follicle

primary oocyte begins meiosis I - stops at prophase I until puberty

break down oogenesis from puberty

hormones stimulate primary oocyte to complete meiosis I

produces secondary oocyte (n) and much smaller primary polar body (n)

primary follicles → secondary follicles → Graafian follicles

ovulation - Graafian follicle migrates to ovary surface

secondary oocyte released into fallopian tube

secondary oocyte begins meiosis II - stops at metaphase II until fertilisation

break down oogenesis after fertilisation

meiosis II completed

produces ovum and second polar body

Graafian follicle → corpus luteum

what is the difference between spermatogenesis and oogenesis:

things produced

spermatogenesis: 4 functional spermatazoam produced

oogenesis: 1 functional ovum produced

what is the difference between spermatogenesis and oogenesis:

arrests/suspensions

spermatogenesis: none (continuous)

oogenesis: 2

what is the difference between spermatogenesis and oogenesis:

polar bodies

spermatogenesis: none made

oogenesis: polar bodies made

what is the difference between spermatogenesis and oogenesis:

when in life

spermatogenesis: puberty → old age

oogenesis: puberty → menopause

what is the difference between spermatogenesis and oogenesis:

motility of gametes

spermatogenesis: motile - move itself

oogenesis: non-motile - moved by cilia

what is the difference between spermatogenesis and oogenesis:

cytoplasm present

spermatogenesis: very little cytoplasm in gamete

oogenesis: much cytoplasm in gamete

what causes a penis to become erect?

vasodilation of arterioles supplying blood to penis

vasoconstriction of venules leaving penis

what causes ejaculation?

movement of penis

muscular contractions of smooth muscle in walls of epididymis, vas deferens and penis

ejaculation of semen into vagina

how does semen enter the uterus?

force of ejaculation causes sperm cells to be propelled

cervix → uterus

what is an orgasm?

the combination of physical and psychological events at maximum intensity

what are the stages of fertilisation?

capacitation

acrosome reaction

fusion of sperm and secondary oocyte membrane

cortical reaction

fusion of sperm and ovum

what happens during capacitation?

cholesterol and glycoproteins removed from acrosome membrane

membrane becomes more fluid and more permeable to Ca2+

what happens during the acrosome reaction?

acrosome membrane fuses with cell surface membrane

releases hydrolytic enzymes

digest cells of corona radiata

on contact with zona pellucida - acrosome releases protease

hydrolyses zona pellucida

what happens during the fusion of the sperm and secondary oocyte membranes?

cell membrane of sperm cell fuses with membrane of secondary oocyte

now called ovum

what happens during the cortical reaction?

oocyte smooth endoplasmic reticulum releases Ca2+ into oocyte cytoplasm

cortical granules fuse with cell membrane

release contents by exocytosis

hardening of zona pellucida

forms fertilisation membrane

prevents polyspermy

what happens during the fusion of the sperm and ovum?

entry of sperm triggers meiosis II to complete

sperm nucleus (n) and ovum nucleus (n) → zygote nucleus (2n)

label the secondary oocyte before fertilisation

label the secondary oocyte after fertilisation

what happens to the zygote prior to implantation?

zygote undergoes cleavage (series of mitotic divisions)

forms morula - solid ball of 16 cells

cleavage continues

hollow ball of cells form - blastocyst

what is the outer layer of cells of the blastocyst called?

trophoblast

what does the trophoblast develop into?

inner cell mass (embryoblast)

trophoblastic villi

chorion

amnion

what causes the implantation window?

blastocyst moves down fallopian tube

endometrial lining of uterus thickens

receives increased blood supply

endometrium receptive to blastocyst

define implantation

the attachment and sinking in of the blastocyst into the endometrium

label the diagram

what is the role of the trophoblastic villi?

penetrate endometrium during implantation

increase surface area for absorption of nutrients from endometrium/mother’s blood

what is the role of the amnion?

contains amniotic fluid

acts as shock absorber

protects fetus from physical injury

what is the role of the chorion?

gives rise to chorionic villi

increase efficientcy of exchange between maternal and fetal blood in placenta

what is the role of the placenta?

endocrine gland

exchange site

physical barrier

provides passive immunity

protects from mother’s immune system

what is an endocrine gland?

produces and releases hormones directly into bloodstream

what hormones are produced by the placenta?

hCG

progesterone

oestrogen

what substances are exchanged between the mother and fetus’s blood?

nutrients

waste products

respiratory gases

M → F: glucose, amino acids, fatty acids

F → M: CO2, urea

are the mother’s and fetus’s blood in contact?

no

how is exchange in the placenta maximised?

microvilli - large surface area

thin walls - most effective for exchange (eg diffusion, pinocytosis)

counter current flow - maintains concentration gradient/equilbrium never reached

what is protected from the mother’s high blood pressure?

fragile fetal capillaries

what is passive immunity and how does this occur in the placenta?

antibodies made by someone else

mother’s antibodies cross placenta

provide protection for the fetus

how does the placenta ensure that the mother’s immune system does not generate an immune response towards the fetus?

cell walls of chorionic villi fuse

no space between them

syncitium forms

ensures 2 bloods do not mix

migratory immune cells (granulocytes) cannot get through to fetal blood

when might the placenta not provide immunological protection?

some spontaneous abortions

Rhesus disease

pre-eclampsia

some viruses (eg rubella)

drugs/alcohol cross the placenta

what is Rhesus disease?

Rhesus -ve mother against Rhesus +ve fetus

destruction of blood cells by antibodies

what is pre-eclampsia?

occurs in 2nd trimester

very high blood pressure

1 cause is abnormal immune response towards placenta

how long is the umbilical chord?

approx 60cm

where does the umbilical chord develop from?

the placenta

where does the umbilical artery go?

2 umbilical arteries

away from fetus

deoxygenated

low in nutrients

high in waste

where does the umbilical vein go?

1 umbilical vein

to the fetus

oxygenated

high in nutrients

low in waste