The Human Reproductive System part 2

Question 1

Interaction of oestrogen, progesterone, FSH and LH in the control of the menstrual cycle

Answer 1

1. the pituitary gland produces FSH which causes the development of a follicle in the ovary
2. as the egg develops inside the follicle, the follicle produces oestrogen
3. the oestrogen causes growth and repair of the lining of the uterus wall. oestrogen inhibits FSH
4. when oestrogen rises to a level it causes a surge in LH from the pituitary which causes ovulation where an egg is released from the follicle
5. the follicle becomes the corpus luteum and this produces progesterone which inhibits FSH and LH production. (negative feedback)
6. progesterone maintains the uterus lining
7. if the egg has not been fertilised, the corpus luteum dies and progesterone levels drop. This causes menstruation

Question 2

contraception methods

Answer 2

natural - avoiding intercourse during fertile period (based on body temp.)
mechanical - physical barriers eg condoms
chemical - hormones eg pill
surgery - vasectomy (sperm duct cut out and sealed)

Question 3

fertilisation outline

Answer 3

location: fallopian tube
1. sperm are attracted towards the egg by chemicals released from egg: chemotaxis
2. the acrosome releases enzymes to digest the egg membrane
3. the sperm loses its tail and the head enters the egg
4. the sperm and egg nuclei fuse to form a zygote

Question 4

sequence of development from fertilised egg

Answer 4

1. morula formation: zygote divides rapidly by mitosis
2. morula formed- solid ball of cells
3. morula moves through fallopian tube towards uterus by peristalsis and cilia
4. blastocyst forms: fluid filled ball
   a. outer layer: trophoblast, develops into placenta
   b. inner cell mass: develops into embryo

Question 5

fate of inner cell mass after embryonic development

Answer 5

forms 3 germ layers of the embryo:

1. ectoderm (outside): forms hair, skin, nervous system
2. mesoderm(middle): forms skeletal system, muscles, excretory system
3. endoderm(inside): forms digestive system, liver, pancreas

Question 6

fate of trophoblast after embryonic development

Answer 6

forms 2 membranes:

1. amnion
2. chorion

Question 7

amnion

Answer 7

what: membrane formed during implantation
function: protection of embryo
feature: fills with amniotic fluid (supports and protects embryo)

Question 8

germ layers

Answer 8

layer of cells that give rise to specific organs or systems

Question 9

chorion

Answer 9

what: membrane surrounding amnion and embryo
function: develops into the placenta (forms chorionic villi)

Question 10

placenta

Answer 10

when formed: after implantation

structure: combination of uterine and embryonic tissues (chorionic villi and endometrium)

Question 11

functions of placenta

Answer 11

1. exchange by diffusion
   - nutrients to embryo: water, oxygen, antibodies to baby
   - wastes to embryo: urea,co2
2. keeps mother and baby blood supplies separate
   - blood pressure from mother could damage the embryo
   - incompatible blood groups can damage red blood cells
3. makes hormone progesterone

Question 12

umbilical cord

Answer 12

what: connects the embryo with the placenta
function: takes blood from the embryo to the placenta and back again

Question 13

endometrium

Answer 13

provides nourishment for the developing embryo

Question 14

stages of embryo development

Answer 14

1-3: zygote divides, morula forms and reaches uterus
7-14: implantation of blastocyst into endometrium
4 weeks: heart forms and beats, brain develops, umbilical cord forms
5-6 weeks: limbs form, all internal organs start forming, eyes nose, ears develop
8 weeks: tail has diminished, ossification begins; bone replaces cartilage, embryo becomes foetus
12 weeks: gender of foetus can be seen, more ossification occurs, muscles and nerves function, foetus kicks

Question 15

length of pregnancy

Answer 15

38 weeks

9 months

Question 16

birth

Answer 16

labour:
-hormone: progesterone up, oxytocin down (causes contractions)
-amniotic sac bursts releasing amniotic fluid, waters break
cervix dilates

stage 2:

• the foetus passes through the cervix and birth canal head first
• umbilical cord is tied and cut

afterbirth:

• uterus contracts
• expels placenta

Question 17

lactation outline

Answer 17

milk contains colostrum- contains antibodies to protect against infection
progesterone and oestrogen drop, stimulates prolactin production

Question 18

prolactin

Answer 18

site of production: pituitary gland

function: milk production

Question 19

breastfeeding advantages

Answer 19

1. supply of antibodies
2. sterile - less danger of infection
3. reduces risk of breast cancer in the mother

Question 20

mitosis

Answer 20

location: animals: all somatic cells
plants: meristematic zone of root, apical bud

function:

unicellular: asexual reproduction
multicellular: growth and repair of cells

stages: prophase, metaphase, anaphase, telophase

resulting cells: 2 daughter cells
genetically identical

Question 21

meiosis

Answer 21

location:
animals: ovaries and testes
plants: ovary and anther

function:
multicellular: sexual reproduction, allows variation

resulting cells:
4 daughter cells
not genetically identical to each other or parent