Biology Human reproduction

Question 1

Describe the 4 steps of fertilisation in humans

Answer 1

The acrosome reaction releases hydrolases which digest the zona pellucida.
The genetic material of the sperm cell enters the secondary oocyte.
This triggers the cortical reaction to prevent polyspermy and also triggers meiosis II.
Gametes fuse to form a diploid zygote.

Question 2

Explain the functions of the hormones oestrogen and
progesterone during pregnancy

Answer 2

Placenta secretes high levels of progesterone and oestrogen.
FSH and LH secretion are inhibited.
Progesterone maintains endometrium.
Oestrogen stimulates the growth of the uterus and the development of the mammary glands.

Question 3

Vas deferens

Answer 3

Carries sperm towards the penis during ejaculation.

Question 4

Testes

Answer 4

Produces gametes (spermatozoa) and the hormone testosterone. Surrounded in a skin sac called the scrotum.

Question 5

Seminal vesicle

Answer 5

Secretes an alkaline, nutrient rich fluid onto the sperm in the vas deferens forming semen.

Question 6

Prostate gland

Answer 6

Secretes an alkaline fluid containing zinc ions onto sperm in the vas deferens.

Question 7

Urethra function in males

Answer 7

Carries semen and urine out of the body.

Question 8

Epididymis and seminiferous tubules

Answer 8

Spermatozoa are made by spermatogenesis in the seminiferous tubules and stored in the epididymis to mature and become mobile

Question 9

Interstitial cells function in males

Answer 9

Inbetween seminiferous tubules secrete testosterone to stimulate spermatogenesis.

Question 10

Fallopian tube/ oviduct

Answer 10

Tube lined with ciliated epithelium which waft the secondary oocyte from the ovary to the uterus

Question 11

Ovary

Answer 11

Produces gametes up to secondary oocyte stage. Also produces hormones progesterone and oestrogen.

Question 12

Uterus

Answer 12

A specialist organ where the embryo implants into the blood rich endometrial layer and grows to term. If there is no fertilisation, this layer is shed during menstruation.

Question 13

Where does oogenesis take place

Answer 13

In an ovary up to secondary oocyte stage prior to birth

Question 14

Describe what happens in the ovary at ovulation

Answer 14

One graafian follicle migrates to the surface of the ovary and bursts releasing the secondary oocyte.

Question 15

What is capacitation

Answer 15

During fertilisation, capacitation increases the permeability of the membrane in front of the acrosome.

Question 16

Describe the cortical reaction

Answer 16

Cortical granules fuse with the cell membrane and alter the zona pellucida to form the fertilisation membrane; this prevents polyspermy.

Question 17

What occurs immediately after fertillisation

Answer 17

Mitotic divisions of the newly formed zygote occur (cleavage) to form a ball of cells called the blastocyst which implants into the endometrial lining of the uterus. The placenta begins to develop from the trophoblast cells.

Question 18

What forms the placenta

Answer 18

The placenta forms from the outer blastocyst cells (trophoblast cells) that extend into the endometrium linking the foetus to the mother’s tissues to collect nutrients.

Question 19

3 functions of progesterone produced by the corpus luteum

Answer 19

Maintains the endometrium, inhibits the production of FSH and LH, supresses contraction of the uterine wall.

Question 20

Function and adaptations of the chorionic villi in the placenta

Answer 20

Extend into the maternal blood and have microvilli to increase surface area, thin walls for easy diffusion and blood flows in a counter current direction to the maternal blood to maintain diffusion gradients along the whole blood vessel.

Question 21

Function of the intervillous spaces in the placenta

Answer 21

Contain maternal blood and bathe chorionic villi. This means mothers blood and foetal blood do not mix

Question 22

Function of the umbilical arteries in the placenta

Answer 22

Carries deoxygenated blood and waste materials away from the foetus to the chorionic villi where gas exchange and excretion occurs.

Question 23

Function of the umbilical veins in the placenta

Answer 23

Carries oxygenated blood and nutrients to the foetus.

Question 24

Function of amniotic fluid

Answer 24

Acts as shock absorber thus protecting the foetus from injury during development.

Question 25

Where are FSH and LH released from

Answer 25

The anterior pituitary gland

Question 26

Describe the hormone changes that occur before birth

Answer 26

Just before birth oestrogen levels increase and progesterone levels decrease - the uterine wall can now contract. The posterior pituitary gland secretes oxytocin that simulates uterine contractions (positive feedback). The anterior pituitary gland secretes prolactin stimulating the production of milk by the mammary glands

Question 27

Cervix

Answer 27

A narrow ring of connective tissue and muscle, it acts as a barrier between the uterus and the outside environment during pregnancy.

Question 28

Function of sertoli cells

Answer 28

They provide nourishment for spermatids and protection against the male's immune system.

Question 29

Zona pelucida

Answer 29

A jelly like coat secreted by the Corona radiata (follicle cells around oocyte) that surrounds the secondary oocyte

Question 30

3 functions of the placenta

Answer 30

Exchange of gases and nutrients, providing barrier between maternal and foetal blood, secretion of hormones

Question 31

3 effects of oestrogen secretion

Answer 31

stimulates Lutenising hormone (LH) production by anterior pituitary gland, inhibits secretion of FSH, triggers rebuilding of endometrium.

Question 32

3 effects of LH secretion

Answer 32

stimulates secretion of FSH, induces ovulation on day 14, stimulates conversion of Graafian follicle into corpus luteum.

Question 33

Following fertilisation what hormone does the developing embryo (blastocyst) secrete

Answer 33

hCG to maintain the corpus luteum for the first 16 weeks of pregnancy until the corpus luteum degenerates and the placenta takes over responsibility for the secretions of progesterone and oestrogen.

Question 34

4 effects of the corpus luteum secretions of oestrogen and progesterone during early pregnancy

Answer 34

inhibit FSH, preventing development of any follicles, inhibit LH, preventing ovulation, oestrogen stimulates growth of the uterus to accommodate the growing foetus, progesterone maintains the wall of the endometrium,

Question 35

Describe spermatogenesis

Answer 35

Spermatogonia (mitosis) -> primary spermatocyte (meiosis I) -> secondary spermatocyte (meiosis II) -> spermatids (mature to spermatozoa)

Question 36

When does spermatogenesis begin

Answer 36

At puberty

Question 37

Describe oogenesis

Answer 37

Oogonia (mitosis) -> primary oocyte (meiosis I) -> secondary oocyte + 1st polar body (meiosis II) -> ovum + 2nd polar body

Question 38

Name the two membranes that surround the mature ovum

Answer 38

Zona pellucida and corona radiata

Question 39

What part of oogenesis occurs during puberty

Answer 39

Secondary oocyte + 1st polar body are formed. Secondary oocyte (n) - Meiosis I competed just before ovulation. Meiosis II stops at metaphase II (only completed if fertilisation occurs)

Question 40

State the stages of implantation

Answer 40

Ovum is fertilised, sperm and egg nuclei fuse to form zygote, cleavage (mitosis but cells split without growing) occurs to forms 16 cell morula, uneven divisions create the blastocyst that implants into the endometrium