human reproduction

Question 1

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what is the function of the tesitis

Answer 1

Each testis contains around one thousand
seminiferous tubules where spermatozoa are
formed.

Question 2

where do spermatozoa go after being produced in the seminiferous tubules

Answer 2

Spermatozoa collect in the epididymis where their motility improves.

Question 3

what is the role of seminal vesicles

Answer 3

Seminal vesicles secrete mucus and prostate fluid
mixes with spermatozoa during ejaculation.

Question 4

wha do the fluids produced from the seminal vesicles contain and what is it’s function

Answer 4

These fluids maintain sperm mobility, provide
nutrients, e.g. fructose, and are alkaline which
neutralises acidity found in urine and the vagina.

Question 5

what is semen

Answer 5

The resultant fluid containing sperm is called
semen, and leaves the penis by the urethra.

Question 6

where are the function of the two ovaries

Answer 6

where oocytes mature from
germinal epithelial cells.

Question 7

what happens every month during ovulation

Answer 7

Each month, one secondary oocyte is released
during ovulation from the surface of one of the
ovaries.

Question 8

what is the role of the cilia in the fallopian tube

Answer 8

Cilia lining the fallopian tube (oviduct) waft the
secondary oocyte along.

Question 9

what are the muscle layers of the uterus and their functions

Answer 9

• The uterus consists of a thin outer layer called
  the perimetrium. Inside this is the muscle layer or myometrium.
• The endometrium is the innermost layer
  consisting of a mucous membrane which is well
  supplied with blood. This layer is shed each month
  during the menstrual cycle if an embryo fails to
  implant.

Question 10

what is gametogenesis and what are the two types

Answer 10

Gametogenesis is the production of gametes through a series of mitotic and meiotic divisions in the testis and ovaries:
1. Sperm are produced by spermatogenesis.
2. Eggs are produced by oogenesis.

Question 11

describe the process of spermatogenesis

Answer 11

• As you move from the outside towards the centre
  of the seminiferous tubule, the cells become more
  mature.
  ■ Diploid germinal epithelial cells divide by means
  of mitosis to produce diploid spermatogonia.
  ■ Primary spermatocytes (2n) divide by meiosis I to
  produce secondary spermatocytes (n).
  ■ Secondary spermatocytes (n) undergo meiosis II
  to make spermatids (n).
  ■ Spermatids differentiate and mature into
  spermatozoa (n).
  .

Question 12

what is the role of steroli cells in spermatogenesis

Answer 12

provide spermatozoa with nutrients and protect them from the male’s immune system.

Question 13

what is the role of instertitial cells in spermatogenesis

Answer 13

Interstitial cells secrete testosterone.

Question 14

describe the process of oogenesis before fertilisation occurs

Answer 14

• Before birth, germinal epithelial cells divide by
  means of mitosis to produce oogonia (2n) and
  then primary oocytes (2n).
  ■ Primary oocytes are surrounded by germinal
  epithelial cells which form the primary follicle.
  ■ Primary oocytes begin meiosis I but stop at
  prophase I. Division resumes from puberty.
  ■ Each month, a primary oocyte continues meiosis I
  to produce a secondary oocyte and a polar body,
  both of which are haploid.
  ■ The primary follicle also develops into a secondary
  follicle, which matures into a Graa an follicle. This
  migrates to the surface and bursts releasing the
  secondary oocyte (ovulation).
  ■ The secondary oocyte undergoes meiosis II,
  stopping at metaphase II.

Question 15

describe the process of oogenesis after fertiliation occurs

Answer 15

• If a sperm meets the secondary oocyte and enters,
  meiosis II is completed resulting in the production
  of the ovum (n) and second polar body (n).
  ■ The sperm pronucleus can now fuse with the
  ovum pronucleus to produce a diploid zygote.
  ■ Following fertilisation, the Graa an follicle
  becomes the corpus luteum and produces
  progesterone. If no fertilisation occurs it regresses.

Question 16

describe the structure of a human speratozoon

Answer 16

• Each spermatozoon head is approximately 5 μm
  long, with a 50 μm tail.
  ■ Within the head is a haploid nucleus, and the
  acrosome which contains proteases to digest the
  cells of the corona radiata and zona pellucida.
  ■ Mid piece contains many mitochondria which
  provide ATP for movement.
  ■ The tail ( agellum) moves in a circular wave
  motion to propel the spermatozoon forward.

Question 17

describe the structure of a human secondary oocyte

Answer 17

■ A typical ovum measures 120 μm in diameter, and
is one of the largest cells in the human body.
■ Fats and albumins contained within the cytoplasm
provide nutrition for the developing embryo
until it implants in the wall of the uterus and the
placenta can provide nutrients.
■ Changes to the zona pellucida following entry of
a single spermatozoon prevent polyspermy (entry
of additional sperm).

Question 18

describe the human menstrual cycle from day 1 - day 14

Answer 18

• The human menstrual cycle takes about one month to complete.
• The process is controlled by gonadotrophic hormones from the anterior pituitary and hormones from the ovary itself.
• From about day 5 of the cycle, FSH (follicle- stimulating hormone) is released from the anterior pituitary promoting maturation of the Graafian follicle stimulating production of the steroid hormone oestrogen by the ovary.
• Oestrogen has the effect of increasing the thickness and vascularity of the uterus lining, the endometrium, in preparation for the implantation of a fertilised ovum.

Question 19

describe the human menstrual cycle after day 14

Answer 19

• By about day 14 oestrogen levels are high enough to inhibit further production of FSH by negative feedback and stimulate release of luteinising hormone (LH).
• The sudden release of LH induces ovulation.
• It also promotes the formation of a corpus luteum and stimulates the release from it of another steroid hormone, progesterone.
• High levels of progesterone building up over the next 10 days inhibit both FSH and LH.
• Oestrogen and progesterone levels drop and the endometrial lining breaks down resulting
  in menstruation.
• If fertilisation has occurred, progesterone levels will remain high and this will inhibit the release of FSH and LH by the pituitary.

Question 20

capacitation

Answer 20

changes in the sperm membranes that increase its fluidity and allow the acrosome reaction to occur.

Question 21

acrosome reaction

Answer 21

acrosome enzymes digest the zona pellucida allowing
the sperm and oocyte cell membranes to fuse.

Question 22

cortical reaction

Answer 22

• occurs when the cortical granule membranes fuse with the oocyte cell membrane.
• The zona pellucida is converted into a fertilisation
  membrane.

Question 23

describe what happens during sexual intercourse

Answer 23

• During sexual intercourse, the erect penis is inserted into the vagina, and following movements of the penis, semen is ejaculated into the vagina by
  contractions of the smooth muscle in the walls of the epididymis, vas deferens and penis.
  The force of ejaculation propels some sperm through the cervix and into the uterus, with the remainder collecting at the top of the vagina.

Question 24

describe what happens after sexual intercourse

Answer 24

• Sperm respond to chemicals produced by the oocyte and begin to swim through the uterus and into the oviduct.
• Once there, sperm can remain viable for a few days, but are most fertile in the 12–24 hours following intercourse.
• The oocyte remains viable for only 24 hours following ovulation, so needs to be fertilised relatively quickly after ovulation.

Question 25

what are the events that lead to fertilisation

Answer 25

* Cholesterol and glycoproteins are removed from the cell membrane covering the sperm’s acrosome making the membrane more fluid. * This is called capacitation, and occurs several hours after sperm are deposited. * The acrosome releases protease enzymes which digest cells forming the corona radiate surrounding the oocyte allowing the sperm head to contact the zona pellucida. * Now acrosin (another protease) hydrolyses the zona pellucida, allowing the head to enter the oocyte. * This is called the acrosome reaction. * The cell membranes of the sperm and oocyte fuse, the male nucleus can begin to enter the oocyte cytoplasm. * This triggers the cortical reaction, where cortical granule membranes fuse with the oocyte cell membrane causing it to expand and harden forming the fertilisation membrane which prevents polyspermy –the further entry of sperm. * Meanwhile the second meiotic division completes, and the ovum is formed containing the female nucleus and a second polar body. * Fertilisation is the sequence of events from the point when the sperm and oocyte make contact until the male and female chromosomes join on the mitotic equator * The first mitotic division produces two cells, and the resulting cell is referred to as an embryo.

Question 26

tropoblast

Answer 26

cells froming the outer layer of the blastocyst

Question 27

implatation

Answer 27

sinking of the blastocyst into the endometrium

Question 28

describe what happens after fertilisation

Answer 28

* The embryo continues to divide by mitosis as it passes down the oviduct, forming a ball of cells called a morula by day 3, by a process called cleavage. * By day 7 a hollow ball of cells called a blastocyst forms which has an outer layer of cells referred to as a trophoblast which develops protrusions called trophoblastic villi. * The endometrium thickens allowing implantation of the blastocyst to occur by day 8–10.

Question 29

how is the placenta formed

Answer 29

* The chorion develops from the trophoblast, forming the larger chorionic villi which acquire capillaries and embed into the endometrium. * They are supplied by the developing umbilical artery and vein, and form the placenta.

Question 30

as an embryo develops into a foetus (where distinct organs are visble from about 10 weeks of pregnancy) what is the roles of the placenta

Answer 30

■ Allows exchange of oxygen, carbon dioxide, nutrients and waste between mother’s and foetus’s blood. * The blood is never in direct contact, but is separated by just a few mm, and a counter current blood flow ensures that concentration gradients are maintained across the entire length of the placenta. ■ Produces hormones to support pregnancy. ■ Acts as a physical barrier between the two circulations. * This is important as maternal blood pressure is much higher and would rupture delicate capillaries in the foetus, and it separates the maternal immune system from the foetus preventing an immune response. ■ Antibodies can cross the placenta giving the foetus some passive immunity to diseases. * However, some microorganisms can cross the placenta, e.g. Rubella virus, and many drugs, e.g. nicotine and heroin.

Question 31

how does blood enter and leave the foetus

Answer 31

* Blood leaves the foetus through the umbilical artery carrying waste including carbon dioxide to the placenta. * The umbilical vein carries blood rich in nutrients, e.g. glucose and amino acids, back towards the foetus.

Question 32

describe the process of pregnancy

Answer 32

* Pregnancy lasts for around 39 weeks, is divided into three trimesters and runs from the first day of the last period until birth. * As the foetus develops it is enclosed by a membrane called the amnion, which produces amniotic fluid by the fiffth week.

Question 33

what are the functions of amniotic fluid

Answer 33

■ Acts as a shock absorber protecting the developing foetus. ■ Helps to maintain the foetus’s body temperature. ■ Provides lubrication. ■ Allows movement.

Question 34

describe the roles of hormones during pregnancy

Answer 34

* Human chorionic gonadotrophin (hCG) is secreted by the blastocyst, and later the chorion. * hCG is responsible for maintaining the corpus luteum which secretes progesterone (maintains endometrium) up to about 16 weeks when progesterone is produced directly by the placenta. * During pregnancy, progesterone also inhibits oxytocin preventing contraction of the myometrium, and oestrogen stimulates growth of the uterus and mammary glands.

Question 35

describe the role of hormones during birth

Answer 35

* To initiate birth, oxytocin is secreted by the posterior pituitary gland resulting in contractions of the myometrium. * The contractions in turn cause an increased secretion of oxytocin and so on (positive feedback) causing more frequent and stronger contractions.

Question 36

describe the role of hormones for production of milk

Answer 36

* Prolactin is secreted by the anterior pituitary gland causing milk to be produced, * and is expelled from the nipples by contraction of muscles around the milk ducts brought about by oxytocin.