chapter 18: reproduction in humans

Question 1

what is the testis?
( the male reproductive system)

Answer 1

• there are two testes, each testis produces sperms
• also produces male sex hormones like testosterones
  > the male hormones are responsible for the development and maintenance of the secondary sexual characteristics in males
• each testis receives blood from blood vessels in a SPERMATIC CORD
• leading from the end of each testis is a narrow, much-coiled tube called the EPIDIDYMIS
  >epididymis stores inactive sperms from testis before they enter the sperm duct

Question 2

what is the scrotum?
( the male reproductive system)

Answer 2

• the testes lie between the thighs in a pair of pouch-like sacs called the SCROTUM or SCROTAL SACS
  > scrotums are outside the main body cavity
  > slightly lower temperature than body temperature
  > the lower temperature is essential for the sperms to develop properly

Question 3

what is the sperm duct?
( the male reproductive system)

Answer 3

• each sperm duct or vas deferens loops over a ureter then opens into the urethra
• after sperms are released from a testis, they travel through a sperm duct

Question 4

what are the glands in the male reproductive system and what are their secretions?

Answer 4

• prostate gland is at the base of the urinary bladder
  > where two sperm ducts join the urethra
• Cowper’s gland is beneath the prostate gland
• the seminal vesicle is a gland that opens into each sperm duct
  > stores sperms temporarily before they are released through the urethra
• the prostate gland, Cowper’s gland and seminal vesicle gland secrete a fluid which mixes with the sperms
• this fluid contains nutrients and enzymes which nourish the sperms and stimulate them to swim actively
  > mixture and fluid is called semen!

Question 5

what is the urethra?
( the male reproductive system)

Answer 5

• the urethra is a tube which passes from the bladder through the centre of the penis to the outside of the body
  >both semen and urine pass out of the body through the urethra

Question 6

what is the penis?
( the male reproductive system)

Answer 6

• the penis is an erectile organ
  > it enters the vagina of a woman during sexual intercourse to deposit semen, containing sperms

Question 7

what are sperms?
( the male reproductive system)

Answer 7

• numerous sperms are produced throughout the life of a male human after he has become physically mature
  > sperms also called SPERMATOZOA

head:
- bout 2.5 μm wide
- contains a large nucleus with small amount of cytoplasm
> the nucleus carries a haploid set of chromosomes
- an ACROSOME is also present
> a vesicle containing enzymes
> enzymes break down part of the egg membranes so that the sperm can penetrate the egg during fertilisation

middle piece:
- the middle piece contains numerous mitochondria
> provides energy for the sperm to swim towards the egg

tail:
- the beating movement of the tail or FLAGELLUM
> enables the sperm to swim towards the egg
> sperm is motile

Question 8

what is the ovary?
(female reproductive system)

Answer 8

• the two ovaries produce eggs
• each ovary also produces hormones such as oestrogen and progesterone
• the female sex hormones are responsible for the development and maintenance of secondary sexual characteristics in females
• when the eggs become mature, they are released from the ovaries

Question 9

what is the oviduct?
(female reproductive system)

Answer 9

• each ovary releases mature eggs into an oviduct or fallopian tube
• each oviduct is a narrow muscular tube leading from the ovary to the uterus
  > it has a funnel-like opening lying close to the ovary which makes it easier for the egg to enter the oviduct
  > egg is usually fertilised in the oviduct

Question 10

what is the uterus?
(female reproductive system)

Answer 10

• the uterus or womb is where the fetus develops during pregnancy
  > the uterus is shaped like an upside-down pear
  > has elastic muscular walls
  > the smooth muscle tissue in the walls of the uterus contract to push the fetus out during birth
• the soft, smooth inner lining of the uterus is called the uterine lining
  > where the embryo implants

Question 11

what is the cervix?
(female reproductive system)

Answer 11

• it is the lower portion of the uterus where it joins the vagina
  > the opening of the cervix allows menstrual blood to flow out into the vagina during menstruation

Question 12

what is the vagina?
(female reproductive system)

Answer 12

• leading from the cervix to the outside is the vagina
• the opening of the vagina is the vulva
• the semen is deposited in the vagina during sexual intercourse

Question 13

what is the ovum?
(female reproductive system)

Answer 13

• the ovum is the female gamete
• a female is born with all the potential eggs she will ever have
  > at birth, about 70 000 potential egg cells are already present in the ovaries
  > however only about 500 will ever become mature within two ovaries
  > usually only one mature egg is released every month from the time a female becomes physically mature until about 45-55 of age
• the egg is spherical and about 120

Question 14

what is the ovum?
(female reproductive system)

Answer 14

• the ovum is the female gamete
• a female is born with all the potential eggs she will ever have
  > at birth, about 70 000 potential egg cells are already present in the ovaries
  > however only about 500 will ever become mature within two ovaries
  > usually only one mature egg is released every month from the time a female becomes physically mature until about 45-55 of age
• the egg is spherical and about 120μm to 150μm wide
  the egg:
• has a large nucleus containing one haploid set of chromosomes
• has abundant cytoplasm which may contain a small amount of yolk
• is surrounded by a cell surface membrane which in turn is surrounded by an outer membrane

Question 15

what is puberty?

Answer 15

• it is the stage of human growth and development in which a person becomes physically mature
  > body begins to change from that of a child to an adult
  > 11 for females and 14 for males
• during puberty, reproductive system of a young person begins to function
  > sex organs mature and begin to produce gametes
  > changes brought by sex hormones are called SECONDARY SEXUAL CHARACTERISTICS
• females sex hormones: oestrogen and progsterone
• male sex hormones: testosterone

Question 16

what are the secondary sexual characteristics in males?

Answer 16

• facial hair starts to grow and hair appears in pubic region and under armpits
• the penis and testicles increases in size
• larynx enlarges and voice deepens
• production of sperms starts

Question 17

what are the secondary characteristics in females?

Answer 17

• hair appears in the pubic region and under armpits
• the breasts and uterus enlarge
• hips broaden
• menstruation and ovulation starts

Question 18

what is the menstrual cycle?

Answer 18

• for females, monthly discharge of blood (menses) from the uterus via the vagina is a sign of puberty
  > MENSTRUATION
• the menstrual period usually lasts about 5 days
  > length of the menstrual period and the amount of blood lost vary from female to female

Question 19

what is natural variation in the menstrual cycle and what causes it?

Answer 19

• the average menstrual cycle for an adult female is 28 days
  > menstrual cycles ranging from21 -33 days are not abnormal
• stress, tiredness, illness, unbalanced diet or malnutrition
  > may alter or stop the menstrual cycle and change the interval between periods
• as females ages, the ovaries will eventually stop releasing eggs and the menstrual cycle will stop
  > MENOPAUSE
• menopause will usually take place between 45 and 55 years of age

Question 20

what are the changes in a follicle during the menstrual cycle?

Answer 20

• ovaries contain many developing follicles

1. PRIMARY FOLLICLES
   - young follicles
   > each primary follicle consists of a potential egg cell surrounded by a layer of smaller cells known as follicle cells
2. GRAAFIAN FOLLICLE
   - a primary follicle may develop into a Graafian follicle
   > the Graafian follicle contains an egg surrounded by follicle cells and a fluid-filled space
   > the egg has a haploid number of chromosomes
   - usually, only one egg is released every month
   > ovaries takes turn to release an egg
3. OVULATION
   - on day 14 of a 28-day cycle, the Graafian follicle ruptures and releases the egg into the oviduct through the funnel-like opening
   > the release of the egg from the ovary is called ovulation
4. CORPUS LUTEUM
   - after ovulation, the Graafian follicle develops into a corpus luteum
   > the corpus luteum produces hormones that prepares the body for pregnancy
5. CORPUS LUTEUM BREAKS DOWN
   - if no fertilisation occurs, the corpus luteum will persist for some time and then eventually breaks down

Question 21

what are the stages in the menstrual cycle?

Answer 21

menstrual flow stage ( day 1-5)
- the first day of menstruation is the first day of the menstrual cycle
> uterine lining breaks down and flows from the uterus out of the body through the vagina
> the pituitary gland secretes FOLLICLE-STIMULATING HORMONES (FSH)

follicle stage ( day 6-13)
1. effects of FSH
- FSH stimulates the development of the follicles in the ovaries
> usually one follicle will develop into a graafian follicle in one of the ovaries during each cycle
- it stimulates the follicles in the ovaries to secrete oestrogen
2. effects of oestrogen
- causes the repair and growth of the uterine lining
> the uterine lining becomes thick and spongy with blood vessels
- oestrogen when present in high concentration inhibits FSH production
> preventing the maturation and development of more follicles
- oestrogen at high concentration also stimulates the pituitary gland to secrete LUTENISING HORMONE (LH)

ovulation (day 14)
- LH causes ovulation
> also causes the formation of corpus luteum from the remains of the Graafian follicle
> the corpus luteum secretes progesterone and some oestrogen

corpus luteum stage ( day 15-28)
- effects of progesterone:
> it maintains the uterine lining by causing it to thicken further and be richly supplied with blood capillaries, preparing it for the implantation of the embryo
- inhibits ovulation
- also inhibits FSH production

Question 22

what if no egg fertilisation occurs?

Answer 22

• the egg will break down
• eventually, LH production is inhibited by high concentration of progesterone in the blood
  > the drop in the LH level in the blood causes the corpus luteum to break down
• when the corpus luteum breaks down, the progesterone is not secreted
• without progesterone, the thickened uterine lining cannot be maintained
  > so it breaks down
• the lining flows from the uterus together with some blood though the vagina
  > the beginning of menstruation
  > occurs around the 28th day from the beginning of the previous menstruation
• FSH is again produced by the pituitary gland and the whole cycle is repeated

Question 23

what happens if fertilisation occurs?

Answer 23

• the fertilised egg becomes a zygote
• the zygote develops into an embryo
• the embryo embeds itself in the uterine lining
• the embryo secretes a hormone which prevents the corpus luteum from breaking down until a structure called a placenta is formed
• the corpus luteum continues to secrete progesterone and oestrogen until the placenta is able to is able to take over the production of progesterone and oestrogen

Question 24

what are the fertile and infertile periods of the menstrual cycle?

Answer 24

• after an egg is released from its ovary, it can survive for one to two days in the female reproductive system
• for a 28-day cycle, ovulation occurs around day 14
  > egg can survive approximately from 14-16
• during this time, it travels to the oviduct
• sperms can live for approximately three to four days in the female reproductive system
  > sperms released into the vagina on around day 11 can fertilise the ovum and bring about pregnancy
  > fertilisation is possible from around day 11 to day 16
  > FERTILE PERIOD

> rest of the days make up the infertile period

Question 25

what happens during mating or sexual intercourse?

Answer 25

• when a male becomes sexually stimulated or aroused
  > blood is pumped into the penis faster than it can return to the bloodstream via the veins
  > hence, blood fills the spaces in the spongy tissue of the penis
• this causes the penis to become stiff and erect to allow it to enter the vagina of a female
  > known as mating, COPULATION or SEXUAL INTERCOURSE
• semen containing the sperms is ejaculated into the vagina
  > along with a liquid made by the male seminal vesicles and prostate gland
• the sperms are able to swim up the oviducts of the female in this liquid
  > the chemicals in this liquid also make the sperm tails beat to propel the sperms along the oviducts
  > if sperm meets an egg in the oviduct, fertilisation may occur
• millions of sperms are released into the vagina during one ejaculation
  > only one of them will fertilise the egg

Question 26

what happens during fertilisation?

Answer 26

• the egg released from the ovary is usually surrounded by a few layers of follicle cells
  > to penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes
• only one sperm nucleus enters the egg
  > the haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed
• as soon as the sperm has entered the egg, the membrane of the egg changes
  > so that no other sperms can enter
• the remaining sperms, which do not fertilise the egg, eventually die

Question 27

what happens during implantation?
(development of the embryo)

Answer 27

• the cilia lining the inner surface of the oviduct sweep the fertilised egg (zygote) along the oviduct
  > the peristaltic movements in the wall of the oviduct also help move the zygote to the uterus
• the zygote divides by mitosis to form a ball of cells called the embryo
  > takes about 5 days for the embryo to reach the uterus
  > the embryo may float freely in the uterus for about two days
• eventually, the embryo becomes embedded in the uterine lining
  > implantation
  > which occurs about seven days after fertilisation

Question 28

what happens after implantation?

Answer 28

the development of the placenta

• after implantation, finger-like projections called villi begin to grow from the embryo into the uterine lining
  > they contain blood capillaries of the embryo
• the villi and the uterine lining in which the villi are embedded
  > make up the PLACENTA
  > the placenta formed partly from EMBRYONIC TISSUE and partly from the uterine lining
• a tube known as the unbilical cord attaches the embryo to the placenta

Question 29

describe the development of the amniotic sac

Answer 29

• a membrane called the AMNIOTIC SAC or AMNION begins to develop at about the same time as the placenta
  > the amniotic sac encloses the embryo in a fluid-filled space known as the amniotic cavity
  > the fluid is called the amniotic fluid

Question 30

why is the fetal blood system not continuous with the mother’s blood system?

Answer 30

• the blood pressure of the mother would kill the fetus as it is much higher than that of the fetus
• the blood group of the fetus may not be the same as the mother’s
  > if the fetus and the mother have different blood groups and the two blood systems were mixed
  > antibodies in the mother’s blood may cause the fetal blood cells to agglutinate
  > dangerous for both the mother and the fetus

Question 31

what are the functions of the placenta?

Answer 31

• allows oxygen and dissolved food substances to diffuse from the mother’s blood into the fetal blood
  > eg: glucose, amino acids and mineral salts
• it allows metabolic waste or excretory products to diffuse from the fetus’s blood into the mother’s blood
  > eg. urea and carbon dioxide
• allows protective antibodies to diffuse from the mother’s blood into the fetal blood
  > antibodies protect the fetus against certain diseases such as German measles
• it produces progesterone which maintains the uterine lining in a healthy state during pregnancy

Question 32

what are the functions of the unbilical cord?

Answer 32

the unbilical cord attaches the fetus to the placenta
> contains the blood vessels of the fetus

• two umbilical arteries
  > transport deoxygenated blood and metabolic waste products from the fetus to the placenta
• one umbilical vein which transports oxygenated blood and food substances from the placenta to the fetus

Question 33

what are the functions of the amniotic fluid?

Answer 33

amniotic sac encloses the fetus in the amniotic cavity
> contains amniotic fluid

functions of amniotic fluid:
- it supports and cushions the fetus before birth

• a shock absorber
• it cannot be compressed
  > it protects the fetus against physical injury
• allows the fetus a certain degree of movement
  > promotes muscular development
• during birth, it lubricates and reduces friction in the vagina or the birth canal

Question 34

what are sexually transmitted infections and what are they caused by?

Answer 34

a disease that may be transmitted through sexual intercourse is called an STI
> can result in irreversible physical damage or even death

STI are caused by bacteria or viruses
> the bacteria or viruses carried in the bloodstream of the infected person may be transmitted to an uninfected person:

• through semen when it comes into contact with mucous membrane in the vagina
• though fluid in the vagina when it comes into contact with mucuous membrane of the urethra
• when blood from an infected person gets into the bloodstream of an uninfected person

Question 35

what is AIDS?

Answer 35

• acquired immune deficiency syndrome (AIDS)
  > caused by a virus called Human Immunodeficiency Virus (HIV)
  > AIDS refers to the most advanced stages of HIV
  > HIV destroys the body’s immune system which protects a person against infection
• normally when foreign particles such as bacteria and virus enter bloodstream
  > white blood cells ( lymphocytes) can identify them
  > lymphocytes are stimulated to produce antibodies to destroy bacteria and viruses
  > immune system protects our bodies against many diseases

-HIV destroys a person’s immune system by destroying lymphocytes
> body unable to produce sufficient antibodies to protect the person against many other diseases
> infections which are normally mild may prove to be fatal to a person with AIDS

Question 36

what are the signs and symptoms of AIDS?

Answer 36

can take months to years before HIV develops into AIDS
- chronic or persistent fever
- severe diarrhoea lasting for months
-pneumonia
- cancer of the blood vessels ( Kaposi’s sarcoma)
- brain infection
- widespread tuberculosis (lung disease) affecting many organs at the same time

> called a syndrome cuz many symptoms occur at the same time
victims usually die within 2 years

Question 37

what are the modes of transmission of STI?

Answer 37

• sexual intercourse with an infected person
• sharing hypodermic needles with an infected person
  > tattooing, acupuncture
• blood transfusion with blood from an infected person
• during pregnancy, virus may pass from infected mother to the fetus

Question 38

what are the modes of transmission of STI?

Answer 38

• sexual intercourse with an infected person
• sharing hypodermic needles with an infected person
  > tattooing, acupuncture
• blood transfusion with blood from an infected person
• during pregnancy, virus may pass from infected mother to the fetus

Question 39

what are some prevention and control measures against STIs?

Answer 39

• keep to one sex partner or NO SEX
• males wear a condom
• do not abuse drugs
  > drug addicts tend to share needles
• do not share instruments that are likely to break the skin and be contaminated with blood
  > toothbrush and razors
• go to reliable operators for acupuncture, ear-piercing or tattooing
  > make sure needles are sterilised or insist on using disposable instruments