Draw and label the human male reproductive system
ii) Describe how the mammalian male reproductive system is adapted to perform its functions
Penis
- is highly vascularised/spongy
- has a sensitive glands
- becomes erect to allow entry into the vagina
Scrotum
- contains the testes outside the body on whose walls the process of spermatogenesis takes place
- the process is favored by lower temperature
- it contains sertoli cells which nourish sperms until they are mature
Epididymis
- long and coiled for the purpose of sperm storage
Vas deferens
- muscular
- upon contraction pushes sperms out and allows ejaculation
Gametes
- produced in large numbers to increase chances of fertilization
- the sperms have a tail for swimming/large number of mitochondria to provide energy/allow swimming to reach the egg
Accessory glands
- are seminal vesicle, Cowper’s gland and prostate gland
- they produce seminal fluid to provide a medium/ nutrients for sperms to swim
iii) How is the sperm adapted to perform its function?
- acrosomes contain enzymes to digest egg membrane
- nucleus contains genetic material
- mitochondria produce energy to move the tail back and forth
- the lashing movement of the tail enables the sperm to move/propulsion in fluid medium towards the egg
- it is streamlined for faster/easier movement/swimming to meet the egg
c) i) Draw and label the human female reproductive system
ii) Describe how the various structures of the human female reproductive system are adapted to their function
Ovaries
- have several graafian follicles that develop and burst open to release/produce mature ova
- secretes sex hormones)oestrogen) which initiate/control development of secondary sexual characteristics
- produce hormones oestrogen and progesterone which prepare the uterus for implantation and subsequent nourishment of the embryo
Oviducts (fallopian tube)
- are thin narrow and tubular to increase flowing speed of semen containing sperms
- are funnel shaped on the end next to ovary which enables them to receive the ovum
- their lining contains cilia which propel the ovum towards the uterus
- has peristaltic muscles that enable movement of zygote/ovum to the uterus for implantation
- is fairly long to increase surface area for fertilization
Uterus
- is muscular for protection of developing embryo
- has elastic wall that allows growth and development of foetus/embryo
- has a highly vascularised endometrium that provides nutrients/gaseous exchange to developing embryo
Cervix
- has valves that close the lower end of the uterus to ensure continued pregnancy during gestation period
- is capable of dilating
- has narrow entrance/neck-like entrance to uterus that enables quick swimming of sperms to uterus
- has suction mechanism that draws up/pulls sperms into uterus
- has a “W” shape that fits well with the glands of the penis to ensure sperms are deposited at the right point
Vagina
- is elastic and muscular to enable good accommodation or penetration of the penis thus proper deposition of sperms and for easy parturition
- allows menstrual flow
- has sensitive labial walls which secrete/produce lubricating substances that ensure/enable/facilitate good coition
- capable of considerable enlargement, due to elastic muscles, to accommodate baby during parturition
Clitoris
- has sensitive cells for orgasm
iii) Explain how the ovum is adapted to its function
- nucleus contains genetic material
- ventelline membrane encloses plasma membrane which encloses yolky cytoplasm
- yolky cytoplasm provides nourishment
- jelly coat protects ovum against dehydration
iv) Explain the differences between sperm and ovum
| Sperm | Ovum |
| long with a tail and head smalllocomotorystores little foodhas acrosome (tip with lytic enzymes)nucleus prominent but cytoplasm negligible | sphericallargestationarya lot of food stored in yolky cytoplasmlacks acrosomea lot of cytoplasm |
d) i) Explain the process of fertilization
- a process whereby the egg and sperm are brought together and fuse to form a zygote
- occurs in the fallopian tube after copulation
- sperm head penetrates the outer coat of the ovum while the tail remains outside
- penetration is due to reaction of acrosome
- acrosome digests the vitelline membrane
- thereafter a zygote is formed
- zygote which is diploid undergoes rapid cell division to form a mass of cells called blastocyst
- after fertilization a membrane forms around the ovum to prevent further entry of sperms
- blastocyst eventually develops into an embryo
i) Explain the process of implantation
- this is the embedding and attaching of the embryo in the uterine wall/endometrium
- implantation marks the beginning of pregnancy
- sometimes implantation occurs in the oviduct wall which is abnormal and results in ectopic pregnancy which is fatal
- the outer wall of the blastocyst develops fingerlike projections which project into the uterine wall for attachment
- the projections are called villi
- the villi and endometrium develop into an organ that is called the placenta
- the embryo is attached to the placenta through a cord called the umbilical cord
State the functions of umbilical cord
- it contains blood vessels umbilical artery, iliac arteries and umbilical veins)
- it joins the placenta to the embryo
- passage for nutrients from the mother
- passage of excretory substances from foetus to mother for final discharge
- gaseous exchange
- passage of antibodies from mother to foetus, for protection of foetus against diseases
iv) State the role of placenta
- exchange of gases between mother and foetus
- exchange of nutrients and nitrogenous wastes
- anchorage/attachment of foetus
- produces hormones (oestrogen and progesterone)
e) i) What is gestation period?
- time taken from fertilization to birth/pregnancy
ii) Explain the functions of the membranes associated with placenta
Chorion
- surrounds the embryo
- has fingerlike projections that attach embryo to the uterus
Amnion
- contains amniotic fluid
- fluid surrounds embryo
- protects embryo from mechanical injury by acting as shock absorbers
- fluid also protects embryo from dehydration
- distributes pressure equally over embryo
Yolk sac
- surround the yolk
- produces blood cells for embryo until its own liver is able to perform the task
Allantois
- present only for a short time
- removes and store waste material
- it eventually becomes the umbilical cord
iii) Explain the events that take place to facilitate parturition
- near birth the placenta produces less progesterone
- oxytocin hormone is produced by posterior lobe of pituitary gland
- because progesterone level has decreased the uterus becomes sensitive to oxytocin
- oxytocin causes the contraction of the uterus (myometrium)
- these contractions are called labour pains
- just before parturition the head turns downwards
- the contractions eventually push the baby through the vagina
- amnion breaks and amniotic fluid is released
- oxytocin dilates the cervix
- foetus is expelled through cervix with head coming out first
- finally the whole infant comes out
- the umbilical cord is cut and the placenta is expelled as afterbirth
iv) State the reasons why later in pregnancy the ovary will b e removed without disturbing the pregnancy
- corpus luteum in the ovary secretes progesterone which maintains pregnancy and development of foetus after conception
- after four months pregnancy is maintained by progesterone from the placenta
f) i) What are secondary sexual characteristics
– Characteristics (physiological and anatomical) that start developing at puberty due to the influence of male and female hormones
ii) State the main secondary changes in Boys
- deepening of the voice
- growth of hair on face, pubic part, chest, legs
- penis and testes become bigger
- muscular development
- sperm production begins at puberty and may continue throughout life
Girls
- growth of hair on pubic part and armpits
- widening/enlargement of hips
- development of breasts
- menstrual cycle starts as ovaries mature
- body acquires extra fat
iii) Describe the role of hormones in secondary sexual characteristics inBoys
Follicle stimulation hormone (FSH)
- from pituitary
- stimulates production of androgens(male hormones) mainly testosterone by testis
Testosterone
- secondary sexual characteristics
Girls
FHS
- from pituitary
- development of follicles
- stimulates oestrogen production by ovary
LH
- from pituitary
- ovulation
- stimulates release of progesterone by ovary
Oestrogen
- stimulates release of LH
- secondary sexual characteristics
Progesterone
- also from placenta
- sustains pregnancy as it inhibits prolactin and oxytocin during pregnancy
Prolactin
- milk formation
Oxytocin
- parturition
- milk ejection
g) i) What is menstruation?
– vaginal discharge due to disintegration of endometrium
ii) Describe the role of hormones in the human menstrual cycle
- it is controlled by sex hormones which are responsible for the onset of secondary sexual characteristics and also control of the menstrual cycle
- the onset is signaled by discharge of blood/menses 14 days following the start of menstruation
- anterior lobe of pituitary gland secretes follicle stimulating hormone(FSH)
- Follicle stimulating hormone causes graafian follicle to develop in the ovary. It also stimulates tissues of the ovary/wall (theca) to secrete oestrogen
- oestrogen causes repair/healing of uterine wall
- oestrogen stimulates anterior lobe of pituitary to produce luteinising hormonge (LH)
- LH causes ovulation. It also causes graafian follicle to change into corpus luteum. LH stimulates corpus luteum to secrete progesterone
- Progesterone causes proliferation/thickening of uterine wall
- Oesterogen/progesterone inhibits the production of FSH by anterior lobe of pituitary, thus no more follicles develop and oestrogen production reduces
- In the next two weeks progesterone level rises and inhibits production of LH from anterior lobe of pituitary
- The corpus lutetium stops secreting progesterone and menstruation occurs when the level of progesterone drops
- Anterior lobe of pituitary starts secreting FSH again.
iii) What is menopause?
- end of ovulation in women
- occurs after age of 45 years
- does not occur in males
