Human Reproduction Flashcards
What makes up the reproductive organs?
- primary sex organs
- ducts
- accessory glands
- external genitalia
What are the primary sex organs in male reproductive organs?
- the testis
What are the ducts in male reproductive organs?
- epididymis
- sperm duct (vas deferens)
- urethra
What are the accessory glands in male reproductive organs?
- prostate gland
What is the external genitalia in male reproductive organs?
- the penis
What does the scrotum contain?
- the scrotum contains the testis
What are the functions of the scrotum?
- The scrotum acts as a temperature regulator
- The scrotum houses and protects the testis
At what temperature does the scrotum keep the testis?
- 2 to 3 degrees Celsius lower than body temperature
Why is temperature regulation of the testis necessary?
- the lower temperature is necessary for the formation of fertile sperm
What happens to the testis in cold conditions?
- the testis are pulled closer to the abdomen for warmth
What happens to the testis in warm weather?
- the testis are suspended well away from the body
What are the testis?
- two oval structures that are suspended outside the body in the scrotum
Where are the testis in the embryonic stage?
- the testis are in the abdominal cavity just below the kidneys
When do the testis descend into the scrotum?
- before birth
What to the testis consist of?
- many compartments/lobules
- which contain highly convoluted tubules
What are the highly convoluted tubules contained by the lobules in the testis called?
- the seminiferous tubules
How long are the seminiferous tubules?
- they total about 250 metres in each testis
What lines the tubules in the lobules of the testis?
- germinal epithelium
What lies between the tubules in the lobules of the testis?
- groups of endocrine cells
What are the endocrine cells that lie between the tubules in the lobules of the testis called?
- interstitial cells/cells of Leydig
What do the testis produce?
- Sperm (male gametes) by the germinal layer
- Testosterone (a male hormone) by the interstitial cells
What are the ducts included in the male reproductive organs?
- epididymis
- sperm duct (vas deferens)
- urethra
What is the epididymis?
- a highly convoluted tubule
- about 5 metres long
How is the epididymis formed?
- the seminiferous tubules join to form the epididymis
What are the functions of the epididymis?
Immature sperm enter the epididymis where they:
1. mature, to become motile and fertile
2. are stored for several months
What happens if sperm cells stay in the epididymis for too long?
- they are broken down by the epithelial cells of the epididymis
- re-absorbed into the body
What is the sperm duct (vas deferens)?
- a muscular continuation of the epididymis
Where does the sperm duct (vas deferens) lead?
- it leaves the scrotum
- passes through the prostate gland
- then enters the urethra
What is the function of the sperm duct (vas deferens)?
- the sperm duct pushes mature sperm forward through ejaculation
What is ejaculation?
- when the mature sperm are pushed forward by strong peristaltic waves
- from the epididymis into the urethra
What is a peristaltic wave?
- a strong contraction of smooth muscle in the walls of ducts
What is the urethra?
- the duct at the end of the uro-genital system leading to the exterior
What is the function of the urethra?
- forms a common duct for the transportation of semen and urine
What is the prostate gland?
- a plum-sized gland
- surrounds the urethra at the base of the bladder
What may happen to the prostate with age?
- it may enlarge, exerting pressure on the urethra
- which slows down the emptying of the bladder
What is the function of the prostate gland?
- secretes a fluid
What is the function of the fluid secreted by the prostate gland?
- aids the transport of the sperm
- contains enzymes that make sperm more active
- (this fluid makes up about 1/3 of the seminal fluid)
Where are the Cowper’s glands located?
- at the base of the penis
How many Cowper’s glands does a male typically have?
- 2
What do the Cowper’s glands produce?
- an alkaline mucous-like fluid
When do the Cowper’s gland produce fluid?
- when sexually aroused
What are the functions of the fluid produced by the Cowper’s glands?
- Neutralizes acidic urine that may still be present in the urethra
- Lubricates the urethra and external urethral opening
Why does the fluid produced by the Cowper’s gland need to lubricate the urethra and external urethral opening?
- to protect sperm from mechanical damage during ejaculation
What passes down the penis?
- the urethra
What does the penis consist of?
- special spongy tissue (erectile tissue)
What is there running the length of the penis?
- three sections of erectile tissue
Where are the sections of erectile tissue situated?
- two sections are situated on the dorsal side
- one section is situated on the ventral side
Which sections of erectile tissue are situated on the dorsal side of the penis?
- the corpus cavernosa
Which section of erectile tissue is situated on the ventral side of the penis?
- the corpus spongiosum
What is the primary mechanism that brings about an erection?
- the dilations of dorsal and central arteries supplying blood to the penis
How does the dilation of the dorsal and central arteries supplying blood to the penis bring about an erection?
- the dilation allows more blood to fill the three spongy erectile tissue chambers
- causing the penis to lengthen and stiffen
What is unable to occur without an erection?
- without an erection, sperm cannot be transferred to the female’s vagina during sexual intercourse
What is the function of the penis?
- to deposit semen with sperm into the female’s vagina during copulation
What is distinctive about the human penis in terms of the erectile bone?
- the human male is the only mammal that has no erectile bone in the penis
- it relies entirely on engorgement with blood to reach its erect state
What is distinctive about the human penis in terms of attachment to the abdominal wall?
- the human penis is not attached to the abdominal wall but hangs free
- this is in contrast to most other mammals, where the penis is stored internally until erect
What is the erectile bone found in other mammals known as?
- the baculum
What does semen consist of?
- sperm from the testis
- seminal fluid from the sperm duct and accessory glands (e.g. prostate)
What is the average volume of semen for an ejaculation?
- 2,5 to 5ml
What is the average number of sperm ejaculated per ml?
- 50 to 150 million per ml
- i.e. 700 million per ejaculation
When is semen considered infertile?
- when it has a sperm count of less than 20 million per ml
What is the difference between an erection and ejaculation?
- an erection is the stiffening of the penis
- ejaculation is the expulsion of semen
What are the female reproductive organs?
- ovaries
- accessory organs
- external genitalia
What are the accessory organs in the female reproductive system?
- fallopian tubes (oviduct)
- uterus
- vagina
What is the external genitalia in the female reproductive system?
- the vulva
What are the ovaries?
- 2 almond shaped organs
- found in the pelvic cavity
- and held in position by ligaments
What surrounds each ovary?
- a layer of germinal epithelium
What are embedded in the outer layer of the ovaries?
- primary follicles
What are primary follicles?
- tiny sac-like structures
- containing an immature egg
When is the total number of eggs carried by a female determined and why?
- at birth
- because females are born with all of their primary follicles
What does a primary follicle develop into?
- a mature follicle
What is a mature follicle called?
- a Graafian follicle
When does the Graafian follicle form the corpus luteum?
- after ovulation (the release of an egg)
What are the functions of the ovaries?
- To form and release eggs
- To produce oestrogen and progesterone
How many fallopian tubes are there?
- 2
What are the fallopian tubes?
- muscular tubes lined with cilia
Where are the fallopian tubes situated?
- they stretch from each ovary to the uterus
What does each fallopian tube end in?
- a funnel shaped structure
What is the funnel shaped structure at the end of each fallopian tube called?
- the infundibulum
What do the infundibulum have?
- finger-like outgrowths
- called fimbria
What are the functions of the fallopian tubes?
- Provide a pathway between uterus and ovary for eggs, sperm and the zygote
- Are the site of fertilisation and initial cell division of the zygote
- Enable the egg or developing zygote to move towards uterus (by the action of muscles and cilia)
What are the physical characteristics of the uterus?
- hollow
- pear-shaped
- thick-walled
- muscular
Where is the uterus situated?
- between the bladder and the rectum
What happens to the uterus during and after pregnancy?
- during pregnancy it enlarges considerably
- soon after birth it almost returns to its original size
What is the lower part of the uterus called?
- the cervix
Where does the cervix go?
- it projects into the vagina
How large is the opening of the cervix normally?
- normally only millimetres in diameter
Why does the cervix have an opening (aside from to birth a child)?
- to allow menstrual blood to leave the body
- and sperm to gain access
What keeps the uterus closed during pregnancy and why?
- the sphincter muscles of the cervix
- to prevent a miscarriage
What does the uterine wall consist of?
- myometrium
- endometrium
What is the myometrium?
- a thick, involuntary muscle layer of the uterine wall
What is the endometrium?
- a lining of the uterine wall that is richly supplied with blood vessels
Why do the walls of the uterus need to be thick?
- so that it can stretch when a baby develops inside it
What happens to the endometrium at ovulation?
- progesterone causes the endometrium to thicken
- to prepare for the implantation of the blastocyst
What happens to the endometrium if fertilisation does not occur?
- the upper layer of the endometrium becomes detached
- and is passed out together with the unfertilised egg
- (menstruation)
What are the functions of the uterus?
- The uterus is the organ in which the blastocyst implants, develops and grows
- The contraction of the myometrium enables the baby to be pushed out during birth
What does the myometrium do?
- contracts to enable the baby to be pushed out during birth
What is the vagina/birth canal?
- a muscular passage between the uterus and the outside of the body
What are the physical characteristics of the vagina?
- it has very elastic, folded walls
What is the significance of the elastic, folded walls of the vagina?
- this allows the vagina to stretch during intercourse and childbirth
What is the pH of the vagina like and why?
- normally quite acidic
- which helps keeps the vagina healthy and free from infection
What are the functions of the vagina?
- Is the place where sperm are deposited during sexual intercourse
- Forms a birth canal during birth
What is the vulva?
- the vulva forms the external genitalia
What is the role of the vulva in the reproductive process?
- it plays no role in the reproductive process
What is the clitoris?
- a small mass of erectile tissue
Where is the clitoris found?
- at the anterior end of the vulva
What is the clitoris the female counterpart of?
- it is the female counterpart of the penis
What does the clitoris play a role in?
- in the sexual excitement of the female
What is puberty?
- the process of physical and physiological changes catalysed by the release of gonadotropins
What does puberty lead to?
- the development of secondary sex characteristics
- an immature individual (child) becoming capable of reproduction
What affects the age at which puberty begins?
- genetic factors
When does puberty typically occur?
- in girls: between 11 and 14
- in boys: between 14 and 16
How does climate affect puberty?
- puberty can start earlier in warmer climates
- puberty can start one or two years later in colder climates
What is adolescence?
- the period of physical, physiological and psychological change
- that extends from the start of puberty until the age of 17 to 20 in females and 18 to 21 in males
How does puberty start?
- the pituitary gland, under stimulation from the hypothalamus, releases gonadotropins which initiate puberty
What are gonadotropins?
- hormones that stimulate the gonads
What is the gonadotropin in males?
- interstitial-cell-stimulating hormone (ICSH)
What does interstitial-cell-stimulating hormone (ICSH) do?
- stimulates the testis to secrete testosterone
What is the gonadotropin in females?
- follicle-stimulating hormone (FSH)
What does follicle-stimulating hormone (FSH) do?
- stimulates the ovaries to produce oestrogen
What does the release of testosterone and oestrogen do?
- initiate changes to the gonads and to other parts of the body
What are the results of changes to the gonads called and why?
- these result in primary sexual characteristics
- as they influence the process of reproduction
What are the other physical changes aside from the changes to the gonads called and why?
- secondary sexual characteristics
- as they have nothing to do with the actual reproductive process
What physical changes occur in girls during puberty regarding breast tissue?
- breast development occurs
- normally the first sign of puberty
What physical changes occur in girls during puberty regarding hair?
- growth of hair in the pubic area and armpits
- often the second noticeable change
What physical changes occur in girls during puberty regarding their reproductive organs?
- increase in size of uterus, ovaries and the primary follicles
What physical changes occur in girls during puberty regarding bone structure?
- widening of pelvis (and thus the hips)
- to provide a wider birth canal
What physical changes occur in girls during puberty regarding fat deposition?
- deposition of fat on hips, thighs, upper arms and buttocks
What physical changes occur in girls during puberty regarding menstruation?
- start of the 28-day menstrual cycle
- average age of starting is between 12 and 18
What is the first menstrual bleeding known as?
- menarche
What physical changes occur in girls during puberty regarding ovulation?
- ovulation begins
- (which in about 80% of girls only occurs after the first year of menstruating)
What physical changes occur in girls during puberty regarding physical growth?
- growth spurt lasting two to three years occurs
What physical changes occur in girls during puberty regarding skin?
- possible acne, as skin gets oilier
What physical changes occur in boys during puberty regarding the testis and penis?
- enlargement of testis and penis
- usually the first sign of puberty
When is the maximum size of the testis and penis reached?
- about 6 years after the onset of puberty
What physical changes occur in boys during puberty regarding hair growth?
- hair growth in the pubic area and armpits
- at about 13 to 14 years
- (facial hair only grows later)
What physical changes occur in boys during puberty regarding their voices?
- increase in size of larynx (voice box)
- thickening of vocal cords
- causing the voice to deepen
What physical changes occur in boys during puberty regarding physical structure?
- enlargement of skeletal muscles
- broadening of shoulders
What physical changes occur in boys during puberty regarding sperm?
- sperm production begins
What physical changes occur in boys during puberty regarding growth?
- growth spurt of two to three years
What physical changes occur in boys during puberty regarding skin?
- acne can occur
- more common in boys than girls
What is distinctive about human males in terms of fertility?
- human males are sexually fertile all the time
- males of most mammalian species are not
What is distinctive about humans regarding menstruation?
- menstruation is unique to humans and close primate relatives such as chimpanzees
How does menstruation differ in females of other placental mammal species?
- they do not menstruate as they have oestrous cycles
- in which the animal reabsorbs the endometrium if fertilisation does not occur during that cycle
What does ‘oestrous’ mean?
- a time when females ovulate and can be impregnated
What is distinctive about humans in terms of mating?
- mating is not confined to the period when ovulation occurs
- this mating is designed to reinforce pair-bonding; which is especially necessary where care of the young is prolonged as in humans
What are nocturnal emissions and in whom do they occur?
- nocturnal emissions are ‘wet dreams’
- occur in celibate males
What does ‘celibate’ mean?
- abstaining from sex
What is gametogenesis?
- the formation of mature gametes by the reproductive glands (gonads)
What are gametes?
- sperm and eggs
What does gametogenesis involve?
- meiosis
- a nuclear division which results in a halving of the number of chromosomes: from 46 (in body cells) to 23 (in gametes)
Why does meiosis occur?
- to ensure that in fertilisation, the number of chromosomes returns to 46 in the zygote
What is a zygote?
- a fertilised egg
What is spermatogenesis?
- the sequence of events during which mature, haploid sperm are produced
- from the germinal epithelium in the seminiferous tubules of the testis
What hormone is essential for the making of sperm?
- testosterone
When does spermatogenesis occur?
- it begins at puberty and continues throughout life
What happens to the immature sperm in spermatogenesis?
- immature sperm are moved into the epididymis
- where they mature
- becoming motile and fertile
What is the summarised process of spermatogenesis?
- diploid cells in the seminiferous tubules of the testis undergo meiosis
- to form haploid sperm cells
What are the 4 main parts of a sperm?
- head
- neck
- body
- tail
What does the head of a sperm contain?
- acrosome
- nucleus
What is the purpose of the nucleus in the head of the sperm?
- contains haploid set of chromosomes
- which contains genetic material of the male
What is the purpose of the acrosome in the head of the sperm?
- contains hydrolytic enzymes
- to digest outer layers surrounding egg cell
- allow sperm to penetrate
What is found in the body of the sperm?
- mitochondria
What is the purpose of the mitochondria in the body of a sperm?
- provides energy for movements of tail
What is found in the tail of a sperm?
- contractile fibres
What is the purpose of the contractile fibres found in the tail of a sperm?
- responsible for whip-like movements of tail
What is the typical length of a sperm?
- 0,05mm
How long can sperm survive in the female reproductive tract once ejaculated?
- about 48 hours
How is it possible for the sperm to survive in the female reproductive tract?
- the sperm obtains nourishment from seminal fluid and female secretions
What is oogenesis?
- the production of haploid, mature eggs
- in the follicles of the ovaries
What is the difference between spermatogenesis and oogenesis in terms of the number of sperm/eggs?
- in oogenesis, the number of eggs is determined before birth
- whereas sperm are formed after puberty
How are oogonia produced?
- by mitosis
- and growth from the germ cells of the germinal epithelium before birth
What is the difference between spermatogenesis and oogenesis in terms of mature eggs and sperm?
- mature sperm are formed continuously throughout life
- mature eggs are form once puberty starts until menopause
What is the difference between spermatogenesis and oogenesis in terms of cycles?
- oogenesis occurs in a monthly cycle
- sperm are produced daily
What is ovulation?
- the release of a mature egg from a Graafian follicle in the ovary
- every 28 days
What is the summarised process of oogenesis?
- diploid cells in the ovary undergo meiosis
- to form a primary follicle consisting of haploid cells
- once cell develops into an ovum contained in a Graafian follicle
What is the range of time of the menstrual cycle in human women?
- 21 to 35 days
- 28 days on average
What cycles make up the menstrual cycle?
- the ovarian cycle
- the uterine cycle
What are the uterine and ovarian cycles controlled by?
- by the endocrine system
When do the uterine and ovarian cycles occur?
- from puberty until menopause