11: Human Reproduction L1-L5

Seminal vesicle

secretes a fluid that is rich in sugars and is the main component of semen

prostate gland

secretes an alkaline fluid that helps activate sperm

bulbo-urethral gland

secretes a fluid (pre-ejaculate) that becomes part of the semen

vas deferens

tube down which sperm travels to urethra and semen forms

urethra

tube that carries sperm and urine out of the body

epididymis

stores sperm while they finish maturing

testes

produces sperm and hormones

foreskin

covers the head of the end of the penis, may be removed by circumcision

scrotum

supports the tested outside of the body keeping them cooler for optimal sperm production

erectile tissue in penis

engorges with blood for the penis to become erect

structure of testicles

testes are responsible for making testosterone, the primary male sex hormone, and for generating sperm. Within the testes are lobed structures consisting of tightly coiled tubes called seminiferous tubules

sperm releasing pathway

• sperm is produced in the seminiferous tubules of the testes

• sperm travels from the epididymis through the vas deferens and then inti the urethra,

• On its journey through the vas deferences, the sperm receives secretions from glands to become semen.

making semen

• seminal vesicle: secretes a fluid that is rich in sugars and is the main component of semen.

• prostate gland: secretes an alkaline fluid that helps activate sperm

• bulbo-urethral gland: secretes a fluid that becomes part of the semen.

sperm (spermatozoa)

male sex cells (gametes) that carry a man’s genetic material.

spem structure

• head - contains nucleus which carries the 23 chromosomes

• acrosome - forms a cap over the head. contains enzymes which break down the follivle surrounding the ovum and permit fertllization.

• middle piece (collar) - contains mitochondria to provide power for the tail.

• tail - flagella. acts like a propeller.

semen

also known as seminal fluid, is a milky-clear fluid that may contain spermatozoa and other fluids.

Semen content

• spermatozoa (sperm)

• fluids to provide nutritional support and transport media.

semen content

• spermatozoa. 2-5%. male gamete. formed in testes, stored in epididymis

• seminal fluid. 60-75%. alkaline fluid - primarily responsible for nutritional support through amino acids, enzymes and fructose sugar.

• prostate fluid. 25-30%. secretes an alkaline fluid that helps activate sperm

• bulbo-urethral glands. 1-5% contribute to the final volume of semen by producing a lubricant mucous secretion.

spermatogenesis

the formation of spermatozoa in the testes.

the end result in males is four spermatids in which the cytoplasm has been evenly divided. Spermatids then mature into spermatozoa.

male reproductive system: hormones

• follicle stimulating hormone

  • in men, this hormone targets the cells of the seminiferous tubules and stimulate spermatogenesis

• luteinising hormone

  • in men, this hormone targets the interstitial cells of the testes and stimulate the production of male sex hormones (e.g. testosterone)

cross section of testes

• epididymis where sperm mature

• lobules of testes consisting of seminiferous tubules where spermatgenesis takes place (FSH)

cross-section of seminiferous tubules

• immature spermatids

• germ cells undergoing meiosis

• interstitial cells secrete testosterone

purpose of female reproductive system

designed to receive sperm and combine it with the ova that it produces.

once fertilisation is complete the female reproductive system then nurtures the zygote for 9 months and then gives birth

uterus

contains embryo/foetus during pregnancy

uterine/fallopian tube

carries eggs to uterus (1/2)

fimbriae

small finger-like projections on the outer, distal ends of the fallopian tubes that directs eggs into the fallopian tubes

ovary

produces eggs and hormones

cervix

opening to uterus

clitoris

contains erectile tissue

labia minora

not covered in hair, internal folds of skin at opening of vagina

labia majora

covered in hair, external folds of skin at opening of vagina

vagina

• around 10 cm long and receives the penis during sex

• can stretch considerably for childbrith; birth canal

• during menstruation blood will leave the body through it

• also has a slightly acidic environment and natural bacteria to stop infection

cervix

• lower end of the uterus that protrudes into the vagina

• can be cancerous

  • regular pap smears and HPV vaccines help prevent against

uterus (aka. womb)

• contains endometrium (uterine lining) which is shed and rebuilt through menstruation and holds the foetus suring pregnancy

endometriosis

disease that occurs when cells similar to those that line the uterus are found in other parts of the female body.

fallopian tubes

pair of tubes along which eggs travel from the ovaries to the uterus. fertilisation takes place here.

ovaries

• female gonads (organ that produces gametes)

• once a month, they produce the ova/egg. they also produce the female hormone oestrogen

• the ______ are also responsible for producing the female sex hormones oestrogen and progesterone.

spermatogenesis

produces male gametes (sperm)

where does spermatogenesis occur, and how many sperm are produced?

• occurs in the seminiferous tubules in testes

• involves meiosis, occurs throughout life after puberty

• may produce 400,000,000 per day.

outcome of spermatogenesis

primary spermatocyte divide equally to form two similar spermatocytes. one spermatogonium produces four functional spermatozoa.

oogenesis

produces female gametes (oocytes)

when and where does oogensis occur?

• occurs in the ovaries

• involves meiosis, occurs after puberty until menopause

• humans normally produce one oocyte during each ovarian cycle.

outcome of oogenesis

primary oocyte divide unequally to form one large secondary oocyte and a small polar body. An oogonium produces one functional ovum and three non-functional polar bodies.

ovarian cycle

recurring series of events that take place within the ovary of a non-pregnant female, associated with the maturation of an egg.

duration of the ovarian cycle

ranges between 20-40 days (avg. 28 days)

oocyte

immature egg (gamete)

a cell in an ovary which may undergo meiotic division to form an ovum (egg)

ovum

mature egg that is ready to fuse with the male gamete.

ovarian cycle from birth

• the ovaries of a human female contain about 400,000 immature eggs (oocytes)

• other cells within the ovary surround each immature egg to produce a sphere composed of a single layer of cells

• the immature eggs remain in a resting phase for many years (dormant or primary follicle)

primary follicle

immature follicle consisting of an oocyte (egg) surrounded by a single layer of tall, supporting granulose cells.
- usually takes 10-14 days for a ___________ to develop into a mature follicle

from puberty (ovarian cycle)

several primary follicles may commence development to become secondary follicles in each ovarian cycle.

usually only one completes development to become a mature follicle.

secondary follicle

a maturing ovarian follicle consisting of an oocyte surrounded by two or more layers of tall, supporting granulosa cells.

mature (graafian) follicle

similar in appearance to the secondary follicle, but it is larger and contains more fluid

• located near surface of ovary ready for ovulation.

ovulation

release of ovum from the follicle

• occurs about day 14 of the ovarian cycle

• egg is gradually swept down the uterine tube towards the uterus by cilia.

after ovulation

ruptured follicle collapses and corpus luteum is formed.

corpus luteum

acts as a temporary endocrine gland - secretes hormones (oestrogen and progesterone) that influence the development of the lining of the uterus.

end of ovarian cycle. option 1: no fertilisation

corpus albicans: degenerated corpus luteum (fibrous scar tissue mass) - formed 8-10 days after ovulation if egg has not been fertilised

end of ovarian cycle. option 2: fertlisation

corpus luteum continues to develop (for three months into pregnancy) and then slowly degenerates ovarian cycle ceases - resumes after mother is no longer breast feeding.

ovum development

before birth, all of a female’s primary oocytes have already formed. Maturation of these cells are “paused” in PROPHASE I and do not continue their maturation until puberty.

hormones if fertilisation occurs

HCG is released (by zygote itself) which maintains the corpus luteum. This leads to the maintainede levels of high progesterone. Which in turn maintains the lining of the endometrium for implantation.

follicle stimulating hormone

• secreted by the pituitary gland

• stimulates the growth of ovarian follicles in female mammals

luteinising hormone

• secreted by the pituitary gland. In females, an acute rise of ______ triggers ovulation and development of the corpus luteum.

oestrogen

• developing follicles produce small amounts of _______ and progesterone. rising levels of _______ reach a point that causes a rapid rise in LH. More _____ is produced by corpus luteum.

Progesterone

after ovulation, corpus luteum produces ______.

Menstruation

the periodic discharge of blood and tissue due to the breakdown of the lining of the uterus

menarche

when menstruation first begins (first period)

menopause

menstrual cycle becomes irregular over a series of years before eventually ceasing (45-55y/o)

menstrual cycle

the lining of the uterus becomes thicker with more blood vessels during the menstrual cycle.

these changes occur in preparation for fertilization and a developing embryo

a fertilised egg will bury itself (implant) in the uterus lining. The egg needs a plentiful supply of oxygen and nutrients to develop.

menstrual cycle: menstruation

time span: day 1-4

events: uterine bleeding, accompanied by shedding of the endometrium

menstrual cycle: preovulation

time span: day 5-12

events: endometrial repair begins; development of ovarian follicle; uterine lining gradually thickens

menstrual cycle: ovulation

time span: days 13-15

events: rupture of mature follicle, releasing egg

menstrual cycle: secretion

time span: days 16-20

events: secretion of watery mucus by glands of endometrium, cervix and uterine tubes; movement and breakdown of unfertilised egg; development of corpus luteum

menstrual cycle: premenstruation

time span: days 21-28

events: degeneration of corpus lutuem; deterioration of endometrium.

menses

start of menstrual cycle

menses and proliferation phase

• oestrogen and progesterone levels are low

• these low levels signal the pituitary gland to produce follicle stimulating hormone, which stimulates the maturation of a follicle.

ovulation phase

• follicle produces increasing amounts of oestrogen.

• around day 12-14, increased oestrogen levels trigger a sharp rise in luteinising hormone from the pituitary gland, causing release of the egg from the follicle.

secretory and pre-menstrual phase

• the ruptured follicle (corpus lutuem) now secretes progesterone and oestrogen to continue to prepare the uterus for pregnancy

• if the egg is not fertilised, oestrogen and progesterone levels drop and, on day 28, the menses begins again.

oestrogen in the menstrual cycle

• levels are low at Day 1 of cycle and slowly increase due to follicle development: stimulates regrowth of the endometrium

• rising levels of oestrogen reach a point that causes a rapid rise in LH resulting in ovulation.

• more oestrogen is produced by corpus luteum to help maintain uterine lining.

progesterone in the menstrual cycle

• levels low at day 1 of cycle, through to ovulation

• after ovulation, produced by corpus luteum; maintains endometrium