WEEK 12 - REPRODUCTIVE SYSTEM

Question 1

The Reproductive System

Answer 1

The reproductive system is vital to procreation (‘breeding’).
As a part of sexual intercourse, sperm is delivered from the male to the female.
If fertilisation of the ovum (egg) with the sperm occurs inside the fallopian tube, it will develop into a fetus (in the uterus), which will be born as an infant 9 months later.

Question 2

FEMALE REPRODUCTIVE SYSTEM

Answer 2

Manufactures gametes (oogenesis)
Reception and transport of sperm from the male
Houses fertilised ovum and maintains pregnancy
Hormone production: oestrogen and progesterone
Lactation (secretion of milk by the mammary glands of breasts).

Question 3

MALE REPRODUCTIVE SYSTEM

Answer 3

Manufactures gametes (spermatogenesis) and deliver these to the female
Hormone production: testosterone

Question 4

What are gonads?

Answer 4

GONADS: an organ that produces gametes (sex cells) - the testes or ovaries

Question 5

MALE EXTERNAL ANATOMY

Answer 5

SCROTUM
Sac of skin containing the testes, that hang outside the body. The temperature is cooler here which is important for sperm production and survival.
Note: Tight underwear is discouraged as it brings the testicles closer to the body, raising the temperature inside the scrotum which may be unsuitable for spermatogenesis.
TESTES (plural)
Contained within scrotum
Site of spermatogenesis (formation of sperm)
PENIS
Delivery of sperm into vagina

Question 6

PENIS

Answer 6

Sperm delivery to vagina
3 regions:
Root (attached)
Shaft
Glans (enlarged tip)
Contains urethra: pathway for semen and urine
Two chambers called the corpus spongiosum and corpus cavernosa: they run the length of the penis, which contain a maze of vessels shaped like a sponge - for engorgement & erection.

Question 7

TESTES

Answer 7

A pair of glandular organs (4 cm long x 2.5 cm wide) that are responsible for the production of sperm cells and the sex hormone testosterone.
Homologous to the female ovaries.
Each testis is divided into 250 lobules containing seminiferous tubules. These are surrounded by myoid cells (smooth muscle cells) to squeeze sperm out of the testes.

Question 8

TESTES cont.

Answer 8

Seminiferous tubule (spermatogenesis)
↓
Straight tubule
↓
Rete testes
↓
Epididymis
(sperm mature here & are stored until ejaculation)

Question 9

Male Duct System

Answer 9

Epididymis
Contains 6 metres of coiled duct
20 days for sperm to move through
Sperm ejaculated from epididymis, not testes
Sperm can be stored for months

Ductus Deferens (Vas Deferens)
45 cm long
Smooth muscle walls to propel sperm

Urethra
Terminal portion of duct system
Conveys both urine and sperm
3 regions: prostatic, membranous, spongy

Question 10

Semen

Answer 10

Mixture of sperm, testicular fluid and accessory gland secretions.
Contains nutrients and chemicals to protect, activate and facilitate sperm movement.
Contains prostaglandins to reduce viscosity of cervical mucus in female and facilitate entry of sperm into uterus.
Has an alkaline pH to neutralise acidic environment of female reproductive tract.
Can suppress immune response of female reproductive tract.
Coagulation factors to allow for adherence to vaginal walls.
2 - 5 ml with each ejaculation (released from penis at orgasm - sexual climax), but only 2 - 10% sperm.

Question 11

Structures for semen production

Answer 11

Seminal Vesicles
Contains and secretes substances to enhance sperm motility & fertility (70% of volume of semen from here).
Prostate Gland
Size of a peach pip, surrounds urethra
Secretions suspend and nourish sperm (30% of semen volume from here).
Smooth muscle to aid ejaculation
Bulbourethral Glands

Question 12

SPERMATOGENESIS

Answer 12

Sequence of events for sperm production within seminiferous tubules.
Begins around age 14 and continues throughout life.
400 million of new sperm produced daily.
Each sperm (spermatozoa) contains 23 chromosomes (half the genetic material = haploid) due to a process called meiosis.
During fertilisation, male and female gametes fuse to produce a diploid (paired chromosomes) ‘zygote’.

Question 13

MALE SEXUAL RESPONSE: ERECTION

Answer 13

ERECTION
Erection begins with signals sent from your brain or via a parasympathetic spinal reflex which triggers release of the neurotransmitter nitric oxide (NO), causing DILATION of penile arterioles.
The erectile tissue becomes engorged with blood leading to erection.
The urethra remains open for semen release (important).
When not aroused, penile arterioles are constricted.
To maintain erection, both parasympathetic reflex and psychogenic factors must function together.

POINT (erection - under Parasympathetic control)

Question 14

MALE SEXUAL RESPONSE: EJACULATION

Answer 14

Under the control of the sympathetic spinal reflex
3 stages:
Bladder sphincter muscle constricts - prevents expulsion of urine.
Contraction of smooth muscle of accessory glands and ducts to expel seminal fluid with sperm (semen).
Semen detected in the urethra stimulates penile muscles at the base of the penis to rapidly contract (every 0.8 seconds) to propel semen out of penis.
Followed by a ‘resolution phase’ (physiological relaxation) and a refractory period

SHOOT (ejaculation - under Sympathetic control)

Question 15

HORMONAL REGULATION: TESTOSTERONE

Answer 15

Hypothalamus produces gonadotropin releasing hormone (GnRH) to act on anterior pituitary to stimulate release of follicle stimulating hormone (FSH) and luteinising hormone (LH) into bloodstream.
↓
FSH and LH act on the testes to stimulate spermatogenesis. FSH stimulates sperm production while LH causes testosterone production (which causes the male secondary sex characteristics and maintains spermatogenesis).
↓
As spermatogenesis increases, special testicular cells produce inhibin, together with the rising levels of testosterone inhibit release of FSH and LH via negative feedback.

Question 16

FEMALE ANATOMY: VAGINA

Answer 16

VAGINA
Thin, stretchy wall, 8 - 10 cm long
Acidic environment to repel infection & sperm
Birth canal

UTERUS
Hollow and thick walled, 3 layers:
Perimetrium (outermost)
Myometrium (smooth muscle)
Endometrium (sheds monthly)
Receives and nourishes ovum
Cervix communicates with vagina

Q). Cervical mucus changes with menstrual cycle - less viscous mid-cycle.
A). Wet and slippery to make it easy for sperm to swim up to meet an egg at ovulation

Question 17

FEMALE: INTERNAL ANATOMY

Answer 17

Ovaries (plural)
Paired structures that houses forming gametes
Ovarian follicles contain oocyte
Site of ovulation
Hormone production: oestrogen & progesterone

Fallopian/uterine tubes
Fimbriae (finger-like projections) help capture oocyte after ovulation and sweep into tube
Site of fertilisation (and sometimes the site of ectopic pregnancy).

Question 18

FEMALE: EXTERNAL ANATOMY

Answer 18

Mammary Glands
Site of milk production
Only in response to pregnancy
Internally 15 - 25 lobes which contain alveoli that produce milk
Milk passes from lactiferous duct to nipple
Ejection of milk controlled by a positive feedback mechanism
Breast size determined by amount of fatty tissue, not number of lobules!

Question 19

OOGENESIS

Answer 19

‘Production of ovum’
Begins in fetal life
Females born with lifetime supply of primary oocytes
Held in suspended animation until puberty (when only around 300,000 remain)
Puberty: One primary oocyte is selected and matures each month
Becomes an ovum which is expelled from the ovary and can be fertilised

Question 20

The Ovarian and Uterine Cycles

Answer 20

Events of the ovarian cycle vary in response to hormones secreted by anterior pituitary gland (FSH and LH).
Events of the uterine cycle occur in response to hormones secreted by ovaries (oestrogen and progesterone).

Question 21

The ovarian cycle

Answer 21

28 day cycle that describes the events at the ovary, 2 phases:

FOLLICULAR PHASE (DAYS 1-14)
Characterised by follicle growth and maturation of an ovum.
Ovarian follicle secretes: OESTROGEN
Ovulation: approx. day 14 (‘mid-cycle’), rupturing of the follicle to release a mature ovum (secondary oocyte) from an ovary with the hope of fertilisation in the fallopian tube

LUTEAL PHASE (DAYS 15-28)
Ruptured follicle forms into a structure called the corpus luteum.
Corpus luteum secretes: OESTROGEN AND PROGESTERONE
If no fertilisation occurs after 10 days, the corpus luteum degenerates and hormonal output ends. If fertilisation occurs, it keeps producing hormones to maintain pregnancy until the placenta takes over

Question 22

The uterine cycle (menstrual cycle)

Answer 22

Series of cyclic changes affecting the endometrium (uterine lining) in response to ovarian hormones in the blood stream.
3 phases:

MENSTRUAL PHASE (~days 1 - 5): Shedding of endometrium occurs because fertilisation did not happen. Trigger for menstruation to begin is a fast drop in oestrogen and progesterone levels due to the corpus luteum degenerating. First day of bleeding signals the start of a fresh cycle (day 1).

PROLIFERATIVE PHASE (~days 6 - 14): Rebuilding of endometrium, in anticipation of the next fertilisation. Stimulated by ↑ oestrogen concentration from maturing ovarian follicle. Spiral arteries form and grow and cervical mucus becomes thin to facilitate sperm entry.

SECRETORY PHASE (~days 15 - 28): Secretion of various nutrients in preparation to house and nourish a fertilised ovum (‘embryo’)/maintenance of pregnancy. Corpus luteum secrets progesterone causing further growth of spiral arteries. Cervical mucus thickens to act as a plug to limit entry of sperm and pathogens.

Question 23

OVARIAN + UTERINE CYCLE

Answer 23

GnRH (hypothalamus) stimulates LH/FSH release (anterior pituitary)
FSH stimulates follicles to grow
Follicle secretes oestrogen. This ↑ in oestrogen feeds back to the hypothalamus (-ve feedback) to ↓ GnRH, which ↓ FSH/LH = FSH ‘dip’
However, the ↑ oestrogen levels (due to the growing follicle) exerts a +ve feedback effect on anterior pituitary to induce LH surge.
Due to the LH surge, ovulation occurs, where a follicle ruptures to release a secondary oocyte (with the hope of fertilisation).
LH surge also helps form the corpus luteum, which then produces progesterone and oestrogen.

IF FERTILISATION DOES NOT OCCUR: ↑ progesterone and oestrogen causes cessation of GnRH, LH and FSH release (-ve feedback), causing the corpus luteum to degenerate. Now the fast ↓ levels of progesterone and oestrogen brings about menstruation and fresh output of FSH.

IF FERTILISATION DOES OCCUR: corpus luteum maintained for ~4 months. Once placenta is formed, it releases a hormone called HCG to maintain the corpus luteum (this is the hormone you check during the pregnancy test!). Placenta eventually becomes active in releasing oestrogen and progesterone to support pregnancy.

Question 24

MENOPAUSE

Answer 24

Occurs around 46 - 54 years.
“The end of the menstrual cycle”.
Ovaries no longer release an ovum.
Ovarian cycle becomes irregular until it ceases.
Uterine cycle becomes irregular until it ceases.
Decline in oestrogen production.
Post-menopausal women are infertile because they are no longer producing or releasing ovum.

Question 25

MALE VS FEMALE FERTILITY

Answer 25

MALE
- beings @ puberty
- spermatogenesis = 400 mil/day until death
- error rate of sperm with chromosome number defect is 3-4%
- male fertility = till death

FEMAIL
- lifetime supply of primary oocytes @ birth
- oogenesis = 1 mature ovum per month
(puberty → menopause)
- error rate of ovum with chromosome number defect is 20%
- fertility declines with age (less number of eggs)

Question 26

Contraceptive Pill

Answer 26

Contraceptive pills provide synthetic oestrogen & progesterone (or progesterone only), which eliminates hormonal fluctuations seen in the natural cycle
The pill mimics the secretory phase of the uterine cycle or the luteal phase of the ovarian cycle.

↑ oestrogen and progesterone, ↓ GnRH and FSH/LH - the oocyte cannot be matured or released, meaning that ovulation does not occur.
No drop in oestrogen or progesterone also means menstruation will not occur.

After 2-3 ‘sugar pills’ the drop in hormones is enough to signal menstruation, however you never take them long enough to signal ovulation.

The endometrium does not proliferate to the extent it would if the pill was not being taken, which is why most women report ‘lighter periods’ (and also why it maybe prescribed in cases of endometriosis).

While it can be taken for months to avoid menstruation completely, break through bleeding may occur - as the longer you take them the thicker your endometrium becomes.