Week 8 Bioscience

Question 1

Reproductive system

Answer 1

• primary role of the reproductive system is to produce offspring
  → produces gametes (sex cells- sperm & oocyte
  → provide an environment for the development of offspring (uterus)
• Reproductive system is made up of primary sex organs (gonads-testes & ovaries) plus accessory reproductive organs (ducts, glands & external genitalia)

Question 2

Similarities

Answer 2

• become active at puberty
• produces sex hormones:
  ○ androgens, e.g. testosterone (males),
  ○ oestrogens and progesterone (females)
• sex hormones play roles in:
  ○ development and function of the reproductive organs
  ○ sexual behaviour and drives
  growth and development of many other organs and tissues

Question 3

Male Reproductive system

Answer 3

• role of male reproductive system is to:
  ○ manufacture sperm
  ○ deliver sperm to female reproductive tract
• in order to achieve these roles, the male has specific:
  ○ glands and ducts hormones

Question 4

The Penis

Answer 4

• designed to deliver sperm into the female reproductive tract
  → 3 cylindrical columns of erectile tissue

Question 5

The Scrotum

Answer 5

• sac of skin housing the testes outside the body
• essential for temperature regulation of testes (site of spermatogenesis)
• maintains optimal temperature (34oC)
• temperature regulation achieved by two muscles:
  ○ Dartos muscle (smooth muscle) - contracts to make scrotum wrinkled and thick, decreases heat loss
  ○ Cremaster muscle (skeletal muscle) – contracts to bring scrotum and testes closer to body
  ○ both muscles contract in cold, and relax in warm, temperatures

Question 6

Penile erection

Answer 6

Parasympathetic nerves to penile arterioles release nitric oxide (NO)
NO relaxes smooth muscle:
1. blood vessels dilate
2. increased blood flow to penis
3. vascular spaces become engorged with blood
4. erection of penis occurs

Question 7

The Testes

Answer 7

• internally contains seminiferous tubules
  ○ fluid filled tubes
  ○ factory for sperm production (spermatogenesis)
• each seminiferous tubule is surrounded by smooth muscle to help squeeze sperm into the epididymis

Question 8

Cells of the Testes

Answer 8

• sustentocytes: support cells within the seminiferous tubule, produce testicular fluid, provide developing sperm with nutrients and produces androgen binding protein (ABP)
• interstitial cells : located in the testes but outside of seminiferous tubules and produce testosterone

Question 9

Epididymis

Answer 9

• surrounds the posterior edge of the testes and is a series of coiled tubes
• sperm arrive as immature and non-motile
• functions:
  
  1. stores, nourishes and protects sperm
  2. facilitates functional maturation (can swim)
  3. recycles damaged sperm
  4. ejaculates the sperm into the ductus deferens
     sperm can be stored in the tail of the epididymis for several months

Question 10

A sperm’s travel plans:

Answer 10

• sperm travel through a series of tubes to get from the testes to outside of the body:
  ○ seminiferous tubules
  ○ epididymis
  ○ ductus deferens
  ○ ejaculatory duct
  ○ urethra
• along the way, secretions of the accessory glands are added to the sperm to produce semen :
  ○ seminal vesicles
  ○ prostate
  ○ bulbourethral glands

Question 11

Ductus Deferens & Seminal Vesicles

Answer 11

• sperm ejaculated from the epididymis into ductus deferens
  ○ ductus deferens: tube that runs from the scrotal sac to the urethra
• Seminal vesicles (accessory glands) attach to the ductus deferens.
  ○ release a viscous fluid which makes up 60-70% of semen volume and contains substances that enhance sperm motility and their ability to fertilise an oocyte:
• fructose (energy), prostaglandins (smooth muscle contraction) and fibrinogen (clots ejaculated semen)

Question 12

Ejaculatory Duct, Urethra & Prostate

Answer 12

• after the seminal vesicles join the ductus deferens, the tube becomes known as the ejaculatory duct
• ejaculatory duct is very short and immediately joins the urethra and travels through the prostate gland
• prostate gland - a doughnut shaped gland that surrounds the urethra and produces fluid that accounts for up to 30% of semen volume
• contains nutrients and enzymes that breakdown seminal clot

Question 13

Urethra & Bulbourethral gland

Answer 13

• urethra descends through the prostate and down to the tip of the penis
  ○ functions to convey both urine and semen
• paired bulbourethral glands are located inferior to the prostate on either side of the urethra
• produce a thick mucus which lubricates the glans penis and neutralises traces of urine in the urethra prior to ejaculation (urine is acidic and cause sperm to be sluggish)

Question 14

Ejaculation

Answer 14

• ejaculation is the propulsion of semen from the male reproductive system
  ○ under sympathetic control (erection under parasympathetic control)
  ○ bladder sphincter muscle constricts: prevent urine entering semen
  ○ reproductive ducts and accessory glands contract: to release their contents into urethra

Question 15

Meiosis: making gametes

Answer 15

Most body cells contain:
* 46 chromosomes reproduced by mitosis

Gametes (sperm and oocytes) contain:
○ 23 chromosomes reproduced by meiosis

Fertilisation: sperm and oocyte combine
○ 46 chromosomes in fertilised egg

Question 16

Spermatogenesis: production of sperm

Answer 16

○ begins at puberty and continues throughout adult life
○ occurs in the seminiferous tubules of the testes
○ driven by testosterone produced by interstitial cells
○ supported by sustentocytes in seminiferous tubules

Question 17

Structure of sperm

Answer 17

Major regions
1. Head: genetic region; nucleus and a helmet-like cap called acrosome -containing enzymes that enable the sperm to penetrate an oocyte
2. Midpiece: metabolic region; mitochondria - energy production
3. Tail: locomotor region; flagellum - movement

Question 18

Semen

Answer 18

• ejaculation is approximately 2-5 ml of semen
• semen consists of:
  ○ epididymal secretions: 5% (e.g. fluid and sperm)
  ○ seminal vesicle secretions: 60-70%
  ○ prostate secretions: 30%
  bulbourethral secretions: <5%

Question 19

Role of Testosterone

Answer 19

At puberty and thereafter:
* stimulates spermatogenesis
* increases growth of reproductive ducts and glands
* increases size of penis
* enhances ability to maintain erection and obtain ejaculation
* stimulates male secondary sex characteristics i.e.
○ appearance of pubic, auxiliary and facial hair
○ enlargement of larynx
○ increased size and density of bones
○ Increased skeletal muscle mass
○ Influence behaviour such as sex drive

Question 20

External genitalia

Answer 20

• external structures (the vulva) include:
  ○ labia majora – 2 fatty skin folds
  ○ labia minora – 2 thin, hair-free skin folds
  ○ vestibule- greater vestibular glands – release mucus to lubricate for intercourse
  ○ clitoris – erectile tissue, richly innervated, sexual arousal

Question 21

Internal genitalia

Answer 21

the vagina, uterus and uterine tubes make up the female duct system and provide a passage way for conception and birth

Question 22

The vagina

Answer 22

• provides a passageway to:
  ○ eliminate menstrual fluids
  ○ receive the penis during intercourse
  ○ expel fetus during child birth
• both muscular and elastic  stretch and recoil
• acidic environment helps keep the vagina free of infection but makes it hostile to sperm

Question 23

Uterine tubes

Answer 23

• receive ovulated oocytes
• not continuous with the ovary
• ciliated finger-like projections (fimbriae) sweep over the ovary to draw the oocyte into the tube
• muscular movements and beating cilia carry the oocyte towards the uterus
• site of fertilisation

Question 24

The ovaries

Answer 24

• located at the end of the uterine tubes
  ○ produce female gametes: oocytes
  ○ secrete female sex hormones (oestrogens and progesterone)
  ○ follicles are the functional unit of the ovary: consist of oocytes surrounded by follicular cells

Question 25

Oogenesis: production of oocytes

Answer 25

○ occurs in the ovaries
○ begins in the fetal period
- oocytes stay in a suspended state until puberty
○ a small number of primary oocytes are recruited each month – but only one is selected to go through meiosis to form the mature oocyte

Question 26

Ovarian cycle: Follicular Phase

Answer 26

□ day 1-14
□ follicle grows due to FSH
□ oocyte enlarges
□ follicular cells formed around oocyte: provide nourishment and produce oestrogens
□ oocyte produces zona pellucida
□ fluid accumulates called antrum helps to flush the oocyte out of the follicle
□ Ovulation
* the bulging follicle eventually ruptures the wall of the ovary and the oocyte is released
* ovulation triggered by increases in LH (and FSH)
* occurs around 14d of the ovarian cycle

Question 27

Hormonal regulation of follicular phase

Answer 27

1. GnRH released by the hypothalamus stimulates the anterior pituitary gland to release FSH and LH
2. FSH stimulates follicle maturation
3. FSH stimulates follicular cells to produce and secrete oestrogens
4. Increasing levels of oestrogens stimulate a surge in LH secretion which triggers ovulation and development of corpus luteum (CL)

Question 28

Ovarian cycle: Luteal Phase without fertilisation

Answer 28

○ day 15-28
* ruptured follicular cells are now called corpus luteum (CL) due to LH
* CL produces progesterone and some oestrogen:
○ progesterone maintains the functional layer of the endometrium
○ if fertilisation does not occur:
○ CL degenerate to corpus albicans
○ progesterone and oestrogen levels drop
○ triggers shedding of endometrial lining menstruation
○ decreased progesterone and oestrogen stimulate release of GnRH, LH an FSH to start follicular phase again

Question 29

Hormonal regulation of Luteal phase

Answer 29

1. LH surge transforms the ruptured follicle into the CL
2. The CL produces large amount of progesterone and oestrogen
3. If fertilisation does not occur the CL degenerates, hormone levels decline and the cycle begins again

Question 30

The uterine (menstrual) cycle

Answer 30

• Menstrual phase (menses)
  ○ day 1-5
  ○ shedding of the functional layer of the endometrium
  ➢ oestrogen and progesterone are low
• Proliferative phase
  ○ day 6-14
  ○ rebuilding of the functional layer of the endometrium
  ○ cervical mucus becomes less viscous and sticky – to allow entry of sperm
  ➢ this phase is stimulated and sustained by ovarian oestrogens
  □ ovulation occurs at the end of this phase
• Secretory phase
  ○ day 15-28
  ○ begins immediately after ovulation
  ○ progesterone (& oestrogens) from CL stimulates endometrium and prepares for implantation
  ➢(arteries elongate, glands enlarge and secrete glycogen-rich mucus)
  □ if fertilisation does not occur, the CL degenerates → low progesterone → breakdown of the endometrium → menses begins again

Question 31

Effects of oestrogen and progesterone

Answer 31

• at puberty oestrogens:
  ○ promote oogenesis
  ○ increase growth of the vagina, uterus and uterine tubes
  ○ stimulates female secondary sex characteristics
• oestrogen and progesterone work together to:
  ○ regulate uterine cycle and promote changes in cervical mucus
  → oestrogen promotes repair and regeneration of the functional layer
  → progesterone promotes blood vessel and gland growth and secretion
  ○ progesterone (also known as the pregnancy hormone) maintain pregnancy and stimulate breast growth etc

Question 32

Female secondary sex characteristics

Answer 32

• induced by female sex hormones (e.g. oestrogen)
  ○ induce initial growth spurt but then close the growth plates of long bones
  ○ pubic and axillary hair
  ○ growth of breasts
  ○ increased subcutaneous fat (hips and breasts)
  ○ widening of the pelvis

Question 33

Fertilisation

Answer 33

sperm that make it to the uterine tube before they can fertilise the oocyte the sperm needs to undergo capacitation
freshly deposited sperm into the female reproductive tract are incapable of fertilisation

Question 34

Capacitation

Answer 34

• process that thins the plasma membrane overlying the acrosome
• facilitates release of acrosomal (hydrolytic) enzymes necessary for penetrating the zona pellucida
• enhances sperm motility
• begins with exposure to secretions in female reproductive tract
• takes between 2-10 hours to occur
• capacitation prevents acrosomal enzymes from causing damage

Question 35

Steps to Fertilisation

Answer 35

Once sperm reach the oocyte:

1. Sperm weave through the follicular cells.
2. Sperm bind to zona pellucida
   * rise in calcium levels in the sperm
   * complete breakdown of the acrosomal membranes
   * release of the acrosomal enzymes called the acrosomal reaction
3. Acrosomal enzymes are released and digest holes in the zona pellucida. It takes the enzymes from many sperm to digest complete holes in the zona pellucida.
4. The sperm binds to receptors on the oocyte membrane
5. The sperm and oocyte membranes fuse
   * sperm DNA released into the oocyte
6. Entry of sperm DNA causes increased calcium levels in the oocyte
   - triggers the cortical reaction which destroys sperm receptors and hardens the zona pellucida preventing further entry of sperm.

Question 36

Implantation

Answer 36

• implantation occurs halfway through the secretory phase:
  ➢ well developed blood supply
  ➢ uterine glands producing lots of glycogen-rich mucus
• special proteins on the trophoblast cells allow the embryo to attach to endometrium
• successful implantation usually complete just before menstruation would normally occur
• menstruation would result in shedding of the functional layer and loss of the implanted embryo
• menstruation is prevented by the embryo signalling to the CL to continue to produce progesterone and oestrogen
• this signalling occurs via the hormone human chorionic gonadotropin (hCG) produced by the trophoblast cells
  ➢hCG bypasses hypothalamic and pituitary control of the ovarian cycle

Question 37

Importance of hCG and progesterone

Answer 37

• hCG signals to the CL to continue to produce progesterone and oestrogen until 8-12 weeks
• promotes placenta development

Question 38

Pregnancy testing

Answer 38

• hCG levels are present in the mother’s blood one week after fertilisation and continue to rise until the end of the second month
• hCG can be detected in the urine using a home pregnancy test 7-12 days following conception (2-7 days before menstruation would normally occur)