Week 8 Bioscience Flashcards
1
Q
Reproductive system
A
- 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)
2
Q
Similarities
A
- 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
3
Q
Male Reproductive system
A
- 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
4
Q
The Penis
A
- designed to deliver sperm into the female reproductive tract
→ 3 cylindrical columns of erectile tissue
5
Q
The Scrotum
A
- 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
6
Q
Penile erection
A
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
7
Q
The Testes
A
- 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
8
Q
Cells of the Testes
A
- 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
9
Q
Epididymis
A
- surrounds the posterior edge of the testes and is a series of coiled tubes
- sperm arrive as immature and non-motile
- functions:
- stores, nourishes and protects sperm
- facilitates functional maturation (can swim)
- recycles damaged sperm
- ejaculates the sperm into the ductus deferens
sperm can be stored in the tail of the epididymis for several months
10
Q
A sperm’s travel plans:
A
- 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
11
Q
Ductus Deferens & Seminal Vesicles
A
- 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)
12
Q
Ejaculatory Duct, Urethra & Prostate
A
- 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
13
Q
Urethra & Bulbourethral gland
A
- 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)
14
Q
Ejaculation
A
- 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
15
Q
Meiosis: making gametes
A
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
16
Q
Spermatogenesis: production of sperm
A
○ 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
17
Q
Structure of sperm
A
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
18
Q
Semen
A
- 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%
19
Q
Role of Testosterone
A
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
20
Q
External genitalia
A
- 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
21
Q
Internal genitalia
A
the vagina, uterus and uterine tubes make up the female duct system and provide a passage way for conception and birth
22
Q
The vagina
A
- 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
23
Q
Uterine tubes
A
- 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
24
Q
The ovaries
A
- 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
25
Oogenesis: production of oocytes
○ 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
26
Ovarian cycle: Follicular Phase
□ 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
27
Hormonal regulation of follicular phase
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)
28
Ovarian cycle: Luteal Phase without fertilisation
○ 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
29
Hormonal regulation of Luteal phase
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
30
The uterine (menstrual) cycle
* 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
31
Effects of oestrogen and progesterone
* 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
32
Female secondary sex characteristics
* 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
33
Fertilisation
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
34
Capacitation
* 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
35
Steps to Fertilisation
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.
36
Implantation
* 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
37
Importance of hCG and progesterone
* hCG signals to the CL to continue to produce progesterone and oestrogen until 8-12 weeks
* promotes placenta development
38
Pregnancy testing
* 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)
