12. Reproductive System Flashcards
Reproduction
- Reproduction describes the production of new offspring.
- ‘Sexual reproduction’ involved meiosis & fertilisation.
- Meiosis produces male (sperm) and female (ova) gametes, which are haploid (23 chromosomes).
- The offspring has a mix of genes inherited from each parent (produces genetic variability).
- Fertilisationproduces a‘zygote’, which contains 46 chromosomes.
Reproductive System: Functions, Female
- Formation of ova (female gametes).
- Reception of spermatozoa (male gametes).
- Provide suitable environment for fertilisation/foetus.
- Parturition (childbirth).
- Lactation.
Reproductive System: Functions, Male
- Production of spermatozoa (male gametes).
2. Transmission of spermatozoa to the female.
Breasts/Mammary glands
- The breasts are accessory glands of the female reproductive system.
- Within each breast is a mammary gland –a modified sweat gland producing milk.
- Each mammary gland consists of 15-20 lobes, separated by adipose tissue. Lobes contain small grapelike clusters of glands called alveoli.
- ‘Suspensory ligaments’ support the breast between the skin & underlying fascia.
Lactation:
- Contraction of myoepithelial cells surrounding alveoli help propel milk into lactiferous ducts.
- Milk can be stored in lactiferous sinuses.
- After birth, the hormone ‘prolactin’stimulates milk synthesis, whilst ‘suckling’ stimulates ‘oxytocin’,which causes milk ejection.
Uterus
The uterus serves as a pathway for sperm, the site of zygote implantation and location for foetal development. The uterus contractsto initiate labour.
Uterus: Tissue layers
- Perimetrium: Outer layer (visceral peritoneum).
- Myometrium: Three smooth muscle layers.
- Endometrium: The highly vascular inner layer that is divided into the‘stratum functionalis’ (sloughs off during menses) &‘stratum basalis’, which is the permanent deeper layer that regenerates the stratum functionalis.
Uterus: Structure
• The uterus consists of the fundus, body and cervix.
• The uterus is held in place by ligaments such as the
‘broad ligament’.
• The cervix is the narrowed inferior portion of the uterus that leads into the vagina.
• The uterus is situated between the bladder
(anteriorly) and rectum (posteriorly); it is the size &
shape of an inverted pear.
Endometrium
- The endometrium is the highly vascularised inner layer of the uterus.
- During a ‘period’ (“menses”), the stratum functionalis sheds, leaving behind the stratum basalis.
- After shedding, the endometrium re-builds to prepare for implantation of a fertilised egg.
- If the egg is fertilised, the zygote is embedded in the endometrium.
- In the first 8 weeks, the embedded zygote is an embryo.
- After 8 weeks, the embryo becomes a foetus.
Placenta
- The placenta is the site of exchange of nutrients and wastes between the mother and foetus, attached to the endometrium.
- The placenta also produces hormones that are needed to maintain the pregnancy.
- By the beginning of the twelfth week, the placenta contains two distinct regions.
- The placenta is unique because it develops from two individuals (maternal part from endometrium).
- The actual connection between the placenta and embryo/foetus is through the umbilical cord, which is 50–60cm in length.
- The placenta allows oxygen and nutrients to diffuse from maternal blood into foetal blood, whilst carbon dioxide and wastes move in the opposite direction.
- Provides a protective barrier because most micro-organisms cannot pass through it. Some organisms such as HIV, measles and polio can. Alcohol and many drugs can pass freely and can cause birth defects.
- Blood cellscannotcross the placenta.
- Nutrient transfer to the foetus is mediated by proteins called nutrient transporters.
Placental Hormones
Progesterone Oestrogen human Chorionic Gonadotrpin (hCG) human PlacentalLactogen (hPL) Relaxin Corticotropin releasing hormone (CRH)
Progesterone
- Maintains endometrial liningto sustain and nourish the foetus.
- Produced by corpus luteum until 8 weeks.
Oestrogen
- Promotes growth of breast tissueand myometrium.
* Produced by corpus luteumuntil 8 weeks.
human Chorionic Gonadotrpin (hCG)
- Only produced during pregnancy(test!)
- Maintains corpus luteum for 8 weeks and increases transfer of nutrients to foetus.
- Related to morning sickness.
human PlacentalLactogen (hPL)
Increase the amount of glucose & lipids in maternal blood.
Relaxin
- Targets ligamentsand relaxes them.
* Produced by the corpus luteum and placenta.
Corticotropin releasing hormone (CRH)
- Triggers release of cortisolfrom the adrenals.
* Prevents rejection of foetus / placenta.
Placenta Praevia
- Occurs when the placenta attaches to the lower part of the uterine wall, potentially occluding the opening of the cervix.
- Risk with multiple births because more placentas.
- 1st trimester can resolve itself as uterus stretches.
- 2nd or 3rd trimester (>20 weeks) prone to haemorrhage. Wall of cervix stretches and can detach from the placenta. Uterine vessels rupture and often presents as painless, ante-partum vaginal bleeding.
- Treatment depends on the condition of the baby and mother. C-section preferred.
Placenta Accreta
- Abnormally deep attachment of the placenta through the endometrium into the myometrium.
- If invades myometrium = increta. If through uterine wall to viscera such as the bladder = percreta.
- Due to inadequate (thin) basalis layer of endometrium. The placenta has to “dig in deeper” when implanting.
- Occurs due to: C-section, curettage (scraping procedure), fibroid removal or placenta praevia.
- Risk of post-partum haemorrhage.
Placental Abruption
- Rupture of blood vessels adhering the placenta to the uterine wall leading to separation of the placenta from the uterus.
- Risk factors include smoking & maternal hypertension (pre-eclampsia).
- Presents as abdominal pain and ante-partum bleeding.
- An obstetric emergency after 20 weeks:
- > 30 weeks: delivery.
- <30 weeks and stable vitals monitor until baby is old enough to safely deliver. Mature foetal lungs with corticosteroids.
- Occurs in 1% of pregnancies worldwide.
Twins: Monozygotic (30%)
- Identical twins (same genetic information).
- Originate from a single fertilised ovum (One egg, one sperm).
- The zygote splits into 2 embryos, but share 1 placenta.
Twins: Dizygotic (70%)
- Non-identical.
- Release of two ova and fertilisation of each. Implanted independently.
- Two eggs, two sperms
- Two different placentas.
Fallopian Tubes
- The fallopian (or uterine) tubes extend laterally from the uterus (~10cm tubes).
- The tubes provide a route for the sperm to meet the ova and for the ova (or fertilised ova) to reach the uterus.
- Finger-like projections calledfimbriae surround the ovary and ‘sweep the ova’ into the fallopian tube.
- The tubes are lined with ciliated columnar epithelium, which function to help move the ova towards the uterus.
- The smooth muscle layer performs peristalsis to assist in ova movement.
Ovaries
- The ovaries are the female gonads and exist as paired glands.
- The ovaries resemble almondsin their shape and size, although atrophy after menopause.
- The ovarian ligament anchors the ovaries to the uterus, whilst the broad ligament also assists in maintaining the position of the ovaries.
- The ovaries produce female gametes (‘secondary oocytes’ via oogenesis).
- Ovaries secrete sex hormones: oestrogen & progesterone.
Oogenesis: Pre-pubertal
• Oogenesis is referring to the formation of female gametes (ova) in the ovaries.
• Oogenesis begins in the foetus.
• Primary oocytes are formed from germ cells during foetal development.
• The formation of primary oocytes stops at birth (leaving approx. 20,000-2,000,000).
• Primary oocytes are surrounded by a layer of
follicular cells – the entire structure is called a primordial follicle.
• During a woman’s reproductive life-time about 400 follicles will mature & ovulate.
The remainder degenerate.
Oogenesis: Post-pubertal
- Every month anterior pituitary hormones stimulate the development of a primordial follicle into a mature ovum.
- FSH stimulates maturation of the primordial follicles -> primary follicles -> secondary follicles -> mature follicle.
- A surge of LH triggers ovulation–release of the ovum (secondary oocyte).
- The remains of the ovarian follicle (follicular cells) that has ovulated becomes the corpus luteum. This produces progesterone & some oestrogen.
- The corpus luteum degrades into the corpus albicans if no fertilisation. If fertilisation occurs, hCGprevents degradation of the corpus luteum.
Oogenesis
- Whilst rapid maturation during final stages only takes about 14 days, follicle growth from primordial stage to full maturity takes about a year –meaning that a follicle that ovulates started its growth to maturity 10-12 ovarian cycles earlier.
- FSH drives development of the most mature follicle into a mature ovum.
Menstrual Cycle
- The menstrual cycle generally lasts 24-35 days.
* 28 days is average.
Menstrual Cycle: Phases
- Menstrual phase (day 1-5).
- Pre-ovulatory phase (day 6-13).
- Ovulation (day 14).
- Post-ovulatory phase (day 15-28).
Menstrual phase (day 1-5)
Menstruation
In the Uterus: Endometrium is being shed in response to a sudden drop in progesterone
IN OVARIES:
Follicles are developing under the influence of FSH.
Pre-ovulatory phase (day 6-13)
Between end of menses and ovulation
In the Uterus: The endometrium thickens in response to rising oestrogen levels
IN OVARIES:
Follicle starts to mature& secretes oestrogen.
Follicles secrete inhibinwhich decreases the secretion of FSH. Thisstops other follicles developing.
Ovulations phase (Day 14)
Release of the egg.
Ovulation tests work by detecting rising levels of LH.
IN OVARIES:
High oestrogen levels create negative feedback loop which stimulates LH secretion.
LH causes rupture of the mature follicle & expulsion of the egg= ovulation.
Post Ovulatory phase
Days 15-28
Between ovulation & next menses
The corpus luteum is now essential in establishing & maintaining pregnancy.
The corpus luteum forms from the follicle wall & produces progesterone and some oestrogen.
These maintain endometrium in preparation for pregnancy.
Pituitary hormones
FSH & LH control the ovaries (following release of GnRH)
Ovarian hormones
Oestrogen & progesterone control the uterus.
Fertilised Egg (Ova)
• The zygote embeds in the uterine wall.
• Human chorionic gonadotropin (hCG) (produced by the embryo) maintains & stimulates the corpus luteum to produce progesterone & oestrogen.
• After a few weeks the placenta takes over the role
of producing hCG & progesterone, maintaining the
pregnancy.
Non-Fertilised Egg (Ova)
- After 14 days the corpus luteum degeneratesinto the corpus albicans.
- The levels of progesterone & oestrogen drop & a new cycle starts with menstruation.
Puberty (Females)
- The period when the potential for sexual reproduction is reached.
- Occurs between 10–14 years of age.
- The onset of puberty is marked by pulses of LH and FSH, each triggered by a burst of Gonadotropin Releasing Hormone (GnRH).
- As puberty advances, the hormone pulses occur during the day as well as night, increasing over 3-4 years.
- Internal reproductive organs reach maturity -> menarche.
- Breast development, hair growth (pubic/axillary/legs), hips widen (more fat deposited in hips & breasts), voice deepens.
Menopause
- The menopause is the permanent cessation of menstruation for 12 consecutive months.
- Naturally occurs at 45 –55 years of age.
- Occurs as a result of ‘ovarian aging’, whereby the number of follicles become exhausted .
- decrease in oestrogen production > decline in ovulation > decrease inprogesterone production
- Declined oestrogen & progesterone levels affects negative feedbackleading tohigh FSH & LH levels.
- Menopause can be surgically induced following hysterectomy.
Menopause: Signs and Symptoms
- Hot flushes & increased sweating.
- Vaginal dryness and atrophy of mucosal lining leads to painful intercourse.
- Increased risk of UTIs due to urogenital atrophy.
- Mood changes, irritability, anxiety.
- Decreased libido & sleep disturbances.
- Breast shrinkage. Sparse pubic & axillary hair.
- Osteoporosis (loss of oestrogen = decrease in osteoblasts).
HRT
- Can be used to relieve menopausal symptoms and reduce the risk of osteoporosis, but only delays the menopause.
- HRT increases the riskof breast & endometrial cancer, heart disease, stroke & DVT.
Penis
• Consists of a root (within pelvic cavity) and body.
• Urethral canal has both reproductive & urinary functions.
Body consists of:
• 3 cylindrical masses of erectile tissue.
• Fills with blood during sexual arousal (&REM sleep).
• Contains the enlarged ending (‘glans penis’).
• Erectile tissue and involuntary muscle are stimulated by the parasympathetic nervous system –produce Nitric Oxide that causes vasodilation.
Testes
- The testes develop in the pelvic cavity (near the kidneys) and descend into the scrotum via the inguinal canals between 7-9 months utero.
- Site of spermatogenesis:
- In the Seminiferous tubules (takes about 70 days). Regulated by FSH.
- Site of testosterone production & secretion:
- From cholesterol in the ‘Leydig cells’.
- Regulated by LH.
- Each testis divided into 200-300 lobules. Each lobule contains seminiferous tubules.
- Spermatozoa mature & are stored in the epididymis.
Sperm
- 300 Million produced each day by spermatogenesis.
- Sperm can live for several months in the epididymis.
- Normally 100 million per ml/ejaculate.
- Spermatogenesis occurs best 3oC below body temperature.
- Sperm have a head, body & tail:
- Headfilled with the nucleus (n).
- Acrosomeis a vesicle covering the head of the sperm that contains enzymes topenetrate the egg.
- Bodyfilled with mitochondria to fuel tail.
- Tail to swim.
Ejaculate
- Spermatozoa are expelled from the epididymis through the vas deferens and into the ejaculatory duct.
- Here seminal fluid is secreted and mixed with the sperm.
Seminal Fluid Glands
Seminal vesicles
Prostate Gland
Seminal Vesicles
- A pair of glands located behind the bladder.
- Secrete alkaline seminal fluid (60% of semen).
- Nutrients (e.g. fructose) to nourish sperm.
Prostate Gland
- Secretes a thin milky fluid that makes up 30% of semen.
- Contains nutrients for ATP production and anticoagulants to fluidity: citric acid, proteolytic enzymes: Prostate Specific Antigen, pepsinogen.
Ejaculate
- Seminal fluid (semen) is alkaline to protect sperm from urethral & vaginal acidity.
- Sperm comprises only 10% of the semen.
Bulbourethral glands (Cowper’s Glands)
- Secrete an alkaline, mucous fluid that neutralises urinary acids in the urethra prior to ejaculation and lubricates the end of the penis.
- During sexual arousal contraction of smooth muscles in the epididymis & vas deferens propels sperminto the ejaculatory ducts.
- Muscles surrounding the base of the urethra cause semen to eject out of the penis during orgasm.
Menarche
The age of the first period.
Metorrhagia
Mid-cycle bleeding.
Menorrhagia
Increased menstrual bleeding.
Amenorrhoea
Absense of periods
Dysmenorrhoea
Painful, heavy periods
Polymenorrhoea
Short cycle, frequent periods.
Oligomenorrhea
Infrequent cycles
Galactorrhoea
Lactation without pregnancy
Dyspareunia
Pain on intercourse (female)
Gynaecomastia
Presence of enlarged breast tissue in a male
