12. Reproductive System Flashcards
Reproduction: definition
The production of new offspring
What does sexual reproduction involve?
Meiosis
Fertilisation
What happens in meiosis?
This produces male (sperm) and female (ova) gametes
These are haploid so have 23 chromosomes each
What is genetic variability?
Offspring having a mix of genes inherited from each parent
What does fertilisation produce?
A zygote (46 chromosomes)
Functions of female reproduction system:
Formation of ova (female gametes)
Reception of spermatozoa (male gametes)
Provide suitable environment for fertilisation/foetus
Parturition (childbirth)
Lactation
Functions of male reproduction system:
Production of spermatozoa (male gametes)
Transmission of spermatozoa to the female
What are breasts?
Accessory glands of the female reproductive system
What is a mammary gland?
A modified sweat gland that produces milk
What does each mammary gland consist of?
15-20 lobes separated by adipose tissue
Each lobe contains small, grapelike clusters of glands called alveoli
What are suspensory ligaments?
These support the breast between the skin and the underlying fascia
What happens during lactation?
Myoepithelial cells surrounding the alveoli contract and propel milk into the lactiferous ducts
Where can milk be stored?
In the lactiferous sinuses
What does prolactin do?
Stimulates the production of milk
What does oxytocin do?
Causes milk ejection during suckling
What does the uterus do?
Pathway for sperm
Site of zygote implantation
Location for foetal development
Contracts to initiate labour
What is a zygote?
Fertilised ovum
Uterus walls: layers
- Perimetrium
- Myometrium
- Endometrium
Perimetrium
The outer layer of the uterus wall
Visceral peritoneum
Myometrium
The middle layer of the uterus wall
With three layers of smooth muscle
Endometrium
The inner layer of the uterus wall High vascular (rich supply of blood vessels) Divided into the: 1. Stratum functionalis 2. Stratum basalis
Stratum functionalis
Layer of the endometrium that sloughs off during menstruation
Stratum basalis
Permanent deeper layer of the endometrium
Regenerates the stratum functionalis ready for the implantation of a fertilised egg (zygote)
Uterus: uterine regions
Fundus (top bit)
Body (hollow bit)
Cervix (narrow bit)
Size and shape of a pear
What holds the uterus and ovaries in place ?
The broad ligament
Uterus: location
Posterior to the bladder
Anterior to the rectum
What is an embryo?
The developmental stage following a zygote.
Lasts until ~8 weeks
What is a foetus?
Developmental stage following an embryo
After around 8 weeks
Placenta: functions
Allows oxygen and nutrients to diffuse from maternal blood into foetal blood
Allows carbon dioxide and waste to move in the opposite direction
Produces hormones that are needed to maintain the pregnancy
What is the placenta attached to?
The endometrium
Why is the placenta unique?
By the beginning of the 12th week, it contains 2 distinct regions from two individuals
What is the umbilical cord?
Connects the placenta to the embryo/foetus
Around 50-60cm long
What can’t pass through the protective barrier in the placenta?
Blood cells
Most micro-organisms
What can pass through the protective barrier in the placenta?
HIV Measles Polio Chicken pox Alcohol Drugs
What mediates the transfer of nutrients to the foetus?
Proteins called nutrient transporters
Placenta: hormones
Progesterone Oestrogen Human Chorionic Gonadotrophin (hCG) Human Placental Lactogen (hPL) Relaxin Corticotrophin Releasing Hormone (CRH)
Progesterone
Maintains endometrial lining to sustain and nourish the foetus
Produced by corpus luteum until 8 weeks
Oestrogen
Promotes growth of breast tissue and myometrium
Produced by corpus luteum until 8 weeks
Human Chorionic Gonadotrophin (hCG)
Only produced during pregnancy
Maintains corpus luteum for 8 weeks and increases transfer of nutrients to foetus
Initially produced by the embryo then by the placenta after a few weeks
Related to morning sickness
Human Placental Lactogen (hPL)
Increases the amount of glucose and lipids in the maternal blood
Relaxin
Targets ligaments and relaxes them
Produced by the corpus luteum and then placenta
How is Corticotrophin Releasing Hormone (CRH) involved in pregnancy ?
Triggers release of cortisol from the adrenal glands
Prevents rejection of foetus/placenta (as seen as ‘foreign invaders’)
Risks of placenta praevia
Obstructing the opening of the cervix (more risk with multiple births as more placentas present)
When is it possible for placenta praevia to resolve itself?
During 1st trimester
What can happen in placenta praevia during the 2nd and 3rd trimester?
Prone to haemorrhage
Wall of cervix stretches and can detach from placenta
Uterine vessels rupture and cause ante-partum vaginal bleeding
What is the treatment for placenta praevia in the later stages?
C-section
Placenta Accreta
Abnormally deep attachment of the placenta through the endometrium into the myometrium
Increta
If the placenta invades the myometrium
Percreta
If the placenta goes through the uterine wall to surrounding viscera e.g. the bladder
What causes placenta accreta?
Thin, inadequate stratum basalis in endometrium
Placenta has to dig deeper when implanting
Due to previous C-section, curettage (scraping procedure), fibroid removal, placenta praevia
Risks of placenta accreta
Post-partum haemorrhage
Placenta Abruption
When the blood vessels adhering the placenta to the uterine wall rupture, leading to separation of the placenta from the uterus
Risk factors for placenta abruption
Smoking
Maternal hypertension (pre-eclampsia)
Considered obstetric emergency after 20 weeks
Signs and symptoms of placenta abruption
Abdominal pain
Ante-partum bleeding
Placenta abruption: epidemiology
Occurs in 1% of pregnancies worldwide
In placenta abruption, what happens to the baby <30 weeks?
Monitor vitals until baby is old enough to deliver safely
Foetal lungs matured with corticosteroids
In placenta abruption, what happens to the baby >30 weeks?
Delivery
Twins: definition
Siblings that result from same pregnancy
Monozygotic twins
Identical twins with same genetic information
Originate from a single fertilised ovum
One egg, one sperm
The zygote splits into two embryos but share same placenta
Dizygotic twins
Non-identical
Release of two ova with both being fertilised and implanted independently
Two eggs, two sperm
Two different placentas
(Two separate pregnancies in one)
Fallopian tubes
These extend laterally from the uterus to the ovaries
Provide a route for sperm to meet the ova - and for the ova to reach the uterus
What are fimbriae?
Finger-like projections that surround the ovary and sweep the ova into the fallopian tubes
How does the fallopian tube move the ova from the ovary to the uterus?
- Tubes are lined with ciliated columnar epithelium that help move the ova towards the uterus
- Smooth muscle layer performs peristalsis to assist in ova movement