WEEK 14 (Foetus & Placenta) Flashcards
Describe the foetal period
- Beginning of Week 9 to birth
- Characterised by maturation of tissues and organs and rapid growth of the body
What is the length of the foetus indicated by?
CROWN-RUMP LENGTH (CRL) or CROWN-HEEL LENGTH (CHL)
What advances happen on the third month?
- Eyes move to ventral aspect of face & ears move to the side of head
- Limbs reach their relative length in comparison with the rest of body (lower limbs little shorter + less well developed)
- External genitalia develop -> SEX OF FOETUS DETERMINED
What advances happen on the fourth and fifth months?
- CRL is around 15cm (half the total length of the newborn)
- Weight is less than 500g
- Foetus is covered with fine hair called LANUGO HAIR
- Eyebrows and head hair are visible
During which month can movements of the foetus be felt by the mother?
Fifth month
What advances happen on the sixth month?
- Foetus weight increases considerably
- Skin of foetus is reddish and has a wrinkled appearance due to lack of underlying connective tissue
- Respiratory system and CNS have not differentiated sufficiently
What is the length of the foetus indicated by?
CROWN-RUMP LENGTH (CRL) or CROWN-HEEL LENGTH (CHL)
How long is a normal pregnancy?
280 days (40 weeks) after the last normal menstrual period OR 266 days (38 weeks) after fertilisation
By 6.5 to 7 months, what are the chances of survival?
90%
What advances happen during the last 2 months?
- Skin is covered by a whitish, fatty substance composed of secretory products from SEBACEOUS GLANDS
- Sexual characteristics are pronounced
What are the statistics of a normal foetus during the time of birth?
- 3-3.4kg
- CRL = 36cm
- CHL = 50cm
What is the placenta?
The organ that facilitates nutrient and gas exchange between maternal and foetal compartments
What is the foetal component and the maternal component derived from?
- Foetal component = Trophoblast and extra embryonic mesoderm
- Maternal component = Uterine endometrium
Which components make up the placenta?
- CHORION FRONDOSUM (foetal portion)
- DECIDUA BASALIS (maternal portion)
What is the only portion of the chorion participating in the exchange process?
Chorion frondosum
Describe the Full-term placenta
- Divided into a number of compartments (COTYLEDONS)
- Placenta enlarges as foetus grows
- 15-25cm, 3cm thick & weighs 500-600g
- Foetal surface of the placenta is covered entirely by CHORIONIC PLATE
What converges to form the Umbilical cord?
- Large arteries
- Large veins
- Chorionic vessels
Describe the circulation of the Placenta
COTYLEDONS receive blood through SPIRAL ARTERIES that pierce the DECIDUAL PLATE and enter the INTERVILLOUS SPACES -> Pressure in the arteries force blood deep into the INTERVILLOUS SPACES -> As pressure decreases, blood flows back from the CHORIONIC PLATE towards the DECIDUA where it enters the ENDOMETRIAL VEINS
What are the functions of the placenta?
- Metabolism
- Transport
- Endocrine secretion
- Protection
- Excretion
Describe foetal immunity
Immunoglobins consist almost entirely of MATERNAL IMMUNOGLOBIN G (IgG) which is transported to the foetus at 14 weeks -> Foetus gains passive immunity -> Newborns begin to produce their own gig but adult levels are not attained until 3 years old
What is attachment of the umbilical cord to the foetal membranes called?
Velamentous insertion of the cord
What can excessively long and short umbilical cords cause?
SHORT = Premature separation of the placenta from the wall of the uterus during delivery
LONG = Tendency to prolapse and/or coil around the foetus
Why is prompt recognition of the prolapse of the umbilical cord important?
The cord may be compressed between the presenting body part of the foetus and the mother’s bony pelvis -> Foetal HYPOXIA or ANOXIA -> If the deficiency of oxygen is more than 5 minutes the neonate’s brain may be damaged
Describe the structure of the umbilical cord
Two arteries and one large vein which are surrounded by mucoid connective tissue (Wharton jelly)
What’s the difference between False knots and True knots?
False knots = no significance
True knots = may tighten and cause foetal death resulting from anoxia
[CAUSE: Because the umbilical vessels are longer than the cord, twisting and bending of the vessels are common causing knots]
Describe the formation of the Amniotic sac
The thin but tough amnion forms a fluid-filled, membranous AMNIOTIC SAC that surrounds the embryo and the foetus -> The sac contains AMNIOTIC FLUID -> As AMNION enlarges, it gradually obliterates the chorionic cavity and forms the epithelial covering of the umbilical cord
What is amniotic fluid secreted by?
- Amnion cells
- Foetal respiratory ad gastrointestinal tracts
Why is amniotic fluid similar to foetal tissue fluid?
Before KERATINISATION of the skin occurs, a major pathway for passage of water and solutes in tissue fluid from the foetus to the amniotic cavity is THROUGH THE SKIN
Describe the circulation of amniotic fluid
Amniotic fluid is swallowed by the foetus and is absorbed by the foetus’ respiratory and digestive tracts -> Excess water in foetal blood is excreted by the FOETAL KIDNEYS and returned to the amniotic sac through the FOETAL URINARY TRACT
What is the composition of Amniotic fluid?
- An aqueous solution in which undissolved material is suspended
- Half is protein
- Other half is carbohydrates, fats, enzymes, hormones and pigments
What is Amniocentesis and what is its importance?
Amniocentesis = A needle is inserted through the lower abdominal and uterine walls into the amniotic cavity. A syringe is attached and amniotic fluid is withdrawn for diagnostic purposes.
Since foetal urine enters the amniotic fluid -> Fluid removed by AMNIOCENTESIS -> Studies of cells allow for diagnosis of chromosomal abnormalities
What do high and low levels of alpha fetoprotein usually indicate?
High levels = presence of a severe neural tube defect
Low levels = chromosomal aberrations
What is the function of Amniotic fluid?
- Allows symmetric external growth of foetus
- Barrier to infection
- Allows normal foetal lung development
- Cushions the embryo
- Maintains foetus’ body temperature
- Enables foetus to move freely -> aids muscular development
- Maintains homeostasis of fluid and electrolytes
How does the body prepare for labor?
- MYOMETRIUM thickens in the upper region of the uterus
- Softening and thinning of the lower region and cervix
What are the stages of labor?
1) Effacement (thinning and shortening) and dilation of the cervix
2) Delivery of the foetus
3) Delivery of the placenta and foetal membranes
What is Parturition?
The process during which the foetus, placenta and foetal membranes are expelled from the mother’s reproductive tract
Describe the first stage of delivery (Effacement and dilation of the cervix)
Produced by uterine contractions that force the amniotic sac against the cervical canal -> If membranes have ruptured, pressure will be exerted by the foetal head
What is stage two and three of labor aided by?
- Uterine contractions
- Intra-abdominal pressure
Which hormones are involved in birth?
- OXYTOCIN
- PROSTAGLANDINS (promote uterine contractions)
- ESTROGENS (increase myometrial contractile activity + release of oxytocin and prostaglandins)
Describe Oxytocin
- Cause uterine smooth muscle contractions
- Released by the NEUROHYPOPHYSIS of the pituitary gland
- Stimulates release of prostaglandins
What does partial spitting of the primitive node and streak result in?
Formation of conjoined twins
