Placentation, Gestation, Parturition Flashcards
5 structures that make up the placenta in domestic animal
Chorion (outermost) Amnion (surrounds embryo) Allantois Yolk sac umbilical cord
What is the allantois
Cavity originating as outpouching of hindgut, continuous with urachus
4 ways to classify placentation
Shape
Degree of invasiveness
Intimacy of attachment
Nature of fetal placental vasculature
4 shapes of placentas
Diffuse
Cotyledonary
Zonary
Discoid
Who has a diffuse placenta?
Horse, pig, camelid
Who has a Cotyledonary placenta?
Cow, sheep, goat
Who has a Zonary placenta?
Dog, cat
Who has a discoid placenta?
Human, mouse
4 degrees of invasiveness of placenta
Epitheliochorial
Syndesmochorial
Endotheliochorial
Hemochorial
What is an epitheliochorial placenta and who has it?
It has intact membranes on both sides.
Cow, pig, horse
What is a syndesmochorial placenta and who has it?
It’s a fetal-maternal syncytium
Sheep, cow
What’s an endotheliochorial placenta and who has it?
It has one layer between fetal and maternal endothelial cells.
Dog and cat
What’s a hemochorial placenta and who has it?
Maternal blood is in DIRECT contact with chorion.
Human, mouse, guinea pig
2 ways to classify intimacy of attachment?
Adeciduate
Deciduate
What is an adeciduate intimacy of attachment?
Loose fitting of villi with endometrium. Villi pull free without disrupting endometrium during parturition
Horse, pig, ruminants
What is a deciduate intimacy of attachment?
Close fitting of villi-endometrium. Villi pull free and cause erosion of endometrium during parturition.
Dog, cat, human
Bovine placenta characteristics:
Cotyledonary, chorioallantoic, epitheliochorial and syndesmochorial, adeciduate
Characteristics of equine placenta:
Diffuse, chorioallantoic, epitheliochorial, villous, adeciduate
Characteristics of canine placenta:
Zonary, chorioallantoic, endotheliochorial, deciduate
What are endometrial cups? Purpose?
Found in equine placenta. Form during pregnancy and are source of equine chorionic gonadotropin (eCG). Purpose is to increase immunological tolerance of mare in order to protect developing foal
Other structures of equine placenta
Allantoic vesicles Cervical star Amniotic plaques Yolk sac Hippomane
Bovine placenta characteristics?
Amniotic plaques Allantoic calcification mineralization Allantoic calculi = "bovimane" Necrotic tips of chorion Adventitious / adventitial placentation
Characteristics of pig placenta
Necrotic tips
Areolae
Characteristics of dog placenta
Marginal hematoma
Yolk sac
Unique about camelid placenta?
Epitheliochorial but also has horizontal line “epithelion” across placenta
Cow fetal period? What happens at this point?
After 45d
Fetus has organs, placenta
It’s a period of growth
6 hormones produced in conjunction with placenta?
Progesterone Estrogen Relaxin Placental lactogen Chorionic gonadotrophin Prolactin
What’s unique about progesterone in equine pregnancy?
There’s no native progesterone in late equine pregnancy because the pregnancy is maintained by 5alpha-pregnanes which interacts with progesterone receptors and acts like progesterone
What is unique about estrogen in late equine pregnancy?
There are high circulating levels of unique estrogens, equilin & equilenin. There’s also an industry for pregnant mare urine bc its used to make hormone replacement for human women.
What is the function of fetal fluids?
Protection, nutrient reservoir, water reservoir
T or F: progesterone is a requirement for mammalian pregnancy
T
Where does progesterone come from?
Ovary and placenta
Unique about progesterone?
It’s a C21 steroid and it can also be called “prostagen”
4 functions of progesterone:
Placental development / function
Myometrial quiescence
Cervical closure
Immune mediation
What are the 3 maternal cardiovascular responses to pregnancy?
- Uterine blood flow increase (decreased vascular resistance / new blood vessel growth)
- CO increases
- BV increases
4 physiological changes of pregnancy?
- Increased circulating volume (decreased hematocrit)
- Increased insulin resistance
- Decreased residual volume
- Kidney, GI, immune tolerance
What diseases could result in an increased insulin resistance during pregnancy?
- Risk of laminitis
- Risk of frank diabetes
How do physiological changes in pregnancy affect anesthesia?
Have to give less anesthesia
5 triggers for parturition?
- Fetal hypothalamic-pituitary-adrenal axis
- Sustained fetal hypoxemia in late pregnancy
- Placental adequacy, rapidly growing fetus
- Fetal maturation
- High cortisol levels: highly bound, rapidly metabolized
How is cortisol made?
CRH –> ACTH –> Cortisol
What happens to fetus when cortisol levels are elevated?
Final maturation of fetal lung, kidneys, Brian
Induces P450C17 enzymes
(In primate and guinea pigs)
What do P450C17 enzymes do?
Progesterone –> androgens –> estrogens
Switch in P4:E2 ratio
Increased production of prostaglandins by placenta and uterus
Functions of prostaglandin F2alpha?
Further stimulates fetal secretion of CRH
Stimulus P450 system
Myotonic (inability to relax voluntary muscle after rigorous effort)
Functions of estrogen?
Synergistic with relaxin
Breaks down disulphide bonds in collagen (softens ligaments, cervical ripening)
-also functions in activating relaxin in cow (in ovary) and mare (in placenta)
What are cytokines responsible for in parturition?
Recruiting leukocytes to placenta, endometrium, cervix, and contributing enzymes to cervical ripening, placental detachment, and uterine remodeling
4 main activities of myometrium in pregnancy:
- Free intracellular Ca2+
- MLCK activation (via calmodulin) / phosphorylation
- PGF2alpha and oxytocin
- Relaxin stimulation
Mechanism of PGF2a?
SR binds calcium = free calcium = Calmodulin + MLCK bind = Actin + Myosin –> contraction!!!!!
What is fergusson’s reflex?
Pressure in cervix/vagina which increases secretion of oxytocin and an urge to push fetus
Where does cervical dilation start and what happens during it?
Starts at vaginal end. Gets progressively shorter.
Major trigger of parturition is fetal production of:
Cortisol
Where is amniotic fluid absorbed during a fetus’ first breath?
Absorbed from lung into pulmonary circulation
What is the main stimulation of fetus’ first breath?
Cold. Touch and sound also stimulate respiration
What is the role of central chemoreceptors in fetus’ first breath?
Increase respiratory drive
What stimulates central chemoreceptors?
Hypoxia, hypercarbia
What kind of pressure is present when fetus is born?
High NEGATIVE inspiratory pressure
What does the high negative inspiratory pressure contribute to in initial breathing of fetus?
Airway resistance, fluid in airways, and surface tension of alveoli
What are the effects of production of surfactant by type II pneumocytes during a fetus’ first breath?
Cortisol is produced. Epi is produced (or inj. Can be given), alveolar distention happens to stimulate breathing
Where is the respiratory rhythm generated?
Ventrolateral medulla
What is respiratory rhythm modulated by?
Central chemoreceptors (in response to changing CO2, pH, O2)
What do peripheral chemoreceptors function as?
Sensing high O2 in neonate. Silent at first. Adapt over 48 hrs.
What are the peripheral chemoreceptors?
Aortic and carotid bodies
What is the initial response to hypoxia?
Tachypnea followed by reversion to fetal response
Where is oxygenated blood delivered in fetus?
Brain, myocardium
Where is returning oxygenated blood delivered in fetus?
Ductus venosus, foramen ovale
What is the function of the ductus venosus?
Bypasses liver to vena cava
Function of foramen ovale?
Shunt from R to L atrium
Where is deoxygenated blood in fetus delivered?
RA, RV, pulm a.
How much blood does ductus arteriosus deviate to aorta?
80%
What closes at birth?
Foramen ovale
Ductus arteriosus
Ductus venosus
What happens when ductus venosus closes?
Reverse flow
What happens when ductus arteriosus closes?
ALL BLOOD CAN NOW TRAVEL TO LUNGS VIA PULM AA.
Drop in pulmonary pressure
Increase in systemic vascular resistance
Reverse flow
Increased PO2
Decreased PGE2
Why do neonates lose heat so quickly?
High surface:volume ratio (dont weight much)
Limited SQ fat for insulation
Evaporate heat loss bc WET
How to stimulate thermogenesis?
Limb movement
Stimulation of brown fat (triglycerides + free FAs)
Is stimulation of brown fat sympathetic or parasympathetic?
SYMPATHETIC
What’s important about hepatic function in neonates?
Gradually increases over first 3 months
What is true about renal function in neonates?
Glomeruli + nephrons present at birth but immature
Lack osmotic gradient (cant concentrate anything)
LOWER GFR than adult
What does it mean that neonates have a lower GFR than adults?
Susceptible to dehydration + volume overload (bc they feel dehydrated so want to drink more fluid but end up not being able to properly filter so system is overloaded with water)
What stimulates lactation?
Progesterone, estradiol, prolactin, placental lactogens (ONLY some species)
Importance of colostrum?
Immunoglobulins
Immune cells
Nutritive
What is the milk-ejection reflex?
Stimulus: suckling is the sensory input —> hypothalamus —> AP releases prolactin = milk production and PP releases oxytocin = milk ejection
