7 - physiology of placenta; pregancy and childbirth

List 2 main adaptations of maternal physiology during pregnancy

• 30% increased blood flow and heart enlarges

• 20% increased respiration

List 3 additional adaptations of maternal physiology during pregnancy

• nutrient diversion

• increased hepatic function

• hypercalcaemia to facilitate fetal skeleton

When does the placenta develop?

after embryo implantation

What kind of organ is the placenta?

endocrine

What kind of tissue is the placenta comprised of?

maternal and fetal tissue

List 2 functions of the placenta (image)

• exchange of oxygen between maternal and fetal blood

• secretes

  • hCG

  • estrogens

  • progesteron

List 2 functions of hCG

• maintains corpus luteum during pregnance

• stimulates testosterone synthesis in developing testes of XY embryos

List 2 functions of estrogens

• stimulate endometrial growth

• stimulate proliferation of mammary tissue in preparation for lactation

List 4 functions of progesterone

• promotes formation of cervical mucus plug

• suppresses uterine contractions

• stimulates differentiation of lobulalveolar system of mammary glands

• prevents subsequent follicle development and ovulation

What is the cervical mucus plug and whats its purpose

a collection of thick mucus that forms in the cervix during pregnancy

acts as a protective barrier, preventing bacteria and other harmful substances from entering the uterus and potentially harming the fetus

What does human chorionic somatomammotropin do?

increasese availability of glucose and free fatty acids to cells

List 2 functions of relaxin

• softens cervix

• parturition - cervical dilation

What does placental PTHRP do?

increaes maternal calcium

Describe hormonal changes within the 1st trimester of pregancy (3 points)

placenta secretes hCG

• activates LH

• activates chorionic gonadotropin to stimulate progesterone and estadiol synthesis

Describe hormonal changes within the 2nd and 3rd trimester of pregancy (2 points)

placenta secretes progesterone and estradiol

produces estriol from fetal adrenal androgen substrate

List 2 effects of estrogen on the uterus

• increased contraction of smooth muscle

• increased responsiveness to oxytocin

List 1 effect of estrogen on the anterior pituitaty and what this leads to

prolactin secretion whcih stimulates growth and development of breast tissue

List 3 effects of estrogen on breasts

• growth of duct tissue

• fat deposition

• high levels suppress lactation

List 1 effect of progesterone on the uterus and what this leads to

suppression of contractile activity and responsiveness to oxytocin in order to maintain secretory phase conditions

List 2 effects of progesterone on breasts

• growth of glandular tissue

• high levels suppress lactation

Define partuition

uterin econtractions prior to pregancny

List 4 theories of what triggers partuition

1. high levels of estrogen

2. oxytocin

3. CRH from placenta

4. inflammation

How may high levels of estrogen contribute to partuition? (3 points)

• upregulates connexin-gap junctions

• upregulates myometrial receptors for oxytocin

• stimulates local prostoglandin synthesis

How may oxytocin contribute to partuition? (2 points)

• myometrial responsiveness exceeds critical threshold

• increase of calcium activates MLC kinase

How may CRH contribute to partuition? (2 points)

• may increase estrogen synthesis

• increases cortisol (increases prosataglandin synthesis and promotes bronchodilation)

How may inflammation contribute to partuition?

increased nuclear factor K-B upregulates inflammatory cytokines and increases local prostaglandin synthesis

Describe the fergusson reflex (image) (3 points)

• uterine contractions push fetus against cervix, triggering a neuroendocrine reflex that leads to oxytocin secretion

• oxytocin increases utrerine contractions

• oxytocin upregulates prostaglandin production which also increases uterine contractions

Describe the lactation reflex arc (3 points)

• information of baby suckling is send down the afferent arc via the spinal chord to the brain via the spinal cord

• stimulates anterior pituitary gland to produce prolactin which stimulates milk production in mammary alveoli

• stimulates posterior pituitary gland to produce ocytocin which stimulates uterine contractions and milk ejection in myoepithelial cells