Parturition, lactation, and neonatal physiology

Question 1

when does Human birth occur and what does parturition involve?

Answer 1

Human birth usually occurs at 40 weeks gestation (s3 weeks fetal age)

Parturition involves:

• Transformation of the myometrium from quiescent to highly contractilve
• Remodeling of the uterine cervix to soften and dilate it
• rupture of the fetal membranes
• expulsion of the uterine contents
• return of the uterus to its prepregnant state

Question 2

What are the changes that occur in the uterine activity during parturition?

Answer 2

Most pregnancy uterus is relaxed, quiescent, relatively insensitive to hormones that stimulate contractions (prostglandins and oxytocin)

uterus grows and distends to acccommodate the developing fetus, placenta, and amniotic fluid

Uterine myometrial cells undergo significant hypotrophy

weak irregular contractions, braxton hicks contractions, occur towards end of pregnancy

• not powerful enough to induce labor
• thought to prepare the uterus for parturition

Question 3

Hormonal changes in Progesterone for parturition?

Answer 3

Progesterone:

• promotes the myometrial relaxation during pregnancy
• blocks contractions of labor
• treatment with nuclear progesterone antagonists increases myometrial contractility (can induce labor at any stage of pregnancy)

Thought to be a desensitization of uterine cells to the actions of progesterone

• functional rather than systemic withdrawal
• leads to an increase in estrogen receptor expression

Question 4

Hormonal changes in estrogen for parturition

Answer 4

Estrogens:

• following progesterone desensitization in uterine cells, increase in estrogen receptor expression
• increase myometrial contractility and cervical dilation

oppose the actions of progesterone by increasing responsiveness to oxytocin and prostglandins

• stimulate formation of gap junctions
• increase number of oxytocin receptors in myometrium and decidual tissue

Increase production and release of prostaglandins by fetal membranes

stimulate expression of proteolytic enzymes in the cervix i.e. collagenase

Question 5

hormonal changes in prostaglandins in parturition

Answer 5

Prostaglandins:

• stimulate strong myometrial contraction
• will initiate labor via large dose of PGF2a and PGE2 can induce myometrial contractions at any stage of gestation

PGF2a potentiates oxytocin induced contractions by promotion of gap junctions
-stimulate effacement of cervix in labor

synthesis of prostaglandins stimulated by:

• estrogen in fetal membranes
• oxytocin in uterine cells
• uterine stretch

Question 6

hormonal changes in oxytocin in parturition?

Answer 6

Oxytocin:

Uterus is insensitive to oxytocin until week 20

Estrogen increases the oxytocin receptor numbers

• 80x higher than baseline at 36 weeks
• 200x by early labor
• uterine myometrium for smooth muscle contraction
• decidual tissues stimulate PGF2a production

Question 7

what is the fergusion reflex?

Answer 7

During labor, oxytocin stimulates uterine contractions that sustain labor that stimulates the production of PGF2a production in decidual cells

this is released in bursts during active labor that increases its frequency as labor progresses

this primary stimulus for release is distention of the cervix that creates a positive feedback loop to enhance labor

Question 8

hormonal changes in relaxin in parturition

Answer 8

Relaxin:

• cytokine structurally related to insulin
• produced by the corpus luteum, placenta, and decidua
• plays a role in keeping uterus in a quite state during pregnancy
• maximal plasma concentration at weeks 38-42
• may soften and help dilate the cervix
• elevated levels at 30 weeks associated with premature birth

Question 9

mechanical changes that occur in parturition

Answer 9

Uterine size:

• a factor in regulating parturition
• stretch of smooth muscle increases ferguson reflex positive feedback and thus further contractions
• uterine stretch also increases prostaglandin production
• twins average 19 day shorter gestation

Cervical remodeling is necessary for expulsion of fetus
-structural changes resulting in change from fetal support to birth canal

Question 10

Initiation of labor

Answer 10

Placenta produces corticotropin releasing hormone (CRH)

• maternal levels rise during late pregnancy and labor
• promotes myometrial contractions (sensitizing uterus to prostaglandins and oxytocin
• accumulates in fetal circulation

Stimulates fetal secretion

• increase fetal adrenal cortisol production which stimulates furthur placental CRH release
• increase fetoplacental estrogen which enhances myometrial contractility

Question 11

how do contractions occur in pregnancy, labor, and parturition

Answer 11

Most of pregnancy, uterus undergoes periodic episodes of weak and slow contractions
-braxton hicks contractions

Become exceptionally strong during last hours of pregnancy into active labor

• begin to stretch cervix, shorten muscle walls
• retract lower uterine segment and cervix upward
• cervix becomes increasingly dilated and is drawn up to just below the pelvic inlet

Fully dilated cervix is drawn up just below the pelvic inlet

subsequent uteine contractions push fetus downward and through the pelvis

Entire process varies in duration

• first stage occupies most of the time
• second stage is generally less than an hour

Question 12

5 Phases of delivery

Answer 12

1) presentation of head
2) rotation and delivery of anterior shoulder
3) delivery of posterior shoulder
4) delivery of lower body and umbilical cord
5) expulsion of the placenta

Question 13

How does the body expulse the placenta?

Answer 13

Uterus contracts reducing area of attachment

separation of placenta results in bleeding and clotting

• oxytocin constricts uterine blood vessels
• nipple stimulation induces oxytocin release
• synthetic oxytocin sometimes given to assist uterine contractions

Question 14

what does surfactant do in the lungs?

Answer 14

Secreted by type II alveolar epithelial cells

synthesis begins in the last semester

once alveoli open, harder to close them when exhaling with surfactant

this is because surfactant decreases the surface tension

Question 15

what is the stimuli of breathing at birth and what if it is delayed

Answer 15

Breathing initiates within seconds of birth

stimuli:

• Asphyxiation during birth
• sudden drop in temperature/cooling of the skin

delayed breathing upon birth

• use of general anesthesia during delivery
• prolonged labor
• head trauma, depressed respiratory center

Question 16

pressure changes for the first breath

Answer 16

At birth alveoli are collapsed and amniotic fluid fills them

more than 25mmHg negative inspiratory pressure needed to overcome surface tension and open the alveoli

1st inspiration the infant is capable of 60mmHg of O2
1st inspiratory movements brings in nearly 40 ml of air

deflation requires strong positive power
-must overcome viscous resistance of fluid in bronchioles

Question 17

pressure changes for the second breath?

Answer 17

Second breath requires less effort and so forth

doesnt become normal until 40 min after birth

settles to 40 breaths per minute and the tidal volume of 6-10ml/kg

Question 18

fetal blood flow vi the placenta

Answer 18

Massive blood flow to placenta shunts blood away from the lower trunk

umbilical arteries

• branch repeatedly
• returns deoxygenated blood
• dense capillary network at terminal villi
• legs connect to the inferior vena cava

umbilical vein:

• returns oxygenated blood to fetus from placenta
• PO2 = 30-35 mmHg
• blood enters ductus venosus

Question 19

what is the ductus venosus

Answer 19

liver bypass

• liver is largely non functional
• direct route from umbilical vein to the inferior vena cava

Question 20

function of the foramen ovale

Answer 20

Hole in septum dividing the atria found in the posterior aspect of the right atrium

• right to left shunt
• bypass around the right ventricle
• PO2 about 27mmHg inferior vena cava right through to left ventricle to supply the carotid and brain
• of blood entering the right atrium 27% is shunted through the foramen ovale

Question 21

function of the ductus arteriosus

Answer 21

Pulmonary artery to aorta

• another right to left shunt
• substantial amount of smooth muscle that is being dilated by prostaglandins (PGE2)

Question 22

how does closure of the foramen ovale occur?

Answer 22

Reversal of pressure gradient across the atria

pushes foramen ovales valve shut

due to:

• increased venous return to left atrium and elevated left atrial pressure
• decreased right atrial pressure

eventually flap will seal

Question 23

how does the ductus arteriosus close?

Answer 23

Aortic pressure rises above the pilmonary artery pressure making blood flow the wrong way

now well oxygenated aortic blood flows through the ductus arteriosus

• high pO2 causes vasoconstriction within an hour
• falling prostaglandin levels
• 1-8 day constriction is sufficent
• 1-4 mo anatomically occluded

Question 24

what does closure of the ductus arteriosus and foramen ovale establish?

Answer 24

a right and left circulatory system

• sytemic
• pulmonary

Question 25

what is a patent foramen ovale

Answer 25

In 20percent of individuals by 2 years of age the foramen ovale does not close permanetly - increased right atrial pressure can push open the flap - sustained pulmonary hypertension or transient increases (bowel movement, coughing, and sneezing)

Question 26

patent ductus arteriosus (PDA)

Answer 26

Heart problem occurs soon after birth - van be heard as a heart murmur on stethoscope - oxygenated blood in aorta mixes with deoxygenated blood in pulmonary artery - puts strain on heart and increases pulmonary blood pressure

Question 27

how does the ductus venosus close?

Answer 27

Immediately after birth, most portal blood flow through ductus venosus - 1-3 hours muscle wall of ductus venosus contracts and closes - portal venosus pressure rises forcing venous blood through liver sinus - rarely fails to close

Question 28

Characteristics of the fetal kidney

Answer 28

nephrogenesis begins at 8 weeks gestation and completed at 36 weeks urine production begins as early as 10 weeks through 20 weeks gestation fetal urine accounts for 70-80 percent of amniotic fluid renal function matures rapidly in the 3rd trimester -body fluid balance, acid-base balance, and electrolyte balance Functional development completes closet to `1 month of age

Question 29

Characteristics of the fetal liver

Answer 29

Poor conjugation of bilirubin, deficiency in forming plasma proteins and coagulation factors, deficient gluconeogenesis -blood glucose levels the 1st day could be as low as 30-40mg/dL infant uses its stored fats and proteins for metabolism until mothers milk can be provided

Question 30

Characteristics of the fetal hemoglobin

Answer 30

``` Hb F (a2y2) is the major hemoglobin of fetal life -oxygen has a higher binding affinity than to an adults Hb A (a2b2) ``` normal adult levels of HB A2 are achieved by the 12th week of life

Question 31

what are the nutritional needs of the neonate?

Answer 31

Ca+ and vitamin D for rpid ossification of bones -normally the adequate amount can be supplied by the usual diet of milk Iron: - liver has stored enough iron to keep forming blood for 6 months - iron content of breast milk is low, but high bioavailabillity - this is the reverse in formula Vitamin C: - vitamin C is not stored in significant quantities in the fetal tissues - adequate amounts can be provided by the mothers breast milk

Question 32

Characteristics of neonatal immunity

Answer 32

Neonate inherits a great degree of immunity from the mother and does not form antibodies of its own to a significant extent antibodies inherited from the mother protect the infant for about 6 months against most major diseases Baby own immune system begins to form antibodies and gamma globulin concentrations return to normal by age of 12-20 months

Question 33

Breast development from birth to sexual maturity

Answer 33

At birth, mammary gland almost entirely lactiferous duct with few alveoli -apart from some branch development, the breast remains in this state until puberty under the actions of estrogens, lactiferous ducts sprout and branch -ends form small solid, spheroidal masses of cells which develop into alveoli as menstrual cycle is establishe, mammary tissue is exposed to estrogen and progesterone -induces additional ductal-lobular-alveolar growth breast increases in size - deposition of adipose and connective tissue - involution - some secretory activity occurs - breast tenderness

Question 34

cells of the breast tissue

Answer 34

Alveolar epithelium: - luminal epithelial - cells responsible for milk synthesis and secretion Myoepithelial cells: - between epithelial cells and basement membrane - contractile function - move milk from alveoli to duct

Question 35

Hormones that affect breast development

Answer 35

puberty: - estrogens - progesterone pregnancy: - prolactin - hPL - estrogens - progesterones these homones that affect the breast are: - mammogenic: promoting the proliferation of alveolar and duct cells - lactogenic: promoting contraction of myoepithelial cells and thus milk ejection - galactopoietic: maintaining milk production after it has been established

Question 36

what are the 5 main ways that alveolar epithelial cells excrete milk?

Answer 36

1) secretory pathway through the ER and Golgi 2) Transcellular endocytosis and exocytosis 3) Lipid pathway via milk lipids 4) Transcellular salt and water transport 5) paracellular pathway

Question 37

4 effects of suckling on hormone release

Answer 37

1) suckling stimuli or sight of a child - activates afferent neural pathway from breast to spinal cord and then to hypothalamus 2) Dopamine release is inhibited - releases inhibition of lactotrophs and results in release of prolactin which stimulates milk production 3) Stimulation of production and release of oxytocin from posterior pituitary - interacts with myoepithelial cells resulting in let down of milk 4) inhibition of hypothalamus GnRH production - results in decreased release of LH and FSH and inhibits the ovarian cycle

Question 38

Cessation of lactation

Answer 38

When the suc\kling stimulus is discontinued milk accumulates - distension and mechanical atrophy of epithelial structures - rupture of alveolar walls - compression of capillaries resulting in alveolar hypoxia Cell and glandular debris are phagocytosed lobular acinar structures become smaller ductal system predominates full involution can take up to 3 months