Flashcards in Neonatal physiology and lactation Deck (62):
What are the stimuli to lung inflation?
1. Tying/breaking the cord
2. Cold exposure
3. Sensory stimuli
What are the circulatory changes in the fetus at birth?
1. Decreased pulmonary vascular resistance
2. Increased pulmonary blood flow
3. Closure of foramen ovale and initiation of closure of ductus arteriosus
What are the main neonatal fuel reserves?
1. Liver glycogen
2. Muscle glycogen
What are the stimuli for mobilisation of hepatic glycogen?
1. Increased catecholamine levels at birth
2. Direct splanchnic innervation
3. Changes in insulin/glucagon ratio
How long can the human neonate survive without significant calorific intake?
How do endocrine glands change postnatally?
1. Alter set-point
2. Alter sensitivity
How do neonates survive insults well?
1. Large fuel reserves
2. Capacity for non-shivering thermogenesis (brown fat)
3. Resistance to anoxia and hypoglycaemia
What is each mammary lobe subdivided into?
What connects mammary gland lobes to the nipple?
What triggers breast development at puberty?
1. Ovarian oestrogen
2. Adrenal steroids
3. Growth hormone
What occurs to mammary glands during pregnancy?
1. Rapid growth and branching of terminal portions of lobules
2. Increased vascularity
3. Formation of glandular acini
When does alveolar secretion begin?
Not fully activated until after birth
What is the composition of human breast milk?
Trace minerals, hormones, growth factors and amino acids
What is the main energy source in milk?
How does colostrum differ from mature milk?
1. Less fat and lactose
2. More proteins, Ig and fat-soluble vitamins (A, D, E, K)
Which pathways are involved in milk formation?
2. Lipid transfer
3. Apical transport
Which enzymes are required for lactose formation?
1. Lactose synthase
Which hormones are required for the onset of lactation?
1. Withdrawal of progesterone and oestrogen
2. Presence of prolactin
What causes a decrease in progesterone and oestrogen after birth?
Delivery of the placenta
What does prolactin do?
Stimulates alveoli protein and fat synthesis
How can lactogenesis be inhibited?
1. Administration of oestrogen
2. Inhibiting prolactin secretion with dopamine agonists, such as bromocriptine
How is lactation maintained?
Mechanical stimulation of the nipple
Removal of milk products removes their inhibition of further synthesis of lactose
How are suckling reflexes mediated?
Anterolateral columns in spinal cord
PVN and SON in hypothalamus
Which responses are evoked by suckling?
1. Release of prolactin and other hormones forming the lactogenic complex (ACTH and GH)
2. Release of oxytocin pulses
3. Inhibition of GnRH release
What is the effect of oxytocin pulses?
Causes contraction of myoepithelial cells around ducts, causing milk let down and milk ejection
What is the effect of GnRH inhibition?
Inhibits gonadotrophin release and ovulation
How might lactational reflexes be conditioned?
1. Sound of crying baby
2. Demand feeding
How do infants express milk from the nipple?
Strip out milk stored in lactiferous sinus using tongues and hard palates
Does not have to generate negative pressure to breast feed (though it does to bottle feed)
How does vertical transmission of HIV occur?
Most occurs during delivery
Additional risk from breastfeeding is 10-14%
What are the factors influencing the circulatory changes at birth?
Deposition of connective tissue
Why is there minimal digestive activity in the first 24 hours of life?
Need to absorb macromolecules such as gamma globulins from the colostrum
(not in humans)
How can thermogenesis occur in human neonates?
2. Non-shivering thermogenesis
What does non-shivering thermogenesis depend on?
Presence of brown fat
How much of human infant body weight does brown fat account for?
How does brown fat warm the baby?
It is positioned to warm blood entering from the periphery into the main veins
How is brown fat stimulated to increase heat production?
1. Circulating catecholamines
2. Thyroid hormones
3. Stimulation of the sympathetic nerves
How does a baby prevent heat gain?
Mechanisms are poorly developed
Little sweating, with a higher threshold
Susceptibility to dehydration
Tendency to gain heat in high ambient temperatures
Requires intelligent parental intervention to circumvent problems
Which endocrine glands show changes in activity during the perinatal period?
1. Pituitary-adrenal axis
2. Thyroid gland
How does the pituitary-adrenal axis change perinatally?
Prepartum activation essential for neonatal adaptation
How does the thyroid gland change prenatally?
Prepartum increases in T3 with resetting of the axis after birth in association with the need for thermoregulation
How does the pancreas change around birth?
Becomes important in the control of glycaemia
Large changes in the insulin and glucagon concentrations at birth which are involved in activating gluconeogenesis
What are the clinical problems common to premature infants?
1. Respiratory distress syndrome
4. Immaturity of neural mechanisms
5. Increased susceptibility to infection
How many lobes in a human mammary gland?
15-25 irregular lobes radiating out from the nipple and surrounded by connective and adipose tissue
Which hormones are required for milk secretion?
2. Adrenal steroids
How long does it take the contents of milk to reach the mature composition?
What milk components are exocytosed?
2. Milk proteins, eg. lactalbumin
What enzyme is lactose formation dependent on?
What is lactose synthetase?
A combination of α-lactalbumin and galactosyltransferase
How are triglycerides made in the SER exported in milk?
As fat droplets which form an emulsion with the aqueous phase
Which milk components are carried by apical transport?
3. Certain monosaccharides
Which milk components are transported by transcytosis?
Extra-alveoli proteins, such as IgG
How does oestrogen affect lactation?
Inhibits the action of prolactin
How does progesterone affect lactation?
Inhibits the action of lactose synthetase
What is the milk ejection reflex?
Suckling causes release of oxytocin pulses from the posterior pituitary
This causes contraction of the myoepithelial cells surrounding the ducts, which in turn, causes milk let down
What is galactokinesis?
Milk let down
What is the worst feeding regime for HIV positive mothers in Africa?
Mixed feeding regime as this exposes the infants to a high risk of enteritis and the damaged gut lining then may allow the HIV virus to enter the infant more readily
What is kernicterus?
Lack of conjugation of bilirubin post-natally allows it to enter the CNS and cause brain damage
How is pre-natal bilirubin excreted?
In fat soluble, unconjugated form across the placenta
How is post-natal bilirubin excreted?
Water soluble, conjugated form into bile and urine
Why is prenatal conjugation bad?
It traps bilirubin in the fetus
How are bilirubin levels controlled after birth?
Increase in bilirubin levels after delivery induces enzymes for bilirubin conjugation, so the enzyme is only synthesised when needed