Good morning, ladies and gentlemen,
my name is Iva Švandová and I have a privilege to spend today’s lecture with you. Today, we have to run through basic /very, very basic/ paediatric anatomy and physiology. Why is this topic worth-mention?
I hope every one of you has ever seen a child. They are sweet, they are cute /at least until you become a parent/, and people often regard their babies as a diminutive version of themselves. However, speaking in terms of anatomy and physiology, CHILDREN ARE NOT JUST SMALL ADULTS. This knowledge is crucial for medical management of the child, from basic care through medication of the child to, for instance, specific child airway management during resuscitation code.
There are many differences between children, adolescents and adults – physiological, anatomical, cognitive, social and emotional. Growth and development consists of a continuum of biologic events that includes somatic growth or neurobehavioral maturation, and this is related to changes in body composition, development of organs and organ systems and change in these organs’ functions.
Three branches of science – anatomy, physiology and embryology – provide the foundation for understanding the biophysical development of children:
Anatomy is the science of body structures and parts, and the relationship among these structures;
Physiology is the science relating how the body functions.
Embryology is the science concerned with the origins and development of the human organism from unicellular embryo or zygote to the birth of a unique human being.
Age stage or age group is a term used to broadly outline key periods in the human development timeline. During each stage growth and development occur in the primary developmental domains including physical, intellectual, language and social – emotional. We recognise following age groups:
· Newborn or Neonate - birth to 28 days
· Infant - 1 to 12 months
· Toddler - 1 to 3 years
· Preschooler - 3 to 6 years
· School Age - 6 to 11 years
· Preteen or Tween - 11 to 12 years
· Teen - 13 and older
As mentioned, children and adults are different. We will discuss some aspects of
· physical appearance
· skeletal system
· nervous system
· cardiovascular system /CVS/
· respiratory system
· renal system
· digestive system and
· immune system
PHYSICAL APPEARANCE
One of the most dramatic difference is physical size. The normal weight of a baby who reaches full term between 37 and 40 weeks is 2.7–4.1kg (6 – 9 lbs), with an average weight of 3.5kg (7.7 lbs). The normal length of a newly arrived baby who reaches full term is 50–53cm, with an average length of 51cm. Notice that head is large compared to the adult, and often in newborns it exceeds the circumference of the chest. Arms and legs are shorted and underdeveloped at birth, with well-developed nails in full-term baby. Regarding the body proportions, midpoint in length on child is umbilicus, whereas midpoint in length on an adult is the symphysis pubis. At birth the infant head is of the proportion 1:4; in the adult it is 1:8. The infant lower limbs are 15 per cent of the total body weight compared to 30 per cent in the adult.
The first 2–3 years of postnatal life is a period of particularly rapid growth and development. Both height and weight increase most during these years. Body weight doubles by 5 months, and triples by 1 year. Body length increases by 50 % during the first year, and doubles by 4 years. Body surface area (BSA) doubles by the first birthday and triples by 4 years. Growth velocity decreases rapidly from 10 % per month at birth to 4 % at 1 year, and down to 1 % for most of the rest of childhood. The growth of the child can be evaluated using grow charts (height-for-age, weight-for-age, head circumference-for-age etc.) and Z-scores (= the deviation of an individual's value from the median value of a reference population, divided by the standard deviation of the reference population, or transformed to normal distribution).
physically and pharmacologically.
The proportions of body weight contributed by fat, protein, and intracellular water (ICW) change significantly during infancy and childhood. Total body water (TBW = ICW + ECW) constitutes 85 % of body weight in the preterm neonate and 70–75 % in term neonates. This decreases to approximately 60 % at 4 months and remains relatively constant from this age onwards. Extracellular water decreases all through childhood. The percentage of body weight contributed by fat is 3 % in a 1.5 kg premature neonate compared with 12 % in a term neonate; this proportion doubles by 4–5 months of age. “Baby fat” is lost when the infant starts walking and muscle protein mass increases from 20 % in the term neonate to 50 % in the adult. All these changes in body composition influence i.e. pharmacokinetics. Pharmacokinetics and proper dosage of the child is also dependent on body surface area (BSA).
Relative body surface is greatest at birth, as compared to body size BSA can be computed using West nomogram, or using several formulas (the most widely used is the Du Bois formula, a commonly used and simple one is the Mosteller formula). BSA doubles by the first birthday and triples by 4 years. Babies and infants have a large surface area to weight ratio with minimal subcutaneous fat. They have poorly developed shivering, sweating and vasoconstriction mechanisms. Average BSA for children of various ages, for men, and for women, are taken to be:
Neonate (newborn) / 0.25 / m²Child of 2 years / 0.5 / m²
9 years / 1.07 / m²
10 years / 1.14 / m²
12–13 years / 1.33 / m²
Women / 1.6 / m²
Men / 1.9 / m²
For many clinical purposes BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass. Nevertheless, there have been several important critiques of the use of BSA in determining the dosage of medications with a narrow therapeutic index, such as chemotherapy. (Typically there is a 4–10 fold variation in drug clearance between individuals due to differing the activity of drug elimination processes related to genetic and environmental factors. This can lead to significant overdosing and underdosing (and increased risk of disease recurrence). There is a clear distinction in regard to pharmacokinetic between children ≥2 years of age and infants <2 years of (postnatal) age. In children ≥2 years, pharmacokinetic parameters can be predicted from adult data using size differences in pharmacokinetic models. When young infants (especially neonates) are being considered, although size is still an important factor, the maturation processes and status are even more important. Age then becomes essential for defining pharmacokinetic in infants compared with children. Some rules for a proper dosage calculation in infants and children you can see in the presentation.
SKELETAL SYSTEM
The skeleton commences its development early in foetal life; the maternal calcium stores will become depleted if this mineral is not ingested to support the foetal changes.
The infant’s head shows the skull bones to be thin and the facial bones small. It possess fontanels soft spots allowing the scull to grow. Nose is flat and jaw is tiny, which helps baby with sucking. (Resuscitation in children under seven years of age demands a different technique to that of adults, as the head and neck anatomy results in relatively high positions of larynx and trachea and the ribcage is more compliant.) Small children have small facial sinuses which do not reach adult size until the age of ten/twelve years. The vertebral spine has
two primary curves present at birth, but normally by adolescence four vertebral curves are evident; the cervical (lordotic), the thoracic (primary curve), the lumbar (lordotic) and the sacral (primary curve).
A newborn is toothless, however, primary teeth start to form during the embryo phase of pregnancy. The development of primary teeth starts at the sixth week of tooth development as the dental lamina. This process starts at the midline and then spreads back into the posterior region. By the time the embryo is eight weeks old, there are ten buds on the upper and lower arches that will eventually become the primary (deciduous) dentition. These teeth will continue to form until they erupt in the mouth. In the primary dentition there are a total of twenty teeth: five per quadrant and ten per arch. The eruption of these teeth ("teething") begins at the age of six months and continues until twenty-five to thirty-three months of age during the primary dentition period. Usually, the first teeth seen in the mouth are the mandibular centrals and the last are the maxillary second molars.
Normal tooth eruption has two stages:
1) There are 20 temporary or deciduous teeth and they erupt between ± 6 – 10 months of age for the lower jaw (7-12 months of age for the upper jaw) and ± 30 months;
2) There are 28 permanent teeth (32 with wisdom teeth) and they appear between ± 6 and 13 years of age.
Girls often have a faster dental development than boys. Primary dentition will be completed between the second and third years of age, and some primary teeth will remain in the mouth until about 12 years of age.
NERVOUS SYSTEM
The nervous system coordinates and controls all body systems to a greater or lesser degree and, together with the hormones of the endocrine system, fine-tunes a delicate homeostasis.
Brain development occurs at several stages during childhood. The critical period for brain growth appears to be during the first sixteen weeks of life. At birth, a baby’s brain weighs approximately 25 per cent of its future adult weight. By the time the child is two years old the brain has increased to 75 per cent, and by six years, 90 per cent of its eventual weight. This, then, indicates phenomenal growth of the central nervous system during the early years. Peripheral nerves continue to become myelinated and fine physical control appears as the child moves towards adult status. The plastic nervous system constantly matures and changes as demands are put upon it.
The most active parts of the brain at birth are the sensorimotor cortex, the thalamus, the brain stem and the cerebellum. All the major surface features of the cerebral hemispheres are present at birth, but the cerebral cortex is only half its adult thickness. The spinal cord is about 15–18 cm long, with its lower end opposite either the second or third lumbar vertebra.The spinal cord does not grow as much as the vertebral canal and therefore appears to rise up as the child grows in length. All the major sensory tracts are fairly well myelinated, but the motor tracts less so. However, the local reflexes related to swallowing and sucking appear before birth and have their nerve pathways well myelinated.
The spinal cord terminates at a much more caudad level in neonates and in infants compared to adults. The conus medullaris ends at approximately L1 in adults and at the L2 or L3 level in neonates and infants. The dural sac in neonates and infants also terminates in a more caudad location compared to adults, usually at about the level of S3 compared to the adult level of S1. This have implications fro e.g. a spinal anaesthesia application. The more caudad termination of the dural sac makes it more likely to have an inadvertent dural puncture during performance of a single-shot caudal block if the caudal needle is advanced too far into the caudal epidural space. In order to avoid potential injury to the spinal cord, dural puncture should be performed below the level of the spinal cord, i.e. below L2-L3 in neonates and infants. Cerebrospinal fluid (CSF) volume is larger on a mL/kg basis in infants and neonates (4mL/kg) compared to their adult counterparts (2mL/kg). This may, in part, account for the higher local anesthetic dose requirements and shorter duration of action of spinal anesthesia in this population.
As our brain is an integrated system consisting of many functionally specialized networks, it is of critical importance to further understand the interaction among different networks. Five predefined networks are recognised: motor-sensory, visual, default network (spontaneous cognition, task settings) and two other higher order networks: dorsal attention (orientating ones focus on a particular task) and fronto-parietal control (highly adaptive control processes, mental health) network. The segregation/synchronization of the five networks across the first two years of life can be simultaneously characterized. In neonates, except for the motor-sensory network (red) and the visual network (blue), which are already well organized into cohesive clusters, the remaining three higher-order cognitive networks are rather scattered in separated clusters. The synchronization of higher-order cognitive networks takes a more prolonged time.
Psychomotor development of a child is a sign of nervous system maturation. Expresses the becoming of different areas of the nervous system of a child in particular periods of life. The assessment of psychomotor development of a child is carried out during every prophylactic check up using a table, in which age peculiarities of psychomotor development of a child are given. The assessment is carried out on the following criteria:
· Motorics - purposeful manipulation activity of a child
· Statics - fixation and holding of definite parts of the body in necessary position
· Sensory reactions - formation of corresponding reactions on light, sound, pain, touch
· Speech - expressive speech and understanding the speech
· Psychic development - positive and negative emotions, formation of social age