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Lecture 3

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University of Toronto St. George
Susan Pfeiffer

Lecture 3 – Bone Growth S1 Foetal bone Growth  206 bones in the adult skeleton, 460 OCs at birth, 806 OCs at 10 weeks gestation  At 10 weeks gestation, the sphenoid bone in the skull has already begun ossification (early!)  No carpals are ossified at birth! It takes 6 years for all the carpals to mineralized  As OCs fuse together into a single OC, the number of OCs decrease S2 Human Growth Trajectory  Human are not unusual in the stages they go through but are unusual in the timing of the stages compared to other primates  Notice that human gestation period is not a lot longer than that of the orangutan  The human infancy period is 5 years which is roughly equal to the 3.5 years of the great apes  The human gestation stage is briefer (% wise, relative to full life span) so that the baby can pass through the birth canal and thus human infants are highly dependent and childhood growth in the human has features similar to fetal growth in the beginning (because we’re born a little early relative to our growth trajectory) S3 Endochondral Bone Formation  Chondrocytes make cartilage, osteoblasts makes bone  Osteoclasts remove bone, osteocytes maintain bone  Osteocytes are trapped osteoblasts (in bone)  Osteoblasts and osteblasts work together, influenced by genes, diet, environment S4 Factors Affecting Bone  Sun light allows the body to produce Vitamin D which is essential for bone growth and maintenance  Estrogens and androgens tends to stimulate bone formation  Parathyroid hormone (PTH) tends to stimulate bone removal  Post-menopausal bone loss is largely due to lower estrogen levels S5 Maxims  In order for a baby to grow into adult proportion, 1) her face has to grow larger to catch up to the vault, 2) arms and legs has to grow faster than the rest of the body  From birth, size increases allometrically in size: Skull x2, Torso x3, Arms x4, Legs x5  Each long bone has one end of it that is going to be growing fast than the other. That end is going to start first, end last and grow faster in between  The growth is “strongest” and “longest” at the shoulder wrist and knee  Knowing which end is the primary growing end will help determine which way the nutrient foramen points S6 Bone Growth Stages  a) Cartilaginous template  c) diaphysis becomes innervated and vascularised and starts to ossify  f) epiphyses is vascularised and ossifies separately  i) at puberty, epiphyses fuse to the diaphysis S7 Femur Growth  At birth, the femur has 3 OCs (1 for epiphysis (femoral head), 1 for diaphsis, 1 for distal end of femur (the condyles))  By 5 years, an additional OC appears (the greater trochanter) th  By 15 years, a 5 OC appears (the lesser trochanter)  After 15 years, fusion starts from the hip end and finish at the knee end  Bone not only grows in size, it must also be remodelled (in shape) S8 Gailleileo’s Drawings  If skeletons just got bigger, they would be too heavy, thus needs to be remodelled as it grows S9 Femur  The diaphysis continues to be thinner in the middle and wider at the ends  The wall of the femur on the endosteal side must be removed during remodelling so that the medullary cavity becomes wider as the wall of the femur moves outwards  This is a coordination between osteoblasts and osteoclasts S10 Growth Charts  Charts for girls and boys look similar in the first 9 years of life  Normal children will be within the percentile lines S11 Growth Rates  2 ways to plot: 1) Distance (height) vs time 2) Growth velocity  Fetal growth velocity is the highest  GR is very high in the first 36 months, in mid childhood it slows down, and in puberty it shoots up again  Girls and boys are basically the same size at birth and their grow rates are similar during mid childhood  Girls begin puberty ~ 2 years earlier and the grow rates are lower as compared to boys S13 Growth Rates and Cause of Death  If growth rates lagged before death, it means illness can be cause of death (chronic)  If growth rates does not lagged before death, it suggest acute cause of death (i.e accidents) S14 Growth of Body Systems (Scammon Curves)  Types of curves: 1) General, a.k.a “body” curve include bone, brawn, blood, breathing, bowel and bladder  2) Neural, including brain, eye, head dimensions  3) Lyphoid, including the thymus  The growth of the skeleton follows the “general curve” but there are aspects of the skull that follows the neural curve  The lymphoid curve overshoots adulthood level in mid-childhood and drops back down to adulthood level. This is because the kids are building up their immunity and their immune system must be especially active  The skull follows 2 curves, the vault follows the neural curve while the face follows t
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