WEEK 10 ADOLESCENTS & ADULTHOOD

Age Group Revisited

• Pre-Adolescence: The period of life before puberty, marked by significant physiological changes preparing the body for sexual maturation and the development of secondary sexual characteristics.

• Adolescence: The transitional period between childhood and adulthood, typically spanning from ages 10 to 18, characterized by rapid physical, hormonal, and emotional changes. Its onset and termination are highly variable depending on genetic, environmental, and lifestyle factors.

  • Males: 10 - 22 years

  • Females: 8 - 19 years

• Adulthood: The stage of life from age 20 until death, encompassing various sub-stages each with distinct physiological and social characteristics.

  • Young Adult: 20-40 years, a period marked by peak physical condition, career establishment, and often family formation.

  • Middle age: 40-65 years, characterized by gradual physiological decline and potential onset of age-related diseases.

  • Older Adult: 65 years to death, marked by increased vulnerability to disease and disability, though also wisdom and experience.

Adolescents and Adulthood

• Adolescence: Characterized by:

  • Body systems reaching maturity both structurally, achieving full size and development, and functionally, operating at peak efficiency.

  • Sexual maturity, including the development of reproductive organs and secondary sexual characteristics enabling reproduction.

  • The timing and tempo of changes are highly variable between individuals and sexes, influenced by genetic, nutritional, and environmental factors.

• Adulthood: Characterized by:

  • Attainment of full maturity across all body systems, with physical and cognitive capabilities at their peak.

  • Peak performance and development in physical, cognitive, and social domains, although gradual decline begins in middle age.

Proportion Changes

• Head: x 2 (The head doubles in size from infancy to adulthood.)

• Arms: x 4 (The arms quadruple in length from infancy to adulthood.)

• Trunk: x 3 (The trunk triples in length from infancy to adulthood.)

• Legs: x 5 (The legs increase fivefold in length from infancy to adulthood.)

Sitting Height/Stature Ratio

• Reflects relative leg length and trunk length, providing insights into growth patterns and body proportions.

• Infants have smaller legs relative to their trunk size, reflecting their early developmental stage.

• Lower extremities grow faster than the trunk during childhood and adolescence, a growth pattern that changes body proportions.

• In late adolescence, the trunk grows after leg growth has ceased, contributing to final adult height and proportions.

• Females generally have shorter lower extremities than males, a sex-specific difference influenced by hormonal factors and genetics.

Shoulder to Hip Ratio

• Biiliocristal Breadth to Biacromial Breadth ratio, comparing the width of the hips to the width of the shoulders.

• Breadth of hips compared to shoulders, indicating the distribution of body mass in the upper and lower body.

• Ratio is higher in females, indicating females' hips make up a greater percentage of their shoulders due to wider pelvic structure.

• Males' ratio declines as shoulder size increases faster and greater than their hips, leading to a more inverted triangle shape.

Velocity Curve for Height

• Shows height changes over age for boys and girls, illustrating the rate of growth at different developmental stages.

• Includes phases of deceleration, slowing of growth rate; acceleration, rapid increase in growth rate; and peak height velocity (PHV), the point of maximum growth rate during adolescence.

• Initiation of adolescent spurt, the beginning of rapid growth acceleration during puberty.

• Peak height velocity (PHV) = maximum rate of growth in stature, a key indicator of adolescent growth spurt intensity and timing.

Difference in Adult Stature

• Boys experience approximately 2 years more of preadolescent growth than girls, contributing to their greater average adult height.

• Males grow ~ 5cm/year before the adolescent growth spurt resulting in ~ 10 cm of growth that females don’t experience, highlighting the extended growth period in males.

• Males have a higher peak height velocity, leading to a more pronounced growth spurt compared to females.

• Testosterone increases Ca^{2+} deposition, leading to bone growth and greater stature in males.

• Mid-growth spurt during childhood (6.5-8.5 years) is not always apparent and more common in males, suggesting hormonal influences on growth patterns.

• Attainment of adult stature:

  • Growth can continue into the mid-20s, though at a significantly reduced rate.

  • Annual increment of less than 1.0 cm, indicating near cessation of growth.

  • Four successive months increments of less than 0.5 cm, confirming minimal height increase.

Bone

• Bone Matrix: The structural framework of bone comprising both organic and inorganic components.

  • 35% organic: Collagen and Proteoglycans provide flexible strength, allowing bone to withstand bending and twisting forces.

  • 65% inorganic: Minerals (calcium and phosphate) provide weight-bearing strength, enabling bone to resist compression.

• Bone Cells: Cells responsible for bone formation, maintenance, and remodeling.

  • Osteoblasts: Bone-forming cells that produce organic material (osteoid) which then mineralizes to form new bone.

  • Osteocytes: Osteoblasts surrounded by bone matrix, maintaining bone structure and regulating mineral homeostasis.

  • Osteoclasts: Bone-destroying cells involved in reabsorption or break-down of bone tissue, essential for bone remodeling and calcium regulation.

• Growth occurs at the Epiphyseal Plate: A cartilaginous region located between the epiphysis and diaphysis of long bones, responsible for longitudinal bone growth.

  • Zone of Resting: Chondrocytes do not divide, serving as a reserve of cells for future growth.

  • Zone of Proliferation: Chondrocytes produce new cartilage through rapid cell division, increasing the length of the epiphyseal plate.

  • Zone of Hypertrophy: Chondrocytes produced in the Zone of Proliferation enlarge and mature, further contributing to bone lengthening.

  • Zone of Calcification: Hypertrophied chondrocytes die, blood vessels from the diaphysis grow, osteoblasts deposit new bone matrix, ossifying the cartilage.

• Reach adult size: when the Epiphyseal plate ossifies and becomes a line, ceasing longitudinal bone growth.

Growth in Bone Length & Articular Cartilage

• Articular cartilage at the end of the bone grows similarly to inside the bone, enabling joint movement and cushioning.

• No clear-cut zones are present in articular cartilage, differing from the distinct zones in the epiphyseal plate.

• Outer cartilage is similar to the zone of resting, providing a reserve of cells.

• Inner cartilage calcifies and ossifies, contributing to bone growth at the joint surface.

• When it reaches full size, bone stops replacing cartilage, maintaining the joint's smooth surface.

• This cartilage doesn’t become ossified, unlike the epiphyseal plate, preserving the articular surface throughout life.

Growth in Bone

• Bone is deposited by osteoblasts on the outer surface, increasing bone thickness and strength.

• Bone is reabsorbed by osteoclasts on the inner surface, remodeling bone and maintaining marrow space.

Velocity curve for Weight

• Initiation of Adolescent spurt, the onset of rapid weight gain during puberty.

• Peak, maximum rate of weight gain during adolescence.

• Weight-for-stature is not accurate during the adolescence growth spurt, as generally height increases, followed by weight, leading to fluctuations in BMI.

Human Physique

• Somatotyping: A system of classifying body types in terms of three categories, providing a comprehensive assessment of physical build.

  • Endomorphy (relative fatness), indicating the proportion of body mass that is composed of fat.

  • Mesomorphy (relative musculoskeletal robustness), indicating the proportion of body mass that is composed of muscle and bone.

  • Ectomorphy (relative linearity or slenderness of a physique), indicating the proportion of body mass that is characterized by height and thinness.

• Classified on a scale from 1 to 7 (though higher ratings are possible) in each of the three categories, allowing for a nuanced evaluation of body composition.

• The three numbers together give a somatotype number, with the Endomorphy score first, then Mesomorphy, and finally Ectomorphy (e.g., 1-5-2), providing a concise representation of body type.

• The scores may also be plotted in a shield diagram or somatograph, representing the somatotype on a two-dimensional scale, for visual analysis.

Ectomorphy

• Ectomorphic characteristics: Traits associated with a slender and linear physique.

  • Tall and thin, characterized by long limbs and minimal muscle mass.

  • Narrow body, with limited breadth in the shoulders and hips.

  • Thin arms and legs, with minimal subcutaneous fat.

  • Little body fat, resulting in a lean appearance.

  • Wiry muscles, with a focus on endurance rather than strength.

• The calculation for the ectomorphy rating is based on the measurements of:

  • height, a primary determinant of ectomorphic physique.

  • weight, reflecting overall body mass and leanness.

  • height/weight ratio, providing an index of body proportionality.

Mesomorphy

• Mesomorphic characteristics: Traits associated with a muscular and athletic physique.

  • Strongly built, with a solid and robust frame.

  • Broad muscular chest and shoulders, contributing to a V-shaped torso in males.

  • Very muscular arms and legs, showcasing well-developed musculature.

  • Little body fat, resulting in a defined and athletic appearance.

• The calculation for the mesomorphy rating is based on the measurements of:

  • height, providing a baseline for proportionality.

  • breadths of the humerus and femur, indicating bone size and muscle attachment points.

  • girths of the biceps (flexed and relaxed) and calf, reflecting muscle mass and development.

• The girths are corrected for body fat using the skinfold measure, isolating muscle mass from subcutaneous fat.

Endomorphy

• Endomorphic characteristics include: Traits associated with a round and soft physique.

  • Stocky, with a compact and solid build.

  • Large round body, characterized by a predominance of soft tissue.

  • Short thick neck, reflecting increased fat deposition in the upper body region.

  • Short arms and legs, contributing to a stocky appearance.

  • Tendency to store body fat, leading to a higher proportion of body fat mass.

• The calculation for the endomorphy rating is based only on:

  • the sum of 3 skinfolds (triceps, subscapular, supraspinale), corrected for height, providing an estimate of subcutaneous fat.

• Therefore, the higher the skinfolds, the higher your endomorphy score, indicating a greater proportion of body fat.

Puberty

• Puberty = the period of time in which secondary sex characteristics develop, marking the transition from childhood to sexual maturity.

• Characterised by:

  • Accelerated body growth, including a rapid increase in height and weight.

  • Rapid growth of the gonads, the testes in males and ovaries in females, leading to increased hormone production.

  • Increased production of gonadal hormones, such as testosterone and estrogen, driving the development of secondary sexual characteristics.

  • External genital development in boys, including enlargement of the penis and testes.

  • Breast development and menarche in females, the onset of menstruation.

  • Pubic hair in both sexes, a key secondary sexual characteristic.

  • = Attainment of the capacity to procreate, marking reproductive capability.

• The hypothalamic-pituitary-gonadal axis secretions throughout Infancy and Childhood are low, maintaining a prepubertal state.

• Possibly due to inhibition of neurons, resulting in low GnRH (gonadotropin-releasing hormone) secretion.

• During puberty, there is a marked increase in the production of sex steroids/hormones, initiating the development of secondary sexual characteristics.

• GnRH = increase in LH (luteinizing hormone) and FSH (follicle-stimulating hormone), stimulating gonadal function.

Puberty in Females

• Estrogen (feminizing hormone) A key hormone responsible for the development of female secondary sexual characteristics.

  • Growth of ovaries and secondary sex characteristics, including breast development and widening of the hips.

  • Stimulates GH = increase in height and pelvic widening, leading to skeletal maturation and sexual dimorphism.

  • Stimulates fat deposition on the hips, thighs, buttocks, and breasts, contributing to the characteristic female body shape.

  • Supresses FSH and LH, regulating the menstrual cycle.

• Progesterone A hormone involved in the regulation of the menstrual cycle and pregnancy.

  • Acts on the uterus to prepare for fertilization, thickening the endometrial lining.

  • Supresses FSH and LH, preventing ovulation during pregnancy.

• Inhibin – supresses FSH, providing negative feedback on follicle development.

Puberty in Females

• Thelarche: Breast Development, the initial stage of puberty in females.

  • Formation of lobules and ducts by estrogen, progesterone, and prolactin, stimulating mammary gland growth.

  • Completion by glucocorticoids and GH, ensuring full breast development.

  • Adipose tissue and fibrous tissue enlarge the breast, contributing to increased breast size.

• Pubarche: Pubic and axillary hair growth, stimulated by adrenal androgens.

  • Stimulated by androgens from the ovaries and adrenal cortex, leading to the appearance of pubic and underarm hair.

• Menarche – 1st episode of menstrual bleeding, marking the onset of reproductive capability.

  • Occurs between age 11 and 16, with variation depending on genetic and environmental factors.

  • Less that 17% body fat can delay this event, highlighting the importance of adequate nutrition for reproductive function.

  • Consider dancers and gymnasts, who may experience delayed menarche due to low body fat.

Follicle Development

• Gamete: sex cells (sperm cell or oocyte), essential for sexual reproduction.

• The number of primary oocytes females are born with is the maximum they will ever have, impacting reproductive lifespan.

  • Birth to Puberty Primary Oocyte Primordial follicle, the initial stage of follicle development.

Ovulation

• Ovulation: The secondary Oocyte is released, a key event in the menstrual cycle enabling fertilization.

  • Pregnancy, potential outcome if the oocyte is fertilized.

  • Remaining granulosa cells corpus luteum cells, forming an endocrine gland within the ovary.

  • Secretes progesterone and small amounts of estrogen, maintaining the uterine lining during early pregnancy.

  • Remains active throughout pregnancy, if fertilization occurs.

  • No fertilization

  • Corpus Luteum remains active for 10-12 days then degenerates corpus albicans, a non-functional scar tissue.

• Typically a 28-day cycle, though variation is common.

  • Follicular Phase: Development of follicles, stimulated by FSH.

  • Proliferation Phase: Of the Uterine mucosa, induced by estrogen.

  • Luteal Phase: Existence of the corpus luteum, secreting progesterone.

  • Secretory Phase: Maturation and secretion by uterine glands, preparing the uterus for implantation.

Ovarian Cycle

• Events in the ovaries, involving the development and release of oocytes.

• Events prior to ovulation

  • GnRH secretion =

  • ⇑FHS – stimulates the granulosa cells

  • ⇑ LH – stimulates the theca interna cells

  • = follicle growth and maturation

• During follicle maturation, there is an increase in estrogen levels prior to ovulation.

• Maturing follicles will secrete Inhibin = ⇓ in FSH, providing negative feedback and preventing overstimulation.

• Increased estrogen = +ve feedback on LH and FSH = LH and FSH surge, triggering ovulation.

• LH surge initiates ovulation + generation of corpus luteum, a critical step in the ovarian cycle.

Ovarian Cycle

• After ovulation = ⇓ estrogen, as the follicle transitions into the corpus luteum.

• Corpus luteum secretes progesterone = ⇑ in levels, preparing the uterus for implantation.

• Progesterone and estrogen provide – ve feedback on GnRH = ⇓ in LH and FSH, maintaining hormonal balance.

• No fertilization = degeneration of the corpus luteum, leading to a decline in hormone levels.

• = ⇓ in estrogen and progesterone

• = menses, the shedding of the uterine lining.

Uterine Cycle

• Changes in the endometrium of the uterus, preparing for implantation of a fertilized egg.

• Primary purpose: prepare the lining of the uterus to create a suitable environment for a fertilized egg, ensuring survival and development.

• After menses, the remaining Endometrium epithelial cells of the uterus begins to proliferate (divide and replace old cells)

• Caused by estrogen

• Also increases progesterone receptors, enhancing the uterus's responsiveness to progesterone.

• Cells become columnar and create folds = tubular spiral glands, increasing surface area and secretory capacity.

• Spiral arteries project and supply nutrients, ensuring adequate blood flow to the endometrium.

Uterine Cycle

• 7 days after ovulation, the uterus is prepared, optimized for implantation.

• Progesterone from the corpus luteum causes endometrium cells to become secretory, producing glycogen-rich secretions.

• No fertilization = degeneration of corpus luteum = low levels of estrogen and progesterone = degeneration of lining, triggering menstruation.

• Spiral arteries constrict due to low progesterone = arteries become ischemic and necrotic = base of spiral glands die

Puberty in Males

• 12-14 years of age, the typical range for the onset of puberty in males.

• Before puberty small amounts of testosterone inhibits GnRH, maintaining a prepubertal state.

• Puberty = Increase in GnRH, initiating the hormonal cascade.

• Increase in FSH and LH

• Testosterone still provides negative feed-back to hypothalamus but doesn’t completely inhibit, maintaining hormonal balance.

• Inhibin inhibits FSH, regulating sperm production.

Testosterone

• Responsible for:

  • Maturity of the male genitals, including enlargement of the penis and testes.

  • Sperm cell production, enabling reproduction.

  • Hair growth, including facial, pubic, and body hair.

  • Skin to become rougher and darker, a characteristic secondary sexual trait.

  • Increases Sebaceous gland secretion, contributing to acne.

  • Hypertrophy of the Larynx and change in voice, leading to a deeper voice.

  • Simulates metabolism, increasing energy expenditure.

  • Higher rate compared with females, contributing to greater muscle mass.

  • Increases erythropoietin production = increase in RBC, enhancing oxygen-carrying capacity.

  • Greater % of body weight is muscle mass compared with females, contributing to strength and power.

  • Rapid bone growth = increased height

  • Stimulates the ossification of epiphyseal plate = reach maximum height quicker, leading to earlier cessation of growth compared to females.

Hormonal Sex Differences

• Males = high levels of testosterone and lower levels of estrogen opposite for females, determining sexual dimorphism.

• Male hormones are secreted continuously and simultaneously whereas females have a more cyclical and sequential secretion, regulating menstrual cycles and reproduction.

Cardiovascular Alterations

• SV increases as we grow, enhancing cardiac output.

  • Pre adolescent growth spurt = 40 ml

  • Growth spurt = 60 ml at rest

  • Untrained adult male = 70-80 ml

  • Trained aerobically = 100-110 ml

• During exercise

  • Untrained = 110-120 ml

  • Trained = 200 ml (ave = 150-170ml)

• Heart Rate decreases as we age, reflecting improved cardiovascular efficiency.

  • Decline by 50% from birth to maturity

  • Late adolescents

  • Males = 57-60 bpm