Unit 2 BHS: Body shape, sexual dimorphism and puberty

Question 1

4 factors by which we distinguish between the 2 sexes

Answer 1

1. appearance
2. smell
3. behaviour
4. sound

Question 2

Four components of sex

Answer 2

1. genetic sex - xx/xy
2. anatomical sex - genitalia
3. physiological sex - presence of testosterone
4. gender role - socially prescribed roles

Question 3

Klinefelters’ syndrome

Answer 3

• XXY
• 1/700

1. taller than average height
2. gynaecomastia
3. reduced facial hair
4. reduced body hair
5. osteoporosis
6. feminine fat distribution
7. testicular atrophy

Question 4

Turner syndrome

Answer 4

• XO
• 1/2500

1. short stature
2. low hairline
3. shield-shaped thorax
4. widely spaced nipples
5. short metacarpal IV
6. small fingernails
7. brown spots
8. folds of skin on neck
9. constriction of aorta
10. poor breast development
11. elbow deformity
12. rudimentary ovaries
13. no mentruation

Question 5

Supermale syndrome

Answer 5

• XYY (1/1000)

1. normal sexual development
2. increased stature (at least 7cm taller than expected)
3. acne
4. behavioural and learning difficulties

Question 6

SRY Translocation

Answer 6

• XX male (1/25000)
• SRY translocated onto X chromosome, thus female genotype and male phenotype
• small testicles but otherwise appear as normal male

Question 7

SRY absence or mutation

Answer 7

• XY or XXY female (1/2500)
• SRY absent from Y chromosome
• tall, slim, little body hair, no acne
• androgen insensitivity
• internal testes (risk of testicular cancer)

Question 8

Explain the establishment of anatomical sex

Answer 8

determined by testosterone during foetal life
1. if testosterone is present in foetal life:
- secretion of testosterone (10 to 11 weeks post menstrual)
- causes the expression of SRY
this leads to:
development of external genitalia as males, and testes to migrate out of abdomen into the scrotum

2. if testosterone is not present:
   - visual features of a female develop

Question 9

Explain the establishment of physiological sex

Answer 9

• at puberty, gonadotrophins are released in a pulsatile manner during sleep. This causes sex hormones to be secreted and testes & ovaries to become reproductively functional.
• this is determined by the presence of testosterone during foetal life. If testosterone was absent, pituitary secretes cyclically resulting in development of female repro cycle. If testosterone was present, the cycle was broken and pituitary secretes constantly resulting in male pattern.

Question 10

Sexual dimorphism at birth

Answer 10

1. boys are heavier than girls
2. girls have more advanced skeletal age
3. boys have longer forearms than girls
4. boys have less fat than girls

Question 11

Sexual dimorphism in childhood

Answer 11

1. skeletal and mental age more advanced in girls
2. boys are slightly taller and heavier than girls
3. boys have less fat
4. limb proportions are slightly different

Question 12

Sexual dimorphism in puberty

Answer 12

1. girls’ menarche occur when growth spurt is near completion, and boys’ first ejaculation occurs before growth spurt.
2. girls’ voices deepen gradually while boys’ voice change is abrupt
3. boys’ growth spurt are more drastic and lasts longer than girls’

Question 13

Sexual dimorphism in adulthood

Answer 13

• sexual dimorphism in 3 forms after puberty: body form, fat, hair.

1. body form:
   a) height difference: mainly due to difference in leg length
   b) width difference: bi-iliac vs. bi-acromial diameter
   c) upper limb: men have longer forearms and wider hands
   d) facial features: male have larger nose, more prominent jaw, more super-ciliary development; women have higher forehead, fatter face, and longer neck.
2. distribution of body fat:
   - female: fat is laid down all over during puberty, thickest at thighs and breasts. Fat disappears from waist, giving the hourglass body shape.

• male: fat disappears during puberty especially from limbs, some fat are laid on the waist giving the square trunk body shape. Women who are treated with testosterone gain fat at waist.

Question 14

First signs of puberty in girls

Answer 14

1. swelling of areola tissue (breast bud) around 11 years of age
2. growth spurt starts and peaks about 1 to 2 years after breast bud
3. public hair appears and apocrine glands develop
4. menarche starts when growth spurt is near completion and breast at stage 4 (or 5), subcutaneous fat develops
5. skin becomes coarser
6. voice drops in pitch
7. axillary hair develops last

Question 15

First signs of puberty in boys

Answer 15

1. testes enlarge at about 11.5 years
2. growth spurt around 13 years of age and is more intense and lasts longer than girls
3. penis growth and pubic hair appears long with growth spurt
4. 1st ejaculation around the same time girls develop breast buds but before growth spurt
5. voice deepens abruptly and late