Essentials of Anatomy and Physiology

482

Table 21–2 GROWTH OF THE EMBRYO–FETUS

Month of Approximate Overall

Gestation (end) Aspects of Development Size in Inches

1 2 3 4 5 6 7 8 9

• Heart begins to beat; limb buds form; backbone forms; facial fea-
  tures not distinct


• Calcification of bones begins; fingers and toes are apparent on
  limbs; facial features more distinct; body systems are established


• Facial features distinct but eyes are still closed; nails develop on fin-
  gers and toes; ossification of skeleton continues; fetus is distinguish-
  able as male or female


• Head still quite large in proportion to body, but the arms and
  legs lengthen; hair appears on head; body systems continue to
  develop


• Skeletal muscles become active (“quickening” may be felt by the
  mother); body grows more rapidly than head; body is covered with
  fine hair (lanugo)


• Eyelashes and eyebrows form; eyelids open; skin is quite wrinkled;
  pulmonary surfactant is first produced


• Head and body approach normal infant proportions; deposition of
  subcutaneous fat makes skin less wrinkled


• Testes of male fetus descend into scrotum; more subcutaneous fat is
  deposited; production of pulmonary surfactant is sufficient to permit
  breathing if birth is premature


• Lanugo is shed; nails are fully developed; cranial bones are ossified
  with fontanels present; lungs are more mature

0.25

1.25–1.5

3

5–7

10–12

11–14

13–17

16–18

19–21

Table 21–3 MATERNAL CHANGES DURING PREGNANCY

Aspect Change

Weight

Uterus

Thyroid gland

Skin

Circulatory system

Digestive system

Urinary system

Respiratory system

Skeletal system

• Gain of 2–3 pounds for each month of gestation


• Enlarges considerably and displaces abdominal organs upward


• Increases secretion of thyroxine, which increases metabolic rate


• Appearance of striae (stretch marks) on abdomen


• Heart rate increases, as do stroke volume and cardiac output; blood volume increases; vari-
  cose veins may develop in the legs and anal canal


• Nausea and vomiting may occur in early pregnancy (morning sickness); constipation may
  occur in later pregnancy


• Kidney activity increases; frequency of urination often increases in later pregnancy (bladder is
  compressed by uterus)


• Respiratory rate increases; lung capacity decreases as diaphragm is forced upward by com-
  pressed abdominal organs in later pregnancy


• Lordosis may occur with increased weight at front of abdomen; sacroiliac joints and pubic
  symphysis become more flexible prior to birth