Answer the following questions in 10 - 20 words:
1. What biochemical event initiates differentiation of early gonads into testes around the seventh week?
Minimum complete answer:
TDF
More elaborate answer:
Cells in the indifferent gonads begin
to express the SRY gene and thereby produce testis development factor (TDF),
also called H-Y androgen. This single event initiates sex differentiation
of the male embryo.
Common wrong answer(s):
Testosterone or other androgens do not
initiate differentiation. These are produced after the gonads have
already differentiated into testes.
2. What causes female pseudohermaphroditism?
Minimum complete answer:
Androgen exposure in utero
More elaborate answer:
Female pseudohermaphrodites possess a
normal complement of female sex chromosomes (XX) and develop normal ovaries.
However, exposure to excessive androgens in utero leads to virilization
of the external genitalia, particularly clitoral enlargement and labial
fusion. The most common cause of this condition is congenital adrenal
hyperplasia. Two other minor causes are the administration of adrogenic
agents to the mother and androgen-producing maternal tumors.
Common wrong answer(s):
Minimum complete answer:
Hole in the interatrial septum to shunt
oxygenated blood from right to left atria.
More elaborate answer:
The foramen ovale is an anatomic adaptation
in the fetus to allow oxygenated blood coming from the umbilical vein via
the inferior vena cava to bypass the pulmonary circulation. Due to
higher pressure on the right side of the heart, blood is shunted from the
right atrium through a hole in the interatrial septum to the left atrium,
from where it continues into the left ventricle and hence to the systemic
circulation. Functional closure of the foramen ovale normally occurs
at birth.
Common wrong answer(s):
Minimum complete answer:
Conduit between the umbilical vein and
the inferior vena cava that shunts oxygenated blood past the liver.
Elaborate answer:
The ductus venosus is a fetal anatomic
adaptation that allows roughly half the oxygenated blood coming from the
umbilical vein to bypass the liver microcirculation and continue straight
to the heart via the IVC. The ductus venosus degenerates after birth.
Common wrong answer(s):
The fetus develops in an environment that is relatively low in oxygen compared to after birth. Discuss two non-anatomic adaptations that help ensure adequate delivery of oxygen to fetal tissues.
We discussed four non-anatomic adaptations in lecture and discussion:
Define plasticity in the context of growth and development, and give two situations in which the tissues of an adult’s body might demonstrate plasticity?
Everyone received some credit here. The best answers defined plasticity as the ability of cells and tissues to alter their structure and function in response to genetic and environmental cues, especially during critical periods.
The biggest problem was that many students included disease processes in their definition of plasticity. The body may attempt to compensate or adapt in specific ways to maintain adequate structure and function in response to disease, but the damage caused by diseases or defects does not in and of itself illustrate plasticity. Plasticity is the sculptor continually reshaping her sculpture to please her changing aesthetics. Disease is someone else attempting to take a sledgehammer to it.