QUESTION: 141

Askydiver landing forcefully on his right lower limb suffered a central fracture of the acetabulum with dislocation of the femoral head into the pelvis. The acetabulum is formed by the joining of the ilium, ischium, and pubis. These three bones are completely fused by which of the following periods?

birth
6 years
puberty
16 years
23 years

Answer(s): E

Explanation:

Fusion of the ilium, ischium, and pubis at the acetabulum is usually complete by age 23. From birth to the early 20s (choices AD), the three bones are held together by a Y-shaped cartilage.

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QUESTION: 142

In the coronal section of the head shown in following figure arrow 2 points to a structure that belongs to which of the following?

ethmoid bone
inferior nasal concha
maxillary bone
nasal septum
vomer bone

Answer(s): A

Explanation:

Arrow 2 points to the middle nasal concha, which is part of the ethmoid bone. Arrow 3 points to the ethmoid sinus, which also belongs to the ethmoid bone. The inferior nasal concha (arrow 1) is a separate bone (choice B). The maxillary bone (choice C) is located more laterally and does not contribute to the nasal conchae. The maxillary sinus, a part of the maxillary bone, is indicated by arrow 4. The vomer bone (choice E) forms part of the nasal septum (choice D), which can be seen here as the thin line between the nasal conchae. The nasal conchae have no attachment to the septum.

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QUESTION: 143

The hands and nails of a 45-year-old woman show the discolorations indicated in below figure. The woman states that she had pulmonary tuberculosis about 10 years ago. The clinician prescribes cortisol, but counsels her that as a side effect it might lead to thin skin and thinning of her limbs because of an increase in which of the following?

adrenocorticotropic hormone (ACTH) secretion
corticotrophin-releasing hormone (CRH) secretion
insulin sensitivity in muscle
protein degradation
wound healing

Answer(s): D

Explanation:

Tuberculosis is known to increase the susceptibility of developing chronic adrenal insufficiency, also known as hypocortisolism, or Addison disease. It leads to hyperpigmentation as seen in the palmar skin creases and nails of the woman. Administration of cortisol replaces the inadequate release of glandular cortisol.
Cortisol decreases protein synthesis and increases protein degradation. The newly available amino acids are then used for gluconeogenesis, which lead to the name "glucocorticoid" for cortisol. Increasing serum cortisol levels will decrease, not increase, secretion of ACTH (choice A) and CRH (choice B) by feedback inhibition. Cortisol decreases, not increases, the sensitivity of cells to insulin (choice C) by decreasing the translocation of glucose transporters to the cell membrane. Because cortisol decreases utilization of glucose by muscle and adipose tissue, blood glucose rises. This provides a stimulus to release insulin.
Thus, prolonged exposure to high levels of cortisol can lead to diabetes mellitus due to exhaustion of pancreatic beta cells. Although cortisol acts as an anti- inflammatory agent, it has a negative, not a positive, effect on wound healing (choice E). Cortisol suppresses the activity of leukocytes which are important for debriding the wound. Cortisol increases catabolism, which leads to the breakdown of nutrients that are needed for generating new tissue. Cortisol stimulates catecholamines leading to vasoconstriction and consequent reduction of oxygen, nutrient, and white blood cell delivery. Cortisol may also inhibit collagen production.

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QUESTION: 144

A healthy 17-year-old male tells his doctor during a normal check-up visit that "his muscles gave out" when he recently attempted to lift a heavy load. On questioning, he answers that he did not experience any other neuromuscular problems after this experience. What is the most likely mechanism responsible for the abrupt cessation of skeletal muscle contraction?

activation of alpha motor neurons
activation of gamma motor neurons
activation of Golgi tendon organs
activation of muscle spindles
skeletal muscle ischemia

Answer(s): C

Explanation:

When there is danger of damage to the tendons or bones to which the muscles are attached, Golgi tendon organs are activated and elicit rapid responses through neural connections located within the spinal cord that result in muscle relaxation. Golgi tendon organs are muscle proprioceptors that are found close to the junction between tendon and muscle fibers. They are in series with the muscle fibers and respond to the stretch of tendons which accompanies muscle tension. The threshold for activating them in this manner is high and it is therefore believed that they play an important role in the reflex response of a muscle after excessive force ("muscles give out"). In the spinal reflex pathways, the Ib afferent axons from the Golgi tendon organ synapse on inhibitory spinal cord interneurons, which then inhibit, not activate, alpha motor neuron activity serving the same muscles (choice A). Gamma motor neurons (choice B) innervate muscle spindles. These neurons control the sensitivity of the spindle by maintaining the proportions between spindle and muscle length and by dampening the function of the spindle, regardless of change in muscle length. This is important for normal movements. Muscle spindles (choice D) continuously signal information about the length of a muscle and the rate of change in length. They are important for conscious appreciation of the body's position, for planning and execution of controlled movements. Low oxygenation of the muscle or ischemia (choice E) is not the primary trigger for spinal reflexes, and will occur gradually, not suddenly as described in the question.

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QUESTION: 141

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QUESTION: 142

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QUESTION: 143

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QUESTION: 144

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