MDS PREP
What is the primary action of endorphins on the body?
1) Inhibition of pain
2) Stimulation of growth
3) Regulation of mood and emotions
4) Increased blood pressure
E. Regulation of sleep-wake cycle
Endorphins, particularly ?-endorphin, are opioid peptides that act as natural painkillers. They are released during stress and pain and bind to opioid receptors in the brain and spinal cord to inhibit the transmission of pain signals. While they do have secondary effects on mood and stress response, their primary function is pain inhibition.
What is the primary site of vitamin B12 absorption in the intestine?
1) Stomach
2) Duodenum
3) Jejunum
4) Ileum
Physiology
Answer: 4
The ileum is the primary site of vitamin B12 absorption, facilitated by intrinsic factor binding to specific receptors.
Which of the following is a characteristic of the absolute refractory period during an action potential?
1) The membrane is fully depolarized.
2) The membrane is fully repolarized.
3) The membrane is inexcitable regardless of the strength of the stimulus.
4) The membrane is hyperpolarized.
E. The membrane is depolarized.
The absolute refractory period occurs during the initial phase of repolarization after an action potential. During this period, the membrane is inactivated and cannot be depolarized to generate another action potential, regardless of the stimulus strength. This ensures that action potentials are unidirectional and do not propagate backward along the axon.
What is the typical pH of gastric chyme when it enters the duodenum?
1) 1.0-2.0 (very acidic)
2) 2.0-4.0 (slightly acidic)
3) 4.0-6.0 (weakly acidic)
4) 6.0-8.0 (slightly alkaline)
E) 8.0-10.0 (alkaline)
Gastric chyme, which is the mixture of food and gastric juice, is highly acidic due to the presence of hydrochloric acid secreted by parietal cells. The pH typically ranges from 1.0 to 2.0 when it enters the duodenum. This acidity helps to denature proteins and provides the optimal environment for pepsin activity. Once in the duodenum, the chyme is neutralized by the secretion of bicarbonate from the pancreas and bile from the liver.
Which hormone is primarily responsible for the conversion of 7-dehydrocholesterol to cholecalciferol in the skin?
1) Parathyroid hormone (PTH)
2) Vitamin D
3) Ultraviolet B (UV2) light
4) 25-hydroxyvitamin D3
Physiology
Answer: 3
The conversion of 7-dehydrocholesterol to cholecalciferol (vitamin D3) in the skin is initiated by the action of UVB light from sunlight, not by any specific hormone.
What is the function of the lateral nucleus of the hypothalamus?
1) It acts as the feeding center
2) It acts as the satiety center
3) It regulates the sympathetic nervous system
4) It controls the release of pituitary hormones
Answer: 1) The lateral nucleus of the hypothalamus is considered the feeding center, which stimulates appetite and food intake.
What is the role of the corpus luteum in the second half of the menstrual cycle?
1) It secretes FSH
2) It secretes LH
3) It secretes estrogen and progesterone
4) It secretes inhibin
Physiology
Answer: 3
The corpus luteum, which forms after ovulation, secretes estrogen and progesterone. These hormones are essential for preparing the endometrium for potential implantation and supporting early pregnancy.
MCQ: The physiological capacity of the bladder, at which micturition is normally effected, ranges between:
1) 150 ml - 250 ml
2) 250 ml - 450 ml
3) 450 ml - 750 ml
4) 750 ml - 1000 ml
The physiological capacity of the bladder, at which micturition is normally effected, ranges between 250 ml - 450 ml, indicating the volume at which the urge to urinate is felt.