35) Burmese pythons are a uniquely useful model for studies of cardiac hypertrop

Question

35) Burmese pythons are a uniquely useful model for studies of cardiac hypertrophy because their... a. heart anatomy is very similar to that of humans. b. hearts increase in size very rapidly in response to exercise training c. hearts increase in size very rapidly in response to feeding. d. hearts are highly resistant to atrophy and hypertrophy. 300 200 1001- 0 WT MKO 36) The figure above shows before and after endurance training for WT and MKO mice. What best explains the results for the experimental group of mice on the right of the figure? a. The group of mice on the right lacked PGC-1. b. The group of mice on the right was the control group. c. The group of mice on the right had an extra copy of PGC-1a. d. The group of mice on the right lacked myostatin 37) The conversion of stimulus energy into an electrical signal is known as a. transference b. transduction. c. an action potential. d. a graded potential.

Explanation / Answer

35) c. hearts increase in size very rapidly in response to feeding.

Cardiac hypertrophy refers to an abnormal increase in the heart muscle mass. In contrast to most carnivores which are able to chew, tear or crush their prey, snakes swallow their prey and their stomach does the rest of the job. Oxygen consumption therefore increases significantly during this period to sustain the metabolic demands and this gives rise to an extra load on the cardiovascular system. Researchers have reported that the Burmese pythons pump 50% more blood per heartbeat when digesting a meal rather when locomoting. This is aided by a 40% increase in the ventricular muscle mass (cardiac hypertrophy) within 48 hours post feeding, due to increased gene expression of muscle contractile proteins. This enlarges the heart and boosts its pumping capacity.

36) a. The group of mice on the right lacked PGC-1a

Endurance training in mice leads to selective hypertrophy (increase in size) of type I muscle fibres. This hypertrophy is due to increase in number of capillaries per muscle fibre and also due to capillary density. This can be correlated with an increase in the mitochondria number and performance. PGC-1a is the master regulator of mitochondrial biogenesis and its transcription increases during exercise. Inducible expression of PGC-1a increased mRNA and protein content of mitochondrial respiratory chain proteins and ATP synthase. Likewise, whole body PGC-1 knockout (KO) and muscle-specific knockout (MKO) of PGC-1 in mice reduced the same. Hence there was no increase in capillary per muscle fibre in the MKO mice post endurance training. The wild type WT mice served as control. Myostatin is reduced with exercise and it is a myokine that increases fat oxidation, increases adiposity, and results in obesity and muscle weakness.

37) b. transduction

Transduction typically refers to a physical stimulus being converted into an action potential, which is transmitted along the axons of the neuronal cells. The receptor cells converts the energy present in the stimulus into a electrical potential change, which is conducted across its membrane. This depolarizes the plasma membrane, allowing the action potential to be transmitted to the central nervous system.

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