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3 pages/≈1650 words
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Biological & Biomedical Sciences
English (U.S.)
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Senior Seminar: Gastric and Pyloric Sphincter Muscle Function (Essay Sample)


Article summary
The following format must be followed.
Background: What were the questions that led to this study? How does it fit into the overall literature?
Hypothesis: What is the specific biological hypothesis that was tested in this study?
Experimental Design: What was the experimental strategy that was used to test the hypothesis? Do not just list the procedures. Why did they use these procedures and how do they allow the investigators to specifically test the proposed hypothesis?
Analysis: How were the data analyzed? Why were the tests chosen and are they appropriate?
Results: Summarize the findings succinctly.
Interpretation and Conclusions: How did the authors interpret the results? What conclusions were drawn relevant to the original hypothesis? Do you agree that the conclusions are valid? What future work should be done?


Article Summary
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Article Summary
Sobchak, C., Fajardo, A. F., Shifrin, Y., Pan, J., & Belik, J. (2016). Gastric and pyloric sphincter muscle function and the developmental-dependent regulation of gastric content emptying in the rat. American Journal of Physiology-Gastrointestinal and Liver Physiology, 310(11), G1169-G1175.
Feeding intolerance has been found to be a major problem in care of preterm babies. By definition, preterm babies are neonates born at fewer than 37 weeks of the gestation period. The intolerance usually exhibits itself as delay in gastric contents emptying, which poses a problem since the causes of the condition are poorly understood. The condition can lead to malnutrition and premature newborn may lose up to 20% of their weight in the first week of their lives (Khashana & Moussa, 2016). Based on this findings the investigators of this articles sought to comparatively study age-related function of pyloric and gastric smooth muscles together with their regulators using rat samples to help understand the condition much better.
Recently collected data illustrates that gastric emptying function do not exist before 24 weeks of pregnancy and gradually develop with progression of the fetal development before the full term. According to pressure recordings of Duodenal- jejunal intraluminal obtained in premature newborns, the intestinal motor activities are characterized by poorly coordinated and random low- amplitude in prior 31 weeks of gestations. This age- dependent function has also been observed in the gastric antrum where the pressure of intragastric before 32 weeks of pregnancy amounted to 50% of those found in fully developed newborns. Contractions Gastric contents emptying are reliant on a coordinated functioning of the gastro-pyloric motor that involves antrum and fundus muscle contraction as pyloric sphincter relaxes.
Over the past two decades, age-dependent transformation in agonist-induced force has been observed in antrum muscle strips and gastric fundus of cats, guinea pigs, and rabbits. In this regard, the use of rats by the investigators was appropriate, and it makes the study fit the overall literature, as their gastric activity is comparable to human being. In fact, the gastrointestinal function of a 1-2 weeks old rat is comparable to that of 32 weeks gestation newborn. Theoretically, it is proposed that age-dependent changes are dependent on decreased intracellular mobilization of calcium ions following agonist stimulation in neonates compared to adult stomach muscle.
Calcium is known to influence activities of muscle myosin light chain (MLC) kinase and Rho-associated kinase two involved in gastric muscle contractions. Relaxation of muscle occurs when phosphorylation of MLC reduce due to decreased release of calcium ions in the cell or reduced entry into the cell with increased dephosphorylation initiated by NO. The vice versa of this happens during contraction coupled with inhibition of MLCP dephosphorylation by Rho kinase which leads to greater sensitization of myofilaments to calcium resulting in a powerful contraction.
The investigators hypothesized that the reduced contraction of gastric muscle is the cause of delayed stomach emptying in the newborns. They anticipated that changes dependent on development in Rho-associated kinase 2 (ROCK-2) and muscle myosin light chain kinase (MLCK) expression in stomach muscle and pyloric sphincter leads to possibilities of having decreased gastric- emptying in the early life. In addition, they also predicted that Low amounts of NO early in life might lead to pyloric sphincter not relaxing enough
Experimental Design
Sobchak, Fajardo, Shifrin, Pan & Belik to test their hypothesis they used 1, 2, and >3 weeks (adult) of age rats. The animals gastric was first stimulated using KCI to contract, and observation was made to ascertain whether there are real differences between the force of contraction. This step was meant to determine whether there is a relationship between reduced gastric muscle contraction and the age of the animals. KCI is used as a stimulant since when potassium ions are increased outside a cell, hyperpolarization is suppressed which enables Calcium ions to depolarize the cell causing contraction. Thus by increasing KCL, K+ concentration rises causing greater sensitivity to calcium. They then used an electric field to stimulate contraction of the cells. Notably, electric field opens the voltage-gated Ca+ channels causing the entry of more calcium ions. The last stimulation involved use of Carbachol, which is a cholinergic agoni...
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