- Cephalic or neurogenic phase: This phase is initiated by the sight, smell, taste, or thought of food that causes stimulation of vagal nuclei in the brain. Vagus nerve directly stimulates parietal cells to secrete acid; in addition, it also stimulates antral G cells to secrete gastrin in blood (which is also a potent stimulus for gastric acid secretion) (Figure 859.2). Cephalic phase is abolished by vagotomy.
- Gastric phase: Entry of swallowed food into the stomach causes gastric distension and induces gastric phase. Distension of antrum and increase in pH due to neutralization of acid by food stimulate antral G cells to secrete gastrin into the circulation. Gastrin, in turn, causes release of hydrochloric acid from parietal cells.
- Intestinal phase: Entry of digested proteins into the duodenum causes an increase in acid output from the stomach. It is thought that certain hormones and absorbed amino acids stimulate parietal cells to secrete acid.
- Hydrochloric acid (HCl): This is secreted by the parietal cells of the fundus and the body of the stomach. HCl provides the high acidic pH necessary for activation of pepsinogen to pepsin. Gastric acid secretion is stimulated by histamine, acetylcholine, and gastrin (Figure 859.2). HCl kills most microorganisms entering the stomach and also denatures proteins (breaks hydrogen bonds making polypeptide chains to unfold). Its secretion is inhibited by somatostatin (secreted by D cells in pancreas and by mucosa of intestine), gastric inhibitory peptide (secreted by K cells in duodenum and jejunum), prostaglandin, and secretin (secreted by S cells in duodenum).
- Pepsin: Pepsin is secreted by chief cells in stomach. Pepsin causes partial digestion of proteins leading to the formation of large polypeptide molecules (optimal function at pH 1.0 to 3.0). Its secretion is enhanced by vagal stimulation.
- Intrinsic factor (IF): IF is necessary for absorption of vitamin B12 in the terminal ileum. It is secreted by parietal cells of stomach.
Learning the art of ECG interpretation requires intellect, commitment, effort and perhaps most importantly...an organized approach. I personally have spent thousands of hours (yes thousands) looking at 12-lead ECG tracings, studying ECGs for the cardiology boards, interpreting ECGs for direct patient care and developing the ECG tutorials and quizzes of LearnTheHeart.com.
I assume that most of you reading this blog do not have that much time...so let me share with you what I have discovered in my years teaching ECGs to make the process more simple and perhaps even enjoyable.
Read more: 10 Steps to Learn ECG Interpretation
- Learn and remember vital concepts easily thanks to short, easy-to-read, masterfully edited chapters and a user-friendly full-color design.
- See core concepts applied to real-life situations with clinical vignettes throughout the text.
- Discover the newest in physiology with updates that reflect the latest advances in molecular biology, cardiovascular, neurophysiology, and gastrointestinal topics.
- Visualize physiologic principles clearly with over 1000 bold, full-color drawings and diagrams.
- Distinguish core concepts from more in-depth material with a layout that uses gray shading to clearly differentiate between "need-to-know" and "nice-to-know" information.
- Access the complete contents online at Student Consult along with bonus resources such as image banks, self-assessment questions, physiology animations, and more!