NORMAL GASTRIC ANATOMY AND PHYSIOLOGY

Published in Clinical Pathology
Friday, 08 September 2017 01:21
Anatomically, stomach is divided into four parts: cardia, fundus, body, and pyloric part. Cardia is the upper part surrounding the entrance of the esophagus and is lined by the mucus-secreting epithelium. The epithelium of the fundus and the body of the stomach is composed of different cell types including: (i) mucus-secreting cells which protect gastric mucosa from self-digestion by forming an overlying thick layer of mucus, (ii) parietal cells which secrete hydrochloric acid and intrinsic factor, and (iii) peptic cells or chief cells which secrete the proteolytic enzyme pepsinogen. Pyloric part is divided into pyloric antrum and pyloric canal. It is lined by mucus-secreting cells and gastrin-secreting neuroendocrine cells (G cells) (Figure 859.1).
 
Figure 859.1 Parts of stomach and their lining cells
Figure 859.1 Parts of stomach and their lining cells 
 
In the stomach, ingested food is mechanically and chemically broken down to form semi-digested liquid called chyme. Following relaxation of pyloric sphincter, chyme passes into the duodenum.
 
There are three phases of gastric acid secretion: cephalic, gastric, and intestinal.
 
  • 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.
 
The secretion from the stomach is called as gastric juice. The chief constituents of the gastric juice are:
 
  • 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.
  • Mucus
  • Intrinsic factor (IF): IF is necessary for absorption of vitamin B12 in the terminal ileum. It is secreted by parietal cells of stomach.
 
Figure 859.2 Stimulation of gastric acid secretion
Figure 859.2 Stimulation of gastric acid secretion. Three receptors on parietal cells stimulate acid secretion: histamine (H2) receptor, acetylcholine or cholinergic receptor, and gastrin/CCK-B receptor. Histamine is released by enterochromaffin-like cells in lamina propria. Acetylcholine is released from nerve endings. Gastrin is released from G cells in antrum (in response to amino acids in food, antral distention, and gastrin-releasing peptide). After binding to receptors, H+ is secreted in exchange for K+ by proton pump

Physiology

Published in Physiology
Monday, 04 September 2017 17:39
Physiology (/ˌfɪziˈɒləi/; from Ancient Greek φύσις (physis), meaning 'nature, origin', and -λογία (-logia), meaning 'study of') is the scientific study of normal mechanisms, and their interactions, which works within a living system. A sub-discipline of biology, its focus is in how organisms, organ systems, organs, cells, and biomolecules carry out the chemical or physical functions that exist in a living system. Given the size of the field, it is divided into, among others, animal physiology (including that of humans), plant physiology, cellular physiology, microbial physiology (microbial metabolism), bacterial physiology, and viral physiology.
 
Central to an understanding of physiological functioning is its integrated nature with other disciplines such as chemistry and physics, coordinated homeostatic control mechanisms, and continuous communication between cells.
 
The Nobel Prize in Physiology or Medicine is awarded to those who make significant achievements in this discipline by the Royal Swedish Academy of Sciences. In medicine, a physiologic state is one occurring from normal body function, rather than pathologically, which is centered on the abnormalities that occur in animal diseases, including humans.

10 Steps to Learn ECG Interpretation

Published in Physiology
Saturday, 08 October 2016 15:59

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

Guyton and Hall Textbook of Medical Physiology - 12th Edition

Published in Downloads
Wednesday, 04 May 2016 19:18
Description: The twelfth edition of Guyton and Hall Textbook of Medical Physiology continues this best-selling title's long tradition as one of the world's favorite physiology textbooks. The immense success of this book is due to its description of complex physiologic principles in language that is easy to read and understand. Now with an improved color art program, thorough updates reflecting today's medicine and science, and accessible online at Student Consult, this textbook is an excellent source for mastering essential human physiology knowledge.
  • 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!
This new edition continues the long tradition of "Guyton" as one of the world's favorite physiology textbooks.

Clinical Physiology Made Ridiculously Simple by Stephen Goldberg, M.D.

Published in Downloads
Monday, 02 May 2016 11:26
Description: A brief, to-the-point presentation of the foremost details in clinical physiology. allows the reader to ascertain cardio-pulmonary-renal physiology furthermore as immunologyand different areas as a transparent abstract whole.
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