Hans Adolf Krebs

From Wikipedia

Sir Hans Adolf Krebs (English /krɛbz/ or /krɛps/) (25 August 1900 – 22 November 1981) was a German-born British physician and biochemist. He was the pioneer scientist in study of cellular respiration, a biochemical pathway in cells for production of energy. He is best known for his discoveries of two important chemical reactions in the body, namely the urea cycle and the citric acid cycle. The latter, the key sequence of metabolic reactions that produces energy in cells, often eponymously known as the “Krebs cycle”, earned him a Nobel Prize in Physiology or Medicine in 1953. With Hans Kornberg, he also discovered the glyoxylate cycle, which is a slight variation of the citric acid cycle found in plants, bacteria, protists, and fungi.


Early life and education

Sir Hans Adolf Krebs
Sir Hans Adolf Krebs

Krebs was born in Hildesheim, Germany, to Georg Krebs, an ear, nose, and throat surgeon, and Alma Krebs (née Davidson). He was the middle of three children, older sister Elisabeth and younger brother Wolfgang. He attended the famous old Gymnasium Andreanum in his home town. Before completing his secondary school education (by six months) he was conscripted into the Imperial German Army in September 1918, during World War I. He was allowed to appear in an emergency examination for the higher school leaving certificate, which he passed in such a good grade that he suspected the examiners of being “unduly lenient and sympathetic”. The war ended after two months and his conscription ended. He decided to follow his father’s profession and entered the University of Göttingen in December 1918 to study medicine. In 1919 he transferred to the University of Freiburg. In 1923 he published his first technical paper on tissue staining technique, the study which he started under the guidance of his teacher Wilhelm von Mollendorf in 1920. He completed his medical course in December 1923. To obtain a medical licence he spent one year at the Third Medical Clinic in the University of Berlin. By then he turned his ambition from becoming a practicing physician to medical researcher, particularly towards chemistry. In 1924 he studied at the Department of Chemistry at the Pathological Institute of the Charité Hospital, Berlin, for informal training in chemistry and biochemistry. He finally earned his M.D. degree in 1925 from the University of Hamburg. Continue reading “Hans Adolf Krebs” »

Cardiac cycle

From Wikipedia

The cardiac cycle refers to the sequence of mechanical and electrical events that repeats with every heartbeat. It includes the phase of relaxation diastole and the phase of contraction systole. The human heart being a four chambered organ, thus there are atrial systole, atrial diastole, ventricular systole and ventricular diastole. The frequency of the cardiac cycle is described by the heart rate, which is typically expressed as beats per minute. Each cycle of the heart, from the point of view of the ventricles and the status of their valves, involves a minimum of four major stages: Inflow phase, Isovolumetric contraction, outflow phase and Isovolumetric relaxation.

The first and the fourth stages, together constitute the “ventricular diastole” stage, involve the movement of blood from the atria into the ventricles. Stages 2 and 3 involve the “ventricular systole” i.e. the movement of blood from the ventricles to the pulmonary artery (in the case of the right ventricle) and the aorta (in the case of the left ventricle).

“Ventricular diastole,” begins when the ventricles starts to relax. At this point, some blood of the previous cycle’s systole is still flowing out of the ventricles through the semilunar valves, due to the inertia of the moving blood column, which overcomes the higher pressure in the aorta/pulmonary trunk with respect to the pressure in the ventricles. This short lasting phase, called “protodiastole” ends with the closure of the semilunar valves, producing the second heart sound (S2). Now that both the AV valves and the semilunar valves are closed, the ventricles are now closed chambers. Hence, this phase is known as isovolumetric (also called isovolumic, isometric) relaxation phase. Then the atrioventricular (AV) valves (the mitral valve and the tricuspid valve) open, allowing blood to fill the ventricles. This ventricular inflow phase can be sub-divided into the ‘first rapid filling phase’ as blood rushes in from the atria as a result of ventricular dilation; a phase of slow ventricular filling called ‘Diastasis’, and the ‘last rapid filling phase’ due to atrial contraction (systole).

As the ventricular systole begins, pressure within the ventricle rises and the AV valve closes producing the ‘first heart sound’ (S1). The semilunar valves remain closed. The contracting ventricles become closed chambers again and this phase is termed as “isovolumic contraction”. As the name implies, there is no change in volume, but intra-ventricular pressure rises. The outflow phase, “ventricular ejection,” is when the intra-ventricular pressure has achieved a higher pressure than the blood in the aorta (or the pulmonary trunk), the corresponding semilunar valves open. Ejection phase begins.

Throughout the cardiac cycle, blood pressure increases and decreases. The cardiac cycle is coordinated by a series of electrical impulses that are produced by specialised pacemaker cells found within the sinoatrial node and the atrioventricular node. The cardiac muscle is composed of myocytes which initiate their own contraction without the help of external nerves (with the exception of modifying the heart rate due to metabolic demand). The duration of the cardiac cycle is the reciprocal of heart rate. Assuming a heart rate of 75 beats per minute, each cycle takes 0.8 seconds.

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Post hoc ergo propter hoc

From Wikipedia

Post hoc ergo propter hoc (Latin: “after this, therefore because of this”) is a logical fallacy (of the questionable cause variety) that states “Since event Y followed event X, event Y must have been caused by event X.” It is often shortened to simply post hoc fallacy. It is subtly different from the fallacy cum hoc ergo propter hoc (“with this, therefore because of this”), in which two things or events occur simultaneously or the chronological ordering is insignificant or unknown. Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality. The fallacy lies in coming to a conclusion based solely on the order of events, rather than taking into account other factors that might rule out the connection.

he following is a simple example:

The rooster crows immediately before sunrise;
therefore the rooster causes the sun to rise.


The form of the post hoc fallacy can be expressed as follows:

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Arnold Orville Beckman

Excerpt from Wikipedia

(photo link) https://commons.wikimedia.org/w/index.php?curid=31972432

By Chemical Heritage Foundation, CC BY-SA 3.0,
By Chemical Heritage Foundation, CC BY-SA 3.0,

Arnold Orville Beckman (April 10, 1900 – May 18, 2004) was an American chemist, inventor, investor, and philanthropist. While a professor at California Institute of Technology, he founded Beckman Instruments based on his 1934 invention of the pH meter, a device for measuring acidity, later considered to have “revolutionized the study of chemistry and biology”. He also developed the DU spectrophotometer, “probably the most important instrument ever developed towards the advancement of bioscience”.Beckman funded the first transistor company, thus giving rise to Silicon Valley. After retirement, he and his wife Mabel (1900-1989) were numbered among the top philanthropists in the United States.

Teaching and consultancy at Caltech

Arnold Beckman’s laboratory at Caltech

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Hein Wellens

Hein Wellens
From Wikipedia, the free encyclopedia

Hein J Wellens MD, Emeritus Professor of Cardiology, University of Maastricht, The Netherlands
Hein J Wellens MD, Emeritus Professor of Cardiology, University of Maastricht, The Netherlands

, M.D., (born 13 November 1935, The Hague) is a Dutch cardiologist who is considered one of the founding fathers of the cardiology subspecialty known as clinical cardiac electrophysiology. Clinical cardiac electrophysiology enables patients with cardiac arrhythmmias to be subjected to catheter electrode mapping and stimulation studies. Paul Puech, first in Mexico and later in France; Benjamin Scherlag and Onkar Narula in the USA; and Dirk Durrer and Philippe Coumel in Europe were the field’s pioneers in the 1950s and 1960s. The field’s second wave of innovators used these techniques to unravel the mechanisms of tachycardia in humans and set the bases for their treatment. Among them, Hein Wellens in Europe and Kenneth Rosen, John Gallagher, and Mark Josephson in the USA had the greatest impact as researchers and teachers. Josephson is the author of the first and most successful textbook of clinical cardiac electrophysiology, now in its fourth edition.

Wellens, known among European cardiologists as “the giant of Maastricht”, has for many years been associated with the University of Limburg School of Medicine in Maastricht, Netherlands. At his department of cardiology, many future clinical cardiac electrophysiologists trained from 1976 until his retirement in 2002.


As a pupil and collaborator of the late Professor Dirk Durrer in Amsterdam, Dr. Wellens was involved in the early developments in programmed electrical stimulation of the heart in patients with the Wolff-Parkinson-White syndrome. In these patients, cardiac arrhythmias it was shown for the very first time that were first shown to be possibly initiated and terminated by critically timed premature beats. In 1971, he reported on the use of programmed electrical stimulation of the heart in patients with atrial flutter, AV nodal tachycardia, and accessory atrioventricular connections. In 1972, he showed that the arrhythmia of patients with ventricular tachycardia could also reproducibly be initiated and terminated by timed premature stimuli. These investigations were the basis for the new surgical and pacing approaches to the treatment of cardiac arrhythmias that became known as “cardiac electrophysiology”.[3] to be Wellens also demonstrated that the reproducible initiation and termination of arrhythmias by programmed electrical stimulation of the heart allowed the study of the effect of antiarrhythmic drugs on the mechanism of the arrhythmia. In 1977, he moved to the new University of Limburg in Maastricht, Netherlands, to develop academic cardiology there. Starting from scratch, he created an internationally known center for the study and treatment of cardiac arrhythmias.[3]

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