Atrioventricular Node

Skipped Beats Ekg

In the normal heart, the only pathway for an action potential to travel to the ventricles is through the AV node. As noted above, propagation through the AV node is quite slow compared to propagation in other cardiac cells. This slowed conduction is primarily due to a decreased density of sodium channels, which yields a decreased upstroke Figure 14.17 Twelve-lead ECG recording of Wolff-Parkinson-White syndrome, identifiable by the shortened P-Q interval (because the AV delay is circumvented)...

Insulin Oscillations with Intermediate Frequency

Insulin also oscillates with a period of about 10-20 minutes Figs. 19.11 and 19.12 . Because these oscillations occur in islets and the isolated pancreas, it appears that unlike the ultradian oscillations, they are caused by a mechanism intrinsic to the pancreatic islets. These oscillations also occur in the experimental perifusion system depicted in Fig. 19.16. A thin layer of insulin-secreting -cells is sandwiched between beads and exposed to the flow of a solution, the perifusate, with flow...

Pulsatile Insulin Secretion

Pulsatile Testosterone Secretion Men

Hormones secreted from cells in the pancreas are responsible for the control of glucose, amino acids, and other molecules that are necessary for metabolism. The pancreas contains a large number of secretory cells, grouped into about one million islets of Langerhans consisting of approximately 2,500 cells each. There are three principal Figure 19.9 Pulsatile secretion of LH, FSH, and testosterone in men. Berne and Levy, 1993, Fig. 48-15, p. 912. Figure 19.9 Pulsatile secretion of LH, FSH, and...

Ultradian Oscillations

Glucose Insulin Delay Equation Liver

Ultradian insulin oscillations have a number of observable features. First, oscillations occur during constant intravenous glucose infusion and are not dependent on periodic nutrient absorption from the gut. However, damped oscillations occur after a single stimulus such as a meal. Second, glucose and insulin concentrations are highly correlated, with the glucose peak occurring about 10-20 minutes earlier than that of insulin. Third, the amplitude of the oscillations is an increasing function...

The Juxtaglomerular Apparatus

Complex Juxtaglomerular Apparatus

The need for autoregulation of the glomerular filtration rate is apparent. If the flow rate of filtrate is too slow, then we expect reabsorption to be too high, and the kidney fails to eliminate necessary waste products. On the other hand, at too high a flow rate, the tubules are unable to reabsorb those substances that need to be preserved and not eliminated, so that valuable substances are lost into the urine. The idea of how to regulate the flow of filtrate is simple to understand. If you...

Multicompartment Circulatory System

Symbolic Diagram Circulatory System

To construct a more detailed linear model of the circulatory system, we assume that the systemic and pulmonary loops each consist of two compliance vessels, the arterial and venous systems, connected by the capillaries, a pure resistance. Further, we assume that the heart has two chambers, the left and right hearts. A schematic diagram of the model is given in Fig. 15.8. We must write equations for the flow through each of these compartments and keep track of the total volume of blood contained...