LEC 9+10 Physiology/2nd stage PDF

ÆċÂÀ°÷¥ ­¦ČĀð¯ úÌï ¬¸øÌë LEC 9+10 ¬Čÿ¦´÷¥ ¬ø»Æ}¥ ǭdz˅߼Ǫ Ǵ˅˕̑˷Ǫ ˰‫ݔ‬Ǫ DZ˲̙.dz dijlah_library dijlah12345 1000 2024 Lecture 9 Physiology/2nd stage Dr. Fa...

ÆċÂÀ°÷¥ ­¦ČĀð¯ úÌï ¬¸øÌë LEC 9+10 ¬Čÿ¦´÷¥ ¬ø»Æ}¥ ǭdz˅߼Ǫ Ǵ˅˕̑˷Ǫ ˰‫ݔ‬Ǫ DZ˲̙.dz dijlah_library dijlah12345 1000 2024 Lecture 9 Physiology/2nd stage Dr. Farah Altaay Starling's Law of the heart: In the late19th century, Otto Frank found using isolated frog heart that the strength of ventricular contraction was increased when the ventricle was stretched prior to contraction. This observation was extended by the studies of Ernest Starling in the early 20th century who found that increasing venous return to the heart, will increase the filling pressure (left ventricular end-diastolic pressure; LVEDP) of the ventricle caused the stroke volume (SV) to increase. Conversely, decreasing venous return decreased stroke volume. This cardiac response to changes in venous return and ventricular filling pressure is intrinsic to the heart and does not depend on extrinsic neurohumoral mechanisms. So, the ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return is called the Frank-Starling mechanism (or Starling's Law of the heart). In other words, Frank–Starling law of the heart indicates that the increased filling pressure of the heart results in increased cardiac output 2 Lecture 9 Physiology/2nd stage Dr. Farah Altaay Frank-Starling curves: Frank-Starling curves show how changes in ventricular preload lead to changes in stroke volume. 3 Lecture 9 Physiology/2nd stage Dr. Farah Altaay When venous return is increased, there is increased filling of the ventricle, leading to an increase in end-diastolic volume (see Figure above). This will increase stroke volume, to match physiological increases in venous return. This is not, however, the case for ventricles that are in failure. What is the physiological significance of the Frank-Starling law of the heart for blood circulation? The Frank-Starling mechanism is a physiological principle that explains how the heart responds to changes in venous return. Increases in venous return cause the heart's chambers to fill with more blood, which then causes the heart to stretch and contract more forcefully, and pump more blood out to the rest of the body. So, he greater the preload, the greater will be the volume of blood in the heart at the end of diastole. Starlings' Law is therefore representing the relationship between the contractility and the afterload. thanx 4 Lecture 10 Physiology/2nd stage Dr. Farah Altaay The autonomic nervous system (ANS): is a component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and glandular functions (secretions) of the body. The ANS has two interacting systems: the sympathetic and parasympathetic systems. It is controlled by centers located in the spinal cord, brain stem, and hypothalamus. 2 Lecture 10 Physiology/2nd stage Dr. Farah Altaay  Heartbeats originate from the rhythmic pacing discharge from the sinoatrial (SA) node within the heart itself. In the absence of extrinsic neural or hormonal influences, the SA node pacing rate would be about 100 beats per minute. Heart rate and cardiac output, however, must vary in response to the needs of the body’s cells for oxygen and nutrients under varying conditions.  In order to respond rapidly to the changing requirements of the body’s tissues, the heart rate and contractility are regulated by the autonomic nervous system, hormones, and other factors.  sympathetic and parasympathetic neurons exert antagonistic effects on the heart. The sympathetic system prepares the body for energy expenditure, emergency or stressful situations.  Conversely, the parasympathetic system is most active under restful conditions. The parasympathetic counteracts the sympathetic system after a stressful event and restores the body to a restful state.  The sympathetic nervous system releases norepinephrine (NE) while the parasympathetic nervous system releases acetylcholine (ACh). 3 Lecture 10 Physiology/2nd stage Dr. Farah Altaay What is the effect of Sympathetic stimulation on cardiovascular system? During exercise, emotional excitement, or under various pathological conditions (e.g., heart failure), the sympathetic nervous system is activated. The stimulation of the sympathetic nervous system causes: 1. increase heart rate. 2. Increase myocardial contractility. 3. blood vessel constriction. 4. increases renin secretion by the kidneys, which leads to a series of actions that rapidly leads to increased systemic blood pressure. What is the effect of Parasympathetic stimulation on cardiovascular system? In contrast, the parasympathetic counteracts the sympathetic system after a stressful event and restores the body to a restful state. 1. Parasympathetic stimulation decreases heart rate. 2. It decreases cardiac output. 3. The parasympathetic stimulation decreases blood pressure. 4. Parasympathetic stimulation does not cause vasodilatation because most blood vessels lack parasympathetic innervations and their diameter is regulated by sympathetic nervous system only, so that it is a decrease in sympathetic stimulation or tone that allows vasodilatation. 4 Lecture 10 Physiology/2nd stage Dr. Farah Altaay Sympathetic neurotransmitters: Neurotransmitters are chemical substances released into the synaptic cleft from nerve terminals. They transmit signals from a neuron to a target cell across a synapse, e.g., acetylcholine for neuromuscular junctions. While the preganglionic neurons of both the sympathetic and parasympathetic system secret acetylcholine (ACh) which is why they are referred to as cholinergic, the majority of the postganglionic endings of the sympathetic nervous system release NE, which resembles epinephrine (i.e., adrenalin). Thus, these sympathetic postganglionic fibers are commonly called adrenergic fibers. Sympathetic receptors: There are two types of adrenergic receptors: β and α. In the cardiovascular system there are β1, β2, α1, and α2 adrenergic receptors. 5 Lecture 10 Physiology/2nd stage Dr. Farah Altaay Sympathetic and parasympathetic receptors and their functions in the heart and vessels Heart Vessels Function Receptor Function Receptor Inotropy Chronotropy α1 + + α1 Vasoconstriction Norepinephrine β1 + + β1 Vasoconstriction β2 + + β2 Vasodilation Acetylcholine M2 - - M2 Vasodilation Parasympathetic neurotransmitters: Acetylcholine is the predominant neurotransmitter from the parasympathetic nervous system, in both the preganglionic and postganglionic neurons. Acetylcholine inhibits the contraction of cardiomyocytes by activating muscarinic receptors (M2). These parasympathetic postganglionic fibers are commonly called cholinergic fibers because they secrete acetylcholine at their nerve endings. Parasympathetic Receptors: The parasympathetic postganglionic fibers are cholinergic. Acetylcholine can bind to two types of cholinergic receptors called nicotinic receptors and muscarinic receptors. THANK YOU 6