Physiology Lecture (10) PDF

Physiology Sympathetic & Para sympathetic under different conditi LECTURE (10) DR. El-Sawy 0  Physiology...

Physiology Sympathetic & Para sympathetic under different conditi LECTURE (10) DR. El-Sawy 0  Physiology Sympathetic & Para sympathetic under different conditions A. At rest → called tone : Sympathetic Tone Parasympathetic Tone  Continuous basal discharge of sympathetic impulses  Continuous basal discharge of parasympathetic to the supplied organs during rest  leading to mild impulses to the supplied organs during rest  Def activity. leading to mild activity.  Continuous discharge of sympathetic nerves.  Continuous afferent impulses from baroreceptors in Causes  Continuous basal secretion of adrenaline and carotid sinus & aortic arch along sinus &aortic nerves noradrenaline from adrenal medulla. to cardioinhibitory center in medulla oblongata. a) In the heart :  Sympathetic supply to blood vessels → decreasing Decreases SAN rhythm from 120 to 70 beat / its maximal diameter to its half (partial VC )  min. Example Maintains normal arterial blood pressure : b) In the GIT : a. ↑ Sympathetic  more vasoconstriction Maintains its normal motility. b. ↓ Sympathetic  vasodilatation 1. ↑ parasympathetic activity →↑ motility 2. ↓ parasympathetic activity →↓ motility. DR. El-Sawy 1  Physiology Sympathetic & Para sympathetic under different conditions Cutting of nerves Sympathectomy Cutting sympathetic nerves leads to immediate maximal vasodilatation. After sometime, intrinsic tone of smooth muscles of blood vessels increase, restoring vasoconstriction again, thus returning normal level of arterial blood pressure. Vagotomy Cutting parasympathetic nerve leading to: 1. Heart: increases its rate from 70 to 120 beat/min. 2. GIT: leads to serious prolonged GIT atony. DR. El-Sawy 2  Physiology Sympathetic & Para sympathetic under different conditions B. To certain organs → isolated or localized. Sympathetic Parasympathetic  In some cases, Sympathetic stimulation occurs Def in isolated portion of the system.  Hot weather: a. Parasympathetic cardiovascular reflexes : It affects only skin blood vessels & sweat Act only on heart. glands without affecting other organs. b. Parasympathetic GIT reflexes : Example  Hand writing: Act only on GIT. Sweat secretion occurs from hand to make a good grip. DR. El-Sawy 3  Physiology Sympathetic & Para sympathetic under different conditions C. To whole body → generalized (Mass) actions. Sympathetic mass discharge (stress response) Parasympathetic mass stimulation  State of generalized sympathetic excitement  It is fatal.  Occurs in : emergency or stress conditions as:  Due to association between closely 1) Hemorrhage. related parasympathetic functions  Def 2) Hypoglycemia one parasympathetic reflex may initiate 3) Severe cold & Pain & Sever exercise. another one. 4) Fear, fight and flight & Emotions.  Rectal emptying reflex initiates bladder emptying reflex  simultaneous  Enables person to face stressful situations. emptying of bladder and rectum.  Increase the capacity of the body to perform Example  Salivary secretion  activates gastric vigorous muscular activity. secretion  activates pancreatic secretions. DR. El-Sawy 4  Physiology Sympathetic & Para sympathetic under different conditi Sympathetic mass stimulation during stress produces the following effects:  Pupillary dilatations, exophthalmos and widening of the Eye palpebral fissure, thus increasing the field of vision.  Accelerates the heart beat, increases the force of myocardial Heart contraction and raises the blood pressure, providing increased blood flow to vital organs and active muscles.  Dilates the bronchioles to ensure better lung ventilation and more Thorax oxygen supply to the blood.  Constriction of blood vessels in skin →limits bleeding of wounds.  Dilatation of blood vessels of skeletal muscles and cardiac muscle with vasoconstriction to other areas. This help in shifting a great Somatic part of the cardiac output to the active areas.  Increases the strength of skeletal muscles contraction and delays the onset of fatigue (Orbelli Phenomenon).  Contraction of splenic capsule leading to ejection of some blood Spleen rich in red blood cells into the general circulation, thus increasing blood volume as well as oxygen carrying capacity of the blood.  Secretion of adrenaline and noradrenaline potentiates the adrenal stimulation of sympathetic system (sympatho-adrenal system). medulla  Adrenaline elevates the blood glucose and free fatty acid level (supplying more energy). Liver  Increases glycogenolysis in the liver, and glycolysis in the muscle.  Increases mental activity and cellular metabolism throughout the body Other  Increases sweat secretion, which by its evaporation increases heat loss from the body. DR. El-Sawy 5