Chapter 10, Part 5. Cardiorespiratory System. Cardiorespiratory Control. Neural Control. Regulation of the CV System. Nervous System Components

Transcription

1 Cardiorespiratory System Chapter 10, Part 5 Cardiorespiratory Control Pulmonary ventilation Gas exchange Left heart Arterial system Tissues Right heart Lungs Pulmonary ventilation Cardiorespiratory Control Neural Control Central command motor cortex Medulla cardiorespiratory centers Network of nerve cells Cardioacceleration center Cardioinhibitory center Respiratory response RR and TV Chemical changes in blood Inspiratory center Expiratory center Circulatory effects HR, SV, contractility, VC, VD Regulation of the CV System Interrelated and overlapping mechanisms Mechanical events Muscle action affects VR which influences SV & Q Neural control Neurohormonal control Nervous System Components CNS Sensory division Peripheral nervous system Motor division Somatic (voluntary) Autonomic (involuntary) Sympathetic Parasympathetic 1

2 Nervous System Components Sensory division receives information from Mechanoreceptors (pressure, touch, stretch) Thermoreceptors (temperature) Nociceptors (pain) Photoreceptors (light) Chemoreceptors (chemical stimuli) Nervous System Components Motor Division efferents CNS transmits information to effect a response Autonomic nervous system HR, BP, blood distribution, respiration Sympathetic nervous system Fight or flight, prepares for crisis Increases HR, contractility Dilates coronary vessels VC in most tissues Bronchodilation Parasympathetic nervous system Decreases HR, VC coronary vessels Bronchoconstriction Sympathetic nerves innervate primarily ventricles Parasympathetic nerves innervate primarily Sinus node AV node Neurotransmitters To send signal from nervous system to intended site About 40 different NT Parasympathetic Acetylcholine-primary NT for motor neurons that innervate skeletal muscle Cholinergic receptors Sympathetic Norepinephrine excitatory or inhibitory, depending on receptors Adrenergic receptors 2

3 CV centers in brain stem Cardio accel-sends signals via sym Cardio inhib-sends signals via vagus Vasomotor center Innervates visceral arterioles-vc Innervate skel musc arterioles-vd Neural Control Factors Affecting CV Control CV centers influenced by various stimuli 1. Central Command Higher centers of the brain- Cerebral cortex Hypothalamus Nature of signals to match BF and metabolism with exercise not well understood Speed of CV/R response suggests central neural command signal Influence of the motor cortex and hypothalamus during exercise termed central command 2. Neural input from the periphery Muscle receptors Mechanical mechanoreceptors Metabolic metaboreceptors Located in joints and muscles Send impulses to brain (CV center) Stimulated by muscle contraction Increase HR, contractility, VD in active muscle 2. Neural input from periphery (cont) Muscle Receptors Feedback information from changes in: Temperature of working muscle Tension development Pain or discomfort Muscle afferents-types I, II, III, and IV Types I and II are highly myelinated nerve fibers for muscle spindles and golgi tendon organs No effect on CV function 2. Neural input from periphery (cont) Types III and IV are excited by mechanical, thermal and chemical stimuli Feedback to CV center to increase HR to raise BP, increase contractility and VC blood vessels Type III-sensitive to stretch and mechanical deformation Type IV more responsive to chemical stimuli, decreased ph. 3

4 3. Humoral Stimuli-changes in chemical state of blood and cerebral spinal fluid Central Chemoreceptors-medulla Detect changes in PCO 2 and ph Regulate ventilation by affecting inspiratory center 3. Humoral Stimuli (cont) Peripheral chemoreceptors Located in aortic and carotid arteries Sensitive to arterial blood PO 2, CO 2, H + Increase in CO 2, H + or decrease in PO 2 causes reflex VC in arterioles Chemoreceptors establish a set point and work by negative feedback Changes from set point are sensed, feedback sent to CV control center 4. Physical Stimuli Systemic Receptors Found in large veins, heart and arterial system Provide sensory information to CV control centers for reflex action Baroreceptors in aortic and carotid bodies Respond to increased MAP to PS outflow and Sym outflow Stretch receptors in right atrium Respond to increase in VR Baroreceptors Work from a set point Low pressure BR Atria, ventricles, pulmonary artery and vein Decrease in BP triggers BR to signal CV center to correct Increase HR, contractility, TPR-increase BP Increase in resting BP, BR fire for about 24 h to reduce BP If unsuccessful, BR reset at new level. Baroreceptors Rest Return BP to baseline (set point) Exercise Don t want resting set point Reset at higher level Increase in HR and BP needed for exercise is possible 4

5 CV Control CV control during exercise CV response matched to type and intensity of exercise Blood pressure changes matched to muscle mass involved and what % maximal contraction CV response mediated by PS and Sym nervous activity Pulmonary Control Pons-2 neural centers Pneumotaxic center inhibitory Apneustic center stimulates Make sure that the transitions between inhalation and exhalation are smooth Pulmonary Control Muscle action, thus rate and depth of br controlled by NS Based on O 2, CO 2, energy need Two respiratory centers-medulla Inspiratory centersignals on for 2 s Expiratory centersignals off for 3 s Sensors that influence Ventilation Ventilatory Control Chemoreceptors Central Cerebral spinal fluid, medulla ph; PCO 2 Stimulate inspiratory center Peripheral Arterial blood Carotid and aortic bodies PCO 2, PO 2 and ph-stimulate inspiratory center 5

6 Cardiovascular Adjustments to Exercise A Summary of Cardiovascu lar Control During Exercise Fig 9.23 Fig