Unformatted text preview: Lecture 24 Lecture Respiration Circulation 6 December 2010 Unloading of Oxygen in Metabolically Active Tissue Metabolically Note the corrected arrow. Respiratory System in Acid-Base Balance Acid
Hemoglobin functions as a buffer H+ + HbO2 O2 + Hb + H+ HbH Bicarbonate buffer system CO2 + H2O H2CO3 H+ + HCO3- Blood pH = 6.1 + log [HCO3-] / [CO2] At normal arterial pH = 7.4, [HCO3-] / [CO2] = 20:1 Respiratory system regulates CO2 Kidneys regulate HCO3- Chemoreceptor Reflex Chemoreceptor Arterial CO2, mainly through arterial H+, is through is much more important than O2 in the control of in respiration. respiration.
Very little response Very despite large change in PO2 Large response despite small change in PCO2 The Root Effect The pH pH oxygen carrying capacity of Hb, oxygen even when Hb is 100% saturated Panel A: pH O2 capacity, thus O2 content, of pH content, fish red blood cells at saturating PO2. In human fish In blood cells ( ), no Root effect. blood ), 6.0 6.5 7.0 pH 7.5 8.0 8.5 Reference: Waser, W and Heisler, N. 2005. Oxygen Reference: Waser and Heisler N. delivery to the fish eye: Root effect as crucial factor for elevated retinal PO2. J. Exp. Biol. 208: 4035-4047. elevated Panel B: pH PO2 in a suspension of fish red blood pH in cells. In human blood cells ( ), no Root effect. cells. ), Reference: Waser, W and Heisler, N. 2005. Oxygen Reference: Waser and Heisler N. delivery to the fish eye: Root effect as crucial factor for elevated retinal PO2. J. Exp. Biol. 208: 4035-4047. elevated Recall: PO2 ↔ Dissolved O2 PO2 Dissolved O2 PO2 Dissolved O2 The Root effect. Acidification lowers the oxygen carrying capacity of hemoglobin. capacity Molecular oxygen is released from hemoglogin, thus causing Molecular hemoglogin thus an increase in the partial pressure of O2 in the blood. an An increase in the partial pressure gradient from blood to An tissue causes an increase in the rate of diffusion of O2 tissue into cells of the retina, or into the swim bladder. into The Root effect and fish swimbladder. swimbladder
Swimbladders are homologous to vertebrate lungs: they share an identical evolutionary origin but serve different functions. Swimbladders provide bouyancy. TOP: Open swimbladder of physostomes Bottom: Closed swimbladder of physoclists The Root effect and fish swimbladder. swimbladder Swimbladder The Root effect and fish swimbladder. swimbladder Blood leaving the venous portion of the rete must have a higher PO2 despite a lower O2 content than blood in the arterial portion. The Root effect and fish swimbladder. The A rete 1 cm long can secrete oxygen up to 2000 atm (depth of 20,000 m) Blood leaving the venous portion of the rete must have a higher PO2 despite a lower O2 content than blood in the arterial portion. Blood Volume is lower Blood is in pulmonary than in systemic circulation. systemic Blood pressure is lower is in pulmonary than in systemic circulation. systemic Blood flow is equal in Blood pulmonary and systemic circulation. In other words, right ventricular C.O. = left ventricular C.O. left Circuits of the Cardiovascular System
– Pulmonary circuit
• Supplied by right side of heart • Blood vessels from heart to lungs and from lungs to heart Series Blood Flow Between the Two Series Between – Systemic circuit
• Supplied by left side of heart • Blood vessels from heart to systemic tissues and from tissues to heart Systemic (or Pulmonary) Circuit
– Aorta arteries arterioles capillaries – Capillaries venules veins – Oxygenated blood Parallel Blood Flow Within the Parallel Within enters each systemic capillary bed – Parallel flow allows independent regulation of blood flow to organs The Heart’s Conducting System The
Pacemaker cells Purkinje fibers – specialized cardiac cells conduct action potential very rapidly throughout ventricular myocardium. The Heart is Myogenic, Not Neurogenic The Depolarization of the heart begins with an action potential that develops in and propagates from the SA node.
40 ms are required for depolarization to spread from the SA to the AV node, ... … but an additional 50 ms elapse before both atria are fully depolarized. Depolarization is delayed in the AV node and arrives at the bundle branches 120 ms after it reaches the AV node. Time is shown in fractions of a second The electrical delay of the AV node allows the atria to fully depolarize and contract before ventricular depolarization begins. This delay is reflected in the P-R segment of the ECG. Pacemaker potential due to declining K+ permeability and increasing Na+ permeability followed by an increase in Ca++ permeability. Rapid depolarization is due to a sharp increase in Ca++ permeability. Cardiac Rhythm Arises in Pacemaker Cells Cardiac Depolarization spreads rapidly from cell to cell through gap junctions at intercalated disks.
Structurally similar Structurally in many ways to skeletal muscle, except ……. …… Branched Fibers Intercalated Disk The heart is frequently described as a functional syncytium.
Gap junctions: rapid communication between cells; contraction as a unit Desmosomes: protein fibers form physical bonds between cells, which resist stress Electrocardiogram The ECG is a recording of surface potentials (not membrane potentials). It records electrical differences between different points on the outer surface of the heart. Cardiac muscle sustains its contraction due to the plateau phase of the cardiac action potential and thus prolonged depolarization.
Rapid depolarization is due to high Na+ permeability and an inward Na+ current. Plateau phase is due to high Ca++ permeability and an inward Ca++ current. Repolarization is due to K+ efflux. Electrical activity initiates the cardiac cycle.
This diagram presents a mammalian cardiac cycle for the left side of the heart. depolarization contraction ↑ blood pressure blood flow open valves ↓ volume The heart is the ultimate source of pressure that drives blood through the vascular system. Aortic Pressure During Cardiac Cycle Systolic Pressure Systolic Mean Arterial Pressure Diastolic Pressure MAP = DP + 1/3 PP PP = pulse pressure = SP-DP During the cardiac cycle, blood flow from the heart is intermittent, … but capillary perfusion (forced blood flow) is continuous. Aorta has elastic elements in its wall which stretch and store pressure during systole. Stored energy is released back into the blood during diastole, thus maintaining blood flow. The aorta and other arteries dampen pressure oscillations and serve as pressure reservoir. Cardiac Output Cardiac
Volume of blood pumped by each ventricle per minute – Cardiac Output = C.O. = SV x HR
– Regulation of C.O. by control of SV and HR
– Extrinsic regulation via nerves and hormones – Intrinsic regulation via autoregulation Regulation of Heart Rate: Regulation Pacemaker Potentials
Extrinsic Control: Sympathetic stimulation increases HR Parasympathetic stimulation decreases HR Stroke Volume (SV) – EDV = volume of blood in ventricle at end of diastole – ESV = volume of blood in ventricle at end of systole – SV = volume of blood ejected from heart each cycle – SV = EDV - ESV EJECTION FRACTION: Fraction of end-diastolic volume ejected during a single heartbeat Ejection fraction = Ejection SV / EDV SV = 70 mL / 130 mL = 0.54 70 mL 130 mL Regulation of Stroke Volume: Regulation Family of Starling Curves
Intrinsic Control: Frank-Starling Extrinsic Control: Sympathetic stimulation increases ventricular contractility Autonomic Regulation of Cardiac Autonomic Output Involves SV and HR ...
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