Rishi Desai, MD, MPH

Control of blood flow circulation

CONTROL OF BLOOD FLOW CIRCULATION osms.it/blood-flow ▪ Blood ﬂow regulation ▫ Intrinsic (local): humoral, myogenic control ▫ Extrinsic (systemic): hormonal, neural  LOCAL (INTRINSIC) BLOOD FLOW CONTROL Mechanisms ▪ Humoral: mediated by vasoactive substances ▫ Histamine, nitric oxide (arteriole dilation) ▫ Endothelin, serotonin ▪ Autoregulation: maintains constant blood ﬂow via direct control of arterial resistance ▫ Present in organs such as kidneys, brain, heart, skeletal muscle (e.g. ↓ coronary artery pressure → compensatory arteriole vasodilation → ↓ vessel resistance → constant blood ﬂow) ▪ Active hyperemia: ↑ blood ﬂow directed to organ/tissue associated with ↑ metabolic activity (e.g. ↑ blood ﬂow in active skeletal muscle) ▪ Reactive hyperemia: temporary ↑ blood ﬂow following ischemia (↓ blood ﬂow) in organ (e.g. arterial occlusion → ↓ blood ﬂow → ↑ O2 debt → vasodilation, ↑ blood ﬂow) ▪ Myogenic hypothesis for autoregulation ▫ Focus on arteriolar resistance: vascular smooth muscle contracts upon stretching (↑ wall tension) and vice versa ▫ ↑ blood ﬂow → arteriole stretching → contraction → ↑ resistance → constant blood ﬂow ▫ ↓ blood ﬂow → ↓ arteriole stretching → relaxation → ↓ resistance → constant blood ﬂow ▫ Explained by law of Laplace: ↑ pressure (P) + ↓ radius (r) → tension (T) remains constant (T=P x r)  154 OSMOSIS.ORG  ▪ Metabolic hypothesis for autoregulation, active, reactive hyperemia ▫ O2 distribution changes in response to O2 consumption via altering arteriolar resistance ▫ ↑ metabolism → ↑ vasodilating metabolites (CO2, H+, K+, lactate, adenosine) → arteriole vasodilation → ↓ resistance → ↑ blood ﬂow, O2 distribution ▫ Certain tissues more susceptible to certain metabolites (coronary circulation—PO2, adenosine; cerebral circulation—PCO2)  NEURAL & HORMONAL (EXTRINSIC) CONTROL ▪ Neural: sympathetic nervous system acts on vascular smooth muscle ▫ ɑ1: vasoconstriction → skin, intestines ▫ β2: vasodilation → lungs, skeletal muscles ▪ Hormonal: vasopressin released from anterior pituitary → vasoconstriction   

Cardiovascular system anatomy and physiology

Lymphatic system anatomy and physiology

Coronary circulation

Anatomy and physiology

Abnormal heart sounds

Normal heart sounds

Auscultation of the heart

Baroreceptors

Chemoreceptors

Renin-angiotensin-aldosterone system

Blood pressure regulation

Cardiac cycle

Cardiac work

Changes in pressure-volume loops

Pressure-volume loops

Cardiac cycle and pressure-volume loops

Cardiac and vascular function curves

Altering cardiac and vascular function curves

Cardiac afterload

Cardiac contractility

Cardiac preload

Frank-Starling relationship

Law of Laplace

Measuring cardiac output (Fick principle)

Stroke volume, ejection fraction, and cardiac output

Cardiac output

Physiological changes during exercise

Cardiovascular changes during hemorrhage

Cardiovascular changes during postural change

Cardiovascular physiological responses

Cardiac conduction velocity

Electrical conduction in the heart

ECG basics

ECG normal sinus rhythm

ECG intervals

ECG QRS transition

ECG axis

ECG rate and rhythm

ECG cardiac infarction and ischemia

ECG cardiac hypertrophy and enlargement

Electrocardiography

Microcirculation and Starling forces

Blood pressure, blood flow, and resistance

Compliance of blood vessels

Laminar flow and Reynolds number

Pressures in the cardiovascular system

Resistance to blood flow

Hemodynamics

Action potentials in myocytes

Action potentials in pacemaker cells

Cardiac excitation-contraction coupling

Excitability and refractory periods

Myocyte electrophysiology

Cardiovascular system

Control of blood flow circulation

Videos

Notes