lecture 2 reading

DISORDERS OF BLOOD FLOW AND BLOOD PRESSURE REGULATION

BLOOD VESSEL STRUCTURE AND FUNCTION

  • Endothelium: Specialized tissue lining blood vessels, crucial for vascular function.

  • Vascular Smooth Muscle Cells (VSMCs): Constrict and dilate blood vessels, important for blood flow regulation.

REGULATION OF SYSTEMIC ARTERIAL BLOOD PRESSURE

Mechanisms of Blood Pressure Regulation

  • Acute Regulation: Rapid adjustments via neural and hormonal responses (e.g., during exercise).

  • Long-Term Regulation: Kidney function and blood volume regulation to maintain arterial pressure.

  • Circadian Variations: Natural fluctuations in blood pressure throughout the day.

DISORDERS OF SYSTEMIC ARTERIAL BLOOD FLOW

Dyslipidemia

  • Classification of Lipoproteins: Groups include chylomicrons, VLDL, IDL, LDL, and HDL based on densities.

  • Etiology and Pathogenesis: Elevated lipid levels from various sources (diet, genetics).

Atherosclerosis

  • Etiology and Risk Factors: Influenced by hypercholesterolemia, smoking, hypertension.

  • Pathogenesis: Formation of fibrofatty plaques in arterial walls.

  • Clinical Manifestations: Chest pain, heart attack risks, etc.

Vasculitis

  • Types: Includes Giant Cell Temporal Arteritis affecting medium to large arteries, causing systemic issues.

Arterial Disease of the Extremities

  • Acute Arterial Occlusion: Sudden loss of blood flow, often caused by embolism or thrombosis.

  • Chronic Conditions: Progressive occlusion leads to symptoms like claudication, pain in limbs.

DISORDERS OF SYSTEMIC VENOUS CIRCULATION

Varicose Veins

  • Etiology and Pathogenesis: Weakness in valves leads to pooled blood, especially in superficial veins.

  • Clinical Manifestations: Visible veins, aching, swelling.

Chronic Venous Insufficiency

  • Pathophysiology: High venous pressure affects tissue perfusion leading to stasis dermatitis and ulcers.

DISORDERS OF BLOOD PRESSURE REGULATION

Hypertension

  • Definition: Sustained high blood pressure, a major risk factor for cardiovascular disease.

  • Clinical Manifestations: Often asymptomatic until severe.

  • Types of Hypertension: Primary (essential) and secondary forms.

Orthostatic Hypotension

  • Definition: Drop in blood pressure upon standing; symptoms include dizziness and fainting.

  • Etiology: Blood volume issues, medication side effects, aging, etc.

SUMMARY

  • Blood Pressure Regulation: Critical for adequate perfusion; requires neural and humoral mechanisms for acute control and renal function for long-term control.

  • Major Conditions: Hypertension and orthostatic hypotension are prevalent and tied to significant morbidity.

GERIATRIC CONSIDERATIONS

  • Age-related changes affect blood pressure regulation; increased risk of hypertension and venous insufficiency.

PEDIATRIC CONSIDERATIONS

  • Increasing hypertension among children linked to lifestyle factors, necessitating tailored management approaches.

Hemodynamics of Blood Flow

Components and Function of the Vascular System

  • Function: Delivery of oxygen and nutrients; removal of wastes from tissues.

  • Components:

    • Arteries and arterioles

    • Capillaries

    • Venules and veins

Composition of Blood Vessels

  • Tunica externa (adventitia): Outermost fibrous and connective tissue supporting the vessel.

  • Tunica media: Middle layer, predominantly smooth muscle for vessel diameter regulation.

  • Tunica intima: Inner elastic layer with endothelial cells adjacent to blood.

Arteries, Veins, and Capillaries

  • Composition of the Arterial System:

    • Arteries: Thick-walled with elastic fibers, stretch during systole and recoil during diastole.

    • Arterioles: Serve as resistance vessels, regulating blood flow into capillaries.

Effects of Peripheral Resistance and Regulation of Blood Flow

  • Formula: Blood pressure (BP) = Cardiac output (CO) × Peripheral vascular resistance (PVR)

  • Regulation: Baroreceptor reflex maintains pressure and perfusion.

Blood Vessel Structure

  • Capillaries: Single-layer endothelium for nutrient and gas exchange; connect arterioles and venules.

  • Veins: Thin-walled, muscular, and compliant, with valves preventing retrograde flow.

    • Central venous pressure (CVP): Measured using a catheter, normal range 8-12 mmHg.

Compliance of Blood Vessels

  • Compliance (C) = V/P; veins are 24 times more compliant than arteries.

Cardiomyopathy and Congestive Heart Failure (CHF)

  • Right Ventricular Dysfunction: Leads to peripheral edema.

  • Left Ventricular Dysfunction: Causes pulmonary congestion/edema.

Principles of Blood Flow Hemodynamics

  • Cardiac output distribution depends on vascular properties and blood volume returning to the heart.

  • Blood flow determined by pressure differences and total peripheral resistance.

    • Resistance factors: Vessel radius, blood viscosity, and vessel length.

Resistance and Flow Dynamics

  • Poiseuille's Law: Resistance inversely proportional to the 4th power of vessel radius.

  • Laminar vs. Turbulent Flow: Laminar flow reduces friction; turbulent flow is disordered.

Function of the Microcirculation

  • Capillary Exchange: Governed by hydrostatic and osmotic pressures; lymphatic system drains excess interstitial fluid.

Humoral and Local Control of Blood Flow

  • Mediated by various substances (e.g., norepinephrine, angiotensin II).

  • Autoregulation: Adjusted by local tissue factors such as oxygen levels and metabolic byproducts.

Factors Controlling Fluid Movement and Edema

  • Fluid movement influenced by pressure differences and osmotic forces; edema results from imbalances in these controls.

Autonomic Control Centers

  • Located in the medulla oblongata; regulate cardiac function and blood pressure via sympathetic and parasympathetic innervation.

Baroreceptors and Chemoreceptors

  • Baroreceptors: Monitor blood pressure.

  • Chemoreceptors: Monitor oxygenation, carbon dioxide, and pH levels.