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.