CV System

Cardiovascular System Study Guide

Circulation Overview

  • Presenter: Kasey Brockelsby

  • Course: BIOL 214

  • Semester: Spring 2026

  • Institution: Highland Community College

Blood Vessels

Arteries and Veins

  • Blood circulation throughout the body occurs via blood vessels.

  • Arteries:

    • Function: Carry blood away from the heart.

  • Veins:

    • Function: Carry blood towards the heart.

Capillaries

  • Capillary Formation:

    • Arteries branch into smaller vessels called capillaries at target tissue sites.

  • Gas Exchange:

    • Capillaries are the sites where oxygen (O2) is picked up in the lungs and dropped off in tissues.

  • Blood Flow Post-Capillaries:

    • After passing through capillary beds, small vessels rejoin to form veins, which merge back into the heart.

Shared Blood Vessel Structures

  • Vascular Wall Composition:

    • Both arteries and veins consist of a vascular wall with three layers surrounding a lumen (the hollow part where blood flows).

    • Structural details differ between arteries and veins.

Blood Vessel Structure Details

General Characteristics

  • Arteries:

    • Thicker vascular walls and narrower diameters to withstand high blood pressure.

    • Maintain a circular shape more effectively due to their structure.

  • Veins:

    • Typically larger lumens and thinner walls, adapted to carry blood at lower pressure.

Tunics of Blood Vessels

  1. Tunica Intima

    • Innermost layer made of a thin endothelial lining.

    • Endothelium Function: Secretes endothelins regulating blood pressure.

    • Damage to endothelium exposes collagen, contributing to clot formation.

    • Includes a flexible internal elastic membrane in arteries and valves in veins.

  2. Tunica Media

    • Muscular layer, much thicker in arteries.

    • Contains smooth muscle layers supported by elastic fibers.

    • Responsible for vasoconstriction (muscle contraction) and vasodilation (muscle relaxation).

    • Innervation by vascular nerves (nervi vasorum).

    • Contains a collagenous framework rich in elastin; large arteries have an external elastic membrane.

  3. Tunica Externa

    • Composed of thick collagenous connective tissue anchoring vessels.

    • Thickest tunic in veins.

    • Houses vasa vasorum, small blood vessels supplying the larger blood vessels.

Comparison of Arteries and Veins

  • Arteries vs. Veins:

    • Arterial Structure:

    • Elastic arteries near the heart with thick tunics for expansion and recoil.

    • Muscular arteries found further from the heart for powerful vasoconstriction.

    • Arteriole Characteristics:

    • Small arteries empty into capillaries, with thick tunics only a few cells thick.

Capillary Structure and Function

  • Capillaries:

    • Smallest blood vessels (~5 micrometers in diameter), only allow single erythrocyte passage.

    • Site of gas and material transfer, possessing extremely thin walls (endothelium and basement membrane).

Types of Capillaries

  • Continuous Capillaries:

    • Most common with intercellular clefts.

  • Fenestrated Capillaries:

    • Found in kidneys and endocrine glands, with small holes (fenestrae) for regulated flow.

  • Sinusoid Capillaries:

    • Located in liver and spleen, characterized by large gaps in endothelium for significant material transfer.

Capillary Beds

  • Metarteriole Function:

    • Branches from arterioles to lead into capillary beds.

    • Each capillary is gated by precapillary sphincters, controlling blood flow based on tissue oxygen demands.

    • Blood may bypass capillaries via thoroughfare channels.

Blood Flow Regulation

  • Vasomotion:

    • Unique pulsating flow in capillaries regulated by chemoreceptors.

    • Adjusts blood flow based on immediate tissue needs, e.g., increased blood flow during digestion or muscle activity.

Venules and Veins

  • Post-Capillary Venules:

    • Receive deoxygenated blood from capillaries; have thin walls, site for leukocyte emigration.

  • Structure of Veins:

    • Composed of large, irregular lumens; thin-walled with little musculature.

    • Possess valves to prevent backflow of blood due to low pressure.

Blood Vessel Disorders

Edema

  • Definition: Buildup of fluid in tissues, often due to leaky blood vessels.

  • Causes include hypertension, heart failure, or kidney failure.

  • Varicose Veins:

    • A specific type of edema from venous valve failure, causing vein swelling.

Blood Vessel Properties

  • Reservoir Function:

    • Veins can hold more blood due to larger diameter and flexibility; capacitance refers to their capacity for blood storage.

Blood Flow Dynamics

General Principles

  • Blood Flow Definition: Amount of blood moved through a certain area in a given time frame.

  • Blood flows from high pressure to low pressure areas.

  • Blood Pressure Concepts:

    • Systolic Pressure: Peak pressure post-ventricular contraction.

    • Diastolic Pressure: Minimum pressure post-ventricular relaxation.

    • Pulse Pressure: Difference between systolic and diastolic pressures.

    • Mean Arterial Pressure: Overall average pressure, crucial for understanding blood pressure regulation.

Typical Measurements

  • Blood Pressure Normal Values:

    • Systolic: 120 mmHg, Diastolic: 80 mmHg (average written as 120/80).

    • Mean arterial pressure: typically 70-110 mmHg.

  • Significance of Low Blood Pressure:

    • Sustained levels below 60 mmHg can lead to ischemia.

Factors Affecting Blood Flow and Pressure

  • Five main variables impacting flow and pressure:

    1. Cardiac output

    2. Vessel compliance

    3. Blood volume

    4. Blood viscosity

    5. Vessel length and diameter

Blood Volume Effects

  • High Blood Volume: Increases blood pressure;

  • Low Blood Volume (Hypovolemia): Can result from severe blood loss or dehydration.

  • High Blood Volume (Hypervolemia): Often due to heart or kidney failure.

Physics of Resistance

  • Resistance: Friction between fluid and vessel walls; influenced by numerous variables including vessel radius, length, and blood viscosity.

  • Poiseuille's Law: Indicates relationship between pressure difference, resistance, and flow (formula not provided).

Resistance Factors in Detail

  1. Blood Viscosity:

    • Directly proportional to resistance; increases due to higher cell concentrations or plasma proteins.

  2. Blood Vessel Length:

    • Longer vessels increase friction and resistance.

  3. Blood Vessel Diameter:

    • Inversely proportional to resistance; larger diameters lead to lower resistance and higher flow.

    • Notably, small changes in diameter have large impacts on flow rates.

Blood Vessel Disorders: Arteriosclerosis and Atherosclerosis

  • Arteriosclerosis:

    • Chronic narrowing or stiffening of arteries; reduces compliance and affects blood flow.

  • Atherosclerosis:

    • Type of arteriosclerosis due to plaque buildup (e.g., lipids, clots) causing artery narrowing and hardening.

Additional Blood Flow Considerations

  • Venous Blood Flow:

    • Driven by skeletal muscle contractions and aided by valves preventing backflow.

    • Respiratory pump: changes in thoracic cavity pressure during breathing assist blood return to the heart.

Capillary Exchange Mechanisms

  • Exchange mechanisms through capillary walls include filtration and reabsorption governed by hydrostatic and osmotic pressures.

  • Key Pressures in Exchange:**

    • Hydrostatic Pressure: Motivates filtration into tissues.

    • Osmotic Pressure: Draws fluids back into blood vessels when solute concentrations create gradients.

Calculating Net Filtration Pressure

  • Net Filtration Pressure (NFP): Interaction of hydrostatic and osmotic pressures during exchange.

    • Arterial end typically has positive NFP; mid-capillary may see no net movement; venous end sees negative NFP favoring reabsorption.

Blood Flow Regulation and Homeostasis

  • Blood flow adjusts based on specific tissue needs, influenced by vessel diameter, cardiac output, and blood volume.

Nervous and Endocrine Regulation of Circulation

  • Neural Mechanisms:

    • Sensory receptors (baroreceptors, chemoreceptors) feedback into the cardiovascular centers in the brain, adjusting blood flow and pressure based on needs.

  • Endocrine Mechanisms:

    • Hormones like epinephrine and norepinephrine adjust heart rate and vascular tone in response to conditions greatly influencing blood pressure.

    • Renin-angiotensin-aldosterone system (RAAS) also plays a pivotal role in regulating volume and pressure.

Autoregulation of Blood Flow

  • Local autoregulation through precapillary sphincters influenced by chemical conditions (O2/CO2 levels, metabolic waste) without needing long-range signaling.

Vascular Homeostasis Disruption and Responses

  • Hypertension: Chronic high blood pressure can lead to severe cardiovascular complications.

  • Hemorrhage Response: Includes neural and endocrine responses aiming to stabilize blood volume and pressure, with a focus on retaining fluids and increasing red blood cell production.

  • Circulatory Shock Types:

    • Hypovolemic Shock: Low blood volume;

    • Cardiogenic Shock: Heart failure-related;

    • Vascular Shock: Loss of vascular tone;

    • Obstructive Shock: Due to vessel blockage.

Major Circulatory Pathways

Pulmonary and Systemic Circulation

  • Pulmonary Circuit: Blood flow from the pulmonary trunk to lungs and back to the heart via pulmonary veins.

  • Systemic Circuit Pathways: Description of aorta branches and their systemic implications for blood flow distribution to the body organs.

Hepatic Portal System

  • Key in biochemical processing and nutrient absorption; all digestive absorption is routed to the liver before general circulation.

Course Competencies

  • Explain the structure and function of various blood vessels (tunic composition, types of vessels).

  • Describe factors affecting blood pressure and how regulation can be achieved.

  • Discuss how age and medical conditions impact cardiovascular function.