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Chap20 PPT

Chapter Overview

  • Focuses on the circulatory system, specifically blood vessels and their functions and anatomy.

  • Essential information and terms are organized by categories for easy understanding.

20.1 General Anatomy of Blood Vessels

  • Expected Learning Outcomes

    • Describe structure of blood vessels.

    • Identify types of arteries, capillaries, veins.

    • Trace blood's route from heart and its variations.

  • Blood Vessel Categories

    • Arteries: Carry blood away from the heart.

    • Veins: Return blood to the heart.

    • Capillaries: Connect smallest arteries to smallest veins, facilitating nutrient and gas exchange.

20.1a Vessel Wall Structure

  • Three Layers (Tunics) of Blood Vessels

    • Tunica Interna (Tunica Intima)

      • Lines the vessel; endothelium composed of simple squamous epithelium.

      • Acts as a selectively permeable barrier.

      • Secretes molecules controlling blood vessel dilation/contraction.

      • Under inflammation, may produce cell-adhesion molecules for leukocyte support.

    • Tunica Media

      • Middle layer made of smooth muscle, collagen, and elastic tissues.

      • Functions to strengthen the vessel and regulate blood pressure through muscle contraction.

    • Tunica Externa (Tunica Adventitia)

      • Outermost layer composed of loose connective tissue, anchoring vessels, containing nerves and lymphatics.

      • Contains vasa vasorum: small vessels nourishing external part of the vessel wall.

20.1b Artery Classification

  • Three Classes of Arteries

    • Conducting (Elastic or Large) Arteries

      • Largest arteries (e.g., aorta).

      • Contain internal/external elastic lamina for expansion/recoil, maintaining blood pressure.

    • Distributing (Muscular or Medium) Arteries

      • Supply blood to specific organs (e.g., brachial, femoral arteries).

      • Thick smooth muscle in wall; significant control over blood flow.

    • Resistance (Small) Arteries

      • Smaller arterioles; control blood distribution to organs with thicker tunica media.

20.1c Capillaries

  • Function and Structure

    • Capillaries are exchange vessels where materials are exchanged between blood and tissues (oxygen, CO2, nutrients).

    • Types of Capillaries:

      • Continuous Capillaries: Most common; tight junctions, allow small solutes.

      • Fenestrated Capillaries: Found in kidneys and intestines; allow rapid exchange due to filtration pores.

      • Sinusoids: Found in the liver and spleen with wide gaps for large molecules (proteins, blood cells).

20.1d Veins

  • General Characteristics

    • Capacitance vessels; larger capacity for blood containment.

    • Thin walls and flaccid structure; under lower pressure compared to arteries.

    • Types (from smallest to largest):

      • Postcapillary Venules: Very permeable; exit for leukocytes.

      • Muscular Venules: Slightly larger, contain smooth muscle.

      • Medium Veins: Valves present to prevent backflow; varicose veins if valves fail.

      • Large Veins: Thickest walls, e.g., venae cavae.

20.2 Blood Pressure, Resistance, and Flow

  • Expected Learning Outcomes

    • Explain relationships between blood pressure (BP), flow, and resistance.

    • Describe measurement of BP and its significance.

  • Key Concepts

    • Flow: Volume of blood through a vessel in a given time.

    • Perfusion: Flow per tissue volume.

    • Hemodynamics: Study of blood flow, influenced by pressure and resistance.

  • Blood Pressure Measurement

    • Measured at brachial artery using sphygmomanometer.

    • Two readings: Systolic/Diastolic (e.g., 120/80 mm Hg).

  • Regulation of Blood Flow

    • Influences include local, neural, and hormonal factors affecting artery diameter and blood distribution.

20.3 Capillaries and Fluid Exchange

  • Expected Learning Outcomes

    • Describe fluid movement across capillary walls.

    • Discuss the forces involved in filtration and reabsorption, including effects leading to edema.

  • Fluid Exchange Processes

    • Diffusion: Main mechanism where solutes pass based on concentration gradients.

    • Transcytosis: Vesicle-mediated transport for certain substances.

    • Filtration and Reabsorption: Opposing forces of hydrostatic pressure and osmotic pressure determine fluid movement.

20.4 Venous Return and Circulatory Shock

  • Venous Return Mechanisms

    • Pressure Gradient, Skeletal Muscle Pump, Thoracic Area Pressure (influenced by breathing).

  • Types of Circulatory Shock

    • Hypovolemic Shock, Obstructive Shock, Distributive Shock (e.g., septic shock).

  • Responses to Shock

    • Compensated Shock: Homeostatic mechanisms restore blood flow.

    • Decompensated Shock: Failure of homeostasis, leads to worsening condition.

20.5 Special Circulatory Routes

  • Brain Blood Flow

    • Brain’s autoregulation to ensure steady perfusion despite arterial pressure changes.

  • Muscular Activity

    • Blood flow rerouted to active muscles during physical exertion at the cost of resting areas.

Final Notes

  • Important for understanding how blood vessels function independently and collectively within the circulatory system.

  • Special attention should be given to conditions affecting blood flow, including atherosclerosis and hypertension.