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.