Biology2-31%20Jan

Introduction to the Mammalian Transport System

  • Focus on blood vessels and blood plasma or tissue fluid.

  • Learning objectives: understand structure of arteries, veins, capillaries; differentiate between blood plasma and tissue fluid.

Cardiovascular System

  • Also called the circulatory system, comprising:

    • Blood vessels

    • Blood

    • Lymph

    • Heart

  • Functions: transport nutrients and oxygen, dispose of waste (urea, CO2), transport hormones, circulate blood cells (red and white).

Circulatory System Types

Open vs Closed Circulatory System

  • Closed circulatory system:

    • Blood contained within vessels.

  • Open circulatory system:

    • Blood pumped into body cavities.

Components of the Blood Vascular System

  • Includes:

    • Arteries and arterioles (smaller arteries)

    • Veins and venules (smaller veins)

    • Capillaries

    • Heart (pumps blood)

  • Blood vessels: an intricate network, classified into arterial and venous systems.

  • Arterial system: arteries, arterioles, capillaries (transport away from heart).

  • Venous system: venules, veins (transport toward heart).

Structures of Blood Vessels

Arteries

  • Carry oxygenated blood away from the heart (except pulmonary artery).

  • Characteristics:

    • Thick walls due to high pressure; smaller lumen (diameter).

    • Contain elastic fibers, smooth muscles, collagen fibers.

    • Maintains blood pressure and allows vessel stretch/recoil.

  • Types:

    • Elastic artery: near heart, accommodates high pressure; more elastic fibers.

    • Muscular artery: further from heart, more smooth muscle; control blood flow.

Atrioles

  • Connect arteries to capillaries.

  • Consist of few layers of smooth muscle; thinner wall than arteries.

  • Function: control blood flow into capillaries.

Capillaries

  • Tiny blood vessels (3-7 micrometers): facilitate gas and nutrient exchange.

  • Characteristics:

    • One-cell-thick walls of endothelial cells.

    • Pores allow small substances (water, ions, glucose) to pass through.

    • High surface area increases exchange efficiency.

    • Form capillary beds for tissue nourishment.

Veins

  • Return deoxygenated blood to the heart; wider lumen, thinner walls than arteries.

  • Lower blood pressure compared to arteries.

  • Contain valves to prevent backflow; supported by surrounding muscles during movement.

  • Types include large veins, medium veins, and venules.

Functions of Blood Vessels

  • Arteries:

    • High-pressure blood flow, thick walls, narrow lumens.

    • Vascular control (dilation/constriction) regulates blood flow.

  • Veins:

    • Low-pressure blood return; valves ensure unidirectional flow.

  • Capillaries:

    • Site of nutrient and waste exchange; slow blood flow for efficient diffusion.

Blood Plasma vs Tissue Fluid

Blood Plasma Composition

  • In centrifuged blood: red blood cells (bottom), white blood cells and platelets (middle), plasma (top).

  • Plasma consists of:

    • Water, ions, proteins, nutrients (glucose, amino acids), waste (urea), gases (O2, CO2).

  • Comprises about 55% of blood volume.

Tissue Fluid Formation

  • Formed when blood plasma exits capillaries due to high pressure.

  • Differences from intracellular fluid:

    • Tissue fluid is between cells; intracellular fluid is within cells.

  • Contains:

    • Water, gases, glucose, fatty acids, urea, ions, smaller proteins.

    • Lower oxygen concentration than plasma; lacks larger proteins and red blood cells.

  • Tissue fluid returns to capillaries under lower pressure conditions; excess drained to lymphatic system.

Clinical Relevance

Edema

  • Caused by high blood pressure pushing excess fluid out of capillaries into tissues; symptoms like swelling in hands/legs.

Kwashiorkor

  • Malnutrition leading to fluid retention under the skin due to insufficient protein intake.

Summary of Key Points

  • Arteries: Thick-walled, narrow lumen, high pressure; elastic and muscular types for different functions.

  • Veins: Thinner walls, wider lumen, valves to prevent backflow; return deoxygenated blood to heart.

  • Capillaries: Thin-walled, effective for gas/nutrient exchange; connect atrioles to venules.

  • Blood Plasma: Liquid portion of blood; carries nutrients and waste.

  • Tissue Fluid: Derived from blood plasma; facilitates exchange between blood and cells.