Study Notes on Transport in Mammals

Chapter 8: Transport in Mammals

Overview of Transport Systems in Mammals

  • Mammals require efficient transport systems due to their size, complexity, and metabolic activity.

  • Transport systems are essential for:

    • Supplying nutrients to individual cells.

    • Removing waste products from cells.

  • Mammals are significantly more active than plants, necessitating greater oxygen intake, which is facilitated by:

    • Haemoglobin present in red blood cells.

The Mammalian Cardiovascular System

  • Definition: The mammalian cardiovascular system comprises a pump (the heart), an extensive network of blood vessels, and blood composed of red blood cells suspended in plasma.

  • Characteristics:

    • The blood remains within blood vessels, resulting in a closed blood system.

    • Blood circulates in two circuits (double circulation).

Structure of the Cardiovascular System

  • Circuits in the cardiovascular system:

    • Pulmonary Circulation: Blood travels from the heart to the lungs for oxygenation and back to the heart.

    • Systemic Circulation: Oxygenated blood is pumped from the heart to the rest of the body.

Comparison with Fish Circulatory Systems

Distinguishing Features

  • Mammals possess a double circulatory system, while fish have a single circulatory system.

    • Fish System: Blood exits the heart, flows to the gills to get oxygen, then proceeds to the rest of the body.

    • Mammal System: Blood returns to the heart after oxygen uptake in the lungs before being pumped throughout the body.

Advantages of Mammalian Circulatory System

  • Higher pressure in mammal circulation allows:

    • Faster oxygen transport to cells.

    • More efficient nutrient delivery and waste removal compared to fish, which experience pressure loss in gill capillaries.

Blood Vessels

  • Types of blood vessels:

    • Arteries: Carry blood away from the heart.

    • Veins: Return blood to the heart.

    • Capillaries: Facilitate exchange of substances between blood and tissues.

Structure of Arteries and Veins

  • Similarities: Both structures are composed of three main layers.

    • Tunica Intima: Innermost layer of endothelial cells.

    • Tunica Media: Middle layer containing smooth muscle and elastic fibers.

    • Tunica Externa: Outermost layer made of connective tissue.

Specific Characteristics

  • Arteries: Strong and elastic walls to withstand high pressure.

    • Blood pressure in the human aorta: Approximately 120 mmHg (or 16 kPa).

  • Veins: Thinner walls suitable for lower pressure; typical venous pressure is 5 mmHg.

Arterioles

  • Branch from muscular arteries and lead to capillaries.

  • Function:

    • Regulate blood flow and pressure through vasoconstriction and vasodilation.

Capillaries

  • Smallest blood vessels, approximately 7μm in diameter.

  • Composed of a single layer of endothelial cells, facilitating rapid exchange of substances (e.g., oxygen, nutrients, waste).

  • Blood pressure in capillaries fluctuates, starting around 35 mmHg and dropping to 10 mmHg.

Tissue Fluid

  • Definition: Tissue fluid originates from plasma that leaks out of capillaries, allowing for nutrient exchange with cells.

  • Composition: Similar to plasma but lower in protein concentration.

  • Formed due to opposing forces:

    • Hydrostatic Pressure: Drives fluid out at the arterial end.

    • Osmotic Pressure: Pulls fluid back into capillaries at the venous end.

  • Excess fluid can cause oedema if blood pressure is too high.

Blood Composition

  • Average human blood volume: Approximately 5 dm³ with 5 kg mass.

  • Constituents:

    • Red Blood Cells (RBCs): Approximately 2.5 × 10¹³; carry oxygen.

    • White Blood Cells (WBCs): Approximately 5 × 10¹¹; involved in immune responses.

    • Platelets: Around 6 × 10¹²; play a role in clotting.

Red Blood Cells

  • Also known as erythrocytes; characterized by:

    • Biconcave shape for increased surface area and gas diffusion.

    • Lack of nucleus and organelles to maximize haemoglobin content.

    • Flexibility enabling passage through narrow capillaries.

  • Haemoglobin: Oxygen-transporting protein; can bind up to four oxygen molecules.

Haemoglobin Functionality

  • Two key processes:

    • Oxygen uptake in lungs (high partial pressure).

    • Oxygen release in tissues (low partial pressure).

  • The Bohr effect indicates higher carbon dioxide concentration facilitates more oxygen release.

The Heart

  • Structure: Adult human heart weighs about 300g, consists of four chambers (atria and ventricles), muscle (cardiac muscle) interlinked for coordinated contraction.

  • Atria: Upper chambers receiving blood.

  • Ventricles: Lower chambers pumping blood into arteries.

  • Major blood vessels include:

    • Aorta: Main artery from the heart.

    • Vena Cavae: Major veins returning blood to heart.

    • Pulmonary Arteries and Veins: Transport blood to and from the lungs.

Cardiac Cycle

  • Sequence of events constituting one heartbeat (around 70 beats per minute).

  • Phases:

    1. Atrial Systole: Atria contract, pushing blood into ventricles.

    2. Ventricular Systole: Ventricles contract, ejecting blood into aorta and pulmonary arteries.

    3. Diastole: Heart muscle relaxes, allowing filling of chambers.

  • Valve mechanics ensure unidirectional blood flow.

Rhythm Control

  • The heart's rhythm is myogenic, originating at the sinoatrial node (SAN) or pacemaker.

  • Electrical signals propagate through the heart via the atrioventricular node (AVN) and Purkinje fibers, ensuring coordinated contraction.

Fibrillation

  • Disordered electrical activity leads to uncoordinated heart contractions (fibrillation), typically fatal without intervention.

Electrocardiograms (ECGs)

  • Monitoring heart activity by recording electrical signals, revealing heart rate and rhythm dynamics.

  • PQRST pattern indicates atrial and ventricular excitation and recovery phases.