Transport in mammals part1

CIE A Level Biology 8.1 The Circulatory System

Contents

• Circulatory Systems
• The Main Blood Vessels
• Observing & Drawing Blood Vessels
• Blood Vessels: Structures & Functions
• Cells of the Blood
• The Role of Water in Circulation
• Blood, Tissue Fluid & Lymph

Circulatory Systems

Closed Double Circulatory System

• The need for a circulatory system:
  • Cells require a constant supply of reactants for metabolism, such as oxygen and glucose.
  • Single-celled organisms can obtain these directly from their environments via diffusion.
  • Larger organisms have increased cellular layers, and diffusion over long distances is inefficient.
  • To combat this, larger organisms require a mass transport system.

Mass Transport System

• Definition: Mass transport is the bulk movement of gases or liquids in one direction through vessels and tubes.
• In mammals, the circulatory system is a prominent example where blood flow is unidirectional, transporting essential nutrients and gases to cells.

Types of Circulatory Systems

1. Open Circulatory System:
   • Blood is not confined to blood vessels but pumps directly into body cavities.
   • Found in arthropods and many mollusks.
2. Closed Circulatory System:
   • Blood is always contained within a network of blood vessels.
   • Present in all vertebrates and many invertebrates.

Human Circulatory System

• Humans exhibit a closed double circulatory system.
  • Circulation route: Blood passes through the heart twice in one complete circuit.
  • Pulmonary circulation: Right side of the heart pumps deoxygenated blood to the lungs for gas exchange.
  • Systemic circulation: Left side of the heart pumps oxygenated blood at high pressure to the body.

Main Blood Vessels

Overview of Blood Circulation

• The pulmonary and systemic circulatory systems are integral to the double circulatory system.
  • Pulmonary System: Transports deoxygenated blood to the lungs for gas exchange.
  • Systemic System: Delivers oxygenated blood to body tissues.

Main Blood Vessels Table

Worked Example

• Question: Identify the advantage of the endothelial layer of squamous cells lining blood vessels. Options include:
  • A) Reduction in friction
  • B) Resisting increases in blood pressure
  • C) Increased elasticity of the vessel
  • D) Reduced damage to the blood vessel
• Correct Answer: C - Squamous epithelial cells do not increase vascular elasticity.

Important Exam Tip

• Larger blood vessels transport blood faster, but their surface area is much smaller compared to capillaries due to the latter's vast numbers throughout the body.

Observing & Drawing Blood Vessels

Structural Differences

• Arteries, veins, and capillaries have distinct structures related to their functions.
• Arteries: Carry blood at high pressures from the heart, have thick walls for pressure tolerance, containing elastic and muscular tissue.
• Veins: Carry blood back to the heart at low pressures, with thinner walls and valves to prevent backflow.
• Capillaries: The smallest vessels (5-10 µm) that enable efficient nutrient and gas exchange, featuring walls that are one-cell thick.

Diagrams of Blood Vessels

• Plan diagrams can be depicted in transverse section (TS) and longitudinal section (LS).

Characteristics of Arteries, Veins, and Capillaries

• Arteries:

  • Thick walls contain more elastic fibers closer to the heart to accommodate blood surges.
  • Narrow lumen for maintaining high pressure.
  • Elastic arteries found closer to the heart; muscular arteries further from the heart.
  • Blood pressure in arterioles is lower than in arteries.

• Capillaries:

  • Form networks (capillary beds) within body tissues to facilitate diffusion.
  • Endothelial walls are thin to allow easy diffusion of gases and nutrients.
  • Gaps between cells assist in the leakage of substances.

• Veins:

  • Have a large lumen to minimize resistance and accommodate low-pressure blood.
  • Walls are composed of collagen, with a tough outer layer.
  • Skeletal muscle contractions help raise the temporary blood pressure within veins.

Micrograph Observations

• Photomicrographs: Photographs taken via light microscopes.
• Electron Micrographs: Taken via electron microscopes to observe fine details.

Exam Tip on Magnification vs. Resolution

• Magnification: Size comparison between image and actual object (e.g., X 10, X 100).
• Resolution: Ability to distinguish two close objects (0.1 mm for the naked eye; 0.2 µm for light microscope; 0.1-1 nm for electron microscope).

Blood Vessels: Structures & Functions

Blood Vessel Structure and Function Table

Worked Example

• Question: Identify the correct features of elastic arteries, muscular arteries, veins, and capillaries in a table format.
• Correct Answer: B
  • Elastic arteries have fewer smooth muscle, enabling flexibility, while muscular arteries have significantly more smooth muscle and able to perform vasoconstriction/vasodilation.

Cells of the Blood

Types of Blood Cells

• Red Blood Cells (Erythrocytes):

  • Approximately 5 million per mm³ of blood.
  • Contain hemoglobin for oxygen binding.
  • Distinctive biconcave shape due to lack of nucleus.

• Monocytes:

  • Largest leukocytes with a kidney or bean-shaped nucleus that stains lighter than other leukocytes.

• Neutrophils:

  • Account for up to 70% of leukocytes with multi-lobed nuclei.
  • Granules typically stain pink/purple-blue.

• Lymphocytes:

  • Small leukocytes with large, dark-staining nuclei, making up about 20-25% of leukocyte count.

The Role of Water in Circulation

Water Composition and Functions

• Main component: 95% of plasma in blood is water, making it a good solvent for transporting substances.
• Tissue Fluid: Formed when plasma passes through capillaries and leaks into interstitial spaces, mainly composed of water.
• Transport Examples: Glucose and urea are both transported dissolved in water.

Specific Heat Capacity

• Definition: Amount of energy required to raise 1 kg of a substance by 1°C.
• Water has a high specific heat capacity of 4200 J/kg·°C, absorbing heat without significant temperature changes, essential for maintaining body temperature.

Blood, Tissue Fluid & Lymph

Composition Overview

• Plasma: Approximately 55% of blood, composed mainly of water (95%), serving as a solvent for various transport molecules.
• Formation of Tissue Fluid: Occurs through plasma leakage, but differs from plasma primarily due to the lack of proteins (too large to pass through capillary walls).
• Tissue Fluid Function: Bathes cells outside the circulatory system, allowing for substance exchange, such as oxygen and carbon dioxide.

Dynamics of Tissue Fluid Formation

• Arterial end of the capillary: High hydrostatic pressure pushes fluid out while proteins remain in the blood, creating a water potential difference.
• Venous end: Lower hydrostatic pressure means reduced fluid outflow, but the water potential remains the same, allowing for some re-entry of fluid back into capillaries.

Impact of Blood Pressure

• High blood pressure (hypertension) increases fluid loss, potentially causing edema (fluid accumulation around tissues).

Formation of Lymph

• Tissue fluid re-enters capillaries or enters lymph capillaries with large pores for larger molecules.

• Movement in lymph vessels aided by body movement and one-way valves prevent backflow.

• Lymph eventually re-enters the bloodstream through veins near the heart, recycling plasma proteins lost during filtration.

• Post-digestion, lipids are transported from intestines to bloodstream via lymphatic systems.