Chapter 10: Transport in Humans and Animals

Learning Objectives

By the end of this chapter, you should be able to:

• Compare different types of circulatory systems across animal groups
• Explain the structure and function of the human circulatory system
• Understand blood components and their roles
• Describe mechanisms of blood clotting
• Analyze adaptations for efficient transport in various organisms

Overview

Transport systems are essential for distributing nutrients, oxygen, hormones, and waste products throughout an organism's body. Different animals have evolved various transport mechanisms ranging from simple diffusion to complex circulatory systems. This chapter explores the diverse transport adaptations in the animal kingdom, with a detailed focus on the human circulatory system.

Types of Circulatory Systems

Transport Mechanisms Comparison

Animals employ different transport strategies based on size, complexity, and environmental adaptations:

Open Circulatory Systems

Characteristics:

• Blood (Hemolymph) pumped from heart into body cavities (hemocoel)
• Direct Contact: Hemolymph bathes organs directly
• Lower Pressure: No high-pressure vessels
• Slower Flow: Less efficient transport

Examples:

• Insects: Tubular heart with ostia (openings)
• Crustaceans: Accessory hearts in appendages
• Mollusks: Heart with auricles and ventricle

Advantages:

• Lower energy requirements
• Suitable for less active organisms
• Efficient for small body sizes

Disadvantages:

• Limited to certain body sizes
• Less precise control over blood flow
• Cannot maintain high pressures

Closed Circulatory Systems

Characteristics:

• Blood contained within vessels
• High Pressure: Allows efficient distribution
• Rapid Flow: Faster transport rates
• Precise Control: Can direct blood to specific tissues

Examples:

• Annelids: Earthworms with dorsal and ventral vessels
• Vertebrates: Complete closed system with heart and vessels

Advantages:

• Highly efficient transport
• Can maintain high pressures
• Precise blood flow control
• Suitable for large, active organisms

Disadvantages:

• Higher energy requirements
• More complex system to maintain
• Vulnerable to vessel damage

Single vs. Double Circulation

Single Circulation (Fish):

• Blood Path: Heart → Gills → Body → Heart
• Oxygenation: Blood oxygenated in gills
• Pressure: Lower pressure in systemic circulation
• Efficiency: Adequate for fish metabolism

Double Circulation (Amphibians, Reptiles, Birds, Mammals):

• Two Separate Circuits:
  1. Pulmonary Circulation: Heart → Lungs → Heart
  2. Systemic Circulation: Heart → Body → Heart
• Advantages: Higher oxygen delivery, independent control of circuits
• Pressure: Higher pressure in systemic circulation

Did You Know? The human heart beats approximately 100,000 times per day, pumping about 7,500 liters of blood daily - enough to fill three large swimming pools in a year!

Cardiac Output Formula:

$$\text{Cardiac Output} = \text{Heart Rate} \times \text{Stroke Volume}$$ $$CO = HR \times SV$$

The Human Circulatory System

Heart Structure and Function

Anatomy:

• Location: Thoracic cavity, between lungs, behind sternum
• Size: Approximately fist-sized, weighs 250-350 grams
• Layers:
  • Endocardium: Inner lining
  • Myocardium: Heart muscle tissue
  • Pericardium: Outer protective sac

Chambers:

• Atria (Receiving Chambers): Right and left atria
• Ventricles (Pumping Chambers): Right and left ventricles

Valves:

• Atrioventricular (AV) Valves: Between atria and ventricles
  • Tricuspid valve (right side)
  • Bicuspid/mitral valve (left side)
• Semilunar Valves: Between ventricles and major arteries
  • Pulmonary semilunar valve
  • Aortic semilunar valve

Heart Wall Structure:

Heart Wall Equations:

$$\text{Blood Pressure} = \frac{\text{Cardiac Output}}{\text{Peripheral Resistance}}$$ $$\text{Work Done} = \text{Pressure} \times \text{Stroke Volume}$$

Cardiac Cycle

Definition: The sequence of events that occurs during one heartbeat

Phases:

Heart Sounds:

• "Lub": Closure of AV valves at beginning of ventricular systole
• "Dub": Closure of semilunar valves at beginning of ventricular diastole

Heartbeat Control

Autonomic Nervous System:

• Sympathetic: Increases heart rate (fight or flight)
• Parasympathetic: Decreases heart rate (rest and digest)

Cardiac Center:

• Medulla oblongata contains cardiovascular centers
• Sensory receptors monitor blood pressure and chemistry

Electrical Conduction System:

• SA Node (Sinoatrial Node): Natural pacemaker (initiates heartbeat)
• AV Node (Atrioventricular Node): Delays signal to ventricles
• Bundle of His: Conducts signal to ventricles
• Purkinje Fibers: Distributes signal throughout ventricular myocardium

Blood Vessels

Types and Functions:

Capillary Structure and Function:

Walls: Single cell layer thick Exchange Mechanisms:

• Diffusion: Simple movement down concentration gradients
• Facilitated Diffusion: Carrier-mediated transport
• Active Transport: Requires ATP energy
• Osmosis: Water movement with solutes
• Bulk Flow: Pressure-driven movement of fluids

Diffusion Equations:

$$\text{Rate of Diffusion} = \frac{\text{Surface Area} \times \text{Concentration Gradient}}{\text{Thickness}}$$ $$J = -D \frac{dC}{dx}$$

where $J$ = flux, $D$ = diffusion coefficient, $\frac{dC}{dx}$ = concentration gradient

Blood Composition and Function

Blood Plasma (55% of blood volume):

• Water: 90-92% of plasma
• Proteins: 6-8% (albumin, globulins, fibrinogen)
• Electrolytes: Na⁺, Cl⁻, K⁺, C$a^2$⁺, HC$O_3$⁻
• Nutrients: Glucose, amino acids, lipids
• Waste products: Urea, C$O_2$, hormones
• Gases: $O_2$, C$O_2$, $N_2$

Formed Elements (45% of blood volume):

Red Blood Cells (Erythrocytes)

• Structure: Biconcave discs, no nucleus (mature), flexible
• Hemoglobin: Contains iron, binds $O_2$ and C$O_2$
• Lifespan: 120 days
• Production: Bone marrow (erythropoiesis)
• Destruction: Spleen and liver (phagocytosis)

Hemoglobin Oxygen Binding Equation:

$$\text{Hb} + 4\text{O}_2 \rightleftharpoons \text{Hb(O}_2\text{)}_4$$

Oxygen Dissociation Curve:

$$\text{Percent Saturation} = \frac{[\text{HbO}_2]}{[\text{Hb}] + [\text{HbO}_2]} \times 100\%$$

White Blood Cells (Leukocytes)

• Types:
  • Neutrophils: Phagocytosis of bacteria
  • Lymphocytes: Antibody production, cellular immunity
  • Monocytes: Phagocytosis, antigen presentation
  • Eosinophils: Defense against parasites
  • Basophils: Release histamine, inflammatory response
• Function: Immune defense and disease resistance

Platelets (Thrombocytes)

• Structure: Cell fragments, no nucleus
• Function: Blood clotting and wound healing
• Lifespan: 5-9 days
• Production: Bone marrow megakaryocytes

Blood Clotting Mechanism

The Coagulation Cascade

Process: Series of enzymatic reactions leading to fibrin formation

Key Steps:

1. Vessel Injury: Damaged tissues and platelets release thrombokinase

2. Prothrombin Activation:

   Thrombokinase + C$a^2$⁺ + Vitamin K → Prothrombin (inactive) → Thrombin (active)
   

3. Fibrinogen Conversion:

   Thrombin → Fibrinogen (soluble) → Fibrin (insoluble threads)
   

4. Clot Formation:

   • Fibrin threads form a mesh
   • Red blood cells and platelets trapped in mesh
   • Creates solid clot that seals wound

Clot Retraction and Dissolution:

• Platelet contraction reduces clot size
• Fibrinolysis breaks down clot when healing complete
• Plasmin enzyme digests fibrin

Coagulation Cascade Key Reactions:

$$\text{Thrombokinase} + \text{Ca}^{2+} + \text{Vitamin K} \rightarrow \text{Thrombin}$$ $$\text{Thrombin} + \text{Fibrinogen} \rightarrow \text{Fibrin}$$ $$\text{Fibrin} \rightarrow \text{Fibrin Mesh (Clot)}$$

Anticoagulant Mechanisms

Natural Anticoagulants:

• Heparin: Antithrombin enhances natural inhibitor
• Antithrombin: Inhibits thrombin and other clotting factors
• Prostacyclin: Inhibits platelet aggregation

Prevention of Clotting in Blood Vessels:

• Smooth endothelium: Reduces platelet adhesion
• Heparin-like molecules: Natural anticoagulants
• Fibrinolytic system: Prevents unwanted clot formation

Transport Adaptations in Animals

Respiratory Pigments

Types and Functions:

Hemoglobin Variations:

• Fetal Hemoglobin: Higher $O_2$ affinity for maternal blood transfer
• Myoglobin: Muscle oxygen storage, higher affinity than hemoglobin
• Abnormal Hemoglobins: Sickle cell, hemoglobin variants

Circulatory Adaptations

Environmental Adaptations:

Activity-Related Adaptations:

• Endurance athletes: Increased capillary density, larger heart size
• Diving mammals: Enhanced oxygen storage, slower heart rate
• Flying birds: High pressure system, efficient oxygen utilization

Cardiovascular Health and Disorders

Common Cardiovascular Disorders

Cardiovascular Health Practices

Preventive Measures:

• Regular exercise: Improves cardiovascular function
• Healthy diet: Low in saturated fats, high in fiber
• Stress management: Reduces hypertension risk
• Avoid smoking: Prevents vascular damage
• Regular check-ups: Monitor blood pressure and cholesterol

Laboratory Investigation of Circulatory System

Blood Tests:

• Complete Blood Count (CBC): RBC, WBC, platelet counts
• Hemoglobin/Hematocrit: Oxygen-carrying capacity
• Blood Typing: ABO and Rh systems
• Cholesterol Profile: HDL, LDL, triglycerides

Heart Function Tests:

• Electrocardiogram (ECG/EKG): Electrical activity
• Echocardiogram: Heart structure and function
• Stress Tests: Heart response to exercise
• Blood Pressure Monitoring: Hypertension assessment

Practice Tips for SPM Students

Key Concepts to Master

1. Circulatory system types across different animal groups
2. Heart structure and cardiac cycle mechanics
3. Blood components and their specific functions
4. Clotting mechanisms and anticoagulant systems
5. Transport adaptations for different environments

Experimental Skills

1. Identify circulatory structures from diagrams and models
2. Calculate blood flow rates and pressure changes
3. Interpret blood test results and health implications
4. Design experiments to study heart function and blood properties

Problem-Solving Strategies

1. Pressure calculations: Use cardiovascular physics principles
2. Blood type problems: Understand inheritance and compatibility
3. Clotting mechanism analysis: Follow the cascade of reactions
4. Adaptation questions: Relate structure to function in different environments

Environmental and Health Connections

Environmental Impact on Circulatory System

• Air pollution increases cardiovascular disease risk
• Climate change affects cardiovascular adaptation patterns
• Altitude changes require circulatory system adjustments
• Chemical exposure can damage blood vessels and organs

Public Health Significance

• Cardiovascular diseases are leading global causes of death
• Blood pressure screening helps prevent hypertension complications
• Cholesterol management reduces heart disease risk
• Heart-healthy lifestyles promote cardiovascular wellness

Biomedical Applications

• Blood transfusions and blood banking systems
• Artificial hearts and cardiac assist devices
• Stent technology for blocked arteries
• Gene therapy for blood disorders

Summary

• Animals have evolved diverse transport systems from simple diffusion to complex circulatory systems
• The human circulatory system is a closed, double-circuit system with a four-chambered heart
• Blood consists of plasma and formed elements (RBCs, WBCs, platelets)
• Blood clotting is a complex mechanism involving thrombin and fibrin formation
• Various adaptations optimize transport for different environments and activities
• Understanding the circulatory system is crucial for health and medical applications

Related Topics

• Chapter 8: Respiratory Systems in Humans and Animals
• Chapter 9: Nutrition and the Human Digestive System
• Chapter 11: Immunity in Humans
• Chapter 12: Coordination and Response in Humans