Sciences - Co-ordinated (Double) (0654) | Transport in animals

🩸 B9 Transport in animals: The Body's Delivery System

Hello future biologist! This chapter is all about how your body moves essential materials around. Think of your body as a massive city: you need roads for delivery trucks (nutrients, oxygen) and waste removal vehicles (carbon dioxide, urea). The circulatory system is that complex, efficient road network!

Understanding transport in animals is crucial because every single cell needs a constant supply of energy and oxygen, and a quick way to get rid of waste. If the system stops, everything stops. Let's dive in and see how this incredible system works!

B9.1 Circulatory Systems: The Core Network

The Mammalian Circulatory System (Core)

The circulatory system in animals, especially mammals, is a complex, closed network designed for efficiency.

• It consists of blood vessels (the 'roads').
• A pump (the heart) to push the blood around.
• Valves, ensuring the one-way flow of blood and preventing backflow.

Single vs. Double Circulation (Supplement)

Not all animals use the same system. We need to compare the simple single circulation found in animals like fish with the sophisticated double circulation found in mammals.

1. Single Circulation (e.g., Fish):

• Blood passes through the heart only once in a complete circuit.
• The heart pumps blood to the gills (where gas exchange occurs).
• The blood then travels directly to the rest of the body before returning to the heart.

2. Double Circulation (e.g., Mammals):

The blood is pumped through the heart twice for every complete circuit:

1. Pulmonary Circuit: Heart → Lungs → Heart (Carries deoxygenated blood to the lungs and oxygenated blood back).
2. Systemic Circuit: Heart → Body Tissues → Heart (Carries oxygenated blood to the body and deoxygenated blood back).

Why is Double Circulation Better? (Advantages)

Imagine you are delivering packages (oxygen) to skyscrapers (body cells). You want a high-pressure system!
Double circulation offers two main advantages:

1. Higher Pressure: The heart can pump the blood to the body tissues at a much higher pressure after it leaves the lungs. This means blood moves faster, allowing for a higher metabolic rate (more energy!).
2. Efficient Separation: Oxygenated blood (clean fuel) is kept completely separate from deoxygenated blood (waste-filled), ensuring that the tissues always receive the maximum concentration of oxygen.

B9.2 Heart: The Power Pump

Structure of the Mammalian Heart (Core)

The heart is a muscular organ divided into four chambers by the septum (a thick wall that prevents mixing of blood).

• Atria (Left and Right): Upper, receiving chambers.
• Ventricles (Left and Right): Lower, pumping chambers.
• Muscular Wall: The walls of the heart are made of cardiac muscle. The left ventricle wall is much thicker than the right, as it needs to pump blood around the entire body (systemic circuit).
• One-way Valves: Found between the atria and ventricles, and where the major arteries leave the ventricles. They ensure blood flows in the correct direction.
• Coronary Arteries: These blood vessels supply the heart muscle itself with oxygen and nutrients. (They are incredibly important!)

How the Heart Functions (Supplement)

The heart beats through a rhythmic cycle of contraction and relaxation.

1. The atria contract, pushing blood into the ventricles.
2. The ventricles contract strongly, forcing blood out into the major arteries (to the lungs and body).
3. The valves close immediately after contraction, producing the characteristic 'lub-dub' sound, preventing backflow into the atria or ventricles.

Core Concept: Blood Flow Direction

Blood is pumped away from the heart in arteries and returns to the heart in veins.

Monitoring Heart Activity (Core & Supplement)

The heart's activity can be monitored in several ways:

• Pulse Rate: The number of times your heart beats per minute. We measure this via the pulsing of arteries.
• ECG (Electrocardiogram): Measures the electrical activity of the heart muscle.
• Listening to sounds: Using a stethoscope to hear the sounds of the valves closing.

Effect of Physical Activity on Heart Rate (Core & Supplement)

When you exercise, your muscles respire faster, needing much more oxygen and needing to remove carbon dioxide quickly.

The heart rate increases (and heart beats are stronger) during and after physical activity. Why?

• The brain (specifically the medulla) detects the increased concentration of carbon dioxide in the blood.
• It sends signals to the heart, telling it to pump blood faster and harder.
• This delivers oxygen and glucose to the muscles faster, and removes waste CO₂ more quickly.

Coronary Heart Disease (CHD) (Core)

CHD occurs when the coronary arteries become blocked, usually by fatty deposits called plaques. This reduces the oxygen supply to the heart muscle, potentially leading to a heart attack.

Risk Factors for CHD:

You must know these factors that increase the risk of CHD:

1. Diet: High intake of saturated fats and salt.
2. Lack of Exercise: Exercise strengthens the heart and keeps arteries flexible.
3. Smoking: Nicotine damages artery walls and increases blood pressure.
4. Stress: Prolonged stress raises blood pressure.
5. Genetic Predisposition: A family history of CHD.
6. Age and Sex: Risk generally increases with age; men are typically at higher risk earlier than women.

Reducing the Risk of CHD:

• Dietary changes: Reducing saturated fat intake (lowering blood cholesterol) and salt intake (lowering blood pressure).
• Exercise: Regular aerobic exercise strengthens the heart muscle and improves circulation efficiency.

B9.3 Blood Vessels: Arteries, Veins, and Capillaries

Blood vessels form three main types of tubes: arteries, veins, and capillaries. Their structure is perfectly adapted to their job.

Comparing Structures (Core & Supplement)

Feature	Artery	Vein	Capillary
Direction of Blood	Away from the heart	Towards the heart	Links arteries and veins
Relative Wall Thickness	Thick (Muscular and elastic)	Thin	Very thin (One cell thick)
Lumen Diameter	Narrow	Wide	Very narrow (Just fits one RBC)
Valves	None (except in the heart exit)	Present throughout	None
Blood Pressure	Highest	Lowest	Decreases as blood passes through

Relation of Structure to Function (Supplement):

• Arteries: Have thick, elastic walls to withstand the high pressure generated by the heart, preventing them from bursting. The elasticity helps maintain pressure even when the heart relaxes.
• Veins: Have large lumens (wide diameters) to reduce resistance to blood flow, which is now at low pressure. They contain valves to stop the low-pressure blood from flowing backwards (due to gravity).
• Capillaries: They have walls only one cell thick, and a very small lumen. This ensures that the distance for diffusion of oxygen, nutrients, and waste products between the blood and tissue cells is kept minimal, allowing rapid exchange (Core Function).

Major Blood Vessels (Supplement)

You need to know the major vessels connecting the heart and lungs:

• Vena Cava: Brings deoxygenated blood from the body tissues back to the right atrium of the heart.
• Aorta: Takes oxygenated blood away from the left ventricle to the rest of the body.
• Pulmonary Artery: Takes deoxygenated blood away from the right ventricle to the LUNGS.
• Pulmonary Vein: Brings oxygenated blood back from the LUNGS to the left atrium.

Memory Trick: Think of the letter 'A': Artery takes blood Away from the heart. Pulmonary is the exception: the Pulmonary Artery takes blood AWAY but it is deoxygenated.

B9.4 Blood: The River of Life

Blood is a vital tissue, constantly flowing through the circulatory system. It is a mixture of liquid and several types of cells.

Components of Blood (Core)

Blood is made up of four main components:

1. Plasma (The Liquid Part)
2. Red Blood Cells (RBCs)
3. White Blood Cells (WBCs)
4. Platelets (Small Fragments)

Functions of Blood Components (Core & Supplement)

1. Plasma

Plasma is the straw-coloured liquid component (about 55% of blood volume).

• Function: It acts as the transport medium for almost everything:
  • Blood cells (RBCs, WBCs, Platelets)
  • Ions (minerals like sodium, potassium)
  • Nutrients (e.g., glucose, amino acids)
  • Waste products (e.g., urea)
  • Hormones
  • Carbon dioxide (mostly carried as hydrogencarbonate ions)

2. Red Blood Cells (Erythrocytes)

• Structure: Contain no nucleus and have a biconcave shape (a flattened disc shape) to increase surface area for oxygen uptake.
• Function: Transport oxygen from the lungs to the respiring tissues.
• Role of Haemoglobin: RBCs contain the red pigment haemoglobin, which binds reversibly with oxygen (forming oxyhaemoglobin) to carry it efficiently.

3. White Blood Cells (Leukocytes) (Core & Supplement)

These are the body’s defenders against disease-causing organisms (pathogens). There are two main types:

(a) Phagocytes

• Function: Carry out phagocytosis. This is the process of engulfing (swallowing up) and digesting foreign particles, such as bacteria and dead cells. (Think of them as the 'Pac-Men' of your blood!)

(b) Lymphocytes

• Function: Responsible for antibody production. Antibodies are proteins that bind specifically to antigens (markers on pathogens) to destroy them or mark them for destruction by phagocytes.

4. Platelets

• Structure: Small cell fragments (details of clotting process are not required).
• Role of Blood Clotting (Core & Supplement): Platelets initiate the process of blood clotting. The two essential roles of clotting are:
  1. Preventing blood loss (Sealing the wound).
  2. Preventing the entry of pathogens into the body through the wound.