Science - Combined (0653) | Transport in animals

Transport in Animals (B9)

Hello future scientists! This chapter dives into one of the most vital processes in your body: transport. Just like a massive city needs roads and delivery trucks to function, your body needs a complex system to move essential substances (like oxygen and food) to every cell and carry away waste products (like carbon dioxide).

We'll be exploring the fascinating world of the circulatory system, featuring the heart, blood vessels, and blood itself. Don't worry if the names seem complicated; we will break down each component step-by-step!

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B9.1 The Circulatory System: Overview

The circulatory system is essentially a closed loop designed to move substances efficiently around the body. It relies on three main components:

1. The Pump: The Heart
2. The Pipes: Blood Vessels (Arteries, Veins, Capillaries)
3. The Transport Fluid: Blood

Function of the Circulatory System (Core)

The circulatory system is described as a system of blood vessels with a pump (the heart) and valves to ensure one-way flow of blood.

Analogy: Think of the circulatory system as a double-decker bus route. One loop (the pulmonary circulation) takes passengers (blood) to the lungs to pick up oxygen. The second, longer loop (the systemic circulation) delivers the oxygen to all the other stops (body tissues) before returning home.

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B9.2 The Heart: The Central Pump

The heart is a muscular organ that pumps blood around the body.

Structure of the Mammalian Heart (Core)

You need to be able to identify and know the roles of the main structures in diagrams:

• Muscular wall: This is made of strong muscle tissue. The walls of the ventricles are thicker than the walls of the atria because ventricles must pump blood out of the heart (often long distances).
• Septum: The wall separating the left side of the heart from the right side. It ensures oxygenated blood (left side) does not mix with deoxygenated blood (right side).
• Left and Right Ventricles: The lower chambers that pump blood out of the heart. The left ventricle has a much thicker muscular wall as it must pump blood all around the body (high pressure).
• Left and Right Atria (or Atriums): The upper chambers that receive blood returning to the heart.
• One-way valves: These are essential to ensure blood flows in the correct direction and prevents backflow.
• Coronary arteries: These are blood vessels on the surface of the heart muscle itself. They supply the heart muscle with its own oxygen and nutrients so it can keep pumping.

How the Heart Works (Core & Supplement)

The heart works through a continuous cycle of contraction and relaxation:

1. Blood fills the atria.
2. The muscle walls of the atria contract, pushing blood through the valves into the ventricles.
3. The muscle walls of the ventricles contract forcefully (a heartbeat), forcing blood out into the arteries and away from the heart.

Action of Valves (Core & Supplement)

The one-way valves are crucial. When the ventricles contract, the increase in pressure forces the valves shut immediately, preventing blood from flowing backwards into the atria. This is what creates the "lub-dub" sound you hear when listening to a heart.

Blood Flow Direction (Core)

• Blood is pumped away from the heart in arteries. (Mnemonic: A for Artery, A for Away!)
• Blood returns to the heart in veins.

Monitoring Heart Activity (Core)

The activity of the heart can be monitored in several ways:

• Pulse Rate: Counting the number of beats per minute (often felt at the wrist or neck).
• Listening to sounds of valves closing: Doctors use a stethoscope to listen to heart sounds, checking for healthy valve function.
• ECG (Electrocardiogram): This machine records the electrical activity of the heart muscle.

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

When you exercise, your muscles need far more energy. To release this energy through respiration, they require more oxygen and glucose, and they produce more waste carbon dioxide.

Explanation (Supplement):

Physical activity causes the heart rate to increase because the cells need a faster and larger supply of oxygen and nutrients, and waste products like CO₂ need to be removed quickly. The brain detects the increased demand and sends signals (hormonal and nervous) to the heart to contract more frequently and forcefully.

Coronary Heart Disease (CHD) (Supplement)

This is a serious condition where the coronary arteries (the ones supplying the heart muscle itself) become blocked, usually by fatty deposits.

Risk Factors for CHD:

• Diet: High intake of saturated fats and salt.
• Lack of Exercise: A sedentary lifestyle.
• Smoking: Damages artery walls.
• Stress: Contributes to high blood pressure.
• Genetic Predisposition: If it runs in your family.
• Age and Sex: Risk generally increases with age, and pre-menopausal men tend to have higher risk than women.

Reducing the Risk of CHD:

The roles of diet and exercise in reducing CHD are:

• Diet: Maintaining a balanced diet low in saturated fat and cholesterol helps prevent fatty deposits in arteries.
• Exercise: Regular physical activity strengthens the heart muscle and helps maintain a healthy weight, lowering blood pressure.

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B9.3 Blood Vessels: The Transport Network

There are three main types of blood vessels: arteries, veins, and capillaries. They are specialised for their different roles based on the blood pressure they carry.

Structure and Function of Blood Vessels (Core & Supplement)

Vessel Type	Wall Thickness	Lumen Diameter	Valves Present?	Function and Pressure
Artery	Very thick and muscular (to withstand high pressure)	Narrow/Small	No	Carries blood away from the heart under high pressure.
Vein	Thin (less pressure)	Wide/Large	Yes (to prevent backflow)	Carries blood to the heart under low pressure.
Capillary	Extremely thin (one cell thick)	Very tiny (often only wide enough for one red blood cell)	No	Allows rapid exchange of substances (gases, nutrients, waste) between blood and cells. Very low pressure.

The Structure-Pressure Relationship (Supplement)

The thick, elastic walls of the arteries are essential. They stretch when the blood is pumped out of the heart (high pressure) and recoil, helping to maintain blood pressure and push the blood forward.

Since blood pressure is very low in the veins (it has lost most of its force passing through the capillaries), blood flow relies on muscle contractions squeezing the veins. The valves in veins ensure that this squeezing only moves the blood toward the heart, preventing it from falling backwards due to gravity.

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B9.4 Blood: The Fluid of Life

Blood is a tissue made up of different components, each with a specific job.

Components of Blood (Core)

Blood is composed of four main parts:

1. Red Blood Cells
2. White Blood Cells
3. Platelets
4. Plasma

You must be able to identify Red Blood Cells (small, biconcave discs, no nucleus) and White Blood Cells (larger, irregular shape, distinct nucleus) in diagrams or photomicrographs.

Functions of Blood Components (Core)

1. Red Blood Cells (RBCs)

• Function: Transporting oxygen.
• Role of Haemoglobin: RBCs contain haemoglobin, a protein that binds reversibly with oxygen. In the lungs, haemoglobin picks up oxygen; in the tissues, it releases oxygen.

2. White Blood Cells (WBCs)

WBCs are the soldiers of the immune system, defending the body against pathogens (disease-causing organisms).

• Phagocytosis: Some white blood cells perform phagocytosis, which means they engulf and digest foreign particles and pathogens.
• Antibody Production: Other white blood cells produce antibodies, specific proteins that stick to pathogens and mark them for destruction.

3. Platelets

• Function: Involved in blood clotting.

4. Plasma

Plasma is the liquid component (a straw-coloured fluid, mostly water). It is the transport medium for almost everything else:

• Blood cells (RBCs and WBCs)
• Ions (e.g., mineral salts)
• Nutrients (e.g., glucose, amino acids, absorbed from the digestive system)
• Urea (waste product from the liver, carried to the kidneys)
• Hormones
• Carbon Dioxide (mostly transported as dissolved hydrogencarbonate ions, or dissolved in the plasma itself).

The Role of Blood Clotting (Supplement)

When a blood vessel is damaged, platelets initiate a complex process called clotting (coagulation). The two main roles of blood clotting are:

1. Preventing blood loss (sealing the wound).
2. Preventing the entry of pathogens (microorganisms) into the body through the break in the skin.

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Key Takeaway from Transport in Animals

The transport system is a marvel of efficiency. The heart acts as a robust pump, the blood vessels (arteries, veins, capillaries) form a perfectly adapted network of pipes, and the blood carries out vital tasks from delivering oxygen (RBCs) to fighting infections (WBCs) and healing wounds (Platelets).