Transport in Animals

Why do multicellular organisms require transport systems?

Large size (small SA:V), high metabolic rate so demand for oxygen is high

Summarise the different types of circulatory system

Open = blood can diffuse out of vessels (insects)

Closed = blood confined to vessels (mammals)

Single = blood passes through pump once per circuit of body

Double = blood passes through heart twice per circuit of the body

How are arteries adapted to their function?

Thick muscular walls - handles high pressure, elastic tissue - allows recoil to prevent pressure surges, narrow lumen - to maintain pressure

How are veins adapted to their function?

Thin walls - due to low pressure

Valves - ensures blood doesn’t flow backwards

Less muscular and elastic tissue - don’t have to control blood flow

How are capillaries adapted to their function?

Walls are one cell thick - short diffusion pathway, very narrow - can permeate tissues and only one RBC wide so effective oxygen delivery, highly branched - large surface area

What is the role of arterioles and venules in the circulatory system?

branch off arteries and veins in order to feed blood into capillaries

How are arterioles and venules adapted to their function?

Smaller than arteries and veins so that the change in pressure is more gradual as blood passes through increasingly small vessels

What is tissue fluid?

A watery substance containing glucose, amino acids, oxygen and other nutrients

What types of pressure influence formation of tissue fluid?

Hydrostatic pressure - higher at arterial end of capillary than venous

Oncotic pressure - changing water potential of the capillaries as water moves out, induced by proteins in the plasma

What is hydrostatic pressure?

The pressure in a liquid due to the force of gravity

What is oncotic pressure?

The force exerted by proteins in the blood that draws water into the blood vessels

How is tissue fluid formed?

As blood is pumped through increasing small vessels, hydrostatic pressure is greater than oncotic pressure, so fluid moves out of the capillaries

How does tissue fluid differ from blood?

It doesnt contain red blood cells, platelets and other solutes present in blood

How does tissue fluid differ from lymph?

After tissue fluid has bathed cells it loses oxygen and nutrients and contains more waste products, so becomes lymph

What is 1?

Pulmonary artery

What is 2?

Aorta

What is 3?

Pulmonary vein

What is 4?

Left atrium

What is 5?

Semilunar valves

What is 6?

Bicuspid valve

What is 7?

Left ventricle

What is 8?

Right ventricle

What is 9?

Tricuspid valve

What is 10?

Right atrium

What is 11?

Vena cava

Describe what happens during cardiac diastole

Blood enters atria, atrioventricular valves open, blood flows into ventricles, semilunar valves remain closed

Describe what happens during atrial systole

Atria contracts, pushing any remaining blood into the ventricles

Describe what happens during ventricular systole

Ventricles contract making pressure increase, closing the atrioventricular valves to prevent back flow, and opening the semilunar valves. Blood flows into the arteries

How do you calculate cardiac output?

Heart rate x stroke volume

What does myogenic mean?

The heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses

Explain how the heart contracts

• SAN initates and spreads impulse across the atria, so they contract

• AVN receives, delays and then conveys the impulse down the bundle of His

• Impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up

What is an electrocardiogram (ECG)?

A graph showing the amount of electrical activity in the heart during the cardiac cycle

What is tachycardia?

Fast heartbeat (over 100bpm)

What is bradycardia?

Slow heartbeat (under 60bpm)

What is fibrillation?

Irregular, fast heartbeat

What is ectopic (seen on an ECG)?

Early or extra heartbeats

Describe the role of haemoglobin

Present in RBC. Oxygen molecules bind to the haem groups and are carried around the body, then released when they are needed in respiring tissues

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

As partial pressure of oxygen increases the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin. (When partial pressure is low, oxygen is released from haemoglobin)

What is partial pressure?

The pressure an individual gas exerts within a mixture

What is affinity?

The strength of the attraction between two substances

What do oxyhemoglobin dissociation curves show?

Saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa)

What do curves further to the left on oxyhaemoglobin dissociation curves show?

The haemoglobin has a higher affinity for oxygen

Describe the Bohr effect

As partial pressure of CO2 increases, the conditions become acidic causing haemoglobin to change shape. The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin.

Explain the role of carbonic anhydride in the Bohr effect

• carbonic anhydase is present in red blood cells

• converts CO2 to carbonic acid, which dissociates to produce H+ ions

• these combine with the haemoglobin to form haemoglobinic acid

• encourages oxygen to dissociate from haemoglobin

Explain the role of bicarbonate ions (HCO3-)

Produced alongside carbonic acid. 70% of carbon dioxide is carried in this form. In the lungs, bicarbonate ions are converted back into carbon dioxide which we breathe out

Describe the chloride shift

The intake of chloride ions across a red blood cell membrane. This repolarises the cell after bicarbonate ions have diffused out.

How does foetal haemoglobin differ from adult haemoglobin?

The partial pressure of oxygen is low by the time it reaches the foetus, therefore foetal haemoglobin has a higher affinity for oxygen than adult. Allows both mother’s and child’s oxygen needs to be met