Bio Dr P: Animal Transport

The need for a transport system depends on 3 factors

• Size

• Metabolic activity

• SA:V

Invertebrate circulatory systems diagram

(need to be able to label the aorta and heart in neat notes pg 11)

Invertebrate circulatory system

• Some invertebrates (insects) have an open circulatory system which are not enclosed in blood vessels

• The haemolymph (fluid) flows freely through the body cavity

How does the circulatory system work in invertebrates?

• Invertebrate hearts are segmented

• They contract in a wave from the back of the abdomen to the front called peristalsis

• The heart pumps haemolymph into a single main artery (aorta) which opens up into body cavity and allows fluid to flow around the insects organs supplying nutrients

• The fluid then returns into heart segments through a series of valves to be recirculated again

Vertebrate circulatory systems

All vertebrates have a closed circulatory system so blood is enclosed in blood vessels

Fish circulatory system diagram

Fish circulatory system

• Fish have a single circulatory system

• As blood passes through the gills to body blood pressure decreases

• So blood flows slowly and rate at which oxygen and nutrients are delivered to respiring tissues and carbon dioxide and urea are removed is limited

Why is this type of ciculatory system sufficient for fish?

Because they are not as metabolically active as mammals

Mammalian circulatory system diagram

Mammalian circulatory system

Mammals have a double circulatory system consisting of:

• Pulmonary circuit- the right side of the heart pumps blood to the lungs which then returns to the left side

• Systemic circuit- the left side of the heart pumps blood to the body which then returns to the right side

What does the double circulatory system in metablically active mammals allow?

• Allows the heart to increase pressure so the rate of flow is fast

• Pressure can be controlled (kept low in pulmonary circuit and high in systemic circuit)

Role of arteries

Arteries carry blood away from the heart at high pressure to the lungs or the rest of the body

Arteries diagram

3 different layers in the arteries and their function

• Tunica intima- has a layer of smooth endothelial cells to reduce friction + a thin layer of elastic tissue to allow stretch and recoil to maintain blood pressure

• Tunica media- has a thick layer of smooth muscle which contracts to constrict the artery narrowing the lumen so blood pressure can be increased and maintained

• Tunica adventitia- has a thick layer of collagen and elastic tissue to provide mechanical strength to withstand pressure + to recoil to maintain pressure

Role of veins

Veins carry blood to the heart under low pressure

Veins diagram

Key features of veins

• Large lumen to ease blood flow. The larger the diameter of the vessel the less resistance there is to blood flow

• Thinner layers of collagen, smooth muscle and elastic tissue as they don't need to stretch and recoil

• Have valves to prevent the backflow of blood. Movement of blood is controlled by contraction of skeletal muscle

Role of capillaries

Involved in carrying out the exchange of substances between the blood and the tissues

Capillaries diagram

Key features of capillaries

• Consist of a single layer of endothelial cells

• Very narrow lumen so red blood cells are squeezed against the walls helping oxygen transport

• Fenestrations (gaps in the walls) allow movement of dissolved substances

Role of arterioles

• They occur between arteries and capillaries

• They are smaller vessels that have a layer of smooth muscle

• Contstriction of the arteriole walls can divert blood

Role of venules

They collect blood from the capillary bed and have layers similar to veins

Heart diagram

Structure of the heart

• The heart is divided into 4 chambers

• It consists of cardiac muscle and adipose tissue on the outside for external protection

• The septum separates the ventricles from each other ensuring that oxygenated blood in the left side and deoxygenated blood in the right side of the heart are kept separate

• Coronary arteries supply the heart with oxygen

How is pressure in the heart generated?

It is generated by the cardiac muscle contracting

Atria and ventricles

• Atria are thinner than ventricles as they don't need to generate much pressure

• Walls of right ventricle are thinner than left ventricle as they only pump deoxygenated blood to the lungs

• If blood pressure is too high in right ventricle then alveoli will be damaged

Insufficient supply of oxygen to the heart can lead to

Angina or myocardial infarction (heart attack)

What is the cardiac cycle?

The coordinated sequence of events that allow the heart to fill with blood before pumping it away into the pulmonary and systemic circuits

Explain each stage of the cardiac cycle

• Atrial and ventricular diastole- both atria and both ventricles are relaxed, blood passively enters atria then flows through AV valves into both ventricles

• Atrial systole- both atria contract decreasing volume + increasing pressure in atria, more glood flows through AV valves into ventricles increasing ventricular volume and ventricular pressure

• Ventricular systole- both ventricles contract decreasing volume and increasing the pressure in the ventricles, AV valves close + SL valve opens, blood flows into pulmonary arteries and aorta

• At the end of ventricular systole atria relax + blood flows into atria (beginning of atrial diastole)

What creates the lub-dub heart beat sounds?

Opening and closing of valves

AV valves

• During diastole when ventricles relax pressure falls as atria are passively filling with blood causing atrial pressure to rise above ventricular pressure and AV valves open allowing blood to flow through

• When atria relax and ventricles begin to contract ventricular pressure rises above atrial pressure and blood flows up forcing AV valve to shut

What prevents the valves from inverting?

Tendinous chords (heart strings) and papillary muscles

SL valves

• During ventricular systole ventricular pressure rises above pressure in major arteries which opens the SL valves and allows blood to flow through

• During diastole as ventricles relax ventricular pressure falls below arterial pressure + blood flows down forcing the valve to shut