Chapter 8 Transport in Animals Flashcards
The need for specialised transport system in animals
As organisms get bigger the distances between cells and the outside body get greater, so diffusion, osmosis, active transport etc. would be too slow
the metabolic demands of most multicellular animals are high
molecules such as hormones or enzymes need to get from one place to another.
food digested in one organ system needs to transport that energy to the rest of the body
waste products of metabolism need to be removed from the cells and transported to excretory organs.
What is a mass transport system?
when substances are transported in a mass of fluid with a mechanism for moving the fluid around the body. Large multicellular organisms have this as an open circulatory system or a closed circulatory system.
What is an open circulatory system and how does it work and where is it most common?
In an open circulatory system there are very few vessels to contain the transport medium. It is pumped straight from the heart into the body cavity of the animal. This open Body cavity is called the haemocoel. In the haemocoel the transport medium is under low pressure to stop it coming into Direct contact with the tissues and the cells. This is where exchange takes place between the transport medium and the cells. the transport medium returns to the heart through an open-ended vessel.
These are mostly found in invertebrates which are insects and some molluscs. Insects’ blood is called haemolymph. It doesn’t carry any gases like carbon dioxide and oxygen, it transports food and nitrogenous waste products and the cells involved in defence against disease. The haemolymph Circulates but steep diffusion gradients cannot be maintained for efficient diffusion.
Closed Circulatory Systems
The blood is always in blood vessels and doesn’t come into contact with cells directly. The heart pumps blood around the body under pressure and then the blood returns back to the heart. Substance leave and enter the blood by diffusion.
They are found in marine animals and mammals.
Single closed ciruclatory system
They are found in fish and annelid worms.
The blood travels only once through the heart for each circulation around the body.
The blood passes past two sets of capillaries before it return to the heart. In the first it exchanges oxygen and carbon dioxide. In the second it gives substances from the blood to the cells.
As the blood is travelling two sets of capillaries pressure can drop so blood takes time to return back to the heart so it is less efficient.
Why are fish an exception of the inefficiency of the single closed circulatory system
They have countercurrent gaseous exchange mechanism in their gills that allows them to take a lot oxygen from the water. Their body weight is supported by the water in which they live and they do not maintain their own body temperature. This greatly reduces the metabolic demands on their bodies.
What is a double closed circulatory system, how does it work and where is it used?
Birds and most mamals use it because they are active land animals and have to maintain their own body temperature.
There are two separate circulations:
1. Blood is pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide and then return to the heart.
2. Blood flows through the heart and is pumped out to travel all around the body before returning to the heart again.
It passes through the heart twice meaning pressure can be maintained.
Different components making up blood vessel
Elastic fibres - these are composed of elastin and can stretch and recoil providing vessel walls with flexibility
Smooth muscle - contracts or relaxes with change the size of the lumen.
Collagen - provides structural support to maintain the shape and volume of the vessel.
Arteries
Usually carry oxygenated blood at high pressure, except pulmonary artery not carrying deoxygenated blood from heart to the lungs.
Contains elastic fibres enabling them to withstand the force of the blood pumped out of the heart and stretch to take the larger blood volume.
Arterioles
Arterioles are smaller than arteries, but with a comparatively larger lumen. Their walls have more smooth muscle and less elastin as they do not need to withstand such high pressures.
Capillaries
The capillaries have small lumen.
Substances are exchanged through the tissue cells and the blood.
They have large gaps between the endothelial cells that make up the capillary walls in most areas of the body. This is where the substances pass out of the capillaries into the fluid surrounding the cells. Blood entering the capillaries is oxygenated.
Capillaries provide a very large SA for diffusion.
The total cross sectional area of the capillaries is always greater than the arteriole supplying them so the rate of blood flow falls. The relatively slow movement of blood through capillaries gives more time for the exchange of materials by diffusion between the blood and the cells.
The walls are a single endothelial cell thick, giving a very thin layer for diffusion.
Vasoconstriction and Vasodilation
The smooth muscle in arteries and arterioles means they are adapted to control the blood flow through them.
They do this through the following mechanisms:
Vasoconstriction - Smooth muscle contracts, constricting the blood vessel and decreasing blood flow.
Vasodilation - Smooth muscle relaxes, dilating the blood vessel and increasing blood flow.
What blood is flowing through the veins and the track of the blood before and after the veins.
Carry blood away from the cells to the heart carrying deoxygenated blood.
Two exceptions:
Pulmonary vein carries oxygenated blood from the lungs to the heart and the umbilical vein during pregnancy carries oxygenated blood from the placenta to the fetus.
Deoxygenated blood flows from the capillaries into very small veins called venules and then into larger veins. Then into the vena cava inferior or superior depending on where from the body it is coming. Inferior - lower half, superior - upper half.
Veins don’t have a pulse because the surges from the heart pumping are lost - but they hold 60% of the blood in the body at any one time.
Structure of the walls of veins and lumen
Walls contain lots of collagen and relatively little elastic fibre. and the vessels have a wide lumen and a smooth, lining known as endothelium so the blood flows easily.
Low blood pressure. so have valves to prevent back flow in medium-sized veins.
Venules
link the capillaries with the veins. They have very thin walls with just a little smooth muscle. Several venules join to form a vein.
Adaptations of the body to overcome the problem of low pressure in the veins
The majority of veins have one way valves at intervales. These are flaps or infoldings of the inner lining of the vein. When flows in the direction of the heart, the valves open so the blood can pass through.
Many of the veins run between the big, active muscles in the body e.g. arms and legs. When the muscle contracts they squeeze the veins, forcing the blood towards the heart. The valves prevent backflow when the muscles relax
The breathing movements of the chest act as a pump. The pressure changes and the squeezing actions move blood in the veins of the chest and abdomen towards the heart.
Composition of the blood
Plasm - carries dissolved glucose, amino acids, mineral ions, hormones, and proteins.
Red blood cells - carry oxygen to the cells and also give the blood its red appearance
White blood cells - immune response
Platelets - framents of large cells called megakaryocytes found in the red bone marrow, and they are involved in the clotting mechainisms of the blood.
Plasma makes up 55% of the blood.
Functions of the blood
Transport of oxygen to, carbon dioxide from respiring cells.
digested food from the small intestine
nitrogenous waste products from the cells to the excretory organs
chemical messages ( hormones)
platelets
white blood cells
The blood also contributes to maintenance of a steady body temperature and acts as a buffer, minimising pH changes.
What is tissue fluid and how does it change as you go down the capillary
Capillaries have high solute potential with loads of proteins, so low water potential. As a result, water moves into the capillaries from the surrounding fluid by osmosis. The tendency of water to move into the blood by osmosis is called ONCOTIC pressure and it is about -3.3kPa.
As blood flows through the arterioles into the capillaries it is still under pressure from the surge of blood that occurs every time the heart contracts. This is hydrostatic pressure. At the arterial end this is high at 4.6kPa. but around 2.3kPa at the venule end.
At the arterial end there will be a net flow of tissue fluid out of the capilalry to form tissue fluid.
At the venous end net flow of fluid back into capillary due to the oncotic pressure of blood.
What is lymph
10% of the liquid that leaves the blood vessels drains into a system of blind-ended tubes called lymph capillaries, where it is known as lymph.
Lymph has a similar composition to plasma and tissue fluid but has less oxygen and fewer nutrients.
It also contains fatty acids which have absorbed into the lymph from the villi of the small intestine. The lymph capillaries join up to form large vessels.
The fluid is transported by the squeezing of body muscles. One way valves prevent back flow in the lymph.
Eventually the lymph returns to the blood flowing into the right and left subclavian veins.
Roles of the lymph
lymph vessels have lymph nodes.
Lymphocytes build up in the lymph nodes and produce antibodies, which are passed into the blood.
Lymph nodes also intercept bacteria and other debris from the lymph, which are ingested by phagocytes found in the nodes.
the lymphatic system plays a major role in the defence mechanisms of the body.
What is the cause of enlarged lymph nodes
usually a sign that the body is fighting off an invading pathogen. This is why doctors often examine the neck, armpits, stomach or groin of their patients - these are the sites of the major lymph nodes.
What are the adaptations of erthyrocytes?
have a biconcave shape, with a large SA allowing more diffusion of gases. It also helps them to pass through narrow capillaries.
Erthrocytes are formed continually in red bone marrow and once mature they have lost their nucleus which allows them to carry more haemoglobin.
This also limits their life span to 120 days.
Role of haemoglobin
the red pigment carries oxygen and also gives them their colour. It is a large conjugated protein made up of four peptide chains, each with an iron-containing haem prosthetic group.
Each haemoglobin molecule binds to 4 oxygen molecules forming oxyhaemoglobin.
HAVEN’T DONE 8.4
What is the heart and its structure overview
the heart is the organ that moves the blood around the body. In some animal groups it is no more than a simple muscular tube. In mammals the heart is a complex, 4-chambered muscular ‘bag’ found in the chest, enclosed by the ribs and sternum.
The two pumps in the human heart
Deoxygenated blood from the body flows into the right side of the heart, which pumps it to the lungs.
Oxygenated blood from the lungs returns to the left side of the heart, which pumps it to the body. The blood from the two sides of the heart doesn’t mix.
What is the heart made up of, in terms of muscles etc. and the role of coronary arteries
is made of cardiac muscle, which contracts and relaxes in a regular rhythm. It doesn’t get fatigued and need rest like skeletal muscle. The coronary arteries supply the cardiac muscle with the oxygenated blood it needs to keep contracting and relaxing all the time.
The heart is surrounded by inelastic pericardial membranes which help prevent the heart from over-distending (over filling and stretching) with blood.
Explain what happens in the right side of the atrium in one cycle
Deoxygenated blood enters the right atrium through the inferior and superior vena cava at relatively low pressure.
As the blood flows in, slight pressure builds up until the atrio-ventricular valve opens to let blood pass into the right ventricle. When both the atrium and ventricel are filled with blood the atrium contracts forcing all the blood into the right ventricle and stretches the ventricle walls. As the right ventricle starts to contract the tricuspid valve closes to prevent backflow and the tendinous cords make sure the valves aren’t turned inside out by the pressures exerted when the ventricle contracts. The right ventricle contracts fully and pumps deoxygenated blood through the semilunar valves into the pulmonary artery which transports it to the capillary bed of the lungs. They prevent the backflow of the blood into the heart.
Explain what happens on the left side of the heart in one cycle
oxygenated blood enters from the lungs into the left atrium from the pulmomonary vein. As pressure in the atrium build the bicuspid valve opens between the left atrium and the left ventricle so the ventricle fills with oxygenated blood. When both the atrium and ventricle are full the atrium contracts, forcing the oxygenated blood into the left ventricle. The left ventricle also then contracts and pumps the blood through the semilunar valves and out through the aorta around the body. As the ventricle contracts the bicuspid valve closes, preventing any backflow of blood into the atrium.
What muscles are there in the heart walls and what is different about them
the wall of the left ventricle is much thicker because the blood has to be pumped all around the body, wheras the right ventricle only pumps to the lungs which are quite close.
What is the septum
it is the inner dividing wall of the heart which prevents the mixing of deoxygenated and oxygenated blood.
The left and right side of the heart fill and empty at the same time.
What are the three events in the cardiac cycle and how long is it
cardiac cycle is 0.8s long in a human adult.
In diastole the heart relaxes, the atria and then the ventricles fill with blood. The volume and pressure of the blood in the heart build as the heart fills, but the pressure in the arteries is at a minimum.
In artial systole the atria contracts and then in ventricular systole the ventricle contracts .
The pressure in the heart increases a lot during systoles and the blood is forced out of the heart after it. At the end of the systole the volume and pressure in the heart are low but the blood pressure ins high.
Heart sounds
the create a lub-dub heartbeat.
The first sound comes as the blood is forced agains the atrio-ventricular valves as the ventricles contract and the second sound comes as a backflow of blood closes the semilunar valves in the aorta and pulmonary artery as the ventricles relax.
The basic rhythm of the heart
and a description of the wave
Cardiac cycle is myogenic - it has its own intrinsic rhythm. This means the body doesn’t waste any resources maintianing the basic heart rate.
The basic rhythm is maintained by a wave of electrical excitation rather like a nerve impulse
A wave of electrical excitation begins in the pacemaker area called the sino-atrial node(SAN), causing the atria to contract and so intiating the heartbeat. A layer of non-conducting tissue prevents the excitation passing directly to the ventricles. The electrical activity from SAN is picked up by the atrio-ventricular node(AVN). This imposes a slight delay befor the simulating the bundle of his, a bundle of conducting tissue made of purkyne fibres which penetrate through the septum between the ventricles. The bundle of His splits into two branches at the bottom of the heart and conduct the wave of excitation.
at the apex the purkyne fibres spread out through the walls of the ventricles on both sides. The spread of excitiation triggers the contraction of the ventricles, starting at the apex.
The way that the excitiation spreads through the heart from the SAN with AVN delay makes sure the atria have stopped contracting before the ventricles start.
What is an electrocardiogram
it measures the spread of electrical excitation through the heart as a way of recording what happens as it contracts. This recording of electrical activity of the heart is called an electrocardiogram ECG. An ECG doesn’t directly measure the electrical activity of the heart. It measures the tiny electrical differences in your skin, which result from the electrical activity of the heart.
How does an electrocardiogram work
the electrodes are stuck to clean skin to get good contacts needed for reliable results. The signal from each of teh electrodes is fed into the machine, which produces an ECG.
Example of what ECGs can diagnose
if someone is having a heart attack a recognisable change take places in the electrical activity of the heart.
Heart rhythm abnormalities: Tachycardia
when the heartbeat is very rapid, over 100bpm. This is often normal for instance when you exercise if you have a fever, if you are frightened or angry. If it is abnormal it may be caused by problems in the electriccal control of the hear tand may need to be treated by medication or by surgery.
Heart rhythm abnormalities: Bradycardia
when the heart rate slows down to below 60bpm. Many people have bradycardia because they are fit - training makes the heart beat more slowly efficient.
Severe bradycaria can be serious and may need an artificial pascemaker to keep the heart beating steadily.
Heart rhythm abnormalities: Ectopic heartbeat
extra heartbeats that are out of the normal rhythm. Most people have at least one a day. They are usually normal but they can be linked to serious conditions when they are very frequent.
Heart rhythm abnormalities: Atrial fibrilation
this is an example of arrhythmia which means an abnormal rhythm of the heart. Rapoid electrical impulses are generated in the atria. They contract very fast up to 400 times a minute. However,they don’t contract properly and only some of the impulses are passed on to the ventricles, which contract much less often. As a result the heart doesn’t pump blood very effectively.
