Transports In Animal Flashcards
Multicellular Organisms need Transport Systems
1) As you saw on page 68, single-celled organisms can get substances that
they need by arrusion across their outer membrane.
2) If you’re multicellular though, it’s a bit harder to supply all your cells with everything they need
- multicellular organisms are relatively big, they have a low surface area to volume ratio and a higher metabolic rate (the speed at which chemical reactions take place in the body).
3) A lot of multicellular organisms (e.g. mammals) are also very active. This means that a large number of cells are all respiring very quickly, so they need a constant, rapid supply of glucose and oxygen.
To make sure that every cell has a good enough supply, multicellular organisms need a transport system.
5) In mammals, this is the circulatory system, which uses blood to carry glucose and oxygen around the body.
It also carries hormones, antibodies (to fight disease) and waste (like CO2).
Fish and Mammals have Different Circulatory Systems
Not all organisms have the same type of circulatory system
- fish have a single circulatory system and mammals have a double circulatory system.
1) In a single circulatory system, blood only passes through the heart once for each complete circuit of the body.
2) In a double circulatory system, the blood passes through the heart twice for each complete circuit of the body.
Fish and Mammals have Different Circulatory Systems : Fish
In fish, the heart pumps blood to the gills (to pick up rest of body oxygens and then on oxygenated blood through the rest of the body (to deliver the oxygen) in a single circuit.
Fish and Mammals have Different Circulatory Systems: Mammals
In mammals, the heart is divided down the middle, so it’s really like two hearts joined together.
1) The right side of the heart pumps blood to the lungs (to pick up oxygen).
2) From the lungs it travels to the left side of the heart, which pumps it to the rest of the body.
3) When blood returns to the heart, it enters the right side again.
Fish and Mammals have Different Circulatory Systems:
So, our circulatory system is really two linked loops.
One sends blood to the lungs - this is called the pulmonary system, and the other sends blood to the rest of the body - this is called the systemic system.
An advantage of the mammalian double circulatory system is that the heart can give the blood an extra push between the lungs and the rest of the body. This makes the blood travel faster, so oxygen is delivered to the
tissues more quickly.
Circulatory Systems can be Open or Closed
1) The heart pumps blood into arteries. These branch out into millions of capillaries (see p. 78).
2) Substances like oxygen and glucose diffuse from the blood in the capillaries into the body cells, but the blood stays inside the blood vessels as it circulates.
3) Veins take the blood back to the heart.
1)The heart is segmented. It contracts in a wave, starting from the back, pumping the blood into a single main artery.
2)
That artery opens up into the body cavity.
3) The blood flows around the insect’s organs, gradually making its way back into the heart segments through a series of valves.
The circulatory system supplies the insect’s cells with nutrients, and transports things like hormones around the body. It doesn’t supply the insect’s cells with oxygen though - this is done by a system of tubes called the tracheal system (see p. 75 for more).
Blood Vessels Transport Substances Round the Body
1) Arteries carry blood from the heart to the rest of the body. Their walls are thick and muscular and have elastic tissue to stretch and recoil as the heart beats, which helps maintain the high pressure. The inner lining (endothelium) is folded, allowing the artery to expand - this also helps it to maintain the high pressure. All arteries carry oxygenated blood except for the pulmonary arteries, which take deoxygenated blood to the lungs.
2)Arteries branch into arterioles, which are much smaller than arteries.
Like arteries, arterioles have a layer of smooth muscle, but they have less elastic tissue. The smooth muscle allows them to expand or contract, thus controlling the amount of blood flowing to tissues.
3) Arterioles branch into capillaries, which are the smallest of the blood vessels. Substances like glucose and oxvgen are exchanged between cells and capitaries, so they re adapted for emicient anrusion, e.g. their wals are only one cell thick.
4) Capillaries connect to venules, which have very thin walls that can contain some muscle cells. Venules join together to form veins.
Veins take blood back to the heart under low pressure. They have a wider lumen than equivalent arteries, with very little elastic or muscle tissue.
Veins contain valves to stop the blood flowing backwards (see p. 80).
Blood flow through the veins is helped by contraction of the body muscles surrounding them. All veins carry deoxygenated blood (because oxygen has been used up by body cells), except for the pulmonary veins, which carry oxygenated blood to the heart from the lungs.
Tissue Fluid is Formed from Blood
Tissue fluid is the fluid that surrounds cells in tissues. It’s made from substances that leave the blood plasma, e.g. oxygen, water and nutrients. (Unlike blood, tissue fluid doesn’t contain red blood cells or big proteins, because they’re too large to be pushed out through the capillary walls.) Cells take in oxygen and nutrients from the tissue
TiuId, and release metabolic waste into it. in a capinary bed ithe network of capiaries in an area or uissues.
substances move out of the capillaries, into the tissue fluid, by pressure filtration:
substances move out of the capillaries, into the tissue fluid, by pressure filtration:
1)At the start of the capillary bed, nearest the arteries, the hydrostatic (liquid) pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid.
This difference in hydrostatic pressure forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid.
2) As fluid leaves, the hydrostatic pressure reduces in the
capillaries - so me nyarostauc pressure is mucn lower at the end of the capillary bed that’s nearest to the venules.
3) There is another form of pressure at work here called oncotic pressure - this is generated by plasma proteins present in the capillaries which lower the water potential.
At the venule end ot the capillary bed, the water potential in the capillaries is lower than the water potential in the tissue fluid due to the fluid loss from the capillaries and the high oncotic pressure. This means some water re-enters the capillaries from the tissue fluid at the venule end by osmosis.
Excess Tissue Fluid Drains into the Lymph Vessels
Not all of the tissue fluid re-enters the capillaries at the venule end of the capillary bed -some excess tissue fluid is left over. This extra fluid eventually gets returned to the blood through the lymphatic system - a kind of drainage system, made up of lymph vessels.
1) The smallest lymph vessels are the lymph capillaries.
2) Excess tissue fluid passes into lymph vessels. Once inside, it’s called lymph.
3) Valves in the lymph vessels stop the lymph going backwards.
4) Lymph gradually moves towards the main lymph vessels in the thorax (chest cavity). Here, it’s
returned to the blood. near the heart.
Valves in the Heart Prevent Blood Flowing the Wrong Way
The atrioventricular valves link the atria to the ventricles, and the semi-lunar valves link the ventricles to the pulmonary artery and aorta
- they all stop blood flowing the wrong way. Here’s how they work:
The valves only open one way - whether they’re open or closed depends on the relative pressure of the heart chambers.
2) If there’s higher pressure behind a valve, it’s forced open.
3) If pressure is higher in front of the valve, it’s forced shut.
The Cardiac Cycle Pumps Blood Round the Body
The cardiac cycle is an ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body. The volumes of the atria and ventricles change as they contract and relax, altering the pressure in each chamber. This causes valves to open and close, which directs the blood flow through
the heart.
The cardiac cycle can be simplified into three stages:
(1) (Ventricles relax, atria contract
The ventricles are relaxed. The atria contract, which decreases their volume and increases their pressure. This pushes the blood into the ventricles through the atrioventricular valves. There’s a slight increase in ventricular pressure and volume as the ventricles receive the ejected blood from the contracting atria
2)Ventricles contract, atria relax
The atria relax. The ventricles contract (decreasing their volume), increasing their pressure
The pressure becomes higher in the ventricles than the atria, which forces the atrioventricular valves shut to prevent back-flow. The high pressure in the ventricles opens the semi-lunar valves - blood id forced out into the pulmonary artery and aorta
3)Ventricles relax, atria relax
The ventricles and the atria both relax. The higher pressure in the pulmonary artery and aorta causes the semi-lunar valves to close, preventing back-flow.
The atria fill with blood (increasing their pressure)
Que to me nigner pressure in me vena cava and pulmonary vein. As the ventricles continue to relax, their pressure falls below the pressure in the atria.
This causes the atrioventricular valves to open and blood flows passively (without being pushed by atrial
contraction into the ventricles from the atria. me atria contract, and the whole process begins again
Cardiac Muscle Controls the Regular Beating of the Heart
1) The process starts in the sino-atrial node (SAN), which is in the wall of
waves of electrical
the right atrium.
2) The SAN is like a pacemaker-it sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls.
3)This causes the right and left atria
to contract at the same fime.
4)A band of non-conducting collagen
uissue prevents the waves or electrical activity from being passed directly from the atria to the ventricles.
5)Instead. these waves of electrical
activitv are transterred from the SAN to the atrioventricular node (AVN).
6)The AVN is responsible for passing the waves of electrical activity on to the bundle of His. But, there’s a slight delay
before the AVN reacts, to make sure the ventricles contract after the atria have emptied.
7) The bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right and left ventricle walls, called the Purkyne tissue.
8)The Purkyne tissue carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simurtaneously, from the bottom up.
