M3C8 - Transport in animals

Question 1

Why do animals need transport systems?

Answer 1

-SA:V ratio is too small for sufficient diffusion of materials to/from cells
-Distance to innermost cells is too great
-Remove waste from cells to organs of excretion.
-Metabolic demands are too high so diffusion over long distances isn’t enough to supply quantities needed

Question 2

Describe an open circulatory system

Answer 2

-It carries food, nitrogenous waste and the cells involved in defence against pathogens.
-It does not carry oxygen or carbon dioxide.
-Very few vessels

Question 3

Describe the open circulatory system in insects

Answer 3

-Haemolymph found in body cavity
-Cells and tissues bathed directly by Haemolymph containing nutrients & removes wastes.
-Along dorsal surface (back) of insect is a muscular tube (heart) containing open ended pores (ostia).
-When heart relaxes, blood is drawn back into heart through ostia.
-Blood is directly pumped along arteries from tubular ‘heart’ to the head by peristalsis, where pours back into the haemocoel via the open-ended artery.
-Some active or larger insects have further tubes to direct haemolymph to active body parts such as leg, wing.

Question 4

What are some advantages of an open circulatory system?

Answer 4

-Ideal for small animals with low metabolic demands since less energy is needed.
-Diffusion can occur quickly.
-Insects have a separate system (tracheal system) for gas exchange, so doesn’t rely on blood for gas exchange.

Question 5

What are some disadvantages of an open circulatory system?

Answer 5

-Blood flows at low pressure, so therefore is slow
-Can’t change the volume of haemolymph flowing to a particular organ to meet varying demands.
-Although it circulates, haemolymph doesn’t maintain steep diffusion gradients for efficient diffusion.

Question 6

What are some features of single closed circulatory systems?

Answer 6

-Blood stays in vessels. Blood passes through the heart once for every complete circuit of the body.
-Blood passes through TWO sets of capillaries before returning to the heart - Co2 and O are exchanged in the first, substances are exchanged in the second.
-Tissue fluid moves out of vessels to bathe cells and exchange materials.

Question 7

What are some advantages of single closed circulatory systems?

Answer 7

-Blood confined to vessels, so can be pumped at a higher pressure, so travels more quickly.
-Width of vessels can be changed to increase/decrease the volume of blood delivered to cells.
-Faster delivery of nutrients and oxygen & removal of wastes.

Question 8

What are some disadvantages of single closed circulatory systems?

Answer 8

-Reduced blood pressure as blood flows through gill capillaries (very narrow = high resistance)
-Blood flow still relatively slow, limits rate of exchange of materials with cells – e.g., may be insufficient transport of materials for fish in warm conditions to provide for rapidly respiring tissues.

Question 9

What are some features of double closed circulatory systems?

Answer 9

-Has 2 circuits
-pulmonary circulation; blood goes to lungs for gas exchange between air and blood
-Systemic circulation; blood pumped to body tissues for exchange of material between blood and cells.
-Heart has evolved to pump both circuits simultaneously so blood passes through heart twice for one complete circuit of the body.

Question 10

What are some advantages of double closed circulatory systems?

Answer 10

-Fast flow maintained
-Keeps oxygenated and deoxygenated blood separate
-Heart increases blood pressure in systematic circulation after blood has been through capillaries of lungs (high resistance of capillaries reduces blood pressure)
-Maintains lower blood pressure for pulmonary circulation (high blood pressure could rupture fragile lung capillaries)

Question 11

What are the functions of arteries?

Answer 11

-The arteries carry blood away from the heart to the tissues in the rest of the body.
-They carry oxygenated blood

Question 12

What are the layers of an artery staring from the inside working out?

Answer 12

-Lumen
-Endothelium
-Elastic fibres + smooth muscle
-Fibrous coat

Question 13

Describe the structure and function of the fibrous coat

Answer 13

-Forms a tough outer layer
-Made of collagen and prevents collapse.

Question 14

Describe the structure and function of the Elastic fibres

Answer 14

-Enable arteries to withstand force of blood pumped out of the heart.
-Can stretch to take a larger blood volume.
-In between contractions of heart elastic fibres recoil and return to original length- helps to even the surges of blood pumped from the heart to give a continuous flow.

Question 15

Describe the structure and function of the smooth muscle

Answer 15

-Smooth muscle contracts and relaxes- changing the size of the lumen.
-Smooth muscle contracts after blood passes through the artery to help maintain the pressure.

Question 16

Describe the structure and function of the endothelium

Answer 16

-The endothelium forms the lining of an artery
-It is made from a thin layer of simple squamos cells which are smooth so the blood flows easily over it.

Question 17

What is vasodilation?

Answer 17

When the smooth muscle in the arteriole relaxes, blood flows into the capillary bed.

Question 18

What is vasoconstriction?

Answer 18

When the smooth muscle in the arteriole contracts it constricts the vessel and prevents blood flowing into the capillary bed.

Question 19

Describe the structure and function of arterioles

Answer 19

-Arterioles are small (0.03mm-0.4mm in diameter)
-They have more smooth muscle and less elastin in their walls than arteries, as they have little pulse surge, but can constrict or dilate to control the flow of blood into individual organs.

Question 20

Describe the structure and function of capillaries

Answer 20

-Link the arterioles with the venules.
-Fenestrations in walls so substances are exchanged between tissue cells and blood.
-Blood entering the capillaries is mostly oxygenated from arterioles. By the time it flows to the venules it is de-oxygenated.

Question 21

Describe the adaptations of capillaries

Answer 21

-They provide a very large surface area for the diffusion.
-Cross-sectional area of capillaries is greater than arterioles so rate of blood flow falls - Slower movement of blood through capillaries gives more time for the exchange of materials by diffusion between the blood and the cells.
-Very thin layer for diffusion – only one endothelial cell thick.

Question 22

Describe the structure of veins

Answer 22

-Their walls contain lots of collagen and little elastic fibre.
-They have a wide lumen and a smooth, thin lining (endothelium) so blood flows easily.
-Blood pressure in the veins is very low and needs to move against gravity.
-Contain valves to prevent backflow of blood

Question 23

Describe the functions of veins and venules

Answer 23

-Veins and venules carry blood towards the heart and away from the cells in the rest of the body.
-They carry de-oxygenated blood

Question 24

Describe the adaptations of veins

Answer 24

-Most veins have one-way valves. These prevent the backflow of blood.
-Many veins run between active muscles. When the muscles contract they squeeze the veins, forcing blood towards the heart. The valves prevent backflow when the muscles relax.

Question 25

Describe the formation of tissue fluid

Answer 25

-Blood arriving at the capillaries is still under high hydrostatic pressure. -Small molecules are forced through fenestrations (gaps) in the capillary wall. -Most blood cells and large molecules (e.g. plasma proteins) are too large to pass through. -The resulting liquid that passes out of the capillary is tissue fluid. It flows between cells. -Materials e.g. nutrients and gases are exchanged between the tissue fluid and the cells by diffusion and facilitated diffusion. **>**Plasma proteins (particularly albumin) left behind in the capillary have an osmotic effect: Blood has a high solute potential (*therefore a relatively low water potential*) compared to the fluid surrounding the cells. **>**Water moves back into the blood in the capillaries from the fluid by osmosis, this is **oncotic pressure**.

Question 26

Describe the lymphatic system

Answer 26

-About 10% of tissue fluid is drained into **lymphatic vessels** (tubes which join and empty into the left and right **subclavian veins**), under the collar bone. -**Lymph nodes** contain *lymphocytes*; the nodes filter bacteria and foreign matter from lymph, the lymphocytes ingest them, and produce antibodies. -Lymph is moved by the squeezing of the body’s muscles, valves maintain flow in one direction.

Question 27

Compare the compositions of blood, tissue fluid, and lymph

Answer 27

-Tissue fluid + lymph don't contain erythrocytes but blood does. -Tissue fluid + lymph don't contain platelets but blood does. -All contain leucocytes -Blood contains more O2 than tissue fluid + lymph. -Blood contains less CO2 than tissue fluid + lymph. -Blood contains more amino acids than tissue fluid.

Question 28

Name the internal structures of the heart from left to right:

Answer 28

superior vena cava, inferior vena cava, right atrium, tricuspid valve, right ventricle, semi-lunar valve, left ventricle, bicuspid valve, left atrium, pulmonary vein (higher - both sides of heart), pulmonary artery (lower - both sides of heart), aorta.

Question 29

Describe and name the external structures of the heart

Answer 29

-Made of cardiac muscle, supplied with oxygen for contraction by coronary artery. -Pericardial membranes surround the heart, they can’t stretch so the heart does not over distend (swell) with blood.

Question 30

Describe the cardiac cycle:

Answer 30

1) Atrial systole- The pressure in the left atrium is greater than that in the left ventricle. Blood flows from the atria into the ventricles. The bicuspid valve is open. 2)The ventricle starts to contract (ventricular systole). The valve between the ventricle and atrium (bicuspid) closes preventing the backflow of blood into the heart – the pressure in the ventricle is greater than the atrium. 3)The ventricle continues to contract, pressure rises. The valve in the aorta (semi-lunar) opens- the pressure in the ventricle is greater than the aorta. 4)The ventricle stops contracting. The valve in the aorta (semi-lunar) closes as the pressure in the ventricle is lower than that in the aorta. The closing of the semi-lunar valve causes the ‘dub’ sound. 6)Diastole: relaxation of atria and ventricles. The atrium volume increases as blood enters the heart.

Question 31

How is the heart initiated and coordinated?

Answer 31

To prevent fibrillation, the heart is synchronised by: -Its own ‘pacemaker’, the sinoatrial node (SAN), -The atrioventricular node (AVN) -The Purkinje tissue

Question 32

Describe the process of myogenic stimulation:

Answer 32

-The heartbeat is initiated in the right atrium by the sinoatrial node (SAN) or the pacemaker. -The SAN starts **waves of excitation**. The waves spread out over the membranes of muscle tissue of the two atrial walls so that they contract. This is atrial systole. -A layer of non-conducting tissue prevents the excitation passing directly to the ventricles. -The electrical activity is picked up by the AV node. The AVN imposes a slight delay before stimulating the bundle of his, a bundle of conducting tissue made up of purkinye fibres, which penetrate through the septum between the ventricles. -The bundle of his splits into 2 branches and conducts the wave of excitation to the bottom of the heart. -At the apex (bottom) the purkinye fibres spread out through the walls of the ventricles on both sides, the spread of excitation triggers the contraction of the ventricles. -Since there is a time delay, by now the atria have finished contracting and the ventricles have filled with blood. -This causes the ventricles to contract (ventricular systole) from the base upwards ensuring that the blood is forced up and out in the vessels leaving the heart.

Question 33

What is Bradycardia?

Answer 33

When the heart rate slows down to below 60bpm. Many people have bradycardia because they are fit – training makes the heart beat more slowly and efficiently. Severe bradycardia can be serious and may need an artificial pacemaker to keep the heart beating steadily.

Question 34

What is tachycardia?

Answer 34

When the heartbeat is very rapid, over 100 bpm. This is often normal, e.g. during exercise, if you have a fever, if you are scared or angry. If it is abnormal it might be caused by problems in the electrical control of the heart and may need to be treated by medication or by surgery.

Question 35

What is ectopic heartbeat?

Answer 35

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.

Question 36

What is fibrillation?

Answer 36

An example of an arrhythmia, which means an abnormal rhythm of the heart. The heart doesn’t pump blood very effectively due to abnormal contraction of atria and ventricles.

Question 37

Describe the process of transporting Co2:

Answer 37

-Co2 diffuses into erythrocytes from tissues. -Co2 then reacts with water, producing **carbonic acid**. This reaction is *catalysed* by **carbonic anhydrase**, an enzyme in the cell. -Carbonic acid ionises into H+ and HCO3– (**bicarbonate**) Haemoglobin combines with H+ ions to form **haemoglobinic acid** (very weak). -Carbonic acid ions diffuse into blood plasma where it is able to be transported to the lungs. -**Chloride ions** diffuse into the red blood cell from the plasma, counteracting the build up of positive charge from the H+ ions. This is called the **chloride shift**. -This whole process reverses once the blood reaches the lungs.

Question 38

What does an oxygen dissociation curve show?

Answer 38

Shows the affinity of haemoglobin for oxygen.

Question 39

Describe a fetal haemoglobin dissociation curve:

Answer 39

-Foetal haemoglobin has a dissociative curve to left of maternal, so it has a higher affinity for oxygen than maternal haemoglobin. -Significance – foetal haemoglobin can take oxygen from maternal haemoglobin at the same partial pressure of oxygen in the placenta.

Question 40

What is the Bohr effect?

Answer 40

-Changes in the oxygen dissociation curve as a result of carbon dioxide levels. -When the partial **pressure** of **carbon dioxide** in the blood is high, haemoglobin’s **affinity** for oxygen is **reduced**. -This occurs because CO2 **lowers the pH** of the blood. -On a graph showing the dissociation curve, the curve shifts to the right when CO2 levels increase.