3.1.2 transport in animals

Question 1

The need for specialised transport systems in animals

Answer 1

• Metabolic demands of most multicellular animals are high so diffusion over long distances is not enough to provide the quantities needed.
• The SA:V gets smaller as organisms get bigger, so the surface area available to absorb/remove substances also decreases.
• Molecules, e.g. hormones or enzymes, may be made in one place but needed in another.
• Food will be digested in one organ system but needs to be transported to every cell for cell metabolism.
• Waste products of metabolism need to be removed from cells and transported to excretory organs.

Question 2

Circulatory systems

Answer 2

Most circulatory systems have:
- A liquid transport medium that circulates around the system.
- They have vessels that carry the transport system.
- They have a pumping mechanism to move fluid around the system.

• When substances are transported in a mass of fluid with a mechanism for moving the fluid it is known as a mass transport system.

Question 3

Open circulatory systems

Answer 3

• There are very few vessels to contain in the transport medium.
• It is pumped straight from the heart into the body cavity of the animal.
• The open body cavity is called the haemocoel. In this area the transport medium is under low pressure. It comes into direct contact with the tissues and cells. This is where gas exchange takes place.
• The transport medium returns to the heart through an open ended vessel.
• These systems are mainly found in invertebrae. Insect blood is called haemolymph, it dosent carry oxygen or carbon dioxide. The haemolymph circulates but steep concentration gradients cannot be maintained for efficient diffusion.

Question 4

Closed circulatory systems

Answer 4

• In this system the blood is enclosed in blood vessels and does not come directly into countact with the cells of the body.
• Substances leave and enter the blood by diffusion through the walls of the blood vessels.
• The ammount of blood flowing to a particular tissue can be adjusted by widening or narrowing blood vessels.
• These systems are found in all mammals

Question 5

Single closed circulatory systems

Answer 5

• In these systems the blood flows through the heart and is pumped out to travel all around the body before returning to the heart.
• In a single closed circulation the blood passes through 2 sets of capillaries before it returns to the heart.
• In the first set of capillaries it exchanges oxygen and carbon dioxide. In the second substances are exchanged between the blood and cells. As a reult of passing through these very narrow vessels the blood pressure in the system drops so blood returns to the heart slowly. This limits the eficiency of this gas exchange process.
• Fish are the exeception as they have a counter current system.

Question 6

Double closed circulatory system

Answer 6

• It involves 2 seperate circulations:
  1. Blood is pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide, then returns 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.

Question 7

Advantages of double circulatory system over singular

Answer 7

• Double sustains a higher pressure over both exchange surfaces and the pressure can be differentiated.
• Double circulatory allows for a more rapid speed of flow.

Question 8

Arteries

Answer 8

• Direction of blood = heart > capillaries
• Type of blood = oxygenated (except in pulmonary artery and umbilical artery)
• High blood pressure

Layers of wall:
- Tunica externa = collagen, thik outer layer of non elastic fibrous tissue gives structure and support.
- Tunica media = elastic fibres, enables expansion of lumen to withstand pressure from the heart, elastic recoil maintains high pressure and smooths blood flow.
- Smooth muscle = contraction of muscle narrows lumen, controls bloodflow and pressure to tissues, important in vasoconstriction and vasodilation.
- Tunica intima (endothelium) = inner layers of cells folded to increase SA.

Question 9

Veins

Answer 9

• Direction of blood = capillaries > heart
• Deoxygenated blood except in pulmonary vein and umbilical vein.
• Low blood pressure
• Tissue arrangement in the layers are the same as artery but thinner
• Tunica externa is relatively thick to give support for large volume of blood in the lumen.
• Semilunar valve prevents backflow due to gravity.
• Skeletal muscle contaction aids movement of blood through veins.

Question 10

Capillaries

Answer 10

• Links arteries and veins
• Site for exchange between blood and tissues.
• Very narrow lumen, RBCs travel in line which facilitates the diffusion of oxygen.
• Endothelial cell wall is only 1 cell thick so short diffusion distance.
• Capilary walls have pores to allow for filtration.
• Extensive network creates large SA.

Question 11

The human heart

Answer 11

• The heart consists of 2 pumps.
• Deoxygenated blood from the body flows into the right side of the heart which flows to the lungs.
• Oxygenated blood from the lungs returns to the left side of the lungs.
• The heart is made from cardiac muscles.
• The heart is surrounded by inelastic pericardinal membranes which help prevent the heart from over distending with blood.

Question 12

Structure and function of the heart

Answer 12

• Deoxygenated blood enters the right atrium from the upper body and head in the superior vena cava, and from the lower body in the inferior vena cava at relatively low pressure.
• The atria have thin muscular walls.
• As blood flows in, slight pressure builds up until the atrio-ventricular valve opens to let blood pass through to the right ventricle.
• When both the atrium and ventricle are filedwith blood the atrium contracts, forcing all of the blood into the right ventricle.
• As the right ventricle starts to contract, the tricuspid valve closes, preventing any backflow of blood to the atrium.
• The right ventricle contracts fully and pumps deoxygenated blood through the semilunar valves into the pulmonary artery.
• At the same time oxygenated blood from the lungs enters the left atrium from the pulmonary vein.
• As the pressure in the atrium builds the biscuspid valve opens between the left atrium and the left ventricle so the ventricle also fills with oxygenated blood.
• When both the atrium and ventricle are full the atrium contracts, forcing all the oxygenated blood into the left ventricle.
• The left ventricle then contracts and pumps oxygenated blood through the semilunar valves into the aorta and around the body. As ventricle contracts the tricuspid valve closes which prevents backflow.

Question 13

The cardiac cycle and the heartbeat

Answer 13

• The cradiac cycle describes the events in a single heartbeat. This lasts about 0.8s in a human adult.
• In diastole the heart relaxes. The atria and ventricles fill with blood.
• In systole the atria contract closely followed by the ventricles.

Question 14

Cardiac cycle stages

Answer 14

• Stage 1 = atrial systole and ventricular diastole. Blood flows into the ventricles from atria because the pressure is greater in atria. The atrio ventricular valves are open.
• Stage 2 = Ventricular systole and atrial diastole. Blood is pumped from ventricle to aorta because pressure pressure is larger in the ventricle. Semilunar valves are open. Force/pressure of contractions closes the atrioventricular valves so no backflow into atria.
• Stage 3 = Ventricular diastole and atrial diastole. Blood flows from atria to ventricles passively due to gravity + relaxed state of ventricles. Atrioventricular valves are pushed open.

Question 15

Heart sounds

Answer 15

• The sounds of the heartbeat are made by blood pressure closing the heart valves.
• The first 2 sounds of a heart beat are described as ‘lub-dub’
• The first sound comes as the blood is forced against the atrioventricular valves as the ventricles contract.
• The second sound comes as a backflow of blood closes the semilunar valves in the aorta and pulmonary artery as ventricles relax.

Question 16

The basic rhythm of the heart

Answer 16

• Cardiac muscle is myogenic, it has its own intrinsic rhythm at around 60 bpm. This prevents the body wasting resources maintaining heart rate.
• The basic rhythm of the heart is maintained by a wave of electrical excitation.
• A wave of electrical excitation begins in the pacemaker area called the sinoatrial node (SAN), causing the atria to contract and so iniating the heartbeat. A layer of non conducting tissue prevents the excitation passing directly to the ventricles.
• The electrical activity from the SAN is picked up by the atrioventricular node (AVN) . The AVN imposes a slight delay berfore stimulating the bundle of his, this is a bundle of conducting tissue made up of Purkyne fibres. These penetrate through the septum between the ventricles.
• The bundle of his splits into 2 branches and conducts the wave of excitation to the apex (bottom) of the heart.
• At the apex the Purkyne fibres spread out through the walls of the ventricles on both sides. The spread of excitation triggers the contraction of the ventricles, starting at the apex. This allows for more efficient emptying of the ventricles.

Question 17

Electrocardiograms (ECGs)

Answer 17

• ECG is a recording of electrical activity in the heart.
• It measures electrical differences in the skin which the heart has caused.
• Electrodes are used to pick up these changes.

Question 18

Heart rhythm abnormalities

Answer 18

• Tachycardia = when the heartbeat is very rapid (over 100 bpm).
• Bradycardia = when the heart rate slows down to below 60bpm. Many people have this because they are fit as training makes heart beat more slowly and efficiently. Sever bradycardia may require a pacemaker to help heart keep up.
• Ectopic heart beat = extra heart beats that are out of normal rhythm.
• Atrial fibrillation = this is an example of arrhythmia, which means an abnormal rhythm of the heart. Rapid electrical impulses are generated in the atria. The contract very fast (fibrillate) up to 400 times a minute. However they dont contract properly and only some of the impulses are passed on to the ventricles, which contract much less often. This means the blood does not pump blood very efficiently.

Question 19

Blood

Answer 19

• Blood consists of a yellow liquid called plasma.
• Plasma carries a variety of other substances e.g. dissolved glucose and amino acids, mineral ions, hormones, large plasmam proteins.
• Plasma also transports red blood cells and WBCs.
• Plasma carries platelets
• Plasma makes up 55% of blood.

Question 20

Functions of the blood

Answer 20

• Transports oxygen to and carbon dioxide from respiring cells.
• Transported digested food from small intestine.
• Transports nitrogenous waste products from the cells to exectory organs.
• transports hormones.
• transports food molecules from storage compounds to cells that need them.
• transports platelets to damaged areas.
• Transports cells an antibodies involved in the immune response.

Question 21

Tissue fluid

Answer 21

• The substances dissolved in plasma can dissolve through the fenestrations in capilary walls except from large plasma proteins.
• These plasma proteins have an osmotic effect. They give blood in the capillaries a high solute potential (and so a low water potential) compared with surrounding fluid. This means that water has a tendency to move into the blood in the capillaries from surrouding fluid by osmosis. this is called oncotic pressure and is -3.3 kPa.
• However as blood flows through the artioles in the capillaries, it is still under pressure from the surge of blood that occurs every time the heart contracts. This is known as hydrostatic pressure.
• At the arterial end of the capillaries, the hydrostatic pressure forcing fluid out of the capillaries is relatively high at 4.6kPa. It is higher than the oncotic pressure attracting water in by osmosis so fluid is squeezed out of the capillaries. This fluid fills the spaces between cells and is called tissue fluid.
• As blood moves through the capillaries towards the venous system, the balance of force changes. The hydrostatic pressure falls to around 2.3kPa in the vessels as fluid has moved out. The oncotic pressure is still -3.3kPa so it is now stronger than the hydrostatic pressure, meaning water moves back into the capillaries via osmosis as it approaches the venous end of the capillaries.

Question 22

Lymph

Answer 22

• 10% of the liquid that leaves the blood vessels drains into a system of blind ended tubes called lymph capillaries.
• Lymph is similiar in composition to plasma but has less oxygen and fewer nutrience. It also contains fatty acids which have been absorbed into the lymph from the villi of the small intestine.
• The fluid is transported through them by the squeezing of muscles.
• Lymphocytes build up in the lymph nodes when necessary and produce antibodies which are then passed into the blood.
• Lymph nodes also intercept bacteria and other debris from the lymph which are ingested by phagocytes found in the nodes.

Question 23

Transporting oxygen

Answer 23

• Ethrocytes are specialised and have a number of adaptations for transporting oxygens. They have a biconcave shape.
• Erythrocytes contain haemoglobin.
• each haemoglobin molecule can bind to 4 oxygen molecules.
• Oxygen binds quite loosely to the haemoglobin forming oxyhaemoglobin.
• Hb + 4O2 -> Hb(O2)4

Question 24

Carrying oxygen

Answer 24

• When erthrocytes enter the capillaries in the lungs, the oxygen levels are relatively low. This creates a steep concentration gradient between the inside of the erythrocytes and the air in the alveoli.
• Oxygen moves into the erthrocytes and binds to the haemoglobin.
• The arrangement of the haemoglobin molecule means that as soon as one oxygen binds to a haem group, the molecule changes shape, making it easier for the next oxygen molecules to bind. This is known as positive cooperativity.
• When blood reaches the body tissue the situation is reversed.
• The concentration of oxygen in the cyptoplasm of the body cells is lower than in the erythrocytes. As a result oxygen moves out of the erythrocytes down a concentration gradient.

Question 25

Oxygen dissociation curve

Answer 25

* look at textbook page

Question 26

The effect of CO2

Answer 26

- As the partial pressure of CO2 rises Hb gives up oxygen more easily. This change is known as the Bohr effect. The Bohr effect is important because: - in active tissues with a high partial pressure of CO2 Hb gives up its oxygen more readily. - In the lungs where the proportion of CO2 in the air is relatively low, oxygen binds to the Hb molecules easily.

Question 27

Fetal haemoglobin

Answer 27

- Oxygen blood from the Mother runs close to the deoxygenated fetal blood in the placenta. - Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin at each point along the dissociation curve.

Question 28

Transporting carbon dioxide

Answer 28

- Around 5% of CO2 is dissolved in plasma - 10-20% is combined with amino groups in the polypeptide chains of haemoglobin to form carbaminohaemoglobin. - 75-85% is converted into hydrogen carbonate ions in the cyptoplasm of RBCs. Look at textbook