chapter 8 p1

Question 1

The need for specialised transport systems in animals:

Answer 1

In single-celled organisms, processes such as diffusion, osmosis, active transport, endocytosis and exocytosis can supply everything the cell needs to import or export.
These processes are also important in multicellular organisms, transporting substances within and between individual cells.
However, as organisms get bigger, the distances between the cells and the outside of the body get greater.
Diffusion would transport substances into and out of the inner core of the body, but it would be so slow that the organism would not survive.

Question 2

Specialised transport systems are needed because:
p1

Answer 2

the metabolic demands of most multicellular animals are high they need lots of oxygen and food, they produce lots of waste products) so diffusion over the long distances is not enough to supply the quantities needed

the surface area to volume (SA:V) ratio gets smaller as multicellular organisms get bigger so not only do the diffusion distances get bigger but the amount of surface area available to absorb or remove substances becomes relatively smaller

Question 3

Specialised transport systems are needed because:
p2

Answer 3

molecules such as 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 use in respiration and other aspects of cell metabolism

waste products of metabolism need to be removed from the cells and transported to excretory organs.

Question 4

Types of circulatory systems:

Answer 4

Most large, multicellular animals have specialised circulatory systems (transport systems) which carry gases such as oxygen and carbon dioxide, nutrients, waste products and hormones around the body.

Question 5

Features most circulatory systems have in common:

Answer 5

They have a liquid transport medium that circulates around the system (blood).
They have vessels that carry the transport medium.
They have a pumping mechanism to move the fluid around the system.

Question 6

Mass Transport Systems in Animals:

Answer 6

When substances are transported in a mass of fluid with a mechanism for moving the fluid around the body it is known as a mass transport system.
Large, multicellular animals usually have either an open circulatory system or a closed circulatory system.

Question 7

Open circulatory systems: p1

Answer 7

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.

Question 8

Open circulatory systems: p2

Answer 8

In the haemocoel the transport medium is under low pressure.
It comes 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

Question 9

Insect Open Circulatory System:
p1

Answer 9

These open-ended circulatory systems are found mainly in invertebrate animals, including most insects and some molluscs.
Remember that in insects, gas exchange takes place in the tracheal system. Insect blood is called haemolymph.
It doesn’t carry oxygen or carbon dioxide.
It transports food and nitrogenous waste products and the cells involved in defence against disease.

Question 10

Insect Open Circulatory System:
p2

Answer 10

The body cavity is split by a membrane and the heart extends along the length of the thorax and the abdomen of the insect.
The haemolymph circulates but steep diffusion gradients cannot be maintained for efficient diffusion.
The amount of haemolymph flowing to a particular tissue cannot be varied to meet changing demands.

Question 11

Closed circulatory systems:

Answer 11

In a closed circulatory system, the blood is enclosed in blood vessels and does not come directly into contact with the cells of the body.
The heart pumps the blood around the body under pressure and relatively quickly, and the blood returns directly to the heart.
Substances leave and enter the blood by diffusion through the walls of the blood vessels.
The amount of blood flowing to a particular tissue can be adjusted by widening or narrowing blood vessels.
Most closed circulatory systems contain a blood pigment that carries the respiratory gases

Question 12

Where are closed circulatory systems found:

Answer 12

Closed circulatory systems are found in many different animal phyla, including echinoderms (animals such as sea urchins and starfish), cephalopod molluscs including the octopods and squid, annelid worms including the common earthworm, and all of the vertebrate groups, including the mammals.

Question 13

Single closed circulatory systems:

Answer 13

Single closed circulatory systems are found in a number of groups including fish and annelid worms.
In single circulatory systems the blood flows through the heart and is pumped out to travel all around the body before returning to the heart.
In other words, the blood travels only once through the heart for each complete circulation of the body.

Question 14

Efficiency and Limitations of Single Closed Circulation

Answer 14

In a single closed circulation, the blood passes through two sets of capillaries (microscopic blood vessels) before it returns to the heart.
In the first, it exchanges oxygen and carbon dioxide.
In the second set of capillaries, in the different organ systems, substances are exchanged between the blood and the cells.
As a result of passing through these two sets of very narrow vessels, the blood pressure in the system drops considerably so the blood returns to the heart quite slowly.
This limits the efficiency of the exchange processes so the activity levels of animals with single closed circulations tends to be relatively low.

Question 15

Single Circulatory System in fish

Answer 15

Fish are something of an exception - They have a relatively efficient single circulatory system, which means they can be very active.
They have a countercurrent gaseous exchange mechanism in their gills that allows them to take a lot of 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 and, combined with their efficient gaseous exchange, explains how fish can be so active with a single closed circulatory system.

Question 16

Double closed circulatory systems:

Answer 16

Birds and most mammals are very active land animals that maintain their own body temperature.
This way of life is made possible in part by their double closed circulatory system (Figure 5).
This is the most efficient system for transporting substances around the body.
It involves two separate circulations:

Question 17

two separate circulations in Double closed circulatory systems:

Answer 17

Blood is pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide, and then returns to the heart.
Blood flows through the heart and is pumped out to travel all around the body before returning to the heart again.

So in a double circulatory system, the blood travels twice through the heart for each circuit of the body.
Each circuit - to the lungs and to the body - only passes through one capillary network, which means a relatively high pressure and fast flow of blood can be maintained.

Question 18

Blood vessels in circulatory system:

Answer 18

Circulation in humans is typical of a mammalian circulatory system.
It is estimated that if all the blood vessels of an average adult human were laid end to end they would stretch to 100000 miles - that is the equivalent of about four times around the circumference of the Earth.
There are several different types of blood vessels in the body and their structural composition is closely related to their function.

Question 19

examples of different components utilised in some blood vessels are:

Answer 19

Elastic fibres
Smooth muscle
Collagen

Question 20

Elastic fibres

Answer 20

these are composed of elastin and can stretch and recoil, providing vessel walls with flexibility.

Question 21

Smooth muscle -

Answer 21

contracts or relaxes, which changes the size of the lumen (the channel within the blood vessel).

Question 22

Collagen

Answer 22

provides structural support to maintain the shape and volume of the vessel.

Question 23

The arteries

Answer 23

carry blood away from the heart to the tissues of the body.
They carry oxygenated blood except in the pulmonary artery, which carries deoxygenated blood from the heart to the lungs, and (during pregnancy) the umbilical artery, which carries deoxygenated blood from the fetus to the placenta.
The blood in the arteries is under higher pressure than the blood in the veins.

Question 24

Artery Structure and Function: p1

Answer 24

Artery walls contain elastic fibres, smooth muscle and collagen
The elastic fibres enable them to withstand the force of the blood pumped out of the heart and stretch (within limits maintained by collagen) to take the larger blood volume.

Question 25

Artery Structure and Function: p2

Answer 25

In between the contractions of the heart, the elastic fibres recoil and return to their original length.
This helps to even out the surges of blood pumped from the heart to give a continuous flow.
However, you can still feel a pulse (surge of blood) when the heart contracts, which the elastic fibres cannot completely eliminate.
The lining of an artery (endothelium) is smooth so the blood flows easily over it.
Arterioles link the arteries and the capillaries.

Question 26

Arterioles:

Answer 26

Arterioles 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.
When the smooth muscle in the arteriole contracts it constricts the vessel and prevents blood flowing into a capillary bed - This is vasoconstriction.
When the smooth muscle in the wall of an arteriole relaxes, blood flows through into the capillary bed - This is vasodilation.

Question 27

Answer 27

Question 28

Aortic Aneurysms

Answer 28

Aneurysm is a bulge or weakness in a blood vessel.
Most common places for aneurysms are in the aorta and in the arteries of the brain.
Most people do not know they have an aneurysm until it bursts; this is very serious and can be fatal.
High blood pressure is one factor that increases the risk of an aneurysm.
However, scientists have also discovered changes in the proportion of collagen to elastin in the aorta wall.
The ratio of collagen: elastin in a normal aorta is 1.85: 1.
In a small aneurysm, it increases to around 3.75:1, and in large aortic aneurysms, it is 7.91: 1.
Research is continuing to see if this apparent link is real - and, if so, whether it can be used to predict who is at risk so they can have regular aortic screening.

Question 29

capillaries:

Answer 29

The capillaries are microscopic blood vessels that link the arterioles with the venules.
They form an extensive network through all the tissues of the body.
The lumen of a capillary is so small that red blood cells (which have a diameter of only 7.5-8 um) have to travel through in single file

Question 30

Substance Exchange in capillaries p1

Answer 30

Substances are exchanged through the capillary walls between the tissue cells and the blood.
The gaps between the endothelial cells that make up the capillary walls in most areas of the body are relatively large.
This is where many substances pass out of the capillaries into the fluid surrounding the cells.
The exception is the capillaries in the central nervous system, which have very tight junctions between the cells.

Question 31

Substance Exchange in capillaries p2

Answer 31

In most organs of the body the blood entering the capillaries from the arterioles is oxygenated.
By the time it leaves the capillaries for the venules it has less oxygen and more carbon dioxide (it is deoxygenated).
Again, the lungs and the placenta are the exceptions, with deoxygenated blood entering the capillaries and oxygenated blood leaving in the venules.

Question 32

Ways in which capillaries are adapted for their role:

Answer 32

They provide a very large surface area for the diffusion of substances into and out of the blood.
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.

Question 33

veins

Answer 33

carry blood away from the cells of the body towards the heart and, with two exceptions, they carry deoxygenated blood.

Question 34

veins blood flow

Answer 34

• The pulmonary vein carries oxygenated blood from the lungs to the heart, and (during pregnancy) the umbilical vein 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.
• Finally it reaches the two main vessels carrying deoxygenated blood back to the heart - the inferior vena cava from the lower parts of the body and the superior vena cava from the head and upper body.
• Veins do not have a pulse - the surges from the heart pumping are lost as the blood passes through the narrow capillaries.
• However, they do hold a large reservoir of blood - up to 60% of your blood volume is in your veins at any one time.

Question 35

Vein Characteristics and Structure:

Answer 35

The blood pressure in the veins is very low compared with the pressure in the arteries.
Medium-sized veins (the majority of the venous system) have valves to prevent the backflow of blood (see next page).
The walls contain lots of collagen and relatively little elastic fibre, and the vessels have a wide lumen and a smooth, thin lining (known as the endothelium) so the blood flows easily (Figure 4).
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.

Question 36

Answer 36