Chapter 8.1

Question 1

The need for a circulatory system

Answer 1

• All organisms need to exchange materials with their environments
• Small animals with large surface area to volume ratios (or relatively inactive animals like jellyfish) can rely on diffusion alone to exchange oxygen, carbon dioxide and nutrients with their environment
• Larger animals have smaller surface area to volume ratios, so diffusion alone is insufficient for exchange of materials between cells further from the surface of the organism with the environment
• Circulatory systems are systems which carry around fluids containing materials needed by the organism, as well as waste materials that need to be removed

Question 2

Open & closed systems

Answer 2

-In a closed circulatory system, blood is pumped around the body and is always contained within a network of blood vessels

–All vertebrates and many invertebrates have closed circulatory systems -In an open circulatory system, blood is not contained within blood vessels but is pumped directly into body cavities

–Organisms such as arthropods and molluscs have open circulatory systems.

Question 3

Humans have a closed double circulatory system:

Answer 3

in one complete circuit of the body blood passes through the heart (the pump) twice

• The right side of the heart pumps blood deoxygenated blood to the lungs for gas exchange; this is the pulmonary circulatory system
• Blood then returns to the left side of the heart, so that oxygenated blood can be pumped efficiently (at high pressure) around the body; this is the systemic circulatory system

Question 4

function: Heart

Answer 4

a hallow, muscular organ located in the chest cavity which pumps blood. Cardiac muscle tissue is specialized for repeated involuntary contraction without rest

Question 5

function: Arteries

Answer 5

Blood vessels which carry blood away from the heart. The walls of the arteries contain lots of muscle and elastic tissue and a narrow lumen, to maintain high blood pressure. -Arteries range from 0.4-2.5cm in diameter

Question 6

function: Arterioles

Answer 6

Small arteries which branch from larger arteries and connect to capillaries these are around 30 Micro meters in diameter

Question 7

function: Capillaries

Answer 7

Tiny blood vessels (5-10 Mirometer) which connect arterioles and venules. Their size means they directly past cells and tissue and perform gas exchange and exchange of substance such as glucose

Question 8

function: Venules

Answer 8

small veins which join capillaries to larger veins. They have a diameter of 7 micro meters to 1mm

Question 9

function: Veins

Answer 9

• Blood vessels which carry blood back towards the heart.
• The walls of veins are thin in comparison to arteries, having less muscles and elastic tissues but wider lumen.
• Valves help maintain blood flow back towards the heart

Question 10

A photomicrograph

Answer 10

is a photograph taken of a specimen observed using a light microscope

Question 11

An electron micrograph

Answer 11

is a photograph taken of a specimen observed using an electron microscope

Question 12

The lumen of the arteries is relatively narrow;

Answer 12

this ensures that blood remains at relatively high pressure for efficient delivery to the tissues whilst also providing resistance to blood flow to allow gas exchange as blood passes through the tissues

Question 13

The walls of arteries are composed of

Answer 13

elastic and muscular tissue, as well as collagen fibres

-Arteries closer to the heart contain a higher proportion of elastic fibres

– the walls of these arteries must be able to stretch and recoil to accommodate blood surging through, preventing them from bursting or from the blood pressure dropping

-These arteries are described as being elastic Arteries further from the heart contain less elastic and more smooth muscle tissue

– the diameter of these arteries can be adjusted to alter the blood flowing to different tissues

–These arteries are described as being muscular and they branch into smaller arteries (arterioles)

-The blood pressure in the arterioles is lower than that of the arteries

Question 14

Arterioles branch into the smallest blood vessel

Answer 14

– the capillaries

– which form networks throughout most tissues of the body (where they are described as capillary beds)

–Capillaries have a diameter of between 5-10 μm and most cells of the body are no more than a few μm from one The diameter of a typical red blood cell is 7 μm

Question 15

features of capillaries

Answer 15

Blood flowing through the capillaries is brought close to the cells of the body to allow efficient exchange of materials (particularly the diffusion of oxygen)

• The endothelial wall of the capillaries is only one-cell thick, which ensures that substances can diffuse easily between the capillary and neighbouring cells
• The walls are also “leaky”, there are small gaps between individual squamous epithelial cells that form the wall to allow small substances to leak out of the blood into the fluid surrounding the cells of the body

Question 16

The outer layer of the veins is relatively

Answer 16

tough, composed largely of collagen fibres Conversely, the middle layer of the veins is relatively thin in comparison and contains only a small amount of smooth muscle and elastic fibre

-This is because the blood flowing through veins is under very low pressures so the walls of the veins do not have to stretch and recoil to accommodate blood flow

—The lumen of veins is characteristically large

Question 17

Skeletal muscle contraction helps

Answer 17

raise blood pressure temporarily within the veins, and the presence of one-way valves keeps blood moving back towards the hearth

Question 18

Structure: Muscular artery

Answer 18

• Thinner unica media mainly composed of smooth muscle= Able to perform vasoconstriction and vasodilation
• Much less elastin than elastic arteries=cannot stretch and recoil
• Narrow lumen = blood flows under high pressure

Question 19

Structure: elastic artery

Answer 19

• Thinker Tunica media mainly composed of elastin and collagen=Gives the artery the ability to stretch in response to each pulse
• relatively few smooth muscle fibres = cannot preform vasoconstriction or vasodilation
• Narrow lumen = Blood flows under high pressure

Question 20

Structure: vein

Answer 20

• One-way valves= close to prevent the backflow of blood
• Wide lumen= Blood pressure is reduced in veins with no surges
• less smooth muscles and elastin = no need for veins to stretch and recoil
• lots of collagen=increased strength and structure

Question 21

Structure: Capillary

Answer 21

• very small diameter= Blood travels relatively slowly, giving more opportunity for diffusion to occur
• capillaries branch between cells= substances can diffuse quickly between cells and the blood quickly
• Thin walls, no elastic, smooth muscle or collagen = Capillaries can fit between individual cells and diffusion is rapid

Question 22

Cells of the Blood

Answer 22

• Blood is a tissue composed of a number of important specialised cells
• Red blood cells, monocytes, neutrophils and lymphocytes all have distinguishable structures which enable them to be recognised on microscope slides, in photomicrographs and in electron micrographs

Question 23

Red blood cells

Answer 23

• There are approximately 5 million red blood cells per mm3 of blood
• Red blood cells contain haemoglobin, a protein with a quaternary structure that contains haem iron groups which can bind reversibly to oxygen
• Distinctive features of erythrocytes when viewed under a microscope, are their distinctive biconcave disc shape (caused by their lack of nucleus)

Question 24

Monocytes

Answer 24

• Monocytes are identifiable by their size – they are the largest of the leukocytes and have a nucleus shaped like a kidney or a bean
• The nucleus of monocytes tends to appear lighter after staining than other leukocytes
• The nucleus should appear a light blue colour, while the chromatin inside is distinct and fine

Question 25

Neutrophils

Answer 25

• Neutrophils are distinguished by their multi-lobed nuclei
• Up to 70% of all leukocytes are neutrophils

– this makes them easy to spot on a micrograph

-The granules of neutrophils typically stain pink or purple-blue

Question 26

Lymphocytes

Answer 26

• Lymphocytes are small leukocytes that are identifiable by their very large nuclei, which typically stains a dark colour
• Lymphocytes constitute around 20-25% of all leukocytes
• Lymphocytes are around the size of red blood cells

Question 27

Formation of lymph

Answer 27

• Some tissue fluid reenters the capillaries while some enters the lymph capillaries
• The lymph capillaries are separate from the circulatory system

–They have closed ends and large pores that allow large molecules to pass through

• Larger molecules that are not able to pass through the capillary wall enter the lymphatic system as lymph
• Small valves in the vessel walls are the entry point to the lymphatic system -The liquid moves along the larger vessels of this system by compression caused by body movement. Any backflow is prevented by valves
• This is why people who have been sedentary on planes can experience swollen lower limbs
• The lymph eventually reenters the bloodstream through veins located close to the heart -Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries

–If plasma proteins were not removed from tissue fluid they could lower the water potential (of the tissue fluid) and prevent the reabsorption of water into the blood in the capillaries

-After digestion lipids are transported from the intestines to the bloodstream by the lymph system

Question 28

Tissue fluid formation

Answer 28

• How much liquid leaves the plasma to form tissue fluid depends on two opposing forces
• When blood is at the arterial end of a capillary, the hydrostatic pressure is great enough to push molecules out of the capillary
• Proteins remain in the blood; the increased protein content creates a water potential between the capillary and the tissue fluid
• However, overall movement of water is out from the capillaries into the tissue fluid
• At the venous end of the capillary, less fluid is pushed out of the capillary as pressure within the capillary is reduced
• The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end, so water begins to flow back into the capillary from the tissue fluid
• Overall, more fluid leaves the capillary than returns, leaving tissue fluid behind to bathe cells
• If blood pressure is high (hypertension) then the pressure at the arterial end is even greater
• This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema

Question 29

Plasma

Answer 29

is a straw-coloured liquid that constitutes around 55% of the blood

• Plasma is largely composed of water (95%) and because water is a good solvent, many substances can dissolve in it, allowing them to be transported around the body
• As blood passes through capillaries, some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body

–This results in the formation of tissue fluid

• The composition of plasma and tissue fluid are virtually the same, although tissue fluid contains far fewer proteins
• Proteins are too large to fit through gaps in the capillary walls and so remain in the blood
• Tissue fluid bathes almost all the cells of the body outside of the circulatory system -Exchange of substances between cells and the blood occurs via the tissue fluid

Question 30

Transport of oxygen

Answer 30

• The majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells
• Each molecule of haemoglobin contains four haem groups, each able to bond with one molecule of oxygen
• This means that each molecule of haemoglobin can carry four oxygen molecules (eight oxygen atoms in total)

Question 31

When oxygen binds to haemoglobin,

Answer 31

-4O2 + Hb (Haemoglobin) → HbO8 (Oxyhaemoglobin)

Question 32

Oxygen can also dissolve in the water of

Answer 32

blood plasma; at normal body temperatures about 0.025 cm3 of oxygen can dissolve in water 1 dm3 of blood contains 150 g of haemoglobin, which can carry up to 19.5 dm3 oxygen,

• The binding of the first oxygen molecule results in a conformational change in the structure of the haemoglobin molecule, making it easier for each successive oxygen molecule to bind
• The reverse of this process happens when oxygen dissociates in the tissues The dissociation of the last oxygen molecule is the hardest

Question 33

Carbon dioxide transport

Answer 33

• Waste carbon dioxide diffuses from tissues and into the blood following aerobic respiration
• There are three main ways in which carbon dioxide is transported around the body
• A very small percentage of carbon dioxide (~ 10 %) dissolves in blood plasma, forming H2CO3
• A much larger percentage (~ 70 %) of carbon dioxide dissolves in the cytoplasm of red blood cells
• Hydrogen ions (protons) can combine with haemoglobin, forming haemoglobinic acid -Carbon dioxide can also bind to amino acids and therefore haemoglobin, forming carbaminohaemoglobin (~ 20 % of carbon dioxide transport in the blood)

Question 34

Red blood cells contain the enzyme

Answer 34

carbonic anhydrase which catalyses the reaction between carbon dioxide and water

–Without carbonic anhydrase this reaction proceeds very slowly. The plasma contains very little carbon anhydrase hence H2CO3 forms much more slowly in plasma than in the cytoplasm of red blood cells

–Carbonic acid dissociates readily into H+ and HCO3- ions : CO2 + H2O ⇌ H2CO3 ⇌ HCO3– + H+

Question 35

When there is to much carbon present this resilts in

Answer 35

• The increase in H+ concentration results in a decrease in blood pH, which alters the structure of haemoglobin, encouraging the dissociation of oxyhaemoglobin to release oxygen
• This is beneficial – when levels of carbon dioxide are higher, rates of aerobic respiration are greater and therefore the need for oxygen is higher
• Hydrogen ions (protons) can combine with haemoglobin, forming haemoglobinic acid
• Carbon dioxide can also bind to amino acids and therefore haemoglobin, forming carbaminohaemoglobin – this accounts for ~ 20 % of carbon dioxide transport in the blood

Question 36

Haemoglobin is a large

Answer 36

globular protein composed of four polypeptide chains, each chain containing an iron group

Question 37

Haemoglobin and oxygen

Answer 37

• each haemoglobin molecule can pick up four oxygen molecules
• This is a reversible reaction and forms oxyhaemoglobin: 4O2 + Hb (Haemoglobin) → HbO8 (Oxyhaemoglobin)
• The binding of the first oxygen molecule alters the formation of the molecules and so the other three oxygen molecules are able to bind much faster than the first
• The reverse of this process happens when oxygen dissociates at the tissues and the last oxygen molecule is the hardest to remove

Question 38

haemoglobin and Carbon dioxide

Answer 38

• Waste carbon dioxide diffuses from tissues and into the blood following aerobic respiration
• There are three main ways in which carbon dioxide is transported around the body
• A very small percentage of carbon dioxide (~ 10 %) dissolves in blood plasma, forming H2CO3 -A much larger percentage (~ 70 %) of carbon dioxide dissolves in the cytoplasm of red blood cells

Question 39

Red blood cells contain the enzyme carbonic anhydrase which

Answer 39

catalyses the reaction between carbon dioxide and water

–Without carbonic anhydrase this reaction proceeds very slowly. The plasma contains very little carbon anhydrase hence H2CO3 forms much more slowly in plasma than in the cytoplasm of red blood cells

-Carbonic acid dissociates readily into H+ and HCO3- ions : CO2 + H2O ⇌ H2CO3 ⇌ HCO3– + H+

Question 40

Carbonic acid dissociates readily into H+ and HCO3- ions when there is a high concentration this..

Answer 40

-causes the increase in H+ concentration which results in a decrease in blood pH, which alters the structure of haemoglobin, encouraging the dissociation of oxyhaemoglobin to release oxygen

—This is beneficial – when levels of carbon dioxide are higher, rates of aerobic respiration are greater and therefore the need for oxygen is higher

• Hydrogen ions (protons) can combine with haemoglobin, forming haemoglobinic acid
• Carbon dioxide can also bind to amino acids and therefore haemoglobin, forming carbaminohaemoglobin

– this accounts for ~ 20 % of carbon dioxide transport in the blood

Question 41

The Bohr Shift

Answer 41

• Changes in the oxygen dissociation curve as a result of carbon dioxide levels are known as the Bohr shift or Bohr effect
• The Bohr effect explains how the ability of haemoglobin to bind to, and release its oxygen changes

Question 42

The higher the partial pressure of oxygen

Answer 42

• the greater the saturation of haemoglobin with oxygen, and vice versa
• The more carbon dioxide there is, the line on the graph shifts to the right (the lower of the two lines)
• This shows that more dissociation has occurred, as the percentage saturation of oxygen is lower
• This is an important change, as it means that where there is a lot of carbon dioxide, such as at respiring tissues, haemoglobin gives up its oxygen to the nearby tissues

Question 43

When the partial pressure of carbon dioxide is high

Answer 43

in respiring tissues for example, haemoglobin’s affinity for oxygen is reduced

• This is a helpful change, because it means that haemoglobin gives up its oxygen much more readily
• This occurs because CO2 lowers the pH of the blood (by forming carbonic acid), which causes haemoglobin to release its oxygen
• Carbon dioxide levels in the lungs are comparatively very low, haemoglobin’s affinity for oxygen is increased, which makes it easier for oxygen to bind to haemoglobin

Question 44

Red Blood Cells & Altitude: Exposure to high altitudes trigger changes in the numbers of red blood cells in the body

Answer 44

• This is because the air is ‘thinner’ at high altitudes
• This means that the barometric pressure of the air is reduced and so is the partial pressure of oxygen
• To cope, the body compensates by increasing the mass of red blood cells and haemoglobin
• Given a chance to adapt, red blood cells can occupy 60% of blood volume instead of 45% -This change is demonstrated on an oxygen dissociation graph with a shift to the left (the upper line)