Module 4: Circulation and Gas Exchange

Question 1

how does respiration work on a cellular level for all organisms?

Answer 1

> energy rich fuel molecules from food
O2 is added, CO2 is released and ATP is produced
goes through the circulatory system
released through passive diffusion on the respiratory surface

Question 2

what are the important partial pressures in relation to respiration?

Answer 2

> partial pressure = the pressure exerted by a particular gas in a mixture of gases
-pO2 = 0.21 x 760 = 160 mmHg
e.g., usually air contains 21% O2 and, at sea level, atmospheric pressure = 760mmHg
- hence, pO2 = 0.21 x 760 = 160 mmHg
partial pressure applies to liquids ( henry’s law)
- solutibilty of gas in liquid is directly proportional to pp of that gas in equilibrium with the liquid (e.g., 4-8mL O2/L of marine and freshwater environments)
gases diffuse from regions of high to low partial pressure

Question 3

explain the respiratory system in fish

Answer 3

> gills
movement of the respiratory medium over the respiratory surface, a process called ventilation, maintains the partial pressure gradients of O2 and CO2 across the gill that are necessary for gas exchange
The arrangement of capillaries in a fish gill allows for countercurrent exchange.
because blood flows in the opposite direction to that of water passing over the gills, at each point in its travel blood is less saturated with O2 than the water it meets
as blood enters the gill capillary, it encounters water that is completing its passage through the gill. Depleted of much of its dissolved oxygen, this water nevertheless has a higher pO2 than the incoming blood, and O2 transfer takes place. As the blood continues its passage, its pO2 steadily increases, but so does that of the fresh, new water it encounters, since each successive position in the blood’s travel corresponds to an earlier position in the water’s passage over the gills. Thus, a partial pressure gradient favouring diffusion of O2 from water to blood exists along the entire length of the capillary.

Question 4

describe the respiration system of insects

Answer 4

> branched internal tubes.
largest tube - trachea, connects to external openings spaced along the insect’s body surface.
air sacs are found near organs that need large supply of oxygen
rings of chitin keep tracheae open, air passes to tracheoles
tracheoles deliver air directly to cells throughout the body.

Question 5

explain the pathway of respiration in humans

Answer 5

> air travels through nasal cavity and pharynx
to larynx, trachea
bronchi to bronchioles
bronchioles end in microscopic alveoli lined by thin moist epithehelium.
branches of the pulmonary arteries convey oxygen poor blood to alveoli
branches of the pulmonary veins transport oxygen-rich blood from the alveoli back to the heart.
huge surface ares for gas exchange:
- 300 million alveoli
- 80-100m2 in humans

Question 6

how do amphibians breath?

Answer 6

> ventilate its lungs by positive pressure breathing

> inflating lungs with forced airflow

Question 7

describe pleural sacs

Answer 7

> forms a double membrane surrounding the lung, similar to a fluid-filled balloon surrounding an air-filled balloon.

Question 8

describe negative pressure breathing

Answer 8

> using muscle contraction to actively expand the thoracic cavity lowers the air pressure in the lungs below that of air outside the body.
Gas flows from regions of high pressure to low pressure, therefore air rushes through nostrils and mouth and down breathing tubes to alveoli.
exhalation:
muscles relax, volume of cavity is reduced, air is forced out again.
inhalation requires energy, exhalation is passive.

Question 9

what is the total lung capacity?

Answer 9

5800mL
Residual volume = 1200mL
expiratory reserve volume = 1100mL
Tidal volume = 500mL
Inspiratory reserve volume = 3000mL

Question 10

describe the homeostatic control of breathing

Answer 10

HOMEOSTASIS:
> blood pH of about 7.4
STIMULUS:
> rising level of CO2 in tissues lowers blood pH (such as when exercising)
CO2 + O2 -> H2CO3 -> H+ + HCO3- -> decreases pH
SENSOR/CONTROL CENTRE:
> cerebrospinal fluid
>medulla oblongata
- medulla detects decrease in pH of cerebrospinal fluid
> sensors in major blood vessels detect decrease in blood pH
- carotid arteries
- aorta
RESPONSE:
> signals from the medulla to rib muscles and diaphragm increase rate and depth of ventilation
> CO2 level decreases, restoring pH to normal.
BACK TO HOMEOSTASIS

Question 11

what are the mechanisms for transport of large quantities of O2 and CO2?

Answer 11

> gases diffuse down pressure gradients
- Fick’s law of diffusion
- depends on differences in partial pressure of gases
respiratory pigments transport gases in blood
- overcome the low solubility of gases in blood
- haemocyanin - arthropods, molluscs
- haemoglobin - many invertebrates, all vertebrates
- increase from 4.5mL of dissolved O2/L blood
to 200mL O2 carried by respiratory pigments/L of blood in mammals
- note: uses 2L O2 per min in intense exercise

Question 12

how is circulation and gas exchange coordinated?

Answer 12

> > gases diffuse down pressure gradients

• Fick’s law of diffusion
• depends on differences in partial pressure of gases
• partial pressure of O2 and CO2 can vary
  
  • in different parts of the circulatory system
  • in inhaled compared to exhaled air

Question 13

what are the partial pressures of O2 and CO2 in inhaled and exhaled air?

Answer 13

INHALED
> pO2 = 160mmHg
>pCO2 = 0.2mmHg
EXHALED
> pO2 = 120mmHg
> PCO2 = 27mmHg

Question 14

state the partical pressures of CO2 and O2 at different stages in the circulatory system

Answer 14

1) inhaled air
- O2 = 160
- CO2 = 0.2
2) alveolar spaces
- O2 = 104
- CO2 = 40
3) pulmonary veins
- O2 = 104
- CO2 = 40
4) systemic arteries
- O2 = 104
- CO2 = 40
5) body tissue
- O2 = 45
6) systemic veins
- O2 = 40
- CO2 = 45
7) pulmonary arteries
- O2 = 40
- CO2 = 45
8) exhaled air
- O2 = 120
- CO2 = 27

Question 15

how does haemoglobin load and unload oxygen?

Answer 15

> positive cooperativity
- depends of cooperativity of between the haemoglobin subunits
- when O2 binds to one subunit, the others change shape slightly, increasing the affinity for O2.
- when four molecules of O2 are bound and one subunit unloads its O2, the other three subunits more readily unload O2, as an associated shape change lowers their affinity for O2.
KNOW DISASSOCIATION CURVES

Question 16

what are the differences between a closed and open circulatory system?

Answer 16

> open = haemolymph surrounding body tissues also acts as the circulatory fluid

• simple, easy to maintain
• less energy/lower pressures

> closed = interstital fluid surrounding body tissues is distinct from blood acting as the circulatory fluid
- higher pressures = increased efficiency for meeting high metabolic demand

Question 17

describe the differences between single and double circulatory systems

Answer 17

Single:
> single circuit of blood flow and single circulatory pump - a heart with two chambers
> bony fishes, rays and sharks
Double:
> two circuits of blood flow and two pumps fused into a multi-chambered heart.
> amphibians - 1 ventricle, 2 atriums
>reptiles - two ventricles and two atriums with incomplete septum = 3 chambered
> mammals and birds - four chambered. 2 atriums an 2 ventricles.

Question 18

describe the path of blood flow in the human heart

Answer 18

1) right ventricle
- semilunar valve
2) pulmonary arteries
3) lungs
4) pulmonary vein
5) left atrium
- AV valve
6) left ventricle
- semilunar valve (tricuspid)
7) aorta
8) capillaries of body
9) superior and inferior vena cava
10) right atrium
- AV valve

Question 19

describe the steps in the cardiac cycle

Answer 19

1) atrial and ventricular diastole
> during relaxation phase, blood returning from the large veins flows into the atria and then into the ventricles through the AV valves
2) Atrial systole and ventricular diastole
> a brief period of atrial contraction that forces all blood remaining in the atria into the ventricles
3) Ventricular systole and atrial diastole
> during the remainder of the cycle, ventricular contraction pumps blood into the large arteries through the semilunar valves

Question 20

describe the different muscle types

Answer 20

> skeletal
- voluntary, striated
> cardiac
- involuntary, striated
> smooth
- gut, bladder, vessels
- non-striated

Question 21

how does the heart maintain rhythm electrically?

Answer 21

> some cardiac muscles are self excitable, meaning they contact without any signal from the nervous system
called pacemaker cells
1) a region of the heart called the sinoatrial node (SA). or pacemaker
- sets the rate and timing at which all cardiac muscle cells contract
pacemaker starts electrical impulse, the atria muscles contract because the impulse has spread quickly through gap junctions to these cells.
2) the impulse then travels to the atrioventricular node (AV)
- the impulses are delayed
3) then the impulses are sent down the bundle of His and then to the purkinje fibres, which cause the ventricles to contract.

Question 22

how does the heart change rhythm physiologically?

Answer 22

> parasympathetic and sympathetic nervous systems act in concert to regulate heart rate.
hormones secreted into the blood also influence the rate of contraction (adrenaline)
body temperature

Question 23

describe the structure of an artery

Answer 23

> endothelium
smooth muscle
connective tissue
thick and strong
accommodating blood at high pressures
elastic recoil that help maintains blood pressure
nervous system and hormones control act on the smooth muscle in arteries and arterioles, dilating or constricting these vessels and thus controlling blood flow to different parts of the body.

Question 24

describe the structure of a vein

Answer 24

>endothelium
> valves
> smooth muscle
> connective tissue
> do not have thick walls
> 1/3 as thick as an artery
> valves maintain unidirectional flow despite low blood pressure

Question 25

describe the structure of capillaries

Answer 25

> endothelium
basal lamina
very thin walls
used so that exchange of molecules in and out of the walls

Question 26

how does skeletal muscle help in returning blood to the heart?

Answer 26

> skeletal muscle contraction squeezes and constricts veins. flaps of tissue within the veins act as one-way valves that keep blood moving only towards the heart.

Question 27

what happens in capillary exchange?

Answer 27

> the critical exchange of substances between the blood and interstitial fluid.
takes place across the thin endothelium walls of the capillaries.
through pores

Question 28

what can be transferred through the capillary wall and how?

Answer 28

> exchangeable proteins are moves across by vesicular transport
small, water-soluble substances pass through the pores
lipid-soluble substances pass through the endothelial cells
plasma proteins generally cannot cross the capillary wall.

Question 29

explain how blood and osmotic pressure control capillary exchange

Answer 29

> the difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end
DIAGRAM
~ 85% of fluid leaving the capillaries re-enters due to osmotic pressure

Question 30

describe how the amount of blood in capillaries can vary

Answer 30

> capillaries in major organs are usually filled to capacity
- but many other sites, the blood supply varies
two mechanisms
- regulate the distribution of blood in capillary beds
- contraction of the smooth muscle layer in the wall of arteriole constricts the vessel
- stops blood from going through every capillary in the capillary bed. digestive tract for example.
Precapillary sphincters
- regulate the passage of blood into capillary beds
- some blood flows directly from arterioles to venules through the thoroughfare channel

Question 31

how is the lymphatic system involved in circulation?

Answer 31

> remaining interstitial fluid is returned to blood via the lymphatic system
also plays an important role in body’s defense mechanisms
1) interstitial fluid bathing the tissues, along with the white blood cells in it, continually enters the lymphatic system.
2) lymphatic vessels return lymph to the blood via two large ducts that drain into veins near shoulders.

Question 32

what are the blood pressure differences in the large arteries compared to the left ventricle?

Answer 32

> systolic pressure is always kept very high in the arteries due to its elasticity
in the left ventricle it reaches the same systolic pressure, but drops very very low in diastolic pressure, unlike the arteries.

Question 33

wha is blood pressure?

Answer 33

> blood pressure:
- is the hydrostatic pressure that blood exerts against the wall of a vessel
systolic pressure:
- is the pressure in the arteries during ventricular systole
- is the highest pressure in the arteries
diastolic pressure:
- is the pressure in the arteries during diastole of the ventricles
- is lower than systolic pressure

Question 34

how do you measure blood pressure?

Answer 34

1) a sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure in an artery. The cuff is inflated until the pressure closes the artery. Pressure now exceeds pressure in the artery.
2) the cuff is allowed to deflate gradually. when the pressure exerted by blood pulses into the forearm, it changes from laminar flow to turbulent flow, generating sounds that can be heard by with the stethoscope. the pressure measured at this point is the systolic pressure.
3) the cuff is allowed to deflate further, just until the blood flows freely through the artery and the sounds below the cuff disappear. the pressure at this point is the diastolic pressure.

Question 35

how is blood pressure regulated?

Answer 35

> blood pressure is determined by cardiac output.
nervous and hormonal stimuli can affect the contraction of smooth muscles in the arterioles
- when smooth muscle contracts (vasoconstriction), the arterioles narrow and upstream blood pressure increases
- when smooth muscle relaxes (vasodilation), the diameter of the arteriole increases and blood pressure falls
- this process allows for the regional control of blood flow

Question 36

what is blood composition of plasma?

Answer 36

PLASMA 55%
> water
- solvent
>ions (blood electrolytes)
- sodium, potassium, calcium, magnesium, chloride, bicarbonate
- osmotic balance, pH buffering and regulation of membrane permeability
> plasma proteins
- albumin, immunoglonulins (antibodies), apolipoproteins, fibrinogen
- cannot leave the capillary
- osmotic balance, pH buffering, defence, lipid transport, clotting
> substances transported by blood
- nutrients
- waste products of metabolism
- respiratory gases
- hormones

Question 37

what are the cellular elements of blood?

Answer 37

> leukocytes (WBC) 
- defence and immunity
- basophils
-lymphocytes
- eosinophilis
- neutrophils
- monocytes
> platelets
- blood clotting
> erythrocytes 
-red blood cells

Question 38

how are red blood cells made?

Answer 38

> there is a reduced oxygen carrying capacity - i.e., less red blood cells
kidney produces erythropoietin
erythropoietin stimulates the development of erythrocytes in bone marrow
these are released and an increase in oxygen carrying capacity is achieved.

Question 39

what happens in blood clotting?

Answer 39

1) the clotting process begins when the endothelium layer of a vessel is damaged, exposing connective tissue in the vessel wall to blood. platelets adhere to the collagen fibres in the connective tissue and release a substance that makes nearby platelets sticky.
2) the platelets form a plug that provides emergency protection against blood loss.
3) this plug is reinforced by a fibrin clot when vessel damage is severe.

Question 40

how is a fibrin clot formed?

Answer 40

> clotting factors released from the clumped platelets or damaged cells mix with clotting factors in the plasma.
forms an enzymatic cascade
converts plasma protein prothrombin to thrombin
thrombin enzyme catalyses fibrinogen to fibrin.
fibrin becomes interwoven into a clot.