Ch 42: Circulation and Gas Exchange Flashcards
(156 cards)
1
Q
At which level does the exchange of substances between an animal and its surroundings occur?
A
At the cellular level!
2
Q
What types of substances are exchanged?
A
Resources that animal cells require - nutrients, oxygen - enter the cytoplasm by crossing the plasma membrane.
Metabolic by-products - carbon dioxide - exit the cell by crossing the same membrane.
3
Q
What types of substances are exchanged?
A
Resources that animal cells require - nutrients, oxygen
4
Q
What types of substances are exchanged?
A
Resources that animal cells require - nutrients, oxygen
5
Q
How does exchange in unicellular organisms occur?
A
Directly with the environment.
6
Q
How does each cell of an animal exchange molecules with the environment?
A
In certain invertebrates, by maintaining a body size and shape that keep many or all cells in direct contact with the environment = Direct exchange
In other animals, via a circulatory system that moves fluid between each cell’s immediate surroundings and the tissues where exchange with the environment occurs
7
Q
What places a substantial constraint on the body plant of any animal?
A
The relationship between diffusion time and distance;
Diffusion time is proportional to (distance)^2
= Really slow for longer distances!
8
Q
How does each cell of an animal exchange molecules with the environment?
A
In certain invertebrates, by
9
Q
What is a central gastrovascular cavity?
A
In hydras, jellies, and other cnidarians, the cavity that functions in the distribution of substances throughout the body and in digestion.
An opening at one end connects the cavity to the surrounding water.
Fluid bathes both the inner and outer tissue layers = Facilitated exchange!
Only the cells lining the cavity have direct access to nutrients released by digestion.
Nutrients need diffuse only a short distance, to reach the cells of the outer tissue layer.
10
Q
How does a flat body optimize diffusional exchange?
A
It increases surface area, which minimizes diffusion distances.
11
Q
What are the three basic components of a circulatory system?
A
- Circulatory fluid
- Set of interconnecting vessels
- Muscular pump (heart)
12
Q
What does the heart do?
A
It powers circulation, by using metabolic energy to elevate the hydrostatic pressure of the circulatory fluid, which then flows through the vessels and back to the heart.
13
Q
What are the functions of the circulatory system?
A
- Connecting the aqueous environment of the body cells to the organs that exchange gases
- Absorb nutrients
- Dispose of wastes
14
Q
How do the basic types of circulatory systems vary?
A
- Open/closed
- Number of circuits in the body
- Pumps differing in structure and organization
15
Q
What is an open circulatory system?
A
In which the circulatory fluid bathes the organs directly. Commonly in arthropods and molluscs.
16
Q
What is hemolymph?
A
The circulatory fluid of animals with an open circulatory system, which is also the interstitial fluid that bathes body cells.
17
Q
How does hemolymph move across the circulatory system?
A
Contraction of one or more hearts pumps the hemolymph through the circulatory vessels into interconnected sinuses, spaces surrounding the organs.
Within the sinuses, chemical exchange occurs between the hemolymph and body cells.
Relaxation of the heart draws hemolymph back in through pores, which are equipped with valves that close when the heart contracts.
Body movements help circulate the hemolymph by periodically squeezing the sinuses.
18
Q
What does the open circulatory system of larger crustaceans consist of?
A
A more extensive system of vessels, as well as an accessory pump.
19
Q
What is a closed circulatory system?
A
In which the circulatory fluid, blood, is confined to vessels and is distinct from the interstitial fluid.
20
Q
How does exchange occur in a closed circulatory system?
A
- One or more hearts pump blood into large vessels that branch into smaller ones –> Infiltrates the organs
- Chemical exchange occurs between the blood & interstitial fluid, and the interstitial fluid & body cells.
21
Q
What species have closed circulatory systems?
A
Annelids, cephalopods, all vertebrates
22
Q
What are the advantages of an open circulatory system?
A
- Lower hydrostatic pressures = Less costly in energy expenditure
- Can serve additional functions
23
Q
What are the advantages of a closed circulatory system?
A
- Relatively high blood pressures = Effective delivery and oxygen and nutrients to larger, more active animals
- Suited to regulating the distribution of blood to different organs
24
Q
What is another common name for the closed circulatory system?
A
Cardiovascular system
25
What are the three main types of blood vessels?
- Arteries
- Veins
- Capillaries
26
How does blood flow within each blood vessel?
In only one direction!
27
What are arteries?
Blood vessels carry blood away from the heart, to organs throughout the body.
Arteries within organs branch into smaller arteries (arterioles), that convey blood to the capillaries.
28
What are capillaries?
Microscopic vessels with very thin, porous walls.
29
What are capillary beds?
A network of capillaries that infiltrate every tissue, passing within a few cell diameters of every cell in the body.
30
What is exchanged across the thin walls of capillaries?
Chemicals included dissolved gases, exchanged by diffusion between the blood and the interstitial fluid around the tissue cells.
31
Capillaries converge into _______ at their downstream end.
Venules
32
What are veins?
Venules converge into veins, the vessels that carry blood back to the heart.
33
How are arteries and veins distinguished?
By the DIRECTION of blood flow, not by oxygen content.
34
Arteries carry blood from the heart _______ capillaries, while veins return blood to the heart ______ capillaries.
Toward; From
35
How many muscular chambers do the hearts of vertebrates contain?
At least two!
36
What are atria? What are ventricles?
Atria are the chambers that receive the blood entering the heart;
Ventricles are the chambers that pump blood out of the heart.
37
What is single circulation?
An arrangement in which the blood passes through the heart once in each complete circuit, seen in fish.
38
How does single circulation work in fish?
Blood collects in the atrium --> Enters the ventricle.
The ventricle contracts --> Pumps blood to the arteries leading to the gills.
The gill capillaries diffuse oxygen to the blood, as carbon dioxide leaves the blood.
Blood travels to the rest of the body from the gills --> Releasing oxygen before the blood returns to the heart.
39
What are the disadvantages of a single circuit in fish?
- Blood pressure drops passing through the gill capillaries = Reduced efficiency of the circulation
- Heart is forced to rely upon deoxygenated blood for its own metabolic needs
40
What is a double circulation system?
In which blood moving between the heart and the rest of the body - SYSTEMIC CIRCUIT - is separated from the blood travelling between the heart and the respiratory surface - PULMONARY CIRCUIT.
41
What is a pulmocutaneous circuit?
Incomplete separation of systemic and pulmonary circuits.
In frogs and other amphibians, who have a heart with three chambers - two atria and one ventricle.
The right atrium collects blood from the body;
The left atrium collects blood from respiratory surfaces.
Both atria empty into a single ventricle, with a ridge within the ventricle separating the two flows of blood.
The animals respire through lungs and skin --> Can control the relative amount of blood flowing.
42
Which species have four-chambered hearts?
Mammals and birds - two atria, two ventricles.
Left side of heart: Receives and pumps oxygen-rich blood
Right side of heart: Receives and pumps oxygen-poor blood.
43
What are the advantages of four-chambered hearts?
-Separate systemic and pulmonary circuits = Independent regulation of blood pressure in the two circuits = Powerful!
44
How does the mammalian cardiovascular system work?
1. Contraction of the right ventricle pumps blood to the lungs via the pulmonary arteries;
2. Blood flows through capillary beds in the left and right lungs, loading oxygen and unloading carbon dioxide;
3. Oxygen-rich blood returns from the lungs via the pulmonary veins, to the left atrium of the heart;
4. Oxygen-rich blood flows into the heart's left ventricle, pumping oxygen-rich blood out to body tissues, through the systemic circuit.
5. Blood leaves the left ventricle via the aorta, conveying blood to the arteries, throughout the body.
a. Aorta --> Coronary arteries, supplying blood to the heart muscle;
b. Aorta --> Capillary beds in the head and arms;
c. Aorta --> Abdomen, supplying oxygen-rich blood to arteries leading to capillary beds in the abdominal organs and legs: oxygen from the blood into the tissues, carbon dioxide into the blood.
6. Capillaries rejoin, forming venules, conveying blood to veins.
7. Oxygen-poor blood from the head, neck, and forelimbs is channelled into a large vein - superior vena cava.
8. The inferior vena cava - another large vein - drains blood from the trunk and hind limbs.
9. The two vena cava empty their blood into the right atrium: oxygen-poor blood flows into the right ventricle.
45
The dual circuits operate ________ in a mammalian cardiovascular system.
Simultaneously
46
What is the mammalian heart consisted of?
Mostly cardiac muscle
47
What are the characteristics of the heart's components?
Two atria: Relatively thin walls, serve as collection chambers for blood returning to the heart from lungs/other body tissues.
Two ventricles: Thicker walls, contract much more forcefully than the atria.
48
Where does the blood that enters the atria flow into?
The ventricles, while all heart chambers are relaxed (mostly).
The remainder is transferred by contraction of the atria before the ventricles begin to contract.
49
What is a characteristic of the left ventricle?
It pumps blood to all body organs through the systemic circuit, thus contracting with greater force.
50
The left and right ventricles pump _______ volumes of blood during each contraction.
Equal
51
What is the cardiac cycle?
One complete sequence of pumping and filling of the heart.
52
When do the chambers fill with blood?
When the heart relaxes.
53
What are the two phases of the cardiac cycle?
1. Systole: Contraction phase
| 2. Diastole: Relaxation phase
54
What is the cardiac output?
The volume of blood each ventricle pumps per minute, determined by...
- HEART RATE (rate of contraction)
- STROKE VOLUME (amount of blood pumped/contraction).
55
What is the function of the heart valves?
To prevent backflow, keep blood moving in the correct direction.
56
What are the characteristics of heart valves?
- Made of flaps of connective tissue
| - Open when pushed from one side, close when pushed from the other
57
What is an atrioventricular (AV) valve?
Lies between each atrium and ventricle.
Anchored by strong fibres that prevent them from turning inside out.
Pressure generated by the ventricles' powerful contraction closes the AV valve --> Blood flows back into the atria.
58
What are the semilunar valves?
Located at the two exists of the heart...
- Where the aorta leaves the left ventricle;
- Where the pulmonary artery leaves the right ventricle
Pushed open by the pressure generated during ventricle contraction.
When ventricles relax, blood pressure built up in the aorta closes the semilunar valves, preventing backflow.
59
Some cardiac muscle cells are __________.
Autorhythmic: They contract and relax repeatedly without any signal from the nervous system.
60
How are the contractions of the cardiac muscle cells coordinated?
The sinoatrial (SA) node, "pacemaker", is a cluster of cells that sets the rate and timing at which all cardiac muscle cells contract.
61
How does the SA node work?
It produces electrical impulses, which spread rapidly to the cardiac muscle cells.
1. Impulses spread rapidly through walls of atria --> Atria contract in unison
2. Impulses reach other autorhythmic cells located in the wall between the left and right atria. These cells form a relay point, the atrioventricular (AV) node.
a. This impulse delay allows the atria to completely empty, before the ventricles contract.
3. Signals from the AV node --> Heart apex --> Ventricular walls, thanks to bundle branches and Purkinje fibres.
These impulses generate currents that are conducted to the skin, via body fluids.
62
What is an electrocardiogram (ECG)
In which the SA node currents are recorded by electrodes placed on the skin.
63
What regulates the pacemaker function of the SA node?
Physiological cues.
- Nervous system: Sympathetic (speeds up) and parasympathetic (slows down) divisions.
- Hormones secreted into the blood: Epinephrine = 'Fight-or-flight'
- Body temperature
64
What is endothelium?
A single layer of flattened epithelial cells, lining the central lumen (cavity) of blood cells.
Its smooth surface minimizes resistance to the flow of blood.
65
What surrounds the endothelium?
Layers of tissue, that differ in capillaries, arteries, veins = Specialized vessel functions
66
Capillaries: Structural organization
- Smallest blood cells: Diameter = That of red blood cell
- Thin walls: Endothelium + its basal lamina
- -> Facilitates the exchange of substances between the blood in capillaries and the interstitial fluid.
67
Arteries: Structural organization
- Two layers of tissue surrounding the endothelium:
a. Outer layer of connective tissue containing elastic fibres --> Vessels can stretch and recoil
b. Middle layer containing smooth muscle and more elastic fibres.
- Thick and strong walls: Blood pumped at high pressure by the heart
- Walls have an elastic recoil, that helps them maintain blood pressure and flow to capillaries when the heart relaxes between contractions
68
What controls the blood flow to different parts of the body?
Signals from the nervous system and hormones = Smooth muscle in arteries and arterioles --> DIlation, constriction
69
Veins: Structural organization
- Two layers of tissue surrounding the endothelium:
a. Outer layer of connective tissue containing elastic fibres --> Vessels can stretch and recoil
b. Middle layer containing smooth muscle and more elastic fibres.
- They don't have thick walls (1/3 that of an artery)
- Valves inside the veins maintain a uni-directional blood flow, despite low pressure.
70
Blood _____ as it moves from arteries to arterioles, to the much narrower capillaries. Why?
There are MANY capillaries.
Each artery conveys blood to so many capillaries, that the total cross-sectional area is much greater in capillary beds!
= Dramatic velocity decrease, from the arteries to the capillaries.
71
Why is the reduced velocity of blood flow in capillaries essential to the function of the circulatory system?
The exchange of substances b/w blood and interstitial fluid occurs ONLY in capillaries --> Thin walls permitting this transfer.
Slower flow = Time for exchange to occur
72
After passing through the capillaries, the blood speeds up as it enters the venules and veins. Why?
They have smaller TOTAL cross-sectional areas than the capillaries.
73
Blood flows from areas of _______ pressure to _______ pressure.
Higher; lower
74
What generates blood pressure?
Contraction of a heart ventricle = Force in all directions
- Lengthwise in an artery: Blood flows away from the heart
- Against the elastic wall of an artery = Stretches the wall
- Arterioles and capillaries = Resistance to flow
75
Where is the site of highest pressure?
The heart
76
What dissipates the pressure generated by the pumping heart?
The narrow diameter of the arterioles and capillaries.
77
What is systolic pressure?
When arterial blood pressure is highest, being when the heart contracts during ventricular systole.
Caused by the powerful contractions of the ventricles, stretching the arteries.
78
What is a pulse?
The rhythmic bulging of the artery walls with each heartbeat.
79
What causes the surge in blood pressure?
The narrow openings of arterioles, impeding the exit of blood from the arteries = Stretching of the vessels
80
What is diastolic pressure?
Occurs when the ventricles are relaxed, and the elastic walls of the arteries snap back.
81
How does blood continuously flow into arterioles and capillaries?
Not all blood flows into the arterioles (relieve arterial pressure) before the heart contracts again.
82
What is vasoconstriction?
Physical/emotional stress triggers nervous and hormonal responses, causing muscles in arteriole walls to contract, and the arterioles to narrow.
This narrowing increases BP upstream in the arteries.
83
What is vasodilation?
The arterioles react when the smooth muscles relax. This increase in diameter causes blood pressure to fall.
84
What allows for a greater flow of oxygen-rich blood to the muscles during heavy exercise?
The arterioles in working muscles dilate
85
What is the role of cardiac output in maintaining blood pressure?
Changes in cardiac output affect blood pressure.
86
What is the effect of gravity on blood pressure?
As we pump blood against gravity! It is challenging to make the return upwards.
87
How much of the body's capillaries have blood flowing through them at any given time?
5%-10%, since blood supply is diverted from one destination to another, depending on needs.
88
How is blood flow in capillary beds altered?
1. Contraction of the smooth muscle in the wall of an arteriole, reducing the vessel's diameter, decreasing blood flow to adjoining capillary beds.
2. Precapillary sphincters: Rings of smooth muscle located at the entrance to capillary beds.
The signals regulating blood flow include nerve impulses, hormones in the bloodstream, chemicals produced locally.
89
What two opposing forces control the movement of fluid between the capillaries and the surrounding tissues?
Blood pressure tends to drive fluid out of the capillaries;
Blood proteins pull fluid back
90
How do small molecules move through the capillary wall?
Through the microscopic pores, or...
| Across the endothelial cells by diffusion.
91
How do blood proteins move between the capillaries and the surrounding tissues?
They don't! They remain in the capillaries and are responsible for the blood's osmotic pressure.
92
There is usually a ________ of fluid from capillaries.
Net loss, since blood pressure typically exceeds osmotic pressure.
93
How do lost fluid and lost proteins return to the blood?
Via the lymphatic system, which includes a network of tiny vessels intermingled among capillaries of the cardiovascular system = Diffusion
94
What is lymph?
The fluid lost by capillaries, with its composition about the same as that of interstitial fluid.
95
Where does the lymphatic system drain into?
Large veins of the circulatory system at the base of the neck.
96
What is a similarity between lymph vessels and veins?
They have valves that prevent the backflow of fluid.
97
What do disruptions in the movement of lymph cause?
Edema: Swelling resulting from excessive accumulation of fluid in tissues
98
What are lymph nodes?
Organs along a lymph vessel, that filter the lymph and house cells that attack viruses and bacteria = Body's defence
99
Why do lymph nodes become swollen and tender?
The white blood cells that fill the lymph nodes multiply rapidly when the body fights an infection.
100
What is plasma?
The liquid in which vertebrate blood, a tissue consisting of cells, is suspended in
101
Plasma constituent: Water
Solvent for carrying other substances
102
What occupies 45% of the volume of blood? What about the other part?
```
Cellular elements (cells, cell fragments) = 45%
Remainder - Plasma
```
103
Plasma constituent: Ions (blood electrolytes)
Osmotic balance, pH buffering, regulation of membrane permeability
104
Plasma constituent: Proteins (Albumin, Fibrinogen, Immunoglobulins (antibodies))
Albumin = Osmotic balance, pH buffering
Fibrinogen = Clotting
Immunoglobulins = Defence
105
Plasma constituent: Substances transported by the blood
- Nutrients
- Waste products of metabolism
- Respiratory gases
- Hormones
106
Cellular elements: Leukocytes (white blood cells)
Defence and immunity - Fight infections!
107
Cellular elements: Platelets
Fragments of cells that are involved in the clotting process, serving both structural and molecular functions.
108
Cellular elements: Erythrocytes (red blood cells)
In large quantity! Transports oxygen as their main function.
Small discs that are thinner in the centre than at ages = Increased surface area = Enhanced rate of diffusion of oxygen across their plasma membranes.
Mature mammalian erythrocytes lack nuclei and mitochondria.
109
What is hemoglobin?
The iron-containing protein within erythrocytes transports oxygen.
Each molecule of hemoglobin binds up to four molecules of oxygen.
110
How do erythrocytes generate their ATP?
By anaerobic metabolism.
111
What is sickle-cell disease?
In which an abnormal form of hemoglobin polymerized into aggregates, with the concentration of hemoglobin becoming so high that the erythrocytes become an elongated, curved shape = Impaired function of the circulatory system.
112
How does blood clotting work?
A break in a blood vessel wall exposes proteins that attract platelets and initiate coagulation: Liquid components of blood --> Solid clot
113
What is fibrinogen?
Inactive form, in which the coagulant/sealant circulates.
114
What is thrombin?
An enzyme that converts fibrinogen to fibrin, triggered by the signals sent by platelets.
115
What is hemophilia?
A disease characterized by excessive bleeding and bruising from even minor cuts and bumps.
116
What is a thrombus?
A clot forming within a blood vessel, blocking the flow of blood.
117
What is the role of stem cells?
They replenish the body's blood cell populations, developing erythrocytes, leukocytes, platelets.
118
Why are stem cells named multipotent?
They have the ability to form multiple types of cells.
119
What is gas exchange?
The uptake of molecular oxygen from the environment and the discharge of carbon dioxide to the environment.
120
How does gas exchange take place?
Entirely by diffusion, across moist respiratory surfaces.
121
What is the rate of diffusion proportional and inversely proportional to?
Proportional to the surface area across which it occurs;
Inversely proportional to the (distance)^2 through which molecules must move
122
When is gas exchange fast?
- Large area for diffusion
| - Short path for diffusion
123
The respiratory surface must remain...
Moist!
124
What are gills?
OUTFOLDINGS of the body surface that are suspended in the water.
They have a total surface area much greater than the rest of the body's exterior.
125
What is ventilation?
Movement of the respiratory medium over the respiration surface, maintaining the partial pressure gradients of oxygen and carbon dioxide across the gill --> Necessary for gas exchange.
126
What is countercurrent exchange?
The exchange of a substance/heat between two fluids flowing in opposite directions, thanks to the arrangement of capillaries in a fish.
127
How do fish ventilate?
Continuously pump water through its mouth and over gill arches, using coordinated movements of the jaws and operculum (gill cover).
128
What is the tracheal system of insects?
System made up of air tubes that branch throughout the body.
The largest tubes - trachae - open to the outside.
The finest branches extend close to the surface of every cell = Gas exchange by diffusion, across the moist epithelium lining the tips of the tracheal branches
129
What are lungs?
Localized respiratory organs (vs tracheal systems branching throughout the insect body).
INFOLDING of the body surface, subdivided into numerous pockets.
The gap between the respiratory surface of a lung and other body parts is bridged by the circulatory system --> Gas exchange
130
How does the mammalian respiratory system work?
1. Air enters through the nostrils, is filtered by hairs
2. Air flows through maze of spaces in the nasal cavity
3. Nasal cavity intersects with the pharynx: Paths for air and food cross
4. The larynx (upper respiratory tract) moves upwards when food is swallowed, tipping the epiglottis over the glottis.
5. Food goes down the esophagus to the stomach.
131
Where does gas exchange in mammals occur?
In alveoli, air sacs clustered at the tips of the tiniest bronchioles.
132
What is breathing?
The process that ventilates lung, with an alternating inhalation and exhalation of air.
133
What is positive pressure breathing?
Inflation of the lungs with forced airflow, seen in amphibians.
134
Why do the ventilation features in bird make the breathing system highly efficient?
- They pass air over the gas surface in ONE direction
| - Incoming fresh air does not mix with air that has already carried out gas exchange
135
How do mammals breathe?
They employ negative pressure breathing, pulling (not pushing) air into their lungs.
Changing the air pressure within its lungs relative to the pressure of the outside.
Rib cage expands as rib muscles contract, and vise versa.
136
What is breathing regulated by?
Involuntary mechanisms, ensuring that gas exchange is coordinated with blood circulation and metabolic demand.
137
Where are the neurons regulating breath located?
In the medulla oblongata, near the base of the brain.
'Breathing control centres' that establish the breathing rhythm.
138
How does the medulla measure blood CO2 concentration in regular breathing?
The pH of the surrounding tissue!
139
Breathing control is only effective if...
Ventilation is matched to blood flow through alveolar capillaries.
140
Alveolar capillaries: Carbon dioxide diffuses down its partial pressure gradient, from ______ to __________.
From the blood, to the air in the alveoli.
141
Alveolar capillaries: How does oxygen circulate?
Oxygen in the air dissolves in the fluid coating the alveolar epithelium, and diffuses into the blood.
142
Tissue capillaries: Gas exchange
Diffusion of oxygen OUT of the blood, carbon dioxide INTO the blood.
The gradients of partial pressure exist because cellular respiration removes oxygen from, and adds carbon dioxide to, the surrounding interstitial fluid.
143
What poses a problem for animals that rely on the circulatory system to deliver oxygen?
The low solubility of water in water, and thus in blood.
144
How do animals transport most of their oxygen?
While bound to RESPIRATORY PIGMENTS, proteins circulating with the blood/hemolymph, and often contained within specialized cells.
145
What is the function of respiratory pigments?
They greatly increase the amount of oxygen that can be carried in the circulatory fluid.
146
Which respiratory pigment is most common in animals?
HEMOGLOBIN!
147
What is the hemoglobin structure?
- Four subunits: Polypeptide chains
- Each subunit has a cofactor: Heme group
- Each heme group has an iron atom at its centre
- Each iron atom binds to one molecule of oxygen
148
How many molecules of oxygen can a hemoglobin molecule carry?
Four (4)
149
What is the cooperativity seen between the hemoglobin units?
When oxygen binds to one subunit, the others change in shape, increasing their affinity for oxygen.
150
Hemoglobin binds oxygen _________.
Reversibly - it can bind or unload!
151
What happens when four oxygen are bound to hemoglobin, and one unit unloads its oxygen?
The other three subunits more readily unload oxygen --> Associated shape change lowers their affinity for oxygen.
152
What promotes the unloading of oxygen by hemoglobin in active tissues?
The production of carbon dioxide during cellular respiration.
153
What is the Bohr shift?
An effect by which low pH decreases the affinity of hemoglobin for oxygen --> Where carbon dioxide production is greater.
154
What is the effect of temperature in oxygen affinity?
High temperature causes a reduction in oxygen activity, favouring unloading.
155
What adaptation of diving mammals allow them to stay for such prolonged times underwater?
They can store large amounts of oxygen!
156
What is myoglobin?
An oxygen-storing protein in the muscles of diving mammals.
