Chapter 47: Respiratory System Flashcards
What are gas exchange systems made up of?
1) Specialized body surfaces where gases are exchanged
2) Ventilation mechanisms (move air/water over environmental side of body surfaces)
3) Perfusion/Circulation mechanisms (for ECF on internal side)
What is diffusion?
Means of gas exchange in which molecules move from areas of high concentration to low concentration
- can occur in water or air
Describe the relationship between gas molecules and pressure.
Gas molecules increase, pressure increases
What is partial pressure? Provide an example.
Concentrations of different gases in a mixture.
Ex: At sea level the atmospheric pressure is 760 mmHg
What does the amount of gas in a liquid depend on?
1) Partial pressure of gas
2) Solubility of gas
*For gases in solution, concentration is not equal to partial pressure, but partial pressure drives diffusion
Is O2 content higher in air or water?
Does O2 diffuse faster in air or water?
Is more energy needed to move water or air over a gas exchange surface?
Air
Air
Water
How does slow diffusion of O2 affect air and water breathing animals? Provide examples.
- Animal cells with low metabolic rates can’t function even a few millimeters away from O2 source in water
- Size and shape limits are present in invertebrates that lack internal systems to distribute O2
Ex:
1) Marine Flatworms: flat, thin body with large external surface area
2) Sponges: bodies made of cells surrounding water channels through which external mediums flow
How does increasing temperature affect terrestrial animals vs aquatic animals?
Terrestrial animals: No effect
Aquatic Animals:
- most are ectotherms (get heat from surrounding environment)
- body temperature and metabolic rate are correlated with water temperature
- more O2 is needed in warmer water but warmer water holds less dissolved O2 which creates respiratory problems
Describe the solubility of oxygen when compared with temperature?
Oxygen is more soluble at lower temperatures and less soluble at higher temperatures.
How does altitude affect partial pressure?
Higher altitude = lower partial pressure O2 meaning less oxygen available
- Amount of gas/volume decreases
- Mt. Everest is about 1/3 partial pressure of sea level
How does CO2 interact with air-breathing animals?
- CO2 diffuses out as O2 diffuses in (rate of diffusion depends on partial pressure of gases)
- For air-breathing animals, partial pressure of CO2 from the body –> environment is large
- CO2 is very water-soluble and easy for aquatic animals to exchange (causes less problems for aquatic animals than not having O2)
What is hypocapnia?
A state of reduced CO2 in the blood usually from hyperventilation
What is breathing and cellular respiration?
What’s the formula for cellular respiration?
Breathing: exchange of gases (O2 and CO2)
Cellular Respiration: obtaining energy by oxidizing food molecules
Glucose + 6O2 + 6H2O = 6CO2 + 12H2O + energy (ATP)
How does oxygen affect the brain?
Brain is very sensitive to oxygen levels, low anaerobic metabolism
- 4-5 min without oxygen = brain damage
What are the bends and how does it occur?
Decompression sickness in scuba divers
1) Scuba divers breath through a regulator that equalizes air pressure in lungs to pressure of water on body
2) At depth, partial pressure of N2 is high and it diffuses from lungs into tissues via blood
3) If a diver comes up too fast, N2 comes out of solution in tissues and blocks blood vessels which lead to pain or death
How does air travel in the human respiratory system?
1) Air enters lung from mouth or nose which join in the pharynx
2) Below the pharynx, the trachea leads to the lungs
3) Trachea branches into 2 bronchi (right and left), then into bronchioles, and then alveoli (gas exchange sites)
What do alveoli do and how many are present in the human body?
Alveoli = sites of gas exchange
300 million alveoli in EACH lung (600M total)
- surface area of alveoli is about 70m^2
How do capillaries help alveoli?
- alveoli have thin walls surrounded by capillaries, diffusion path between blood and air is less than 2 micrometers
What are common diseases that take place in bronchioles and alveoli and how are they caused?
1) Emphysema: inflammation damages and destroys alveoli walls
- caused by smoking/air pollution
- 3rd leading cause of death in US
What do mammalian lungs secrete that help with ventilation? How does that help?
Mucus and surfactant
- Mucus is secreted by cells lining airways to trap dirt and microorganisms
- Other cells have cilia beating constantly to sweep mucus and other dirt up to pharynx where it is swallowed or spit out (ex: Cigarette smoke paralyzes cilia and you cough to clear the mucus since your mucus elevator is broken)
What is surfactant and how does it work?
Surfactant = fatty, detergent-like substance that reduces surface tension of a liquid and lowers work needed to inflate lungs
How does surface tension work in lungs?
Surface tension gives the surface of a liquid the properties of an elastic membrane
- results from attraction between water molecules
- fluid covering the inside of alveoli has surface tension to make the lungs elastic
What is the anatomy of the breathing organs?
- Lungs are in the thoracic cavity which have a diaphragm at the bottom and pleural membranes covering each lung
- Pleural space (thin, moist, slippery) contains fluid to help membranes slide past each other during breathing
How does inhalation (active process) work?
- A larger chest cavity is created by contracting 2 muscles
1) Diaphragm: pulls down on thoracic cavity and pleural membranes
2) Intercostal muscles: muscles between ribs;
a) External intercoastal muscles: lift ribs up and outward to expand thoracic cavity
Since air pressure outside is higher than in the lungs, the oxygen moves from environment –> lungs
How does expiration (passive process) work?
- Diaphragm and intercoastal muscles relax
1) Diaphragm: pulls up via elastic recoil
2) Intercostal Muscles: decrease volume by pushing ribs down and inward
a) Internal Intercostal Muscles: pull ribs down and inward to decrease thoracic cavity
How does the pressure of the alveoli and pleural space compare with the external environment
Intra-alveolar pressure is the same as atmospheric pressure.
Interpleural pressure is still negative to keep lungs from collapsing.
(Inhalation causes interpleural pressure to become negative which causes intra-alveolar pressure to become negative to pull air into lungs)
What happens to the pleural membranes when the thoracic cavity expands?
Increases the tension between them
What happens when you have collapsed lung?
A punctured thoracic cavity can lead to collapsed lung as air can leak into the space between pleural membranes and cause lung to deflate.
- Air is pulled between pleural membranes and alveoli aren’t ventilated
How does oxygen exchange occur?
Oxygen exchange occurs across a concentration gradient.
Lungs –> blood –> tissues
As a tissue gets depleted, more O2 is released there.
What is hemoglobin and what is it made of?
Hemoglobin = a red blood cell protein that transports O2 (increases the capacity of blood to carry more O2, making higher rates of metabolism possible)
- 4 peptide chains containing 1 heme
Heme = Fe which binds O2 - each hemoglobin can carry 4O2 molecules
- affinity for O2 changes with binding of O2
How does carbon monoxide affect Hgb? What is CO produced from?
CO is made from an incomplete combustion of fuels.
CO binds to Hgb with 240x higher affinity than O2 which prevents Hgb from transporting O2
~ 500 deaths/year from CO poisioning
What is positive cooperativity and how does it work?
Positive cooperativity refers to high oxygen affinity
O2 is picked up where partial pressure is high and released where partial pressure is low.
Low partial pressure of O2 changes the hemoglobin structure making it easier for other subunits to bind to hemoglobin.
How is hemoglobin distributed to the body?
- Hgb leaving lungs is 100% saturated (4 O2 molecules) and only tends to drop 1 O2 molecule as it circulates throughout the body (75% saturated when it returns to lungs)
**When tissue is starved of O2 and partial pressure of O2 is below 40 mmHg, small decreases in the partial pressure of O2 release lots of O2 in tissues
What is myoglobin and how does it function?
Myoglobin = O2-binding molecule in muscle cells; single polypeptide molecule (can only bind 1 O2 molecule)
- has a higher affinity for O2 than Hgb and binds it at low partial pressure O2 values when Hgb molecules release their O2
- provides reserves for when metabolic demands are high and blood flow is interrupted
What is the functional different between fetal and adult Hgb?
Fetal Hgb has a higher affinity for O2 than adult Hgb which facilitates O2 transfer in placenta
- lower affinity for O2 causes high metabolism and lowers pH of blood
- low O2 level increase BPG (bisphosphoglyceric acid)
What factors affect Hgb Oxygen Affinity?
1) Concentration of O2 in blood plasma
2) Hemoglobin consumption
a) Normal adult: 2 alpha and 2 beta chains
b) Fetus: 2 alpha and 2 gamma chains (fetus gets O2 from adult Hgb via blood)
3) Blood pH (Bohr effect)
- as blood passes through metabolically active/exercising muscle, it picks up metabolites and blood pH lowers and is more acidic
4) Presence of 2,3-BPG + Hgb (deoxygenated) lowers its affinity for O2 and more O2 is released to tissues
*#4 is higher in pregnant women, elevated altitudes, and active people
Why does blood carry CO2 away from tissues?
CO2 is:
1) highly soluble in blood
2) readily diffuses in plasma
3) mostly converted into bicarbonate ions (HCO3-)
What does carbonic anhydrase do?
CO2 from tissues is transported to lungs in the form of HCO3- and then converted back to CO2 to be exhaled.
CO2 dissolves in water to form H2CO3 which dissociates to make HCO3-.
CO2 + H2O <–> H2CO3 <—> H+ + HCO3-
The reaction among CO2 and H2O is typically slow in the ECF but in endothelial cells and RBCs carbonic anhydrase speeds up the conversion of CO2 –> H2CO3
- Carbonic anhydrase reduces partial pressure of CO2 and helps with diffusion from tissue –> endothelial cells
**Carbonic anhydrase only speeds up the reversible reaction, it does NOT determine direction
What happens when CO2 binds with Hgb?
- In the lungs, the conversion reaction is reversed, CO2 diffuses from the blood into the alveoli and is exhaled
How does carbon dioxide exchange occur?
- It is exchanged across a concentration gradient
tissues –> blood –> lungs
Transported 3 ways:
1) 20% hemoglobin
2) 5% transported in plasma as CO2
3) 75% is transported as bicarbonate (HCO3-)
How is breathing regulated?
- Breathing is controlled by neural circuits in brainstem (involuntary process of CNS)
Phrenic nerve = axons of respiratory motor neurons in medulla
- innervates diaphragm and starts inhalation and controls rhythmic inspiration and expiration
- includes the pons (controls medulla inspiration center)
Chemoreceptors in brainstem sense H+ concentration
**Higher brain areas modify breathing to accommodate speech, eating, coughing, and emotional states
How is partial pressure of CO2 sensed?
Partial pressure of CO2 is the primary metabolic feedback for breathing in mammals
- Small rise in arterial partial pressure CO2 causes a large increase in ventilation
**Different from water-respiring animals as O2 is the primary feedback stimulus for gill ventilation
Ventral surface of the medulla is sensitive to partial pressure of CO2,
How is partial pressure of O2 monitored?
1) Carotid bodies
2) Aortic bodies in blood vessels leaving the heart
- When partial pressure of O2 or blood supply falls, chemoreceptors send nerve impulses to the brain stem to stimulate breathing.
What are inspiratory and expiratory reserve volumes?
Additional amounts of air that we can forcefully inhale or exhale
- Vital capacity (VC) = Tidal volume (TV) + IRV + ERV
*Athletes have a high VC and VC decreases with age because lung tissue stiffens
What is residual volume?
Air that cannot be expelled from lungs
- can be measured using the helium dilution method:
a) a person breathes from a reservoir of a known volume of air with a known volume of helium in it, since helium isn’t absorbed the initial and final volumes are the same
Functional residual volume (FRV):
FRV = ERV + RV
How do you measure lung ventilation?
- Fresh air breathed in at rest is diluted by air remaining in lungs so partial pressure of O2 in lungs is lower than in the atmosphere
- RV contributes to FRV and dilution of O2 in inhaled air
- Diseases that increase RV (like emphysema) impact respiratory ability in a detrimental way
