Physiology of Respiration Flashcards
- Characteristics of lung circulation
- Arteries:
o The pulmonary a. transfers used blood awaiting for gas exchange, from RV to alveolar capillaries
o For 99% of the blood supply the oxygen deficient blood is responsible, originating from the a. pulmonaris.
o For 1% of the blood supply to the lungs oxygen rich blood originating from the aa. bronchiales is responsible
-Veins:
o Two venous systems lead away blood from the lungs.
o 1% of the blood leaves the lung via bronchial vv. Part of the blood goes to the pulmonary vv, thus mixing fresh blood with venous blood.
o A smaller portion goes directly to the RA via the azygos v.
o 99% of the blood coming out of the lungs is oxygenated, and flows to the LA through vv. pulmonales.
*Contaminated by two types of venous blood: vv. Bronchiales and coronary veins.
- The perfusion of the lungs
Regulation:
-Neural factors:
o Parasympathetic: Acethylcholine release from vagus nerve – dilates the vessels
o Sympathetic: Noradrenic fibers contract the blood vessels (alpha receptor stimulation). Adrenalin relaxes the blood vessels (beta receptors). Mostly alpha-receptors in these vessels.
-Hypoxia (little oxygen):
o Affects the diameter of blood vessels opposite to that in the systemic circulation. (Systemic circulation- vasoconstriction)
o Local hypoxia cause local stenosis (constriction), blood redistribution. From the lesser ventilated part, the blood gets to the better ventilated area.
-Blood pressure:
o Increase results in a decrease of the vascular tone.
o The lung’s ability to achieve an extremely high minute volume in the case of increased physical acitivty without any change in the pressure conditions.
- Gas diffusion in the lungs
-Determined by: Partial pressure relations of the gases, gas permeability of the membranes, and the size of the exchange surface.
-Maintenance of the gas exchange: Continuous and varying oxygen consumption and carbon dioxide production of the organism is essential.
-Partial gas pressure values of the alveolar air are constant.
o pO2 = 100 mmHg
o pCO2 = 40 mmHg
-The result of gas exchange taking place in the alveoli differs from the result of the gas exchange of the total lung.
-During the first 200 msec for both gases, a total exchange takes place, despite that pCO2 is much smaller than pO2.
o The reason for this is that the flow of gases is not only determined by the pressure differences, but also by permeability.
-Most of the total length forms a reserve. Even during strong physical exercise the maximal gas exchange is possible.
- Respiratory tracts
-Separated into upper and lower respiratory tracts.
-Upper:
o Nasal cavity: breathing during rest, also has a role in heat transfer, air conditioning and defense against viruses and bacteria.
o Oral cavity: ventilation and respiration only during incr respiration.
o Pharynx: primarily has a defensive function, thanks to its well-developed lymphatic system.
o Larynx: place of voice formation.
-Lower:
o Trachea: protection, goblet cells.
o Bronchus: protection, goblet cells.
o Terminal bronchiole: no more ciliated epithelium.
o Alveolus: basic unit of breathing, where gas-exchange takes place, the gas-exchange is fast. 4 layers
- Respiratory movements
- Inspiration is an active movement, while expiration is a passive movement.
- Respiration is separated into three movements:
1. Active inspiration: diaphragm has the major role; expanding the inner space of the chest. The lung-sections close to the diaphragm and in the parietal region will dilate and ventilate much better.
2. Passive expiration: driven by the collapsing tendency of the lung (due to the surface tension of the alveoli and the elastic elements of the lungs), returning ribs to normal position. Total collapse is prevented by the adhesional forces, provided by the fluid film between the visceral and parietal pleura.
3. Pause of respiration: chest is in rest, balanced status.
- Panting
- Physiological gas-exchange, it is primarily used for heat exchange (thermoregulation).
- It is separated into parietal and central air flow, where the parietal one is slow and the central one is fast and serves the heat exchange and stimulates water release in the mouth (perspiration).
- Hyperventilation of this manner will cause serious alkalosis in other species, thanks to the loss of CO2.
- Volume changes
- The inspired and expired quantity of air and the volume of it in the lungs can be divided to functional fractions. -These volume fractions fundamentally influence the degree of possible gas exchange.
- Measurement: spirometer.
- Contains two cylinders shifted into each other.
- In the lower cylinder there is liquid where the in- and exhalation is carried out into the inner space of the upper cylinder.
- The height of the upper cylinder indicates the size of the given volume fraction, which can be registered by a chart recording instrument.
- Air fractions
-TLC - Total lung capacity: The total maximum air volume of the lung.
-VT – Volume tidal: Amount of air taken in and out during relaxed insp and exp
-FRC – Functional residual capacity: The total air amount remaining in the lung during pause (apnea).
-IRV – Inspiratory reserve volume: Volume of air that can be forced in after relaxed inspiration.
-ERV – Expiratory reserve volume: Volume of air that can be forces out after relaxed expiration.
-RV – Residual volume: The fraction which cannot be eliminated from the lung even by forced expiration.
-VC – Vital capacity: VC = VT + IRV + ERV.
*The maximal volume changes that can actively be attained.
-FVC – Forced vital capacity: VC related to unit time
-VD - Dead volume: Anatomical and physiological dead space which doesn’t contribute directly to the gas exchange.
*Anatomical dead space: The air fraction of the upper and lower resp tracts, where there is no resp epithelium.
*Physiological dead space: The former area and the areas excluded from respiration, covered by epithelium
-“used air” fraction = FRC + VD: The sum of the amount of air in the dead space plus that proportion of air which earlier took part in the gas exchange
“fresh air” fraction = VT – VD: Takes part in gas exchange (not in dead space)
- Ventilation coefficent
-The deepness of insp incr the proportion of fresh air to the used air already present, and thus improves gas exchange
- Pressure changes during respiration
1) During apnea:
•The intrapulmonary P is equal to the atmospheric P
•In the pleural slit a P smaller than the atmospheric one can be measured.
•The collapsing tendency of the lung an the expanding tendency of the chest maintain a balance.
2) During inspiration: The P of the pleural slit further decr as a result of the active work of the insp muscles, which consequently takes the P in the lung beneath the atmospheric P -> air flows into the lung.
3) During expiration:
•Because of the retractive forces of the lung the intrapulmonary P rises above the atmospheric one.
•Meanwhile the intrapleural P goes back to the standstill value.
-The P changes related to respiration get stronger in case the epiglottis is closed. It has significant physiological role in circulation, rumination, and at defection.
-After the closure of epiglottis during the deep inhalation the intrapulmonary and thoracic P significantly decr.
o The ruminants physiologically utilize this phenomenon during rumination (Müller’s experiment).
- Forced expiration while the epiglottis is closed increases the intrapulmonary and thoracic P.
o In animals this effect appears in the process of defecation (Valsalva’s experiment).
- The respiratory work
•Inspiration & forced expiration need muscle work (energy).
•At inspiration the collapsing tendency of lung (due to surface tension + retractive forces of elastic elements) must be overcome.
•Resistance Forces:
o Friction in the resp. tract
o Non-Elastic tissue resistance: of diaphragm, chest, and abdominal structures
o Total elastic resistance of thoracic cavity: stretch of vertebral- and costal-joints,
retractive forces of the lung
- Compliance
- The ability of a hollow organ to change its volume (dV/dP).
- The compliance is the volume change over unit of pressure change.
- In the case of physical objects the compliance is constant.
- In living tissues, such as the lung it varies continuously during inspiration and expiration, because the thickness of the liquid film containing the surfacactants changes during the breathing cycle
- The transport of oxygen
-Oxygen are bound both chemically and physically in the blood. Main actor is haemoglobin.
→ This amount of oxygen must be forwarded from the lungs to the cells by the oxygen transporting system.
→ If forced physical performance this value can be as high as 6000 ml/minute/100 kg.
→ 1 Hb binds 4 O2, saturation is fast (10 msec). The contact is reversible, depending on the amount of CO2. 1g Hb / 1.34 ml O2
-Factors affecting the hemoglobin saturation:
*Partial P of oxygen is the most important regulator of O2 binding by hemoglobin.
1.pH concentration and temperature
*Incr metabolic rate incr CO2 prod and pCO2 leads to an incr in H+ conc. Incr metabolic rate also incr heat prod
2. Partial pressure CO2
3. 2,3 – diphosphoglycerate: binds to hemoglobin. The affinity for 02 is reduced and the saturation curve is shifted to the right, facilitating the unloading of 02.
- The transport of carbon dioxide
→The CO2 produced by the cells quickly appears in the intravasal (capillary) space due to its high diffusibility, and gets into the RBC.
→The majority is being converted to bicarbonate and enters the plasma. Most important transport process.
→The CO2 is also present in the blood in two alternative forms : physically dissolved and protein bound (carbamino-hemoglobin).
→ H+ ion from water molecule reduces the hemoglobin to deoxyhemoglobin. This binds CO2 and ensures the removal.
→ if hemoglobin is not deoxygenated by tissues, then removal of Co2 is also damaged.
→ The membrane of RBC is impermeable for K+ ions. When bicarbonate leaves, Cl- are transported in by the capnophrine transporter to ensure the elecrochemical gradient. (Hamburger shift)
→ The most important H-acceptor is the deprotonated hemoglobin in the blood cell, and the bicarbonate in the plasma, together creating the “buffer base” of the blood.
→ 20% of the CO2 transported to the lungs are bound to proteins, mostly hemoglobin. CO2 binds to the NH2 part of the protein forming carbamino compounds. It binds more easily to deoxyhemoglobin, so the unloading of oxygen increases the capacity of transporting CO2.
→ 70% of the CO2 are transported as HCO3, bicarbonate. Converted by the carbonic anhydrase.
- The regulation of respiration
-Nuclear arrays are responsible for the different aspects of respiration in the medulla oblongata, and the pons.
-These areas can themselves act like receptors: sense the gas tension of blood, and at the same time, rely on other afferent inputs.
•Pneumotaxic center: Inhib insp
•Apneustic center: Stim the insp center
•Primary inspiration center (DRG): Inhib the center of exp and generates continuous spontaneous insp.
•Secondary expiration center (VRG): Inhib the center of insp.
•Nucleus of phrenic nerve: Gets stimulus from the DRG.
-Afferent nervous factor:
*Both insp and exp stim mechanoreceptors. This represents the most important nervous afferentation.
*Hering-Brower reflex: stretch receptors in the lung stim the exp cells of the VRG, the switch-over cells in the pons, and inhibit the inspiratory cell groups (DRG) via the vagus nerve. As a result of this, the facilitation of the nucleus of the phrenic n. stops expiration sets in.
-Other reflexes: The respiration is influenced by a vast number of afferent signals: Emotion, Hyperventilation caused by movement of limbs, Pain (somatic or visceral), Sleep, Baroreceptor effects
-Efferent nervous factors
*Chemical regulation: Through central and peripheral reception
•Central regulation: Sensitive to pCO2 in blood, cerebrospinal fluid, and pH.
•Peripheral reception: Receptors in glomus caroticum and glomus aorticum. Mostly sensitive to pO2.
-Defensive respiratory reflexes
*Sneezing:
o Provoked by chemical and mechanical irritation of the upper respiratory tract.
o Extensive inspiration -> explosive expiration
o Clears the upper respiratory tract.
-Coughing:
o Reinforced excitement of the tracheo-bronchial area occurs.
o Chemoreceptors can be found in large numbers in both the smaller and larger bronchial segments.
-Nociceptice apnea:
o Prevention of inspiration by gases and fumes harmful to the body.
o Sudden provoked break in breathing (apnea).
o Can also happen because of pain, a sudden cooling of the skin of the back etc.
- Diving reflex:
o The irritation results in a defensive type apnea.
o In young animals and humans it is strongly exposed.
o The danger of aspiration (entrance of water into the lung) decreases.
-Combined swallowing:
o Pause in the breathing related to feeding taking place in the moment when the feed touches the wall of the pharynx.
o Prevents choking (entrance of bite into larynx).
