LSM3212_Lecture 10 Resp2

8/3/2019 LSM3212_Lecture 10 Resp2

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Respiratory System (II):LSM 3212

Gas Exchange

Gas Transport

Control of Breathing


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Basis of Gas Laws

Boyles LawDaltons LawHenrys Law

Implication in Respiratory Physiology


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Recall: Breathing

P 1/V (Boyles Law)


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What is Partial Pressure?The pressure exerted by each type of gas, and it isdirectly proportional to its % in a total air mixture

Ptotal= PN2+ PO2 + PCO2+ PN (Daltons Law)

Partial Pressures of Atmospheric Gases (N2 80%; O2 20%)

Sea Level vs. Underwater


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Partial Pressures of Gasesin the Alveoli

Expired air?


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The questions to ask before climbing Mt. Everest (8,800 m):

Up there

What happens to the atmospheric (barometric) pressure?

What is % of O2 in the atmospheric air?

What is the inspired PO2?

What is the alveolar PO2?

Effects of Height

Alveolar Gas Equation:

PAO2 = PIO2 - PACO2/R

= FIO2 (PB - 47) - 1.2(PaCO2)

A: alveolar; I: InspiredF: fraction (%); B: barometricH2O pressure: 47mmHg at 37C

R: respiratory gas exchange ratio (VCO2/VO2)


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Partial Pressures of Gasesin the Blood

Henrys Law: relates gas solubilitytogas partial pressure&temperature

CO2 = very soluble

O2 = 1/20 as soluble as CO2

N2 = virtually insoluble, except

[Gas] dissolved in a fluid depends directly on its partial pressurein a gas mixture

A

PO2 = 100 mmHg PO2 = 40 mmHg

B

Which container will have more O2 in solution?


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O2 Transportin the Blood

Carried in two ways:dissolved in plasma ~1.5%

bound to hemoglobin (Hb) ~98.5%

depends on the partial pressure of oxygen (PO2)

What would happen if there is no Hb in the blood?RBCs

Antarctic Icefish

No Hb!Hb


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O2-HbSaturation Curve

- depends on blood PO2- PO2> 60mmHg (plateau)- PO2< 40mmHg (steep region),O2 release significantly at

tissue level- what is PO2 at tissue levelduring exercise?

What is the physiological

significance of plateau andsteep region, respectively?


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Effects of PCO2 (pH) & Temperatureon O2-Hb Saturation Curve

In an exercising muscle, curve shifts to left orright? why?

Bohr effectP50P50

5050


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Effect of 2,3-DPG onO2-Hb Curve

What is DPG?- 2,3-diphosphoglycerate, by-productof RBC glycolysis- bind with Hb reversibly, thus reduceHbs affinity for O2-like pH & temperature do on thecurve

What is the physiological roleof 2,3-DPG?


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Pigment Types Hb vs. Myoglobin

where is myoglobin?

structure?

O2 affinity?

O2-poor environment in fetus:

Mt. Everest in utero

low PaO2 (~30 mmHg)

physiological adaptation offetus? compared to: adults

high altitude mammals

Myoglobin

HbF HbA


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CO2 Transport in the Blood

dissolved in plasma ~10%

bound to Hb (HbCO2) ~30%

as bicarbonate (HCO3-) ~60%

carbonic anhydrase (in RBCs)

CO2+ H2O H2CO3 HCO3- + H+

carbonic acid bicarbonate


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At tissues: CO2 load/O2 unload

60%30%

10%

How does CO2 loading facilitate O2 unloading?

CO2 transport in the blood


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--Partial pressure gradients

drive the gas movement.

How O2 loading facilitatesCO

2unloading?

At lungs: O2 load/CO2 unload

1. O2 binds to Hb to liberate H+

2. H+ binds with HCO3- to form H2CO33. H2CO3 dissociates to H2O and CO24. CO2 diffuses to alveoli

Steps:

CO2 transport in the blood


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Respiratory Acid-Base Balance Ventilation rate is altered to keep neutral

pH (7.4), how? CO2+ H2O H2CO3 HCO3

- + H+

When pH drops (H+), the reaction favorsthe production of CO2, which is exhaled

out of the lungs.

pH = - log [H+]


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Hypo- vs. Hyper-ventilation

Hypoventilation

Accumulation of CO2 PCO2

pH (H+ )

Respiratory acidosis

Hyperventilation Excessive loss of CO2

PCO2

pH (H+ ) Respiratory alkalosis

CO2+ H2O H2CO3 HCO3- + H+


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Hyperventilation Syndrome Causes: anxiety, stress, hypoxia

Symptoms: numbness & tingling of hands,muscle spasms, dizziness.

Home Tx: breathing into a paper bag, why?

A drop of CO2 level & PCO2

A leftward shift of O2-Hb curve due to alkalosis

Many deaths occurred in underwater swimmers

who hyperventilated excess before breath-holddiving, why?


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Control of Breathing

PonsRespiratory Center

Medulla

Brain Stem Medulla

- generate rhythmiccycle of breathing

Pons

- play the role of finetuning influences over

the medulla center


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Modifying Respiration


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Chemoreceptor Control

2. Peripheral Chemoreceptors

- Carotid body & Aortic bodies- O2 & H

+ sensor

1.

medulla


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Chemical Controlof Breathing

PCO2 main respiratory regulator

mainly affect on central chemoreceptors

CO2 can pass blood-brain barrier

H+ cannot pass the barrier

[H+]

monitored by carotid & aortic bodies

PO2 monitored by carotid & aortic bodies

arterial PO2< 60 mmHg to stimulate peripheralchemoreceptors


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Effect of arterial PCO2 on ventilation

Eff t f t i l CO H


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Effect of arterial non-CO2-H+

on ventilation


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Effect of arterial PO2 on ventilation


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Dive 2000m underwater 1hr to hunt fordelicious giant squids!

Problems encountered underwater: huge pressure

hypoxia

Sperm Whales:champion divers of the sea

Lung collapse

- prevent lung rupture

- lack of nitrogen narcosis &decompression sickness

Enhanced O2 stored in blood & musclesScientific American, August 21 (2006)


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Things to know:

What happens to the pressure below sea level?

What happens to the divers lung volume?

What kind of air he is breathing in from the tank?

At what pressure is he breathing at?

What might happen if he stays deeper than 30mwith extended period of time?

What happens on ascent?

more

SCUBA diving


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What is the technique to allow one to stay longerunderwater during breath-hold diving?

What are the levels of alveolar O2 & CO2 afterhyperventilation and right after descent, respectively?

What is the risk of excessive hyperventilation?

How to avoid?

Breath-hold divingAma diver

LSM3212_Lecture 10 Resp2

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