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Physiology (MPP 3202) > Ch. 16 Day 2 > Flashcards

Ch. 16 Day 2 Flashcards

1
Q

Chemoreceptors

A

Automatic control of breathing influenced by feedback from chemoreceptors - monitor pH of fluids in brain and pH, PCO2, and PO2 in blood

  1. Central chemoreceptors in medulla
  2. Peripheral chemoreceptors in carotid and aorta arteries
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2
Q

Chemoreceptors in Medulla

A

Increased CO2 in fluids of brain decrease pH - sensed by chemoreceptors in medulla, –> increased ventilation

Senses CO2, not H+ which does not cross the BBB

Takes longer, but responsible for 70-80% of increased ventilation

CO2 readily diffuses

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3
Q

Peripheral Chemoreceptors

A

Aortic and carotid bodies respond to rise in H+ due to increased CO2 levels
–chemoreceptors monitor CO2, not O2

Respond faster than medullary chemoreceptors

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4
Q

Effect of Blood PO2 on Ventilation

A

Indirectly affects ventilation by affecting chemoreceptor sensitivity to PCO2

Low blood O2 makes carotid bodies more sensitive to CO2

Hypoxic Drive - carotid bodies respond directly to low oxygen dissolved in plasma (below 70mmHg)

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5
Q

Major control by chemoreceptors is achieved by monitoring ___, not O2.

A

CO2

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6
Q

Gas Exchange

A

Occurs at 3 levels

  1. Atmosphere and lung
  2. Lung and blood
  3. Blood and cells
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7
Q

Partial pressure oxygen changes with?

A

Altitude and location

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8
Q

Causes of Low Alveolar PO2

A

Inspired air has abnormally low oxygen content
–altitude is major factor influencing atmospheric oxygen - as altitude increases, TOTAL atmospheric pressure decreases

Alveolar ventilation is inadequate

  • -Decreased lung compliance: e.g. fibrotic, restrictive pulmonary diseases, lack of surfactant
  • -Increased airway resistance: narrowing/obstruction by mucus, bronchoconstriction
  • -CNS depression: slows breathing rate, decreases depth of breathing (e.g. alcohol poisoning, drug overdose)
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9
Q

Once you decrease PO2 in the alveoli in the lungs, does everything else fall or rise?

A

Fall

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10
Q

Respiratory System Bulk Flow

A

Entire mixture of gases is moving

Flow from regions of higher to lower pressure

Muscular pump creates pressure gradients

Resistance to flow

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11
Q

Partial Pressure of Gases in Blood

A

Alveoli and blood capillaries quickly reach equilibrium for O2 and CO2

  • a) this helps maximize the amount of gas dissolved in fluid
  • b) the amount of gas that can dissolve in liquid depends on:
  • -1) partial pressure of the gases - major determining factor
  • -2) solubility of the gas in the liquid (constant)
  • -3) temperature of the fluid (more gas can dissolve in cold liquid); for blood T = constant
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12
Q

Pulmonary Circulation - High Flow, Low Pressure System

A

R. ventricle –> pulmonary trunk –> pulmonary arteries –> lungs –> pulmonary veins –> L. atrium

BP is low, but resistance to flow is VERY low, so flow through pulmonary circulation is very high

Pulmonary blood flow is equal to cardiac output and is controlled by the factors regulating cardiac output

Important to match blood perfusion and ventilation in the lung

Pulmonary arterioles constrict when alveolar pO2 is low and dilate when pO2 is high
–blood flow to alveoli is increased when they are full of O2 and decreased when not (this is how we match profusion and ventilation)

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13
Q

Hypoxic Vasoconstriction

A

Local mechanism for regulating the distribution of pulmonary blood flow away from hypoxic alveoli

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14
Q

Normal Perfusion of Blood

A

Normal perfusion of blood past alveoli is matched to alveolar ventilation to maximize gas exchange

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15
Q

Ventilation-Perfusion Mismatch

A

Caused by under-ventilation alveoli

If ventilation decreases in a group of alveoli, PCO2 increases and PO2 decreases. Blood flowing past those alveoli does not get oxygenated.

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16
Q

Local Control Mechanisms to Try to Keep Ventilation and Perfusion Matched

A

ex: Hypoxic vasoconstriction

Decreased tissue PO2 around underventilated alveoli constricts their arterioles, diverting blood to better alveoli

  • -low oxygen depolarizes smooth muscle cells of the arteriole wall by inhibiting outward flow of K+
  • -opens voltage-gated Ca2+ channels, which stimulate contraction
  • -the response of pulmonary arterioles to low oxygen levels makes sure that ventilation (O2 into lungs) matches perfusion (blood flow)
17
Q

What is perfusion?

A

Blood flow

18
Q

Diffusion and Solubility Influence Gas Exchange

A

Constants (under normal conditions):

  • -surface area
  • -membrane thickness
  • -diffusion distance (occurs best over a small distance)
  • -temperature

Concentration Gradient:
–primary factor affecting gas exchange

19
Q

Exchange Surface of Alveoli

A

At basal heart rates, RBCs spend about 0.75 seconds in the pulmonary capillaries - 2-3 times the time needed to completely equilibrate w/ alveolar gases

20
Q

Gas Solubility Affects Amount of Dissolved Gas that can be Carried by Plasma

A

Oxygen solubility is low –> very little oxygen can be carried dissolved in plasma

NOTE: even though PO2 is the same in both air and water, [O2} is NOT!

Concentration depends on the gas’s SOLUBILITY

21
Q

Carbon dioxide is __ times more soluble in water than is oxygen.

A

20 times

22
Q

____ transports most of the oxygen in the blood.

A

Hemoglobin

23
Q

More than __% of the oxygen in blood is bound to hemoglobin in RBCs, and less than __% is dissolved in plasma.

A

98%; 2%

24
Q

At rest, cells need?

A

50 mL O2/min

Not enough O2 to meet tissue need if all we could rely on was what’s soluble in the plasma

25
Q

The amount of oxygen bound to hemoglobin (Hb) depends on?

A
  1. Plasma O2, which determines % saturation of Hb
  2. The amount of hemoglobin which determines total number of Hb binding sites calculated from (Hb content per RBC) * (Number of RBCs)

(% saturation of Hb) * ( total number of Hb binding sites)

26
Q

PO2 determines oxygen-hemoglobin binding.

A

97% saturation; 75% saturation
–amount O2 unloaded to tissues…the remainder is a reserve which can be unloaded to tissues if need arises - e.g. during exercise so we can keep aerobic respiration instead of having to go to anaerobic respiration

27
Q

Several factors influence oxygen-Hb binding (5).

A
  1. pH
    - -as pH decreases, affinity decreases, and Hb gives up O2 (Bohr effect)
  2. Temperature
    - -as temp. increases, affinity for O2 decreases
  3. PCO2
    - -as PCO2 increases, affinity for O2 decreases
  4. 2,3-DPG (2,3-diphosphoglycerate)
    - -as 2,3-DPG increases (chronic hypoxia [anemia, high altitude]), affinity for O2 decreases
  5. Changes in hemoglobin structure (fetal Hb)
    - -has higher affinity for O2 than maternal Hb

Decreased pH, increased temperature, increased PCO2 decrease O2 bound to hemoglobin

28
Q

CO2 Transport

A

Dissolved: 7%

Converted to bicarbonate ion: 70%

Bound to hemoglobin: 23%

  • -hemoglobin also binds H+
  • -Hb and CO2: carbaminohemoglobin

Physiology (MPP 3202) (32 decks)

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