WEEK 1: WEEK PHYSIOLOGY 2 Flashcards
State the differences between partial pressure and gas content
- PARTIAL PRESSURE: solution in in plasma affected by solubulityand PP of gaseous O2
- GAS CONTENT: varies in form.
Describe the role of haemoglobin in the transport of O2 in the blood
Binds 98%O2 in blood, 4 molecules. of O2 bound per Hb.
HbA: 2 alpha 2 beta
HbA2
subtype of Hb in blood where beta chains replaced by delta
HbF
beta chains replaced by gamma. Higher affinity. Extracts maternaal O2 from maternal.
Myoglobin
cardiac, skel musc. exclusive
- O2 store greater affinity
Explain why the shape of the oxyhaemoglobin dissociation curve is important to O2 loading in the lungs and unloading in the tissues.
- changes in PO2 favours oxygen loading/unloading directions at sites of respiration
- plateau ensures adequate Hb saturation at alveoli even if PP fluctuates
- venous PO2 AT. REST, 75% O2. reserve bound.
Impact of pH on oxygen dissociation
ACIDOSIS - BOHR EFFECT SHIFTS “DROP” RIGHT = ↑O2 LEAVES AT 40mmHg+
BOHR = higher O2 required to unload at periphery
Impact of CO2 on O2 dissociation
↑PCO2 = BOHR EFFECT
Impact of temp on O2 dissociation
↑Temp = BOHR
↓ Temp = ↑Affinity therefore oxygen hoarded and ↓peripheral perfusion
[DPG] impact on O2 dissociation
↑[DPG] = BOHR
HYPOXIA TRIGGERS DPG PRODUCTION
What is the Bohr effect
Decreases affinity and increase in O2 dissociation, curve shifts to right, O2 leaves Hb to oxygenate at relatively higher pO2
Compare oxyhaemoglobin dissociation for adult haemoglobin with that of foetal haemoglobin and myoglobin in relation to their physiological roles.
HbF higher affinity ensuring and “drop” at much lower pO2 ensuring effective extraction of O2 from maternal circulation.
Myoglobin much higher than Hb and HbF.
Identify the forms in which CO2 is carried in the blood.
7% dissolved
95% RBC
23% oxyhaemoglobin
70% => co2+carbonic anhydrase = carbonic acid => bicarb buffer
Explain the action of carbonic anhydrase in CO2 transport
co2+carbonic anhydrase = carbonic acid => bicarb buffer mainting blood pH
↓arterial CO2 = ALKALOSIS
CO2 + H2O <=> H2CO3 <=> HCO3- + H+
shifts reaction to left reducing H+ therefore alkalinity
Identify the factors which favour CO2 unloading to the alveoli at the lungs.
- partial pressure gradient
- ventilation rate: hypervent. or hypovent?
- pH of blood; buffer status
- status of alveolar architecture
Describe the relationship between ventilation and perfusion and its significance in health
V (alveolar, pulmonary) = Q (bloow flow) = optimal
Apex: ventilation (&alv pressure) > perfusion (&BP) , arterioles compressed VQ<1.0
Base: perfusion > ventilation d/t gravity pulling blood
= arterial pressure > alveolar pressure. VQ >1.0
EQUAL OUT AT RIB 3
SHUNT
↓V=↑PCO2 ↓PO2, Q>V
- surrounding arterioles CONSTRICT in response to HYPOXIA
- bronchioles @ sites of relative ↑V DILATE
- BLOOD redirected
alveolar compromise
ALVEOLAR DEAD SPACE
V > Q (often at apex)
surrounding pulmonary vasodilation to increase and redirect blood flow to site to acquire extra O2
Define the five different types of hypoxia
- ANAEMIC HYPOXIA - pO2 normal but total O2 content reduced
- HYPOXAEMIC HYPOXIA - atmos O2 or pathology = ↓o2 diffusion at lungs
- HITOTOXIC HYPOXIA - poisoning e.g. CO
- METABOLIC HYPOXIA - supply fails to meet demand
- STAGNANT HYPOXIA - cardiac disease results in circulatory dysfunction. therefore delivery
Explain how respiratory motor movements are affected by the central nervous system
BRAINSTEM: PONS + MEDULLA
DRG: INSPIRATORY via diaphragm, intercostals
VRG: EXPIRATORY via muscles of exp, maintain basal tone = PATENCY
Factors that can override rhythm of respiration
- EMOTION (limbic)
- VOLUNTARY (higher centres)
- MECHANOSENSORY THORAX (stretch receptors)
- CHEMICAL COMPOSITION OF BLOOD (chemoreceptors)
classes of chemoreceptors and identify the stimuli which activate them.
- CENTRAL (medulla) 1º
- CSF H+ (HYPERCAPNEA/HYPOCAPNEA)
= ventilation response - PERIPHERAL (carotid, aortic bodies) 2º
- pO2, plasma [H+]
* d/t curve, greater reduction of O2 required to stimulaate ventilation. NOT O2 content but PO2
* K+ influx and. dopamine depol.
* responds to ↑[H+]
factors involved in changing ‘respiratory drive’, rate and depth of breathing
- pCO2 in systemic circulation
- pH acidity of BBB
- overdrive inputs
Explain how the peripheral chemoreceptors become important during hypoxia and acid-base imbalance.
- main stimulus is pO2
- indirect detection of CO2 d/t [H+] d/t aleration in H+ by any means (lactic acid e.g.)
↑[H+] = ↑ventilation vice versa (negative feedback)
