Where is the rhythm of breathing generated?

In the CNS, specifically the medulla oblongata

Where is breathing initiated?

In the medulla by specialized neurons

Which structures modify breathing?

Higher brain centers, chemoreceptors, and mechanoreceptors

What are the main respiratory neuron groups in the brainstem?

Pontine respiratory group, dorsal respiratory group, ventral respiratory group

What is the PreBötzinger complex responsible for?

Generating inspiratory rhythm

What is the parafacial respiratory group responsible for?

Generating active expiratory rhythm

What factors require breathing rhythm to change?

Metabolic demands, posture, behaviors, disease

Which part of the brain generates breathing rhythm?

Ventral respiratory group (VRG)

What nerve stimulates the diaphragm?

Phrenic nerve

Which muscles are used for inspiration?

Diaphragm and external intercostals

Which muscles are used for expiration?

Internal intercostals and abdominal muscles

What is hypoxia?

Low PO2

What is hypercapnia?

High PCO2

What is acidosis?

Low pH

What effect do hypoxia, hypercapnia, and acidosis have on ventilation?

Increase ventilation

What do chemoreceptors detect?

PO2, PCO2, and pH

What are peripheral chemoreceptors?

Carotid and aortic bodies

What is the main stimulus for peripheral chemoreceptors?

Low arterial PO2

At what PO2 do peripheral chemoreceptors activate strongly?

Below 60 mmHg

Which cells are chemosensitive in carotid bodies?

Glomus (Type I) cells

What neurotransmitters are released by glomus cells?

ACh, dopamine, norepinephrine, substance P

What cranial nerve carries carotid body signals?

Glossopharyngeal nerve (CN IX)

What do central chemoreceptors detect?

CO2 and pH in brain extracellular fluid

Where are central chemoreceptors located?

Ventral medulla

What percent of hypercapnia response is from central chemoreceptors?

About 70%

Why does CO2 affect central chemoreceptors strongly?

It crosses the blood-brain barrier easily

Why does H+ mainly stimulate peripheral chemoreceptors?

It does not cross the blood-brain barrier easily

What happens during metabolic acidosis?

Increased ventilation (hyperventilation)

What happens to ventilation when PCO2 increases?

It increases

What happens to ventilation when PO2 decreases significantly?

It increases

How is O2 transported in blood?

Dissolved (2%) and bound to hemoglobin (98%)

What is hemoglobin composed of?

4 globin chains and 4 heme groups

How many O2 molecules can hemoglobin carry?

4

What is the reaction for oxygen binding?

O2 + Hb ↔ HbO2

What is Hb saturation?

% of Hb binding sites occupied by O2

What is normal arterial Hb saturation?

~97.5%

What is normal venous Hb saturation?

~75%

What determines O2 content in dissolved form?

PO2 (Henry’s law)

What is cooperative binding?

Binding of one O2 increases affinity for others

What shape is the O2 dissociation curve?

Sigmoidal

What causes a right shift of the O2 dissociation curve?

↑CO2, ↑H+, ↑temperature, ↑DPG

What is the effect of a right shift?

Decreased O2 affinity → more unloading

What causes a left shift?

Opposite conditions (↓CO2, ↓H+, ↓temp)

What is the effect of a left shift?

Increased O2 affinity → less unloading

What is the plateau region of the curve?

60–100 mmHg PO2

Why is the plateau important?

Maintains high saturation despite PO2 changes

What is the steep portion of the curve?

10–60 mmHg PO2

Why is the steep portion important?

Facilitates O2 unloading in tissues

What is anemia?

Low hemoglobin concentration

What is polycythemia?

High hemoglobin concentration

What is the effect of CO poisoning on Hb?

Binds strongly and reduces O2 delivery

How is CO2 transported in blood?

Dissolved, bicarbonate, and carbamino compounds

What percent of CO2 is transported as bicarbonate?

60–65%

What enzyme converts CO2 to bicarbonate?

Carbonic anhydrase

What is the chloride shift?

Exchange of HCO3- out and Cl- into RBC

What are carbamino compounds?

CO2 bound to hemoglobin

Which form of Hb binds CO2 better?

Deoxyhemoglobin

What happens to H+ in RBCs?

Binds to hemoglobin for buffering

What is normal blood pH?

~7.4

What is respiratory acidosis?

Increased CO2 due to hypoventilation

What is respiratory alkalosis?

Decreased CO2 due to hyperventilation

What is metabolic acidosis?

Increased H+ independent of CO2

What is metabolic alkalosis?

Decreased H+ independent of CO2

What is ventilation-perfusion (V/Q) ratio?

Balance between ventilation and blood flow

What happens with high V/Q ratio?

Dead space (ventilated but not perfused)

What happens with low V/Q ratio?

Shunt (perfused but not ventilated)

What is anatomical dead space?

Airways not involved in gas exchange

What is alveolar dead space?

Alveoli ventilated but not perfused

What determines alveolar gas levels?

Ventilation and perfusion balance

What happens when ventilation increases?

Alveolar PO2 ↑, PCO2 ↓

What happens when perfusion increases?

Alveolar gases resemble venous blood

What is pulmonary hypoxic vasoconstriction?

Blood diverted away from low O2 regions

Why is this important?

Improves V/Q matching

Where is ventilation greatest in lungs?

Base of lungs

Where is perfusion greatest?

Base of lungs

Where is V/Q highest?

Apex of lungs

What is surfactant?

Substance that reduces surface tension in alveoli

Which cells produce surfactant?

Type II alveolar cells

What are the functions of surfactant?

Reduce surface tension and prevent collapse

What happens without surfactant?

Increased work of breathing (IRDS)

What is lung compliance?

Ease of lung expansion

How does surfactant affect compliance?

Increases compliance

What is the equation for alveolar pressure?

P = 2T/r

How does surfactant stabilize alveoli?

Equalizes pressure between different sized alveoli