Gas Transport in the Bloodstream and Control of Breathing

How is oxygen primarily transported in the blood?

Most oxygen is carried bound to haemoglobin in red blood cells.

What is the role of haemoglobin in oxygen transport?

Haemoglobin binds oxygen to form oxyhaemoglobin (HbO₂), allowing efficient transport of oxygen.

What is the chemical reaction for the formation of oxyhaemoglobin?

Hb + O₂ ⇌ HbO₂

What factors affect haemoglobin's ability to bind or release oxygen?

Partial pressure of oxygen (PO₂), temperature, and pH.

What happens to haemoglobin's affinity for oxygen at high PO₂?

Haemoglobin readily binds oxygen, becoming highly saturated.

How does temperature affect oxygen release from haemoglobin?

Higher temperatures promote oxygen release, which is useful in active tissues.

What is the Bohr effect?

As pH drops, haemoglobin's affinity for oxygen decreases, promoting oxygen release in active tissues.

What is the shape of the oxygen-haemoglobin dissociation curve?

It has a characteristic sigmoidal (S-shaped) curve due to cooperative binding.

What does a right shift in the oxygen-haemoglobin dissociation curve indicate?

It indicates decreased affinity for oxygen, enhancing oxygen release.

What does a left shift in the oxygen-haemoglobin dissociation curve indicate?

It indicates increased affinity for oxygen, reducing oxygen release.

What is the P50 value in relation to haemoglobin?

The P50 value is the PO₂ at which haemoglobin is 50% saturated with oxygen.

How does fetal haemoglobin (HbF) differ from adult haemoglobin (HbA) in terms of oxygen affinity?

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.

At what PO₂ level is fetal haemoglobin more saturated than adult haemoglobin?

At lower PO₂ levels, such as around 20-30 mmHg.

What is the significance of the left shift of the fetal haemoglobin curve?

It allows for efficient oxygen transfer from mother to fetus across the placenta.

What happens to haemoglobin saturation at high PO₂ levels in the lungs?

Haemoglobin is nearly fully saturated (about 97-100%).

How does pH affect the oxygen-haemoglobin dissociation curve?

Lower pH (more acidic) shifts the curve to the right, while higher pH (more alkaline) shifts it to the left.

What is the effect of increased CO₂ on haemoglobin's affinity for oxygen?

It decreases haemoglobin's affinity for oxygen, enhancing oxygen release.

Why is the oxygen-haemoglobin dissociation curve important for oxygen delivery?

It ensures efficient oxygen uptake in the lungs and delivery to tissues based on metabolic activity.

What is the relationship between temperature and oxygen saturation in haemoglobin?

As temperature rises, oxygen saturation declines, enhancing oxygen delivery to active tissues.

How is oxygen transported from maternal blood to fetal blood?

Oxygen moves from maternal blood (lower affinity) to fetal blood (higher affinity) to support fetal oxygenation.

What percentage of carbon dioxide (CO₂) is transported dissolved in plasma?

About 7% of CO₂ is transported simply dissolved in the plasma.

What is carbaminohaemoglobin?

Carbaminohaemoglobin (HbCO₂) is formed when CO₂ binds to haemoglobin, accounting for around 23% of CO₂ transport.

What is the primary method of CO₂ transport in the blood?

About 70% of CO₂ is transported as bicarbonate ions (HCO₃⁻).

What enzyme catalyzes the formation of bicarbonate from CO₂?

Carbonic anhydrase catalyzes the reaction of CO₂ with water to form carbonic acid (H₂CO₃), which dissociates into H⁺ and HCO₃⁻.

Where are the respiratory centers located?

The respiratory centers are located in the brainstem, primarily in the medulla oblongata and pons.

What is the function of the medullary rhythmicity area?

It generates the basic rhythm of breathing and contains inspiratory and expiratory neurons.

What role do inspiratory neurons play in breathing?

Inspiratory neurons stimulate the diaphragm and external intercostal muscles to contract, causing inhalation.

How do the pneumotach area and apneustic area regulate breathing?

The pneumotach area sends inhibitory impulses to inspiratory neurons, while the apneustic area provides stimulatory impulses to promote prolonged inspiration.

What do central chemoreceptors monitor?

Central chemoreceptors monitor CO₂ levels indirectly through changes in pH of the cerebrospinal fluid (CSF).

What happens when CO₂ levels rise in the blood?

Increased CO₂ leads to higher H⁺ concentration, stimulating central chemoreceptors to increase the rate and depth of breathing.

What is the significance of peripheral chemoreceptors?

Peripheral chemoreceptors respond to changes in blood levels of O₂, CO₂, and H⁺, especially detecting low oxygen levels.

What is the hypoxic stimulus for breathing?

The hypoxic stimulus becomes significant when the partial pressure of oxygen (PO₂) falls below about 50 mmHg.

How does CO₂ affect the respiratory center?

CO₂ diffuses into the CSF, forming carbonic acid, which lowers CSF pH and stimulates the respiratory center to increase ventilation.

What are some non-chemical influences on respiration?

Cortical influences, limbic system responses, inflation reflex, neural changes during movement, blood pressure, pain, and temperature.

How does the limbic system affect breathing?

The limbic system alters breathing in response to emotions like anxiety, fear, or excitement.

What is the Hering-Breuer reflex?

The Hering-Breuer reflex prevents overexpansion of the lungs by sending inhibitory signals to the respiratory center when stretch receptors are activated.

How does exercise influence breathing?

Neural changes due to movement stimulate breathing even before significant chemical changes occur, preparing the body for increased oxygen demand.

What effect does body temperature have on respiration?

Increased body temperature leads to faster breathing, while decreased temperature slows it down.