Respiratory Physiology Lecture Notes

Comprehensive practice flashcards covering human respiratory anatomy, mechanics of breathing, lung volumes and capacities, gas exchange, gas transport mechanisms, neural/chemical control of ventilation, and physiological adaptations.

What is the primary site of gas exchange during intrauterine life before birth?

During intrauterine life, the exchange of gases between fetal blood and mother's blood occurs through the placenta.

What are the normal respiratory rates for newborns, early childhood, and late childhood?

Newborn: $30\text{--}60\text{ breaths/minute}$; Early childhood: $20\text{--}40\text{ breaths/minute}$; Late childhood: $15\text{--}25\text{ breaths/minute}$.

Which primary and accessory muscles are involved in inspiration and expiration?

Inspiration: Primary muscles are the diaphragm and external intercostal muscles; accessory muscles include sternocleidomastoid, scalene, anterior serratus, and pectoralis muscles. Expiration: Primary muscles are internal intercostals; accessory muscles are abdominal muscles.

How do inspiration and expiration compare in terms of energy expenditure and duration during quiet breathing?

Inspiration is an active process lasting approximately $2\text{ seconds}$. Expiration is a passive process lasting approximately $3\text{ seconds}$.

What structures separate the upper respiratory system from the lower respiratory system?

The upper respiratory system includes structures from the nose to the vocal cords (pharynx, larynx). The lower respiratory system begins below the vocal cords and includes the trachea, bronchi, and lungs.

What are the three main physiological functions of the paranasal sinuses?

1. Lessen the weight of the skull to make upright posture easier. 2. Offer resonance to the voice. 3. Protect the brain from frontal trauma.

What are the three anatomical divisions of the pharynx and their relative locations?

1. Nasopharynx: Uppermost portion behind the nasal cavities. 2. Oropharynx: Posterior to the oral cavity, below the soft palate. 3. Laryngopharynx: Most inferior portion, opening anteriorly into the larynx and posteriorly into the esophagus.

What is the function of the epiglottis during swallowing?

During swallowing, the larynx is elevated and the epiglottis closes over the top of the larynx like a hinged lid to prevent aspiration of food and liquid into the lower respiratory tract.

Which cranial nerves provide motor innervation to the larynx for speech?

The vagus nerve (CN X) and accessory nerve (CN XI).

What anatomical structure maintains the patency of the trachea?

$16\text{ to }20$ C-shaped pieces of hyaline cartilage, completed dorsally by smooth muscle to allow expansion of the esophagus during swallowing.

How do the right and left primary bronchi differ structurally?

The right primary bronchus is shorter, wider, and more vertical than the left bronchus, making foreign objects more easily aspirated into the right bronchus.

How many generations of airway branching form the conducting zone versus the respiratory zone?

The first $16$ generations of branching form the conducting zone. The respiratory zone extends from generation $17$ (respiratory bronchioles) through generation $23\text{--}24$ (alveolar sacs and alveoli).

What structural feature distinguishes bronchioles from bronchi?

Bronchioles are airway branches that contain no cartilage in their walls, allowing them to contract and relax to regulate airflow.

What are the functional differences between Type I and Type II pneumocytes?

Type I pneumocytes are squamous epithelial cells ($95\%$ of alveolar cells) that form the primary site for gas exchange. Type II pneumocytes are cuboidal cells ($5\%$) that synthesize pulmonary surfactant and retain regenerative capacity.

What is the thickness of the air-blood barrier across which gas exchange occurs in the alveoli?

The total air-blood barrier is only two cells thick (an alveolar cell and a capillary endothelial cell), measuring approximately $2\,\mu m$.

How do the right and left lungs differ in terms of lobes and fissures?

The right lung has three lobes (upper, middle, lower) separated by two fissures (oblique, horizontal). The left lung has two lobes (upper, including the lingula, and lower) separated by an oblique fissure.

What non-respiratory defense mechanisms are present in the respiratory system?

Trapping of particles by mucus, upward mucociliary escalation by ciliated epithelium toward the pharynx, destruction of pathogens by gastric acid or lymphatic tissue (tonsils/adenoids), and phagocytosis by alveolar macrophages.

What is Tidal Volume (TV) and what is its standard value in an adult?

Tidal Volume is the volume of air inspired or expired per breath during quiet breathing, with a normal value of $500\,mL$.

Based on this spirogram, how is Vital Capacity (VC) defined and calculated?

Vital Capacity is the maximum volume of air expired forcefully after a maximal inspiration. $\text{VC} = \text{IRV} + \text{TV} + \text{ERV} = 4,800\,mL$.

Why cannot Residual Volume (RV) and Total Lung Capacity (TLC) be directly measured using a spirometer?

Because Residual Volume is the volume of air remaining in the lungs that cannot be exhaled; since TLC is the sum of VC and RV, it also cannot be directly measured by spirometry.

What is Anatomical Dead Space and what is its normal average volume?

Anatomical Dead Space is the internal volume of conducting airways (nose to terminal bronchioles) that does not participate in gas exchange, averaging $150\,mL$.

What is the formula for calculating Alveolar Ventilation rate per minute?

$\text{Alveolar Ventilation} = (\text{Tidal Volume} - \text{Dead Space Volume}) \times \text{Respiratory Rate}$ (e.g., $(500\,mL - 150\,mL) \times 12\text{ breaths/min} = 4,200\,mL/min$).

What relationship is described by the Law of Laplace regarding alveolar pressure and surface tension?

$P = \frac{2T}{r}$, where $P$ is collapse pressure, $T$ is surface tension, and $r$ is the radius of the alveolus.

What component makes up the largest percentage of pulmonary surfactant and what is its main function?

Phospholipids (specifically phosphatidylcholine, accounting for $70\text{--}80\%$ of total composition), which function to decrease surface tension in the alveoli.

According to Henry's Law, how is the concentration of a dissolved gas in blood calculated?

$\text{Concentration} = \text{Partial Pressure} \times \text{Solubility}$.

In what two forms is oxygen transported in the blood, and what percentages do they represent?

1. Dissolved in plasma: $2\%$. 2. Combined with hemoglobin inside red blood cells: $98\%$.

Which physiological factors cause a rightward shift of the oxygen-hemoglobin dissociation curve?

Increased temperature, increased $P_{CO_2}$, increased $H^+$ concentration (decreased pH, known as the Bohr effect), and increased 2,3-DPG.

What are the three forms of carbon dioxide transport in blood and their relative percentages?

1. Dissolved $CO_2$ in plasma: $10\%$. 2. As carbamino compounds (bound to Hb/proteins): $30\%$. 3. As bicarbonate ion ($HCO_3^-$): $60\%$.

What is the chloride shift (Hamburger effect) in erythrocyte gas transport?

As $HCO_3^-$ generated inside RBCs diffuses out into the plasma along its concentration gradient, $Cl^-$ ions move from the plasma into the RBC to maintain electrical neutrality.

Where is the primary automatic rhythm generator for respiration located in the brain stem?

In the pre-Bötzinger complex of neurons located in the upper part of the ventral respiratory group (VRG) in the medulla oblongata.

What is the physiological role of the Hering-Breuer inflation reflex?

It is a protective reflex initiated by stretch receptors in the walls of the bronchi and bronchioles when tidal volume exceeds $1000\,mL$; sensory vagal impulses inhibit inspiratory centers to prevent overstretching of the lungs.

How do central chemoreceptors indirectly detect changes in arterial $P_{CO_2}$?

Arterial $CO_2$ readily crosses the blood-brain barrier into cerebrospinal fluid (CSF), where it reacts with $H_2O$ via carbonic anhydrase to form $H^+$ and $HCO_3^-$; the resulting increase in CSF $H^+$ directly stimulates the central chemoreceptors.

According to the illustrated mechanism in glomus cells, how does low arterial $P_{O_2}$ trigger sensory nerve impulses?

Low $P_{O_2}$ closes $K^+$ channels, depolarizing the cell. This opens voltage-gated $Ca^{2+}$ channels, causing $Ca^{2+}$ entry and exocytosis of neurotransmitters onto the sensory neuron to initiate action potentials.

Below what threshold of arterial $P_{O_2}$ do peripheral chemoreceptors significantly stimulate ventilation?

Peripheral chemoreceptors significantly stimulate ventilation only when arterial $P_{O_2}$ drops below $60\,mmHg$.

How do arterial $P_{O_2}$ and $P_{CO_2}$ change during moderate exercise?

Arterial $P_{O_2}$ and $P_{CO_2}$ show no change during moderate exercise due to precise matching between ventilation rate, $O_2$ consumption, and $CO_2$ production.

What physiological acclimatization responses occur over days to weeks at high altitude?

1. Increased 2,3-DPG production in RBCs (shifting the curve right to increase $O_2$ unloading). 2. Increased erythropoietin secretion by kidneys, stimulating bone marrow to increase RBC count and hemoglobin content.

What causes Decompression Sickness (Caisson Disease) in deep-sea divers?

Rapid ascent causes high-pressure dissolved nitrogen gas to come out of solution rapidly, forming gas bubbles (air emboli) in blood and tissues, leading to vascular obstruction and tissue ischemia.

What are the four recognized classifications of hypoxia?

1. Hypoxic Hypoxia: Reduced arterial $P_{O_2}$. 2. Anemic Hypoxia: Reduced $O_2$-carrying capacity of blood. 3. Stagnant Hypoxia: Sluggish or reduced blood flow to tissues. 4. Histotoxic Hypoxia: Inability of tissues to utilize delivered $O_2$ (e.g., cyanide poisoning).