Comprehensive Respiratory System: Gas Exchange, Mechanics, and Regulation in Animals

What gas exchange strategy do fishes use?

Countercurrent exchange

What gas exchange strategy do birds use?

Cross current (multi-capillary) exchange

What gas exchange strategy do mammals use?

Tidal volume exchange

What is pulmonary ventilation?

The flow of air into (inhalation) and out of (exhalation) the lungs

What is external respiration?

Gas exchange between alveoli and blood in pulmonary capillaries

What is internal respiration?

Gas exchange between tissue cells and blood in systemic capillaries

What is the function of Type I alveolar cells?

They are thin-walled squamous epithelial cells that serve as the site of gas exchange

What is the function of Type II alveolar cells?

They secrete pulmonary surfactant

What is the role of alveolar macrophages?

To remove dust and debris from alveolar spaces

What is pulmonary compliance?

A measure of the force required to distend or stretch the lungs during inhalation

What is pulmonary surfactant?

A mixture of proteins and lipids that reduces surface tension in the alveoli

How does surfactant affect pulmonary compliance?

It decreases surface tension, which increases pulmonary compliance

Why do premature infants often have difficulty breathing?

They lack sufficient pulmonary surfactant

What is the typical atmospheric pressure at sea level?

760 mm Hg

What is the role of the pleural cavity?

It is an isolated space between pleural membranes with pressure slightly below atmospheric pressure to keep lungs attached to the thoracic wall

What physical law governs pulmonary ventilation?

Boyle's Law (P1V1 = P2V2)

According to Boyle's Law, what happens to volume when pressure decreases?

Volume increases

Which muscles are primarily responsible for quiet inhalation?

The diaphragm and external intercostal muscles

What happens to the thoracic cavity volume when the diaphragm contracts?

It increases

What is the primary mechanism of quiet exhalation?

A passive process involving the relaxation of inspiratory muscles and the elastic recoil of the lungs and thorax

Which muscles are involved in forced exhalation?

Internal intercostal muscles, external oblique muscles, and abdominal muscles

What is the intra-alveolar pressure during normal inspiration?

Approximately 758 mm Hg

What is the intra-alveolar pressure during normal expiration?

Approximately 762 mm Hg

What is the normal intrapleural pressure at rest?

756 mm Hg

What happens to the thoracic cavity volume during exhalation?

The diaphragm and external intercostals relax, causing the chest and lungs to recoil, which decreases thoracic volume.

What is the result of alveolar pressure increasing during exhalation?

Air is forced out of the lungs.

Why is intrapleural pressure always slightly negative?

It allows the parietal pleura to adhere to the thoracic wall.

What is a pneumothorax?

A condition where pleural membranes are compromised, causing intrapleural pressure to equalize with atmospheric pressure, leading to lung collapse.

What is the function of the medullary respiratory center?

It acts as a pacemaker to set the breathing rhythm and integrates sensory information to control inspiration and expiration.

What is Central Hypoventilation Syndrome (Ondine's Curse)?

A condition where an individual loses the automatic control of breathing due to brainstem injury or congenital defects, requiring conscious effort to breathe.

Where are central chemoreceptors located?

On the ventral surface of the medulla near the respiratory centers.

What do central chemoreceptors primarily respond to?

Changes in CO2-induced H+ production in the cerebrospinal fluid, which reflects arterial PCO2 levels.

Where are peripheral chemoreceptors located?

In the carotid bodies and aortic bodies.

What is the primary role of peripheral chemoreceptors regarding oxygen?

They monitor arterial PO2 and trigger increased ventilation if levels drop below approximately 60 mmHg.

How do glomus cells in the carotid body respond to hypoxia?

Low PO2 inhibits K+ channels, causing depolarization, which leads to dopamine release and signals to the respiratory center.

What is the primary difference between air and water as respiratory media?

Water is significantly denser, more viscous, and contains much less dissolved oxygen than air.

How does temperature affect oxygen solubility in water?

As temperature increases, the solubility of oxygen in water decreases.

What is the difference between tidal and unidirectional gas exchange?

Tidal exchange involves reciprocal movement of air in and out of lungs, while water breathing typically uses unidirectional flow over gills.

What are the three main components of fish gill anatomy?

Branchial arches, gill filaments (primary lamellae), and lamellae (secondary lamellae).

What is the function of the lamellae in fish gills?

They are the primary site of gas exchange, providing a large surface area with a very short diffusion distance.

How does activity level correlate with gill structure in fish?

Highly active fish like tuna have more lamellae per mm and thinner lamellar walls compared to slow-moving bottom dwellers.

What is countercurrent exchange in fish gills?

A mechanism where blood flows through gill capillaries in the opposite direction to water flow, maintaining a favorable diffusion gradient along the entire length of the capillary.

What is the buccal-opercular pump in fish?

A mechanism used to create a continuous, unidirectional flow of water over the gills.

What are the three main gas exchange strategies in animals?

Countercurrent exchange, cross-current (multicapillary) exchange, and tidal volume exchange.

How does the avian respiratory system differ from mammals?

Bird lungs are rigid and do not expand; they use air sacs to move air through the system in a one-way flow.

How many breaths are required for a single packet of air to pass through the avian respiratory system?

Two full respiratory cycles (two inhalations and two exhalations).

What are neuroepithelial cells in fish?

Specialized cells embedded in gill epithelia that act as oxygen chemoreceptors, similar to carotid bodies in mammals.

What three functions does the fish medullary respiratory center regulate?

Muscles of the mouth/operculum, cardiac output, and blood perfusion within the gills.

What is Henry's Law?

The principle that gases dissolve in solution in proportion to their partial pressure and solubility.

Why is CO2 more easily exchanged in water than O2?

CO2 is 24 times more soluble in water and diffuses 20 times faster than oxygen.

What is cutaneous respiration in fish?

The process of obtaining oxygen directly through the skin, which is common in larval fish and some adult species.

What is the role of the vagus nerve in fish respiration?

It carries neural signals from the oxygen chemoreceptors to the medulla of the hindbrain.

What is the primary cause of hypercapnia?

Hypoventilation, which leads to an increase in arterial PCO2.