Veterinary Anatomy & Physiology - Lecture 4: The Respiratory System

Comprehensive flashcards covering the anatomy, physiological functions, and mechanics of the respiratory system from Veterinary Anatomy & Physiology Lecture 4.

What is the difference between ventilation (external respiration) and internal respiration?

Ventilation (external respiration) is the exchange of oxygen and carbon dioxide between inhaled air in the lungs and blood flowing through pulmonary capillaries, whereas internal respiration is the exchange of oxygen and carbon dioxide between blood capillaries and body tissues.

Where are the receptors for the sense of smell located within the respiratory tract?

They reside in patches of sensory epithelium located in the olfactory region in the caudal parts of the nasal chambers.

How does the larynx produce voice (phonation)?

Sound is produced when vocal cords stretch across the lumen of the larynx at the glottis and vibrate as air passes over them. Other structures such as the thorax, nose, oral cavity, and sinuses contribute to resonance.

What two mechanisms allow the respiratory system to assist in thermoregulation?

1. Superficial blood vessels under the nasal epithelium warm inhaled air before it reaches the lungs. 2. Panting increases the evaporation of fluid from the mucous membranes of the respiratory passages and mouth, cooling the underlying blood circulation.

How does the respiratory system contribute to blood acid-base balance?

Carbon dioxide dissolves in blood plasma to form carbonic acid, which acidifies the blood. The respiratory system adjusts the rate and volume of breathing to alter $CO_2$ levels and regulate blood $pH$.

What is the rhinarium?

The hairless nose pad of epidermis consisting of a thick, heavily pigmented layer of squamous epithelium that is well supplied with mucous and sweat glands.

Identify the four anatomical landmarks labelled on the dog's nose in this diagram.

Nosepad or rhinarium, alar fold, external nares, and philtrum.

Through which bone do the nerve fibres from the olfactory region pass to reach the forebrain?

The ethmoid bone.

What are paranasal sinuses, and what are their primary functions?

They are air-filled cavities within the facial bones of the skull that connect with the nasal cavity through narrow openings. They lighten skull weight and serve as areas for heat exchange and mucus secretion.

Identify paranasal sinuses 1 and 2 in the skull of the dog shown below.

1 is the maxillary sinus; 2 is the frontal sinus.

How does the soft palate divide the pharynx, and what is its role during swallowing?

The soft palate extends caudally from the hard palate to divide the pharynx into the ventral oropharynx and dorsal nasopharynx. It prevents food from entering the nasal chambers during swallowing.

What is the function of the auditory (Eustachian) tubes that open into the pharynx?

They open into the pharynx from the middle ear to equalise pressure on both sides of the ear drum.

What is the function of the epiglottis during swallowing?

It diverts backwards like a trapdoor to cover the entrance of the larynx, preventing swallowed material from entering the airway and directing it dorsally into the oesophagus.

Why is glottic closure essential during coughing and straining activities like defecation or labour?

During coughing, glottic closure allows pressure to build before explosive air release clears debris. During straining, it prevents abdominal muscle contractions from simply forcing air out of the lungs.

What structural role do the C-shaped hyaline cartilage rings serve in the trachea?

They prevent the trachea from collapsing when thoracic pressure drops, while their open dorsal gap provides flexibility for neck movements and unhindered passage of food boluses through the adjacent oesophagus.

How do the epithelial lining and cilia of the trachea protect the lower airways?

The epithelium secretes mucus to trap foreign particles, while cilia sweep the trapped material upwards toward the pharynx to be spat out or swallowed. Overproduction of mucus triggers a coughing reflex.

How does cartilage support differ between bronchi and bronchioles?

Bronchi are supported by complete cartilage rings, but as the airways branch into smaller divisions, cartilage diminishes and completely disappears, marking the transition to bronchioles.

What structural features of alveoli maximise efficient gaseous exchange?

They are small and thin-walled with a single thin epithelial layer (pulmonary membrane), surrounded by rich capillary networks, and present in millions to create an immense surface area for $O_2$ and $CO_2$ diffusion.

What is the hilus of the lung?

A well-defined area on the medial surface of each lung where air passages, blood vessels, lymphatics, and nerves enter and leave; it is the only site where the lung is physically attached to the body.

Why is the pleural cavity described as a 'relative vacuum'?

It contains no air and only a tiny film of lubricating fluid; its negative pressure ensures the visceral pleura and parietal pleura stay adhered together so the lungs expand as the thoracic wall moves.

Which muscles contract during inspiration and how do they change thoracic cavity volume?

The diaphragm contracts and flattens, while the external intercostal muscles contract to lift the ribs upwards and outwards, thereby expanding the thoracic volume and dropping pleural pressure.

Why is normal expiration described as a passive process, and when do the internal intercostals become active?

Normal expiration requires no muscle contraction because the diaphragm and external intercostals simply relax, allowing elastic recoil. Internal intercostals contract only during forced expiration alongside abdominal muscles.

What is the difference between anatomical dead space and alveolar dead space?

Anatomical dead space includes conducting airways (mouth, trachea, bronchi, bronchioles) where air never contacts alveoli. Alveolar dead space refers to alveoli that receive air but cannot perform gas exchange due to inadequate perfusion.