The Respiratory system

Question 1

Functions of the respiratory system

Answer 1

Primary:
- Brings oxygen into the body and carbon dioxide out of it
Secondary:
- Phonation (voice production)
- Regulation of body temperature
- Regulation of acid-base balance (blood pH)
- Sense of smell (olfaction)

Question 2

Internal and external

Answer 2

• External respiration - exchange of O2 and CO2 between the inhaled air and the blood flowing through the pulmonary capillaries - within the lungs
• Internal respiration - Exchange of O2 and CO2 between the blood in the systemic capillaries and all the cells and tissues of the body - around the body

Question 3

Why the need for gas exchange?

Answer 3

• What is oxygen used for? = aerobic respiration uses O2 to produce ATP
• Where does CO2 come from? = CO2 is released when glucose is broken down (by-product of cellular respiration)

Question 4

Upper respiratory tract

Answer 4

• Nostrils (nares)
• Nasal passages
• Nasal turbinates
• Pharynx
• Larynx
• Trachea

Question 5

Nose and nasal passages

Answer 5

• Nares - external openings of the respiratory tube - leads into the nasal passages
• Nasal passages - between the nostrils and the pharynx
• Nasal septum - separates the left and right nasal passage
• Hard and soft palates - separates the nasal passages from the mouth
• Turbinates (nasal conchae) - thin, scroll-like bones covered in nasal epithelium
• Cilia project from the cell surfaces up into a layer of mucus
• Mucus is secreted by mucous glands and goblet cells
• Nasal passages lined with pseudostratified columnar epithelium

Question 6

Nasal passages functions

Answer 6

Warm, humidify and filter inhaled air
- Air is warmed by blood flowing through blood vessels just beneath the nasal epithelium
- Air is humidified by mucus and other fluids on the epithelial surface
- Air is filtered as it passes through the winding passages produced by the turbinates

Question 7

Paranasal sinuses

Answer 7

• Paranasal sinuses - ciliated outpunching’s of nasal passages continued within spaces in certain skull bones
• Cavities to help make the skull lighter, and increase surface area
• Also have a role in voice resonance, therefore often larger in male animals

Question 8

Pharynx and Larynx

Answer 8

• Common passageway for respiratory and digestive systems
• Larynx and pharynx work together to prevent swallowing from interfering with breathing and vice versa
• Cartilage components - epiglottis, arytenoid cartilages, thyroid cartilage, cricoid cartilage

Question 9

Larynx function

Answer 9

• Voice production
• Vocal chords - two connective tissue bands attached to the arytenoid cartilages
• Vocal chords vibrate as air passes over them
• Muscles attached to the arytenoid cartilages control the tension of the vocal chords

Question 10

Trachea

Answer 10

• Extends from the larynx into the thorax
• Divides into the 2 main bronchi that enter the lungs (bifurcation)
• Composed of fibrous tissue and smooth muscle held open by hyaline cartilage rings
• Lined with ciliated epithelium

Question 11

Lower respiratory tract

Answer 11

• Bronchi
• Bronchioles
• Alveolar ducts
• Alveoli
• Diaphragm
• Each bronchi divide into even smaller tiny bronchioles
• Bronchioles subdivide into alveolar ducts
• Alveolar ducts end in groups of alveoli
• Arranged like bunches of grapes

Question 12

Alveoli

Answer 12

• Site of external respiration - gaseous exchange
• Tiny, thin-walled sacs of simple squamous epithelium
• Surrounded by networks of capillaries

Question 13

Gaseous exchange

Answer 13

• Simple diffusion of gas molecules according to concentration gradient (high to low)
• O2 diffuses from the alveolar air into the blood of the alveolar capillary
• CO2 diffuses from the blood into the alveolus

Question 14

Lungs

Answer 14

• Each lung has a base, an apex, and a lateral surface
• Base is in caudal part of the thoracic cavity - lies directly on the cranial surface of the diaphragm
• Apex lies in cranial portion of thoracic cavity
• Lungs are divided into lobes
• 7 in dogs and cats (3L and 4R)
• Hilum - small, well-defined area on medial side of lung
• Site where air, blood, lymph and nerves enter and leave the lung

Question 15

Thoracic cavity

Answer 15

• Bound by thoracic vertebrae dorsally, ribs and intercostal muscles laterally, the sternum ventrally
• Mediastinum - area between lungs - contains: heart, trachea, oesophagus, blood vessels, nerves, lymphatic structures

Question 16

The pleura

Answer 16

• Thin membrane that lines thoracic cavity and covers organs and structures in the thorax
• Visceral layer covers thoracic organs and structures
• Parietal pleura lines the cavity
• Space between the 2 pleural layers is filled with a small amount of pleural fluid
• In some animals this pleural cavity can fill with other substances besides healthy lubricant e.g. pyothorax

Question 17

The diaphragm

Answer 17

• Thin, dome-shaped muscle sheet
• Forms caudal boundary of thorax
• Important respiratory muscle - flattens when it contracts - enlarges volume of the thorax and aids inspiration
• Smooth muscle

Question 18

Respiratory system

Answer 18

• The diaphragm isn’t directly connected to the lungs. It is separated by the pleural space (a cavity surrounding the lungs. How does the diaphragm cause ventilation if it is not in direct contact with the lungs?)
• Negative pressure - vacuum pressure (sucking/pulling pressure)
• We can refer to this pressure as intrathoracic pressure. Without it, respiration is severely compromised

Question 19

Inspiration

Answer 19

• Process of drawing air into lungs (inhalation)
• Results from enlargement of the volume of the thoracic cavity by the inspiratory muscles
• Main inspiratory muscles: diaphragm and external intercostal muscles

Question 20

Expiration

Answer 20

• Process of pushing air out of the lungs (exhalation)
• Results from decrease in size of thoracic cavity
• Main expiratory muscles: internal intercostal muscles and abdominal muscles

Question 21

Respiratory volumes

Answer 21

• Tidal volume - volume of air inspired and expired during one breath
• Minute volume - volume of air inspired and expired during 1 min of breathing
• Residual volume - volume of air remaining in the lungs after maximum expiration
• Functional residual volume - volume of air remaining in the lungs after normal expiration

Question 22

IPPV

Answer 22

Intermittent positive pressure ventilation (IPPV) is a method of ventilating unconscious patients

Question 23

The respiratory centre

Answer 23

• Area in the medulla oblongata of the brain stem
• Controlled by the autonomic nervous system but can be overridden for brief periods

Question 24

Mechanical control

Answer 24

• Stretch receptors in the lungs set limits for inspiration and expiration ]
• Respiratory centre sends out nerve impulses when lungs inflate to a certain point
• Stops muscle contractions that produce inspiration and starts contractions to produce expiration
• Another set of nerve impulses sent when lungs deflate sufficiently
• Stops expiration and starts the process of inspiration again

Question 25

Chemical control

Answer 25

• Adjusts the normal rhythmic breathing pattern produced by the mechanical control system
• Chemical receptors monitor CO2 levels and pH of blood
• Peripheral chemo receptors - part and carotid bodies
• Increased CO2 in blood and decreased blood pH (CO2 is acidic) triggers respiratory centre to increase rate and depth of respiration
• Decreased CO2 in blood increases blood pH (becomes alkaline) ; triggers respiratory centre to decrease rate and depth of respiration
• Hypoxia - decrease in blood O2 level
• Slight hypoxia triggers respiratory centre to increase the rate and depth of breathing
• Severe hypoxia - neurones of the respiratory centre can become so depressed that adequate nerve impulses cannot be sent to the respiratory muscles
• Can cause breathing to decrease or stop completely

Question 26

Species differences

Answer 26

• The horses and rabbits are obligate nasal breathers
• Air is drawn in through the nostrils which are prevented from closing during inspiration by rims of cartilage

Question 27

Reptilian respiration

Answer 27

• Gaseous exchange occurs in the same way as it does in mammals but the most significant difference is that reptiles lack a diaphragm
• Breathing is accomplished by expansion and contraction of the ribs
• In most snakes the left ling is greatly reduced in size or even absent

Question 28

Birds

Answer 28

• Have lungs and air sacs
• Air sacs permit a unidirectional flow of air through the lungs
• Air moving through the lungs is largely fresh air and has higher oxygen content