Respiratory System

Question 1

Respiration

Answer 1

The exchange of gases between the environment, blood and the cells. O2 is delivered to tissues and removal of wastes (mainly CO2). Gas exchange occurs via diffusion (movement over a very short distance) however this is slow which is why the circulatory system exists to transport the gases faster. In order for this to occur it requires a thin membrane, moist surface, large surface area and underlying blood supply. This typically occurs in lungs, gills and skin.

Question 2

Lung Respiration

Answer 2

For animals with lungs air from outside the body must move into the lungs (inspiration/expiration). The exchange of gases from the lungs to the blood occurs externally however from blood to cells occurs internally. Ventilation (breathing) requires a pump (lungs). Perfusion (blood delivery to an organ) requires a pump (heart).

Question 3

Tetrapod Respiration

Answer 3

The evolutionary trend for these organisms is to increase body size or metabolic rate by increasing the compartmentalisation of the typically paired lungs.

Question 4

Mammal Respiration

Answer 4

For these organisms lung volume is proportional to body size however alveolar surface area (respiratory surface) varies with metabolic rate.

Question 5

Human Respiratory System Functions

Answer 5

Olfaction, non-specific defense against pathogens, acid-base balance, vocal communication, expulsion of abdominal contents, blood pressure regulation, blood and lymph flow and blood filtration. This moves air into and from the body for O2 and CO2 exchange.

Question 6

Embryological Development

Answer 6

From the beginning to the end of week 4 of fetal life 2 tracheal buds will form. From 4-8 weeks of fetal life the lungs will continue to develop until a general structure is achieved. These will continue to grow until pregnancy arrives. In some cases there are errors that can occur

Question 7

Respiratory System Anatomy

Answer 7

This has a conducting zone (anatomical dead space) which is the passages that conduct air to the respiratory zone. The respiratory zone is the area of distal airways where gas exchange occurs. The upper respiratory tract respirates the organs of the head and neck and only has conducting zones. The lower respiratory tract respirates the organs of the thorax and contains both a conducting and respiratory zone.

Question 8

Nasal Cavity

Answer 8

This is the start of the upper respiratory tract which contains a larger passage after the initial tubes which contains hair. The initial entry to this has stratified squamous epithelium to survive abrasion and after this opening the cells become ciliated pseudostratified columnar to capture any pathogens or unwanted substances and force them into the stomach. When inspiration occurs air is forced all around these which is fine during normal function however during intense exercise the mouth is opened as there are higher oxygen needs from the muscles.

Question 9

Nasal Fossae

Answer 9

The nasal cavity is separated (nasal septum) into 2 of these (right and left) each of which house 3 (superior, middle, inferior) conchae which are bony shelves (turbinate bones), covered by respiratory mucosa (epithelium + CT). Each of these has 60cm2 surface area. The conchae have a rich blood supply which engorges one side of the septum in order to recover that side from drying with the main volume of air flowing moving between nostrils every hour.

Question 10

Paranasal Sinuses

Answer 10

There are also these structures around the nasal fossae which are pockets into which air flows (these may close up when you’re sick). This is what causes voice change during sick periods.

Question 11

Palate

Answer 11

Humans have this feature which allows us to breath and chew at the same time. This is useful for herbivores which are required to chew for extended periods of time.

Question 12

Nasal Cavity Basics

Answer 12

The nasal cavity has approximately 10,000L of ambient air pass through the nasal airway per day and 1L of moisture is added to this air. This acts to modify air entering the respiratory tract by cleaning (entry hair to prevent pathogen and inner cilia and mucus), it moistens the air (glands, goblet cells and transudation (passage of fluid through a membrane)), it warms the air with blood sinusoids in CT of underlying epithelium (warms to 32-34C).

Question 13

Pharynx

Answer 13

This is a muscular funnel that extends from the posterior nasal aperture to the larynx. This is divided into 3 parts the nasopharynx which has ciliated pseudostratified columnar epithelium as it only deals with air as well as the oropharynx and laryngopharynx which are covered in stratified squamous epithelium as they deal with food, drink and air.

Question 14

Larynx

Answer 14

This is made up of cartilage (mostly hyaline). It functions to protect the airway and for phonation (speaking/making sounds). It contains ligaments, a hyoid bone, an epiglottis made of elastic cartilage which is highly mobile. This is also where the vocal cords are which have stratified squamous epithelium as they clash against one another to make sound. There are vestibular folds just above the vocal cords

Question 15

Glottis & Epiglottis

Answer 15

The glottis is a region found above the vestibular folds which can close and prevent things from entering the airway. During rest and speech this remains open however in preparation for swallowing this closes to prevent food from entering the lungs.

Question 16

Speech

Answer 16

In humans this is possible due to a reshaping and a descent of the tongue into the pharynx meaning the pharynx is longer and the larynx sits lower. This separates the soft palate and epiglottis which allows the pharynx to be a major vowel producing chamber. The high mobility of the tongue due to its shape and position means a large repertoire of sounds. These features assist with communication however can cause choking.

Question 17

Trachea

Answer 17

This is also known as the windpipe which is made up of 16-20 C-shaped rings of hyaline cartilage and is 12cm long. These rings keep this tube from collapsing during inhalation. The lumen is lined by ciliated pseudostratified columnar epithelium (PCE). It is spanned posteriorly by smooth muscle (trachealis). The gap in cartilage allows from for the esophagus to expand when food is swallowed. This acts as a mucociliary escalator (transporting mucus upward).

Question 18

Smoking Effects

Answer 18

This can cause the paralysis of cilia meaning that mucous removal requires coughing. Metaplasia (decreased mucus secretion and ciliary clearance of particulate matter) occurs making it much more difficult to breath as you continue to smoke.

Question 19

Lungs

Answer 19

These 2 structures are different shapes with a different number of lobes on each structure. The right side one has 3 lobes (superior, middle and inferior) whereas the left side one has 2 lobes (superior and inferior). Both of these structures are referred to as pyramids with an apex (top point) and a base (bottom) and various surfaces e.g. mediastinal (facing the other structure), costal (facing ribs). On mediastinal surfaces there are hilium which are the main entry point for bronchi, blood vessels, lymphatics (for fluid balance) and nerves.

Question 20

Bronchopulmonary Segments

Answer 20

These are smaller functional units of the lungs which work as units of lung tissue which come in groups of 8-10 depending on the lung.

Question 21

Bronchial Tree

Answer 21

At first the trachea branches into the main bronchi (primary), then separate further into lobar bronchi which comes in 3 types (superior, middle and inferior), these will then separate once again into segmental bronchi. The 3 large types (primary/main, secondary/lobar and tertiary/segmental) of bronchi all have cartilage in the walls and are all line with PCE.

Question 22

Bronchioles

Answer 22

These branch from segmental bronchi in which supportive cartilage isn’t found and smooth muscle is found in the walls. These are <1mm in diameter which contains PCE, simple ciliated columnar and cuboidal epithelium each of which divides into 50-80 terminal bronchioles.

Question 23

Terminal Bronchioles

Answer 23

These are the final branching of the conducting zone which are <0.5mm in diameter. These don’t have mucous glands or goblet cells. This epithelium is still ciliated (mucociliary escalator) each gives off 2 or more respiratory bronchioles.

Question 24

Respiratory Bronchioles

Answer 24

These are the branching that begins the respiratory zone as alveoli bud from walls meaning gas exchange can occur. This has some smooth muscle and will divide further down into 2-10 alveolar ducts.

Question 25

Alveolar Ducts

Answer 25

These are tthin walled passages with alveoli along the walls. The epithelium for these is simple squamous and end in alveolar sacs which are clusters of alveoli around a central space (atrium).

Question 26

Blood Supply

Answer 26

This is 98% of lung blood supply which are the way in which lungs receive blood. This has pulmonary arteries which are found throughout the whole body which carry deoxygenated blood from the right ventricle. This is concerned with systemic physiology e.g. gas exchange for all tissues of the body. These structures come after the bronchial tree that supply alveoli.

Question 27

Bronchial Arteries

Answer 27

This is 2% of lung blood supply which is responsible for lung physiology. It carries oxygenated blood from the aorta to the lungs in order to provide blood supply to bronchi, bronchioles, CT, visceral pleura and larger pulmonary blood vessels with O2 and nutrients.

Question 28

Alveoli

Answer 28

There are 2 types with squamous alveolar cells (Type I) and great alveolar cells (Type II) and alveolar macrophages. Type I are made up of simple squamous epithelium and are involved with the gas exchange as they have a small barrier of shared basement membrane with capillaries. Type II are supportive cells which repair Type I and produce surfactant in order to separate and ensure that the walls within lungs don’t stick together. Alveolar macrophages deal with debris within the alveoli and travel up tubes to be trapped by cilia and dealt with in the esophagus.

Question 29

Blood-Gas Barrier

Answer 29

The capillary and alveoli are separated by a shared basement membrane which is thin but tough (collagen). The thin nature of this barrier means that increased blood pressure in capillaries can break the barrier causing blood to leak into their alveoli.

Question 30

Gas Exchange Equilibrium

Answer 30

The efficiency of CO2 unloading and O2 loading via red blood cells (RBCs) depends on how long it takes for each gas to reach the point of fully unloaded/loaded which is typically 0.25 seconds in the capillary blood. This is compared to how long an RBC spends in an alveolar capillary which at rest this can be 0.75 seconds while during vigorous exercise it can be up to 0.3 seconds. This means that even at maximal blood flow this point can be reached. In good health at any one time there is 100mL of blood in alveolar capillaries.

Question 31

Pleura

Answer 31

These are double-layered membranes which surround the lungs and are attached to the thoracic cavity, mediastinum (area between the lungs) and diaphragm. It is involved in compartmentalisation of the lungs, reduction of friction and the creation of a pressure gradient. The outer layer is known as the parietal and the inner is the visceral between both of these there is a thin empty space called the pleural cavity which is filled with fluid. This isn’t truly double-layered as it is a single layer which is folded over itself (at the hilum of the lung) to form 2 layers.

Question 32

How Lungs Move

Answer 32

The pleural cavity is 10-30 micrometers wide (1 cell) and is filled with pleural fluid to prevent the friction of the 2 pleura. The fluid also ensures that the 2 layers of pleura cling to each other better (wet sheets of paper clinging) meaning the lungs are stuck to the thorax. This ensures that the lungs stay stable and together as it is very elastic and without attachment to the thorax they would flop. This means when the thorax moves the lungs do, the lungs don’t ventilate themselves but contain smooth muscles which affects airway diameter with the muscles controlling the lungs being skeletal.

Question 33

Breathing Terms

Answer 33

Normal resting quiet breathing is known as tidal volume. Forced breathing requires both the inspiratory reserve volume and expiratory reserve volume as breaths go beyond the rate of breathing at rest. Residual volume is a small amount of air which remains in the lungs no matter how much you try to remove it (1L). Capacities are 2 or move volumes of air which are added to give total capacity.

Question 34

Diaphragm

Answer 34

This muscle produces 2/3 of pulmonary airflow and is attached to the ribs and costal cartilages (7-12), the xiphoid process of the sternum and some lumbar vertebrae. It is innervated by the phrenic nerves during development these descend into the thorax (from the neck area) ahead of the respiratory tree (neck area) as this muscle forms in the neck region during development. When it contracts it moves inferiorly (1.5cm in relaxed breathing and up to 12 cm in deep breathing). It increases superior - inferior and anterior - posterior dimensions by flattening and pushing outward on the sternum and ribs. When relaxing it bulges upwards and compresses the lungs.

Question 35

Intercostal Muscle

Answer 35

These respiratory muscles are found between the ribs and they stiffen the thoracic cage during respiration and preventing it from caving inward when the diaphragm contracts. It also contributes to the enlargement and contraction of the thoracic cage which contributes 1/3 of the air that ventilates the lungs. It also acts in braking action to smooth the transition from inspiration to expiration.

Question 36

How Lungs are Ventilated

Answer 36

Breaching is a mechanical process which moves air into and out of the lungs. This occurs via aspiration which uses a pump to create negative pressure for air to enter. This involves a rhythmic change in thoracic volume in a cycle of inspiration and expiration. This is called a respiratory cycle (inspiration + expiration). Changing thoracic volume changes the air pressure of the lung relative to the environment. Breathing in increases chest volume and creates negative pressure making air flow in while breathing out decreases chest volume and creates a positive pressure making air flow out.

Question 37

Accessory Muscles for Respiration

Answer 37

These mainly assist forced respiration. For deep inspiration the muscles in the neck may be used to arch the back and elevate the ribs to increase thoracic volume. In forced expiration abdominal muscles can pull down on the ribs and sternum while pushing the abdominal contents superiorly to reduce thoracic volume to a greater degree.

Question 38

Breathing Mechanics

Answer 38

At rest atmospheric pressure is equal to inrapulmonary (inside lung) pressure so there is no airflow, at this point the intrapleural pressure is -5cm H2O and the intraulmonary pressure is 0cm H2O. During inspiration the diaphragm contracts and flattens which increases thoracic cavity space causing air to enter due to the negative intrapulmonary pressure -1cm H2O, the intrapleural pressure is even more negative -8cm H2O. During expiration the diaphragm relaxes and rises which decreases thoracic cavity space causing air to exit due to the increased intrapulmonary pressure +1cm H2O and the intrapleural pressure returns to -5cm H2O.

Question 39

Boyles Law

Answer 39

At a constant temperature the pressure of a given gas quantity is inversely proportional to its volume.

Question 40

Charles’s Law

Answer 40

At a constant pressure the volume of a given quantity of gas is directly proportional to its absolute temperature. Lung inflation is influenced by temperature change as the air inhaled is warmed to 37C by the time it arrives at alveoli. During thermal expansion 500mL of air inhaled of a 16C day will expand to 536mL.

Question 41

Neural Control of Smooth Muscle

Answer 41

Breathing requires repetitive stimuli from the brain. 1 form of neural control is required by smooth muscles of the airways which influences the speed of airflow through bronchodilation (expanding airways) and bronchoconstriction (contracting airways). This is under autonomic nervous control with the sympathetic controlling bronchodilation and the parasympathetic controlling bronchoconstriction.

Question 42

Neural Control of Automatic Breathing

Answer 42

Moving air into and out of the lungs requires skeletal muscles contraction and relaxation. This muscle requires nervous stimulation which is transmits information from the brain stem and cerebrum (small amount). Automatic breathing is controlled by 2 pairs of respiratory centers in the Pons and medulla oblongata (some influence from higher brain centers).

Question 43

Ventral Respiratory Group

Answer 43

For voluntary breathing there is a VRG which generates a rhythm (12 breaths/minutes) and contains inspiratory (I) and expiratory (E) neurons to produce this. When I neurons fire E neurons are inhibited and vise versa. I neurons cause diaphragm and intercostal muscles to contract (2 seconds) while E neurons cause these muscle to relax (3 seconds). The pontine respiratory group (PRG) receives input from higher brain centers (hypothalamus, cerebral cortex, gratification and aversion centers) which also affects depth of

Question 44

Dorsal Respiratory Group

Answer 44

There is also a DRG for voluntary breathing which modifies the basic rhythm of the VRG to adapt to various conditions by affecting the depth and rate (speed) of breaths. The DRG receives input from the Pons, chemoreceptors (medulla and major arteries), airway stretch/irritant receptors and higher brainstem centers (emotion).

Question 45

Pontine Respiratory Group

Answer 45

The PRG receives input from higher brain centers (hypothalamus, cerebral cortex, gratification and aversion centers) which also affects depth of rate of breathing with the outputs of this group going to both the DRG and VRG. It specifically adapts breathing to different activities e.g. sleep, exercise, vocalisation, crying, gasping, laughing etc. This is done to achieve voluntary breathing.

Question 46

Peripheral Chemoreceptors

Answer 46

These respiratory receptors are found in the carotid and aortic bodies of the large arteries above the heart which mostly respond to pH levels but also to O2 and CO2 blood levels. Sensory neurons in the glossopharyngeal (carotid body) and vagus (aortic body) nerves synapse with the DRG neurons.

Question 47

Stretch Receptors

Answer 47

These respiratory receptors are found in the smooth muscle of the bronchi and bronchioles and visceral pleura. These respond to extreme stretching (inflation) of the lungs by inhibiting inspiration (I neurons).

Question 48

Irritant Receptors

Answer 48

These respiratory receptors are nerve ending amongst the epithelial cells of the airway which respond to cold air, pollen, smoke, dust, chemical fumes and excess mucus which can result in coughing, shallow breathing, breath holding and bronchoconstriction.

Question 49

Central Chemoreceptors

Answer 49

These respiratory receptors are found in the medulla which respond to pH changes in CSF. As metabolism depends on the functioning of enzymes which are very sensitive to pH with slight changes able to shut down metabolic pathways and alter the structure and function of macromolecules. Normal pH sits between 7.35-7.45 however excess acids (acidosis) with pH <7 can cause coma and <6.8 can cause death, excess bases (alkalosis) with pH >7.7 can cause death. Excessive changes in pH are resisted by physiological and chemical buffer systems in the body. These buffers minimise changes in pH by releasing or binding H+ ions.

Question 50

pH Change

Answer 50

Neurons in the brainstem respond to pH change in the CSF. The pH change occurs when CO2 crosses the blood-brain-barrier (BBB) and reacts with water to form carbonic acid (CO2 + H2O -> H2CO3 -> HCO3- + H+). This means CSF pH levels are proportional to the level of CO2 in the body. This means that in order to maintain a stable pH breathing can be changed in order reduce the pH as the equation for carbonic acid can be reversed. In order to increase pH (less acidic) requires hyperventilation (over-breathing) blows off CO2 faster than the body can produce it meaning that pH also returns to normal.

Question 51

Voluntary Control of Breathing

Answer 51

This is what allows us to speak, sing and breath hold. This voluntary control originates in the motor cortex and bypasses the brainstem. Efferent neurons send impulses down the corticospinal tracts to integrating centers in the spinal cord. Holding breath raises CO2 blood level until a breakpoint is reached and then automatic control will override or you will faint and cause the automatic control to take over.