Lec 15/16 - Respiratory System

Question 1

whats in the upper vs lower resp tract

Answer 1

upper = nasal cavities, sinuses, pharynx

lower = trachea, bronchi, lungs

Question 2

two functional componenets and what is included in them

Answer 2

conduction portion:
-nasal cavities
-sinuses
-pharynx
-larynx
-trachea
-bronchi
-bronchioles
-terminal bronchioles

respiratory portion:
-respiratory bronchioles
-alveolar ducts
-alveoli

Question 3

three principal functions and other functions

Answer 3

air conduction
* passage across olfactory mucosa in nasal cavity carries stimuli for smell
* passage through larynx used for vocalization

air filtration
* occurs in nasal passages & lungs

gas exchange (respiration)
* occurs in the alveoli of lungs

Other Functions:
- thermoregulation; acid-base balance; metabolism; protection; communication, etc.

Question 4

layers and details of the resp tract

Answer 4

Mucosa/Submucosa
* epithelium varies by location
- pseudostratified ciliated with goblet cells
- simple columnar with cilia
- simple cuboidal
* lamina propria/submucosa (combined)
- irregular CT with elastic fibers
- serous or mucous glands
- sometimes venous sinuses (enlarged venules); lymphoid tissue
* cartilage/bone with perichondrium or periosteum
- bone for sinuses/turbinates (chonchae)
- elsewhere, cartilagenous rings & plates

Muscularis: smooth muscle; complete layers or just a few cells

Adventitia/Serosa: variable depending on location

Question 5

how is air conditioned in the conducting portion, what does the nasal cavity projection, why is there increased surface area

Answer 5

conducting portion of respiratory system conditions air:
* warmed: by vascular plexus & moistened by mucous & serous glands
* filtered: particles removed by hairs & mucus
* immune response: to inhaled
antigens and microorganisms (e.g. pharyngeal tonsil)
* nasal cavity has projecting turbinate bones (also known as conchae)
* increased surface area, blood sinuses for ‘air conditioning’

Question 6

vestibule, resp mucosa, olfactory mucosa; type of epithelium and what is present

Answer 6

Vestibule
* transition from integument to nasal epithelium
* stratified squamous keratinized epithelium

Respiratory mucosa
* most of the nasal cavity
* respiratory epithelium: ciliated pseudostratified columnar epithelium with goblet cells

Olfactory mucosa
* olfactory epithelium: very tall ciliated pseudostratified columnar
epithelium with bipolar neurons no goblet cells

Question 7

respiratory epithelium; classification of epith, abundant cells, other cells present, functions

Answer 7

• pseudostratified columnar epithelium with several cell types; all
  contact basal lamina/basement membrane
• ciliated columnar cells most abundant; hundreds of long cilia on
  apical surface
• small rounded/pyramidal cells at basement membrane are mostly
  stem cells (~30% of cells)
• columnar cells (brush cells) with small apical surfaces bearing tuft
  of short, blunt microvilli: sensory?
• mucus-secreting goblet cells
• intraepithelial lymphocytes & dendritic cells also present in
  respiratory epithelium: immune surveillance

Question 8

olfactory epithelium; where is it, what does the epithelium contain, secretions, flow

Answer 8

• patch of epithelium at top of nasal cavity associated with sense of smell
• pseudostratified columnar epithelium contains:
  -bipolar neurons with long sensory cilia
  -columnar epithelial supporting cells
  -basal cells
• neuron fibres pierce skull through
  cribiform plate to reach olfactory bulb (cranial nerve I)
• basal/stem cells replace both olfactory neurons (every 2-3 months) and epithelial support cells
• serous olfactory glands secrete watery product to dissolve olfactory molecules
• continuous flow of secretions washes older odors away

Question 9

larynx; where is it, epithelium, interconnections, vocal sounds

Answer 9

• short air passage between pharynx and trachea; lined with stratified squamous or respiratory epithelium
• rigid wall reinforced by hyaline cartilage and smaller elastic cartilages (e.g. epiglottis)
• laryngeal cartilages interconnected by ligaments
• vocal folds or ‘cords’ covered by stratified squamous epithelium
• movement of cartilages by striated
  volcalis muscle (VM) responsible for vocal sounds

Question 10

trachea; what makes up the bronchial tree, where is it located, bifurcation

Answer 10

• bronchiole tree consists of trachea, bronchi & bronchioles
• passageways conducting, conditioning & distributing air into lungs
• generally similar plan with cartilage
  components to keep airways open
• trachea largest component, located in mediastinum
• extends from larynx to bifurcation
  point where gives rise to paired primary bronchi
• supported by C-shaped hyaline cartilage rings stacked along length
• smooth muscle & fibroelastic CT bridges gap between ends of cartilage

Question 11

trachea histology, layers

Answer 11

Mucosa/Submucosa
* respiratory epithelium
* lamina propria of loose/elastic CT
* seromucous glands producing watery mucus

Muscularis
* smooth muscle of trachealis muscle
(Cartilagenous layer with perichondrium)

Adventitia

Question 12

bronchial tree - dividing, lung lobe division

Answer 12

• trachea divides into two primary
  bronchi that enter each lung at the hilum, along with arteries, veins and
  lymphatic vessels
• primary bronchi branch into several secondary bronchi; each supplies one lung lobe
• secondary bronchi branch into tertiary and then into smaller bronchi within each lung lobe
• lung lobes divided into multiple segments, each with bronchus, blood supply & CT septum

Question 13

bronchus histology; why is there folding, what is discontinous, glands

Answer 13

• respiratory epithelium & mucosa folded due to contraction of smooth
  muscle
• wall surrounded by discontinuous plates of hyaline cartilage
• contains seromucous glands in submucosa which drain into the lumen

Question 14

bronchus wall; epithelium, lamina propria contains, whats in the submucosa and adventitia, what directly surrounds the adventitia

Answer 14

• epithelial lining of pseudostratified ciliated columnar cells; a few goblet cells
• lamina propria contains distinct layer of smooth muscle surrounding entire bronchus
• submucosa site of supporting cartilage
• adventitia includes blood vessels & nerves
• lung tissue directly surrounds adventitia of bronchi
• in smaller bronchi epithelium is primarily columnar cells with cilia
• fewer goblet cells
• lamina propria has both smooth muscle & small serous glands near cartilage

Question 15

bronchioles; what are they, what does it contain and epithelium in each

Answer 15

• bronchioles are airways with small diameters (~1 mm or less)
• they have no mucosal glands or cartilage
• dense connective tissue associated with smooth muscle
• large bronchioles: ciliated pseudostratified columnar epithelium
• small bronchioles: ciliated simple columnar epithelium
• smallest (terminal) bronchioles: ciliated simple cuboidal epithelium

Question 16

terminal bronchioles; last part of what, layers, cells

Answer 16

• terminal bronchioles: last parts of air conducting system before the sites of gas exchange
• only one or two layers of smooth muscle surrounded by connective tissue
• epithelial layer contains ciliated cuboidal cells and many low columnar nonciliated cells: Club cells

Question 17

club cells; other name, characterized by what, functions

Answer 17

Club cells (Clara cells) are also called
exocrine bronchiolar cells
* characterized by non-ciliated, dome-
shaped apical regions with secretory
granules

Functions:
* secretion of surfactant components,
cytokines, anti-inflammatory peptides & anti-microbial lysozymes
* detoxification of inhaled xenobiotic
compounds by cytochrome p450 enzymes of SER

Question 18

mucocilliary clearance (escalator); where does it begin, what is it important for, action

Answer 18

• begins at ciliated epithelial lining of bronchioles & continues upward
• important for clearing debris & mucus by upward movement along bronchial tree & trachea
• similar action sweeps mucus & debris down from nasopharynx

Question 19

what is the respiratory portion involved in, what is it characterized by, acinus, alveolar ducts, alveolar sacs

Answer 19

Respiratory portion involved in:
* exchange of O 2/CO 2
* removal of particles
* immune defense
* control of air flow- regulates
inspiration & expiration

Characterized by alveoli:
* sacs with extremely thin walls containing mostly blood vessels
* lined by a simple squamous
epithelium = sites of gas exchange

• terminal bronchiole begins functional respiratory unit called acinus
• within acinus, terminal bronchiole subdivides into two or more
  respiratory bronchioles with occasional alveoli in walls
• alveolar ducts are at distal end of respiratory bronchiole; consist of linear series of alveoli, each with smooth muscle fibers around the opening
• alveolar duct ends at terminal alveolar sac, surrounded by alveoli it supplies

Question 20

resp bronchiole; what gives rise to it, epithelium, muscle

Answer 20

-longitudinal section through terminal bronchiole (B) giving rise to respiratory bronchioles (RB) with alveoli in their walls cross section through respiratory bronchiole with alveoli (a) opening into wall of RB

• respiratory bronchioles still have a layer of smooth muscle
• primarily simple cuboidal epithelium (and simple squamous epithelium in connected alveoli)

Question 21

alveolar ducts and sacs; what does each consist of, where do alveoli open into

Answer 21

• alveolar ducts (AD) consist of linear series of alveoli, each with smooth
  muscle fibers around opening
• end in two or more
  alveolar sacs (AS)
• individual alveoli (A) all open either to the alveolar sacs or alveolar ducts

Question 22

alveoli - what are they, function, how are alveolar air spaces separated

Answer 22

• small, rounded pouches that open on one side to a respiratory bronchiole, alveolar duct, or alveolar sac
• alveolar function is exchange of O2
  contained from air inside them with the CO 2 contained in blood carried by surrounding capillaries (C)
• alveoli air spaces separated from one another by alveolar septa (septal walls)
• neighbouring alveoli interconnected by alveolar pores: balance air pressure
• septal walls contain continuous
  capillaries, macrophages, fibroblasts covered by alveolar epithelium

Question 23

alveolar epithelium; vulnerable interface between what, formed by what cell types, cell % and their function

Answer 23

• alveolar epithelium is vulnerable biological interphase between air & blood: exposed to destabilizing forces, inhaled particles, pathogens & toxins

Formed by two cell types:

Type I alveolar cells (type I pneumocytes):
* 40 % of alveolar epithelial cells; cover 95 % of alveolar surface
* thin squamous cells joined by occluding junctions; barrier function
* incapable of cell division.

Type II alveolar cells (type II pneumocytes or septal cells):
* 60 % of the alveolar epithelial cells; cover only 5 % of alveolar surface.
* cuboidal cells that bulge into air space; protective & stem cell function (similar to Club cells)
* apical cytoplasm filled with typical granules known as lamellar bodies, contain surfactant

Question 24

blood air barrier; other name, components, gas exchange

Answer 24

• also called respiratory membrane; three-component layer that separates air in alveoli from capillary blood

Components of the barrier:
a) single layer of type I cells lining the alveolus
b) basal lamina of these cells and of the capillary endothelial cells; sometimes fused
c) thin continuous (non-fenestrated) endothelial cells of the capillaries

Gas exchange:
* O 2 from alveolar air diffuses through the blood-air barrier
* H 2CO 3 inside erythrocytes is converted to CO 2 in lung capillaries
* CO 2 diffuses to the air inside the alveoli & is exhaled

Question 25

type 2 cells; what are they, what do they do, formed by what, secreted by what, facilitates respiration by what

Answer 25

• complex lipoprotein surface agent that lines alveolar interior
• reduces surface tension and prevents luminal adhesion should wall of the airway collapse on itself, particularly during expiration
• formed by combination of phospholipids, neutral lipids & proteins
• secreted by alveolar type II cells via exocytosis of specific storage granules called lamellar bodies
• facilitates respiration by:
• preventing alveolar collapse at exhalation
• permitting alveolar inflation with less inspiration force
• modulates alveolar immune response

Question 26

alveolar macrophages (dust cells); derived from what, present where, function, migration

Answer 26

derived from the blood monocytes (mononuclear phagocytic system)
* present in both connective tissue of septum and air space of alveolus
* phagocytize inhaled particles (dust, pollen, silica, carbon, etc.) in air space
* most migrate to bronchioles, are carried up by the mucociliary apparatus and disposed of by swallowing at the pharynx
* some macrophages may remain in septal connective tissue for a lifetime as septal macrophages

Question 27

pleural membranes; serous layers, epithelium, facilitates what

Answer 27

• serous layers that cover internal wall of thoracic cavity (parietal pleura) and outer surface of lung (visceral pleura)
• simple squamous epithelium (mesothelial cells) on thin layer of CT
  containing collagen & elastin fibers
• pleural cavity lies between parietal and visceral pleura
• both surfaces (lung and thoracic wall) covered by thin layer of serous fluid; facilitates sliding of surfaces during respiration

Question 28

pulmonary circulation in the lung; what happens here

Answer 28

Supplies alveoli; for gas exchange:
* enters lung O 2-depleted and leaves O 2-rich
* arteries/arterioles run parallel to bronchial tree:
- starts with branches of pulmonary artery that leave right ventricle
- arterioles branch into capillaries (blood-air barrier) at level of alveolar
duct
* blood collected by alveolar venules,
then veins, then returned to left atrium

Question 29

bronchial circulation in the lung; what does it supply, blood, branching, drainage

Answer 29

Supplies lung tissue other than alveoli
* carries systemic, nutrient- rich blood
* bronchial arteries branch from aorta
* bronchial arterioles drain into pulmonary capillaries at junction between conducting & respiratory passages
* most blood from bronchial circulation leaves lung via pulmonary circulation, rather than in bronchial veins

Question 30

control of lung function; nerve supply, ventilation … where they are found, what they include and do

Answer 30

Nerve Supply
* usually found in connective tissue surrounding larger elements of bronchial tree
* both parasympathetic and sympathetic autonomic fibers;
regulate smooth muscle contraction in bronchial tree (air flow)
* visceral afferent fibers also present- pain sensation

Ventilation
* involuntary control of respiration is central (CNS)
* based on levels of arterial blood gasses
- aortic & carotid bodies sense partial pressure of blood O 2
- regions in brainstem sense pH and partial pressure of CSF CO 2 (reflective of arterial blood CO 2 levels)
* this information is carried to respiratory centres in brain, coordinated & then efferent signals sent to diaphragm and intercostal muscles