1. HUMAN RESPIRATORY SYSTEM

4. Function Provides airways for respiration
Moistens and warms entering air
Filters inspired air and cleanses it
Serves as resonating chamber for speech
Houses the olfactory (smell) receptors

5. Respiration include four processes:
Pulmonary ventilation (air in/out, gas exchanged in lungs)
External respiration (gas exchanged between blood and alveoli in lungs)
Transport of respiratory gases (transport of oxygen and carbon dioxide)
Internal respiration (gas exchange between blood and tissues)

6. Nose
External nose composed of dense fibrous connective tissue and cartilage attached to nasal, frontal, and maxillary bone
External nares (nostrils) lead into nasal cavity which is divided by the nasal septum (composed of hyaline cartilage and vomer bone)
Nasal cavity entrance contains vestibule with vibrissae
Nasal cavity lined with olfactory mucosa and respiratory mucosa (mucous and serous glands) and contains lateral projections (superior, middle, inferior nasal conchae)
Internal nares in posterior nasa cavity lead into the nasopharynx

7. NOSE/ Pharynx

8. Pharynx
Connects nasal cavity and mouth to larynx and esophagus (throat)
Three regions:
Nasopharynx - lined with pseudostratified epithelium and houses the pharyngeal tonsil (adenoids)
Oropharynx - lined with stratified squamous epithelium, located posterior to oral cavity, include archway (fauces) between uvula and epiglottis, and contain palantine and lingual tonsils
Laryngopharynx - lined with stratified squamous epithelium, common passageway for food and air, posterior to epiglottis

9. Larynx
Voice box attached to hyoid superiorly and inferiorly with trachea
Composed of corniculate, arytenoid, cricoid, and thyroid cartilage
Functions:
Provide open airway
Act as switching mechanism (epiglottis) to route air and food
Voice production (vestibular fold or false vocal chord and vocal fold or true vocal cord)

10. Trachea
Windpipe
Descends from larynx through neck into mediastinum and ends by dividing (at carina) into two primary bronchi
Walls (mucosa, submucosa, hyaline cartilage and adventitia)
lined with pseudostratified epithelium

11. Bronchi and Subdivisions (bronchial tree)
Conducting zone structures - right and left primary (principle) bronchi branch into:
Secondary bronchi (3 on right 2 on left) which branch into
Tertiary (segmental) bronchi which branch into
4th, 5th, etc orders
Until bronchioles then terminal bronchioles
Tissue composition of walls of primary bronchi is same as trachea but decreases in size of conducting tubes, then increase in change in composition with each subsequent subdivision:
Cartilage rings replaced by irregular plates of cartilage
Epithelium: Pseudostratified, then columnar, then cuboidal; cilia and mucus producing cells only in upper bronchioles
Smooth muscle increases with decreasing size of bronchioles

13. Respiratory zone structures -
Terminal bronchioles divide into respiratory bronchioles with scattered air sac outpocketing from walls, branch into
Alveolar ducts with sacs called alveoli (chambers where bulk gas exchange occurs)
Alveolar sacs open into a common chamber called an atrium
Air sacs (alveoli) provide surface area for gas exchange
Respiratory membrane - ingle layer of squamous epithelium (Type I pneumocytes) with pulmonary capillaries
Respiratory membrane (air-blood barrier) site of gas exchange (by diffusion)
Diffusion requires moist membrane, therefore there are cuboidal epithelium (Type II pneumocytes) that secretes surfactant, coating gas-exposed alveolar surfaces
Alveoli contain alveolar macrophages that provide an immunologic defense.

16. Lungs and Plurae
i. Lungs
Three lobes on right and two lobes on left
Occupy the entire thoracic cavity, suspended in its own pleural cavity connected to the mediastinum by vascular and bronchial attachments (roots)
Lung tissue also referred to as stroma
ii. Pluera
Thin, double-layered serosa
Parietal pluera lines the thoracic cavity and visceral pleura covers external lung surface

17. Mechanisms of Breathing (Pulmonary ventilation - inspiration and expiration)
A. Pressure relationships in the thoracic cavity
Respiratory pressures are always given relative to atmospheric pressure
Thoracic cavity
Intrapulmonary pressure - pressure within the alveoli of the lungs; always equal to atmospheric pressure
Intrapleural pressure - pressure within pleural cavity; always 4 mm Hg less than atmospheric pressure in alveoli; results from factors holding lungs to thorax wall and those acting to pull lungs away from wall
Negative pressure in the intrapleural space results from the interaction between factors acting to hold the lungs to the thorax wall and factors acting to pull the lungs away
factors holding lungs to thorax walls:
Adhesive force (surface tension) created by pleural fluid in pleural cavity
Positive pressure within lungs (interpleural pressure is always greater than intrapleural)
Atmospheric pressure acting on thorax (atmospheric pressure pushing on chest is greater than intrapleural pressure, therefore thorax wall tends to be "squeezed" in)
Factors forcing the lungs away from thorax wall
Natural recoil tendency of lungs (due to elasticity)
Surface tension of the fluid film in alveoli (draws the alveoli to smallest possible dimension)
Question: what is the role of the diaphragm and the role of internal/external costal muscles in regulating pressure differentials?

18. Respiration
Respiration = the series of exchanges that leads to the uptake of oxygen by the cells, and the release of carbon dioxide to the lungs
Step 1 = ventilation
Inspiration & expiration
Step 2 = exchange between alveoli (lungs) and pulmonary capillaries (blood)
Referred to as External Respiration
Step 3 = transport of gases in blood
Step 4 = exchange between blood and cells
Referred to as Internal Respiration
Cellular respiration = use of oxygen in ATP synthesis

19. INSPIRATION EXPIRATION
a passive event due to elastic recoil of the lungs. However, when a great deal of air has to be removed quickly, as in exercise, or when the airways narrow excessively during
expiration, as in asthma, the internal intercostal muscles and the anterior abdominal muscles contract and accelerate expiration by raising pleural pressure.
The active part of the breathing process, which is initiated by the respiratory control centre in medulla oblongata (Brain stem). Activation of medulla causes a contraction of the diaphragm and intercostal muscles leading to an expansion of thoracic cavity and a decrease in the pleural space pressure

20. Schematic View of Respiration
External Respiration
Internal Respiration

21. Inspiration Expiration
Pulmonary Ventilation: Inspiration and Expiration
Inspiration 
Inspiratory muscles (external intercostals) contract; diaphragm descends; rib cage rises
Thoracic cavity volume increases
Lungs stretched; intrapulmonary volume increases
Intrapulmonary pressure decreases
Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is zero (equal to atmospheric pressure)
Ribs elevated and sternum flares as external intercostals contract; diaphragm moves inferiorly during contraction
Expiration 
Inspiratory muscles relax (diaphragm rises, ribcage descends due to gravity)
Thoracic cavity volume decreases
Elastic lungs recoil passively; the intrapulmonary volume decrease
Intrapulmonary pressure rises
Air (gases) flows out of lungs down its pressure gradient until intrapulmonary pressure is zero 
Ribs and sternum depressed as external intercostals relax; diaphragm moves superiorly as it relaxes

23. Molecular oxygen is carried in blood in two ways:
Bound to hemoglobin within red blood cells (98.5%)
Dissolved in plasma (1.5%)
Oxyhemoglobin (HbO2) / doexyhemoglon (Hhb)
Hemoglobin - composed of four polypeptide chains each containing and iron (heme) group;
Oxygen binding is result of "cooperation"; first oxygen bound to one heme causing change in shape of hemoglobin so that the other peptides will bind more oxygen
affinity for oxygen increases with each oxygen bound until saturation; conversely, release of oxygen from hemoglobin increases with each oxygen released

25. Carbon Dioxide
Active body cells produce about 200ml of carbon dioxide/minute(released by lungs)
Carbon dioxide is transported in blood in three forms:
Dissolved in plasma (7% to 10%), remainder enter RBCs
Chemically bound to hemoglobin in RBCs (20% to 30%); carried within RBCs as carboaminohemoglobin; carbon dioxide binds to amino acids not heme, therefore does not compete with the oxyhemoglobin transport

27. 2. REGULATION AND CONTROL OF BREATHING
In order to maintain normal levels of partial oxygen and carbon dioxide pressure both the depth and rate of breathing are precisely regulated.
Basic elements of the respiratory control system are
(1)strategically placed sensors
(2) central controller
(3) respiratory muscles

29. CENTRAL CONTROLLER:
Breathing is mainly controlled at the level of brainstem. The normal breathing is triggered and controlled by the respiratory centres located in the pons and medulla.

30. 1. Medullary respiratory centre:
Dorsal medullary respiratory neurones are associated with inspiration: basic rhythm of breathing.
Ventral medullary respiratory neurones are associated with expiration. They are activated during forced expiration when the rate and the depth of the respiration is increased e.g. exercise.
The increased activity of the expiratory system inhibits the inspiratory centre and stimulates muscles of expiration.
The dorsal and ventral groups are bilaterally paired and there is

32. 2.Apneustic Centre:
Nerve impulses from the apneustic centre stimulate the inspiratory centre and without constant influence of this centre respiration becomes shallow and irregular.

33. 3.Pneumotaxic centre:
It is located in the upper pons. This centre is a group of neurones that have an inhibitory effect on the both inspiratory and apneustic centres. It is probably responsible for the termination of inspiration by inhibiting the activity of the dorsal medullar neurones.
Activation of the inspiratory centre stimulates the muscles of inspiration and also the pneumotaxic centre. Then the pneumotaxic centre inhibits both the apneustic and the inspiratory centres resulting in initiation of expiration.

34. RESPIRATORY MUSCLES:

35. summary
The inspiratory muscle contractions allow the flexible bellows (the chest wall) to expand thereby lowering the intrathoracic pressure in the respiratory system air conduits to less than atmospheric pressure. As we know from the principles of physics, air flows into the place where pressure is lower and thus moves down into the alveoli where carbon dioxide and oxygen are exchanged and respiration is completed.
The respiratory center is affected by various stimuli, the most important being the pH of the cerebrospinal fluid bathing that area of the brain. This pH is primarily due to carbon dioxide (CO2) which is freely diffusible throughout the tissues of the body. Low oxygen (O2) can have a similar stimulatory effect on the respiratory center.
The respiratory center can also be affected by the effect of O2 and CO2 on the carotid and aortic bodies as well as by stretch receptors in the smooth muscles of the airways, irritant receptors between the epithelial cells in the airway, joint and muscle receptors, and juxtacapillary (or J) receptors in the alveolar walls.
Expiration during spontaneous breathing is a passive process. Once the inspiratory center ceases to fire, the inspiratory muscles cease to contract, and the elastic recoil of the lungs and chest wall causes the pressure in the airways to rise above atmospheric pressure. The result is movement of the airway gases to the outside of the body. Expiration can also be active via impulses from the cerebral cortex.