Respiratory System

1. Respiratory System The word respiration describes two processes: Internal or cellular respiration: is the process by which glucose or other small molecules are oxidized to produce energy: this requires oxygen and generates carbon dioxide. External respiration (breathing): involves simply: Inhaling (inspiration) - taking in oxygen from the air. Exhaling (expiration) - giving off carbon dioxide to it.

2. The respiratory system is responsible for providing the blood stream with life sustaining oxygen while removing toxic waste gases, enables the production of sound by passing over the vocal cords which in turn cause vibration, and is partially responsible for the compression of the abdominal muscles which assist in urination, defecation, and child birth as well as assists in laughter and other basic bodily functions surrounding the abdomen.

3. The respiratory system is made up of the organs involved in the interchanges of gases, and consists of the : The upper respiratory tract: includes the: nose, nasal cavity, pharynx and larynx. The lower respiratory tract : Airways beyond the larynx are divided into 2 zones: (1)The conducting zone where there is no gas exchange. This consists of the tracheal tube, which branches into two bronchi, one of which enters each lung and makes further branching. (2)The respiratory zone where gas exchange occurs. Consists of respiratory bronchioles with alveoli attached to them.

5. Nose and Nasal Cavity In humans, inspiration and expiration usually takes place through the nose. The nasal cavity is located inside the nose and joins the pharynx. The external openings to the nasal cavity are the external nares and the posterior openings from the nasal cavity into the pharynx are the internal nares.

6. Pharynx: It is the common opening of the digestive and respiratory systems. Receives air from the nasal cavity, and air, food and water from the mouth. Inferiorly, the pharynx leads to separate openings of the respiratory system (larynx) and digestive system (esophagus).

7. Larynx: The larynx consists of an outer casing of nine cartilages connected to each other by muscles and ligaments. Six of the cartilages are paired and three are unpaired.

8. Trachea: The trachea is a membranous tube that consists of dense regular connective and smooth muscle reinforced with 15-20 "C"-shaped pieces of cartilage. The cartilages form the anterior and lateral sides and protect the trachea and maintain an open passageway for air. The posterior wall contains no cartilage and consists of a ligamentous membrane and smooth muscle which can alter the diameter of the trachea.

9. Bronchi: The trachea divides into the right and left primary bronchi. The right bronchus is shorter and wider and is more vertical than the left bronchus. The lining of the bronchi is the same as the trachea and the bronchi are supported by "C"-shaped cartilage rings.

11. The lungs: Are the principal organs of respiration and on a volume basis, they are one of the largest organs of the body. The lungs are enveloped in a membrane called the pleura. The right lung is larger than the left lung as the right lung has three sections, called lobes while the left lung has two lobes. Each lobe is divided into lobules ( Nine lobules in the left lung and ten lobules in the right lung) that are separated from each other by connective tissue but the separations are not visible as surface fissures.

13. Alveoli: The Site of Gas Exchange Alveoli are hollow sacs having open ends continuous with lumens of airways. A pair of human lungs has about 300 million alveoli, providing a respiratory surface of about 70 m2 arranged in clusters like bunches of balloons. The alveolar inner walls lined by a single layer of flat epithelial cells called type I alveolar cells, interspersed by thicker, specialized cells called type II alveolar cells.

15. Mechanics of Breathing: Breathing is an active process - requiring the contraction of skeletal muscles. The muscles of inspiration include the external intercostals muscles (located between the ribs) the diaphragm (a sheet of muscle located between the thoracic and abdominal cavities), sternocleidomastoids and scalenes. The muscles of expiration includes internal intercostals and the abdominals.

17. Inspiration: 1- Contraction of external intercostals muscles elevation of ribs & sternum > increased front- to-back dimension of thoracic cavity. 2- Contraction of diaphragm diaphragm moves downward  increases vertical dimension of thoracic cavity. 3- Increased volume (about 0.5 liter) -->Decreased pulmonary pressure ( -1 mm Hg) air rushes into lungs to fill alveoli. 4- Deep/forced inspirations – as during exercise and pulmonary disease – scalenes, sternocleidomastoid, pectorals are used for more volume expansion of thorax.

18. Expiration: 1- Quiet expiration (exhalation) – simple elasticity of the lungs, relaxation of external intercostals muscles and diaphragm  return of diaphragm, ribs, and sternum to resting position> restores thoracic cavity to preinspiratory volume. 2- Decreases volume increased pulmonary pressure  movement of air out of the lungs. 3- Forced expiration – contraction of abdominal wall muscles (i.e. obliques and transverses abdominus) further decreases volume beyond relaxed point --- > further increased in pulmonary pressure - more air moves out.

22. Pulmonary Ventilation: Ventilation is exchange of air between atmosphere and alveoli. Air moves by bulk flow, from a high pressure to a low pressure region. Flow rate can be found with: F = (Patm - Palv)/R where, Patm, is the atmospheric pressure and Palv is the alveolar pressure. During ventilation, air is moved in and out of lungs by changing alveolar pressure through changes in lung dimensions.

23. Factors Influencing Pulmonary Ventilation A. Respiratory Passageway Resistance : 1. Upper respiratory passageways - relatively large, very little resistance to airflow (unless obstruction such as from food lodging or cancer). 2. Lower respiratory passageways - from medium-sized bronchioles on down, can alter diameter based on autonomic stimulation: a. Parasympathetic - causes bronchioconstriction. b. Sympathetic - inhibits bronchioconstriction. "Epinephrine" - used to treat life-threatening bronchioconstriction such as during asthma and anaphylactic shock (carried by people susceptible to sudden constriction).

24. B- Transpulmonary pressure = Palv - Pip Palv is zero, which means it is same as atmospheric pressure. Pip (intrapleural pressure) is negative, or less than atmospheric pressure because the elastic recoil of the lung inwards and the elastic recoil of chest wall outwards increases volume of intrapleural space between them and decreases the pressure within.. Therefore, transpulmonary pressure is greater than zero and this pressure puts an expanding force equal to the force of elastic recoil of lung and keeps it from collapsing. Volume of lungs is kept stable and there is air inside lungs.

25. C- Lung Compliance : Lung compliance is a measure of elasticity or the magnitude of change in lung volume (ΔVL) that can be produced by a given change in transpulmonary pressure. CL = ΔVL / Δ (Palv - Pip) Determinants of Lung Compliance 1- The elastic recoil of the lung tissue itself which determined by the elastic forces of the elastin and collagen fibers among the lung tissue. 2-The elastic force caused by the surface tension of the fluid that lines the inside walls of the alveoli and other lung air spaces.

26. Gas Exchange in Alveoli It is the process of exchange of O2 and CO2 between external environment and the cells of the body. In steady state, volume of oxygen consumed by body cells per unit time is equal to volume of oxygen added to blood in lungs, and volume of carbon dioxide produced by cells is identical to rate at which it is expired. The ratio of CO2 produced / O2 consumed is called respiratory quotient (RQ), which depends on type of nutrients being used for energy. It occurs by simple diffusion along partial pressure gradients.

27. What is Partial Pressure?: It's the individual pressure exerted independently by a particular gas within a mixture of gasses. The partial pressure exerted by each gas in a mixture equals the total pressure times the fractional composition of the gas in the mixture. So, given that total atmospheric pressure (at sea level) is about 760 mm Hg and, further, that air is about 21% oxygen, then the partial pressure of oxygen in the air is 0.21 times 760 mm Hg or 160 mm Hg.