Respiratory System

Question	Answer
Function of the Respiratory System	• To supply the body with oxygen and dispose of carbon dioxide – respiratory function must involve: 1. Pulmonary ventilation–moving air into and out of the lungs 2. External respiration–gas exchange between the lungs and the blood 3. Transport–transport of oxygen and carbon dioxide between the lungs and tissues 4. Internal respiration–case exchange between systemic blood vessels and tissues
Structures of the Respiratory system	 Nose  Pharynx  Larynx  Trachea  Bronchi  Lungs – alveoli  Diaphragm
Coverings of the Lungs	 Pulmonary (visceral) pleura covers the lung surface  Parietal pleura lines the walls of the thoracic cavity  Pleural fluid fills the area between layers of pleura to allow gliding
Mechanics of Ventilation	 Completely mechanical process  Depends on volume changes in the thoracic cavity  Volume changes lead to pressure changes, which lead to the flow of air to equalize pressure  Air moves from area of higher to area of lower pressure
Volume - Pressure relationship	 Increase volume = decrease pressure  Decrease volume = increase pressure
Mechanics of Ventilation	 Two phases  Inspiration – flow of air into lung  Expiration – air leaving lung
Inspiration. A	- Diaphragm and external intercostal muscles contract - The volume of the thoracic cavity increases (lungs are stretched – increasing intrapulmonary volume)
Inspiration. B	- Increased volume results in decreased intrapulmonary (within the lung) pressure - Air moves from higher atmospheric pressure to lower intrapulmonary, until intrapulmonary pressure = atmospheric pressure
Expiration. A	• Largely a passive process - inspiratory muscles relax and the rib cage descends due to gravity • Thoracic cavity volume decreases • Elastic lungs recoil passively and intrapulmonary volume decreases
Expiration. B	• Intrapulmonary pressure rises above atmospheric pressure • Gases flow out of the lungs down the pressure gradient until intrapulmonary pressure equals atmospheric pressure
Forced Expiration	- An active process - Internal intercostals and abdominals contract - Greater decrease in intrapulmonary volume - Greater increase in intrapulmonary pressure - In healthy lungs this results in a larger volume of air leaving the lung at a greater speed
Intrapleural Pressure	 Normal pressure within the pleural cavity (intrapleural pressure) is always negative (subatmospheric)  Negative intrapleural pressure keeps lungs from collapsing
Respiratory Membrane	- Respiratory membrane (air-blood barrier) - Thin layer of epithelial cells lining alveolar walls - Pulmonary capillaries cover external surfaces of alveoli
Gas Exchange - External Respiration. A	- Gas crosses the respiratory membrane by diffusion (from high to low concentration) - Oxygen moves into the blood - The alveoli always has more oxygen than the blood - Oxygen moves by diffusion towards the area of lower concentration - Pulmonary capillary blood gains oxygen
Gas Exchange - External Respiration. B	- Carbon dioxide moves out of the blood - Blood returning from tissues has higher concentrations of carbon dioxide than air in the alveoli - Pulmonary capillary blood gives up carbon dioxide - Blood leaving the lungs is oxygen-rich and carbon dioxide-poor
Gas Exchange - External Respiration Chem	Gas Exchange - External Respiration Alveoli PO2=104 -> PCO2=40 Capillary PO2=40 <- PCO2=45 P = Partial pressure (mmHg) / Amount of a gas
Gas Exchange – Internal Respiration	- Exchange of gases between blood and body cells - An opposite reaction to what occurs in the lungs - Carbon dioxide diffuses out of tissue to blood  - Oxygen diffuses from blood into tissue
Gas Transport in the Blood	- Oxygen transport in the blood - Inside red blood cells attached to hemoglobin (oxyhemoglobin [HbO2]) - O2 + Hb <---> HbO2 - A small amount is carried dissolved in the plasma
Gas Transport in the Blood	- Carbon dioxide transport in the blood - Most is transported in the plasma as bicarbonate ions (HCO3–)  CO2 + H2O<-> H2CO<->3 H+ + HCO3- ^--------------------->----------------------^ - A small amount is carried inside red blood cells on haemoglobin, but at different binding sites than those of oxygen
Factors Controlling Ventilation Chemical factors. A Neural centers that control rate and depth are located in the medulla (part of brainstem)	- Carbon dioxide levels - Level of carbon dioxide in the arterial blood is the main regulatory chemical for respiration - Increased carbon dioxide increases respiration - Changes in carbon dioxide act directly on chemoreceptors in the medulla - increases neural output to diaphragm and intercostals.
Factors Controlling Ventilation Chemical factors. B	•Increased arterial PCO2 •Stimulates chemoreceptors in medulla •Activates respiratory centre •Increased rate Motor impulses to respiratory muscles •Increased ventilation •Decreases arterial PCO2
Factors Controlling Ventilation Chemical factors. C	- Oxygen levels - Arterial oxygen levels are monitored by peripheral chemoreceptors - Substantial drops in arterial PO2 (to 60 mm Hg) are needed before oxygen levels become a major stimulus for increased ventilation
Factors Controlling Ventilation	• Cortical controls are direct signals from the cerebral motor cortex that bypass medullary controls – Examples: voluntary breath holding, taking a deep breath • Emotional factors-hypothalamic controls act through the limbic system to modify rate and depth of respiration – Example: breath holding that occurs in anger
Other Factors Influencing Ventilation Rate and Depth	- Physical factors  Increased body temperature  Exercise

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	Created by Jonathan Cash almost 9 years ago