Human Respiratory System

Human Respiratory System

• Its main function is to supply O2 for energy metabolism and remove CO2, a byproduct of metabolism.
• It works closely with the cardiovascular system to transport gases.
• Plays a role in vocal communication.
• Provides nonspecific defense against pathogens.
• Helps control the pH of body fluids.

Structure

• Includes all structures that conduct air to and from the lungs.
• Lungs are located within the thoracic cavity for protection against drying out.
• The upper respiratory tract consists of the nose, pharynx (throat), and larynx (voice box).

Airflow

• Air enters through the nose and flows past the pharynx, trachea, bronchi, and finally into the lungs.
• The process involves filtering debris, warming the air, and adding moisture.
• Air that reaches the lungs is at body temperature and saturated with water.
• Nose hairs filter out large particles.
• Mucus, produced by goblet cells in the trachea and bronchial tubes, traps dust, bacteria, and other substances amd moist air passages.
• Cilia in the airway move to keep air passages clean, but cigarette smoke can impair their function.

Air flows from nose to larynx

• Air enters through nose or mouth then flows past the pharynx through the glottis into the larynx, which is protected by the epiglottis.
• The larynx is held open by cartilage that forms the Adam's apple.
• Air flows from the larynx down the trachea to the bronchi.

Vocal Cords

• Located at the edges of the glottis between the cartilages of the larynx (thyroid and arytenoid cartilage).
• Tissues vibrate to create sounds as air passes across them.
• Longer cords vibrate slowly and produce deeper sounds.
• Little boys and girls have short cords and high-pitched voices.
• The larynx enlarges more in males than in females at puberty.
• Adult males have thicker, longer cords that produce lower tones than females.

Swallowing

• The hard and soft palates separate the nasal cavities from the mouth.
• The larynx rises and the glottis closes due to the epiglottis during swallowing.
• Food goes down as the soft palate moves backward covering entrance to nasal canal.

Trachea and Lungs

• The trachea is a tough, flexible tube supported by about 20 c-shaped tracheal cartilages, which prevent collapse or overexpansion during pressure changes.
• The trachea divides into two primery bronchial tubes, one for each lung.
• The right lung has three lobes and is slightly larger than the left lung, which has two lobes.
• Lobes of the lungs are separated by deep fissures.
• Primary bronchial tubes divide into smaller bronchi, which then divide into conducting, terminal and respiratory bronchioles.

Alveoli

• The bronchioles end in alveoli, where O2 and CO2 exchange occurs.
• The alveolar epithelium is composed of thin simple squamous epithelium.
• Alveolar macrophages protect the epithelium.
• The alveolar exchange surface is approximately 140 square meters.
• Surfactant cells make an oily secretion (surfactant) that coats the epithelium.
• Lung surfactant decreases the surface tension of water.
• The walls of the alveoli are very thin, and the surfactant helps prevents them from collapsing

Pleura

• Lungs are covered by two layers called pleura.
• The visceral pleura covers the outer surface of the lungs, while the parietal pleura lines the chest cavity.
• The pleural cavity between these two layers is a potential space.
• A thin layer of fluid provides lubrication, reducing friction and irritation.

Healthy and diseased lungs

• Healthy lungs consist of spongy, pinkish-grayish tissue.
• Polluted lungs have blackened spots due to carcinogens or carbon particles.
• Healthy lungs are elastic.
• Emphysema can cause loss of elasticity.
• When lungs can't expand or transfer oxygen a person has difficulty breathing and tires easily.

Breathing

• Airways must be open and free from inflammation and excess mucus.

Respiration Process

• A respiratory cycle consists of one inhalation and one exhalation.
• Humans breathe using negative pressure.
• During inhalation, lowering the diaphragm and raising the ribs increases the thoracic cavity volume forming negative pressure, causing air under outside greater pressure to flow into the lungs.
• Increases in CO2 and H+ and decreases in O2 stimulate breathing rate.
• Chemoreceptors monitor the chemical content of the blood.
• The aortic and carotid bodies are chemoreceptors.
• Information goes to respiratory center in the medulla oblongata.
• Breathing rate increases when CO2 or H+ rises.
• The center is sensitive to blood reaching the brainstem.

Diaphragm and Breathing Modes

• Quiet breathing : Inhalation --> active Exhalation --> inactive Inhalation: diaphragm ( 70% ) + external intercostal muscles contract --> volume of lungs increase --> pressure decreases --> air rushes into the lungs --> pressure equalize. Exhalation: diaphragm and external intercostal muscles relax, lungs and chest walls push air out because lungs are elastic and tend to turn back to their original form --> volume of lung decrease --> pressure increase --> air moves out
• Forced breathing: Inhalation: active Exhalation : active Inhalation : Diaphragm + external intercostal muscles + neck muscles Exhalation : Internal intercostal muscles + abdominal muscles contract.

Respiratory Volumes

• The respiratory cycle, consisting of inhalation and exhalation, is described with a number of volumes and rates.
• Tidal Volume (TV): The volume of air moving into or out of the lungs during a single respiratory cycle, which averages about 500 ml.
• Only a small portion of air is exchanged during quiet breathing.
• Dead volume : gas volume that doesn't undergo gas exchange.
• TV can be increased with more forceful inhalation and exhalation.
• Expiratory Reserve Volume (ERV): Volume of air that can be voluntarily expelled at the end of a tidal cycle, about 1000 ml.
• Inspiratory Reserve Volume (IRV): Volume of air that can be inhaled over tidal volume, higher in males averaging about 3300ml, than females averaging 1900ml
• Vital Capacity (VC): The sum of IRV, ERV, and TV.
• Residual Volume (RV): About 1200 ml air that remains in the alveoli to prevent the lungs from collapsing.

Gas Exchange and Transport

• Gas exchange happens primarily because of diffusion.

• Atmospheric air contains little CO2, but blood flowing in pulmonary capillaries has higher CO2 concentration.

• CO2 diffuses from blood across walls of alveolar capillaries.

• Blood entering pulmonary capillaries is low in oxygen, alveolar air is oxygen rich.

• Oxygen diffuses in alveoli accross the alveolar membrane, capillaries to reach blood.

• Most of the oxygen is transported by red blood cells bound to Hemoglobin forming oxyhemoglobin.

• Hemoglobin contains four polypeptide chain. Each chain contains an iron containing heme. Iron atoms bind with O2.

• percentage of oxygen binding sites hemoglobin carrying O2 varies partial pressure of O2 in immediate environment.

• At normal partial pressure of O2 in lungs hemoglobin become saturated with O2.

• At the O2 partial pressure in tissues oxyhemoglobin unload O2.

• Acid PH and warmer temprature promote the dissociation oxyhemoglobin.

• Some hemoglobin combines with CO2 to form carbaminohemoglobin.

• Most of CO2 + water -----> carbonic acid ( H2CO3 ) -----> H+ + HCO3 -

• H+ is absorbed by globin protein and HCO3- diffuse out into plasma. Reduced hemoglobin ( HHG ) has a key role in blood PH.

• Carbonic anhydride is enzyme involved in both direction of that reaction.

• Increasing the CO2 concentration promotes the release of Oxygen.

• Carbonic anhydrase speeds up the process.

Control of Respiration

• The rate and depth of breathing is controlled by the nuclei in the pons and medulla of the brain, known as respiratory centers.
• The normal range for adults is 12-18 breaths per minute.
• The normal range for children is 18-20 breaths per minute.
• Normal breathing occurs automatically, without you telling your body to.
• There are two types of reflexes involved:
• Mechanoreceptor: which respond to changes in the volume of the lung/changes of arterial blood pressure.
• The second type of reflex is chemoreceptors: which respond to changes in blood and the cererospinal fluid.
• Chemoreceptors reflexes are very powerful respiratory stimulator which cant be consciously suppressed.
• CO2 levels have more powerful effect than O2 since atrial pO2 does not drop enough to activate oxygen receptor.

Respiration and Health

• When the respiratory tract comes into contact with any air, it is exposed.
• Strep throat is a severe infection caused by streptococcus pyogenes, which can lead to a systemic infection.
• Pneumonia is typically due to viral/bacterial lung infections causing fluid to fill the bronchi.
• Tuberculosis is caused by mycobacterium tuberculosis and can be exposure through skin to be tested.
• Cystic Fibrosis causes lun defects.
• Asthma is caused by bronchiole disease.
• Lung cancer surpasses breast cancer due to smoking. The way to prevent these problems, is to avoid smoking.
• Lung cancer accounts for 35% of cancer deaths.
• From 80-90% are direct results of smoking.