英语论文网

like aggregations protruding into the superior sagittal sinus and adjacent venous lacunae and in other sinuses and large veins. The arachnoid granulations are the locations of the absorbtion of CSF. The subarachnoidal space form widened spaces called cisterns and the cisterna magna is the biggest lying between the medulla and the cerebellum and is continuous with the spinal subarachnoidal space. 
Pia mater 
The pia is a very delicate membrane that covers the surface of the brain and extends into fissures and over sulci. 
Respiratory System 
Pathway 
• Air enters the nostrils 
• passes through the nasopharynx, 
• the oral pharynx 
• through the glottis 
• into the trachea 
• into the right and left bronchi, which branches and rebranches into 
• bronchioles, each of which terminates in a cluster of 
• alveoli 
Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 (almost equal to the singles area of a tennis court and 80 times the area of our skin!). 
Breathing 
• Air enters the nostrils 
• passes through the nasopharynx, 
• the oral pharynx 
• through the glottis 
• into the trachea 
• into the right and left bronchi, which branches and rebranches into 
• bronchioles, each of which terminates in a cluster of 
• alveoli 
Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 (almost equal to the singles area of a tennis court and 80 times the area of our skin!). 
The diaphragm divides the body cavity into the 
• abdominal cavity, which contains the viscera (e.g., stomach and intestines) and the 
• thoracic cavity, which contains the heart and lungs. 
The inner surface of the thoracic cavity and the outer surface of the lungs are lined with pleural membranes which adhere to each other. If air is introduced between them, the adhesion is broken and the natural elasticity of the lung causes it to collapse. This can occur from trauma. And it is sometimes induced deliberately to allow the lung to rest. In either case, reinflation occurs as the air is gradually absorbed by the tissues. 
Because of this adhesion, any action that increases the volume of the thoracic cavity causes the lungs to expand, drawing air into them. 
• During inspiration (inhaling), 
o The external intercostal muscles contract, lifting the ribs up and out. 
o The diaphragm contracts, drawing it down . 
• During expiration (exhaling), these processes are reversed and the natural elasticity of the lungs returns them to their normal volume. At rest, we breath 15-18 times a minute exchanging about 500 ml of air. 
• In more vigorous expiration, 
o The internal intercostal muscles draw the ribs down and inward 
o The wall of the abdomen contracts pushing the stomach and liver upward. 
Under these conditions, an average adult male c本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。