NEET MDS Lessons
Physiology
Ventilation simply means inhaling and exhaling of air from the atmospheric air into lungs and then exhaling it from the lung into the atmospheric air.
Air pressure gradient has to exist between two atmospheres to enable a gas to move from one atmosphere to an other.
During inspiration: the intrathoracic pressure has to be less than that of atmospheric pressure. This could be achieved by decreasing the intrathoracic pressure as follows:
Depending on Boyle`s law , the pressure of gas is inversely proportional to the volume of its container. So increasing the intrathoracic volume will decrease the intrathoracic pressure which will allow the atmospheric air to be inhaled (inspiration) . As decreasing the intrathoracic volume will increase the intrathoracic pressure and causes exhaling of air ( expiration)
So. Inspiration could be actively achieved by the contraction of inspiratory muscles : diaphragm and intercostal muscles. While relaxation of the mentioned muscles will passively cause expiration.
Contraction of diaphragm will pull the diaphragm down the abdominal cavity ( will move inferiorly) , and then increase the intrathoracic volume ( vertically) . Contraction of external intercostal muscle will pull the ribs upward and forward which will additionally increase the intrathoracic volume ( transversely , the net result will be increasing the intrathoracic volume and decreasing the intrathoracic pressure.
Relaxation of diaphragm will move it superiorly during expiration, the relaxation of external intercostal muscles will pull the ribs downward and backward , and the elastic lungs and chest wall will recoil. The net result is decreasing the intrathoracic volume and increasing intrathoracic pressure.
All of this occurs during quiet breathing. During forceful inspiration an accessory inspiratory muscle will be involved ( scaleni , sternocleidomastoid , and others) to increase negativity in the intrathoracic pressure more and more.
During forceful expiration the accessory expiratory muscles ( internal intercostal muscles and abdominal muscles ) will be involved to decrease the intrathoracic volume more and more and then to increase intrathoracic pressure more and more.
The pressure within the alveoli is called intralveolar pressure . Between the two phases of respiration it is equal to the atmospheric pressure. It is decreased during inspiration ( about 1 cm H2O ) and increased during expiration ( about +1 cm H2O ) . This difference allow entering of 0.5 L of air into the lungs.
Intrapleural pressure is the pressure of thin fluid between the two pleural layers . It is a slight negative pressure. At the beginning of inspiration it is about -5 cm H2O and reachs -7.5 cm H2O at the end or inspiration.
At the beginning of expiration the intrapleural pressure is -7.5 cm H2O and reaches -5 cmH2O at the end of expiration.
The difference between intralveolar pressure and intrapleural pressure is called transpulmonary pressure.
Factors , affecting ventilation :
Resistance : Gradual decreasing of the diameter of respiratory airway increase the resistance to air flow.
Compliance : means the ease , which the lungs expand.It depends on both the elastic forces of the lungs and the elastic forces , caused by the the surface tension of the fluid, lining the alveoli.
Surface tension: Molecules of water have tendency to attract each other on the surface of water adjacent to air. In alveoli the surface tension caused by the fluid in the inner surface of the alveoli may cause collapse of alveoli . The surface tension is decreased by the surfactant .
Surfactant is a mixture of phospholipids , proteins and ion m produced by type II pneumocytes.
Immature newborns may suffer from respiratory distress syndrome , due to lack of surfactant which is produced during the last trimester of pregnancy.
The elastic fibers of the thoracic wall also participate in lung compliance.
Structural Divisions of the nervous system:
1) Central Nervous System (CNS) - the brain and spinal cord.
2) Peripheral Nervous System (PNS) - the nerves, ganglia, receptors, etc
Pain, Temperature, and Crude Touch and Pressure
General somatic nociceptors, thermoreceptors, and mechanoreceptors sensitive to crude touch and pressure from the face conduct signals to the brainstem over GSA fibers of cranial nerves V, VII, IX, and X.
The afferent fibers involved are processes of monopolar neurons with cell bodies in the semilunar, geniculate, petrosal, and nodose ganglia, respectively.
The central processes of these neurons enter the spinal tract of V, where they descend through the brainstem for a short distance before terminating in the spinal nucleus of V.
Second-order neurons then cross over the opposite side of the brainstem at various levels to enter the ventral trigeminothalamic tract, where they ascend to the VPM of the thalamus.
Finally, third-order neurons project to the "face" area of the cerebral cortex in areas 3, 1, and 2 .
Discriminating Touch and Pressure
Signals are conducted from general somatic mechanoreceptors over GSA fibers of the trigeminal nerve into the principal sensory nucleus of V, located in the middle pons.
Second-order neurons then conduct the signals to the opposite side of the brainstem, where they ascend in the medial lemniscus to the VPM of the thalamus.
Thalamic neurons then project to the "face" region of areas 3, I, and 2 of the cerebral cortex.
Kinesthesia and Subconscious Proprioception
Proprioceptive input from the face is primarily conducted over GSA fibers of the trigeminal nerve.
The peripheral endings of these neurons are the general somatic mechanoreceptors sensitive to both conscious (kinesthetic) and subconscious proprioceptive input.
Their central processes extend from the mesencephalic nucleus to the principal sensory nucleus of V in the pons
The subconscious component is conducted to the cerebellum, while the conscious component travels to the cerebral cortex.
Certain second-order neurons from the principal sensory nucleus relay proprioceptive information concerning subconscious evaluation and integration into the ipsilateral cerebellum.
Other second-order neurons project to the opposite side of the pons and ascend to the VPM of the thalamus as the dorsal trigeminothalamic tract.
Thalamic projections terminate in the face area of the cerebral cortex.
COPD and Cancer
A. Chronic Obstructive Pulmonary Disease (COPD)
1. Common features of COPD
a. almost all have smoking history
b. dyspnea - chronic "gasping" for air
c. frequent coughing and infections
d. often leads to respiratory failure
2. obstructive emphysema - usually results from smoking
a. enlargement & deterioration of alveoli
b. loss of elasticity of the lungs
c. "barrel chest" from bronchiole opening during inhalation & constriction during exhalation
3. chronic bronchitis - mucus/inflammation of mucosa
B. Lung Cancer
1. squamous cell carcinoma (20-40%) - epithelium of the bronchi and bronchioles
2. adenocarcinoma (25-35%) - cells of bronchiole glands and cells of the alveoli
3. small cell carcinoma (10-20%) - special lymphocyte-like cells of the bronchi
4. 90% of all lung cancers are in people who smoke or have smoked
Functional Divisions of the Nervous System:
1) The Voluntary Nervous System - (ie. somatic division) control of willful control of effectors (skeletal muscles) and conscious perception. Mediates voluntary reflexes.
2) The Autonomic Nervous System - control of autonomic effectors - smooth muscles, cardiac muscle, glands. Responsible for "visceral" reflexes
AdenosineTriphosphate (ATP)
- Animal cells cannot directly use most forms of energy
- Most cellular processes require energy stored in the bonds of a molecule, adenosine triphosphate (ATP)
- ATP is referred to as the energy currency of the cell
It is a nucleotide, formed from:
- the base adenine (the structure with 2 rings),
- the 5 carbon sugar deoxyribose (one ring)
- 3 phosphates
Energy is stored in the bonds between the phosphates and is released when the bonds are broken
Cells, cytoplasm, and organelles:
- Cytoplasm consists of a gelatinous solution and contains microtubules (which serve as a cell's cytoskeleton) and organelles
- Cells also contain a nucleus within which is found DNA (deoxyribonucleic acid) in the form of chromosomes plus nucleoli (within which ribosomes are formed)
- Organelles include:
- Endoplasmic reticulum : 2 forms: smooth and rough; the surface of rough ER is coated with ribosomes; the surface of smooth ER is not , Functions include: mechanical support, synthesis (especially proteins by rough ER), and transport
- Golgi complex consists of a series of flattened sacs (or cisternae) functions include: synthesis (of substances likes phospholipids), packaging of materials for transport (in vesicles), and production of lysosomes
- Lysosome : membrane-enclosed spheres that contain powerful digestive enzymes , functions include destruction of damaged cells & digestion of phagocytosed materials
- Mitochondria : have double-membrane: outer membrane & highly convoluted inner membrane
- inner membrane has folds or shelf-like structures called cristae that contain elementary particles; these particles contain enzymes important in ATP production
- primary function is production of adenosine triphosphate (ATP)
- Ribosome-:composed of rRNA (ribosomal RNA) & protein , primary function is to produce proteins
- Centrioles :paired cylindrical structures located near the nucleas , play an important role in cell division
- Flagella & cilia - hair-like projections from some human cells
- cilia are relatively short & numerous (e.g., those lining trachea)
- a flagellum is relatively long and there's typically just one (e.g., sperm)
-
- Villi Projections of cell membrane that serve to increase surface area of a cell (which is important, for example, for cells that line the intestine)