ISPN Review Passive Transport被动转运
Passive transport happens without the expenditure of energy and can occur across any semipermeable membrane. There are essentially three types of passive transport: diffusion, osmosis, and facilitated diffusion.
不需要消耗能量的转运即为被动转运，可穿过任何的半透膜。被动转运主要分3种：扩散、渗透、易化扩散。
Diffusion 扩散
Diffusion is the movement of a substance from a region of higher concentration to a region of lower concentration. The difference between the concentrations of the substance in the two regions is called the concentration gradient of the substance; usually, the greater the concentration gradient, the faster does the substance move. Movement into and out of a cell is regulated by the cell membrane. Some substances move through channels or pores in the cell membrane. Small substances and materials with no ionic charge move most freely through the channels. Substances with a negative charge move more freely than substances with a positive charge. Substances that move into and out of a cell by diffusion include sodium, potassium, calcium, carbonate, oxygen, bicarbonate, and water.
When a cell is very active and is using energy and oxygen, the concentration of oxygen within the cell decreases. The concentration of oxygen outside the cell remains relatively high, so oxygen moves across the cell membrane (down the concentration gradient) to supply needed oxygen to the inside of the cell. Cells use this process to maintain homeostasis during many activities that occur during their life.
Osmosis 渗透
Osmosis, a special form of diffusion, is the movement of water across a semipermeable membrane from an area that is low in dissolved solutes to one that is high in dissolved solutes. The water is attempting to equalize the dilution of the solutes. This diffusion of water across a cell membrane from an area of high concentration (of water) to an area of low concentration creates pressure on the cell membrane called osmotic pressure. The greater the concentration of solutes in the solution to which the water is flowing, the higher is the osmotic pressure.
A fluid that contains the same concentration of solutes as human plasma is called an isotonic solution. A fluid that contains a higher concentration of solutes than human plasma is a hypertonic solution, and it draws water from cells. A fluid that contains a lower concentration of solutes than human plasma is hypotonic; it loses water to cells. If a human red blood cell, which has a cytoplasm that is isotonic with human plasma, is placed into a hypertonic solution, it shrinks and shrivels because the water inside the cell diffuses out of the cell into the solution. If the same cell is placed into a hypotonic solution, the cell swells and bursts because water moves from the solution into the cell.
Facilitated Diffusion 易化扩散
Sometimes a substance cannot move freely on its own in or out of a cell. Such a substance may attach to another molecule, called a carrier, to be diffused. This form of diffusion, known as facilitated diffusion, does not require energy, just the presence of the carrier. Carriers may be hormones, enzymes, or proteins. Because the carrier required for facilitated diffusion is usually present in a finite amount, this type of diffusion is limited.
Test 1. The client’s ability to take oral medications will be hindered by:
A. Age
B. Dental caries
C. Dysphagia
D. Lifestyle 2. Which of the following will determine nursing interventions for a client on medication?
A. Assessment
B. Diagnoses
C. Implementation
D. Evaluation
本期ISPN Review答案： 1. C. Dysphagia. Dysphagia is difficulty swallowing. This would make administration of oral medications impossible. Other choices do not impair ingestion. 2. B. Diagnoses. The nursing diagnosis is the conclusion derived from the assessment, and it is the component of the nursing process that drives the interventions.
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