恆定性：练习题

• a.A state where the external environment is modified to match the internal body temperature.
• b.A process where positive feedback loops are used to prevent any change in the internal environment.
• c.A state where internal conditions fluctuate within narrow limits around a set point.
• d.A state where internal conditions are kept at an absolutely constant value at all times.

• a.

  Fluctuations in pH cause the blood plasma to become hypertonic, resulting in the lysis of red blood cells due to excessive water uptake via osmosis.

• b.

  A change in pH alters the hydrogen bonding and ionic interactions within the tertiary structure of enzymes, leading to denaturation and a loss of metabolic function.

• c.

  A high blood pH levels stimulate a positive feedback loop within the bicarbonate buffer system, leading to an uncontrolled increase in carbon dioxide concentration.

• d.

  A significant decrease in pH increases the affinity of haemoglobin for oxygen, which prevents the effective release of oxygen to the respiring tissues.

• a.

  The hypothalamus stimulates the release of adrenaline from the adrenal glands to increase the basal metabolic rate.

• b.

  The parasympathetic nervous system stimulates the contraction of erector pili muscles to trap a layer of air.

• c.

  The hypothalamus sends sympathetic nerve impulses to cause vasodilation of peripheral arterioles.

• d.

  Thermoreceptors in the skin send impulses to the cerebrum to initiate voluntary shivering in skeletal muscles.

• a.

  Urea is actively transported out of the limb to increase the water potential of the medulla.

• b.

  Sodium and chloride ions are actively transported out into the interstitial fluid while the limb remains impermeable to water.

• c.

  Sodium and chloride ions diffuse into the tubule from the vasa recta to maintain the osmotic gradient.

• d.

  Water is reabsorbed into the interstitial fluid by osmosis while the limb is impermeable to sodium ions.

• a.

  ADH binds directly to the luminal membrane and acts as a channel protein, allowing water to flow from the filtrate into the cell by active transport.

• b.

  ADH binds to receptors on the basal membrane, triggering a second messenger system that causes vesicles containing aquaporins to fuse with the luminal membrane.

• c.

  ADH enters the cell nucleus and binds to transcription factors to increase the expression of genes that code for sodium-glucose co-transporter proteins.

• d.

  ADH activates sodium-potassium pumps on the luminal membrane, creating a steep electrochemical gradient that pulls water into the blood through simple diffusion.

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。