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Questions and Answers
What is the role of the sensor or receptor in homeostatic control mechanisms?
What is the role of the sensor or receptor in homeostatic control mechanisms?
Which part of the brain is primarily responsible for regulating the endocrine system?
Which part of the brain is primarily responsible for regulating the endocrine system?
What is the primary function of the effector in homeostatic mechanisms?
What is the primary function of the effector in homeostatic mechanisms?
Which of the following is an example of a local control mechanism?
Which of the following is an example of a local control mechanism?
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What type of control mechanism involves communication across long distances?
What type of control mechanism involves communication across long distances?
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Which component of the homeostatic system integrates the information from sensors?
Which component of the homeostatic system integrates the information from sensors?
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Which of the following is NOT a function of the medulla oblongata?
Which of the following is NOT a function of the medulla oblongata?
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What happens when blood pressure is too low according to homeostatic functions?
What happens when blood pressure is too low according to homeostatic functions?
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What causes nearby blood vessels to dilate during tissue hypoxia?
What causes nearby blood vessels to dilate during tissue hypoxia?
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What role does the nervous system play in reflex control for low blood pressure?
What role does the nervous system play in reflex control for low blood pressure?
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What is the primary purpose of negative feedback mechanisms in the body?
What is the primary purpose of negative feedback mechanisms in the body?
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What is homeostasis primarily concerned with?
What is homeostasis primarily concerned with?
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Which of the following is NOT a variable that is under homeostatic control?
Which of the following is NOT a variable that is under homeostatic control?
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Which of the following examples demonstrates an effect of negative feedback?
Which of the following examples demonstrates an effect of negative feedback?
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In reflex control, what types of signals are used to achieve widespread effects in the body?
In reflex control, what types of signals are used to achieve widespread effects in the body?
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What happens when homeostasis is disrupted?
What happens when homeostasis is disrupted?
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During tissue hypoxia, what effect does the dilation of blood vessels have?
During tissue hypoxia, what effect does the dilation of blood vessels have?
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Which of the following best describes positive feedback in biological systems?
Which of the following best describes positive feedback in biological systems?
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What is the main role of extracellular fluid (ECF) in the body?
What is the main role of extracellular fluid (ECF) in the body?
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What is indicated by narrowing of blood vessels in response to low blood pressure?
What is indicated by narrowing of blood vessels in response to low blood pressure?
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What is one consequence of negative feedback in the endocrine system?
What is one consequence of negative feedback in the endocrine system?
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Homeostasis is most accurately defined as the process that:
Homeostasis is most accurately defined as the process that:
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How are diseases grouped based on their origins?
How are diseases grouped based on their origins?
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Which of the following factors would NOT directly affect homeostasis?
Which of the following factors would NOT directly affect homeostasis?
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What is the main characteristic of positive feedback in the body?
What is the main characteristic of positive feedback in the body?
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Which of the following is an example of positive feedback mechanisms in the human body?
Which of the following is an example of positive feedback mechanisms in the human body?
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In the context of excessive bleeding, how does positive feedback contribute to the process?
In the context of excessive bleeding, how does positive feedback contribute to the process?
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How does the body typically manage low blood pressure following blood loss?
How does the body typically manage low blood pressure following blood loss?
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What effect do biological rhythms have on the set point of physiological processes?
What effect do biological rhythms have on the set point of physiological processes?
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What is the total body water (TBW) for a 70 kg man?
What is the total body water (TBW) for a 70 kg man?
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What can be a result of excessive positive feedback in a physiological context?
What can be a result of excessive positive feedback in a physiological context?
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Which ions are found in higher concentrations in the extracellular fluid (ECF) compared to intracellular fluid (ICF)?
Which ions are found in higher concentrations in the extracellular fluid (ECF) compared to intracellular fluid (ICF)?
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During which physiological event is positive feedback beneficial?
During which physiological event is positive feedback beneficial?
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What is a significant characteristic of extracellular fluid?
What is a significant characteristic of extracellular fluid?
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What ultimately happens during positive feedback when a blood vessel is injured?
What ultimately happens during positive feedback when a blood vessel is injured?
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What role do special mechanisms for transporting ions play between ECF and ICF?
What role do special mechanisms for transporting ions play between ECF and ICF?
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What is the purpose of the homeostatic control system?
What is the purpose of the homeostatic control system?
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What type of fluids are transported from cells to the lungs for excretion?
What type of fluids are transported from cells to the lungs for excretion?
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Which of the following is NOT a constituent of extracellular fluid?
Which of the following is NOT a constituent of extracellular fluid?
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What must the homeostatic control system be able to do to maintain steady state levels?
What must the homeostatic control system be able to do to maintain steady state levels?
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Study Notes
Homeostasis
- Homeostasis is a state of maintaining a similar condition, or Internal Stability, to cope with external variability in the environment.
- The body monitors its internal state and takes action to correct disruptions that threaten normal function.
- Failure to maintain homeostasis of critical variables disrupts normal function and may result in disease or a pathological condition.
Intended Learning Outcomes
- Define homeostasis and explain its importance in health and disease.
- Describe the main features of control systems in the body.
- Define negative and positive feedbacks and their role in homeostasis.
- Describe examples of biological rhythm.
Variables under Homeostatic Control
- Environmental factors that affect cells (osmolarity, temperature, pH)
- Materials for cell needs (nutrients, water, sodium, calcium, other inorganic ions, oxygen)
- Internal secretions (hormones and other chemicals that communicate between cells, having general and continuous effects).
Diseases and Homeostasis
- Diseases arise either from internal failure of physiological processes or from external sources.
- When homeostasis is disturbed, the body attempts to compensate.
- Compensation can fail, leading to illness or disease, or succeed, maintaining wellness.
Body's Internal Environment
- Extracellular fluid (ECF) is the watery internal environment surrounding cells, acting as a transition between the organism's external environment and the intracellular fluid (ICF).
- The ECF acts as a buffer zone between cells and the outside world.
- Physiological processes keep the composition of the ECF relatively stable.
Fluid Content of the Body
- Total body water (TBW): 60% of body weight in a 70 kg man is approximately 42 liters.
- Intracellular fluid (ICF): About 28 liters.
- Extracellular fluid (ECF): Approximately 14 liters.
- Intravascular fluid (plasma): ~3 liters.
- Extravascular fluid (~11 liters)
- Interstitial fluid (~10.5 liters).
- Transcellular fluid (~0.5 liters).
Differences Between Extracellular and Intracellular Fluids
- Body compartments are in a dynamic steady state, not equilibrium.
- Ion concentrations are different in the ECF and ICF.
- Special mechanisms transport ions through cell membranes to maintain ion concentration differences between the ECF and ICF.
- Major cations in the ECF include Na+, Ca2+, and Mg2+. Major anions include Cl− and HCO3−.
- Major cations in the ICF include K+, Mg2+, and some Na+. Major anions include PO43−, organic anions and proteins.
The Extracellular Fluid
- Contains large amounts of sodium, chloride, bicarbonate ions and nutrients for the cells (e.g. oxygen, glucose, fatty acids, and amino acids).
- Contains carbon dioxide that is transported from cells to the lungs for excretion.
- Contains cellular waste products transported to the kidneys for excretion.
The Intracellular Fluid
- Contains large amounts of potassium, magnesium, and phosphate ions.
Normal Ranges and Physical Characteristics of Extracellular Fluid Constituents
- A set of values of different factors in the ECF are presented.
Homeostatic Control Systems
- Functionally interconnected network of body systems.
- Maintain given factors in the internal environment.
- Example: temperature, fluid, nutrient levels, chemical composition.
- Achieve steady state from cellular to system levels.
- Detect deviations from normal.
- Integrate information with other relevant information.
- Make appropriate adjustments to return factors to 'normal' or desired steady state levels.
Homeostatic Components
- Input signal (sensed by receptor).
- Controller/integrating center (integrates information; initiates response).
- Output signal (creates response by effector).
Components of Homeostatic Control Mechanisms
- Sensor/receptor: Detects changes in internal or external environment (e.g., chemoreceptors, thermoreceptors, baroreceptors).
- Integrating center/control center: Receives information from sensors, initiates response.
- Effector: Any organ or tissue that brings about the response.
Local Control
- Relatively isolated change occurs in a tissue.
- A nearby cell or group of cells senses the change, usually by releasing a chemical.
- The response is restricted to the region where the change took place.
- Example: Dilation of regional blood vessels in response to tissue hypoxia.
Reflex Control
- Widespread or systemic changes require more complex control systems.
- Uses nervous and/or endocrine systems.
- Output signals may be chemical, electrical, or both.
- Example: Low blood pressure sensed by receptors, signals to the heart, kidneys and blood vessels to increase cardiac output and blood volume (increasing BP).
Negative Feedback
- A initiating stimulus elicits a response that results in an opposite effect, bringing the system back to normal functioning.
- Example: blood pressure regulation, metabolism, body temperature.
Negative Feedback Mechanisms
- Prevent over-activity of hormone systems.
- Controlled variable is often the degree of activity in target tissues..
- Appropriate level of activity in target tissues triggers feedback signals to endocrine glands, slowing further hormone secretion.
- Example: control of thyroid hormone secretion.
Positive Feedback
- Enhances or accelerates output created by an activated stimulus.
- Leads to instability in most cases, but has some exceptions.
- Example: blood clotting, childbirth.
Positive Feedback example in Blood Clotting
- When a blood vessel ruptures, multiple clotting factors are activated.
- These factors activate other factors in the adjacent blood, causing more clotting.
- This continues until the rupture is plugged.
Positive Feedback in Childbirth
- Cervical stretching during childbirth triggers oxytocin release.
- Oxytocin stimulates uterine contractions, further stretching the cervix, initiating more contractions.
- This continues until delivery.
Positive Feedback (Vicious Circle)
- Does not lead to stability, but to instability and can cause death under some circumstances.
- Example: excessive bleeding (Shock) - Reduced blood pressure, reduced cardiac perfusion, decreased cardiac contractility and output, leading to more decrease in BP causing a drop in heart function, followed by death.
Biological Rhythms
- Rather than a fixed steady value, set points can vary over time, producing biological rhythms.
- Example: menstrual cycle, body temperature variations during the cycle, fluctuations in cortisol levels during the day.
Disruptions of Homeostasis
- The body maintains a range for each factor to prevent illness, disease, and death, with the following categories:
- Ideal value: Where body functions are at their most efficient.
- Optimal range: Where body functions are efficient.
- Range of tolerance: Where body functions can still function, but not at optimal.
- Minimum or maximum set point: The maximum or minimum set point where moving past may cause illness and/or death.
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