01-10-21 - Homeostasis Flashcards
Learning outcomes
- Describe the structural hierarchy of the human body
- Explain the importance of physiological control systems
- Explain the importance of controlling the extracellular fluid
- Explain the meaning of homeostasis
- Describe, using physiological examples, the process of homeostatic control
- List the major features of homeostatic control systems
What is the hierarchy of structure in the human body?
What exists in all of these levels?
- Cells
- The basic structural unit
- Approx. 100 trillion cells
- Many specialized cell types
Tissues e.g muscles, epithelial, nervous
• Aggregate of cells with a particular function are called tissue
• Examples are heart tissue or liver tissue
Organs
• Specialised tissues plus connective tissue
• Innervated by nerves and supplied by blood vessels
• Examples are the kidney, heart, liver, pancreas
Systems
• A group of integrated organs that collectively perform a function
• Example is the digestive system, which consists of stomach and intestine, and accessory organs which the support the process of digestion, like the pancreas and gallbladder
• Homeostasis exists at multiple levels
What do all the organ systems in an organ come together to do?
How are they related?
How are they linked together?
What is it important that happens?
- Al of the organ systems in the body create a functional internal environment in order to maintain the health of the organism
- All of the systems are interlinked, and one system can affect other systems e.g respiratory system problems will affect all systems
- The fundamental link between organ systems is the fluid that surrounds all of these systems
- It is therefore important that this fluids environment is properly maintained through homeostasis
- This is to allow the cells in all of these systems to perform their functions effectively
What approximate % of the human body is fluid?
What does this fluid consist of?
How is the fluid divided in the human body?
What fluids are these mostly?
What needs to be regulated and why?
How it this done?
- Approximately 60% of the human body is made up of fluid
- This fluid is a water solution of ions and other substances
• Fluid in the body is divided into 2 compartments:
1) Approximately 70% of fluid is within cells – intracellular fluid (ICF)
2) Approximately 30% of fluid is outside cells – Extracellular fluid (ECF)
- ECF fluids are mostly plasma and interstitial fluid (fluid between cells), but can also contain transcellular fluid (fluid in epithelial lined spaces) such as synovial, CSF etc
- Regulation and control of compositions and concentrations of ICF and ECF, and body processes is crucial to the normal functioning (physiology) of organelles, cells, tissues, systems and the organism
- This is done by compartments being separated by membranes, which can regulate movement into and out of cells
What 2 things contribute to total fluid intake?
What 5 things make up total fluid output?
What are insensible fluid losses?
How does fluid output from different sources change when exercising compared to regular physiology?
What do we need to try and balance and why
• Total fluid intake = fluid ingested + fluid produced from metabolism (e.g water made form biological processes such as respiration)
- Total fluid output is the addition of fluid output from:
- Skin (insensible)
- Lungs (insensible)
- Sweat
- Faeces
- Urine
• Insensible fluid losses are fluid losses that are not regulated and part of normal body function
- This water is lost as apart of normal metabolism, but these processes are not metabolic processes themselves
- Examples of this are the skin and lungs
- In the skin, we lose water through evaporation
- In lungs we lose water through the air we breathe out being saturated with water
- When exercising;
- Fluid loss from lungs increases, as we breathe deeper and harder
- Fluid loss from sweat increases as the body tris to cool down
- Fluid loss from urine decreases, as we try to conserve water
• We need to balance total water intake and total water output in order to maintain homeostasis in the body.
What is the definition of homeostasis?
How does homeostasis occur?
What it the result of?
- Homeostasis is when physiological control systems maintain a relatively stable internal environment (within safe limits/normal range) in a fluctuating environment
- Homeostasis does not occur by chance, it is the result of organized ‘self-government’
How is homoeostasis maintained?
How is this done within cells?
What 2 ways is homeostasis maintained in/between tissues, organs/systems?
How do these differ?
What are 4 features of control systems?
- Homeostasis is maintained/regulated by control systems
- Homeostasis is maintained/regulated within cells by genetics
• Homeostasis is maintained/regulated within tissues/organs/systems through:
1) The nervous system – quick response (milliseconds-seconds), short duration
2) Endocrine system, - longer response (minutes-weeks), longer duration
• Control systems:
1) There are many thousands of control systems
2) Control systems require multiple elements
3) Many control systems are interlinked
4) Most (not all) use negative feedback
5) What are the 3 different types of control systems?
1) Open loop – no feedback
2) Closed loop – negative or positive feedback
3) Feedforward – anticipatory
How is open loop feedback influenced?
Why is this?
What does this mean?
What could this result in?
What is an example of this using a radiator?
What are open loopback feedbacks not good for?
What is an example of open loop feedback in the body?
- Open loop feedbacks are not influenced by resulting conditions ie no feedback present
- This is because the output of the mechanism has no effect on the controller of the mechanism
- This means nothing at the end of the system is there to say enough or too much – there is no monitoring to see if output has been effective
- This can potentially result in runaway reactions
- Radiator switched on by timer independent of how hot or cold the room is, and does not take into how comfortable someone in the room may be
- Open loop feedbacks are not very useful for maintaining homeostasis
- An example of open loop feedback is glucose being absorbed in gut epithelial cells
- Gut epithelial cells don’t report back to the gut lumen on how much glucose they have absorbed
- This allows them to continue to absorb glucose
How are closed loop feedbacks influenced?
What 2 feedback mechanisms do they contain?
How does a mechanism return a variable to set point?
What are the 4 steps of negative feedback of the control of blood pressure?
• Closed loop feedback is influenced by resulting conditions
• Closed look feedback can contain:
1) Negative feedback mechanism – returns the variable to set point
• if the variable goes into the upper limits, negative feedback will decrease mechanism to reduce the variable to setpoint.
• If the variable goes into the lower limits, negative feedback will increase mechanism to increase variable to set point.
• This is done by the output of the mechanism having influences over the controller of the mechanism through sensors
2) Positive feedback – moves variable away from the setpoint and promotes change in one direction
• Negative feedback in the control of blood pressure:
1) Sensors
• Baroreceptors (stretch receptors in carotid arteries and aortic arch) detect blood pressure and send signals to the control centre
2) Control centre
• The control centre is located in the solitary nucleus in the medulla oblongata
• The control centre references the set point blood pressure, and identifies the change that is needed to get to this blood pressure
• The medulla oblongata then sends a signal to effectors, such as the heart and blood vessels
3) Effectors
• The heart and blood vessels respond to this signal to return the variable to its set point
• E.x effectors can cause an increase in cardio output and vasoconstriction in blood vessels in order to increase blood pressure if it is low
• This controls the variable and puts it back to its set point
4) Sensors
• This new blood pressure is detected by baroreceptors and the cycle repeats
What is the graph like for thermoregulation of temperature within the normal range?
What 3 reasons might cause the range of healthy temperature to change?
What is the fluctuation of temperature normally like?
What are the approximate safe limits?
• Healthy temperature range may vary due to:
1) Different times of the day
2) Menstrual cycle
3) Temperature being taken in different places
• There is constant fluctuation of temperature within safe limits around 37 degrees C (around 36.7-37.2)
How often does the set point of a variable change?
What may cause the set-point to chance?
What is hunting in terms of the negative feedback system?
What are the 5 steps that bring about hunting when the set point changes?
What determines the depth/extent of hunting?
- Setpoints are very dynamic and frequently change
- The set-point of a variable may change in times of metabolic/physiological stress, such as a fever, exercise, or high altitude
- Hunting in terms of the negative feedback mechanism is known as over shoot
• Occurrence of hunting in negative feedback:
1) Set point of variable (e.g temperature) changes
2) There is a lag in detecting what the temperature is, which results in a lag in initiating effector muscles and other processes
3) This will likely result in hunting, where the temperature will increase beyond safe limits
4) The converse will likely happen after, where the temperature will also drop below safe limits
5) Over time, this will decrease, and the temperature will fluctuate within the safe limits of the new set-point
• The depth and extent of the hunting is dependent on the properties of the elements of the feedback system
What is gain?
How is it calculated?
What is an example of how gain is calculated?
How does gain vary?
What is the gain in thermoregulation?
- Gain is the degree of effectiveness of a negative feedback control system
- Gain is calculating by using the formula Correction/error
• An example of when gain can be calculated is blood transfusion in the same patient under 2 conditions:
1) Baroreceptors not functioning – Arterial BP raised from 100 to 175 mmHg – increase of 75
2) Baroreceptors functioning – Arterial BP rises from 100 to 125 mmHg – increase of 25
- The increase in arterial BP from 100 – 125 is the error (25mmHg), as the system was better, but not perfect
- There was also a correction of -50mmHg (175 to 125mmHg)
- The gain is therefor -50/25 = -2
- Gain varies between different systems
- Thermoregulation gain is approximately 27, making it very effective
What does positive feedback control do in closed loop feedback?
How commonly are they found?
What do positive feedback controls need?
What would happen without this?
When might positive feedback be physiologically important?
What are 3 cases when positive feedback controls are important?
What can instability of positive feedback control cause?
- In closed loop feedback, positive feedback control moves the variable away from the homeostatic set point
- Positive feedback controls are found less often physiologically
- They require a termination mechanism
- Without this, the system would cause a run-away reaction
- Positive feedback controls are physiologically important sometimes when we need a quick response e.g depolarization from opening Na+ channels
- 3 cases when positive feedback controls are used?
1) Initial response in action potential In opening of Na+ channel to cause depolarization
2) Child birth – release of oxytocin
3) Blood clotting
• Instability in positive feedback control can lead to disease, but not always
What is the function of oxytocin?
Describe the 5 steps in the positive feedback control mechanism during child birth
- Oxytocin is responsible for contraction of the uterine wall during birth
- These are powerful contractions that, when paired with voluntary abdominal contractions, cause the birth of the baby
• Positive feedback control in child birth:
1) The babies head pushes against the cervix, which triggers a neuroendocrine response (both neural and hormonal response)
2) This stimulates the increase of oxytocin release, which also stimulates the release of prostaglandin from the decidua. Both of these stimulate uterine contraction
3) This cycle continues to positively feedback to the uterine wall, causing the uterus to become increasingly responsive to oxytocin
4) This results in uterine contractions becoming stronger, more coordinated, and more frequent towards the end of labour
5) This cycle is broken by removing the stimulus – birth is the termination of this mechanism, as the cervix is no longer pushes against to stimulate oxytocin secretion
Describe the 5 steps in the positive feedback control of blood clotting
1) Break in blood vessel wall, which indices bleeding
2) This induces markers of coagulation (d-dimer, fibrinogen - proteins) and clotting factors to be released
3) As long as the wound remains open, more and more clotting factors are released.
4) This generates a positive feedback loop, which increases the speed and efficiency of clotting
5) The clot forming is the termination mechanism of this process
What are the circadian rhythms of the following physiological variables (changes in set point):
1) Body temperature
2) Systolic blood pressure (mmHg)
3) Cortisol hormone secretion
