Define homeostasis, acceptor, avoider, regulator, paracrine, autocrine, endocrine, sensor, error signal, controller, effector, afferent, efferent, gain, set point, latency, negative feedback, positive feedback, unreferenced and referenced feedback.
- Homeostasis- The maintenance of a similar internal environment. (Note that the internal environment doesn't remain completely constant, but rather within a nice range.)
- Acceptor- An organism that just accepts environmental changes as they come. An example of this is the aquatic snail, which has different enzymes that work under different temperature conditions.
- Avoider- An organism that uses behavioural changes to regulate a variable. For example, lizards go into the sun to stay warm.
- Regulator- An organism that uses physiology to regulate a variable. Most of our variables are regulated.
- Paracrine- A hormone that is released into the extracellular fluid and affects nearby cells. Also known as an autacoid.
- Autocrine- A hormone that acts on the same cell that released it.
- Endocrine- A hormone that travels through the blood and affects a distant cell.
- Sensor- The component of a control system that detects a variable (e.g. baroreceptors detect blood pressure).
- Error signal- The difference between the "set point" and measured variable.
- Controller- The component of a control system that produces output to limit the error signal.
- Effector- The component of a control system that produces the response dictated by the controller. This usually works to bring the variable closer to the set point.
- Afferent- Pathway going towards something (e.g. afferent nerves go towards the brain).
- Efferent- Pathway going away from something. I remember the difference between afferent and efferent in that EFFerent is like EFF off.
- Gain- A measure of how much a change is increased or reduced due to the effects of a feedback system.
- Set point- The value that a control system regulates to (e.g. pH is maintained between 7.35 and 7.45).
- Latency- The response time for the control system
- Negative feedback- A self-limiting control loop. An example is in the reproductive system: FSH stimulates follicles to produce inhibin, which goes back and inhibits production of FSH.
- Positive feedback- An amplifying control loop. An example is the LH surge during ovulation.
- Unreferenced feedback- Feedback loops that do not rely on a set point. This may work through the use of two opposing systems. An example of this is the regulation of cardiac output and venous pressure.
- Referenced feedback- Feedback loops that rely on a set point. An example of this is control of pH- it is kept between 7.35 and 7.45.
Describe the levels of cellular control and communication giving an example for each.
- Cell-to-cell: Occurs through gap junctions between cells. An example of this is cardiac muscle.
- Paracrine: Hormones are sent through the extracellular fluid to neighbouring cells. An example of this is histamine release during inflammation.
- Autocrine: A hormone acts on the same cell that produced it. An example of this occurs during the stretch response in smooth muscle.
- Endocrine: A hormone travels through the blood to its destination. An example of this is FSH (follicle-stimulating hormone), which travels from the anterior pituitary to the gonads.
- Nervous: A nerve stimulates a target cell by releasing neurotransmitters across a synapse. An example of this is noradrenaline.
- Neuroendocrine system: A nerve releases a neurotransmitter into the blood. An example of this is ADH (anti-diuretic hormone/vasopressin).
List the components of a referenced negative feedback system.
I've already done this above, but here they are again in case you can't be bothered scrolling up:
- Sensor- The component of a control system that detects a variable (e.g. baroreceptors detect blood pressure).
- Error signal- The difference between the "set point" and measured variable.
- Controller- The component of a control system that produces output to limit the error signal.
- Effector- The component of a control system that produces the response dictated by the controller. This usually works to bring the variable closer to the set point.
Referenced feedback relies on a set point (e.g. pH between 7.35 and 7.45), whereas unreferenced feedback does not. An example of referenced feedback is, well, pH, whereas an example of unreferenced feedback is the control of venous pressure and cardiac output, in which there is no set venous pressure or cardiac output to "work towards."
Explain how negative feedback limits the change in the controlled variable using baroreceptors and muscle spindle reflexes as examples.
For baroreceptors, see previous post: Control of Blood Pressure.
Muscle spindle reflexes refer to a reflex shortening when a muscle is lengthened, such as when your knee is tapped. The sensors here are the muscle spindle fibres, which travel through nerve fibres to the spinal cord. In the spinal cord, the sensory neuron synapses with a motor neuron, which causes a twitch in muscle.
Calculate the gain of a control system
To calculate the gain of a control system, first we need to learn some terminology.
ΔR: difference from set point after feedback
ΔC: difference from set point without feedback
ΔE = ΔR - ΔC (i.e. the difference between the non-feedback and feedback measurements)
Gain of control system (G) = ΔE/ΔR
Alternatively, G = (ΔR - ΔC) / ΔR.
The gain of control can be a bit hard to interpret. If there is a -3 gain, this means that the change with feedback is 1/4 what it would be if we didn't have feedback. (The negative sign means that the change occurs in a negative direction, such as a drop in blood pressure or something.) If there is a -33 gain, then the amount of change with feedback is 1/34 what it would be if we didn't have feedback.
List and explain the organs and systems involved in delivery of oxygen
I think this was mainly stuck in as an example to show us that we need all of our body systems to work together. Oxygen delivery not only relies on the lungs, but also factors affecting the inflation of the lungs (muscles, nerves, receptors that regulate our breathing), factors affecting transport of oxygen around the body (oxygen content of blood, haemoglobin, erythropoietin produced by the kidneys), factors affecting our circulation (heart, blood vessels, other regulators of mean arterial pressure), and so on. We are complicated!
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