Unit 6: Homeostasis Flashcards
Define
Regulator
Organisms that maintain homeostasis for a condition within a narrow range
Ex: humans maintain a blood pH from between 7.35 and 7.45.
Define
Conformer
Organisms that don’t maintain homeostasis for a condition within a narrow range. They often conform to and tolerate the conditions around them
Ex: starfish interstitial fluids have a pH around 8.1 - 8.4, which is roughly the pH of their marine environment
Define
Negative feedback
A system where the response negates the original stimulus, which returns conditions back to the original levels
What is
Interstitial fluid
A fluid that bathes all cells in animals
This must be kept in homeostasis to allow individual cells to maintain homeostasis
Define
Homeostasis
Maintaining a relatively stable internal environment, even if external conditions change
Note: Internal refers both to the cell itself and, in multicellular organisms, the organism as a whole
Define
Positive feedback
A system where the response amplifies the original stimulus, pushing conditions further from the original levels
This usually continues until some breaking point, causing the conditions to return to normal or to be set at a new level
Examples of negative feedback
Anything that is involved in maintaining homeostasis
Ex:
Thermoregulation (if temps rise above set, then the response is to lower temp)
pH regulation (if pH levels drop, then the response is to increase pH)
Examples of positive feedback
Childbirth – contractions cause pressure from the baby on the cervix, which causes a release of oxytocin, which increases the frequency and strength of contractions
Breast-feeding – increased breastfeeding / emptying of the milk ducts causes a release of prolactin, which increases the production of milk in the breast tissue
Global climate change – increased temperatures reduce snow cover on Earth, which reduces how much light is reflected, increasing the absorption of light (and heat)
Severe fevers – increased temperatures cause faster chemical reactions in the body, which generates more heat
What are fevers?
An increase to the body’s set point for temperature in response to some pathogens
Note that this is still an example of negative feedback unless the temperature gets too high
List the
Parts of a Negative Feedback Loop
- Stimulus
- Sensor
- Control center
- Effector
Define
Stimulus
Any changes to internal or external conditions, which can be sensed to elicit a response
Define
Sensor
Any part of the body that can detect a stimulus
Define
Control center
The part of the body that receives signals from a sensor and sends signals to an effector
Define
Effector
Any part of the body that receives signals from a control center and responds accordingly
What can cause the body’s temperature to change?
Increase: Exercise, hot environment
Decrease: Cold environment
Outline how humans maintain body temperature
Stimulus: Above set point (37 ℃)
* Sensor: Thermoreceptors in skin and in brain
* Control center: Hypothalamus
* Effectors: sweat glands, which secrete sweat; blood vessels in the extremities, which vasodilate (widen) to allow more blood to the arms and legs
Stimulus: Below set point
* Sensor: Thermoreceptors in skin and in brain
* Control center: Hypothalamus
* Effectors: blood vessels in extremities, which vasoconstrict (narrow) to keep blood in the core; large muscles, which shiver to generate heat; small muscles in the skin, which raise hair to reduce airflow/heat loss (goosebumps!)
Outline how humans maintain blood sugar levels
Stimulus: Blood glucose levels increase due to eating
* Sensor: Pancreas
* Control center: Also pancreas, which secretes the hormone insulin
* Effectors: Liver and muscle cells, which respond to insulin by taking in glucose from the blood and storing it as glycogen
Stimulus: Blood glucose levels drop due to fasting or exercising
* Sensor: Pancreas
* Control center: Also pancreas, which secretes the hormone glucogon
* Effector: Liver cells, which respond to glucagon by breaking down glycogen and releasing the glucose back into the blood
List the levels of biological organization, from cell to organism
Cell
Tissue
Organ
Organ system
Organism
What is the function of the
circulatory system?
Circulate blood, which brings nutrients from the digestive and respiratory systems to the interstitial fluid and moves wastes from the interstitial fluid to the excretory and respiratory systems
What is the function of the
respiratory system?
Bring oxygen into the body to diffuse into the blood, and remove CO2 from the blood to be exhaled
What is the function of the
digestive system?
Bring nutrients into the body and break them down so that they can diffuse into the blood
What is the function of the
excretory system?
Remove wastes from the blood and move them into the bladder to be excreted (peed out)
Regulate the amount of water / solutes in the blood
Compare and contrast the endocrine and nervous systems
Both: Use cell signaling to coordinate bodily functions
Nervous: much faster and short-lived responses; uses nerves/neurotransmitters
Endocrine: slower and long-lived responses; uses hormones that move into the blood stream
Describe the parts of a
Neuron
- A - dendrites: receive signals
- B - cell body: contains nucleus and other organelles
- C - axon: sends signal; can be VERY long and may have a layer (called a myelin sheath) around it to insulate
- D - terminal ends: send signals
Describe the parts of a
Synapse
- A - presynaptic neuron: the dendrite of a neuron which is sending the signal / releasing neurotransmitters
- B - vesicles that contain neurotransmittesr
- C - synapse; the gap between the neurons into which the neurotransmitters is released
- D - postsynaptic neuron: contains the receptors
What does homeostasis have to do with cell signaling?!
Each step (sensing, integrating the information at the control center, and the effectors’ responses) are mediated by CELL SIGNALING.
