Homeostasis Flashcards
If internal environment within cells were not regulated, what would happen?
Would not be able to release waste (e.g CO2 and urea)
What are the two main concepts that drive the structure and function of multicellular organisms?
- Surface area to volume ratio (issue for larger organisms)
2. Rate of diffusion (main way in which cells exchange with environment)
What is the size of organisms limited by?
Limited unless exchange surfaces and transport systems evolve.
What is the rate of diffusion limited by?
Distance.
In order to keep inner cells healthy, what must be organised?
Cells of complex organisms are organised into functional units.
What are the functional units into which complex organisms are organised?
- cells of related types form tissues
- tissues function together to form organs
- organs work together in systems
- organisms are made up of multiple systems
Do all animals have the same major organ systems? Why or why not?
No. This is because the environment and animal type dictates the evolution of a particular system.
What are the four major types of tissue?
- connective tissue (e.g BLOOD, bone, cartilage)
- muscle (smooth which lines digestive tract and controls blood flow, cardiac, skeletal)
- epithelium (barriers/borders: protection, secretion, absorption. E.g skin)
- nervous tissue (nervous and glial cells)
What is the function of glial cells?
Part of nervous tissue. Acts as supporting, regulating network. Helps mediate neurons.
What type of tissue is blood?
Connective tissue.
Where do specialised cells come from?
They come from stem cells which are cells that have the potential to become specialised.
What is differentiation?
The process by which structure and function become specialised.
What are the two types of stem cells?
Some stem cells can become any cell type = totipotent
Adult stem cells are less flexible = multipotent. E.g bone marrow stem cells only produce red and white blood cells.
Define homeostasis.
The tendency to maintain a relatively stable internal environment.
What type of feedback do physiological mechanisms that maintain homeostasis rely on?
All rely on negative feedback which reduces the error signal that triggered the regulatory mechanism. (Minimises change)
List some examples of variables maintained by homeostasis,
- blood pressure
- water balance
What is the difference between negative and positive feedback?
Negative feedback = reduces change
Positive feedback = amplifies change
How is heat generated by the body?
Via cellular respiration. Therefore the more your cells respire, the more heat is produced.
Describe the relationship between thermal energy generation and loss for warm blooded and cold blooded animals.
Warm blooded: thermal energy loss = thermal energy generated, therefore constant temperature maintained.
Cold blooded;
Thermal energy loss < thermal energy produced, hotter
Thermal energy loss > thermal energy produced, cooler
What are the costs and benefits of homeostasis in general?
Costs:
- uses energy, very expensive in terms of metabolic costs
- risk of predation
Benefits:
- metabolic efficiency achieved
- less dependent on environment
What is the stimulus response model?
Stimulus > receptor > control centre (integratory system) > effector > response
What happens if the set point is drifted from in homeostasis?
Something physiological happens to bring back set point.
What are the costs and benefits involved in using homeostasis to maintain body temperature?
Costs:
- metabolically expensive to stay warm in cool environment
- water loss for cooling (e.g sweating, panting)
Benefits:
- high efficiency as enzymes are optimised for one temperature
- can remain active in cold, more time to forage, less risk of predation as they still have the energy to run away
- able to use wider range of environments
Describe what occurs with the homeostasis of blood gas (holding in breath) and name the type of feedback occurring.
- Holding in breath causes decrease in oxygen and increase in CO2.
- Increase in CO2 leads to increase in carbonic acid which is detected by the body as it measures pH which indirectly measures CO2.
- when the urge to breathe is too great, the concentration of blood CO2 is the highest and therefore deep breaths are taken to decrease the CO2 concentration (NEGATIVE FEEDBACK reduces stimulus).
- overshoot occurs and acts to correct via reduced breathing
What is positive feedback? List some examples.
When responses increase the change from the set point (increase the stimulus).
E.g sneezing, blood clotting, contractions during childbirth, LH surge in female reproductive cycle, Na+ ions entering nerve cell activate more Na+ channels to open, severely hypothermic person undressing
NOT homeostasis
Describe the positive feedback process of birth contractions in steps.
- neural reflex triggers pituitary gland to release oxytocin
- oxytocin triggers uterine contractions which stretch the cervix
- stretching the cervix triggers neural reflex, cycle continues
What are the 2 internal systems of communication?
Nerves and hormones.
Describe local forms of cell communication.
- cell to cell direct contact
- chemical signals
Describe distance forms of cell communication.
Neural: fast and specific
Endocrine: slower and widespread
What are nerves efficient at?
Rapid point to point signalling
Describe the structure of a neuron.
Dendrites branch out from soma, soma connects to axon via axon hillock, axon is long rod covered in myelin sheath, ends at axon terminal which has output terminals at ends
Which direction does action potential and therefore output travel in the neuron?
From dendrites to axon terminal
What is the function of dendrites?
Receives message/signal.
What is a synapse?
Junction/ gap between two nerve cells across which impulses pass by diffusion of a neurotransmitter
When are neurotransmitters released? What does it trigger?
Once action potential reaches the synapse. Triggers action potential or response in next cell
What is action potential always induced by?
Always induced by a change in charge, which will reach a certain threshold for an action potential to occur.
Describe what occurs with the action potential during the resting stage.
Resting: -70mV, more negative inside than outside.
Pump IN K+, pump OUT Na+, NA/K pump maintains concentration gradient of ions.
Difference in charge is a result of the presence of other negatively charged molecules.
Leaky potassium channels are also always open, ontributing to difference in charge.
Describe what occurs with the action potential during the depolarisation stage.
Depolarised: +40mV (more positive inside than outside)
Slight change in membrane potential causes Na+ channels to open, causing influx of Na+ into the cell.
Describe what occurs with the action potential during the repolarisation stage.
Repolarisation: -70mV more negative inside than outside
Depolarisation propagates to adjacent Na+ channels, action potential spreads along axon.
K+ channels open, causing K+ ions to leak out of the cell.
Voltage gated channels refractory - cannot respond for short period
What channels are at the end of the axon?
Ca2+ channels important for releasing synaptic vesicles.
What is a hormone?
Regulatory substance released into, and transported by, fluid in the body.
What is an autocrine signal?
Direct action on cell releasing the chemical
What is a paracrine signal?
Released to act on adjacent cells.
What is an endocrine signal?
Released mostly from glands
Circulate in blood to distant targets
Specific receptors on target organs
Describe the difference between hormone action with a water soluble hormone (peptide) and a lipid soluble hormone (steroid).
Water soluble hormone peptide bonds to receptor on cell membrane, activation of second messengers
Lipid soluble hormone steroid binds to receptor in cytoplasm or nucleus
What two organs are key to many homeostatic mechanisms?
Hypothalamus and the pituitary gland.
Describe structure of posterior pituitary and what it releases.
- neurosecretory neurons connected by long axons to terminals in posterior pituitary
- release oxytocin (uterine contractions and milk production) and antidiuertic hormone (affects urine production and water balance in kidney) into bloodstream
Describe structure of anterior pituitary and what it releases.
Short hypothalamic neurosecretory neurons release “releasing hormones” into portal blood vessels
- Portal blood vessels deliver these hormones to glandular cells in anterior pituitary.
- when sitmulated, anterior pituitary cells then release these into bloodstream
Describe the process of negative feedback with the anterior and posterior pituitary gland.
Anterior: stimuli > hypothalamus releasing hormone > pituitary releasing pituitary hormones > endocrine gland > hormone. Negative feedback exists with all 3 of the latter, including pituitary hormone inhibiting hypothalamus.
Posterior: same as anterior EXCEPT pituitary gland cannot inhibit hypothalamus and vice versa.
