Homeostasis

Question 1

If internal environment within cells were not regulated, what would happen?

Answer 1

Would not be able to release waste (e.g CO2 and urea)

Question 2

What are the two main concepts that drive the structure and function of multicellular organisms?

Answer 2

1. Surface area to volume ratio (issue for larger organisms)

2. Rate of diffusion (main way in which cells exchange with environment)

Question 3

What is the size of organisms limited by?

Answer 3

Limited unless exchange surfaces and transport systems evolve.

Question 4

What is the rate of diffusion limited by?

Answer 4

Distance.

Question 5

In order to keep inner cells healthy, what must be organised?

Answer 5

Cells of complex organisms are organised into functional units.

Question 6

What are the functional units into which complex organisms are organised?

Answer 6

• cells of related types form tissues
• tissues function together to form organs
• organs work together in systems
• organisms are made up of multiple systems

Question 7

Do all animals have the same major organ systems? Why or why not?

Answer 7

No. This is because the environment and animal type dictates the evolution of a particular system.

Question 8

What are the four major types of tissue?

Answer 8

• 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)

Question 9

What is the function of glial cells?

Answer 9

Part of nervous tissue. Acts as supporting, regulating network. Helps mediate neurons.

Question 10

What type of tissue is blood?

Answer 10

Connective tissue.

Question 11

Where do specialised cells come from?

Answer 11

They come from stem cells which are cells that have the potential to become specialised.

Question 12

What is differentiation?

Answer 12

The process by which structure and function become specialised.

Question 13

What are the two types of stem cells?

Answer 13

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.

Question 14

Define homeostasis.

Answer 14

The tendency to maintain a relatively stable internal environment.

Question 15

What type of feedback do physiological mechanisms that maintain homeostasis rely on?

Answer 15

All rely on negative feedback which reduces the error signal that triggered the regulatory mechanism. (Minimises change)

Question 16

List some examples of variables maintained by homeostasis,

Answer 16

• blood pressure

- water balance

Question 17

What is the difference between negative and positive feedback?

Answer 17

Negative feedback = reduces change

Positive feedback = amplifies change

Question 18

How is heat generated by the body?

Answer 18

Via cellular respiration. Therefore the more your cells respire, the more heat is produced.

Question 19

Describe the relationship between thermal energy generation and loss for warm blooded and cold blooded animals.

Answer 19

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

Question 20

What are the costs and benefits of homeostasis in general?

Answer 20

Costs:

• uses energy, very expensive in terms of metabolic costs
• risk of predation

Benefits:

• metabolic efficiency achieved
• less dependent on environment

Question 21

What is the stimulus response model?

Answer 21

Stimulus > receptor > control centre (integratory system) > effector > response

Question 22

What happens if the set point is drifted from in homeostasis?

Answer 22

Something physiological happens to bring back set point.

Question 23

What are the costs and benefits involved in using homeostasis to maintain body temperature?

Answer 23

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

Question 24

Describe what occurs with the homeostasis of blood gas (holding in breath) and name the type of feedback occurring.

Answer 24

• 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

Question 25

What is positive feedback? List some examples.

Answer 25

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

Question 26

Describe the positive feedback process of birth contractions in steps.

Answer 26

• neural reflex triggers pituitary gland to release oxytocin
• oxytocin triggers uterine contractions which stretch the cervix
• stretching the cervix triggers neural reflex, cycle continues

Question 27

What are the 2 internal systems of communication?

Answer 27

Nerves and hormones.

Question 28

Describe local forms of cell communication.

Answer 28

• cell to cell direct contact

- chemical signals

Question 29

Describe distance forms of cell communication.

Answer 29

Neural: fast and specific
Endocrine: slower and widespread

Question 30

What are nerves efficient at?

Answer 30

Rapid point to point signalling

Question 31

Describe the structure of a neuron.

Answer 31

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

Question 32

Which direction does action potential and therefore output travel in the neuron?

Answer 32

From dendrites to axon terminal

Question 33

What is the function of dendrites?

Answer 33

Receives message/signal.

Question 34

What is a synapse?

Answer 34

Junction/ gap between two nerve cells across which impulses pass by diffusion of a neurotransmitter

Question 35

When are neurotransmitters released? What does it trigger?

Answer 35

Once action potential reaches the synapse. Triggers action potential or response in next cell

Question 36

What is action potential always induced by?

Answer 36

Always induced by a change in charge, which will reach a certain threshold for an action potential to occur.

Question 37

Describe what occurs with the action potential during the resting stage.

Answer 37

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.

Question 38

Describe what occurs with the action potential during the depolarisation stage.

Answer 38

Depolarised: +40mV (more positive inside than outside)

Slight change in membrane potential causes Na+ channels to open, causing influx of Na+ into the cell.

Question 39

Describe what occurs with the action potential during the repolarisation stage.

Answer 39

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

Question 40

What channels are at the end of the axon?

Answer 40

Ca2+ channels important for releasing synaptic vesicles.

Question 41

What is a hormone?

Answer 41

Regulatory substance released into, and transported by, fluid in the body.

Question 42

What is an autocrine signal?

Answer 42

Direct action on cell releasing the chemical

Question 43

What is a paracrine signal?

Answer 43

Released to act on adjacent cells.

Question 44

What is an endocrine signal?

Answer 44

Released mostly from glands
Circulate in blood to distant targets
Specific receptors on target organs

Question 45

Describe the difference between hormone action with a water soluble hormone (peptide) and a lipid soluble hormone (steroid).

Answer 45

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

Question 46

What two organs are key to many homeostatic mechanisms?

Answer 46

Hypothalamus and the pituitary gland.

Question 47

Describe structure of posterior pituitary and what it releases.

Answer 47

• 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

Question 48

Describe structure of anterior pituitary and what it releases.

Answer 48

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

Question 49

Describe the process of negative feedback with the anterior and posterior pituitary gland.

Answer 49

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.