7

Question 1

define homeostasis

Answer 1

process of maintaining a constant internal environment despite changing conditions

Question 2

are homeostasis and equilibrium synonymous?

Answer 2

no; homeostasis involves a dynamic steady state with different concentrations of components in the intracellular and extracellular fluids (ICF and ECF)

Question 3

7 reflex steps

Answer 3

1. stimulus
2. sensor or receptor
3. afferent pathway
4. integrating center
5. efferent pathway
6. target or effector
7. response

Question 4

is the set point a singular value?

Answer 4

no; it can have a range of normal values

Question 5

describe oscillation around a set point

Answer 5

• below the normal range of function, the response loop turns on
• above the normal range, the negative feedback turns the response loop off

Question 6

negative feedback

Answer 6

• used for homeostasis
• involves an initial stimulus, response, and decreasing stimulus
• this has a stabilising effect
• stopped once the system has been stabilised

Question 7

positive feedback

Answer 7

• used for change
• involves an initial stimulus, response, and increasing stimulus
• this has a reinforcing effect
• stopped by an outside factor

Question 8

give an example of negative feedback in the body

Answer 8

regulation of cortisol secretion:
- negative feedback action of cortisol suppresses CRH release and ACTH release

Question 9

give an example of positive feedback in the body

Answer 9

oxytocin and the control of uterine contractions:
- baby drops lower in uterus to initiate labor, leading to cervical stretch
- this stimulates oxytocin release, causing uterine contractions
- this pushes the baby against the cervix, causing further cervical stretch

Question 10

is positive feedback homeostatic?

Answer 10

no

Question 11

3 examples of local control

Answer 11

gap junctions, contact-dependent signals, autocrine/paracrine signals

Question 12

maintaining homeostasis and other body functions requires

Answer 12

intracellular communication

Question 13

gap junctions

Answer 13

• form direct cytoplasmic connections between adjacent cells
• small ions and molecules move through gap junctions connecting cells

Question 14

contact-dependent signals

Answer 14

• require interaction between membrane molecules on two cells
• membrane protein binds to membrane protein

Question 15

autocrine/paracrine signals

Answer 15

• autocrine: act on the same cell that secreted them
• paracrine: secreted by one cell and diffuse to adjacent cells
• molecules move through interstitial fluid; short distance

Question 16

2 examples of long-distance communication

Answer 16

• endocrine system
• nervous system (neurotransmitters, neurohormones)

Question 17

endocrine system

Answer 17

• hormones are secreted by endocrine glands or cells into the blood
• only target cells with receptors for the hormone respond to the signal

Question 18

nervous system

Answer 18

• neurotransmitters are chemicals secreted by neurons that diffuse across a small gap to the target cell
• neurohormones are chemicals released by neurons into the blood for action at distant targets

Question 19

distinguish between simple and complex reflexes

Answer 19

• simple are mediated either by the nervous or the endocrine system
• complex reflexes are mediated by both systems and go through several integrating systems

Question 20

local vs reflex control

Answer 20

• in reflex control, cells at a distant site control the response
• in local control, cells in the vicinity of the change initiate the response

Question 21

Two types of sensors for homeostatic reflex pathways

Answer 21

• specialised cells or structures that convert various stimuli into electrical signals (central receptors, peripheral receptors)
• cell membrane or intracellular receptor proteins

Question 22

central receptors

Answer 22

in or close to the brain
- eyes (vision)
- ears (hearing, equilibrium)
- nose (smell)
- tongue (taste_
- central chemoreceptors, osmoreceptors, thermoreceptors

Question 23

peripheral receptors

Answer 23

lie outside the brain
- chemoreceptor (pH, gases, chemicals)
- osmoreceptor (osmolarity)
- thermoreceptor (temperature)
- baroreceptor (pressure)
- proprioreceptor (body position)
- other mechanoreceptors (pain, vibration, touch)

Question 24

3 types of reflex pathway patterns in the nervous system, ordered by increasing complexity

Answer 24

1. simple neural reflex (stimulus > sensory neuron > efferent neuron > neurotransmitter > target cell > response)
2. neuroendocrine reflex (stimulus > sensory neuron > efferent neuron > neurohormone > target cell > response)
3. complex neuroendocrine reflexes (stimulus > sensory neuron > efferent neuron > neurohormone > endocrine cells > hormone > target cell > response)

Question 25

neural reflex vs endocrine reflex - specificity

Answer 25

N: each neuron terminates on a single target cell or a limit number of adjacent target cells E: most cells of the body are exposed to a hormone. the response depends on which cells have receptors for the hormone

Question 26

neural reflex vs endocrine reflex - nature of the signal

Answer 26

N: electrical signal that passes through neuron, then chemical neurotransmitters that carry the signal from cell to cell. in a few cases, signals pass from cell to cell through gap junctions E: chemical signals secreted in the blood for distribution throughout the body

Question 27

neural reflex vs endocrine reflex - speed

Answer 27

N: very rapid E: distribution of the signal and onset of action are much slower than in neural responses

Question 28

neural reflex vs endocrine reflex - duration of action

Answer 28

N: usually very short. responses of longer duration are mediated by neuromodulators E: responses usually last longer than neural responses

Question 29

neural reflex vs endocrine reflex - coding for stimulus intensity

Answer 29

N: each signal is identical in strength. stimulus intensity is correlated with increased frequency of signalling E: stimulus intensity is correlated with amount of hormone secreted

Question 30

exocrine vs endocrine system

Answer 30

exocrine: - secretes hormones into a duct - substances secreted to environment external to self - eg sweat, digestive enzymes, saliva endocrine: - secretes hormones into the bloodstream - widespread, slower effects - eg insulin, cortisol, thyroid hormones

Question 31

primary endocrine organs

Answer 31

- main function is to release hormone - hypothalamus, pineal gland, pituitary gland, thyroid gland, parathyroid gland, adrenal glands, ovaries, testes, placenta

Question 32

secondary endocrine organs

Answer 32

- release hormones and do something else - heart, liver, pancreas, kidneys, stomach and small intestine, adipose tissue, skin

Question 33

how were hormones identified?

Answer 33

based on a 1849 experiment by the German physiologist AA Berthold - remove gland, replace gland, give excess gland and observe results - extract, purify, and test in biological assay