homeostasis

Question 1

how is homeostasis defined by its latin roots

Answer 1

“similar condition” ( not identical condition!)

Question 2

what do our bodies constantly monitor

Answer 2

the internal state and respond to any threat that might disturb the “similar internal conditions” of the body

Question 3

why are our bodies constantly monitoring their internal state

Answer 3

in an effort to prevent disturbance and maintain optimum “similar conditions” or, in other words, a relatively constant internal environment in which all processes work optimally

Question 4

what are examples of substantial changes in our internal environment that our bodies are not very tolerant of

Answer 4

temperature
pH of bodily fluids
concentration of hormones

Question 5

what does failure to adequately correct imbalances in the internal environment of the body lead result in

Answer 5

illness and disease, or pathology (pathos - meaning suffering)

Question 6

give an example of failure to maintain a relatively constant environment

Answer 6

diabetes mellitus occurs when the body can no longer maintain it’s optimal blood glucose concentration

Question 7

what does homeostasis require

Answer 7

integration of organ systems

Question 8

how is an increased energy demand an example of integration of organ systems

Answer 8

Nervous, endocrine and Musculoskeletal system to seek, supply and access nutrients, Respiratory system to supply O2 , Alimentary system to break down food into useable forms and absorb across gut wall into bloodstream, Cardiovascular system to transport O2 and nutrients via the bloodstream to the cells and transport CO2 and waste from the cells to the Respiratory, Alimentary and Renal systems for disposal.
Nervous and Endocrine systems co-ordinate and control all these systems.

Question 9

why must all the systems integrate effectively

Answer 9

in order to maintain an optimum internal environment within the body for all cells to function and ultimately produce energy

Question 10

what is homeostasis

Answer 10

maintaining an optimum internal environment within the body

Question 11

what is the basic concept of homeostasis and how to maintain a constant level

Answer 11

the body usually has a range within which it can tolerate change and so the output must be equal to the input. what we gain, we must lose. what we lose, we must replace.

Question 12

what types of changes result in loss of homeostasis

Answer 12

external and internal changes

Question 13

what could happen when the organism attempts to compensate as a result of a loss of homeostasis

Answer 13

compensation fails - leading to illness or disease

compensation succeeds - leading to wellness

Question 14

what are common everyday challenges to our internal environment

Answer 14

external temperature
access to nutrients
exersice

Question 15

what can a loss of homeostasis impact

Answer 15

body fluid composition
energy stores
body temperature

Question 16

what must act to counteract the potential threats to homeostasis

Answer 16

physiological mechanisms

Question 17

how can external temperature be a threat to homeostasis

Answer 17

In Abu Dhabi the temperature can reach 40oC…but our bodies don’t. Heat loss is triggered by sweating and vasodilation and core body temperature remains close to the optimal 37oC.
Experiments have shown naked humans can maintain core body temperature pretty close to 37oC in external temperatures ranging from 10oC to 55oC!

Question 18

how can access to nutrients be a threat to homeostasis

Answer 18

eat a sugary donut, glucose absorbed across intestinal tract, blood glucose rockets skywards and all sorts of problems ensue…..only they don’t, because the hormone insulin comes along and effectively removes glucose from the blood almost as fast as it enters

Question 19

when does homeostasis become less effective

Answer 19

at extremes

Question 20

what are the 3 main mechanisms in which homeostasis operates

Answer 20

negative feedback
feedforward
positive feedback

Question 21

which of the 3 mechanisms in which homeostasis operates is the most important and the key mechanism by which homeostasis is maintained

Answer 21

negative feedback

Question 22

what is negative feedback

Answer 22

When a condition that is homeostatically regulated (e.g. body temperature), is sensed to have shifted from the normal range, a signal (usually nervous or endocrine), is generated that produces a response (e.g. shivering or sweating), that corrects the original disturbance and brings the regulated condition back within the normal range.
“Negative” feedback because the condition that triggered the homeostatic response becomes switched off/removed by that response.

Question 23

what is the size of the response proportional to

Answer 23

the size of the disturbance

Question 24

what are the characteristics of negative feedback systems

Answer 24

there is oscillation around the set point.

restores the regulated condition after its initial disturbance, but cannot prevent it happening

Question 25

what are feedforward systems

Answer 25

more sophisticated form of negative feedback, additional receptors permit system to anticipate change and therefore activate response earlier.

Question 26

what are positive feedback mechanisms

Answer 26

positive feedback has the opposite effect of negative feedback. Where negative feedback aims to restore disturbed conditions to optimum, positive feedback sets off a train of events that lead to an even greater disturbance. Positive feedback systems are rare in normality but frequently occur in pathophysiology

Question 27

what do these train of events that lead to an even greater disturbance lead to

Answer 27

instability, and are common in pathophysiology, rare in normal physiology. however they do occur e.g. in the nerve action potential

Question 28

explain hoe positive feedback takes place in the action potential (message in the nervous system)

Answer 28

initial triggers allows positively charged Na+ ions to enter a nerve cell. increase in Na+ influx to nerve cell. charge inside cell become more positive (depolarisation). increase Na+ permeability across membrane

Question 29

what is positive feedback associated with

Answer 29

while positive feedback is associated with some elements of normal function, it is more commonly associated with pathology

Question 30

how does negative feedback maintain homeostasis of blood glucose

Answer 30

when you eat a meal, your BG levels increase resulting in the release of insulin. glucose is then taken up by cells leading to a decrease in BG levels

Question 31

how does positive feedback lead to deregulation of homeostasis of blood glucose

Answer 31

when you eat a mean, your BG levels increase. | the lack of glucose uptake by cells leads the body to perceive starvation so the liver produces even more glucose

Question 32

what is the aim of diabetes treatments

Answer 32

to restore homeostatic balance of blood glucose

Question 33

as a generalisation what does medicine aim to do

Answer 33

restore homeostatic control when this is disturbed by illness or disease

Question 34

name a process that is homeostatically controlled and is critical for life

Answer 34

water balance

Question 35

what percentage does water make up of the body

Answer 35

60% of the body weight

Question 36

why is homeostatic maintenance of water crucial

Answer 36

because water affects the concentration of everything else in the body

Question 37

which processes are regulated in order to maintain water balance

Answer 37

input is regulated by the thirst mechanism output by regulation of kidney function (urinary losses) other processes that alter water balance are also regulated, but their control is not aimed at maintaining water balance e.g. sweating is controlled as part of temperature regulation, so possible conflict between water and temperature regulation

Question 38

where is the water in our body

Answer 38

``` it is split between 3 compartments 1. intaccellular fluid 2. interstitual fluid (fluid between cells) 3. plasma (fluid component of blood) 2 and 3 are extracellular fluids ```

Question 39

how does water move between the 3 compartments

Answer 39

it can move freely although movement is subject to forces such as osmosis

Question 40

the body can survive as long as...

Answer 40

the composition of the extracellular fluid (ECF) is maintained in a state compatible with the survival of its individual cells i.e. composition of the ECF is very very important

Question 41

what is the ECF compartment subdivided into

Answer 41

plasma and interstitial fluid. | maternal moving between cels and ECF must cross the cell membrane

Question 42

what is the capillary wall permeable to

Answer 42

everything except plasma protein and blood cells

Question 43

what type of permeability do cell membranes have

Answer 43

selective permeability

Question 44

how much water is in our body

Answer 44

42L

Question 45

how is water distributed in the body

Answer 45

we have twice as much ICF as ECF so 1/3 in ECF and 2/3 in ICF (ICF=24L , ECF=14L)

Question 46

what percentage of ECF is interstitial fluid (ISF)

Answer 46

approximately 80%

Question 47

what percentage of ECF is plasma

Answer 47

approximately 20%

Question 48

what does hyper mean

Answer 48

greater than normal

Question 49

what does hypo mean

Answer 49

less than normal

Question 50

what does aemia/emia mean

Answer 50

in the blood

Question 51

what does uria mean

Answer 51

in the urine

Question 52

what does glyc mean

Answer 52

related to glucose

Question 53

what does glycosuria mean

Answer 53

glucose in the urine

Question 54

what does hypoglycaemia mean

Answer 54

low blood glucose levels

Question 55

how does plasma continuously move

Answer 55

through blood vessels by the pumping action of the heart = dynamic component of the ECF

Question 56

what does plasma exchange with the ISF

Answer 56

it freely exchanges nutrients (e.g. O2, glucose, ions) and waste (e.g. CO2 and urea)

Question 57

how does exchange occur

Answer 57

as blood passes through the capillaries of the body

Question 58

why does exchange not take place in arteries

Answer 58

as the walls of large vessels are too thick

Question 59

what is the difference between the composition of plasma and ISF

Answer 59

they are virtually identical except for plasma proteins, which are too large and, therefore, restricted to the plasma

Question 60

ECF is homogenous with the one exception of...

Answer 60

ISF being devoid of plasma protein

Question 61

how is body fluid volumes measured

Answer 61

using the dilution principle 1. c=m/v => v=m/c 2. only plasma can be sampled so only compartments of which plasma is a component can be measured directly (plasma, ECF, TBW) 3. the nature of barriers which separate compartments is crucial in determining the test substance ``` e.g. m=10m glucose c=1mg/ml glucose v=m/c=10/1=10 mg/(mg/ml) = ml 10ml ```

Question 62

which compartments can be measured directly using the dilution principle

Answer 62

1. Plasma Volume (PV): Since plasma proteins cannot cross the capillary walls, can use dyes or radioactive labels that attach to plasma proteins, e.g. Evans blue or I125albumin. 2. Extracellular Volume (ECF): Need something that freely crosses capillary walls, but cannot cross cell membranes, e.g. inulin, sucrose, mannitol, which are all too large to cross cell membrane or 24Na+ , 36Cl-, which are actively extruded from cells. 3. Total Body Water (TBW): There is no barrier to water in the body, so can use a loading dose of heavy water/ deuterated water (D2O). Other compartments (where plasma is not a component) cannot be directly sampled, therefore calculate volume indirectly; ISF = ECF-PV, ICF = TBW-ECF

Question 63

what is the method of practice of dilution principle

Answer 63

1. Inject a substance that will stay in one compartment only (plasma, ECF, TBW) 2. Then calculate the volume of distribution: = amount injected (minus any removed by excretion or metabolism), divided by the concentration in the sampled fluid. Example using sucrose which is restricted to ECF: 150mg of sucrose injected into plasma of 70kg man, [sucrose] blood sample after distribution = 0.01mg/ml 10mg were excreted or metabolised. What is the volume of ECF? 150-10mg=140mg distributed in ECF. therefore volume of distribution = 140mg/0.01mg/ml = 14000mls ECF volume = 14,000ml or 14L

Question 64

why does the composition of the ICF differ from the ECF

Answer 64

ECF bathing cells must be maintained at a constant composition, however the composition of the ICF differs markedly from the ECF, particularly for ions because cell membrane is a selective barrier

Question 65

why is there a large concentration gradient between ICF and ECF

Answer 65

as it is fundamental for nerve and muscle function

Question 66

what happens if homeostasis does not operate effectively

Answer 66

Consider an example where extracellular potassium concentration ([K+]ECF ) was allowed to increase beyond the normal range: Loss of concentration gradient between ECF and ICF This disrupts nerve and muscle function, including cardiac muscle  ventricular fibrillation and death. ESSENTIAL to regulate ECF K+ (Kidney normally sorts it all out). Disease states and illness are associated with perturbation, and even breakdown, of homeostatic control mechanisms. Eg. in diabetes, breakdown of the normal regulation of blood glucose  Hyperglycaemia (i.e. excess glucose in the blood)

Question 67

how does the proportion of body water vary with age and gender

Answer 67

Females are “less wet”, because they have a higher proportion of body fat, which has less water content than muscle. Muscle contains ~70% water by weight, fat only 10% water. For the same reason, older people have lower water content.

Question 68

what can treating with lipid or H2O soluble drugs depend on and influence

Answer 68

the proportion of body water/fat will influence the rate at which the drug can be eliminated from the body

Question 69

how are changes within the normal range restored

Answer 69

by physiological mechanisms which act to counteract change

Question 70

what do pathophysiological disturbances require out with normal range

Answer 70

intervention to restore variables to normal range

Question 71

what happens if extreme disturbance may fall off the homeostatic plateau

Answer 71

death

Question 72

What is extracellular fluid (ECF) and where is it found

Answer 72

surrounds all cells and is composed of - plasma, the dynamic component of ECF that is contained within blood vessels ( it surrounds blood cells) - internal fluid (ISF), the fluid outside blood vessels that surrounds cells other than blood cells

Question 73

What is intracellular fluid (ICF) and where is it found

Answer 73

found within cells

Question 74

Why do homeostatic mechanisms operate

Answer 74

to maintain constant optimal ECF despite the perturbation of life