Physiological Homeostasis

Question 1

Define “Homeostasis”

Answer 1

The dynamic maintainenance of physiological variables within a predictable range

The word dynamic means that the variable can fluctuate but within a normal range- the size and frequency of these fluctuations depend on the variable

Question 2

what is the purpose of the homeostasis

Answer 2

In the short term- immediate survival

In the medium-long term- health, well-being, reproductive capability

Question 3

Describe how immediate survival is achieved

Answer 3

Fuel homeostasis, blood flow and pressure ensures that there’s SUFFICIENT BLOOD GLUCOSE
blood flow and pressure, lung ventilation ensures that there’s SUFFICIENT BLOOD OXYGEN
Both of the above ensure that there’s enough oxygen and glucose to be supplied to all the cells.

Water intake and excretion and Na/K content ensures that extracellular and intracellular fluid osmolarity and volume is maintained.
H+/HCO3 - content ensures that pH is maintained

Question 4

Describe how medium survival is achieved

Answer 4

temperature and metabolic rate ensures the optimal functioning of organs and tissues

Appetite and Gastro-Intestinal secretions, motility and absorption ensures a fulfilling dietary requirements

Question 5

Describe how long terms survival is achieved

Answer 5

steroid hormone levels ( men- testosterone, women, progesterone, oestrogen) maintains the idea of secondary sexual characteristics and reproductive capability

Question 6

The hierarchy of importance of physiological variables

Answer 6

The idea that variables of greater immediate importance is maintained at the expense of other variables that are of importance in the long term

Question 7

Name the different type of mechanism system

Answer 7

Negative feedback
Feed forward
Positive feedback

Question 8

Negative feedback

Answer 8

A change in the variable being regulated is compared to a set point which will will trigger a response. This response will move the variable back to a set point.

This set point can be changed or override depending on physiological circumstances

( CAN BE neuronal, endocrine, local)

Question 9

Feed forward

Answer 9

The anticipation of change brings about the response before the change can be detected

Question 10

Positive Feedback

Answer 10

A change in the variable triggers a response that causes a FURTHER change in that variable- AMPLIFICATION rather than NORMALISATION

Question 11

Components of negative feedback reflex arcs

Answer 11

Sensors- detect changes in physiological variables

Afferent pathway- carry signals from sensors to the integrating centre

Integrating centre- compare inputs from sensors against the physiological set point and elicit a response ( located in the midbrain and brain stem)

Efferent pathway- carry signals from integrating centre to effectors

Effectors- produce a response that tends to normalise physiological variable

Question 12

Describe what the midbrain and brain stem is comprised of and what it controls

Answer 12

Hypothalamus, pons and medulla

Temperature control, osmolarity control, blood pressure /flow control, blood gas ventilation control

Question 13

Comment on the parasympathetic and sympathetic systems

Answer 13

They oppose each other hence results in the fine tuning of the physiological variables.

eg. Blood vessels diameter, Gi tract, salivary gland secretions, sweat gland secretions, endocrine secretions

Question 14

Negative feedback eg

Answer 14

Body Temperature control

1. Decrease in Room temperature
2. Increase in heat loss from the body
3. Receptors detecting the decrease in body temperature
4. Temperature sensitive neurons - afferent pathways
5. Thermo regulatory neurones in the brain compare to the set point
   Efferent pathwatys
6. Response :

Constriction of skin blood vessels- less heat loss from the body

Shivering- more heat transfer

Negative feed back loop back to the receptors- IMPORTANT

Question 15

Comment on the action of hormones

Answer 15

Hormones act on the target tissues through specific receptors

The response is dependant on the the type of receptor expressed on the target tissue

Question 16

Hormone Types

Answer 16

Glycoproteins- LH, FSH, thyroid stimulating hormone
Polypeptides- growth hormone, insulin
Peptides-ADH, oxytocin
Steroids- progesterone, oestrogen,
Amino acid derivatives- Tyr - Adrenaline + T4

Question 17

Hormone receptors

Answer 17

Peptides, proteins, glycoproteins, catecholamines : receptors founds on plasma membrane—> action is through secondary messenger to change enzyme activity
RAPID and TRANSIENT response

Steroids, thyroid hormones: receptors are intracellular—-> after gene transcription- SLOW, PROLONGED RESPONSE

Question 18

Endocrine hormone reflex arc example-

Answer 18

when blood glucose increases- insulin being secreted

KEY: receptors and integrating centre found in the same place

Question 19

Local Homeostatic response example ( negative feedback)

Answer 19

Sensory receptors, integrating centres and effectors are all located in the same region

eg. muscles working harder means that there’s an increase in pCO2 and lactic acid. this is sensed by the arterioles supplying the lactic acid, which then dilates.This increases the O2 and glucose supply

Question 20

Feed forward

Answer 20

Anticipation for a meal

Parasympathetic activation

Stimulation of saliva and gastric juice production

Prepared for food intake

Question 21

Positive feed back example

Answer 21

Most hormonal- often involving steroid hormone

Altered oestrogen/progesterone balance 
Increased excitability of uterus 
Uterine contractions
Fetus presses on cervix
Signals to hypothalamus 
Oxytocin secretions
(positive feedback) increases excitability of uterus