Homeostasis and Control Systems Flashcards
Learning objectives
define, with examples, what is meant by homeostasis •outline the main components required for a homeostatic control system
•explain how thermoregulatory mechanisms exemplify homeostasis
•identify factors which limit homeostasis
•understand the concept of disease as failure of homeostasis
What is homeostasis? (definition)
Homeostasisis the maintenance of a relatively constant or stable internal environment
What internal environmental factors must be controlled for homeostasis?
- Concentration of nutrient molecules
- Concentration of O2& CO2 (carbonic acid)
- Concentration of waste products
- pH ( 7.35-7.45- enzyme denaturation)
- Concentration of water, salt & electrolytes (cell lysis/ crenation)
- Temperature (amino acid denaturation)
7 .Volume & pressure
What are the 2 classes of homeostatic systems?
- Intrinsic:
•Local control: Regulatory mechanism initiated within an organ and inherent to that organ
•Accomplished by release of chemicals such as paracrines& autocrines
•Example: hypoxic vasodilation of blood vessels
2.Extrinsic/Reflex
•Long-distance control: Regulatory mechanism initiated outside an organ
•Accomplished by nervous and endocrine systems
•Example: blood pressure regulation
What are the components of an extrinsic/ reflex control system?
- A receptor
- A control centre
- An effector
- receptor senses change
- control centre evaluates change & initiates a response
- effectors return conditions toward normal
- deviation from set-point lessens
- effectors are shut off
What are negative feedback mechanisms/loops?
- Are responsible for many of the body’s homeostatic controls e.g. blood pressure control, body temperature
- Consist of pathways where the response opposes or removes the stimulus (graph in lecture slides)
- Stabilise the variable that is being regulated
Negative feedback mechanism of body temperature control
Receptors:
•Peripheral and central thermal receptors- signals sent to ant. hypothalamus
Control centre:
•Hypothalamus- causes vasodilation in skin (radiant heat loss) hair follicles flatten hair and sweat glands open- opposite when body temp too low.
Effectors:
•skin blood vessels, sweat glands, arrector pili muscles, skeletal muscles, endocrine organs
What is positive feedback?
Positive feedback is a process in which the end products of an action cause more of that action to occur in a feedback loop. This amplifies the original action.
-Occurs in fever- in this case it can cause a life-threatening loss of homeostatic control
- It enhances the initial change- Does NOT help maintain stability and is very rare under normal circumstances
2 examples are in labour and in blood clotting.
What is fever/ pyrexia?
Fever or pyrexia is a process where normal body temperature is raised over homeostatic conditions- caused by infection: can stimulate pyrogens which increase the set point in the hypothalamus
Receptor:
•chemoreceptors
Control centre:
•Hypothalamus
Effectors:
•sweat glands, skin blood vessels, skeletal muscle
Factors that limit homestasis
Extremes of Age
Examples of altered control mechanisms:
•Fluid balance- lower thirst, less water conservation, more risk
•Thermoregulation- more dysfunctional than in younger people, vasodilation/constriction
Babies have high surface area/mass ratio, less white fat, large head (large s.a)- need to be kept warm (can’t shiver to preserve heat)
Presence of a pathologic condition
•The usual negative feedback mechanisms become overwhelmed.
What is the relationship between disease and disturbances of homeostatic mechanisms?
Most disease is caused by a disturbance of homeostatic mechanisms known as “homeostatic imbalance”
•Occurs when a factor in the internal environment is controlled inadequately; its level falls outside the normal range
- Example 1: the cardiovascular system
- chronic hypertension
- atherosclerosis
- congestive heart failure
- Example 2: the endocrine system
- Type 1 diabetes
