Thirst and Drinking - 14 Flashcards
What is drive reduction theory?
Thorndike’s Law of Readiness - learning is motivated by an internal state. Hull proposed that a reinforcer supports learning because it alleviates an internal state of deprivation. Emphasis on homeostasis. Imbalance in homeostasis creates ‘arousal’ that initiates action.The goal is to decrease the ‘arousal’. Level of arousal and level of performance are directly related to one another. Ideas by Hull and Cannon.
What is negative feedback?
Early ideas about motivation applied the idea of negative feedback developed in physical systems (like thermostats) to behaviour
Negative feedback = a process whereby the effect produced by an action serves to diminish or terminate that action.
What are the components of a homeostatic “system”?
- System variable: variable controlled by systems (e.g., temp, hydration, nutrients)
- Set-point: the desired level of a variable
- Sensor: a mechanism for measuring the variable
- Effector system: behavioural /physiological mechanism(s) to change variable and restore homeostasis
What is the principle of homeostasis?
A number of physiological variables must be maintained within narrow limits for the body to function: temperature, hydration and nutrients (feeding)
What occurs in the regulation of body temperature?
Humans and all other endotherms (can generate own heat) generate heat by metabolism. Cells in the pre-optic area of the hypothalamus sense brain temperature and we have thermal sensors throughout or periphery. The hypothalamus controls physiological and behavioural response to regulate temperature.
What is involved in thirst and homeostasis?
Water comprises 70% of our lean body mass
As water is lost, cellular processes become inefficient, & eventually excessive water loss is fatal
Fluid loss through evaporation, respiration (H2O), urine and sweating (H2O + salt).
Drinking behaviour is the primary means of replenishing water
What is fluid composition, loss and gain?
About 2/3 of body water is inside cells, the remaining 1/3 is extracellular. Direct water loss occurs primarily from this extracellular compartment. Intracellular & intravascular fluid volume & composition must be kept in precise limits.
What is osmometric thirst/cellular dehydration?
Extracellular fluid consists mainly of water and salts (particularly from sodium chloride). Water loss causes the concentration of salts to increase. This increase in salt causes an osmotic imbalance between extra and intra cellular compartments, & water leave cells to restore balance by osmosis.
What is hypovolemic thirst?
Loss of extracellular fluid (ECL) levels can induce thirst in the absence of osmotic (salt) changes. The thirst stimulus arises from 2 systems which measure blood pressure: 1. in the kidneys 2. in the heart. This combined information stimulates brain sites which leads to drinking.
What is angiotensin and drinking?
Hypovolemia causes the release of the enzyme renin from the kidneys. Renin converts a blood-borne molecule angiotensinogen into angiotensin. Angiotensin stimulates pituitary and kidneys to release a hormone to converse water and salt. This increases blood pressure by vasoconstriction. Stimulates drinking by binding on receptors in the subfornical organ (SFO).
How is thirst a homeostatic motivation?
- Set-point: optimal fluid balance
- Sensors: osmoreceptors in OVLT of brain, baroceptosr in heart and kidneys
- Effector: drinking, salt appetite and water conservation measures.
