Homeostasis

Question 1

What is homeostasis?

Answer 1

• Motivation to maintain optimal conditions for your body e.g., water, sodium, temperature etc.
• Many homeostatic systems are a combination of physiology and behaviour i.e., balance of water and sodium includes a behavioural component of drinking water (thirst).

Question 2

What is the basic concept of homeostasis?

Answer 2

• A homeostatic system requires a set point, a detection mechanism, and mobilisation of behaviour when deviation occurs.

Question 3

What is fluid balance?

Answer 3

• Very little surplus water is stored in the body.
• We coordinate physiology and behaviour to maintain body water concentration at a predetermined set point.
• 67% of water is located inside cells, 7% is blood plasma, and 26% is interstitial fluid (between cells fluid).

Question 4

What is osmotic thirst?

Answer 4

• The motivation to seek and ingest water (Fitzsimons., 1988).
• The body’s extracellular fluid contains 8.5g of sodium chloride per litre.
• Ingestion of salt increases the concentration of sodium chloride in the extracellular fluid, which creates osmotic pressure and forces fluid out of the cell.
• Osmotic thirst = remedied by drinking water

Question 5

What is Endocrine Regulation of Osmotic Thirst?

Answer 5

• Osmoreceptor cells in the hypothalamus detect an increase in osmolarity.
• Antidiuretic hormone (ADH; also called vasopressin) is made by the hypothalamus, and then transported down the nerve fibres to the posterior pituitary gland where it is released into the bloodstream.
• ADH acts to conserve water as blood moves through the kidneys, increasing permeability of renal tubules, and releasing more fluid back into circulation.

Question 6

What is Hypovolemic Thirst?

Answer 6

• Fluids can also be lost by blood loss, vomiting, or diarrhoea without depleting the intracellular fluid -> water solutes are lost.

Question 7

What is Endocrine Regulation of Hypovolemic Thirst?

Answer 7

• Loss of blood volume causes low blood pressure and prevents the kidneys from extracting water efficiently.
• When loss of blood volume is detected, ADH restricts the blood vessels, increasing blood pressure (Gauer & Henry., 1963).

Question 8

Behavioural regulation of hypovolemic thirst:

Answer 8

• Water is consumed > body fluids are diluted > reduced blood plasma osmolality > stimulus to stop drinking.
• Hypovolemic thirst is best remedied by the replacement of water