Topic 1.72 - Hyperosmolarity, hypertonicity. Forms, causes, consequences

What is the osmotic pressure (osmolarity) of all water compartments of the body?

280-300 mOsm/kg

What is the target for osmoregulation?

Regulate the level of water, not regulate the number of osmoles

Where are osmoregulator located? How do they work?

Where

-hypothalamus

Function

-sense the change in size of cells caused by changes in osmolarity

What is the response of osmoregulators in the hypothalamus in response to cell shrinkage and swelling?

Shrinkage - hypertonicity

-increased production of ADH

Swelling - hypotonicity

-decreased production of ADH

What are the 2 important function of ADH?

Increases thirst sensation

Increases water retention in the kidney

When is there a difference between hyperosmolarity and hypertonicity?

When the increased osmolarity is due to increased levels of a substance that can enter cells freely

-urea, ethanol, methanol

What are 5 potential causes of hyperosmolarity and hypertonicity?

Excessive intake of salt

Excessive intake of other osmotically active substances

Diabetes mellitus

Diabetes inspidus

Loss of hypoosmolar fluid, eg. sweat

What is the response of the body to hyperosmolarity (3)?

Increases thirst

Increases ADH release

Potential decrease in aldosterone secretion

What does the consequence to hyperosmolarity depend on?

Whether the hyperosmolarity develops acutely or chronically

What happens in acute increase of osmolarity?

Brain cells shrink -> vessels stretch -> possible bleeding

What happens in a chronic increase of osmolarity?

Brain cells compensate by producing intracellular osmotically active substances, idiogenic molecules, that counteract the hyperosmolarity of the interstitium -> prevention of cells shrinkage

Why must chronic hyperosmolarity be corrected slowly?

To allow brain cells to get rid of the idiogenic osmoles, or else there will be swelling and brain edema