Homeostasis Flashcards
Give me the definition of Homeostasis?
Motivation to maintain optimal conditions for the body such as water, sodium, nutrients and temp
What is the mechanism of homeostasis?
Homeostasis requires a set point, DETECTION MECHANISM, and the mobilisation of behaviour when deviation occurs
e.g the thermostat responds to change in external temperature so acts to keep the room within a certain set point.
Mammals are approx ? water :
A - 2/3
B - 1/2
C - 1/4
A - 2/3
Where is water located in the body ?
3 places
- 67% of water is located inside cells
- 7% is blood plasma
- 26% is intersitial fluid (between cells)
How does your body maintain water concentration?
By coordinating physiology and behaviour to maintain water concentration at a predetermined set point e.g being thirsty, we drink water but when we’ve had enough we stop
What is the definition of osmotic thirst and give me the study
The motivation to seek and ingest water (Fitzsimons, 1998)
What is osmotic thirst?
- motivation to seek and ingest water
- the bodys extracelluar fluid contains 8.5g of sodium chloride per litre
- Ingestion of salt increases the concentration of sodium chloride in the extracellular fluid, this creates osmotic pressure and forces fluid out of the cell
- how is osmotic thirst remedied ? drinking water
Explain Endocrine regulation of Osmotic Thirst
- OSMORECEPTOR cells in hypothalamus detect an increase in osmolarity (where osmotic pressure has forced fluid out of extarcellular cells because of the increase in sodium chloride)
- Antiduiretic hormone (ADH or vasopressin) is made by hypothalamus, sent down nerve fibres to pituitary gland and released into bloodstream
- ADH conserves water as blood moves through kidneys. It works by increases permeability of renal tubules (structure in kidney responsible for filtering blood) so this means there is an increase in what these tubules can allow to pass through them. This releases more fluid back into circulation (rather than to the bladder for elimination)
- if more water is consumed than needed, plasma osmolality is decreased, inhibiting thirdt and supressing the release of ADH
- reduction of ADH sends more fluids to the bladder for elimination
Laymans terms explanation of endocrine regulation of osmotic thirst
Osmoreceptor cells detect high salt levels: Imagine tiny sensors in your brain called osmoreceptor cells. Their job is to detect when there’s too much salt in your body. When they sense this, it means your body needs more water.
Antidiuretic hormone (ADH) helps save water: Your brain (specifically, the hypothalamus) makes a special hormone called ADH, which is like a messenger. It travels to your pituitary gland, which then releases ADH into your bloodstream. ADH tells your kidneys to hold onto water instead of letting it all go to your bladder. This way, your body keeps more water in circulation.
ADH makes kidneys hold onto water: Inside your kidneys, there are tiny structures called renal tubules. ADH makes these tubules more porous, like a sieve with bigger holes. This means more water can pass through them and get back into your bloodstream instead of going to your bladder to be peed out.
Your body regulates ADH based on water intake: If you drink more water than your body needs, your blood becomes less salty (less concentrated). When your osmoreceptor cells sense this, they tell your brain to slow down on making ADH. This means your kidneys won’t hold onto as much water, so more of it goes to your bladder to be eliminated as urine.
**Less ADH means more water in your bladder: **With less ADH around, your kidneys don’t hang onto as much water. Instead, more water goes into your bladder. So, you end up peeing out the extra water your body doesn’t need.
In simple terms, your body has a smart system for managing water levels. When you need more water, ADH helps your kidneys keep it. And when you’ve had enough, your body tells your kidneys to let it go.
Where does ADH (vasopressin) come from and what does it do?
Made in hypothalamus, sent down nerve fibres to pituitary gland, then released into bloostream.
ADHacts to conserve water as blood moves through the kidneys. It increases permeability of the renal tubules, releasing more fluidback into circulation (rather than to the bladder for elimination)
What do osmoreceptors detect?
increase in osmolarity
What do i mean by osmolarity
In this context, osmolarity means the process of how sodium chloride (salt) increasing in blood causes extraceullar fluid to be forced out of cells because of osmotic pressure.
How is osmotic thirst remedied ?
By drinking water
is osmotic thirst a positive or negative feedback loop?
Negative Feedback Loop
Explain the feedback loop of osmotic thirst
- A high sodium (Na+) concentration is detected in the bloodstream.
- The pituitary gland (posterior lobe) is stimulated to release antidiuretic hormone (ADH).
- ADH is carried to the kidney by the blood.
- The kidney increases the reabsorption of water back into the bloodstream, which dilutes the sodium concentration in the blood.
- As a result, the sodium concentration lowers, which diminishes the initial stimulus (high sodium concentration) that triggered the release of ADH.
In a negative feedback loop, the response to a stimulus reduces the original effect of the stimulus, leading to a decrease in the output. This is a common mechanism in homeostasis, where the body maintains a stable internal environment.
What is the definition of Hypovolemic Thirst?
Where fluids can be lost by blood loss, vomiting, or diarrhea - this doesn’t deplete the intracellular fluid (fluid inside cell) because it is separated from the extracellular fluid by the cell membrane, but water and solutes are lost.
Explain endocrine regulation of Hypovolemic thirst
- 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, thereby increasing blood pressure (Gauer and Henry, 1963)
- ADH causes more fluid to be drawn back into circulation from the kidneys
- Kidneys also release angiotension II, which also restricts blood vessels, it leads to the release of aldosterone from the adrenal glabds which decreases the amount of sodium excretedd in urine, thereby helping to restore balance.
Laymans terms explanation of endocrine regulation of hypovolemic thirst
Loss of Blood Volume and Low Blood Pressure: When you lose blood volume due to factors like bleeding or dehydration, your blood pressure can drop. This drop in blood pressure signals to your body that something’s not right and that it needs to do something to fix it.
ADH Constriction: Your body has a hormone called antidiuretic hormone (ADH) that helps regulate water balance. When your body detects low blood volume, it releases ADH. One of the things ADH does is constrict (narrow) your blood vessels. By making your blood vessels narrower, ADH helps increase blood pressure. This helps get blood circulating better throughout your body.
ADH and Fluid Retention: ADH also tells your kidneys to hold onto more water. Normally, your kidneys filter your blood and get rid of excess water and waste as urine. But when ADH is around, your kidneys hold onto more water, sending it back into your bloodstream instead of letting it all go to your bladder. This helps increase your blood volume, which is important for maintaining blood pressure.
Angiotensin II and Aldosterone: When blood volume is low, your kidneys release a substance called angiotensin II. This substance helps constrict your blood vessels, just like ADH does. Angiotensin II also triggers the release of another hormone called aldosterone from your adrenal glands. Aldosterone’s job is to make your kidneys hold onto more sodium and water. By holding onto more sodium, your body retains more water, which helps increase blood volume and blood pressure.
In simple terms, when you lose blood volume, your body has a few tricks up its sleeve to help fix the problem. It releases hormones like ADH and angiotensin II, which help constrict your blood vessels and make your kidneys hold onto more water and sodium. These actions help increase your blood volume and blood pressure, helping your body get back to normal.
