10.2 Thirst Flashcards
Because the concentration of chemicals in water determines the rate of all ____ ____ in the body, the water must be regulated within narrow limits.
chemical reactions
____ constitutes about 70% of the mammalian body.
Water
The body also needs enough ____ in the circulatory system to maintain normal blood pressure.
fluid
If you cannot find enough to drink or if the water tastes bed, you conserve water by excreting more concentrated ____ and decreasing your sweat.
urine
Your posterior pituitary releases the hormone ____ that raises BP by constricting blood vessels. The increased pressure helps compensate for the decreased blood volume.
vasopressin
Vasopressin is also known as ____ ____ (ADH) because it enables the kidneys to reabsorb water from urine and therefore make the urine more concentrated.
antidiuretic hormone
You also increase secretion of vasopressin while you are ____ to preserve body water at a time when you cannot drink.
sleeping
We distinguish two types of ____. Eating salty food causes osmotic thirst, and losing fluid by bleeding or sweating induces hypovolemic thirst.
thirst
The combined concentration of all ____ (molecules in solution) in mammalian body fluids remains at a nearly constant level of 0.15 M (molar).
solutes
(____ is a measure of the number of particles per unit of solution, regardless of the size of each particle. A 1.0 M solution of sugar and a 1.0 M solution of sodium chloride have the same number of molecules per litre.)
Molarity
This fixed concentration of solutes can be regarded as a ___ ____, similar to the set point for temperature. Any deviation activates mechanisms that restore the concentration of solutes to the set point.
set point
____ ____ is the tendency of water to flow across a semipermeable membrane from the area of low solute concentration to an area of higher concentration.
Osmotic pressure
A ____ ____ is one through which water came past but solutes cannot.
semipermeable membrane
The membrane surrounding the cell is almost semipermeable membrane because water flows across it freely and various salutes flow either slowly or not at all between the ____ fluid inside the cell and the ____ fluid outside it.
intracellular : extracellular
Osmotic pressure occurs when solutes are more ____ on one side of the membrane than on the other.
concentrated
If you need something salty, ____ ____ spread through the blood and the extracellular fluid but do not cross the membranes into cells.
sodium ions
The resulting osmotic pressure draws water from the cells into the extracellular fluid. Certain neurons detect their own loss of water and then trigger ____ ____, which helps restore the normal state.
osmotic thirst
The ____ also excrete more concentrated urine to rid the body of excess sodium and maintain as much water as possible.
kidneys
Of all brain areas, those around the ____ ____ have the leakiest blood-brain barrier.
third ventricle
A weak blood-brain barrier would be harmful for most neurons, but it helps cells ____ the contents of the blood.
monitor
The areas important for detecting osmotic pressure and the salt content of the blood include the ____ (organum vasculosum laminae terminalis) and the ____ ____ (SFO).
OVLT : subfornical organ
The OVLT receives input from receptors in the brain itself and from receptors in the digestive tract, enabling the brain to anticipate an ____ ____ before the rest of the body experiences it.
osmotic need
Receptors in the OVLT, the subfornical organ, the stomach, and elsewhere relay their information to several parts of the hypothalamus, including the ____ ____ and the ____ ____ (PVN), which control the rate at which the posterior pituitary releases vasopressin.
supraoptic nucleus : paraventricular nucleus
The body monitors ____ and detects the ____ of the stomach and upper part of the small intestine. Those messages limit drinking too not much more than you need at any given time.
swallowing : distension
Suppose you lose a significant amount of body ____ by bleeding, diarrhoea, or sweating. Your body will react with hormones that constrict blood vessels – vasopressin and angiotensin II.
fluid
When blood volume drops, the kidneys released the enzyme renin, which splits a portion of angiotensinogen, a large protein in the blood to form angiotensin I, which other enzymes convert to ______.
angiotensin II
Like vasopressin, angiotensin II ____ the blood vessels, compensating for the drop in blood pressure.
constricts
Angiotensin II also helps trigger thirst. However, this thirst is different from osmotic thirst, because you need to restore lost salts and not just water. This kind of thirst is known as ____ ____, meaning thirst based on low volume.
hypovolaemic thirst
This preference for saltiness, known as ____ ____, develops automatically as soon as the need exists.
sodium-specific hunger
Sodium-specific hunger depends partly on hormones. When the body’s sodium reserves are low, the adrenal glands produce the hormone ____, which causes the kidneys, salivary glands, and sweat glands to retain salt.
aldosterone
Aldosterone and angiotensin II together change the properties of taste receptors on the tongue, neurons in the nucleus of the tractus solitarius, and neurons elsewhere in the brain to ________.
increase salt intake
