Water and Salt Balance

Question 1

How does the body gain water?

Answer 1

The body gains water via ingestion and internal production,

Question 2

how does the body lose water.

Answer 2

and it loses water via urine, the gastrointestinal tract, and evaporation from the skin and respiratory tract (as insensible loss and sweat).

Question 3

How does the body gain sodium and chloride?

Answer 3

The body gains sodium and chloride by ingestion and loses them via the skin (in sweat), gastrointestinal tract, and urine.
III.

Question 4

What is major homestestatic control for water and sodium?

Answer 4

For both water and sodium, the major homeostatic control point for maintaining stable balance is renal excretion.

Question 5

What is filterable at the glomerulus?

Answer 5

I. Sodium is freely filterable at the glomerulus,

Question 6

What is dependentt upon the NA K ATPase pumps in the basolateral membrane of the tubular epithelium

Answer 6

resorption of sodium

and its reabsorption is a primary active process dependent upon Na,K-ATPase pumps in the basolateral membranes of the tubular epithelium. Sodium is not secreted.

Question 7

What is a primary active process?

Answer 7

and its reabsorption is a primary active process dependent upon Na,K-ATPase pumps in the basolateral membranes of the tubular epithelium. Sodium is not secreted.

Question 8

Where are the Na K ATPase pumps

Answer 8

and its reabsorption is a primary active process dependent upon Na,K-ATPase pumps in the basolateral membranes of the tubular epithelium. Sodium is not secreted.

Question 9

is sodium entry into the cell from the tubular lumen passive or active?

Answer 9

II. Sodium entry into the cell from the tubular lumen is always passive. Depending on the tubular segment, it is either through channels or by cotransport or countertransport with other substances.

Question 10

Where does sodium enter from into the cell?

Answer 10

II. Sodium entry into the cell from the tubular lumen is always passive. Depending on the tubular segment, it is either through channels or by cotransport or countertransport with other substances.

Question 11

what does sodium reabsorption create?

Answer 11

III. Sodium reabsorption creates an osmotic difference across the tubule, which drives water reabsorption, largely through water channels (aquaporins).

Question 12

what is water reabsorption dependent on ?

Answer 12

IV. Water reabsorption is independent of the posterior pituitary hormone vasopressin until the collecting- duct system, where vasopressin increases water permeability.

Question 13

What drives water reabsorption ?

Answer 13

III. Sodium reabsorption creates an osmotic difference across the tubule, which drives water reabsorption, largely through water channels (aquaporins).

Question 14

What is produced when vasopressin concentration is low?

Answer 14

A large volume of dilute urine is produced when plasma vasopressin concentration, and hence water reabsorption by the collecting ducts, is low.

Question 15

What is produced and by what when plasma vasopressin concentration is high?

Answer 15

A small volume of concentrated urine is produced by the renal countercurrent multiplier system when plasma vasopressin concentration is high.

Question 16

concentrated urine is caused by?

Answer 16

A small volume of concentrated urine is produced by the renal countercurrent multiplier system when plasma vasopressin concentration is high.

Question 17

what causes increased osmaliry of the interstitial fluid?

Answer 17

a. The active transport of sodium chloride by the
ascending loop of Henle causes increased osmolarity of the interstitial fluid of the medulla but a dilution of the luminal fluid.

Question 18

what increases the permeability of the cortical collecting ducts to water?

Answer 18

b. Vasopressin increases the permeability of the cortical collecting ducts to water, and so water is reabsorbed by this segment until the luminal fluid is isoosmotic to plasma in the cortical peritubular capillaries.

Question 19

(1) Describe the distribution of water and sodium in the main fluid compartments.

Answer 19

There are 2 main fluid compartments of the body: intracellular compartment contains slightly less than 2/3’s by volume; remaining third is distributed in the extracellular fluid.
There are 2 sub-compartments of the extracellular fluid: blood plasma and interstitial fluid.
In contrast to extracellular fluid, intracellular fluid contains only small amounts of sodium.
Sodium is the predominant electrolyte. And is used to transfer water across membranes as well as osmosis by causing a concentration gradient.

Question 20

(1) Define the terms osmolality, o

Answer 20

Osmolality- the concentration of a solution in terms of osmoles (number of moles of solute that contribute to the osmotic pressure of a solution) of solute per kilogram of solvent.

Question 21

define oncotic pressure

Answer 21

Oncotic pressure- is the ‘pulling force’, pulling fluids from the surroundings tissue into the capillaries as opposed to outside them, because water will naturally seek a state of balance in the concentration of solute(particles). Opposing force to hydrostatic pressure, usually tends to pull water into the circulatory system from a blood vessels plasma.

Question 22

define osmosis

Answer 22

Osmosis- a process by which molecules of a solvent(water) tend to pass through a semipermeable (selectively permeable) membrane from a less concentrated solution into a more concentrated one.

Question 23

When is interstitial fluid formed?

Answer 23

Interstitial fluidis formed whenhydrostaticpressuregenerated by theheartpushes water out of thecapillaries. The water passes from a high concentration outside of the vessels to a low concentration inside of the vessels, butequilibriumis never reached because the constantbloodflow.

Question 24

how does osmotic pressure work

Answer 24

Osmotic pressureworks opposite to hydrostatic pressure, and holds water and substances in the capillaries.

Question 25

where is hydrostatic pressure and osmotic pressure thes strongest?

Answer 25

Hydrostatic pressure is stronger in the arterial ends of the capillaries, while osmotic pressure is stronger at the venous ends of the capillaries.

Question 26

What happens to the interstitial fluid

Answer 26

Interstitial fluid is removed through the surroundinglymphvessels, and eventually ends up rejoining the blood.

Question 27

what happens if the removal of tissue fluid does not work

Answer 27

Sometimes the removal oftissuefluid does not function correctly, and there is a build-up, calledoedema.

Question 28

what does the starling equation do

Answer 28

TheStarling equationdescribes the pressure gradients that drive the movement of water across fluid compartments.

Question 29

(1) Explain how low albumin may lead to fluid shift, such as oedema.

Answer 29

Albumin is only produced in the liver and is the major plasma protein that circulates around the blood stream. Essential for maintaining the oncotic pressure in the vascular system. Also important in the transport of substances like drugs, lipids, hormones, toxins.
As the albumin level drops in liver disease, there is insufficient oncotic pressure to hold fluids within cells. Fluid moves into the interstitial spaces (narrow spaces between tissues or parts of an organ), causing generalized oedema, which is fluid retention.

Question 30

What are the key routes of water loss from the body? Define insensible losses.

Answer 30

Respiration; perspiration; urination; defecation; expectoration(spitting)
Sensible loss is loss that can be perceived by the senses and can be measured. Eg Urine
Insensible losses can neither be perceived nor measured directly. Eg respiratory loss
Insensible losses; Refer solely to water loss, no solute loss occurs. Minimal insensible losses in normal adult is 800ml/day. Fever‐500ml/day for every degree above 37 degrees celcius or by 10% per degree >38 degress celcius. Cardiac Surgery‐1L insensible losses

Question 31

Explain water and sodium homeostasis with reference to;

(a) The hypothalamus and osmoreceptors

Answer 31

Osmoreceptor is a sensory receptor primarily found in the hypothalamus that detects changes in osmotic pressure.When the osmotic pressure of blood changes (i.e. it is more or less dilute), water diffusion into and out of the osmoreceptor cells changes. That is, they expand when the blood plasma is more dilute and contract with higher concentration. This causes an afferent neural signal to be sent to thehypothalamus, which increases or decreasesvasopressin(ADH) secretion from theposterior pituitaryto return blood concentration to normal. An increased amount of ADH causes an increase in sodium reabsorption into the principle cells of the CCT.

Question 32

Explain water and sodium homeostasis with reference to;The posterior pituitary gland and arginine vasopressin

Answer 32

The posterior pituitary gland and arginine vasopressin
The PPG is where vasopressin is secreted into the blood stream to return the blood concentration to normal. AVP has two primary functions: retain water in the body and to constrict blood vessels. It regulates the retention of water by acting to reabsorb water in the kidneys collecting ducts. It also increases peripheral vascular resistance, in turn increasing arterial BP. Lack of AVP causes hypernatremia (increased blood sodium conc).
Water deprivation provides osmotic/volume stimuli, thus releases AVP. Water load inhibits release of AVP.

Question 33

Explain water and sodium homeostasis with reference to;Tci) The role of the kidneys in water conservation

Answer 33

The kidneys reabsorb all of the glucose and as much water and salt (sodium) as the body needs, putting them back into the blood. The concentration of our urine is controlled by ahormonecalledADH.
ADH is produced by thepituitary glandthat is situated just below the brain. The pituitary gland monitors the concentration of the blood plasma. It releases ADH into the bloodstream, which travels in the blood to the kidneys.
The moreconcentratedthe plasma, the more ADH is released into the blood. When the ADH reaches the kidneys, it causes them to reabsorb more water. This keeps more water in the body and produces more concentrated urine.
When the plasma is moredilute, less ADH is released into the bloodstream. This allows more water to leave the kidneys, producing a more dilute urine.
This method of control is an example ofnegative feedback.
In the kidney there are thousands of nephrons, which essentially each are mini hormones. ADH is an anti diuretic hormone and lowers urine volume.

Question 34

5. Explain water and sodium homeostasis with reference to;

(cii. ) In sodium homeostasis (Renin‐angiotensin‐aldosterone‐system

Answer 34

Renin is an enzyme secreted into the blood from specialized cells that encircle the arterioles at the entrance to the glomeruli of the kidneys. These cells are sensitive to changes in blood flow and pressure. Decreased blood flow causes an increase in renin secretion, which may be caused by loss of sodium and water. Renin catalyzes the chain reaction of converting a plasma protein called angiotensinogen into eventually angiotensin II which acts via receptors in the adrenal glands to stimulate secretion of aldosterone stimulating salt and water reabsorption by the kidneys.

Question 35

. Explain water and sodium homeostasis with reference to;

Thirst

Answer 35

vIt is a sensation created by the hypothalamus causing organism to ingest water.
Sodium’s main use is in the sodium/potassium pump. This is used in the pacemaker cells of the heart, action potentials for neurons and muscles. Also baroreceptors use sodium receptors. Too low sodium is called hyponatremia. A too high level is called hyponatremia.

Question 36

In a healthy individual what is the normal homeostatic response to;
(a) Excess fluid (oral or IV)

Answer 36

There is an decrease in the amount of ADH secreated by the posterior pituitary glands. This means that more water is lost in the collecting ducts. Making a more dilute urine.

Question 37

In a healthy individual what is the normal homeostatic response to;

Dehydration
.

Answer 37

Dehydration
Due to low water volume. The hypothalamus activates nerves that active thirst and also the release large amounts of ADH which cause large amounts of water reabsorbtion in the nefron.