Fluid and electrolyte balance

what % of water weight in males and females

60% males and 55% females

what are the compartments of water distribution in the body

60%/55% fluid

2/3 intracellular

1/3 extracellular; 80% interstitial and 20% intravascular

who has a greater body fat; males or females

females

what happens to total body water content as a result of fat accumulation in weight gain

the contribution of their total water weight to their body weight will be decreased.

what are the key electrolytes

sodium

potassium

calcium

chloride

bicarbonate

what is the greatest extracellular ion

sodium

what is the greatest intracellular ion

potassium

what is the difference between sodium and potassium levels

they are the inverse of each other more sodium is present outside of the cell whilst more potassium is present inside of the cell

what is responsible for the distribution of sodium and potassium ions

Na+/K+ ATPase

how does water move between compartments

water will move passively between compartments through aquaporins in the cell membrane, the movement of water between compartments is reliable on a gradient

what is the movement of water between compartments dependant on

a gradient

if a compartment has more solute in it than another, will fluid move in or out of this cell

into the cell to maintain equilibrium

what must the membrane separating compartments of water and solute be permeable to

water only

what does osmosis refer to

the net movement of water

when will water movement between compartments occur until

the activities of water in the two compartments will become equal

what is the net water movement for compartments of different activities

it will move from the compartment of higher water activity to the compartment of lower water activity

what will alter the activity of water

solutes

what does osmotic pressure work alongside for the movement of water

hydrostatic pressure

why odes the net movement of water stop at some point

as water moves between compartments the hydrostatic pressure in lower water compartment will increase this pressure increases the activity of the water acitivity to equal that of the previous higher water activity.

what needs to be applied to stop osmosis

hydrostatic pressure

what compartment would have a higher concentration of solute once the activities have been equalised

the compartment which always had the higher concentration of solute because this has not changed it is only the water which has moved.

what is osmolarity

the total number of dissolved particles in a solution

what is the standard body osmolarity

295mosmol/L

what is isoosmotic

same osmolarity

what is hyperosmotic

higher osmolarity

what is hypoosmotic

a lower osmolarity

150 mmol/L of the following substances are dissolved in pure water. Dissociation of a substance influences osmolarity. With this in mind, which would have the highest osmolarity?

1. Calcium chloride

2. Glucose

3. Sodium chloride

calcium chloride

why is is bad to have too much water

excess fluid in cells causing their swelling

typically fluid and food input which contributes to water

food - 1000ml

fluid 1500ml

how much fluid comes from metabolism

400ml

how much fluid is lost in faeces

100ml

how much fluid is lost in breath

500ml

how much fluid is lost in skin

500ml

how much fluid is lost in urine

1800ml

how is osmolarity levels detected

in neurons of the hypothalamus

what are neurons of the hypothalamus called

osmoreceptor

what is the beneficial location of osmoreceptors

they are located at the blood brain barrier so they have a direct exposure to osmolarity

how do osoreceptors respond to a change in osmolarity

increase the release of ADH that increases water absorption and increase thirst

where is ADH released from

synthesised by neurons in the supra optic and para ventricular nuclei of the hypothalamus and will be released into the blood supply of the posterior pituitary gland

would cells shrink or expand if plasma osmolarity decreased

decreased osmolarity will result in greater water outside of the cells and this water will move into the cells causing them to expand

how does ADH increase water reabsorption

this will increase water reabsorption by the kidneys by inserting aquaporins into the membrane of cells in the collecting duct. water can move down osmotic gradient from collecting duct into the blood stream

what is the half life of ADH in plasma

10-15 minutes

what happens when ADH secretion is suppressed

plasma ADH concentration falls rapidly and the aquaporins are reabsorbed by the cell and the lumen facing membranes are no longer water permeable

what happens when plasma osmolarity rises above 280mosmol/L

ADH will be secreted

at what level of osmolarity does ADH have a maximum effect on water reabsorption in the kidneys

290mosmol/L

what happens when osmolarity reaches 290mosmol/L

thirst is stimulated and the water consumed is conserved due to the effect of ADH us maximal

what happens at higher levels of ADH to renal blood flow

it will increase vascular resistance which decreases renal blood flow, water filtered decreases helping us to conserve water

summarise high plasma osmolarity and how this is restored

high plasma osmolarity → sensation of thirst and ADH release → fluid intake and increase waste reabsorption → water is gained → return to normal

summarise low plasma osmolarity and how this is restored

low plasma osmolarity → thirst and ADH release decreased → decrease in water reabsorption → water is lost → plasma normal

what factors will increase ADH secretion

starting exercise

decreased bp

deep sleep

what will decrease ADH secretion

alcohol

Which urine sample would be mostly likely to have the highest osmolarity?

a samples collecting first thing in the morning

Briefly explain the physiological advantage of increased ADH secretion during deep sleep.

We do not want to wake up from sleep to urinate. By increasing ADH secretion during sleep we decrease the rate of urine formation therefore we prolong the time before the bladder fills to the point of urination is required

Briefly explain the physiological advantage of increased ADH secretion at the start of exercise.

By increasing ADH secretion at the start of exercise, we decrease the rate of urine formation and retain water. This will help us keep hydrated when our body gains heat and sweats.

what does sodium levels determine

ECF volume

What else regulates water movement between compartments?

The membrane separating the two compartments must be permeable to water (semipermeable) and hydrostatic pressure.

 

why is sodium in higher concentrations outside the cell than inside

Sodium is prevented from accumulating in cells through the action of the Na+/K+-ATPase ("sodium pump"). This maintains a much higher concentration of sodium in the ECF than in the cells. Our cells use this gradient to drive the transport of various substances (for example, glucose and ions).

how does the body respond to decreased ECF volume

reabsorb more sodium

thirst and ADH retains water

how does the body respond to increased ECF volume

water reabsorption decreases, reabsorb less sodium

what is sodium content signalled by changes in

ECF volume, specifically by ECF volumes that perfuses our tissues

what is the regulation of sodium balance linked to

blood pressure and blood volume

what are the receptors which detect blood pressure called

baroreceptors

how do baroreceptors and blood volume receptors influence sodium excretions and retension

through the RAAS pathway which will increase sodium reabsorption and the atrial natiuretic peptide which increases sodium in the urine

how do baroreceptors work

they will work by detecting a change to the diameter of a blood vessel, they will sense the stretch, decrease in circulating blood will cause an increase in renin release

what is the RAAS pathway

renin will convert angiotensinogen into angiotensin I

angiotensin I is converted to angiotenin II by ACE

angiotensin II will act on angiotensin receptors located on target tissues to stimulate adrenal glands to produce aldosterone

where are the target receptors of angiotensin II located

adrenal gland, kidney, brain and vasculature

What change would upregulate the renin-angiotensin-aldosterone axis?

A decrease in effective circulating volume would upregulate the renin-angiotensin-aldosterone axis.

what is atrial natiuretic peptide

it is synthesised and stored in atrial myocytes and is released in rrpsinse to stretching of the atrial due to increase effective circulating volume

what is the pathway to decrease the effective circulating volume

alters baroreceptor activity → increased renin from kidneys → increased ang II from vessels → increase aldosterone from adrenal glands

what pathway would be taken for decreased effective circulating volume

decrease stretch receptor activation → decrease ANP → decrease sodium excretion

how much blood will pass through the kidneys in 24 hours

1400L

what is the role of the kidneys

they can quickly and precisely remove excess solutes and fluid or retain them as needed

what is the glomerulus and it role

The first part of the nephron is the glomerulus. The glomerulus is the site of plasma filtration.

what is the proximal tubule and its role

This is the site of bulk reabsorption and is found at the cortex of the nephron. It is here that most of the filtered glucose, amino acids and other filtered solutes are reabsorbed.

what does the cortex of nephron contain

glomeruli, PCT, DCT and initial collecting duct

what is the interstitial fluid of the cortex

isotonic

what does the medulla contain

loop of henle and the remaining distal segment of collecting ducts

what is the osmolatiry of the medulla

hyperosmotic

what is the descending limb of LoH

the region of the nephron that generates the hyperosmotic interstitial fluid in the medulla.

where is the majority of water absorbed in cortical nephron

in the short descending limbs

what are the two types of nephrons

cortical and juxtamedullary

how much % of nephrons do cortical nephrons compromise

80%

what is the feature of cortical nephrons

characterized by having more superficial glomeruli and short loops of Henle

what are the characteristic of juxtamedullary nephrons

fewer in number and have longer loops of Henle that dip deep into the medulla.

what are the two sections of the ascending loop of henle

thick and thin

how does NaCl reabsorption occur in the thin ascending limb

net passive diffusion from the tubule to the interstitial fluid

what does the solute removed by the thin ascending limb create

hyperosmolarity of the medulla

what % of filtered sodium is reabsorbed in the thick ascending limb

25%

how does sodium enter cells for reabsorption in the thick ascending limb

down its electrochemical gradient through an apical Na+. K+ 2Cl- co transporter

what helps to drive sodium across the tight junctions between epithelium cells in the thick ascending limb

positively charge lumen

what two parts make up the distal tubule

the first is lined with the same epithelium as the adjacent ascending limbs of loop of henle, These together with the ascending limb of the loop of henle compromise the diluting segment of the nephron, so called because sodium is removed leaving a silver solution behind.

what is sodium reabsorption increased by in the latter part of DCT

aldosterone

is sodium reabsorbed from both parts of the distal tubule

yes

what is reabsorption of the distal tubule

the distal tubule transport sodium through the cell via a co transporter Na+/Cl-

what transporter is used for sodium reabsorption in the DCT

Na+/Cl-

what is aldosterone

final factor in the RAAS acid and it will increase the number of epithelial sodium channels in the epithelial membrane

what is the collecting duct

all of the remaining flui at the end of the distal tubule enters the collecting duct which runs through the hyperosmotic medulla to drain into the renal pelvic and ureters

what sodium channels are present in the collecting duct

ENaC

what is ENaC under influence of

aldosterone

where does the final adjustment to sodium excretion occur

collecting ducts where the expression of the epithelial sodium channels (ENaC) us under influence of aldosterone.