FLUID AND ELECTROLYTE BALANCE AND RAAS - CHP 20

function of nephron

1. removes metabolic waste from blood

2. regulates volume and composition of body fluids

what is the countercurrent multiplication system and where does it occur

• mechanism in the kidney that helps to concentrate urine and conserve water, playing a crucial role in maintaining the body's fluid and electrolyte balance

• interaction between the descending and ascending limbs of the loop of Henle

• It operates primarily in the loop of Henle within the nephron.

descending loop of henle is permeable and impermeable to what

• impermeable to ions

• permeable to water

• as fluid moves down this limb water is reabsorbed through osmosis into interstitial fluid where concentration of solutes is higher

ascending loop of henle is permeable and impermeable to what

• impermeable to water

• permeable to ions

• actively transports sodium, chloride and other ions into interstitial fluid

• causes filtrate to become diluted as it moves up, while interstitial fluid becomes more concentrated

what are vasa recta

• specialized blood vessels that run parallel to the loop of Henle in the kidneys and play a critical role in maintaining the osmotic gradient created by the countercurrent multiplication system

• fluid and solute exchange in the renal medulla, helping to preserve the concentration gradients essential for water reabsorption

if kidneys have a low osmolarity what colour is urine

dilute

• kidneys are not reabsorbing as much water from the filtrate

• The filtrate has fewer solutes per unit of water.

if kidneys have a high osmolarity what colour is urine

• more concentrated

• kidneys are reabsorbing water but not solute to stay hydrated

define diuresis

removing excess water from kidneys

where is vasopressin secreted form

posterior pituitary gland

primary function of vasopressin

increases water reabsorption in kidneys (secreted when dehydrated)

state of urine with maximal vasopressin

highly concentrated so water is conserved

state of urine without vasopressin

very diluted

where does vasopressin act on

collecting ducts and late distal tubule

what 3 physiological changes will secrete vasopressin

1. increased plasma osmolarity

2. decreased blood pressure

3. decreased blood volume

what are they factors of RAAS

• renin

• angotensin 2

• aldosterone

• vasopressin

where is Na+ reabsorbed (aldosterone acts on)

P cells of distal nephron and collecting duct

function of aldosterone

• increases Na+ reabsorbtion in DCT

• increased K+ excretion

what kind of hormone is aldosterone

steroid hormone, synthesized in adrenal cortex

aldosterone secretion is regulated by

1. increased extracellular K+ concentrations

2. decreased blood pressure - releases angiotensin 2 which stimulates aldosterone

3. decreased plasma Na+, directly stimulates aldosterone secretion

4. increased ECF osmolarity (INHIBITS ALDOSTERONE SECRETION, stops Na+ reabsorbtions)

early response of aldosterone

• apical (outward lumen) Na+ and K+ channels increase permeability

• increased Na+ reabsorbtion and K+ secretion

slower phase of aldosterone secretion

• new ions pumps are inserted into epithelial cell membranes

• allows for quicker response and greater capacity for Na+ reabsorption

RAAS is signalled in response to what

drop in blood pressure, blood volume or sodium levels

stimuli for renin release

• decreased blood pressure in afferent arterioles

• sympathetic activity from cardiac control centers

• paracrine activity from macula densa

where is renin released form

granular cells of kidneys

function of angiotensin 2

• increases MAP by vasoconstricting

• stimulates the release of vasopressin

• increases sympathetic stimulation from cardiac control centres

• increases Na+ and H2O reabsorption in PCT

• stimulates thirst

3 overall effects of RAAS

1. increases blood pressure

2. increased blood volume

3. restore electrolyte balance

stimuli for renin production and release

1. directly detect low BP

2. sympathetic neurons that touch granular cells are activated by the cardiovascular control centre when BP drops

3. receive paracrine feedback from macula-densa to increase secretion due to decreased flow in distal tubule

5 effects of angiotensin 2

1. increases vasopressin secretion

2. stimulates thirst

3. vasoconstricts

4. increased sympathetic output to the heart and blood vessels

5. increases proximal tubule Na+ reabsorption, this is followed by water reabsorption

define natriuresis

excretion of Na+ in urine

2 main natriuretic peptides

1. atrial natriuretic peptide (ANP)

2. brain natriuretic peptide (BNP)

primary roles of ANP and BNP (natriuretic peptides)

• Natriuresis: Promote excretion of sodium in the urine.

• Diuresis: Increase water excretion.

• Inhibition of RAAS: Reduce aldosterone and renin activity, opposing sodium and water retention.

• Vasodilation: Relax blood vessels, reducing blood pressure.

happens when you are hydrated