Regulation of water, electrolyte and acid-base balance

Regulation of Water Balance 

• The Glomerular Filtration Rate (GFR) of all the nephrons of both kidneys is 125 ml/min. or 180L/day
• That is 125 ml of blood is filtered each minute or 180 L of blood is filtered each day.
• Daily urine output is 1-1.5 L/day.
• That means more than 99% of glomerular filtrate is absorbed normally.
• Water reabsorption occurs passively by diffusing along an osmotic difference established by the reabsorption of Na+ and Cl-

Water reabsorption

• Reabsorption from PCT (Obligatiory water reabsorption)
• 60-70% reabsorption occurs due to osmotic difference set by active transport of solutes
• Reabsorption from Loop of Henle
• 5-10% reabsorption occurs here.
• Reabsorption from DCT and CT
• In early part of DCT 5-8% reabsorption occurs secondary to reabsorption of Na+ under the influence of aldosterone.
• In the terminal DCT and CT (Facultative water reabsorption)  reabsorption of 10-12% by the action of ADH hormone.

Regulation of Electrolyte balance

• The concentration of solute in urine varies widely
• In overhydration where there is excess of water, kidneys excrete dilute urine
• In dehydrateion where there is less water, kidneys excrete concentrated urine
• The process involved in excretion of concentrated or diluted urine are
• Variable permeability of the nephron to different solutes
• Passive reabsorption of NaCl by the thin segment of ascending loop of Henle
• Active reabsorption of Na by thich segment of ascending loop of Henle

Kidneys regulate the concentration of water and electrolyte (NaCl) in the blood and thus regulate the blood pressure.

• The mechanism involved in this process is Renin-Angiotensin-Aldosterone system

 

 Acidification of urine

• Our body produces H+ ions during various metabolic process. 
• The H+ ions produced has to be excreted to maintain electrical neutrality in the body.
• Kidneys play an important role in excretion of H+ ions through urine.
• As H+ ions are excreted in urine, the normal urine is acidic in nature (increase in H+ ion concentration)

How do kidneys excrete H+ ions?

The acidification urine or excretion of H+ ions occurs in Distal Convoluted Tubule and Collecting duct of Renal tubule.

The H+ ions excreted in the urine is entirely by process of secretion by the tubular cells.

There are three systems through which H+ ions are excreted

1. Bicarbonate system
2. Dibasic phosphate system
3. Ammonia system

Bicarbonate system

Dibasic phosphate system

Ammonia system

The H+ ions are excreted in combination with the buffer systems, which are

• with bicarbonate as carbonic acid
• with hydrogen phosphate a dihydrogen phosphate
• with ammonia as ammonium ion

Application and Implication in Nursing

Glomerulonephritis

• Inflammation of the glomerulus is called glomerulonephritis. It is caused by antigen-antibody complex.

Pyelonephritis

It is an acute infection of kideny, pelvis and calyces by microorganisms.

It is associated with

• Abscess fomation
• Fever
• Malaise
• Groin pain 
• Burning micturition.

The source of infection may be the uriniary tract or blood-borne.

Nephrotic Syndrome

It is a collection of symptoms which are

• Albuminuria: Albumin lost in urine
• Hypoproteinaemia: Decrease in plasma protein level
• Generalized oedema: Abnormal collection of fluid in intestinal spaces
• Hyperlipidaemia