Water Homeostasis and the urinary system

• Homeostasis:

  standing the same

  • maintaining a constant internal environment (within set limits)
• Examples of homeostasis

  • temperature - blood and skin
  • salt concentration - kidneys
  • water - kidneys
  • proteins, fats, carbohydrates - the liver
• Basic components of a homeostatic system

  • receptor
  • control centre
  • effector
  • negative feedback
• Proportion of body weight represented by water

  • newborn = 80%
  • male = 60%
  • female = 50%
• Distribution of body fluids

  • plasma 3L
  • Interstitial fluid 12L
  • intracellular fluid 25L
  • 40 L in total
• osmosis

  Movement of water through a selectively permeable membrane (plasma membrane) form an area of lower solute concentration to an area of higher solute concentration
• diffusion in cell

  osmosis crossing cell membrane

  filtration (kidney) moves from one compartment to another compartment by pressure

  secretion actively move things from the blood to nephron

  reabsorption move from nephron to the blood
• Water in:

  • water in food = 700ml
  • ingested liquids = 1600ml
  • Tissue catabolism = 200ml
• Water output:

  • lungs = 300ml
  • skin = 600ml
  • kidney = 1500ml
  • intestine = 100ml
• water input must = output
• Component of urinary system:

  • kidney
  • ureters
  • bladder
  • urethra
• 1 million nephrons in the kidney
• Kidney internal structure

  A) Nephron

  B) Collecting duct

  C) papillary duct in renal pyramid

  D) minor calyx

  E) major calyx

  F) renal pelvis

  G) ureter

  H) urinary bladder

  I) renal cortex

  J) renal medulla

  K) renal collumn

  L) Renal pyramid in renal medulla

  M) renal sinus

  N) Renal papilla

  O) fat in renal sinus

  P) renal capsule

  Q) renal hilum

  
• Nephron -selective reabsorption

  A) Glomerular capsule (bowmans)

  B) Glomerulus

  C) Afferent arteriole

  D) Efferetn arteriole

  E) Proximal convoluted tubule

  F) Distil convoluted tubule

  G) Collecting duct

  H) Ascending loop of henle

  I) papillary duct

  J) Descending loop of henle

  
• Renal corpuscle = glomerulus and bowmans capsule
• Bowman's capsule

  • blood enters afferent arteriole and exists efferent arteriole of glomerulus
  • filtration occurs here. Water and all solutes enters Bowman's capsule BUT NOT PROTEINS
• Renal corpuscle

  A) Paretal layer of bowmans capsule

  B) Mesanglia cells

  C) Capsular space

  D) Proximal convoluted tubule

  E) Podocytes of visceral layer of bowmans capsule

  F) Endothelium of bowmans capsule

  G) Efferent arteriole

  H) Ascending loop of henle

  I) macula densa

  J) Juxtaglomerular cell

  K) Afferent arteriole

  L) Pedicel

  
• the afferent arteriole has larger diameter than the efferent therefore high pressure in glomerulus, filtration of the blood occurs
• Filtration membrane

  A) Glomerular epithelia cell pore: all plasma passes

  B) Basal lamina of glomerulus: large proteins held back

  C) Slit membrane between pedicels: medium protein stopped

  D) Blood

  E) Pedicel

  F) Filtration slit

  G) Tubular fluid

  H) Podocytes of visceral layer of bowmans capsule

  
• Proximal convoluted tubule:

  Reabsorption back into blood:

  • Water 65% osmosis
  • Na+ ions 65% (symporter + others)
  • Glucose 100% (symporters)
  • Amino acid 100%
  • Cl- 50%
  • HCO3- 80-90% (bicarbonate)

  Secretion into the tubular fluid

  • H+ (variable)
  • NH4+ (variable)
  • Urea (variable)
• Active transport in PCT requires energy:

  • lots of mitochondria are present
  • Large surface area for reabsorption (microvilli- on apical surface)
• Loop of henle

  Water moves out of descending limb of loop of henle by osmosis because medulla solute concentration increase

  Tubular fluid very concentration at hairpin

  
• Ascending limb of loop of Henle:

  • NaCl diffuses into medulla interstital fluid at base of Loop of Henle
  • Activate transport of NaCl in thick section of loop of Henle, this creates salt concentration gradient in Medulla (ascending limb is impermeable to water)
• Distal convoluted tubule

  Reabsorption back into blood:

  • Na+ ions 5% (increases by action of aldosterone enabling more water reabsorption by osmosis)
  • Water 10-15% (osmosis)
  • Cl- 5%

  Secretion into tubular fluid:

  • H+ (variable)
  • K+ (variable)
  • NH4+ (variable)
  • urea (variable)
• Collecting duct:

  Reabsorption back into blood:

  • water variable (ADH causes insertion of aquaporin 2 water channles into principal cells of collecting duct so CONCENTRATED urine is made)
  • Na+ ions (if no ADH DILUTE urine is made)
  • urea (recycling into base of loop of henle to increase solute concentration in medulla)

  Secretion into tubular fluid

  • K+ (variable)
  • H+ (variable)
• If dehydrated = ADh release promotes water reabsorption
• ADH release

  Water channels in collecting duct.

  Water reabsorbed back into body from tubular fluid

  Concentrated (hyperosmotic urine)
• Nephron Types

  juxtamedullary (15-20%) - Loop of henle extends deep into medulla

  cortical (80-85%)
• Fluid imbalances - dehydration

  • weight loss
  • increasing thirst
  • light headedness
  • kidney failure
• Fluid imbalance - Overhydration (water intoxication)

  • digestive problem
  • behavioural chnages
  • seizures
  • coma
• Dehydration (ADH prevents water loss)

  • Anti diuretic hormone = vasopressin
  • Made in hypothalamus and released from posterior pituitary gland
  • more water reabsorbed from the collecting ducts back into the body
  • Concentrated urine produced
  • water conserved
• Overhydration:

  Atrial natriuretic peptide (ANP)

  • blood volume increase
  • Artria od heart stretch - ANP producec
  • Natriuresis (loss of Na+ and Cl- in urine)
  • Water follows electrolytes = lots of dilute urine
  • Blood volume decrease

  ADH

  • secretion of ADH shuts down therefore less water is reabsorbed in collecting duct
• Renin-angiotensin-aldosterone system in dehydration

  A) Decrease in blood pressure

  B) increase in renin

  C) thirst

  D) Angiotensinogen

  E) Angiotensin II

  F) Arterioles constrict blood flow in glomerulus decreases

  G) Less fluid is filtred out blood pressure increase

  H) increase reabsorption of NaCl anf water in PCT

  I) Blood volume increase

  J) aldosterone

  K) DCT reabosorb more Na and water

  L) increase blood pressure and volume

  
• overhydration RAAS

  A) increase blood pressure and volume

  B) Decrease in renin release

  C) Less thirst

  D) Less angiotensin ii

  E) Angiotensinogen

  F) Arterioles dilate blood flow in glomerulus increases

  G) more fluid filtered out - Blood pressure decreases

  H) Decrease reabsorption of NaCl and water in PCT

  I) Blood volume decreases

  J) reduced aldosterone

  K) DCT reabsorbs less Na and water

  L) increase blood pressure and volume