Kidneys and Water Regulation Flashcards
Functions of kidney
- Regulation of water, inorganic ion balance and acid-base balance
- Removal of metabolic waste products
- Removal of foreign chemicals
- Gluconeogenesis
- Production of hormones/enzymes
Hormone/enzymes produced by the kidney
- EPO
- Renin
- Conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin
Structural components of the kidney
- Nephron
- Renal medulla
- Renal cortex
- Ureter
- Renal pelvis
- Forms a filtrate from blood free from cells and proteins
- Filtrate leaves corpuscle and enters the tubule
- Substances added/removed in tubule
- Remaining fluid combines in collecting ducts
Renal Corpuscle
- Visceral layer of Bowman’s capsule
- Blood in the glomerular is separated from fluid in Bowman’s space by a filtration barrier
* Single cell lining of the capillary endothelium
* Non-cellular protein-rich layer of basement membrane
* Single cell lining of Bowman’s capsule
Podocyte
Specialised for filtering
Glomerular capillaries
- Supply the nephron/tubules with own blood supply
- Form the veins where blood leaves the kidney
Peritubular capillaries
- Renal corpuscle close to cortical-medullary junction
- Henle’s loop plunges deep into medullar
- Generate osmotic gradient for water reabsorption
Juxtamedullary nephrons
- Corpuscle located in outer cortex
- Henle’s loop do not plunge deep into medullar
Cortical nephrons
- Part of ascending loop of Henle
- Contain sensors that detect changes in blood composition
Macula Densa
Functions of juxtaglomerular apparatus
- Secrete renin
- Formation of angiotensin II
- Controls blood pressure
* Vasoconstriction
* Sodium/water retention
Non-penetrating solutes
- Na+ and Cl- on outside
- K+ on inside
Stimuli that cause kidney to secrete renin
- Renal sympathetic nerves
- Intrarenal baroreceptors
- Macula densa
Forces that favour filtration
P-GC - Glomerular Capillary BP
Forces that oppose filtration
- P-BS - fluid pressure in Bowman’s space
- pi-GC - osmotic force due to protein in plasma
Osmotic regulation
1 - Excess H2O ingested
2 - Decreased fluid osmolarity
3 - Decreased firing by hypothalamic osmoreceptors
4 - Posterior pituitary gland - decreased vasopressin secretion
5 - Decreased plasma vasopressin
6 - Collecting ducts - decreased tubular permeability to H2O
7 - H2O reabsorption
8 - Increased H2O excretion
Volume regulation
1 - Decreased plasma volume
2 - Decreased venous, atrial & arterial pressure
3 - Posterior pituitary - increased vasopressin secretion
4 - Increased plasma vasopressin
5 - Collecting ducts - increased tubular permeability to H2O
6 - Increased H2O reabsorption
7 - Decreased H2O excretion
Water permeability
- Depends on pressure of aquaporins
- Always high in proximal tubule
- In cortical and medullary collecting ducts can vary due to physiological control
- Stimulates insertion of aquaporins
- Binding increases production of cAMP
- Activates protein kinase which phosphorylates proteins, increasing rate of fusion of AQP2
- Water into blood vessels through AQP3&4
Antidiuretic Hormone (ADH)
Primary Active Na+ Reabsorption
- Out of cells and into interstitial fluid
- Keeps the intracellular concentration of Na+ low compared to tubular lumen
- Na+ moves downhill out of tubular lumen into tubular epithelial cells
- In proximal tubule, Na+ reabsorption drives reabsorption of co-transported substances and secretion of H+
Coupling of Water Reabsorption to Na+ Reabsorption
1 - Na+ transported from tubular lumen to interstitial fluid across epithelial cells
2 - Removal of solutes from tubular lumen decreases local osmolarity of tubular fluid adjacent to the cell
3 - Appearance of solute in interstitial fluid outside cell increases the local osmolarity
4 - Difference in water concentration causes net diffusion of water into interstitial fluid
5 - Everything dissolved in interstitial fluid move by bulk flow into peritubular capillaries
Countercurrent Multiplier System
- Along ascending limb, Na+ and Cl- are absorbed into interstitial fluid. No water follows, so interstitial fluid becomes hyperosmotic.
- Net diffusion of water out of descending limb into interstitial fluid.
- Osmolarities of descending limb and interstitial fluid are equal and larger than ascending limb.
- The concentrated interstitial fluid draws water out of the collecting ducts if levels of vasopressin are high, which concentrates the urine.
- The osmolarity difference is multiplied as fluid goes deeper.
Form hairpin loops that run parallel to loops of Henle and collecting ducts - blood vessels
Vasa recta
Medullary Circulation
- As blood flows down the loop, Na+ and Cl- diffuse into the vessel and water out of the vessel
- Process reversed in ascending loop
- Minimises excessive loss of solute from interstitium
- Salt and water reabsorbed are carried away by bulk flow
- Amount leaving is 2 fold higher due to reabsorption
