Countercurrent Exchange System
Formed by the vasa recta and provide blood supply to the medulla
Does NOT remove NaCl from medulla
Countercurrent Exchange System: Descending Capillaries
Water diffuses OUT of blood
NaCl diffuses INTO the blood
Countercurrent Exchange System: Ascending Capillaries
Water diffuses INTO the blood
NaCl diffuses OUT of the blood
Production of Concentrated/Dilute Urine
Kidneys regulate water loss in urine
ADH controls whether dilute or concentrated urine is formed
Dilute Urine
Filtrate and blood have equal osmolarity in PCT
Water is reabsorbed in the thin limb, but ions reabsorbed in the thick limb of the loop of Henle create a dilute filtrate
Concentrated Urine
Principal cells and ADH able to remove water from urine
Long loop makes that possible
Na/K/Cl symporters reabsorb Na and Cl from tubular fluid
H20 Reabsorption
PCT: 65%
Loop: 25%
DCT: Variable controlled by hormones
Dilute urine: decreases water removes, although sufficient ions have been absorbed
Aldosterone
Target: distal tubule, collecting duct
Effects: promotes Na+ and K+ secretion and reduces urine volume
Angiotensin II
Target: afferent and efferent arterioles
Effects: constricts arterioles, reduces GFR, stimulates ADH and aldosterone secretion, promotes water intake and reduces urine volume
Antidiuretic Hormone
Target: collecting duct
Effects: promotes H20 reabsorption, reduces urine volume, increases concentration
Atrial Natriuretic Peptide
Target: afferent and efferent arterioles, collecting duct
Effects: dilates afferent arteriole, constricts efferent arteriole, increases GFR, inhibits secretion of renin, ADH, and aldosterone, inhibits NaCl reabsorption by collecting duct, increases urine volume
Epinephrine and Norepinephrine
Target: juxtaglomerular apparatus, afferent arteriole
Effects: induces renin secretion, constricts afferent arteriole, reduces GFR and glomerular fluid
Parathyroid Hormone
Target: proximal and distal tubules, nephron loop
Effects: promotes Ca+ reabsorption by loop and distal tubule and Mg+ reabsorption by proximal tubule, inhibits phosphate reabsorption by proximal tubule, promotes calcitrol synthesis
Diuretics
Substances that slow renal reabsorption of water and causes diuresis (increased urine flow rate)
Used for treatment of congestive heart failure and hypertension
With hyperglycemia and glycosuria…
Diabetes mellitus I and II
Gestational diabetes
With glycosuria but no hyperglycemia…
Renal diabetes
With no hyperglycemia or glycosuria…
Diabetes, ADH hyposecretion
Urinalysis
Analysis of the volume and properties of urine
Normal urine is protein-free but includes filtered and secreted electrolytes (urea, creatinine, uric acid, urobilinogen, fatty acids, enzymes, and hormones)
Blood Tests
Blood urea nitrogen (BUN) test measures urea in the blood
Plasma Creatinine
Skeletal muscle breakdown
Dialysis Therapy
Kidney function is so impaired the blood must be cleansed artificially
Separation of large solutes from smaller ones by a selectively permeable membrane
Histology of Ureters
Mucosa, Muscularis, Adventitia
Mucosa
Transitional epithelium and lamina propria
Has elastic properties, since organ must inflate and deflate
Mucus prevents cells from being contacted by urine
Muscularis
Inner longitudinal and outer circular smooth muscle layer
Peristalsis contributes to urine flow
Adventitia Layer
Loose connective tissue anchors in place
Contains lymphatics and blood vessels to supply ureter
Location of Urinary Bladder
Posterior to pubic symphysis
Anatomy of Urinary Bladder
Hollow, distensible muscular organ with the capacity of 700-800mL in females and 1200mL in men
2 ureteral openings and 1 urethral opening
Which loop is permeable to water?
Descending loop
Where is urine concentrated?
Collecting duct
What hormone increases the permeability of the collecting duct?
ADH
Inserts aquaporins
Micturation
- 200mL urine in bladder, stretch receptors send signal to the spinal cord (S2 and S3)
- Parasympathetic reflex arc from spinal cord, stimulates contraction of detrusor muscle
- Relaxation of internal urethral sphincter
- This reflex predominates in infants
Voluntary Control of Micturation
- Micturition center in pons receives stretch signals and integrates cortical input (voluntary control)
- Sends signal for stimulation of detrusor and relaxes internal urethral sphincter
- To delay urination impulses sent through pudendal nerve to external urethral sphincter keep it contracted until you wish to urinate
- Valsalva maneuver aids in expulsion of urine by increased pressure on bladder
Incontinence
Lack of voluntary control over micturation
Total Body Water
45%
Fluid Compartments
65% intracellular fluid 35% extracellular fluid 25% interstitial fluid 8% blood plasma and lymph 2% transcellular fluid
Water Gain and Loss
About 2,500 mL/day
Regulation of Intake
Dehydration Hypothalamic osmoreceptors Thirst Ingestion of water Rehydration
Dehydration
Increased blood osmolarity Hypothalamus inhibits salivary glands Stimulates osmoreceptors (Angiotensin II and ADH)
Regulation of Output
Most mechanisms adjust Na+
ADH does NOT involve Na+ reabsorption, is inserts aquaporins into the collecting duct
Hypovolemia
Na+ and H2O lost
Osmolarity does not change
Electrolyte Balance
Maintenance is important to contribute to membrane potential and osmolarity of body fluids
Sodium
Responsible for resting membrane potential
Principal cation in ECF
Most important solute for determining water distribution
Hypernatremia
Hypertension, edema
> 145
Hyponatremia
Usually the result of excess water, sweat and replace with plain water
< 130