Kidneys
paired organs located on the posterior abdominal wall outside the peritoneal cavity
Renal capsule
surrounds each kidney
Renal fascia
a fibrous tissue that attaches the kidney to the posterior abdominal wall.
Hilum
a medial indentation in the kidney, entry and exit port for renal blood vessels, nerves, lymphatic vessels and ureter
Cortex
the outer layer of the kidney containing all the glomeruli, most of proximal and some distal tubules
Medullary
forms the inner part of the kidney and consist of pyramids
Pyramids
forms the medullary, extends into the renal pelvis and contains the loops of Henle and collecting ducts.
Calyces
chambers that receive urine from the collecting ducts and form the entry into the renal pelvis
Renal pelvis
...
Lobe
the structural unit of the kidney, composed of a pyramid and overlying cortext
Nephron
the functional unit of the kidney
Cortical nephron
extend partially into the medulla
Juxtamedullary nephrons
deep into the medulla and important for concentrating urine
Renal Corpuscle
forms the glomerulus and bowman capsule
Glomerulus
tuft of capillaries that loops into the bowman capsule
Bowman capsule
...
Mesanglial cells
phagocytic ability and can contract to regulate glomerular capillary blood flow
Bowman Space
space inside the bowman capsule
Glomerular filtration membrane
filters blood components through its three layers forming urine: (1) an inner capillary endothelium (2) a middle basement membrane (3) an outer layer of capillary epithelium (podocytes or visceral epithelium/filtration slits)
Filtration slits
elaborate network of intercellular clefts
Juxtaglomerular apparatus
forms juxtaglomerular cells and the macula densa
Juxtaglomerular cells
a group of specialized cells, renin releasing cells
Macula desna
sodium sensing cells located between the afferent and efferent
Proximal tubule
continues from bowman space and has an initial convoluted segment (pars convoluta) and then a straight segment (pars recta) that descends towards the medulla, contains cuboidal cells
Loop of Henle
extends into the medulla, thin segment squamous cells with no active transport, thick segment are cuboidal and actively transports solute
Distal tubule
extend from the macula densa to the collecting duct
Collecting duct
a large tubule that descends down the cortex through the renal pyramids of the inner and outer medullae and into the minor calyx
Principal cells
reabsorb sodium and secrete potassium
Intercalated cells
reabsorb potassium and bicarbonate and secrete hydrogen
Blood Vessels of the Kidney
Renal arteries: supply blood to the lower, mid and upper thirds of the kidneys
Interlobar arteries
Arcuate arteries
Glomerular capillaries: carries blood to the peritubular capilarries
Peritubular capillaries and vasa recta
Vasa recta: BLOOD SUPPLY TO THE
Ureters
30 cm long
Long, intertwining muscle bundles
Pass obliquely though posterior aspect of bladder
Peristaltic activity affected by urine volume
Micturition compresses the lower end of the ureter to avoid urine reflux
Bladder
forms the Detrusor muscle, coat the bladder
Uroepithelium provides a barrier function to prevent movement of water and solutes between teh urine and blood
Trigone: smooth triangular area between the openings of the two ureters and urethra
Urethra
Internal sphincters: ring of smooth muscle at the junction of the urethra and bladder
external sphincters: striated muscle and under voluntary control
3 to 4 cm in females
18 to 20 cm in males ( prostatic, membranous, and cavernous)
Micturation Reflex
Parasympathetic nervous system
Stimulated in respond to stretching of the tissue, sensing bladder fullness and sending impulses to the sacral level of the cord
Spinal Reflex Arc Stimulation: When the bladder accumulates 250-300 ml of urine, the bladder co
Glomerular filtration rate
the filtration of the plasma per unit of time, which is directly related to the perfusion pressure of the glomerular capillaries
Filtration fraction
the ratio of glomerular filtrate to renal plasma flow per minute
Autoregulation of blood flow
to prevent large changes in GFR when there are increases or decreases in systemic blood pressure
Tubuloglomerular feedback
a mechanism that keeps RBF and GFR constant, as the GFR increases or decreases, the macula densa cells senses increase or decrease in sodium. When the GFR and NA ? the macula densa stimulate the afferent arteriolar vasoconstriction and ? GFR
Neural Regulation
Ganglion and greater splanchnic nerve; ? Systemic arterial pressure ? renal sympathetic nerve activity = stimulation of the renal arteriolar vasoconstriction ? RBF and GFR
Factors that Influence RBF
Exercise, body position, and hypoxia
Hormonal Regulation
Renin-angiotensin system ? systemic arterial pressure and change RBF
Renin is stored in the juxtaglomerular apparatus
Affected by (1)?BP reduces the stretch of the juxtaglomerular cells (2) ?NACL (3) ?adrenergic receptors
Released during hypotension, hypo
Functions of a Nephron
Filters plasma
Reabsorbs and secretes
Tubular reabsorption and secretion
Forms a filtrate of protein-free fluid (ultrafiltraiton)
Regulates the filtrate to maintain fluid volume, electrolytes, and pH
Tubular reabsorption
the movement of fluids and solute fromt eh tubular lumen to the pertubular capillary plasma
Tubular secretion
the transfer of substance fromt he plasma of the peritubular capilary to the tubular lumen
Excretion
Elimination of final urine
Glomerular Filtration
Hydrostatic pressure is the major force for moving water and solutes across the filtration membrane and into Bowman capsule
Net filtration pressure: the sum of foces favoring and opposing filtration
�Glomerular capillary oncotic?
�hydrostatic pressure in
Tubular Transport
Proximal tubule
�Active reabsorption of sodium
Loop of Henle and distal tubule
�Concentration or dilution of urine
Glomerulotubular balance
�Adjustment of reabsorption of sodium and water done by the proximal tubules
Countercurrent Exchange System
Contributes to production of concentrated urine
Fluid flows in opposite direction through parallel tubes
Fluid moves up and down the parallel limbs of the loop of Henle
The longer the loop, the greater the concentration gradient
Concentration and Dilution of Urine
Urea
Aldosterone
Antidiuretic hormone (ADH)
Atrial natriuretic peptide
Diuretics
Renal Hormones
Urodilatin
Inhibits sodium and water reabsorption
Vitamin D
Necessary for the absorption of calcium and phosphate
Erythropoietin
Released when decreased oxygen to the kidney
Test of Urine Function
Clearance and glomerular filtration rate
Inulin
Creatinine
Clearance and renal blood flow
Blood tests
Plasma creatinine concentration
Blood urea nitrogen (BUN)
Urodynamic tests
Cystometry, uroflowmetry, postvoid residual, electromyography, video urodynami
Pediatric Renal Function
Decreased ability to remove excess water and solutes
Decreased concentrating ability
Narrow margin for fluid and electrolyte balance
Increased risk of drug toxicity
Aging and Renal Function
Decrease in renal blood flow and GFR
Altered sodium and water balance
Number of nephrons decrease due to renal vascular and perfusion changes
Response to acid-base changes delayed
Increased risk for drug toxicity
Alterations in thirst and water intake