Structure and Function of the Renal Urologic systems Flashcards
Renal function
- Maintain a stable internal environment for optimal cell and tissue metabolism
- Balance solute and water transport
- Excrete metabolic waste products
- Conserve nutrients
- Regulate acids and bases
- Performs gluconeogenesis: synthesis of glucose from amino acids
- Forms urine
Endocrine functions: Secrete hormones
- Renin: regulation of BP
- Erythropoietin: Production of erythrocytes
- 1,25-dihydroxyvitamin D3: Metabolism of Ca
Forms urine
- Filtration
- Reabsorption
- Secretion by the glomerii and tubules in the kidney
- Storage of the urine in the bladder that it receives from the kidney by way of ureters
- removal of the urine through the urethra
Structures of the kidney
- Kidney
- Renal capsule:Surrounds the kidney
- Renal fascia: fibrous tissue
- Hilium: place where the renal blood vessels, nerves, lymphatic vessels and ureters enter/exit the kidney
- Renal cortex
- Renal medulla
- Renal columns
Renal cortex
- outer layer of the kidney
- Contains glomeruli
- Most of proximal tubules
- Part of the distal tubule
Renal Medulla
- Forms the inner part of the kidney
- Called pyramids
- Contains the tubules and collection duct
Renal columns
-Extend from the cortex between the renal pyramids
Other structures of the kidney
- Minor calyx
- Major calyx
- Renal pelvis
Nephron
- functional unit of the kidney
- Tubular structures w/ subunits that include the renal corpuscle, proximal convulated tubule, loop of henle, distal convoluted tubule, and collecting ducts
- All those structures contribute to formation of urine
Three kinds of nephrons
- Superficial cortical nephrons: make up 85% of nephrons
- midcortical nephrons
- Juxtamedullary nephrons: concentrating urine
Nephron renal corpuscle
-Contains glomerulus, Bowman glomerular capsule, mesangial cells
Mesangial cells
-Have phagocytic properties and release inflammatory cytokines and growth factors
Glomerulus
-Glomerular filtration membrane filters selected blood components through its
Glomerular endothelial cells
- Synthesize nitric oxide (vasodilator)
- Synthesize endothelin-(vasoconstrictor)
- Regulate glomerular blood flow
Filtration of the glomerulus
-Plasma filtrate from glomerulus passes through the glomrular membrane into the bowman space to form the primary urine
Bowman capsule: podocytes
- composed of cells: podocytes
- Form an elaborate network of intracellular clefts called filtration slits: modulate filtration
Glomerulus
- Is supplied by the afferent arteriole and drained by the efferent arteriole
- Juxtaglomerular apparatus: controls renal blood flow, glomerular filtration and renin secretion
Renal tubules
- Substances are reabsorbed from the filtrate or secreted into the filtrate
- Proximal convoluted tubule
- Loop of henle
- Distal convoluted tubule
Loop of Henle
-Hairpin-shaped loop composed of thick and thin portions of a descending segment that goes into the medulla
Collecting duct
- Descends down the cortex through the renal pyramids of the inner and outer medulla, draining urine into the minor calyx
- Consists of: principal cells, intercalated cells
Principal cells
-Reabsorb Na and water and secrete K
Intercalated cells
-Secrete hydrogen and reabsorb K
Blood vessels
- Renal arteries: supply blood to kidneys-arise from abd aorta
- Interlobar arteries
- Arcuate arteries
- Interlobular arteries
- Afferent arterioles
- Glomerular capillaries
- Efferent arterioles
- Peritubular capillaries
- Vasa recta
Efferent arterioles
- convey blood to the peritubular capillaries; an increase or decrease in resistance to the afferent or efferent arterioles
- This will then increase or decrease in GFR
Ureters
- long, interwining smooth muscle bundles
- pass obliquely through the posterior aspect of the bladder
- peristaltic activity propels urine to the bladder
- Micturition compresses the lower end of the ureter to avoid urine refulx
Bladder
- Components: detrusor muscle, trigone
- Transitional epithelium: allows expansion as the bladder fills; serves and transduces info about the luminal pressure and urine composition
Urethra
- Extends outside the body
- Internal and external sphincters
- Shorter in females
- Innervation: parasympathetic fibers, skeletal motor neurons in the pudendal nerve
Bladder and Urethra
Reflex arc is required for micturition-stimulated by mechanoreceptors from stretching-bladder fullness is sensed; impulses sent to sacral level of spinal cord
- When bladder accumulates 250-300mL of urine-contracts and the internal urethral sphincter relaxes from activation of the spinal reflex arc (micturition reflex)
- Urge to void is felt
Renal blood flow
- Kidneys receive 1-1.2L//min of blood
- GFR
- If MAP decreases or vascular resistance increases, then RBF decreases
GFR
- Filtration of plasma into the Bowman space
- 20% of the RPF is filtered here
- directly related to the perfusion pressure in the glomerular capillaries
Autoregulation
- Strict maintenance of 80-180 mm Hg provides constant GFR
- As systemic BP increases, afferent arterioles constrict, preventing an increase in filtration pressure
- Prevents wide fluctuations in the systemic arterial pressure from being transmitted to the glomerular capillaries
- Solute and water excretion is constantly maintained, despite arterial pressure changes
Autoregulation: Myogenic mechanism (stretch)
- As arterial pressure declines, glomerular perfusion increases
- An increase in arterial pressure decreases glomerular perfusion
Autoregulation: Tubuloglomerular feedback
- Sodium chloride content
- When Na filtration increases, GFR decreases
- When Na filtration decreases, the opposite occurs-GFR increases
Renal blood flow: Neural regulation
- Sympathetic nervous system
- Baroreceptor reflex
- Exercise and change of body position
- Severe hypoxia
Sympathetic nervous system and RBF
- Vasoconstriction occurs (diminishes GFR)
- Causes arteriolar vasoconstriction to reduce renal blood flow
Baroreceptors reflex
- Vasoconstriction of afferent arterioles w/ activation of a1-adrenoreceptors
- Decreases glomerular perfusion and GFR
Exercise and change of body position
-Activate renal sympathetic neurons, causes mild vasoconstriction
Severe hypoxia
- Stimulates chemoreceptors (from pulmonary system)
- Decreases RBF by means of sympathetic stimulation
Hormones-RAAS
- Increases systemic arterial pressure, and increases Na reabsorption
- Hormones and other mediators can alter the resistance of renal vasculature by stimulating vasodilation and vasoconstriction
- -In the precence of angiotensin-converting enzyme (ACE), angio 1 is converted to angiotensin 2
Renin
- Enzyme is formed and stored in afferent arterioles of the juxtaglomerular apparatus
- Helps form angiotensin 1
- Released in response to decreased BP, decreased Na concentrations in the distal convulated tubules, and release of prostaglandins, and hypovolemia
Angiotensin 2
- Stimulates the secretion of aldosterone by the adrenal cortex
- Potent vasoconsctrictor
- Stimulates antidiuretic hormone (ADH) secretion and thirst
ACE inhibitors
-Anti-Htn meds which inhibit the formation of angiotensin 2, to help reduce BP
System of RAAS
-Liver hepatocytes release angiotensinogen-then release of renin-forms angio 1-then ACE forms-angio 2-increases plasma volume and BP-negative feedback loop
Hormones: Natiuretic peptides
- Artial natiuretic peptide (ANP)-secreted from myocardial cells in atria
- Brain natiuretic peptides (BNP)-secreted from myocardial cells in the ventricle
- Both: Inhibit Na and water asborption by kidney tubules
- Inhibit secretion of renin and aldosterone
- Vasodilate the afferent arterioles; constrict the efferent artioles
- Increase urine formation leading to decreased blood volume and BP, promote Na and water loss
- Promotes diuresis
Hormones
- C type natiuretic peptide: secreted from vascular endothelium and in the nephron
- Urodilatin: secreted by distal convulated tubules and the collecting ducts
- Causes vasodilation
- Other hormones: adenosine, bradykinin, dopamine, endothelin, histamine, nitric oxide, and prostaglandins
Nephron functions
- Filters the plasma at the glomerulus
- Reabsorbs and secretes substances at various parts of its tubular structure
- Forms filtrate of protein-free plasma (ultrafiltration)
- Regulates filtrate to maintain body fluid volume, electrolyte composition, and pH w/in narrow limits
- Glomerulus w/in bowmans capusle (filtration)-Proximal tubule-Loop of Henle-Distal Tubule-Collecting duct
Proximal tubule
- reabsorption: Na, glucose, K, amino acids, HC03, Po, UREA, h20
- Secretion of: H+, foreign substances
Loop of Henle
- Concentration of urine
- Descending loop: water reabsorption, Na diffuses in
- Ascending loop: Na reabsorption, water stays in
- Urea secretion in thin segment
Distal tubule
- Reabsorption: Na, H20 (adh required), HCO3
- Secretion: K, urea, some drugs
Collecting duct
- Reasborption: H20 (adh required)
- reabsorption or secretion: Na, K,
- Final concentration
Glomerular Filtration
- freely permeable to water and relatively impermeable to large colloids such as plasma proteins
- Contains electrolytes (Na, K, glucose, chloride, creatinine, urea)
Filtration rate
- Total volume of fluid filtered by the glomeruli averages 180L/day
- Filtration of plasma per unit of time is directly related to the perfusion pressure of RBF
GFR increase
-If vasoconstriction of efferent arteriole-filtration pressure increases-GFR increases
GFR decrease
- Vasocontriction of one of the two arterioles produces opposite effects on the glomerular pressure: if afferent arteriole vasoconstricts-decrease in blood flow-drop in glomerular pressure-decrease in GFR and retention of body fluids
- Excessive protein-free fluid loss from vomit, diarrhea, diuretics or sweating can decrease GFR
- Renal tubules and primarily proximal tubules automatically adjust their rate of reasborption of Na and water to balance the change in GFR
Proximal Convulated tubules
- Active reabsorption of Na
- Promotes passive diffusion of water
- Damaged renal tubules: metabolic by products and drugs may accumulate
- Water and electrolytes are cotransported w/ Na
Loop of Henle
-provides the kidney w/ ability to concentrate urine and conserve water for the body
Uromodulin
- Formed on the epithelial surface of thick ascending segment and is first segment of distal tubule
- most abundant urinary protein
- protects against bacterial adhesion and urolithiasis
Distal convulated tubules and collecting duct
- performs final adjustments in urine composition
- Fluids become more diluted as is reaches the distal tubules
Urea
- End product of protein metabolism and the major constituent urine
- 50% of urea is excreted in urine and other 50% recycled by kidneys
Catecholamines
- Norepi and epi promote afferent arioterolar vasoconstriction and decrease GFR and RBF
- Renalase: hormone produced by the kidney that degrades catecholamines and regulates BP
ADH
- controls final concentration of urine
- in presence of ADH water reabsorption is high, causing less urine volume
- Secreted in the posterior pituitary
- Excessive ADH is cause of oliguria; SIADH occurs when posterior pituitary hypersecretes ADH, resulting in excess water reasborption and water excess in the plasma
- Inadequate secretion occurs w/ DI-water excreted in large amounts
Vitamin D
- Calcitriol: active form of Vitamin D3
- Necessary for aborption of Ca and Phosphate in small intestine
- decreased Phos stimulate calcitrol
- Patients w/ renal disease typically have low calcitrol and manifest sx of Ca and phosphate balance
Erythropoietin
Produced by adult kidney-essential for erythropoiesis
Creatinine clearance
Creatinine clearance and GFR provide the best estimate for functioning renal tissue.
-damage to the glomerular membrane and loss of nephrons decreases the GFR
Creatinine
- produced by muscles
- valuable for monitoring progress in chronic rather than acute renal disease
- decrease in GFR see increase in creatinine
Plasma cyst atin concentration
Measures progressive Rena dysfunction
BUN
Blood urea nitrogen
Varies as a result of altered protein intake and protein catabolism
Better indication for hydration status
Increase in dehydration and kidney failure
10-20mg/dL
Aging and renal function
Decreased kidney size Decreased RBF and GFR Decreased number of nephrons from renal vascular and perfusion changes Decreased tubular transport Decreased elimination of drugs
