Lecture 10: The Urinary System Flashcards
what is the urinary system
-removal of metabolic wastes produced by body’s cells
-kidneys remove metabolic wastes from circulation
-main components: kidneys, ureters, urinary bladder, urethra
describe the main components of the urinary system
-kidneys: produce urine
-ureters: transport urine toward the urinary bladder
-urinary bladder: temporarily stores urine prior to urination
-urethra: conducts urine to exterior; in males it also transports semen
what are the three main functions of the urinary system
- excretion: removal of metabolic (nitrogenous) wastes from body fluids
- elimination: discharge of wastes from body
- homeostatic regulation: volume and solute concentration of blood
what are the homeostatic function of the kidneys
-regulation of blood ionic composition; Na+, K+, Cl-
-regulation of blood pH; H+, HCO3-
-regulation of blood volume; H20
-regulation of blood pressure
-maintenance of blood osmolarity
-production of hormones; calcitriol and erythropoietin (RBC production)
-excretion of metabolic wastes and foreign substances (drugs or toxins)
-regulation of blood glucose level
explain the renal anatomy
-The kidneys are retroperitoneal, on either side of T12-L3
-Left kidney is slightly higher right kidney
-Superior surfaces capped by the adrenal gland
-Position maintained by: Overlying peritoneum, Contact with adjacent visceral organs, Supporting connective tissues
what is the renal hilum
-indented area
-entrance for renal artery, renal vein, ureter, nerves, lymphatics
what are the 3 CT layers the protect and stabilize the kidneys from deep to superficial
- renal capsule: dense CT layer, continuous with outer coat of ureter
- perinepheric fat (adipose capsule): fatty tissue surrounding renal capsule, protects and anchors kidney
- renal fascia: dense CT which anchors kidney to surrounding structures
what are the different componenets of the kidney
renal cortex, renal medulla, renal pyramids, renal columns, renal sinus, kidney lobe, major calyx, renal pelvis
what is the renal cortex
outer region of kidney in contact with renal capsule
what is the renal medulla
inner region, comprises renal pyramidsw
what are the renal pyramids
triangular structures within medulla
- base abuts cortex
-apex (renal papilla) projects into renal sinus
-secreting apparatus and tubules
what are the renal columns
anchor the cortex
-bands of cortical tissue that separate adjacent renal pyramids
-extend into medulla
what is the renal sinus
internal cavity within kidney
-stabilizes positions of ureter, renal blood vessels, and nerves
what are the kidney lobes
produces urine; consists of:
-a renal pyramid
-overlying area of renal cortex
-adjacent tissues of renal columns
there are ducts within each renal papilla which discharge urine into a minor calyx
what is the major calyx
formed by four or more minor calyces
what is the renal pelvis
large, funnel-shaped chamber
-formed by two or more calyces
-occupies most of renal sinus
-connected to ureter which drains kidneys
what is the direction of urine flow
renal pyramid-> minor calyx-> major calyx-> renal pelvis-> ureter
blood supply of the kidneys
-nurtrient rich blood: renal artery-> segmental artery-> interlobar artery-> arcuate artery-> cortical radiate artery-> afferent arteriole-> glomerulus capillaries
efferent arteriole
-deoxy blood: peritubular capillary-> venule-> cortical radiate vein-> arcuate vein-> interlobar vein-> renal vein
look at slide 9
blood supply
describe the kidney innervation (2 ways)
renal nerves: through hilum
-innervate kidneys and ureters
-follow branches of renal arteries to individual nephrons
sympathetic innervation
-adjusts rate of urine formation; by changing blood flow at nephron
-influences urine composition; by stimulating release of renin
what is the nephron
-structural and functional units of kidneys that form urine
-consists of two parts: 1. renal corpuscle, 2. renal tubule-> collecting system
what are the two parts of the renal corpuscle
the glomerulus and glomerular capsule
what is the glomerulus (part of renal corpuscle
tuft of capillaries; fed by the afferent arteriole and drains into the efferent arteriole
what is the glomerular (Bowman’s) capsule (part of renal corpuscle
it is the visceral layer of podocytes wrap around the capillaries
-foot processes (pedicels): form inner wall of capsule
-filtrate is collected between the visceral and parietal layers
-filtration slits: between pedicels allow filtrate to pass into capsular space
what are two other parts of the renal corpuscle
-glomerular capillaries: fenestrated capillaries; endothelium contains large-diameter pores
-intraglomerular mesangial cells: located among glomerular capillaries, they provide support/ filtration/ and phagocytosis, control diamter of capillaries
what are the renal tubules
-two convoluted segments: proximal tubule (PCT), and distal convoluted tubule (DCT)
-segments are separated by nephron loop (loop of Henle)= U-shaped tube, extends at least partially into medulla
-filtrate changes in composition, going thorugh the tubule= due to substances being reabsorbed or secreted in various segments or nephron
what is the proximal convoluted tubule (PCT) (in renal tubule)
-first segment of renal tubule
-entrance to PCT lies opposite of connection of afferent and efferent arterioles with glomerulus
-simple cubiodal epitheliu,; microvilli on apical surfaces
-primary function: reabsorption of ions
what is the nephron loop/ Loop of Henle (in renal tubule)
-descending limb: fluid flows toward renal pelvis
-ascending limb: fluid flows towards renal cortex
-segments of limb have thick or thin epithelia: descending thin limb (DTL), ascending thin limb (ATL), thick ascending limb (TAL)
what is the distal convoluted tubule (DCT) (in renal tubule)
-3rd segment of renal tubule
-initial portion passes between afferent and efferent arterioles
-smaller luminal diameter than PCT
-epithelial cells lack microvilli
-primary function: reabsorb H2O and selected ions; actively secretes unwanted substances
what is the juxtaglomerular complex (JGC)
-region of contact between afferent arteriole, efferent arteriole and the distal tubule
-regulates blood pressure and filtrate formation
what does the Juxtaglomerular Complex consist of
- macula densa
- Juxtaglomerular cells
- extraglomerular mesangial cells
what is the macula desna (Juxtaglomerular Complex)
epithelial cells of DCT, near the renal corpuscle; function as chemoreceptors or baroreceptors
what are the juxtaglomerular cells (Juxtaglomerular Complex)
smooth muscle cells in wall of afferent erteriole; function as baroreceptors and secrete renin
what are the extraglomerular mesangial cells (Juxtaglomerular Complex)
between afferent and efferent arterioles; provide feedback control
what is the collecting system of the kidneys
-a series of tubes that carries tubular fluid away from nephrons
-collecting ducts: receive fluid from many nephrons
-each collecting duct: begins in cortex, descends into medulla, carries fluid to papillary duct which drains into a minor calyx
-transports tubular fluid from nephrons to renal pelivs
-adjusts fluid composition
-determines final osmotic concentration and volume of urinen
histology of proximal convoluted tubule (PCT)
simple cuboidal epithelial cells with prominent brush borders of microvilli
histology of nephron loop: descending limb and thin ascending limb
simple squamous epithelial cells
histology of nephron loop: thick ascending limb
simple cuboidal to low columnar epithelial cells
histology of most of distal convoluted tubule (DCT)
simple cuboidal epithelial cells
histology of last part of DCT and all of collecting duct (CD)
simple cuboidal epithelium consisting of principal cells and intercalated cells
what are the hormones involved of tubular reabsorption and tubular secretion
angiotensin II, aldosterone, antidiuretic hormone (ADH), atrial natriuretic peptide (ANP), parathyroid hormone (PTH)
Angiotensin II: what are the major stimule trigger release, mechanism and site of action, effects
-major stimuli that trigger release: low blood volume or low blood pressure stimulates renin-induced production of angiotensin II
-mechanism and site of action: stimulates activity of Na+–H+ antiporters in proximal tubule cells
-effects: increases reabsorption of Na+ and water, which increases blood volume and blood pressure
Aldosterone: what are the major stimule trigger release, mechanism and site of action, effects
-major stimuli that trigger release: increased angiotensin II level and increased level of plasma K+ promote release of aldosterine by adrenal cortex
-mechanism and site of action: enhances activity of sodium-potassium pumps in basolateral membrane and Na+ channels in apical membrane of principal cells in collecting duct
-effects: increases secretion of K+ and reabsorptionof Na+; increases reabsorption of water, which increases blood volume and blood pressure
Antidiuretic Hormone (ADH): what are the major stimule trigger release, mechanism and site of action, effects
-major stimuli that trigger release: increased osmolarity of extracellular fluid or deceased blood volume promotes release of ADH from posterior pituitary gland
-mechanism and site of action: stimulates insertion of water channel proteins (aquaporin-2) into apical membranes of principle cells
-effects: increases facultative reabsorption of water, which decreases osmolarity of body fluids
Atrial Natriuretic Peptide (ANP): what are the major stimule trigger release, mechanism and site of action, effects
-major stimuli that trigger release: stretching of atria of heart stimulates ANP secretion
-mechanism and site of action: suppresses reabsorption of Na+ and water in proximal tubule and collecting duct; inhibits secretion of aldosterine and ADH
-effects: increases excretion of Na+ in urine (natriuresis); increases urine output (diuresis) and thus decreases blood volume and blood pressie
Parathyroid Hormone (PTH): what are the major stimule trigger release, mechanism and site of action, effects
-major stimuli that trigger release: decreased level of plasma Ca2+ promotes release of PTH from parathyroid glands
-mechanism and site of action: stimulates opening of Ca2+ channels in apical membranes of early distal tubule cells
-effects: increases reabsorption of Ca2+
what is the flow of fluid through a cortical nephron
glomerular (bowman’s) capsule-> proximal convoluted tubule-> descending limb of the nephron loop-> ascending limb of nephron loop-> distal convoluted tubule (drains into collecting duct)
what is the flow of fluid through a juxtamedullary nephron
glomerular (bowman’s) capsule-> proximal convoluted tubule-> descending limb of the nephron loop-> thin ascending limb of the nephron loop-> thick ascending limb of the nephron loop-> distal convoluted tubule (drains into collecting duct)
what are the different types of nephrons
- cortical nephrons:
-85% of all nephrons
-located mostly within superficial cortex of kidney - juxtamedullary nephrons
-15% of nephrons
-nephron loop extends deep into medulla
renal physiology
- 180 L of fluid processed by kidney daily, but only 1.5 L of urine is formed
- Kidneys filter body’s entire plasma volume 60x each day
- Consume 20–25% of O2 used by body at rest
- Filtrate (produced by glomerular filtration) is basically blood plasma minus proteins
- Urine is produced from filtrate
how do kidneys maintain homeostasis
-by regulating volume and compositioin of blood
-involves excretion of metabolic wastes
what are the three metabolic wastes from the kidneys
- urea: most abundant organic waste, from amino acids breakdown
- creatinine: breakdown of creatine phosphate by skeletal muscles
- uric acid: recycling of nitrogenous bases
explain organic wastes of the kidneys
-dissolved in the bloodstream
-eliminated only when dissolved in urine
-removal is accompanied by water loss
what are the three processes of urine formation that adjust blood composition
- Glomerular filtration: in the glomerulus, blood plasma and dissolved substances (smaller than most proteins) get filtered into the glomerular capsule
- tubular reabsorption: all along the renal tubule and collecting duct, water, ions, and other substances get reabsorbed from the renal tubule lumen inot the peritubular capillaries and ultimately into the blood
- tubular secretion: all along the renal tubule and collecting duct, substances such as wastes, drugs, and excess ions get secreted from the peritubular capillaries into the renal tubule . these substances ultimately make their way into the urine
what is the excretion of a solute
glomerular filtration + secretion - reabsorption
tubular reabsorption and secretion
much of the filtrate is reabsorbed, especially wate,r glucose, amino acids, and ions
secretion helps to manage pH and rid the body of toxic and foreign substances
what are the reabsorption routes
- paracellular reabsorption: passive fluid leakage between cells (diffusion)
- transcellular reabsorption: directly throiugh the tubule cells
what is the filtration membrane
-porous membrane between blood and interior of glomerular capsule
-allows H2O and solutes smaller than plasma proteins to pass
-normally no cells can pass
what are the three layers of the filtration membrane
-fenestrated endothelium of glomerular capillaries: prevents filtration of blood cells but allows all components of blood plasma to pass through
-basement membrane: fused basal laminae of two other layers, prevents filtration of larger proteins
-foot processes of podocytes with filration slits; slit diaphragms repel macromolecules, prevent filtration of medium-sized proteins
what is glomerular filtration
-a passive process driven by blood pressure
-opposed by capsular hydrostatic pressure and blood colloid osmotic pressure
-water and small molecules more out of the glomerulus
what is the glomerular filtration rate (GFR)
-amount of filtrate formed by both kidneys/ minute (120-125 ml/min)
-homeostasis requires kidneys to maintain a relatively constant GFR
-too high: substances pass too quickly and are not reabsorbed
-too low: nearly all reabsorbed and some waste products are not adequately excreted
what is the glomerular filtration rate (GFR) directly proportional to
-net filtration pressure (NFP): primary pressure is glomerular hydrostatic pressure
-total surface area available for filtration: glomerular mesangial cells control by contracting
-filtration membrane permeability: much more permeable than other capillaries
what are the different types of regulation of glomerular filtration rate
Renal autoregulation: myogenic mechanism, tubuloglomerular feedback, neural regulation
Hormone regulation: angiotensin II. atrial natriuretic peptide (ANP)
what is the major stimulus, mechanism and site of action, and effect on GFR of myogenic mechanism
major stimulus: increased stretching of smooth muscle fibers in afferent arteriole walls due to increased blood pressure
mechanism & site of action: stretched smooth muscle fubers contract, thereby narrowing lumen of afferent arterioles
effect on GFR: decrease
what is the major stimulus, mechanism and site of action, and effect on GFR of tubuloglomerular feedback
major stimulus: rapid delivery of Na+ and Cl- to the macula densa due to high systemic blood pressure
mechanism & site of action: decreased release of nitric oxide (NO) by juxtaglomerular apparatus causes constriction of afferent arterioles
effect on GFR: decrease
what is the major stimulus, mechanism and site of action, and effect on GFR of neural regulation
major stimulus: increase in activity level of renal sympathetic nerves releases norepinepherine
mechanism & site of action: constriction of afferent arterioles through activation of a1 (alpha 1) receptors and increased release of renin
effect on GFR: decrease
what is the major stimulus, mechanism and site of action, and effect on GFR of angiotensin II
major stimulus: decreased blood volume or blood pressure stimulates production of angiotensin II
mechanism & site of action: constriction of afferent and efferent arterioles
effect on GFR: decrease
what is the major stimulus, mechanism and site of action, and effect on GFR of atrial natriuretic peptide (ANP)
major stimulus: stretching of atria of heart stimulates secretion of ANP
mechanism & site of action: relaxation of mesangial cells in glomerulus increases capillaru surface area available for filtration
effect on GFR: increase
what are the outward pressures affecting filtration
forces that promote filtrate formation
Glomerular Blood Hydrostatic Pressure (GBHP): is essentially glomerular blood pressure
-cheif force pusching water and solutes out of blood
-quite high: 55mm Hg; compared to ~26 mm Hg seen in most capillary beds
-reason is that efferent arteriole is a high-resistance vessel with a diameter < (less than) an afferent arteriole
what are the inward pressure affecting filtration
forces inhibiting filtrate formation
a) Capsuler Hydrostatic Pressure (CHP): filtrate pressure in capsule; 15 mm Hg
b) Blood Colloid Osmotic Pressure (BCOP): “pull” of proteins in blood; 30 mm Hg
what is the net filtration pressure (NFP) in the urinary system
-sum of all forces; pressure responsible for filtrate formation
-main controllable factor determining glomerular filtration rate (GFR)
-55 mm Hg forcing out minus 45 mm Hg opposing= net outward force of 10 mm Hg
what is pyelitis
infection of renal pelvis and calyces
what is pyelonephritis
infection of inflammation of entire kidney
-infections in females are usually cause by fecal bacteria entering urinary tract
-severe cases can cause swelling of kidney, abscess formation, and pus may fill renal pelvis
-normally is successfully treated with antibiotics
what are afferent arterioles & efferent arterioles
-afferent arterioles: deliver blood to the glomerulus
-efferent arterioles: carry blood away from the glomerulus
slide 35
