ch25

• regulating total water volume and total solute concentration in water
• regulating ECF ion concentrations
• ensuring long term acid base balance
• removal of matabolic wastes, toxins, drugs

• renin: regualtion of blood pressure
• erythropoietin: regulation of rBC production
• acitvation of vitamin D
• gluconeogensis druing prolonged fasting

• kidneys
• ureters
• urinary bladder
• urethra

• renal fascia: anchoring outer layer of dense fibrous connective tissue
• perirenal fat capsule: fatty cushion
• fibrous capsule: prevents spread of infection to kidney

grandular appearing superficial region

• composed of cone shaped medullary pyramids
• pyramids separated by renal columns

tip of pyramid; releases urine into minor calyx

• medullary pyramid and its surrounding cortical tissue
• 8 per kidney

funnel shaped tube continuous with ureter

drains pyramids at papillae

• collect urine from minor calyces
• empty urine into renal pelvis

• structural and functional units that form urine
• more than 1 million per kidney
• two main parts: renal copuscle and renal tubule

• glomerulus: tuft of capillaries; allows filtrate formation
• bowman's capsule: cup shaped hollow structure surrounding glomerulus

parietal layer: simple squamousvisceral layer: branching epithelial podocytes

• prixmal convoluted tubule
• nephron loop (loop of henle)
• distal convoluted tubule

• cuboidal cells with dense microvillie to increase surface area
• functions in reabsorption and secretion
• confined to cortex

• descending and ascending limbs
• descending: simple squamous epithelium
• ascending limb: cuboidal to columnar cells

• cuboidal cells with very few microvilli
• function more in secretion than reabsorption
• confined to cortex

principle and intercalated cells

• sparse, short microvilli
• maintain water and Na+ balance

• cuboidal cells
• abundant microvilli
• 2 types; a and B; both maintain acid base balance of blood

• reeive filtrate from many nephrons
• run through medullary pyramids
• fuse together to deliver urine through papillae into minor calyces

cortical nephrons and juxtamedullary nephrons

• 85% of nephrons
• almost entirely in cortex

• long nephron loops deeply invade medulla
• ascending limbs have thick and thin segments
• important in production of concentrated urine

• high because afferent artieroles are larger in diamter than efferent artierioles
• arterioles are high resistance vessels

afferent arteriole > glomerulus > efferent arteriole

• low pressure, porous capillaries adapted for absorption of water and solutes
• arise form efferent arterioles
• cling to adjacent renal tubules in cortex
• empty into venules

• long thin walled vessels parallel to long nephron loops of jutamedullary nephrons
• arise fomr efferent arterioles serving juxtamedullary nephrons
• function in formation of concentrated urine

• juxtaglomerular complex
• one per nephron
• involved modified portions of distal portion of ascending limb, and afferent arteriole
• important in regulation of rate of filtrate formation and blood pressure

• macula dense
• granular cells
• extraglomerular mesangial cells

• tall, closely packed cells of ascending limb
• chemoreceptors; sense NaCl content of filtrate

• enlarged, smooth muscle cells of arteriole
• secretory granules contain enzyme renin
• mechanoreceptors; sense blood pressure in afferent arteriole

• betwen areriole and tubule cells
• interconnected with gap junctions
• pass signals between macula densa and granular cells

180; only 1.5 become urine

• glomerular filtration
• tubular reabsorption
• tubular secretion

produces cell and protein free filtrate

selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts

selectively moves substances from blood to filtrate in renal tubules and collecting ducts

• <1% of original filtrate
• contains metabolic wastes and unneeded substances

• passive process
• no metabolic energy required
• hydrostatic pressure forces fluids and solutes through filtration membrane
• no reabsorption into capillaries of glomerulus

• porous membrane between blood and interior of glomerular capsule.
• water, solutes smaller than plasma proteins pass, no cells pass
• has 3 layers

• fenestrated endothelium
• basement membrane
• foot processes of podocytes

a membrane problem

• outward pressures promote filtrate formation
• inward forces inhibiting filtrate formation

pressure responsible for filtrate formation

• volume of filtrate formed per minute by both kidneys
• GFR directly proportional to NFP, total surface area available for filtration, and filtration membrane permeability

myogenic mechanism and tubuloglomerular feedback mechanism

transcellular and paracellular

• apical membrane of tubule cells
• cytosol of tubule cells
• basolateral mebmranes of tubule cells
• endothelium of peritubular capillaries

• between tubule cells
• limited by tight junctions, but leaky in proximal nephron

• Na+ most abundant cation in filtrate
• transport across basolateral membrane
• transport across apical membrane

• Na+ reabsorption by rpimary active transport provides energy and means for reabsorbing most other substances
• creates electrical gradient for passive reabsorption of anions
• organic nutrients reabsorbed by secondary active transport; cotransported with Na+

aquaporins always present in PCT

aquaporins inserted in collecting ducts only if ADH present

• site of more reabsorption
• all nutrients e.g. glucose and amino acids
• 65% of Na+ and water
• many ions
• all uric acid

• descending limb, water can leave, solutes can't
• ascending limb, water can't leave but solutes can

• reabsorption hormonally regulated
• ADH-water
• aldosterone-Na+ (and water)
• atrial naturetic peptride - Na+
• PTH-Ca2+

• antidiuretic hormone
• released by posterior pituitary gland
• causes principal cells of collecting ducts to insert aqauporins in apical membranes for water reabsorption

• targets collecting ducts and distal DCT
• promotes synthesis of luminal Na+ and K+ channels and basolateral Na+-K+ ATPases for Na+ reabsorption; water follows
• functions are to increase blood pressure and decrease K+ levels

• atrial natriuretic peptide
• reduces blood na+ which decreases blood volume and blood pressure
• released by cardiac atrial cels if blood volume or pressure elevated

• number of solutes particles in 1 kg of H2O
• reflects ability to cause osmosis

• kidneys maintain osmolality of plasma at 300 MOsm by regulating urine concentration and volume
• kidneys regulate with countercurrent mechanism

• occurs when fluid flows in opposite directions in two adjacent segments of same tube with hair pin turn
• countercurrent multiplier: interaction of filtrate flow in ascending/descneding limbs of nephron loops of juxtamedullary nephrons
• countercurrent exchanger: blood flow in ascending/descneding limbs of vasa recta

• establish and maintain osmotic gradient from renal cortex through medulla
• allow kidneys to vary urine concentration

• freely permeable to water
• water passes out of filtrate into hyperosmotic medullary interstitial fluid
• filtrate osmolality increases to 1200

• impermeable to water
• selectively permeable to solutes
• Na+ and Cl- actively reabsorbed in thick segment, some passively reabsorbed in thin segment
• filtrate osmolality decreases to 100

• vasa recta
• preserve medullary gradient-prevent rapid removal of salt from interstitial space, remove reabsorbed water
• water entering ascneding vasa rect either from descending vasa recta or reabsorbed from nephron loop and collecting duct

• large volume dilute urine
• ADH production decreases
• if aldosterone present, additional ions are removed

• small volume concentrated urine
• ADH released

99% of water is reabsorbed

• helps form medullary gradient:
• enters filtrate in ascending thin limb of nephron loop by facilitated diffusion
• cortical collectiving duct reabsorbs water and leaves urea
• in deep medullary region now highly concentrated urea > interstitial fluid of medulla > back to ascending thin limb > high osmolality in medulla

• ADH inhibitors (e.g. alcohol)
• Na+ reabsorption inhibitors (caffeine)
• loop diuretics inhibit medullary gradient formation
• osmotic diuretics -substance not reabsorbed so water remains in urine

• volume of palsma kidneys clear of particular substance in given time
• renal clearance tests used to determine GFR

• clear: cloudy may indicate urinary tract infection
• pale to deep yellow: pigment form hemoglobin breakdown, more concentrated urine>deeper color
• abnormal color: food ingestion, bile pigment, blood, drugs

• slightly aromatic when fresh
• develops ammonia odor upon standing
• may be altered by some drugs and vegetables

slightly acidic

Na+, K+ CA2+, Mg2, HCO3, etc.

• mucosa: transitional epithelium
• muscularis: smooth muscle sheets, contracts in response to stretch, propels urine into bladder
• adventitia: outer fibrous connective tissue

• muscular sac for temporary storage of urine
• retroperitoneal on pelvic floor posterior to pubic symphysis

• muscular tube draining urinary bladder
• lining epithelium: mostly pseudostratified columnar epithelium, except transitional near bladder and stratified squamous near external urethral orifice

internal urethral sphincter and external urethral sphincter

• involuntary (smooth muscle) at bladder urethra junction
• contracts to open

voluntary (skeletal muscle) surrounding ureathra as it passes through pelvic floor

• prostatic: within prostate gland
• intermediate part: passes through urogentical diaphragm from prostate to beginning of penis
• spongy: passes through penis; opens via external urethral orifice

urination

• contraction of detrusor muscle by ANS
• opening of internal urethral sphincter by ANS
• opening of external urethral sphincter by somatic nervous system

between ages 2 and 3