ch 25 - urinary system

kidneys, general functions

removes toxins, metabolic wastes, and excess ions from blood

regulates blood volume, chemical composition, and pH

produces erythropoietin, renin

urinary bladder

termporary storage reservoir for urine

ureters

transports urine from kidneys to bladder

urethra

transports urine out of body

internal anatomy of kidney: renal cortex

SUPERFICIAL LAYER → site of initial urine production

renal columns → inward extensions separating the medulla

internal anatomy of kidney: Renal Medulla

middle section

renal pyramids → cone shaped structures, urine production

renal papilla → tip of pyramid draining urine into minor calyx

lobe → one pyramid plus its surrounding cortical tissue

internal anatomy of a kidney: renal pelvis

branched structure forming minor and major calyx

collects urine and passes it to ureter

blood supply: kidney general

¼ of cardiac output goes to kidney, continuously cleanse the blood and adjusts composition

blood supply (renal): FLOW

aorta → renal artery → afferent arterioles → glomerulus → efferent arterioles → peritubular capillaries/vasa recta → renal vein → inferior vena cava

afferent arterioles - peritubular cap = nephron associated blood vessels

nephron: general

structural and functional unit of kidney

nephrons components: renal corpuscle (cortex)

glomerulus

glomerular capsule

nephrons components: renal tubule (cortex and medulla)

proximal convoluted tubule

nephron loop

distal convoluted tubule

collecting duct

renal tubule has what histology?

single layer of epithelium, but each region otherwise has unique histology

renal corpuscle, filtration: glomerulus

(filter)

structure → tuft of fenestrated capillaries (highly porous)

significance → high permeability allows rapid passage of fluid and solutes from blood into the capsule

renal corpuscle, filtration: glomerular capsule, parietal layer

(collector)

external simple squamous epithelium

functions as structural container

renal corpuscle, filtration: glomerular capsule, visceral layer

internal layer composed of podocytes

forms filtration slits that act as final physical sieve for filtrate

anatomical combination of fenestrations and filtration slits ensures…

combination ensures that water and small solutes pass through while large proteins and blood cells are retained

renal tube: proximal convoluted tubule (PCT)

epithelium → simple cuboidal with dense microvilli (brush border)

significance → massive surface area for reabsorption of water, glucose and amino acids

renal tube: nephron loop (loop of henle), descending limb

thin segment

epithelium → simple squamous with FEW mitochondria

significance → high permeability to water only

renal tube: nephron loop (loop of henle), ascending limb

(thick segment)

epithelium → simple cubodial to columnar with ABUNDANT mitochondria

significance → pumps solutes (Na+, Cl-), impermeable to water

renal tubule: distal convoluted tubule (DCT)

epithelium → simple cubodial; few microvilli

significance → more secretion than absorption via hormonal regulation

renal tubule: collecting duct

receives filtrate from many nephrons

preform final adjustments to urine concentration via hormonal regulation (ADH)

principal cells and intercalated cells

renal tubule: collecting duct, principal cells

epithelium → cuboidal cells with sparse microvilli

significance → maintain water and Na+ balance

renal tubule: collecting duct, intercalated cells

epithelium → cuboidal cells with prominent microvilli

significance → regulate acid-base balance

cortical nephrons

85% of nephrons

short nephron loops

almost entirely in cortex

function → excretion and secretion

juxtamedullary nephrons

long nephron loops extended deep into the medulla

extensive thin segments

function → production of concentrated urine

every nephron has 2 capillary beds

first and second cap bed

first capillary bed: function

filtration

ex: glonerulus

second capillary bed: function

reclaims most of filtrate

ex: peritubular capillaries and vasa recta

nephron capillary beds: glomerulus, structure

(high pressure filter)

fed and drained by arterioles

afferent → larger diameter

efferent → smaller diameterne

nephron capillary beds: glomerulus, significance

diameter mismatch creates the high pressure necessary for filtration

pushing fluid out of the body

nephron capillary beds: peritubular capillaries, structure

(low pressure reclaimers)

low pressure, porous vessels arising from efferent arterioles

nephron capillary beds: peritubular capillaries, significance

rapid reabsorption of water and solutes from tubules back to blood

nephron capillary beds: vasa recta, structure

(the concentrators)

long, straight vessels parallel to the nephron loops in the medulla

nephron capillary beds: vasa recta, significance

vital for formation of concentrated urine

nephron capillary beds: flow

afferent arterioles → glomerulus → efferent arterioles → peritubular capillaries/vasa recta

juxtaglomerular complex

one per nephron, important in regulation of filtrate formation and blood pressure

involves:

- distal portion of the ascending limb of the nephron loop

- afferent arteriole

cells of juxtaglomerular complex: granular cells (juxtaglomerular, jg cells)

enlarged, smooth muscle cells of afferent arteriole

secretory granules contain renin

function: act as baroreceptors that senses blood pressure

cells of juxtaglomerular complex: macula densa cells

tall closely packed cells of ascending limb of the nephron loop

function: act as chemoreceptors that sense NaCl content of filtrate

cells of juxtaglomerular complex: extraglomerular mesangial cells

located between Macula densa and Granular cells

interconnected with gap junctions

function: may pass signals btwn macula densa and granular cells

filtration membrane: general and function

porous membrane between blood and capsular space

function → allows passage of water and solutes smaller than most plasma proteins

filtration membrane: three components

1. fenestrated endothelium of glomerular capillaries

2. gel-like basement membrane

3. visceral membrane of glomerular capsule (podocytes w/ food processes and filtration slits)

mechanisms of urine formation: glomerular filtration

liquid, non-cellular portion of blood dumped into glomerular capsule, then renal TUBULES

mechanisms of urine formation: tubular reabsorption

reabsorption (return) of valuable contents of tubule

valuable components returned to blood are:

• all glucose, all amino acids

• 99% of water

• salts

mechanisms of urine formation: tubular secretion

secretion (excretion) of undesirable material into the lumen of tubule

reverse of reabsorption

selective addition to urine

urine formation, glomerular filtration: general

passive mechanical process driven by hydrostatic pressure

urine formation, glomerular filtration: glomerulus efficient because…

1. filtration membrane is very permeable (fenestration)

2. filtration membrane has large surface area

3. glomerular blood pressure is higher (5mm Hg) than other capillaries

• larger afferent arteriole diameter and smaller efferent arteriole diameter

fenestration

permeable

urine formation, glomerular filtration: blood tonicity

to maintain blood tonicity (colloid osmotic pressure) → filter prevents the passage of large molecules

net filtration pressure: general

pressure responsible for filtrate formation

net filtration pressure: HPgc

hydrostatic pressure of glomerular capillaries

net filtration pressure: OPgc

osmotic pressure of glomerular capillaries

net filtration pressure: HPcs

hydrostatic pressure of capsular space

net filtration pressure: osmotic pressure

osmotic pressure of capsular space is almost ZERO as proteins cannot got in through the filtration membrane

net filtration pressure: formula

NFP = HPgc - (OPgc + HPcs) = 10mmHg

outward pressures - inward pressures

glomerular filtration rate: governed/directly proportional to..

1. total surface area available for filtration → relatively stable in health person

2. filtration membrane permeability → relatively stable in health person

3. net filtration pressure (NP) → affected by day to day physiological state

glomerular filtration rate: BP correlation

GFR and BP are closely related. if BP increases, gfr will increase