M22

Urinary System - Nephron

nephron

is the functional unit within each of the pyramid regions of the kidney

• kidney has abt 1 million nephrons

what are parts of nephron?

1. renal corpuscle

2. renal tubule

label nephron

renal corpuscle

• pulling plasma portion out of blood to make the filterate

• called glomerular filterate bcz within renal corpuscle, the capillary beds that produce the filterate form a ball known as the glomerulus

• has glomerular (Bowman’s) capsule

glomerulus

capillary bed that we are pulling the blood plasma out of

• within renal corpuscle

renal tubule

• proximal convoluted tubule→portion that leaves renal corpuscle

• nephron loop (loop of henle)→ portion that dips down into medulla + pyramid region and come back towards cortex

• distal convoluted tube→portion that reaches the cortex again

where is proximal convoluted tubule located?

in renal cortex

what do several distal convoluted tubules create?

connect tog to form collecting ducts

what collecting ducts tog form?

papillary ducts → will have final product, urine

what are the 2 types of nephron

1. cortical nephron (80-85%)

2. juxtamedullary nephron (15-20%)

cortical nephron (80-85%)

• corpuscle is in outer cortex with short nephron loop (makes them diff)

• loop has ascending and descending limbs

• blood supply to loop via peritubular capillaries

juxtamedullary nephron (15-20%)

• corpuscle near medulla in cortex (near the BASE) with long nephron loop

• less abundant

• loop has descending, and thin & thick ascending limbs

  • thin has simple squamous epithelial

  • thick has thicker cells

• blood supply via peritubular capillaries and vasa recta

• can produce dilute or concentrated urine

  • techincally both types of nephrons can make diluted and concentrated urine but the [] gradient is set up by long loop in juxtamedullary nephron

label blood supply to nephron

flow of fluid thru juxtamedullary nephron

goes from glomerulus to minor calyx

label histology of nephron

renal corpuscle

• bowman’s capsule surrounds capsular space

• capsular space is where filtrate accumulates

• glomerular capillaries arise from afferent arteriole & form a ball
  before emptying into efferent arteriole

what does efferent arteriole turn into?

peritubular capillaries

capsule portion

• have parietal layer→ outer layer made of simple squamous cells

• visceral layer →adhere tightly to endothelial cells that make up glomerulus

what are visceral layer cells called?

podocytes

• modified simple squamous cells

• have finger-like projectitons that serve as an extra barrier of filteration

pedicles

finger-like projections on podocytes

capular space

space between visceral and parietal layer

juxtaglomerular apparatus

structure where afferent arteriole makes contact with the ascending limb of nephron loop

• macula densa is thickened part of ascending limb, have sensory receptors attached to them → detect water, Na+/Cl- concentrations

• juxtaglomerular cells are modified smooth muscle cells in arteriole side

• helps to regulate blood pressure in kidneys

what are the modified smooth muscle cells?

1. juxtaglomerular cells

2. mesangial cells

mesangial cells

• located in region of afferent and efferent arterioles , also mixed in some glomerulus as well

• involved in regulation

• reduce surface area of glomerulus + afferent & efferent arterioles when contracted= reduces bloodflow= control how much filterate we are making

what happens when macula densa cells detect high amounts of water, Na+, Cl- []?

indicates that we are making too much filterate too quickly so it won’t be getting reabsorbed fast enough

• how to stop it? sense this at lvl of tubule and send direct signal to juxtaglomerular smooth muscle cells in the afferent arteriole to contract= reduces blood flow= reduces amount of filterate we make

label filteration membrane on small portion of glomerulus

• memorize 3 steps

what layers make up filteration membrane?

1. fenestration (pore) of glomerular endothelial cell

2. basal lamina of glomerulus

3. slit membrane between pedicles

fenestration (pore) of glomerular endothelial cell

prevents filtration of blood cells and platelets, but allows all components of blood plasma to pass through

basal lamina of glomerulus

prevents filtration of larger proteins

slit membrane between pedicles

prevents filtration of medium-sized proteins

cells in proximal convoluted tubule (PCT)

simple cuboidal w/ brush border of microvilli (similar to small intestine)

cells in nephron loop: descending limb and thin ascending limb

simple squamous epithelial cells

cells in nephron loop: thick ascending limb

change from simple cuboidal to low columnar cells

cells in most of of distal convoluted tubule (DCT)

simple cuboidal cells

cells in last part of DCT and all of collecting duct (CD)

simple cuboidal

• also have specialized cells like intercalated and principal cells→ help w/ regulating ions []

intercalated cells

monitoring hydrogen ions and regulating pH

principal cells

under hormonal control, regulate Na+/K+ lvls in blood and renal tubule

label cells of renal tubule + collecting duct

what is blood flow in kidneys (vascular path)?

what is filterate flow in kidneys (tubular path)?