NVCC Bio 212

1
Martinis Visual Anatomy and Physiology First
Edition Martini w Ober
Chapter 23 - Urinary System Lecture 17
2
Lecture Overview

• Introduction to the Urinary System
• Location and function of the kidneys
• Gross anatomy
• Histology
• Urine formation

3
Functions of the Kidneys

• Make urine
• Regulate blood volume and blood pressure
• Regulate plasma concentrations of Na, K, Cl-,
  HCO3-, and other ions
• Help to stabilize blood pH
• Conserve valuable nutrients
• Assist the liver in detoxification and deamination

4
Urinary System
Figure from Holes Human AP, 12th edition, 2010
Kidneys receive about 1.2 L of blood per minute
and filter nearly 180 L of fluid from the
bloodstream every day!
5
Location of Kidneys
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
Located retroperitoneally from T12 to L3 Left
kidney is slightly higher than right
kidney Adrenal glands sit on the medial and
superior part of kidneys
Nephro(s) kidney
6
Location of Kidneys
Helps maintain position of kidney
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
7
Gross Anatomy of the Kidneys
Renal capsule is tough, fibrous capsule (tunica
fibrosa) Hilus is entry point for renal artery,
vein, and nerve (mostly sympathetic fibers) Bases
of renal pyramids face the cortex, apices face
the renal pelvis and end at renal papillae
Pyel(o)-
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
8
Renal Blood Vessels
Figures from Martini, Anatomy Physiology,
Prentice Hall, 2001
Nerves, mainly sympathetic postganglionic fibers
of the ANS, follow arteries to nephrons
9
The Nephron
(80)
(20)
Nephrons are the structural and functional units
of the kidney
Figure from Holes Human AP, 12th edition, 2010
10
Blood Supply of the Nephron
The capillary loop of the vasa recta is a type of
capillary that is closely associated with the
nephron loop of juxtamedullary nephrons
Medulla
Figure from Holes Human AP, 12th edition, 2010
11
Blood Flow Through Kidney and Nephron
Know this!
Figure from Holes Human AP, 12th edition, 2010
12
Renal Corpuscle (Glomerulus Capsule)
Figure from Holes Human AP, 12th edition, 2010
Notice that the efferent arteriole is smaller
than the afferent arteriole This creates a high
pressure (55-60 mm Hg) in the glomerular
capillary bed
Filtrate in capsular space
13
Visceral Glomerular Epithelium
Figure from Holes Human AP, 12th edition, 2010
Material passing out of the blood must be small
enough to fit through the filtration slits (slit
pores)
14
Renal Cortex and Renal Medulla
Figure from Holes Human AP, 12th edition, 2010
15
Specialization of the Nephron
Figure from Holes Human AP, 12th edition, 2010
1. PCT simple cuboidal with a brush border 2.
Thin segment of the descending nephron loop -
simple squamous epithelium 3. Thick ascending
nephron loop - cuboidal/low columnar 4. DCT -
simple cuboidal with no microvilli (specialized
for secretion, not absorption)
(DCT)
(PCT)
The order of the parts of the nephron is
important to know
16
Juxtaglomerular Apparatus
Juxtaglomerular cells (JG) - modified smooth
muscle cells in the wall of the afferent
arteriole that contract (and secrete renin) Cells
of the macula densa (MD) are osmoreceptors
responding to solute concentration of filtrate MD
JG cells juxtaglomerular apparatus
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
17
Glomerular Filtrate and Urine Composition
(1.8 L/day)
Glomerular filtrate is about the same composition
as plasma H2O, glucose, amino acids, urea, uric
acid, creatine, creatinine, Na, Cl, K, HCO3-,
PO43-, SO42-. But notice how different the
composition of urine is. Additionally, note that
protein is not normally present in urine.
18
Urine Formation
About 125 ml/minute (180 L/day) of the total 1200
ml/min of blood that passes through the
glomerulus becomes filtrate

• Glomerular Filtration (GF) Adds to volume of
  urine produced
• substances move from blood to glomerular capsule

• Tubular Reabsorption (TR) Subtracts from volume
  of urine produced
• substances move from renal tubules into blood of
  peritubular capillaries
• glucose, water, urea, proteins, creatine
• amino, lactic, citric, and uric acids
• phosphate, sulfate, calcium, potassium, and
  sodium ions

• Tubular Secretion (TS) Adds to volume of urine
  produced
• substances move from blood of peritubular
  capillaries into renal tubules
• drugs and ions, urea, uric acid, H

? Urine formation GF TS - TR
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Overview of Reabsorption and Secretion
Figure from Holes Human AP, 12th edition, 2010
20
Glomerular Filtration
Figure from Holes Human AP, 12th edition, 2010
Glomerular filtrate is plasma that passes through
1) the fenestrae of the capillary endothelium,
2) the basement membrane around the endothelium,
and 3) the filtration slits (slit pores) of the
pedicels This is called the filtration membrane
Glomerular filtration is a mechanical process
based primarily on molecule size
21
Glomerular Filtration Rate (GFR)
NFP HPg
(HPc OPg)
Net Filtration Pressure force favoring
filtration forces opposing filtration
(glomerular capillary ( capsular
hydrostatic pressure hydrostatic
pressure) glomerular capillary

osmotic pressure )
Net filtration pressure is normally positive,
i.e., favors the movement of fluid out of the
glomerular capillaries
Figure from Holes Human AP, 12th edition, 2010
GFR amount of filtrate produced each minute
(125 ml/min)
22
Afferent/Efferent Arterioles Effect on GFR
Innervated by sympathetic nerves

• Afferent arteriole
• ? radius ? GFR
• ? radius ? GFR ? radius ? GFR
• Efferent arteriole
• ? radius ? 1/GFR
• ? radius ? GFR ? radius ? GFR

23
Amounts of Glomerular Filtrate and Urine
Glomerular Filtration Rate (GFR) is directly
proportional to the net filtration pressure GFR ?
125 ml/min (180 L/day) This means that all of the
plasma is filtered 60x every day (How did we
get this number?) Notice that urine output is
only 0.6 2.5 L per day (an average of about 1.8
L, or about 1 of glomerular filtrate) 99 of
filtrate is reabsorbed!!
Figure from Holes Human AP, 12th edition, 2010
average amounts over a 24 hour period
24
Glomerular Filtration Rate (GFR)
Net filtration pressure, although normally
positive, is relatively low (? 10 mm
Hg) Glomerular hydrostatic pressure is the blood
pressure in the glomerular capillaries, and is
usually higher than other capillary
pressures Capsular hydrostatic pressure tends to
push water and filtrate BACK into the
capillaries Anything that alters the filtration
pressures will alter GFR Blood pressure is the
most important factor altering the glomerular
hydrostatic pressure (and NFP). A MAP fall of
10 will severely impair glomerular filtration a
fall of 15-20 will stop it.
25
Summary of Factors Affecting GFR
Factor Effect
Vasoconstriction (? Sympathetic stimulation)
Afferent arteriole ? GFR
Efferent arteriole ? GFR

Vasodilation (? Sympathetic stimulation)
Afferent arteriole ? GFR
Efferent arteriole ? GFR

Increased capillary hydrostatic pressure ? GFR

Increased colloid osmotic pressure ? GFR

Increased capsular hydrostatic pressure ? GFR
Know this table its important!
26
Regulation of GFR

• Autoregulation
• Maintains GFR despite changes in local blood
  pressure and blood flow (between 90 180 mm Hg
  mean systemic pressure)
• Myogenic mechanism contraction of afferent
  arteriolar vascular smooth muscle when stretched
  (increased BP) relaxation occurs when BP
  declines
• Tubuloglomerular mechanism MD cells detect ?
  flow rate and/or ? osmolarity of filtrate in DCT
  -gt JG cells contract -gt afferent arteriole
  constricts -gt ? GFR

27
Regulation of GFR

• Neural (Autonomic) Regulation
• Mostly sympathetic postganglionic fibers
  vasoconstriction of afferent arterioles ? GFR
  (conserves water, redirects blood to other
  organs)
• Stimulates juxtaglomerular apparatus to secrete
  renin
• May override autoregulatory mechanism at afferent
  arteriole
• Hormonal Regulation
• Renin-angiotensin system stabilizes BP and ECF
  volume
• Atrial Natriuretic Peptide (ANP) - ? GFR, ? fluid
  loss (dilates afferent arteriole, constricts
  efferent arteriole)

28
Renin-Angiotensin System

• Renin is released by the juxtaglomerular
  apparatus due to
• 1) Decline of BP (Renin ? 1/Pressure)
• 2) Juxtaglomerular stimulation by sympathethic
  NS
• 3) Decline in osmotic concentration of tubular
  fluid at macula densa( Renin ? 1/NaCl )

Figure from Holes Human AP, 12th edition, 2010
(ACE)
Stabilizes systemic blood pressure and
extracellular fluid volume
29
Review

• Kidneys
• Are bean-shaped organs located retroperitoneally
  at level of T12 L3
• Are enclosed by a tough, fibrous capsule
• Consist of a cortex and a medulla
• Cortex glomeruli
• Medulla nephron loops, collecting ducts renal
  pyramids, renal papillae
• Renal sinus
• Major and minor calyces
• Renal blood vessels and nerves pass through the
  hilus and branch within the sinus

30
Review
Know this!
Figure from Holes Human AP, 12th edition, 2010
31
Review

• Functions of the Kidneys
• Making urine
• Regulating blood volume and blood pressure
• Regulating plasma concentrations of Na, K, Cl-,
  HCO3-, and other ions
• Helping to stabilize blood pH
• Conserving valuable nutrients
• Assisting the liver in detoxification and
  deamination

32
Review

• The functional unit of the kidney is the nephron
• Glomerulus (filtration)
• Capillaries surrounded by podocytes
• Filter blood
• PCT
• Nephron Loop
• DCT
• Peritubular capillaries
• Surround proximal and distal tubules
• In juxtamedullary nephrons, forms the vasa recta
• Collecting ducts (technically not part of nephron)

33
Review

• Glomerular filtration
• Glomerular filtration rate (GFR)
• Amount of filtrate produced each minute
• Directly proportional to net filtration pressure
• May be determined with creatinine or inulin tests
• Approximately 125 ml/min (180 L/day)
• Factors affecting GFR
• Vasoconstriction / vasodilation
• Capillary hydrostatic pressure
• Capsular hydrostatic pressure
• Capillary osmotic pressure

34
Review

• Glomerular filtration (contd)
• Factors controlling GFR
• Autoregulation
• Myogenic
• Tubuloglomerular
• Hormonal
• Renin-Angiotensin System
• ANP
• Autonomic nervous system