Transcript NVCC Bio 212 - gserianne.com

Marieb’s Human
Anatomy and Physiology
Marieb w Hoehn
Chapter 25
Urinary system
Lecture 15
Lecture Overview
• Introduction to the Urinary System
• Location and function of the kidneys
• Gross anatomy
• Histology
• Urine formation
2
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
3
Urinary System
Figure from: Hole’s Human A&P, 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!
4
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
5
Location of Kidneys
Helps
maintain
position of
kidney
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
6
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)
[Pyel(o)-]
Bases of renal
pyramids face the
cortex, apices face the
renal pelvis and end at
renal papillae
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
7
Renal Blood Vessels
Glomeruli
(Cortical
radiate
arteries)
Minor Calyx
Figures from:
Martini, Anatomy
& Physiology,
Prentice Hall,
2001
Nerves, mainly sympathetic postganglionic fibers of the
ANS, follow arteries to nephrons
8
The Nephron
(80%)
(20%)
Nephrons are
the structural
and functional
units of the
kidney
9
Figure from: Hole’s Human A&P, 12th edition, 2010
Blood Supply of the Nephron
Medulla
The capillary loop of
the vasa recta is a
type of capillary
that is closely
associated with the
nephron loop of
juxtamedullary
nephrons
10
Figure from: Hole’s Human A&P, 12th edition, 2010
Blood Flow Through Kidney and Nephron
Know
this!
11
Figure from: Hole’s Human A&P, 12th edition, 2010
Renal Corpuscle (Glomerulus + Capsule)
Figure from: Hole’s Human A&P, 12th edition, 2010
Filtrate in
capsular
space
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
12
Visceral Glomerular Epithelium
Figure from: Hole’s Human A&P, 12th edition, 2010
Material
passing out of
the blood must
be small
enough to fit
through the
filtration slits
(slit pores)
13
Renal Cortex and Renal Medulla
Figure from: Hole’s Human A&P, 12th edition, 2010
14
Specialization of the Nephron
Figure from: Hole’s Human A&P, 12th edition, 2010
1. PCT – simple
cuboidal with a brush
border
(DCT)
2. Thin segment of the
descending nephron
loop - simple squamous
epithelium
3. Thick ascending
nephron loop cuboidal/low columnar
(PCT)
The order of the
parts of the nephron
is important to know
4. DCT - simple
cuboidal with no
microvilli (specialized
for secretion, not
absorption)
15
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
16
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.
17
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
18
Glomerular Filtration
Figure from: Hole’s Human A&P, 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
19
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 )
Figure from:
Hole’s Human
A&P, 12th
edition, 2010
Net filtration
pressure is normally
positive, i.e., favors
the movement of
fluid out of the
glomerular
capillaries
GFR = amount of
filtrate produced each
minute (~125 ml/min)
20
Afferent/Efferent Arterioles – Effect on GFR
Innervated by sympathetic nerves
• Afferent arteriole
– Δ radius  GFR
–  radius  GFR;  radius  GFR
• Efferent arteriole
– Δ radius  1/GFR
–  radius  GFR;  radius  GFR
21
Amounts of Glomerular Filtrate and Urine
Figure from: Hole’s Human A&P, 12th edition, 2010
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!!
average amounts over a 24 hour period
22
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.
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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 – it’s important!
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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 –afferent arteriolar vascular smooth
muscle contracts when stretched (increased BP); relaxes when
it’s not stretched (decreased BP)
– Tubuloglomerular mechanism – MD cells detect  flow rate
and/or  osmolarity of filtrate in DCT -> JG cells contract ->
afferent arteriole constricts ->  GFR. So…
*If DCT flow increases, GFR 
If DCT flow decreases, GFR 
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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)
26
Renin-Angiotensin System
Figure from:
Hole’s Human
A&P, 12th
edition, 2010
Renin is released by the
juxtaglomerular
apparatus due to:
1) Decline of BP
(Renin  1/Pressure)
(ACE)
2) Juxtaglomerular
stimulation by
sympathethic NS
3) Decline in osmotic
concentration of
tubular fluid at
macula densa
( Renin  1/[NaCl] )
Stabilizes systemic blood pressure and extracellular fluid volume
27
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
28
Review
Know
this!
29
Figure from: Hole’s Human A&P, 12th edition, 2010
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
30
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)
31
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
32
Review
• Glomerular filtration (cont’d)
– Factors controlling GFR
• Autoregulation
– Myogenic
– Tubuloglomerular
• Hormonal
– Renin-Angiotensin System
– ANP
• Autonomic nervous system
33