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Chapter 17
Physiology of the Kidneys
and Renal System
Composition of Renal System
2 Kidneys
 2 ureters
1
1

Kidney Function

Regulate ECF (plasma and interstitial fluid)
through formation of urine.
 ________________________.

Regulate volume of blood plasma.
 BP.


Regulate [waste products] in the blood.
Regulate concentration of electrolytes.
 ____________________ and


other ions.
Regulate ________________.
Secrete erythropoietin.
Regulation of Blood Flow by the
Kidneys

Kidneys produce 180L of filtrate – but we
only have 5.5L of blood? What is going
on?
 Most
____________ is returned to blood
 Only pee about _________L per day
 98+% is returned to blood
Regulation of Blood Flow by the
Kidneys - ADH

Anitdiuretic Hormone (vasopressin)
by hypothalamus – released by ____
 Increase is plasma ____________ as determined by
osmoreceptors in brain
 Produced



Dehydration or excessive salt intake
ADH stimulates water _________________ from filtrate =
decrease urine output
Dilution of blood = decreased osmolality = decreased
_______
Regulation of Blood Flow by the
Kidneys – Aldosterone

Steroid hormone produced by adrenal
cortex
 Stimulates
_______ retention from kidneys
Indirectly affects retention of ________
 Causes increase in blood volume but not an
increase in osmolality = salt and water in
proportional amounts
 Stimulated during _________deprivation – when
blood volume and blood pressure are __________

Regulation of Blood Flow by the
Kidneys – Renin-angiotensin- Aldosterone




Juxtaglomerular apparatus – secretes __________
Renin produces _______________ from angiotensin.
As angiotensin I passes through respiratory system it is
converted to angiotensin II
Angiotensin II produces a ______________ blood
pressure & blood volume




Due in part to ____________________ and part due to increased
blood volume
Triggers _______________centers in hypothalamus = more water
ingested
Stimulates aldosterone secretion
High ______________ ingestion = high blood
pressure/high blood volume = inhibits _________ etc.
Regulation of Blood Flow by the
Kidneys - ANP

Increased blood volume = stimulates Atrial
natriuretic peptide
 Increases
______________ and water
excretion in urine = decrease blood volume
 Produced by ___________ of the heart
 Decreases secretion of ____________ =
vasodilation
 Antagonizes angiotensin II
Kidneys: Gross Structure
Horse: ____________shaped
 Cow: Cluster of ____________
 Sheep: kidney bean
 Pig: small, kidney bean
 Usually found amongst a lot of kidney fat,
especially in older animals
 Sort of a purplish red/brown color
 Vary in size depending on breed of animal

Structure of the Kidney

Outer cortex:

Contains
many
capillaries.
 Dark

Medulla

Lighter
colored
Renal pelvis: collects __________


Transports urine to ureters.
Nephron







____________ of the kidney.
Located in ___________
Produces ______________
Humans: @ 1 million/kidney
Cats: 150,000/kidney
Cow: 4 million/kid
Consists of:

Blood vessels:



Vasa recta.
Peritubular capillaries.
Urinary tubules:




PCT.
LH.
DCT.
CD.
2 Types of Nephrons

Cortical nephron:

Originates in outer
2/3 of cortex.


Involved in solute
reabsorption.
Juxtamedullary
nephron:

Originates in inner
1/3 cortex.


Important in the
ability to produce
a concentrated
urine.
Has longer
______.
Insert fig. 17.6
Nephron Tubules





Glomerular
capsule.
Proximal
convoluted
tubule (PCT).
Descending
and ascending
limbs of Loop
of Henle (LH).
Distal
convoluted
tubule (DCT).
Collecting duct
(CD).
Structure of Nephron

Composed of 2 basic structures
1. _________________ – fluid is filtered
from the blood
2. ______________ – filtered fluid is converted
into urine on its way to the pelvis


Glomerulus: blood ____________ through
afferent arteriole
Blood _____________ through efferent
arterioles
Structure of Nephron
_____________ arteriole brings blood into
a mass of capillaries = glomerulus
(glomeruli)
 Bowman’s capsules: epithelial cells
covering the glomerulus
 Lots of blood coming from an area with
lots of room, into an area with less room.
Stuff will filter out of blood.
 Glomerular capillaries are 100 times more
permeable than other capillaries

Glomerular Capsule

Bowman’s
capsule:
 Surrounds
the
glomerulus.


Location
where
glomerular
filtration
occurs.
Filtrate passes
into the urinary
space into
PCT.
Insert fig. 17.6
Structure of Nephron

Glomerulus is an area of high pressure,
therefore, fluid will leak _______ and enter
the Bowman’s capsule and flow into the
_______________________
Proximal Convoluted Tubule

Single layer of cuboidal cells with millions
of _________________
 Increase

surface area for reabsorption.
PCT functions:
 Reabsorption.
 Secretion.
Loop of Henle
Fluid flows from the proximal tubule to the
______________________
 Loop of Henle travels into the medulla
 2 parts of the L of H

 1.
Descending limb (aka thin segment)
 H20
 2.
reabsorption
Ascending limb (aka thick segment)
Active transport of Na+.
 _____________________________.

Distal Convoluted Tubule
Contains few microvilli.
 Functions:

 Secretion.
 Reabsorption.
Lies in ____________________
 Many (8 or so) from other nephrons come
together
 Terminates in Collecting Duct.

Collecting Duct

Functions:
 Reabsorption.

H20 reabsorption influenced by
______________________
 Secretion.
 Collecting
ducts combine to empty into
_________________________
Renal Blood Vessels

Afferent arteriole:


Glomeruli:


Capillary network that produces filtrate that enters the
_________________________.
Efferent arteriole:


Delivers blood into the ____________________.
Delivers blood from glomeruli to peritubular
capillaries.
Peritubular capillaries:



Deliver blood to ________________________.
Loops of peritubular capillaries that parallel the L of H
Loop down into the medulla from the cortex
Renal Blood Vessels
(continued)
Insert fig. 17.5
Juxtaglomerular Apparatus
(continued)
Insert fig. 17.25
Juxtaglomerular Apparatus


Region in each nephron where the afferent
arteriole comes in contact with the thick
ascending limb LH.
Granular cells within __________________
secrete renin (enzyme that…):




Converts angiotensinogen to angiotensin I.
Initiates the renin-angiotensin-aldosterone system.
Negative feedback.
Macula densa:


Region where ascending limb is in contact with afferent
arteriole.
Inhibits renin secretion when blood [Na+] in blood increases.
Juxtaglomerular Apparatus:

Function:
 1.
regulate amount of blood flowing to kidney
 2. regulate amount of filtration

HOW: Detects changes in Na and Cl, in the
tubular fluid.
 When
Na and Cl are lowered, the MD sends a signal
to the afferent arteriole to dilate (increase in blood and
hydrostatic pressure).
 = more filtrate
Glomerular Filtration Membrane
Endothelial capillary pores are large
 100-400 times more permeable to H20,
and dissolved solutes than capillaries of
skeletal muscles.
 Pores are small enough to prevent RBCs,
platelets, and ____________ from passing
through the pores.

Filtration aided by:

1. Glomeruli (capillaries):


More_____________ than nomal
2. Efferent arterioles:
_________________in diameter than
afferent

increases resistance to blood flow out
Glomerular Ultrafiltrate

Fluid that enters glomerular capsule is called
ultrafiltrate.
 Glomerular filtration:
 Mechanism of producing ultrafiltrate under hydrostatic
pressure of the blood.

Glomerular filtration rate (GFR):
 Volume
of filtrate produced by both kidneys each
minute.


Averages 115 ml/min. in women; 125 ml/min. in men.
About 1 coke can/3 minutes (that is a lot of pee!!!!)
Regulation of GFR

Vasoconstriction or dilation of the
______________ arterioles affects the rate of
blood flow to the glomerulus.
 Affects

GFR.
Mechanisms to regulate GFR:
 Sympathetic
nervous system.
 Autoregulation.
Forces that affect filtration:






1. Constriction of afferent arteriole (decrease in
GFR)
2. Dilation of afferent arteriole (increase in GFR)
3. Constriction of efferent arteriole (increase
GRF)
4. Increase glomerular capillary colloidal osmotic
pressure (decrease GFR)
5. Sympathetic nerve stimulation (decrease GRF)
6. Constriction of both afferent and efferent
arterioles
Renal Autoregulation of GFR




Ability of kidney to maintain a constant GFR under
systemic changes.
 Achieved through effects of locally produced
chemicals on the afferent arterioles.
When MAP drops to 70 mm Hg, afferent arteriole
dilates.
When MAP increases, vasoconstrict afferent
arterioles.
Tubuloglomerular feedback:
 Increased flow of filtrate sensed by macula densa
cells in thick ascending LH.

Signals afferent arterioles to constrict.
Reabsorption of Salt and H20

Return of most of the molecules and
H20 from the urine filtrate back into the
___________ capillaries.
 About
180 L/day of ultrafiltrate produced;
however, only 1–2 L of urine excreted/24
hours.
Tubular Reabsorption:




97-99% of water and solutes are filtered and put
back into the body
Reabsorption sites: ________________,
__________________, ________________
Reabsorption processes: ________,
___________, ________ transport (glucose,
amino acids, some electrolytes)
Glucose and amino acids are especially
reabsorbed via their association with Na in the
proximal tubules
Tubular Reabsorption:




Chloride: reabsorbed in the thick segments of the
ascending limb of the loop of Henle
Glucose: if threshold exceeded – some loss in urine
(diabetes mellitus)
Electrolytes: absorbed by active transport and some by
diffusion
Na: by active transport in many parts, goes into
peritubular capillaries and then increases osmotic
pressure, is an increase in concentration of Na around
the tissues of the nephrons
Proximal Convoluted Tubule

Reabsorption of H20 by osmosis, cannot occur
without active transport:


PCT epithelial cells have lower [Na+].
Low permeability of plasma membrane to Na+.
transport of Na+ out of the cell by Na+/K+
pumps.
 Active

Favors [Na+] gradient:

Na+ diffusion into cell.
PCT

(continued)
Na+/K+ ATPase pump extrudes Na+.
 Creates
potential difference across the wall
of the tubule
 Electrical gradient causes Cl- movement
towards higher [Na+].
 H20 follows by osmosis.
Salt and Water Reabsorption in
Proximal Tubule
Insert fig. 17.14
Significance of PCT Reabsorption


65% Na+, Cl-, and H20 reabsorbed across the
PCT into the vascular system.
90% K+ reabsorbed.
Osmolality of Different Regions of
the Kidney
Insert fig. 17.19
Countercurrent Multiplier
What happens when you eat pizza or foods
with lots of salt?
 Why? Because osmolality is disrupted, to
much salt, not enough water
 What happens when you drink lots of water?
 _________________________
 Why? Because osmolality is disrupted, to
much water, not enough salt
 Must control how much salt is in your body
as well as how much water

Vasa Recta



Countercurrent
exchange.
Recycles NaCl in
medulla.
Transports H20
from interstitial
fluid.
Insert fig. 17.17
Collecting Duct

Medullary area impermeable to high [NaCl]
that surrounds it.
 The


walls of the CD are permeable to H20.
H20 is drawn out of the CD by osmosis.
Permeable to H20 depends upon the
presence of ADH.
Secretion


Secretion of substances from the ___________
capillaries into interstitial fluid.
 Then transported into lumen of tubule, and into the
urine.
Allows the kidneys to rapidly eliminate certain potential
toxins.
Atrial Natriuretic Peptide
Produced by atria (heart) due to stretching
of walls.
 Antagonist to aldosterone.
 Increases Na+ and H20 excretion.
 Acts as an endogenous diuretic.

Kidney Diseases

Acute renal failure:
 Ability
of kidneys to excrete wastes and regulate
homeostasis of blood volume, pH, and electrolytes
impaired.



Rise in blood [creatinine].
Decrease in renal plasma clearance of creatinine.
Glomerulonephritis:
 Inflammation
of the glomeruli.
 Autoimmune disease by which antibodies have been
raised against the glomerulus basement membrane.

Leakage of protein into the urine.
Kidney Diseases

(continued)
Renal insufficiency:
 Nephrons
are destroyed.
 Clinical manifestations:
Salt and H20 retention.
 Uremia.
 Elevated plasma [H+] and [K+].
