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Blood, Sweat and Tears (and urine!)
Ion Regulation: Excretory System
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You are a sack of soup, with the soup made
of water, ions and other substances
Volume and composition of interstitial fluids
(surrounds the cells) must be kept constant
Maintaining homeostasis is the job of the
excretory system
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Blood as fast
food…vampire bats
produce very dilute
urine when feeding
Kangaroo rats
never see free
water…crystals in
urine
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Water enters and leaves the body by osmosis
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Concentrations of ions need to remain stable
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Excretory organs (kidneys) control the volume of
interstitial fluids
– Filter out excess water and metabolic wastes
– Don’t let cells and large molecules leave
– Use passive transport of water
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Metabolic wastes in mammals
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carbohydrates and fats produce carbon
dioxide and water
proteins and nucleic acids produce
nitrogenous wastes (nitrogen-containing) as
well as CO2 and H2O
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ex. Ammonia, NH3
 ammonia build up is toxic, therefore it is
converted to urea
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Functions of Excretory System
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excretion of metabolic waste
 eliminates urea
maintenance of water-salt balance
 regulates blood pressure by regulating volume
maintenance of acid-base balance
 excretes extra H+ to keep blood pH at about 7.4
secretion of hormones
 assist the endocrine system (calcitrol and
erythropoietin)
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The Mammalian Kidney
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The kidneys are bean-shaped excretory
organs in vertebrates
Part of the urinary system, the kidneys filter
wastes (especially urea) from the blood and
excrete them, along with water, as urine
The adjective meaning “kidney-related” is
renal
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Location
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posterior part of the abdomen
one on each side of the spine; the right kidney sits just
below the liver, the left below the diaphragm and adjacent
to the spleen
above each kidney is an adrenal gland (also called the
suprarenal gland)
at the vertebral level T12 to L3, and the right kidney usually
lies slightly lower than the left in order to accommodate the
liver
upper parts of the kidneys are partially protected by the
eleventh and twelfth ribs
each kidney is surrounded by two layers of fat (the perirenal
fat and the pararenal fat) which help to cushion it
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1.
Kidneys produce urine.
2.
Ureters transport urine
3.
Urinary bladder stores urine
4.
Urethra passes urine to outside
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Blood supply
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each kidney filters blood that comes in
through the renal artery
the renal artery branches into arterioles
supplying blood to glomerular arterioles
filtered blood is collected into renal venules
and leaves the kidney via the renal vein.
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Nephron: The basic unit of a kidney
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Nephron
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There are more than a million nephrons in
each normal adult human kidney.
Nephrons:
1.
Filter the blood.
2.
Reabsorb what’s needed
3.
Secrete what’s not needed
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Structures of the Nephron
1. The Glomerulus
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main filter, located in the Bowman’s capsule
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resembles a twisted mass of tiny tubes through which the
blood passes.
semipermeable, allows water and soluble wastes to pass
through using concentration gradients (passive transport)
moves water and solutes, except proteins, from blood
plasma into the Bowman’s capsule (will form urine)
filtered blood passes out of the glomerulus into the arteriole
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Glomerulus and Bowman’s Capsule
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2. Bowman's Capsule
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part of main filter, contains the nephron, the
glomerulus
– within the capsule, the blood is filtered through
the glomerulus and then passes out via the
arteriole
receives filtrate from glomerulus
filtered water and aqueous wastes are passed out
of the Bowman's capsule into the proximal tubule
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 49.18(TE Art)
Bowman's
capsule
Filtration
Glomerulus
Reabsorption to blood
Secretion from
blood
Renal tubule
Excretion
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3. Renal tubule
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in charge of reabsorption and secretion
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most of the water and dissolved solutes that enter
the glomerular filtrate must be returned to the
blood.
– reabsorption of glucose and amino acids, is
driven by active transport carriers
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secretion of waste products involves transport
across capillary membranes and kidney tubules.
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a) Proximal tubule
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The glomerular filtrate passes first into the proximal
convolute tubule.
Energy dependent mechanisms reabsorb all of the
following constituents
– glucose
– amino acids
– potassium
– sodium - about 80% reabsorbed
– bicarbonate
active secretion also transports other compounds e.g.
penicillin
passive reabsorption of water and chloride.
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Transport mechanisms in Proximal Cells
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b) Loop of Henle
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U-shaped tube that consists of a descending
limb and ascending limb
primary role is to concentrate the salt in the
interstitium, the tissue surrounding the loop
– actively reabsorbs sodium ions
– passively reabsorbs chloride and
potassium ions
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descending limb of loop is permeable to
water but completely impermeable to salt
As the filtrate descends deeper into the
hypertonic interstitium of the renal medulla,
water flows freely out of the descending limb
by osmosis
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Unlike the descending limb, the ascending limb of
Henle's loop is impermeable to water
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actively pumps sodium out of the filtrate,
generating a hypertonic interstitium
filtrate becomes hypotonic
hypotonic filtrate is passed to the distal tubule in
the renal cortex.
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Reabsorption of Salt and Water
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Osmotic Gradients In Kidney
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c) Distal tubule
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similar to the proximal tubule in structure and
function
active transport of ions is regulated by the
endocrine system
– some hormones cause reabsorption of ions,
others cause excretion
after travelling the length of the distal convoluted
tubule, only 3% of water remains, and the
remaining salt content is negligible
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4. Collecting Duct
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a pipe-like channel, where urine is concentrated
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normally impermeable to water
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becomes permeable in the presence of antidiuretic
hormone, water is re-absorbed by osmosis
levels of ADH determine whether urine will be
concentrated or dilute (can reabsorb ¾ of water)
reabsorbed water returns to blood
Urine leaves the collecting ducts and enters the ureters to
go to the bladder
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Summary
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Regulation of Kidneys
Antidiuretic Hormone (ADH)
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ADH is polypeptide hormone
secreted by the posterior pituitary
gland .
Its principal action is to regulate the
amount of water excreted by the
kidneys.
ADH, known also as vasopressin,
causes the kidneys to resorb water
directly from the distal tubules, thus
concentrating the salts and waste
products in the liquid, which will
eventually become urine.
ADH secretion by the pituitary is
regulated by neural connections
from the hypothalamus, which is
believed to monitor either the
volume of blood passing through it
or the concentration of water in the
blood.
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Regulation of Kidneys
Antidiuretic Hormone (ADH)
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Dehydration or body stress
will raise ADH secretion
and water will be retained.
Alcohol inhibits ADH
secretion.
Failure of the pituitary to
produce ADH results in
diabetes insipidus.
In pharmacological doses
ADH acts as a
vasoconstrictor. The
structure and chemical
synthesis of ADH was
announced (1953) by
Nobel laureate Vincent Du
Vigneaud and others.
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Hormones Control Homeostatic Functions
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Antidiuretic hormone
– Stimulates reabsorption of water by the
kidneys.
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Aldosterone
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Aldosterone is a steroid hormone
produced by the outer-section of
the adrenal cortex in the adrenal
gland to regulate sodium and
potassium balance in the blood.
It is synthesized from cholesterol
by aldosterone synthase
Aldosterone acts by increasing
sodium reabsorption from the
distal tubule and the collecting
duct.
Aldosterone is responsible for the
reabsorption of about 2% of
filtered sodium in the kidneys,
which is nearly equal to the entire
sodium content in human blood
under normal conditions.
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Aldosterone
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Blood pressure receptors in the juxtaglomerular
apparatus near the glomerulus detect low blood
pressure.
Specialized cells within th structure release rennin,
an enzyme that converts angiotensinogen, a
plasma protein produced by the liver, into
angiotensin.
Angiotensin causes the constriction of of blood
vessels and raises blood pressure.
Secondly, angiotensin causes release of
aldosterone from the adrenal glands to increase
sodium reabsorption and increase blood pressure.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
blood
Fig.Low49.22(TE
Art)
flow
Low blood
pressure
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2
Negative
feedback
Distal
convoluted
tubule
Juxtaglomerular
apparatus
Angiotensinogen
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Renin
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Afferent
arteriole
Glomerulus
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Increased
blood
volume
Angiotensin II
Proximal
convoluted
tubule
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Adrenal
cortex
Efferent
arteriole
Bowman's
capsule
Loop
of Henle
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Aldosterone
Kidney
Increased NaCl
and H2O
reabsorption
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Dialysis and kidney transplants
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Generally, humans can live normally with just one kidney.
Only when the amount of functioning kidney tissue is
greatly diminished will renal failure develop.
If renal function is impaired, various forms of medications
are used, while others are contraindicated. Provided that
treatment is begun early, it may be possible to reverse
chronic kidney failure due to diabetes or high blood
pressure.
If creatinine clearance (a measure of renal function) has
fallen very low ("end-stage renal failure"), or if the renal
dysfunction leads to severe symptoms, dialysis is
commenced.
Dialysis is a medical procedure, performed in various
different forms, where the blood is filtered outside of the
body.
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Kidney Dialysis Machine
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Kidney Dialysis
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Kidney Transplant
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Kidney transplantation is the only cure for end stage renal failure; dialysis, is a
supportive treatment; a form of "buying time" to bridge the inevitable wait for a
suitable organ.
The first successful kidney transplant was announced on March 4, 1954 at
Peter Bent Brigham Hospital in Boston. The surgery was performed by Dr.
Joseph E. Murray, who was awarded the Nobel Prize in Medicine in 1990 for
this feat.
There are two types of kidney transplants: living donor transplant and a
cadaveric (dead donor) transplant.
When a kidney from a living donor, usually a blood relative, is transplanted into
the patient's body, the donor's blood group and tissue type must be judged
compatible with the patient's, and extensive medical tests are done to
determine the health of the donor.
Before a cadaveric donor's organs can be transplanted, a series of medical
tests have to be done to determine if the organs are healthy. Also, in some
countries, the family of the donor must give its consent for the organ donation.
In both cases, the recipient of the new organ needs to take drugs to suppress
their immune system to help prevent their body from rejecting the new kidney.
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Kidney Transplant
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Kidney transplant
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Kidney Transplant
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Structure
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In a normal human adult, each kidney is about 11 cm long and about 5
cm thick, weighing 150 grams.
The kidneys are "bean-shaped" organs, and have a concave side facing
inwards (medially).
On this medial aspect of each kidney is an opening, called the hilum,
which admits the renal artery, the renal vein, nerves, and the ureter.
The outermost portion of the kidney is called the renal cortex, which
sits directly beneath the kidney's loose connective tissue capsule.
Deep to the cortex lies the renal medulla which is divided into 10-20
renal pyramids in humans.
Each pyramid together with the associated overlying cortex forms a
renal lobe.
The tip of each pyramid (called a papilla) empties into a calyx, and the
calyces empty into the renal pelvis. The pelvis transmits urine to the
urinary bladder via the ureter
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