Rania HARATI, PhD
Associate Professor
Department of Pharmacy Practice & Pharmacotherapeutics
College of Pharmacy - University of Sharjah
Room M122 - Bldg M23
E-mail: rharati@sharjah.ac.ae
Human Anatomy & Physiology II
Course No. 1102-120 - Summer 2022/2023
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OUTLINE
 Overview of the main structures and functions of
the urinary system
 The major features of the kidneys
 Urine Formation
 Urinary Disease
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Reading Assignment
Reading Assignment:
1. Essentials of human Anatomy and Physiology by Elaine
Marieb, 10th or 11th Edition – selected sections of Chapter 15
“The Urinary System”.
2. Pathophysiology for the Health Professionals by Barbara
Gould, 4th Edition - selected sections of Chapter 21 “Urinary
System Disorders”.
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Review of the Urinary System
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The Urinary System: Main Structures
The urinary system (or the excretory system) is a body organ system
consisting of the kidneys, the ureter, the urinary bladder and the
urethra.
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The Urinary System: Main Functions
The purpose of the urinary system is to:
1. Remove metabolic wastes (nitrogenous and acidic): the kidneys filter
gallons of fluid from the bloodstream. They then process this filtrate,
allowing wastes and excess ions to leave the body in urine while
returning needed substances to the blood in just the right proportions.
2. Remove hormones, drugs, toxins and other foreign material from the
body
3. Regulate water, electrolytes, and acid-base balance in the body: the
kidneys regulate the blood volume and chemical makeup to maintain the
proper balance between water and salts and between acids and bases.
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The Urinary System: Main Functions
4. Secrete erythropoietin: The hormone erythropoietin released by the
kidneys stimulates red blood cell production in bone marrow
5. Activate vitamin D: Kidney cells convert vitamin D to its active form.
6. Regulate blood pressure through the renin angiotensin-aldosterone
system: By producing the enzyme renin, kidneys help regulate blood
pressure.
Note: The kidneys alone perform the functions just described and manufacture urine in the
process. The other organs of the urinary system (the paired ureters and the single urinary
bladder and urethra) provide temporary storage reservoirs for urine or serve as
transportation channels to carry it from one body region to another.
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The Kidneys
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The Kidneys: Shape & Location
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The Kidneys: Gross Anatomy
 The kidneys are covered by a fibrous capsule and embedded in fat.
 When a kidney is cut lengthwise, three distinct regions become
apparent:
 the renal cortex: outer layer (light in color), in which the majority of the
glomeruli are located.
 the renal medulla: inner section of tissue (a darker reddish-brown
area), which consists primarily of the tubules and collecting ducts.
 Inside the medulla (lateral to the hilum) lie the renal pelvis, through
which urine flows into the ureter.
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The Kidneys: Gross Anatomy
 The renal medulla has many basically triangular regions with a striped
appearance, the renal or medullary pyramids.
 The pyramids are separated by extensions of cortexlike tissue, the renal
columns.
 Extensions of the pelvis, calyces collect urine, which continuously drains
from the tips of the pyramids into the renal pelvis. Urine then flows from
the pelvis into the ureter, which transports it to the bladder for temporary
storage.
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The Kidneys: Blood Supply
 The kidneys continuously cleanse the blood and adjust its composition,
so they have a rich blood supply:
• The arterial supply of each kidney is the renal artery.
• The venous blood draining from the kidney flows through the renal
veins.
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The Bladder
• The bladder is composed of smooth muscle that form an
expandable sac.
• It has openings for the two ureters to bring urine in and an outlet
for the urethra through which urine flows out of the body.
• The renal pelvis, calyces, ureters, and bladder are lined with
transitional epithelium that is not permeable to water and can
resist the irritation of constant contact with urine.
• The mucosa lining the urinary tract is continuous through the
urethra, bladder, and ureter to the pelvis of the kidney →
Organisms can easily enter the system through the urethra, and
this continuous mucosa facilitates the spread of infection
through the urinary tract (an ascending infection).
Urine Formation
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Urine Formation
 Nephrons, the structural and functional units of the kidneys,
are responsible for forming urine.
 The renal collecting ducts collect fluid from nephrons and
transport it to the renal pelvis.
 Urine flows through the renal pelvis into the ureter, which
transports it to the bladder for temporary storage.
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The Nephrons of the Kidneys (Microscopic Anatomy)
 Nephrons are the structural and functional units of the kidneys
and, as such, are responsible for forming urine.
 In addition, there are thousands of collecting ducts, each of
which collects fluid from several nephrons and conveys it to the
renal pelvis.
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The Nephrons of the Kidneys
Each nephron consists of two
main structures:
a renal corpuscle and a renal
tubule.
• Each renal corpuscle consists
of a glomerulus, which is a
knot of capillaries, and a cupshaped hollow structure that
completely surrounds the
glomerulus
called
the
glomerular
capsule
or
Bowman’s capsule.
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The Nephrons of the Kidneys
The inner (visceral)
layer of the capsule
is made up of highly
modified octopuslike
cells
called
podocytes.
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The Nephrons of the Kidneys
The renal tubule:
• Makes up the rest of the
nephron
Has three different regions of :
• the proximal convoluted
tubule (PCT)
• the nephron loop, or loop of
Henle
• the distal convoluted tubule
(DCT).
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The Nephrons of the Kidneys
 Each and every nephron is
associated with two capillary
beds:
the
glomerulus
(mentioned earlier) and the
peritubular capillary Bed.
 The glomerulus is both fed and
drained by arterioles:
- The afferent arteriole, is the
“feeder vessel”
- The efferent arteriole receives
the blood that has passed through
the glomerulus.
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Note: Filtrate is the liquid that is
formed in the kidneys while urine
formation is taking place. When
the filtrate has been processed in
the tubules and collecting ducts, it
is considered to be urine.
The Nephrons of the Kidneys
 The
glomerulus
or
glomerular
capillaries: form the filtration unit for
the blood.
 Because Glomerular capillaries is fed
and drained by arterioles, which are
high-resistance vessels, and because
the afferent arteriole has a larger
diameter than the efferent, → blood
pressure in the glomerular capillaries is
much higher than in other capillary
beds.
This extremely high pressure forces fluid
and solutes (smaller than proteins) out of
the blood into the glomerular capsule.
Note: Unlike the high-pressure glomerulus,
peritubular capillaries are low-pressure,
porous vessels adapted for absorption
instead of filtration.
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Urine Formation
 Urine formation is a result of three processes:
1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion
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Urine Formation
1. Glomerular filtration
 Occurs in the glomerulus that acts as a filter.
 is a nonselective, passive process in which fluid passes from the
blood into the glomerular capsule.
 Once in the capsule, the fluid is called filtrate, and it is essentially
blood plasma without blood proteins.
(proteins and blood cells are too large to pass through the filtration
membrane. Appear in the urine, → there is some problem with the
glomerular filters)
 Normal systemic blood pressure → filtrate will be formed.
 If arterial blood pressure drops too low → glomerular pressure
becomes inadequate to force substances out of the blood into
the tubules → filtrate formation stops.
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The Nephrons of the Kidneys
An abnormally low urinary output is called:
 Oliguria if it is between 100 and 400 ml/day: usually indicates
that glomerular blood pressure is too low to cause filtration.
 anuria if it is less than 100 ml/day, may also result from
transfusion reactions and acute inflammation or from crush
injuries of the kidneys.
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Urine Formation
2. Tubular Reabsorption
 The filtrate contains many useful substances (including water,
glucose, amino acids, and ions), which must be reclaimed from
the filtrate and returned to the blood by tubular reabsorption.
 Tubular reabsorption begins as soon as the filtrate enters the
proximal convoluted tubule.
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Urine Formation
2. Tubular Reabsorption
 The tubule cells take up needed substances from the filtrate and
then passing them out into the extracellular space, from which
they are absorbed into peritubular capillary blood.
 There is an abundance of carriers for substances that need to be
retained, and few or no carriers for substances of no use to the
body. Needed substances (for example, glucose and amino
acids) are usually entirely removed from the filtrate.
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Limit on reabsorption – The transport or tubular maximum
Limit on reabsorption
If a substance such as glucose is present in excessive amounts in the
filtrate, there are insufficient carrier molecules in the tubules for complete
reabsorption into the blood in the peritubular capillaries. Therefore the
excess glucose is present in the urine. This limit on reabsorption is called
the transport or tubular maximum (e.g., approximately 310 mg/min for
glucose). Thus, persistent glucosuria is an indication of hyperglycemia
associated with diabetes mellitus.
Urine Formation
2. Tubular Reabsorption
Various ions are reabsorbed or allowed to go out in the urine,
according to what is needed at a particular time to maintain the
proper pH and electrolyte composition of the blood.
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Urine Formation
3. Tubular Secretion (tubular reabsorption in reverse)
 This process seems to be important for getting rid of substances
not already in the filtrate (such as certain drugs, excess
potassium), or as an additional means for controlling blood pH.
 Some substances, such as hydrogen and potassium ions (H+ and
K+) and nitrogenous waste such as creatinine, also move from
the blood of the peritubular capillaries through the tubule cells
or from the tubule cells themselves into the filtrate to be
eliminated in urine.
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Urine Formation
Note: Nitrogenous waste products are poorly reabsored if not at all
(they are found in high concentrations in urine excreted from the
body). These include the following:
• Urea, formed by the liver as an end product of protein
breakdown when amino-acids are used to produce energy.
• Uric acid, released when nucleic acids are metabolized.
• Creatinine, associated with creatine metabolism in muscle tissue
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Composition of Blood, Filtrate, and Urine
ml
ml
Urine is the nitrogenous liquid form of waste that is excreted from the body with the
help of kidneys through the process of urination. Filtrate is the liquid that is formed
in the kidneys while urine formation is taking place. When the filtrate has been
processed in the tubules and collecting ducts, it is considered to be urine.
Glomerular Filtration Rate (GFR)
GFR = Rate at which the filtrate forms in Bowman’s space
GFR = Kf x ΔP
Normal values of GFR = 90 - 140 ml/min
Kf (filtration coefficient) invariant constant 10-15 ml/min/mmHg
Kf ~ 12 ml/min/mmHg
ΔP (hydrostatic pressures in glomerular capillaries and Bowman’s
space & oncotic pressure) = 10 mmHg
THEREFORE:
GFR = 12 ml/min/mmHg x 10 mmHg = 120 ml/min
hydrostatic and two oncotic pressures affect transcapillary fluid exchange.
Hydrostatic pressure: the pressure that any fluid in a confined space exerts
Oncotic pressure: the pressure exerted by plasma proteins on the capillary wall.
Glomerular Filtration Rate (GFR)
 The pressure in the glomerular capillaries (controlled by the dual
arterioles) is one factor that determines the glomerular filtration
rate (GFR).
 For instance, if the afferent arteriole is dilated and the efferent
arteriole is constricted, hydrostatic pressure in the glomerular
capillaries will increase, and GFR will increase.
Control of Glomerular Filtration Rate (GFR)
Control of Glomerular Filtration Rate (GFR)
The degree of constriction in the arterioles is controlled primarly by
three factors:
1. Local Autoregulation: Autoregulation refers to the small, local
reflex adjustments in the diameter of the arterioles that are
made in response to minor changes in blood flow in the kidneys.
This adjustment maintains the normal filtration rate.
2. The Sympathetic nervous system: (SNS) increases
vasoconstriction in both arterioles when stimulated.
3. Renin-angiotensin system: For instance, to maintain pressure in the
glomerulus and therefore keep the glomerular filtration rate steady,
angiotensin II constricts both the efferent and afferent arteriole, but with a
much greater effect on the efferent arteriole. Remember, the effect of
angiotensin II is greater on the efferent arteriole. This means that the blood
entering the glomerulus has a much harder time leaving it because the exit is
far smaller than the entrance. This causes a backup of blood in the glomerulus,
increases the pressure within it and, therefore, keeps the GFR at an
appropriate rate.
Hormones control the reabsorption of fluid and electrolytes
• Antidiuretic hormone (ADH): from the posterior pituitary gland.
It controls water reabsorption by altering the permeability of the
distal convoluted tubule and the collecting duct.
• Aldosterone: secreted from the adrenal cortex. It controls
sodium and water reabsorption by exchanging the sodium ions
for potassium or hydrogen ions in the distal convoluted tubule.
• Atrial natriuretic hormone: secreted from the heart. It reduce
sodium and fluid reabsorption in the kidneys.
Activities:
Predict the effect of the following factors on the blood pressure:
 The renin-angiotensin-aldosterone system
 Epinephrine & norepinephrine
 Anti-diuretic hormone (vasopressin)
 Atrial natriuretic peptide.
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