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URINARY SYSTEM
Swetaba B. Besh
Assistant professor
Department of Pharmacy, Pharmacology
Sumandeep Vidyapeeth Deemed to be University
• Urinary system is vital excreatory system of human body also known as a Renal system(it
produce, stores and eliminates urine).
• The urinary system plays a vital part in maintaining homeostasis of water and
electrolytes within the body.
• The kidneys produce urine that contains metabolic waste products, including the
nitrogenous compounds urea and uric acid, excessions and some drugs.
• The main functions of the kidneys are: formation of urine, maintaining water, electrolyte
and acid–base balance, excretion of waste products, production and secretion of
erythropoietin (the hormone that stimulates formation of red blood cells production) and
secretion of renin (an important enzyme in the control of blood pressure).
• Urine is stored in the bladder and excreted by the process of micturition.
ANATOMY OF URINARY SYSTEM
• The urinary system is the main excretory system
and consists of the following structures:
 2 Kidneys, which produce and secrete urine
 2 Ureters that convey the urine from the kidneys
to the surinary bladder
 The urinary bladder- which collects and stores
urine until it is voided.
 The urethra through which urine leaves
the body. it contain internal and external sphincter.
 Internal sphincter act as a door between urinary
bladder and urethra.
 External sphincter located between Urethra and
external environment.
KIDNEY
• Kidneys are bean-shaped organs, about 11 cm long, 6 cm
wide, 3 cm thick and weigh 150 g.
• The kidneys lie on the posterior abdominal wall, one
on each side of the vertebral column, behind the
peritoneum and below the diaphragm.
• They extend from the level of the 12th thoracic
vertebra to the 3rd lumbar vertebra, receiving some
protection from the lower rib cage.
• The right kidney is usually slightly lower than the left,
probably because of the considerable space occupied by
the liver.
• kidneys present in Retroperitoneal space (behind
peritoneum).
Organs associated with the kidneys
• As the kidneys lie on either side of the
vertebral column, each is associated with
different structures.
Right kidney
• Superiorly – the right adrenal gland
• Anteriorly – the right lobe of the liver, the
duodenum and the hepatic flexure of the colon
• Posteriorly – the diaphragm, and muscles of
the posterior abdominal wall.
Left kidney
• Superiorly – the left adrenal gland
• Anteriorly – the spleen, stomach, pancreas,
jejunum and splenic flexure of the colon
• Posteriorly – the diaphragm and muscles of the
posterior abdominal wall.
• There are three areas of tissue that can be
distinguished when a longitudinal section of
the kidney is viewed with open eye:
• An outer fibrous capsule, surrounding the
kidney
• The cortex, a reddish-brown layer of tissue
immediately below the capsule and outside
the renal pyramids
• The medulla, the innermost layer,
consisting of pale conical-shaped striations,
the renal pyramids.
• Approx cortex and inner medulla made 18
cone shaped renal lobes.
• The hilum is the concave medial
border of the kidney where the renal
artery enters and ureter and renal vein
exit.
• Urine formed within the kidney passes
through a renal papilla at the apex of a
pyramid into a minor calyx.
• Several minor calyces merge into a
major calyx and two or three major
calyces combine forming the renal
pelvis, a funnel shaped structure that
narrows when it leaves the kidney as
the ureter.
• The walls of the calyces and renal pelvis are lined with transitional epithelium and contain
smooth muscle.
• Peristalsis, intrinsic contraction of smooth muscle, propels urine through the calyces, renal
pelvis and ureters to the bladder.
• The kidney contains about 1–2 million functional units, the nephrons, and a much smaller
number of collecting ducts.
• The collecting ducts transport urine through the pyramids to the calyces, giving the pyramids
their striped appearance. The collecting ducts are supported by connective tissue, containing
blood vessels, nerves and lymph vessels.
Function of Urinary system or Kidneys
• Formation of urine
• Maintain water, electrolytes, acid- base balance.
• Production and secretion of erythropoietin
• Production and secretion of renin.
NEPHRON
• The nephron is essentially a tubule closed at one end
that joins a collecting duct at the other end.
• The closed or blind end is indented to form the cup-
shaped glomerular capsule (Bowman’s capsule),
which almost completely encloses a network of tiny
arterial capillaries, the glomerulus.
• Continuing from the glomerular capsule, the
remainder of thenephron is about 3 cm long and
described in three parts:
1. the proximal convoluted tubule
2. the medullary loop (loop of Henle)
3. the distal convoluted tubule, leading into a
collecting duct
• The collecting ducts unite, forming larger ducts that empty into the minor calyces.The
kidneys receive about 20% of the cardiac output.
• After entering the kidney at the hilum, the renal artery divides into smaller arteries and
arterioles.
• In the cortex an arteriole, the afferent arteriole, enters each glomerular capsule and then
subdivides into a cluster of tiny arterial capillaries, forming the glomerulus.
• Between these capillary loops are connective tissue phagocytic mesangial cells, which
are part of the monocyte–macrophage defence system.
• The blood vessel leading away from the glomerulus is the efferent arteriole.
• The afferent arteriole has a larger diameter than the efferent arteriole, which increases
pressure inside the glomerulus and drives filtration across the glomerular capillary walls.
• The efferent arteriole divides into a second peritubular capillary network, which wraps
around the remainder of the tubule, allowing exchange between the fluid in the tubule and
the blood stream.
• This maintains the local supply of oxygen and nutrients and removes waste products.
• Venous blood drained from this capillary bed eventually leaves the kidney in the renal
vein, which empties into the inferior vena cava.
• The walls of the glomerulus and the glomerular capsule consist of a single layer of
flattened epithelial cells.
• The glomerular walls are more permeable than those of other capillaries.
• The remainder of the nephron and the collecting duct are formed by a single layer of
simple squamous epithelium.
• Renal blood vessels are supplied by both sympathetic and parasympathetic nerves.
• The presence of both divisions of the autonomic nervous system controls renal blood
vessel diameter and renal blood flow independently of autoregulation .
Ureter
• The ureters carry urine from the kidneys to the urinary bladder. They are about 25–30 cm long
with a diameter of approximately 3 mm. The ureter is continuous with the funnel-shaped renal
pelvis.
• It passes downwards through the abdominal cavity, behind the peritoneum in front of the
psoas muscle into the pelvic cavity, and passes obliquely through the posterior wall of the
bladder
Structure
The walls of the ureters consist of three layers of tissue:
• an outer covering of fibrous tissue, continuous with the fibrous capsule of the kidney
• a middle muscular layer consisting of interlacing smooth muscle fibres
• an inner layer, the mucosa, composed of transitional epithelium
Function
• Peristalsis is an intrinsic property of the smooth muscle layer that propels urine along the
ureter.
• Peristaltic waves occur several times per minute, increasing in frequency with the volume of
urine produced.
Urinary Bladder
• The urinary bladder is a reservoir for urine. It lies in the pelvic cavity and its size and position vary,
depending on the volume of urine it contains. When distended, the bladder rises into the abdominal
cavity.
• The bladder wall is composed of three layers:
1. The outer layer of loose connective tissue, containing blood and lymphatic vessels and nerves,
covered on the upper surface by the peritoneum
2. The middle layer, consisting of interlacing smooth muscle fibres and elastic tissue loosely arranged
in three layers. This is called the detrusor muscle and when it contracts, it empties the bladder
3. The inner mucosa, composed of transitional epithelium that readily permits distension of the bladder
as it fills.
• When the bladder is empty the inner lining is arranged in folds, or rugae, which gradually disappear as
it fills.
• The muscle layer has two parts, an inner layer of smooth muscle that is under autonomic nerve control,
and an outer layer of striated (voluntary) muscle surrounding it.
• The striated muscle forms the external urethral sphincter and is under voluntary control. The mucosa is
supported by loose fibroelastic connective tissue containing blood vessels and nerves.
Urethra
• The urethra is a canal extending from the neck of the bladder to the exterior, at
the external urethral orifice.
• The external urethral orifice is guarded by the external urethral sphincter,
which is under voluntary control.
• The striated muscle forms the external urethral sphincter and is under voluntary
control.
• The mucosa is supported by loose fibroelastic connective tissue containing
blood vessels and nerves.
• Proximally it consists of transitional epithelium while distally it is composed of
stratified epithelium.
Formation of Urine:
• The kidneys form urine, which passes to the bladder for storage prior to
excretion.
• The composition of urine reflects exchange of substances between the
nephron and the blood in the renal capillaries.
• Waste products of protein metabolism are excreted, water and electrolyte
levels are controlled and pH (acid–base balance) is maintained by excretion
of hydrogen ions.
• There are three processes involved in the formation of urine:
1. Filtration
2. Selective reabsorption
3. Secretion.
1. Filtration
• This takes place through the semipermeable
walls of the glomerulus and glomerular
capsule.
• Blood is filtered while passing through
glomerular cappilaries by filteration
membrane.
• Water and other small molecules readily pass
through, although some are reabsorbed later.
• Blood cells, plasma proteins and other large
molecules are too large to filter through and
therefore remain in the capillaries.
• Filtration takes place because there is a
difference between the blood pressure in the
glomerulus and the pressure of the filtrate in
• because the efferent arteriole is narrower than the afferent arteriole, a capillary hydrostatic
pressure of about 55 mmHg builds up in the glomerulus.
• This pressure is opposed by the osmotic pressure of the blood, provided mainly by plasma
proteins, about 4 kPa (30 mmHg), and by filtrate hydrostatic pressure of about 15 mmHg
in the glomerular capsule. The volume of filtrate formed by both kidneys each minute is
called the glomerular filtration rate (GFR). In a healthy adult the GFR is about 125
mL/min, i.e. 180 litres of filtrate are formed each day by the two kidneys.
• Nearly all of the filtrate is later reabsorbed from the kidney tubules with less than 1%, i.e. 1–
1.5 litres, excreted as urine.
• The differences in volume and concentration are due to selective reabsorption of some
filtrate constituents and tubular secretion of others.
• Autoregulation: Renal blood flow, and therefore glomerular filtration, is protected by
a mechanism called autoregulation, whereby renal blood flow is maintained at a
constant pressure across a wide range of systolic blood pressures (from around 80–200
mmHg).
• Autoregulation operates independently of nervous control, i.e. if the nerve supply to the
renal blood vessels is interrupted, autoregulation continues to operate.
• It is therefore a property inherent in renal blood vessels; it may be stimulated by
changes in blood pressure in the renal arteries or by fluctuating levels of certain
metabolites, e.g. prostaglandins.
• In severe shock, when the systolic blood pressure falls below 80 mmHg, autoregulation
fails and renal blood flow and the hydrostatic pressure decrease, impairing filtration
within the glomeruli.
Selective reabsorption
• Most reabsorption from the filtrate back into the blood takes place in the proximal
convoluted tubule, whose walls are lined with microvilli to increase surface area for
absorption.
• Many substances are reabsorbed here, including some water, electrolytes and organic
nutrients such as glucose.
• Some reabsorption is passive, but some substances, e.g. glucose, are actively
transported. Only 60–70% of filtrate reaches the medullary loop.
• Much of this, especially water, sodium and chloride, is reabsorbed in the loop, so that
only 15–20% of the original filtrate reaches the distal convoluted tubule, and the
composition of the filtrate is now very different. More electrolytes are reabsorbed here,
especially sodium, so the filtrate entering the collecting ducts is actually quite dilute.
• The main function of the collecting ducts is to reabsorb as much water as
the body needs.
• Active transport takes place at carrier sites in the epithelial membrane, using
chemical energy to transport substances against their concentration gradient.
• Some ions, e.g. sodium and chloride, can be absorbed by both active and
passive mechanisms depending on the site in the nephron.
• Some constituents of glomerular filtrate (e.g. glucose, amino acids) do not
normally appear in urine because they are completely reabsorbed unless blood
levels are excessive.
• Reabsorption of nitrogenous waste products, such as urea, uric acid and
creatinine is very limited.
• The kidneys’ maximum capacity for reabsorption of a substance is the
transport maximum, or renal threshold.
Tubular secretion
• Filtration occurs as blood flows through the glomerulus.
• Substances not required and foreign materials, e.g. drugs. Including penicillin and
aspirin, may not be entirely filtered out of the blood because of the short time it
remains in the glomerulus.
• Such substances are cleared by secretion from the peritubular capillaries into the
filtrate within the convoluted tubules.
• Tubular secretion of hydrogen ions (H+) is important in maintaining normal blood
pH.
Micturition Reflex
• Discharge of urine from the urinary bladder, called
micturition, is also known as urination or voiding.
• Micturition occurs via a combination of involuntary
and voluntary muscle contractions.
• When the volume of urine in the urinary bladder
exceeds 200–400 mL, pressure within the bladder
increases considerably, and stretch receptors in its
wall transmit nerve impulses into the spinal cord.
• These impulses propagate to the micturition center
in sacral spinal cord segments S2 and S3 and
trigger a spinal reflex called the micturition reflex.
• This reflex arc, parasympathetic impulses from the
micturition center propagate to the urinary bladder
wall and internal urethral sphincter.
• The nerve impulses cause contraction of the detrusor muscle and relaxation of
the internal urethral sphincter muscle. Simultaneously, the micturition center
inhibits somatic motor neurons that innervate skeletal muscle in the external urethral
sphincter. As a result it includes:
I. Sphincter striatum relaxation (Somatic innervation)
II. Smooth muscle sphincter are relaxed and bladder neck is opened (Sympathetic
innervation)
III. Contraction of Detrusor muscle (Parasympathetic innervation)
• On contraction of the urinary bladder wall and relaxation of the sphincters,
urination takes place.
• Urinary bladder filling causes a sensation of fullness that initiates a conscious desire
to urinate before the micturition reflex actually occurs.
• Juxtaglomerular Apparatus (JGA) releases renin.
• Renin converts Angiotensinogen into Angiotensin - I
• ACE (Angiotensinogen converting enzyme) converts Angiotensinogen – I into
Angiotensinogen - II
• Angiotensin II affects renal physiology in three main ways:
1. It decreases the glomerular filtration rate by causing vasoconstriction of the afferent
arterioles.
2. It enhances reabsorption of Na+ and water in the proximal convoluted tubule by
stimulating the activity of Na+– H+ antiporters.
3. It stimulates the adrenal cortex to release aldosterone a hormone that in turn stimulates
the principal cells in the collecting ducts to reabsorb more Na+ and secrete more K+. The
osmotic consequence of reabsorbing more Na+ is that more water is reabsorbed, which
causes an increase in blood volume and blood pressure.
Role of RAS in kidney
Role of kidneys in acid base balance
• The kidneys have two main ways to maintain acid-base balance - their
cells reabsorb bicarbonate HCO3− from the urine back to the blood and
they secrete hydrogen H+ ions into the urine. By adjusting the amounts
reabsorbed and secreted, they balance the bloodstream’s pH.
• The kidneys have two very important roles in maintaining the acid–base
balance:
1. They reabsorb bicarbonate from urine.
2. They excrete hydrogen ions into urine.
• The kidneys are slower to compensate than the lungs, but renal physiology has several
powerful mechanisms to control pH by the excretion of excess acid or base. The major,
homeostatic control point for maintaining a stable pH balance is renal excretion.
• Bicarbonate (HCO3−) does not have a transporter, so its reabsorption involves a series of
reactions in the tubule lumen and tubular epithelium. In response to acidosis, the tubular cells
reabsorb more bicarbonate from the tubular fluid, and the collecting duct cells secrete more
hydrogen and generate more bicarbonate, and ammoniagenesis leads to an increase in the
formation of the NH3 buffer.
• In response to alkalosis, the kidneys may excrete more bicarbonate by decreasing hydrogen
ion secretion from the tubular epithelial cells, and lowering the rates of glutamine
metabolism and ammonium excretion.
Disorders of Urinary System
1. Chronic kidney disease (CKD) means kidneys are damaged and can't filter blood
the way they should. The main risk factors for developing kidney disease are
diabetes, high blood pressure, heart disease, and a family history of kidney failure.
2. Acute kidney failure occurs when kidneys suddenly become unable to filter waste
products from the blood. When kidneys lose their filtering ability, harmful levels of
wastes may accumulate, and blood's chemical makeup may get out of balance.
3. Glomerulonephritis is damage to the tiny filters inside the kidneys (the
glomeruli). It's often caused by immune system attacking healthy body tissue. If
glomerulonephritis is mild, it does not usually cause any noticeable symptoms.
4. Polycystic kidney disease (PKD) is a genetic disorder that causes many fluid-
filled cysts to grow in kidneys. PKD cysts can change the shape of kidneys,
including making them much larger.
5. Nephrotic syndrome is a group of symptoms that indicate that kidneys are not working
properly. These symptoms include: too much protein in urine, called proteinuria, low
levels of a protein called albumin in blood, called hypoalbuminemia, swelling in parts
of body, called edema.
6. Dehydration occurs when you use or lose more fluid than you take in, and your body
doesn't have enough water and other fluids to carry out its normal functions.
7. Urinary tract infection (UTI): is an infection in any part of the urinary system. The
urinary system includes the kidneys, ureters, bladder and urethra. Most infections
involve the lower urinary tract — the bladder and the urethra.
8. Kidney stones: it also called renal calculi, nephrolithiasis or urolithiasis are hard
deposits made of minerals and salts that form inside your kidneys. Kidney stones can
affect any part of your urinary tract — from your kidneys to your bladder. Often, stones
form when the urine becomes concentrated, allowing minerals to crystallize and stick
together.

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ANATOMY AND PHYSIOLOGY OF URINARY SYSTEM.pptx

  • 1. URINARY SYSTEM Swetaba B. Besh Assistant professor Department of Pharmacy, Pharmacology Sumandeep Vidyapeeth Deemed to be University
  • 2. • Urinary system is vital excreatory system of human body also known as a Renal system(it produce, stores and eliminates urine). • The urinary system plays a vital part in maintaining homeostasis of water and electrolytes within the body. • The kidneys produce urine that contains metabolic waste products, including the nitrogenous compounds urea and uric acid, excessions and some drugs. • The main functions of the kidneys are: formation of urine, maintaining water, electrolyte and acid–base balance, excretion of waste products, production and secretion of erythropoietin (the hormone that stimulates formation of red blood cells production) and secretion of renin (an important enzyme in the control of blood pressure). • Urine is stored in the bladder and excreted by the process of micturition.
  • 3. ANATOMY OF URINARY SYSTEM • The urinary system is the main excretory system and consists of the following structures:  2 Kidneys, which produce and secrete urine  2 Ureters that convey the urine from the kidneys to the surinary bladder  The urinary bladder- which collects and stores urine until it is voided.  The urethra through which urine leaves the body. it contain internal and external sphincter.  Internal sphincter act as a door between urinary bladder and urethra.  External sphincter located between Urethra and external environment.
  • 4. KIDNEY • Kidneys are bean-shaped organs, about 11 cm long, 6 cm wide, 3 cm thick and weigh 150 g. • The kidneys lie on the posterior abdominal wall, one on each side of the vertebral column, behind the peritoneum and below the diaphragm. • They extend from the level of the 12th thoracic vertebra to the 3rd lumbar vertebra, receiving some protection from the lower rib cage. • The right kidney is usually slightly lower than the left, probably because of the considerable space occupied by the liver. • kidneys present in Retroperitoneal space (behind peritoneum).
  • 5. Organs associated with the kidneys • As the kidneys lie on either side of the vertebral column, each is associated with different structures. Right kidney • Superiorly – the right adrenal gland • Anteriorly – the right lobe of the liver, the duodenum and the hepatic flexure of the colon • Posteriorly – the diaphragm, and muscles of the posterior abdominal wall. Left kidney • Superiorly – the left adrenal gland • Anteriorly – the spleen, stomach, pancreas, jejunum and splenic flexure of the colon • Posteriorly – the diaphragm and muscles of the posterior abdominal wall.
  • 6. • There are three areas of tissue that can be distinguished when a longitudinal section of the kidney is viewed with open eye: • An outer fibrous capsule, surrounding the kidney • The cortex, a reddish-brown layer of tissue immediately below the capsule and outside the renal pyramids • The medulla, the innermost layer, consisting of pale conical-shaped striations, the renal pyramids. • Approx cortex and inner medulla made 18 cone shaped renal lobes.
  • 7. • The hilum is the concave medial border of the kidney where the renal artery enters and ureter and renal vein exit. • Urine formed within the kidney passes through a renal papilla at the apex of a pyramid into a minor calyx. • Several minor calyces merge into a major calyx and two or three major calyces combine forming the renal pelvis, a funnel shaped structure that narrows when it leaves the kidney as the ureter.
  • 8. • The walls of the calyces and renal pelvis are lined with transitional epithelium and contain smooth muscle. • Peristalsis, intrinsic contraction of smooth muscle, propels urine through the calyces, renal pelvis and ureters to the bladder. • The kidney contains about 1–2 million functional units, the nephrons, and a much smaller number of collecting ducts. • The collecting ducts transport urine through the pyramids to the calyces, giving the pyramids their striped appearance. The collecting ducts are supported by connective tissue, containing blood vessels, nerves and lymph vessels.
  • 9. Function of Urinary system or Kidneys • Formation of urine • Maintain water, electrolytes, acid- base balance. • Production and secretion of erythropoietin • Production and secretion of renin.
  • 10. NEPHRON • The nephron is essentially a tubule closed at one end that joins a collecting duct at the other end. • The closed or blind end is indented to form the cup- shaped glomerular capsule (Bowman’s capsule), which almost completely encloses a network of tiny arterial capillaries, the glomerulus. • Continuing from the glomerular capsule, the remainder of thenephron is about 3 cm long and described in three parts: 1. the proximal convoluted tubule 2. the medullary loop (loop of Henle) 3. the distal convoluted tubule, leading into a collecting duct
  • 11. • The collecting ducts unite, forming larger ducts that empty into the minor calyces.The kidneys receive about 20% of the cardiac output. • After entering the kidney at the hilum, the renal artery divides into smaller arteries and arterioles. • In the cortex an arteriole, the afferent arteriole, enters each glomerular capsule and then subdivides into a cluster of tiny arterial capillaries, forming the glomerulus. • Between these capillary loops are connective tissue phagocytic mesangial cells, which are part of the monocyte–macrophage defence system. • The blood vessel leading away from the glomerulus is the efferent arteriole. • The afferent arteriole has a larger diameter than the efferent arteriole, which increases pressure inside the glomerulus and drives filtration across the glomerular capillary walls.
  • 12. • The efferent arteriole divides into a second peritubular capillary network, which wraps around the remainder of the tubule, allowing exchange between the fluid in the tubule and the blood stream. • This maintains the local supply of oxygen and nutrients and removes waste products. • Venous blood drained from this capillary bed eventually leaves the kidney in the renal vein, which empties into the inferior vena cava. • The walls of the glomerulus and the glomerular capsule consist of a single layer of flattened epithelial cells. • The glomerular walls are more permeable than those of other capillaries. • The remainder of the nephron and the collecting duct are formed by a single layer of simple squamous epithelium. • Renal blood vessels are supplied by both sympathetic and parasympathetic nerves. • The presence of both divisions of the autonomic nervous system controls renal blood vessel diameter and renal blood flow independently of autoregulation .
  • 13. Ureter • The ureters carry urine from the kidneys to the urinary bladder. They are about 25–30 cm long with a diameter of approximately 3 mm. The ureter is continuous with the funnel-shaped renal pelvis. • It passes downwards through the abdominal cavity, behind the peritoneum in front of the psoas muscle into the pelvic cavity, and passes obliquely through the posterior wall of the bladder Structure The walls of the ureters consist of three layers of tissue: • an outer covering of fibrous tissue, continuous with the fibrous capsule of the kidney • a middle muscular layer consisting of interlacing smooth muscle fibres • an inner layer, the mucosa, composed of transitional epithelium Function • Peristalsis is an intrinsic property of the smooth muscle layer that propels urine along the ureter. • Peristaltic waves occur several times per minute, increasing in frequency with the volume of urine produced.
  • 14. Urinary Bladder • The urinary bladder is a reservoir for urine. It lies in the pelvic cavity and its size and position vary, depending on the volume of urine it contains. When distended, the bladder rises into the abdominal cavity. • The bladder wall is composed of three layers: 1. The outer layer of loose connective tissue, containing blood and lymphatic vessels and nerves, covered on the upper surface by the peritoneum 2. The middle layer, consisting of interlacing smooth muscle fibres and elastic tissue loosely arranged in three layers. This is called the detrusor muscle and when it contracts, it empties the bladder 3. The inner mucosa, composed of transitional epithelium that readily permits distension of the bladder as it fills. • When the bladder is empty the inner lining is arranged in folds, or rugae, which gradually disappear as it fills. • The muscle layer has two parts, an inner layer of smooth muscle that is under autonomic nerve control, and an outer layer of striated (voluntary) muscle surrounding it. • The striated muscle forms the external urethral sphincter and is under voluntary control. The mucosa is supported by loose fibroelastic connective tissue containing blood vessels and nerves.
  • 15. Urethra • The urethra is a canal extending from the neck of the bladder to the exterior, at the external urethral orifice. • The external urethral orifice is guarded by the external urethral sphincter, which is under voluntary control. • The striated muscle forms the external urethral sphincter and is under voluntary control. • The mucosa is supported by loose fibroelastic connective tissue containing blood vessels and nerves. • Proximally it consists of transitional epithelium while distally it is composed of stratified epithelium.
  • 16. Formation of Urine: • The kidneys form urine, which passes to the bladder for storage prior to excretion. • The composition of urine reflects exchange of substances between the nephron and the blood in the renal capillaries. • Waste products of protein metabolism are excreted, water and electrolyte levels are controlled and pH (acid–base balance) is maintained by excretion of hydrogen ions. • There are three processes involved in the formation of urine: 1. Filtration 2. Selective reabsorption 3. Secretion.
  • 17. 1. Filtration • This takes place through the semipermeable walls of the glomerulus and glomerular capsule. • Blood is filtered while passing through glomerular cappilaries by filteration membrane. • Water and other small molecules readily pass through, although some are reabsorbed later. • Blood cells, plasma proteins and other large molecules are too large to filter through and therefore remain in the capillaries. • Filtration takes place because there is a difference between the blood pressure in the glomerulus and the pressure of the filtrate in
  • 18. • because the efferent arteriole is narrower than the afferent arteriole, a capillary hydrostatic pressure of about 55 mmHg builds up in the glomerulus. • This pressure is opposed by the osmotic pressure of the blood, provided mainly by plasma proteins, about 4 kPa (30 mmHg), and by filtrate hydrostatic pressure of about 15 mmHg in the glomerular capsule. The volume of filtrate formed by both kidneys each minute is called the glomerular filtration rate (GFR). In a healthy adult the GFR is about 125 mL/min, i.e. 180 litres of filtrate are formed each day by the two kidneys. • Nearly all of the filtrate is later reabsorbed from the kidney tubules with less than 1%, i.e. 1– 1.5 litres, excreted as urine. • The differences in volume and concentration are due to selective reabsorption of some filtrate constituents and tubular secretion of others.
  • 19. • Autoregulation: Renal blood flow, and therefore glomerular filtration, is protected by a mechanism called autoregulation, whereby renal blood flow is maintained at a constant pressure across a wide range of systolic blood pressures (from around 80–200 mmHg). • Autoregulation operates independently of nervous control, i.e. if the nerve supply to the renal blood vessels is interrupted, autoregulation continues to operate. • It is therefore a property inherent in renal blood vessels; it may be stimulated by changes in blood pressure in the renal arteries or by fluctuating levels of certain metabolites, e.g. prostaglandins. • In severe shock, when the systolic blood pressure falls below 80 mmHg, autoregulation fails and renal blood flow and the hydrostatic pressure decrease, impairing filtration within the glomeruli.
  • 20. Selective reabsorption • Most reabsorption from the filtrate back into the blood takes place in the proximal convoluted tubule, whose walls are lined with microvilli to increase surface area for absorption. • Many substances are reabsorbed here, including some water, electrolytes and organic nutrients such as glucose. • Some reabsorption is passive, but some substances, e.g. glucose, are actively transported. Only 60–70% of filtrate reaches the medullary loop. • Much of this, especially water, sodium and chloride, is reabsorbed in the loop, so that only 15–20% of the original filtrate reaches the distal convoluted tubule, and the composition of the filtrate is now very different. More electrolytes are reabsorbed here, especially sodium, so the filtrate entering the collecting ducts is actually quite dilute.
  • 21. • The main function of the collecting ducts is to reabsorb as much water as the body needs. • Active transport takes place at carrier sites in the epithelial membrane, using chemical energy to transport substances against their concentration gradient. • Some ions, e.g. sodium and chloride, can be absorbed by both active and passive mechanisms depending on the site in the nephron. • Some constituents of glomerular filtrate (e.g. glucose, amino acids) do not normally appear in urine because they are completely reabsorbed unless blood levels are excessive. • Reabsorption of nitrogenous waste products, such as urea, uric acid and creatinine is very limited. • The kidneys’ maximum capacity for reabsorption of a substance is the transport maximum, or renal threshold.
  • 22. Tubular secretion • Filtration occurs as blood flows through the glomerulus. • Substances not required and foreign materials, e.g. drugs. Including penicillin and aspirin, may not be entirely filtered out of the blood because of the short time it remains in the glomerulus. • Such substances are cleared by secretion from the peritubular capillaries into the filtrate within the convoluted tubules. • Tubular secretion of hydrogen ions (H+) is important in maintaining normal blood pH.
  • 23. Micturition Reflex • Discharge of urine from the urinary bladder, called micturition, is also known as urination or voiding. • Micturition occurs via a combination of involuntary and voluntary muscle contractions. • When the volume of urine in the urinary bladder exceeds 200–400 mL, pressure within the bladder increases considerably, and stretch receptors in its wall transmit nerve impulses into the spinal cord. • These impulses propagate to the micturition center in sacral spinal cord segments S2 and S3 and trigger a spinal reflex called the micturition reflex. • This reflex arc, parasympathetic impulses from the micturition center propagate to the urinary bladder wall and internal urethral sphincter.
  • 24. • The nerve impulses cause contraction of the detrusor muscle and relaxation of the internal urethral sphincter muscle. Simultaneously, the micturition center inhibits somatic motor neurons that innervate skeletal muscle in the external urethral sphincter. As a result it includes: I. Sphincter striatum relaxation (Somatic innervation) II. Smooth muscle sphincter are relaxed and bladder neck is opened (Sympathetic innervation) III. Contraction of Detrusor muscle (Parasympathetic innervation) • On contraction of the urinary bladder wall and relaxation of the sphincters, urination takes place. • Urinary bladder filling causes a sensation of fullness that initiates a conscious desire to urinate before the micturition reflex actually occurs.
  • 25. • Juxtaglomerular Apparatus (JGA) releases renin. • Renin converts Angiotensinogen into Angiotensin - I • ACE (Angiotensinogen converting enzyme) converts Angiotensinogen – I into Angiotensinogen - II • Angiotensin II affects renal physiology in three main ways: 1. It decreases the glomerular filtration rate by causing vasoconstriction of the afferent arterioles. 2. It enhances reabsorption of Na+ and water in the proximal convoluted tubule by stimulating the activity of Na+– H+ antiporters. 3. It stimulates the adrenal cortex to release aldosterone a hormone that in turn stimulates the principal cells in the collecting ducts to reabsorb more Na+ and secrete more K+. The osmotic consequence of reabsorbing more Na+ is that more water is reabsorbed, which causes an increase in blood volume and blood pressure. Role of RAS in kidney
  • 26. Role of kidneys in acid base balance • The kidneys have two main ways to maintain acid-base balance - their cells reabsorb bicarbonate HCO3− from the urine back to the blood and they secrete hydrogen H+ ions into the urine. By adjusting the amounts reabsorbed and secreted, they balance the bloodstream’s pH. • The kidneys have two very important roles in maintaining the acid–base balance: 1. They reabsorb bicarbonate from urine. 2. They excrete hydrogen ions into urine.
  • 27.
  • 28. • The kidneys are slower to compensate than the lungs, but renal physiology has several powerful mechanisms to control pH by the excretion of excess acid or base. The major, homeostatic control point for maintaining a stable pH balance is renal excretion. • Bicarbonate (HCO3−) does not have a transporter, so its reabsorption involves a series of reactions in the tubule lumen and tubular epithelium. In response to acidosis, the tubular cells reabsorb more bicarbonate from the tubular fluid, and the collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to an increase in the formation of the NH3 buffer. • In response to alkalosis, the kidneys may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering the rates of glutamine metabolism and ammonium excretion.
  • 29. Disorders of Urinary System 1. Chronic kidney disease (CKD) means kidneys are damaged and can't filter blood the way they should. The main risk factors for developing kidney disease are diabetes, high blood pressure, heart disease, and a family history of kidney failure. 2. Acute kidney failure occurs when kidneys suddenly become unable to filter waste products from the blood. When kidneys lose their filtering ability, harmful levels of wastes may accumulate, and blood's chemical makeup may get out of balance. 3. Glomerulonephritis is damage to the tiny filters inside the kidneys (the glomeruli). It's often caused by immune system attacking healthy body tissue. If glomerulonephritis is mild, it does not usually cause any noticeable symptoms. 4. Polycystic kidney disease (PKD) is a genetic disorder that causes many fluid- filled cysts to grow in kidneys. PKD cysts can change the shape of kidneys, including making them much larger.
  • 30. 5. Nephrotic syndrome is a group of symptoms that indicate that kidneys are not working properly. These symptoms include: too much protein in urine, called proteinuria, low levels of a protein called albumin in blood, called hypoalbuminemia, swelling in parts of body, called edema. 6. Dehydration occurs when you use or lose more fluid than you take in, and your body doesn't have enough water and other fluids to carry out its normal functions. 7. Urinary tract infection (UTI): is an infection in any part of the urinary system. The urinary system includes the kidneys, ureters, bladder and urethra. Most infections involve the lower urinary tract — the bladder and the urethra. 8. Kidney stones: it also called renal calculi, nephrolithiasis or urolithiasis are hard deposits made of minerals and salts that form inside your kidneys. Kidney stones can affect any part of your urinary tract — from your kidneys to your bladder. Often, stones form when the urine becomes concentrated, allowing minerals to crystallize and stick together.