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THE EXCRETORY SYSTEM

 Functions, Structure & Parts
-
The Functions of the Excretory System
The primary function of the excretory system is:
• To get rid of wastes
• Eliminates useless by-products excreted from
  cells
• Eradicates harmful chemical build-ups
• Maintains a steady, balanced chemical
  concentration
Organs Responsible for Excretion
             1. LUNGS
Lungs are two-sponge like organs localized in each side
of the thorax. They are constituted by pulmonary
alveoli. They are responsible for maintaining life
supporting levels of CO2 and O2 in blood stream by
excreting the extra carbon dioxide and keeping a
regular supply of oxygen. Each and all organism's cells
can take the oxygen through passive diffusion from the
bloodstream and use it in its own metabolism, thus
producing carbon dioxide that will be further excreted
when passing through alveoli circulation. They also
remove some water in the gaseous form (water vapor).
-
2. SKIN
The skin is another part of the system, which
helps regulate the concentration of fluids and
minerals in one’s body while also keeping it cool.
The salt helps evaporate the water, cooling off
the skin. Sweat is excreted through sweat glands.
There are two types of sweat glands: eccrine (or
merocrine) sweat glands and apocrine sweat
glands. The basic purpose of skin is to provide a
waterproof, protective, covering for the body's
complex internal environment.
-
-
-
The skin also plays a key role in helping to
maintain the circulatory and nervous system.
The eccrine glands secrete mostly water and
salt and are used by the body for temperature
control. These glands are located all around
the body but are most profuse around the
soles of the feet, palms of the hands, and the
forehead. They look like coiled tubes, spiraling
towards the exterior of the skin.
3. LARGE INTESTINE
The large intestine, or the colon, is the organ
that removes solid waste from the body. Its
function is not only to remove solid waste but
to collect water from the waste that can be
reused. It is part of the alimentary canal, a
channel that flows through vertebrate
animals. It is about 6 to 7 meters long and
processes, transports, and excretes solid
wastes.
-
4. LIVER
The liver is a vital part of the excretory
system, and the human body. It regulates
glycogen storage, plasma protein synthesis, and
drug detoxification. The liver secretes bile, a base
used for breaking down fats. Therefore, it helps
get rid of unneeded wastes in the body. It
changes toxic ammonia, which is a poisonous gas
, to urea, a harmless fluid. The kidney filters urea
(a mix of sugar and waste) into a liquid called
urine. The liver is the largest gland in the body.
-
The Urinary System
 The Urinary System is a group of organs in the body
concerned with filtering out excess fluid and other
substances from the bloodstream. The urinary system
acts as the regulator of extracellular products of the
body protein foods that we eat, which contain
carbon, hydrogen and oxygen plus nitrogen and other
elements. The waste that is produced when proteins
combine with oxygen is called nitrogenous waste, and
it is more difficult to excrete from the body than gases
like carbon dioxide and water vapor. The substances
are filtered out from the body in the form of urine.
-
-
Urine is a liquid produced by the
kidneys, collected in the bladder and excreted
through the urethra. Urine is used to extract
excess minerals or vitamins, urea, creatinine, as
well as blood corpuscles from the body. The
urinary organs include the
kidneys, ureters, bladder, and urethra. The
urinary system works with the other systems of
the body to help maintain homeostasis. The
kidneys are the main organs of homeostasis
because they maintain the acid base balance and
the water salt balance of the blood.
Functions of the Urinary System
 One of the major functions of the Urinary system
is the process of excretion. Excretion is the
process of eliminating, from an organism, waste
products of metabolism and other materials that
are of no use. The urinary system maintains an
appropriate fluid volume by regulating the
amount of water that is excreted in the urine.
Other aspects of its function include regulating
the concentrations of various electrolytes in the
body fluids and maintaining normal pH of the
blood.
Kidneys
Several body organs carry out excretion, but the
kidneys are the most important excretory organ.
The primary function of the kidneys is to maintain
a stable internal environment (homeostasis) for
optimal cell and tissue metabolism. They do this
by separating urea, mineral salts, toxins, and
other waste products from the blood. They also
do the job of conserving water, salts, and
electrolytes. At least one kidney must function
properly for life to be maintained
Kidneys
 The kidneys are a pair of bean shaped, brown
organs about the size of a fist. A kidney measures
10-12 cm in length. Kidneys are covered by the
renal capsule, which is a tough capsule of fibrous
connective tissue. Adhering to the surface of each
kidney are two layers of fat to help cushion them.
There is a concaved side of the kidney that has a
depression where a renal artery enters, and a
renal vein and a ureter exit the kidney. The
kidneys are located at the rear wall of the
abdominal cavity just above the waistline, and
are protected by the ribcage.
-
-
They are considered retroperitoneal, which means
they lie behind the peritoneum. There are three
major regions of the kidney, renal cortex, renal
medulla and the renal pelvis. The
outer, granulated layer is the renal cortex. The
cortex stretches down in between a radially
striated inner layer. The inner radially striated
layer is the renal medulla. This contains pyramid
shaped tissue called the renal
pyramids, separated by renal columns. The
ureters are continuous with the renal
pelvis, which is the very center of the kidney.
Six Important Roles of the Kidneys
(1) Regulation of plasma ionic composition. Ions
    such as
    sodium, potassium, calcium, magnesium, chl
    oride, bicarbonate, and phosphates are
    regulated by the amount that the kidney
    excretes.
(2) Regulation of plasma osmolarity. The
    kidneys regulate osmolarity because they
    have direct control over how many ions and
    how much water a person excretes.
-
(3) Regulation of plasma volume. The kidneys
  are so important they even have an effect on
  our blood pressure. The kidneys control
  plasma volume by controlling how much
  water a person excretes. The plasma volume
  has a direct effect on the total blood
  volume, which has a direct effect on our blood
  pressure. Salt (NaCl) will cause osmosis to
  happen; the diffusion of water into the blood.
-
(4) Regulation of plasma hydrogen ion
  concentration (pH). The kidneys partner up
  with the lungs and they together control the
  pH. The kidneys have a major role because
  they control the amount of bicarbonate
  excreted or held onto. The kidneys help
  maintain the blood pH mainly by excreting
  hydrogen ions and reabsorbing bicarbonate
  ions as needed.
-
(5) Removal of metabolic waste products and
  foreign substances from the plasma. One of
  the most important things the kidneys excrete
  is nitrogenous waste. As the liver breaks down
  amino acids it also releases ammonia. The
  liver then quickly combines that ammonia
  with carbon dioxide, creating urea which is
  the primary nitrogenous end product of
  metabolism in humans.
-
The liver turns the ammonia into urea because
it is much less toxic. We can also excrete some
ammonia, creatinine and uric acid. The
creatinine comes from the metabolic
breakdown of creatine phospate (a high-
energy phosphate in muscles). Uric acid
comes from the break down of nucleotides.
Uric acid is insoluble and too much uric acid in
the blood will build up and form crystals that
can collect in the joints and cause gout.
-
(6) Secretion of Hormones. The endocrine
  system has assistance from the kidneys when
  releasing hormones. Renin is released by the
  kidneys. Renin leads to the secretion of
  aldosterone which is released from the
  adrenal cortex. Aldosterone promotes the
  kidneys to reabsorb the sodium (Na+) ions.
-
The kidneys also secrete erythropoietin when
the blood doesn't have the capacity to carry
oxygen. Erythropoietin stimulates red blood
cell production. The Vitamin D from the skin is
also activated with help from the kidneys.
Calcium (Ca+) absorption from the digestive
tract is promoted by vitamin D.
Kidneys - Structure
Nephrons
 A nephron is the basic structural and functional unit of
  the kidney. The name nephron comes from the Greek
  word (nephros) meaning kidney. Its chief function is to
  regulate water and soluble substances by filtering the
  blood, reabsorbing what is needed and excreting the
  rest as urine. Nephrons eliminate wastes from the
  body, regulate blood volume and pressure, control
  levels of electrolytes and metabolites, and regulate
  blood pH. Their functions are vital to life and are
  regulated by the endocrine system by hormones such
  as antidiuretic hormone, aldosterone, and parathyroid
  hormone.
-
-
Each nephron has its own supply of blood
from two capillary regions from the renal
artery. Each nephron is composed of an initial
filtering component (the renal corpuscle) and
a tubule specialized for reabsorption and
secretion (the renal tubule). The renal
corpuscle filters out large solutes from the
blood, delivering water and small solutes to
the renal tubule for modification.
-
 Glomerulus
 The glomerulus is a capillary tuft that receives its
blood supply from an afferent arteriole of the
renal circulation. The glomerular blood pressure
provides the driving force for fluid and solutes to
be filtered out of the blood and into the space
made by Bowman's capsule. The remainder of
the blood not filtered into the glomerulus passes
into the narrower efferent arteriole.
-
It then moves into the vasa recta, which are
collecting capillaries intertwined with the
convoluted tubules through the interstitial
space, where the reabsorbed substances will
also enter. This then combines with efferent
venules from other nephrons into the renal
vein, and rejoins with the main bloodstream.
-
-
Afferent/Efferent Arterioles
• The afferent arteriole supplies blood to the
  glomerulus. The efferent arteriole drains the
  glomerulus.
Glomerular Capsule or Bowman's Capsule
• Bowman's capsule (also called the glomerular
  capsule) surrounds the glomerulus and is
  composed of visceral (inner) and parietal (outer)
  layers. The visceral layer lies just beneath the
  thickened glomerular basement membrane.
Between the visceral and parietal layers is
Bowman's space, into which the filtrate enters
after passing through the filtration slits. Unlike
the visceral layer, the parietal layer does not
function in filtration. 99% of glomerular
filtrate will ultimately be reabsorbed.
-
• The process of filtration of the blood in the
  Bowman's capsule is ultrafiltration (or
  glomerular filtration). The filtrate leaving the
  Bowman's capsule is very similar to blood
  plasma in composition as it passes into the
  proximal convoluted tubule. Together, the
  glomerulus and Bowman's capsule are called
  the renal corpuscle.
-
Proximal Convoluted Tubule (PCT)
 The proximal tubule can be anatomically divided
  into two segments: the proximal convoluted
  tubule and the proximal straight tubule. The
  proximal convoluted tubule has one layer of
  cuboidal cells in the lumen. This is the only place
  in the nephron that contains cuboidal cells. These
  cells are covered with millions of microvilli. The
  microvilli serve to increase surface area for
  reabsorption.
-
• Fluid in the filtrate entering the proximal
  convoluted tubule is reabsorbed into the
  peritubular capillaries, including
  approximately two-thirds of the filtered salt
  and water and all filtered organic solutes
  (primarily glucose and amino acids).
• The solutes are absorbed isotonically, in that
  the osmotic potential of the fluid leaving the
  proximal tubule is the same as that of the
  initial glomerular filtrate.
  However, glucose, amino acids, inorganic
  phosphate, and some other solutes are
  reabsorbed via secondary active transport
  through co-transport channels driven by the
  sodium gradient out of the nephron.
-
Loop of the Nephron or Loop of Henle
The loop of Henle (sometimes known as the
nephron loop) is a U-shaped tube that consists of
a descending limb and ascending limb. It begins
in the cortex, receiving filtrate from the proximal
convoluted tubule, extends into the medulla, and
then returns to the cortex to empty into the distal
convoluted tubule. Its primary role is to
concentrate the salt in the interstitium, the tissue
surrounding the loop.
-
-
Distal Convoluted Tubule (DCT)
The distal convoluted tubule is similar to the proximal
convoluted tubule in structure and function. In the
presence of parathyroid hormone, the distal
convoluted tubule reabsorbs more calcium and
excretes more phosphate. When aldosterone is
present, more sodium is reabsorbed and more
potassium excreted. After traveling the length of the
distal convoluted tubule, only 3% of water
remains, and the remaining salt content is negligible.
97.9% of the water in the glomerular filtrate enters the
convoluted tubules and collecting ducts by osmosis.
-
  Collecting ducts
• Each distal convoluted tubule delivers its filtrate
  to a system of collecting ducts, the first segment
  of which is the connecting tubule. The collecting
  duct system begins in the renal cortex and
  extends deep into the medulla.
• Urine leaves the medullary collecting ducts
  through the renal papilla, emptying into the renal
  calyces, the renal pelvis, and finally into the
  bladder via the ureter.
Formation of Urine
Urine is formed in three steps:
  Filtration, Reabsorption, and Secretion:
(1) Filtration
   Blood enters the afferent arteriole and flows into
  the glomerulus. Blood in the glomerulus has both
  filterable blood components and non-filterable
  blood components. Filterable blood components
  move toward the inside of the glomerulus while
  non-filterable blood components bypass the
  filtration process by exiting through the efferent
  arteriole.
-
• Filterable Blood components will then take a
  plasma like form called glomerular filtrate. A few
  of the filterable blood components are
  water, nitrogenous waste, nutrients and salts
  (ions). Nonfilterable blood components include
  formed elements such as blood cells and platelets
  along with plasma proteins. The glomerular
  filtrate is not the same consistency as urine, as
  much of it is reabsorbed into the blood as the
  filtrate passes through the tubules of the
  nephron.
-
(2) Reabsorption
  - Within the peritubular capillary
   network, molecules and ions are reabsorbed
   back into the blood. Sodium Chloride
   reabsorbed into the system increases the
   osmolarity of blood in comparison to the
   glomerular filtrate. This reabsorption process
   allows water (H2O) to pass from the
   glomerular filtrate back into the circulatory
   system.
-
- Glucose and various amino acids also are
   reabsorbed into the circulatory system.
  - Glomerular filtrate has now been separated
   into two forms: Reabsorbed Filtrate and Non-
   reabsorbed Filtrate. Non-reabsorbed filtrate is
   now known as tubular fluid as it passes
   through the collecting duct to be processed
   into urine.
-
Secretion
 Some substances are removed from blood
  through the peritubular capillary network into
  the distal convoluted tubule or collecting duct.
  These substances are Hydrogen
  ions, creatinine, and drugs. Urine is a
  collection of substances that have not been
  reabsorbed during glomerular filtration or
  tubular reabsorbtion.
Ureters
• The ureters are two tubes that drain urine
  from the kidneys to the bladder. Each ureter is
  a muscular tube about 10 inches (25 cm) long.
  Muscles in the walls of the ureters send the
  urine in small spurts into the bladder, (a
  collapsible sac found on the forward part of
  the cavity of the bony pelvis that allows
  temporary storage of urine).
-
• After the urine enters the bladder from the
  ureters, small folds in the bladder mucosa act like
  valves preventing backward flow of the urine. The
  outlet of the bladder is controlled by a sphincter
  muscle. A full bladder stimulates sensory nerves
  in the bladder wall that relax the sphincter and
  allow release of the urine. However, relaxation of
  the sphincter is also in part a learned response
  under voluntary control. The released urine
  enters the urethra.
-
Urinray Bladder
• The urinary bladder is a hollow, muscular and
  distensible or elastic organ that sits on the pelvic
  floor. The urinary bladder can hold approximately
  17 to 18 ounces (500 to 530 ml) of
  urine, however the desire to micturate is usually
  experienced when it contains about 150 to 200
  ml. When the bladder fills with urine (about half
  full), stretch receptors send nerve impulses to the
  spinal cord, which then sends a reflex nerve
  impulse back to the sphincter (muscular valve) at
  the neck of the bladder, causing it to relax and
  allow the flow of urine into the urethra.
-
• The Internal urethral sphincter is involuntary.
  The ureters enter the bladder diagonally from
  its dorsolateral floor in an area called the
  trigone. The urethra exits at the lowest point
  of the triangle of the trigone. The urine in the
  bladder also helps regulate body temperature.
  If the bladder becomes completely void of
  fluid, it causes the patient to chill.
Urethra
The urethra is a muscular tube that connects
the bladder with the outside of the body. The
function of the urethra is to remove urine
from the body. It measures about 1.5 inches
(3.8 cm) in a woman but up to 8 inches (20
cm) in a man. Because the urethra is so much
shorter in a woman it makes it much easier for
a woman to get harmful bacteria in her
bladder this is commonly called a bladder
infection or a UTI.
-
-
-
The urethral sphincter is a collective name for
the muscles used to control the flow of urine
from the urinary bladder. These muscles
surround the urethra, so that when they
contract, the urethra is closed.
There are two distinct areas of muscle: the
internal sphincter, at the bladder neck and the
external, or distal, sphincter.
-
Human males have much stronger sphincter
muscles than females, meaning that they can
retain a large amount of urine for twice as
long.
The external urethral orifice is the external
opening or meatus of the urethra.
The voiding of urine is called urination, also
known as micturition
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The excretory system

  • 1. THE EXCRETORY SYSTEM Functions, Structure & Parts
  • 2. -
  • 3. The Functions of the Excretory System The primary function of the excretory system is: • To get rid of wastes • Eliminates useless by-products excreted from cells • Eradicates harmful chemical build-ups • Maintains a steady, balanced chemical concentration
  • 4. Organs Responsible for Excretion 1. LUNGS Lungs are two-sponge like organs localized in each side of the thorax. They are constituted by pulmonary alveoli. They are responsible for maintaining life supporting levels of CO2 and O2 in blood stream by excreting the extra carbon dioxide and keeping a regular supply of oxygen. Each and all organism's cells can take the oxygen through passive diffusion from the bloodstream and use it in its own metabolism, thus producing carbon dioxide that will be further excreted when passing through alveoli circulation. They also remove some water in the gaseous form (water vapor).
  • 5. -
  • 6. 2. SKIN The skin is another part of the system, which helps regulate the concentration of fluids and minerals in one’s body while also keeping it cool. The salt helps evaporate the water, cooling off the skin. Sweat is excreted through sweat glands. There are two types of sweat glands: eccrine (or merocrine) sweat glands and apocrine sweat glands. The basic purpose of skin is to provide a waterproof, protective, covering for the body's complex internal environment.
  • 7. -
  • 8. -
  • 9. - The skin also plays a key role in helping to maintain the circulatory and nervous system. The eccrine glands secrete mostly water and salt and are used by the body for temperature control. These glands are located all around the body but are most profuse around the soles of the feet, palms of the hands, and the forehead. They look like coiled tubes, spiraling towards the exterior of the skin.
  • 10. 3. LARGE INTESTINE The large intestine, or the colon, is the organ that removes solid waste from the body. Its function is not only to remove solid waste but to collect water from the waste that can be reused. It is part of the alimentary canal, a channel that flows through vertebrate animals. It is about 6 to 7 meters long and processes, transports, and excretes solid wastes.
  • 11. -
  • 12. 4. LIVER The liver is a vital part of the excretory system, and the human body. It regulates glycogen storage, plasma protein synthesis, and drug detoxification. The liver secretes bile, a base used for breaking down fats. Therefore, it helps get rid of unneeded wastes in the body. It changes toxic ammonia, which is a poisonous gas , to urea, a harmless fluid. The kidney filters urea (a mix of sugar and waste) into a liquid called urine. The liver is the largest gland in the body.
  • 13. -
  • 14. The Urinary System The Urinary System is a group of organs in the body concerned with filtering out excess fluid and other substances from the bloodstream. The urinary system acts as the regulator of extracellular products of the body protein foods that we eat, which contain carbon, hydrogen and oxygen plus nitrogen and other elements. The waste that is produced when proteins combine with oxygen is called nitrogenous waste, and it is more difficult to excrete from the body than gases like carbon dioxide and water vapor. The substances are filtered out from the body in the form of urine.
  • 15. -
  • 16. - Urine is a liquid produced by the kidneys, collected in the bladder and excreted through the urethra. Urine is used to extract excess minerals or vitamins, urea, creatinine, as well as blood corpuscles from the body. The urinary organs include the kidneys, ureters, bladder, and urethra. The urinary system works with the other systems of the body to help maintain homeostasis. The kidneys are the main organs of homeostasis because they maintain the acid base balance and the water salt balance of the blood.
  • 17. Functions of the Urinary System One of the major functions of the Urinary system is the process of excretion. Excretion is the process of eliminating, from an organism, waste products of metabolism and other materials that are of no use. The urinary system maintains an appropriate fluid volume by regulating the amount of water that is excreted in the urine. Other aspects of its function include regulating the concentrations of various electrolytes in the body fluids and maintaining normal pH of the blood.
  • 18. Kidneys Several body organs carry out excretion, but the kidneys are the most important excretory organ. The primary function of the kidneys is to maintain a stable internal environment (homeostasis) for optimal cell and tissue metabolism. They do this by separating urea, mineral salts, toxins, and other waste products from the blood. They also do the job of conserving water, salts, and electrolytes. At least one kidney must function properly for life to be maintained
  • 19. Kidneys The kidneys are a pair of bean shaped, brown organs about the size of a fist. A kidney measures 10-12 cm in length. Kidneys are covered by the renal capsule, which is a tough capsule of fibrous connective tissue. Adhering to the surface of each kidney are two layers of fat to help cushion them. There is a concaved side of the kidney that has a depression where a renal artery enters, and a renal vein and a ureter exit the kidney. The kidneys are located at the rear wall of the abdominal cavity just above the waistline, and are protected by the ribcage.
  • 20. -
  • 21. - They are considered retroperitoneal, which means they lie behind the peritoneum. There are three major regions of the kidney, renal cortex, renal medulla and the renal pelvis. The outer, granulated layer is the renal cortex. The cortex stretches down in between a radially striated inner layer. The inner radially striated layer is the renal medulla. This contains pyramid shaped tissue called the renal pyramids, separated by renal columns. The ureters are continuous with the renal pelvis, which is the very center of the kidney.
  • 22. Six Important Roles of the Kidneys (1) Regulation of plasma ionic composition. Ions such as sodium, potassium, calcium, magnesium, chl oride, bicarbonate, and phosphates are regulated by the amount that the kidney excretes. (2) Regulation of plasma osmolarity. The kidneys regulate osmolarity because they have direct control over how many ions and how much water a person excretes.
  • 23. - (3) Regulation of plasma volume. The kidneys are so important they even have an effect on our blood pressure. The kidneys control plasma volume by controlling how much water a person excretes. The plasma volume has a direct effect on the total blood volume, which has a direct effect on our blood pressure. Salt (NaCl) will cause osmosis to happen; the diffusion of water into the blood.
  • 24. - (4) Regulation of plasma hydrogen ion concentration (pH). The kidneys partner up with the lungs and they together control the pH. The kidneys have a major role because they control the amount of bicarbonate excreted or held onto. The kidneys help maintain the blood pH mainly by excreting hydrogen ions and reabsorbing bicarbonate ions as needed.
  • 25. - (5) Removal of metabolic waste products and foreign substances from the plasma. One of the most important things the kidneys excrete is nitrogenous waste. As the liver breaks down amino acids it also releases ammonia. The liver then quickly combines that ammonia with carbon dioxide, creating urea which is the primary nitrogenous end product of metabolism in humans.
  • 26. - The liver turns the ammonia into urea because it is much less toxic. We can also excrete some ammonia, creatinine and uric acid. The creatinine comes from the metabolic breakdown of creatine phospate (a high- energy phosphate in muscles). Uric acid comes from the break down of nucleotides. Uric acid is insoluble and too much uric acid in the blood will build up and form crystals that can collect in the joints and cause gout.
  • 27. - (6) Secretion of Hormones. The endocrine system has assistance from the kidneys when releasing hormones. Renin is released by the kidneys. Renin leads to the secretion of aldosterone which is released from the adrenal cortex. Aldosterone promotes the kidneys to reabsorb the sodium (Na+) ions.
  • 28. - The kidneys also secrete erythropoietin when the blood doesn't have the capacity to carry oxygen. Erythropoietin stimulates red blood cell production. The Vitamin D from the skin is also activated with help from the kidneys. Calcium (Ca+) absorption from the digestive tract is promoted by vitamin D.
  • 29. Kidneys - Structure Nephrons A nephron is the basic structural and functional unit of the kidney. The name nephron comes from the Greek word (nephros) meaning kidney. Its chief function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Nephrons eliminate wastes from the body, regulate blood volume and pressure, control levels of electrolytes and metabolites, and regulate blood pH. Their functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone.
  • 30. -
  • 31. - Each nephron has its own supply of blood from two capillary regions from the renal artery. Each nephron is composed of an initial filtering component (the renal corpuscle) and a tubule specialized for reabsorption and secretion (the renal tubule). The renal corpuscle filters out large solutes from the blood, delivering water and small solutes to the renal tubule for modification.
  • 32. - Glomerulus The glomerulus is a capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation. The glomerular blood pressure provides the driving force for fluid and solutes to be filtered out of the blood and into the space made by Bowman's capsule. The remainder of the blood not filtered into the glomerulus passes into the narrower efferent arteriole.
  • 33. - It then moves into the vasa recta, which are collecting capillaries intertwined with the convoluted tubules through the interstitial space, where the reabsorbed substances will also enter. This then combines with efferent venules from other nephrons into the renal vein, and rejoins with the main bloodstream.
  • 34. -
  • 35. - Afferent/Efferent Arterioles • The afferent arteriole supplies blood to the glomerulus. The efferent arteriole drains the glomerulus. Glomerular Capsule or Bowman's Capsule • Bowman's capsule (also called the glomerular capsule) surrounds the glomerulus and is composed of visceral (inner) and parietal (outer) layers. The visceral layer lies just beneath the thickened glomerular basement membrane.
  • 36. Between the visceral and parietal layers is Bowman's space, into which the filtrate enters after passing through the filtration slits. Unlike the visceral layer, the parietal layer does not function in filtration. 99% of glomerular filtrate will ultimately be reabsorbed.
  • 37. - • The process of filtration of the blood in the Bowman's capsule is ultrafiltration (or glomerular filtration). The filtrate leaving the Bowman's capsule is very similar to blood plasma in composition as it passes into the proximal convoluted tubule. Together, the glomerulus and Bowman's capsule are called the renal corpuscle.
  • 38. - Proximal Convoluted Tubule (PCT) The proximal tubule can be anatomically divided into two segments: the proximal convoluted tubule and the proximal straight tubule. The proximal convoluted tubule has one layer of cuboidal cells in the lumen. This is the only place in the nephron that contains cuboidal cells. These cells are covered with millions of microvilli. The microvilli serve to increase surface area for reabsorption.
  • 39. - • Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the peritubular capillaries, including approximately two-thirds of the filtered salt and water and all filtered organic solutes (primarily glucose and amino acids).
  • 40. • The solutes are absorbed isotonically, in that the osmotic potential of the fluid leaving the proximal tubule is the same as that of the initial glomerular filtrate. However, glucose, amino acids, inorganic phosphate, and some other solutes are reabsorbed via secondary active transport through co-transport channels driven by the sodium gradient out of the nephron.
  • 41. - Loop of the Nephron or Loop of Henle The loop of Henle (sometimes known as the nephron loop) is a U-shaped tube that consists of a descending limb and ascending limb. It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medulla, and then returns to the cortex to empty into the distal convoluted tubule. Its primary role is to concentrate the salt in the interstitium, the tissue surrounding the loop.
  • 42. -
  • 43. - Distal Convoluted Tubule (DCT) The distal convoluted tubule is similar to the proximal convoluted tubule in structure and function. In the presence of parathyroid hormone, the distal convoluted tubule reabsorbs more calcium and excretes more phosphate. When aldosterone is present, more sodium is reabsorbed and more potassium excreted. After traveling the length of the distal convoluted tubule, only 3% of water remains, and the remaining salt content is negligible. 97.9% of the water in the glomerular filtrate enters the convoluted tubules and collecting ducts by osmosis.
  • 44. - Collecting ducts • Each distal convoluted tubule delivers its filtrate to a system of collecting ducts, the first segment of which is the connecting tubule. The collecting duct system begins in the renal cortex and extends deep into the medulla. • Urine leaves the medullary collecting ducts through the renal papilla, emptying into the renal calyces, the renal pelvis, and finally into the bladder via the ureter.
  • 45. Formation of Urine Urine is formed in three steps: Filtration, Reabsorption, and Secretion: (1) Filtration Blood enters the afferent arteriole and flows into the glomerulus. Blood in the glomerulus has both filterable blood components and non-filterable blood components. Filterable blood components move toward the inside of the glomerulus while non-filterable blood components bypass the filtration process by exiting through the efferent arteriole.
  • 46. - • Filterable Blood components will then take a plasma like form called glomerular filtrate. A few of the filterable blood components are water, nitrogenous waste, nutrients and salts (ions). Nonfilterable blood components include formed elements such as blood cells and platelets along with plasma proteins. The glomerular filtrate is not the same consistency as urine, as much of it is reabsorbed into the blood as the filtrate passes through the tubules of the nephron.
  • 47. - (2) Reabsorption - Within the peritubular capillary network, molecules and ions are reabsorbed back into the blood. Sodium Chloride reabsorbed into the system increases the osmolarity of blood in comparison to the glomerular filtrate. This reabsorption process allows water (H2O) to pass from the glomerular filtrate back into the circulatory system.
  • 48. - - Glucose and various amino acids also are reabsorbed into the circulatory system. - Glomerular filtrate has now been separated into two forms: Reabsorbed Filtrate and Non- reabsorbed Filtrate. Non-reabsorbed filtrate is now known as tubular fluid as it passes through the collecting duct to be processed into urine.
  • 49. - Secretion Some substances are removed from blood through the peritubular capillary network into the distal convoluted tubule or collecting duct. These substances are Hydrogen ions, creatinine, and drugs. Urine is a collection of substances that have not been reabsorbed during glomerular filtration or tubular reabsorbtion.
  • 50. Ureters • The ureters are two tubes that drain urine from the kidneys to the bladder. Each ureter is a muscular tube about 10 inches (25 cm) long. Muscles in the walls of the ureters send the urine in small spurts into the bladder, (a collapsible sac found on the forward part of the cavity of the bony pelvis that allows temporary storage of urine).
  • 51. - • After the urine enters the bladder from the ureters, small folds in the bladder mucosa act like valves preventing backward flow of the urine. The outlet of the bladder is controlled by a sphincter muscle. A full bladder stimulates sensory nerves in the bladder wall that relax the sphincter and allow release of the urine. However, relaxation of the sphincter is also in part a learned response under voluntary control. The released urine enters the urethra.
  • 52. -
  • 53. Urinray Bladder • The urinary bladder is a hollow, muscular and distensible or elastic organ that sits on the pelvic floor. The urinary bladder can hold approximately 17 to 18 ounces (500 to 530 ml) of urine, however the desire to micturate is usually experienced when it contains about 150 to 200 ml. When the bladder fills with urine (about half full), stretch receptors send nerve impulses to the spinal cord, which then sends a reflex nerve impulse back to the sphincter (muscular valve) at the neck of the bladder, causing it to relax and allow the flow of urine into the urethra.
  • 54. - • The Internal urethral sphincter is involuntary. The ureters enter the bladder diagonally from its dorsolateral floor in an area called the trigone. The urethra exits at the lowest point of the triangle of the trigone. The urine in the bladder also helps regulate body temperature. If the bladder becomes completely void of fluid, it causes the patient to chill.
  • 55. Urethra The urethra is a muscular tube that connects the bladder with the outside of the body. The function of the urethra is to remove urine from the body. It measures about 1.5 inches (3.8 cm) in a woman but up to 8 inches (20 cm) in a man. Because the urethra is so much shorter in a woman it makes it much easier for a woman to get harmful bacteria in her bladder this is commonly called a bladder infection or a UTI.
  • 56. -
  • 57. -
  • 58. - The urethral sphincter is a collective name for the muscles used to control the flow of urine from the urinary bladder. These muscles surround the urethra, so that when they contract, the urethra is closed. There are two distinct areas of muscle: the internal sphincter, at the bladder neck and the external, or distal, sphincter.
  • 59. - Human males have much stronger sphincter muscles than females, meaning that they can retain a large amount of urine for twice as long. The external urethral orifice is the external opening or meatus of the urethra. The voiding of urine is called urination, also known as micturition
  • 60. Sorry, Have to Go!!!