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Anatomy & Physiology
SIXTH EDITION
Lecture 26: The Urinary System
Lecturer: Dr. Barjis
Room: P313
Phone: (718) 260-5285
E-Mail: [email protected]
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Frederic H. Martini
Fundamentals of
Learning Objectives
• Identify the components and functions of the
urinary system
• Describe the location and structural features of
the kidneys
• Describe the structure of a nephron, and outline
the processes involved in the formation of urine
• Describe the normal characteristics, composition,
and solute concentrations of a representative
urine sample
Learning Objectives
• List and describe the factors that influence
filtration pressure and the rate of filtrate
formation
• Identify the types of transport mechanisms found
along the nephron
• Describe how antidiuretic hormone and
aldosterone levels influence the volume and
concentration of urine
Functions of the urinary system
• Functions of the urinary system includes:
• 1) Excretion
• The removal of organic waste products from body fluids
e.g. urea
• 2) Elimination
• The discharge of waste products into the environment
• 3) Homeostatic regulation of blood plasma
• Regulating blood volume and pressure
• Regulating plasma ion concentrations
• Stabilizing blood pH
• Conserving nutrients i.e. preventing nutrient excretion
by re-absorption
• Detoxification
Urinary system
Organs of Urinary system includes:
• 1) The kidneys
• Produce urine
• 2) The ureters
• Transport urine from the kidneys to the
bladder
• 3) The urinary bladder
• Stores urine
• 4) The urethra
• Eliminates urine
An introduction to the Urinary System
The kidneys
• Left kidney extends slightly more superiorly than
right
• Both kidneys and adrenal glands are
retroperitoneal
• Hilus
• Point of entry and exit for renal artery, renal
nerves and renal veins and ureter
The Urinary System in Gross Dissection
The Kidneys
Sectional anatomy of the kidneys
• Kidneys have two layers: An outer cortex and an
inner medulla
• The medulla consists of 6-18 conical shaped
structures called renal pyramids
• The cortex is composed of roughly 1.25 million
nephrons
• Major and minor calyces along with the pelvis
drain urine to the renal pelvis, and renal pelvis is
connected to the ureters
The Structure of the Kidney
Blood supply of the kidneys
• Pathway of blood flow to the kidnes:
• Renal artery – renal arteries deliver blood to the kidneys
• Segmental artery – renal arteries branch to segmental arteries
• Interlobar artery - Segmental arteries divide into a series of
interlobar arteries
• Arcuate artery - interlobar arteries supply blood to the arcuate
arteries
• Interlobular artery - Each arcuate artery gives rise to a number of
interlobular arteries
• Afferent arterioles - interlobular artery branch to numer of afferent
arterioles
• Glomeruli – afferent arteries deliver blood to capillaries called
glomeruli.
• Glomeruli is network of capilaries found in the corpuscle of
nephrone
• Renal venules follow similar opposing pattern ending with
renal veins
The Blood Supply to the Kidneys
The Blood Supply to the Kidneys
The Nephron
• The nephron consists of :
• 1) Renal corpuscle – the head of the nephron
• The renal corpuscle is composed of Bowman’s capsule and glomeruli
• Bowman’s capsule is the cover of the corpuscle that surrounds
the glomerulus
• the glomerulus is the network of capillaries found inside the
corpuscle
• Blood arrives at glomerulus by way of an afferent arteriole
and departs in an efferent arteriole
• 2) Renal tubule – the tubular passageway of the nephron
• The renal tubule consists of
• Proximal convoluted tubule (PCT)
• Loop of Henle
• Distal convoluted tubule (DCT)
The Nephron
Filtrate is produced at the renal corpuscle of the
nephron
• In renal corpuscle, blood pressure forces fluid and dissolved
solutes out of the glomerular capillaries and into the
capsular space. This process is called filtration
• Filtration produces an essentially protein-free solution, known as a
filtrate
• Filtrate is similar to plasma but without proteins i.e. it contains
organic substrates (e.g. glucose, fatty acids, amino acids), vitamins,
water, electrolytes, waste product and other solutes
• Organic substrates, most water, most electrolytes and vitamins are
recaptured (re-absorbed) by the renal tubes, before filtrate leaves
the kidneys
• From the renal corpuscle, filtrate enters the tubular
passageway of the nephron
The Nephron
• The tubular passageway of the nephron is responsible
for:
• 1. Reabsorbing organic substrates and vitamins
• 2. Reabsorbing water and electrolytes
• 3. Secreting waste products
• From the tubular passageway of the nephron fluid enters into the
collecting system (collecting system are tubes that carry tubular fluid
away from the nephron)
• Collecting ducts carry he fluid to papillary ducts
• Papillary ducts carry the fluid (urine) to the minor calyx
• Minor calyx carry the fluid (urine) to major calyx
• Number of minor calyces join together to form a major calyx
• Major calyx deliver the fluid (urine) to renal pelvis
• Renal pelvis is connected to the ureter
• Ureter transports the urine to the bladder
Summary of fluid flow from the nephron to the Ureter
1) Renal corpuscle - capsular
space.
2) Tubular passageway of the
nephron
• PCT
• Lube of Henle
• DCT
3) Collecting duct
4) Papillary ducts
5) Minor calyx
6) Major calyx
7) Renal pelvis
8) Uureter
The Nephron
The Nephron
Nephron functions include:
• 1) Production of filtrate – this occurs at the
corpuscle of the nephron
• 2) Reabsorption of organic nutrients – this
occurs at the tubular passageway of the
nephron
• 3) Reabsorption of water and ions - this occurs at
the tubular passageway of the nephron
• 4) Secretion of waste products into tubular fluid this occurs at the tubular passageway of the
nephron
The Nephron
There are two types of nephron
• 1) Cortical nephrons
• ~85% of all nephrons
• Located in the cortex
• 2) Juxtamedullary nephrons
• Closer to renal medulla
• Loops of Henle extend deep into renal
pyramids
Cortical and Juxtamedullary Nephrons
Cortical and Juxtamedullary Nephrons
Glomerulus anatomy
• Podocytes cover lamina densa of capillaries
• Project into the capsular space
• Pedicels of podocytes separated by filtration
slits
The Renal Corpuscle
The Renal Corpuscle
Functional anatomy of the nephron
• Tubular passageway of the nephron:
• 1) Proximal convoluted tubule (PCT)
• Actively reabsorbs nutrients, plasma proteins
and ions from filtrate
• The PCT reabsorbs 60-70% of the filtrate
produced
• Reabsorption of most organic nutrients
• Active and passive reabsorption of sodium
and other ions
• Reabsorption of water
• Secretion also occurs in the PCT (this is
mostly function of DCT)
Transport Activities at the PCT
Functional anatomy of the nephron
• Tubular passageway of the nephron:
• 2) Loop of Henle
• Descending limb
• Ascending limb
• Countercurrent multiplication Between
ascending and descending limbs of loop
• Creates osmotic gradient in medulla
• Facilitates reabsorption of water and solutes before the DCT
• Permits passive reabsorption of water from tubular fluid
• Permits passive reabsorption of water from tubular fluid
Countercurrent Multiplication and
Concentration of Urine
Countercurrent Multiplication and
Concentration of Urine
Countercurrent Multiplication and
Concentration of Urine
Functional anatomy of the nephron
• Tubular passageway of the nephron:
• Distal convoluted tubule (DCT)
• DCT performs final adjustment of urine
• Actively secretes ions, toxins, drugs
• Reabsorbs sodium ions from tubular fluid
• Tubular cells actively resorb Na+ and Cl• In exchange for potassium or hydrogen ions
(secreted)
Tubular Secretion and Solute Reabsorption at
the DCT
Animation: Distal Convoluted Tubule (see tutorial)
Tubular Secretion and Solute Reabsorption at
the DCT
Urine production maintains homeostasis
• Regulating blood volume and composition by
excreting or reabsorbing water, sodium, hydroge
and other electrolyte
• Excreting waste products such as:
• Urea
• Creatinine
• Uric acid
Basic processes of urine formation
• 1) Filtration – this is the first process, and it occurs in corpuscle
of nephron
• Filtration occur because blood pressure forces fluid and
dissolved solutes out of the glomerular capillaries and into
the capsular space
• 2) Reabsorption – this is the second process, and it occurs in
tubular passageway of the nephron
• One limitation to the filtration process is that the filtrate
produced in the corpuscle contain organic substrates,
vitamins and other beneficial material. Therefore the second
process will reabsorb water and solutes from the filtrate
• 3) Secretion – this is the third process and it occurs in the
tubular passageway of the nephron
• Transport of solutes from the peritubular fluid into the
tubular fluid
Filtration and Reabsorption
Filtration in the kidneys modified by carrier
mediated transport
• Facilitated diffusion
• Active transport
• Cotransport
• Countertransport
Reabsorption and secretion is accomplished via:
• Diffusion,
• Osmosis, and
• Carrier-mediated transport
Renal function
• Most regions of the nephron perform a
combination of functions
• General functions can be identified
• Filtration in the renal corpuscle
• Nutrient reabsorption along the PCT
• Active secretion at PCT and DCT
• Loops of Henle regulate final volume and
solute concentration
An Overview of Urine Formation
Filtration pressures - Glomerular filtration
• Occurs as fluids move across the glomerulus
• In response to glomerular hydrostatic pressure
(GHP) and blood pressure in the glomerular
capillaries
• Capsular hydrostatic pressure (CsHP) opposes
GHP
• Blood colloid osmotic pressure (BCOP)
opposes GHP
• Net hydrostatic pressure (NHP) = GHP – CsHP
• Filtration (FP) = NHP – BCOP
Glomerular Filtration
Glomerular Filtration
Glomerular filtration rate (GFR)
• GFR is the amount of filtrate produced by the
kidneys in one minute
• Factors that alter filtration pressure will change
the GFR e.g. a drop in pressure will lead to a
decrease in GFR
The Response to a Reduction in the GFR
•
When blood pressure is law, the amount of
filtrate in the corpuscle decreases.
•
Law filtrate stimulates production of renin by
juxtaglomerular nephron (apparatus)
•
Renin converts angiotensin to angiotensin I
•
Angiotensin I is activated to angiotensin II
•
Angiotensin II affects the/ or acts on:
1)
Blood vessel
•
2)
Adrenal gland
•
3)
At the adrenal gland it increases production
of aldosterone. Aldosterone increases
sodium retention. Higher sodium
rentention means higher water retention.
Central nervous system
•
•
Angiotensin II stimulates constriction of
blood vessels
At the central nervous system it
stimulates thirst, increases production
ADH. ADH increases water
reabsorption by the collecting system.
Note that in the absence of ADH no
reabsorption takes place in the
collecting system
All of the above actions will lead to an increase
in the blood pressure
Reabsorption and secretion along the collecting
system
• Water and solute loss is regulated by aldosterone
and ADH
• Reabsorption
• Sodium ion, bicarbonate, and urea are
resorbed
• Secretion
• pH is controlled by secretion of hydrogen or
bicarbonate ions
The Effects of ADH on the DCT and Collecting
Ducts
Function of the vasa recta
• Removes solutes and water
• Balances solute reabsorption and osmosis in
the medulla
Composition of normal urine
• Varies with the metabolic and hormonal events of
the body
• Reflects filtration, absorption and secretion
activity of the nephrons
• Urinalysis is the chemical and physical analysis of
urine
A Summary of Renal Function
A Summary of Renal Function
Urine production ends with fluid entering the
renal pelvis
• Rest of urinary system transports, stores and
eliminates
• Ureters
• Bladder
• Urethra
A Radiographic View of the Urinary System
The ureters and The urinary bladder
The ureters
• Pair of muscular tubes
• Extend from renal pelvis to the bladder
• Peristaltic contractions force urine toward the
urinary bladder
The urinary bladder
• Hollow, muscular organ
• Reservoir for the storage of urine
• Contraction of detrusor muscle voids bladder
Organs for the Collection and storage of Urine
Organs for the Collection and storage of Urine
Organs for the Collection and storage of Urine
The urethra
• Extends from the urinary bladder to the exterior
of the body
• Passes through urogenital diaphragm (external
urinary sphincter)
• Differs in length and function in males and
females
The Histology of the Organs that Collect and
Transport Urine
Micturition reflex and urination
• Urination coordinated by micturition reflex
• Initiated by stretch receptors in wall of bladder
• Urination requires coupling micturition reflex
with relaxation of external urethral sphincter
The Micturition Reflex
Changes with aging include:
• Decline in the number of functional nephrons
• Reduction of GFR
• Reduced sensitivity to ADH
• Problems with the micturition reflex
You should now be familiar with:
• The components of the urinary system and their
functions
• The location and structural features of the
kidneys
• The structure of a nephron, and the processes
involved in the formation of urine
• The normal characteristics, composition, and
solute concentrations of a representative urine
sample
You should now be familiar with:
• The factors that influence filtration pressure and
the rate of filtrate formation
• The types of transport mechanisms found along
the nephron
• How antidiuretic hormone and aldosterone levels
influence the volume and concentration of urine