Download Basic Medical Sciences Introduction to the Structure and Function Of

Basic Medical Sciences
Introduction to the Structure and Function
Of the Urinary System
Dr. Neil Docherty
Prologue
What the Urinary System
Contributes to The Body
Through the production of urine and hormones
1)  WASTE EXCRETION
2) EXTRACELLULAR FLUID SALT/WATER BALANCE
3) REGULATION OF pH in EXTRACELLULAR FLUID
4)REGULATION OF RED BLOOD CELL PRODUCTION
(ERYTHROPOESIS)
Perspective Check
The job of the kidney should not be listed
as “making urine”, rather the production of
urine is a mechanism through which the kidney
delivers on major homeostatic functions (1-3 above).
Together to Today’s Topic
Health Informatics
RECORD
Medical Device Design
Bioengineering
DESIGN
Physical Sciences in Medicine
APPLY
Some Aspects of Urinary Tract Health & Disease Where Paradigm Applies
ENDOSCOPY, URODYNAMICS, RENAL FUNCTION TESTS, NERVE
STIMULATORS, NOVEL SURGICAL TECHNIQUES, BIOMARKERS, TISSUE
ENGINEERING (e.g. BLADDER) TRANSPLANTATION (KIDNEY)
Shared Learning Objec0ves •  Describe the longitudinal and cross-sectional
organisation of the urinary tract
•  Link organisation of the kidney to functional phenomena
(filtration, reabsorption, secretion) and to functional
endpoints (excretion, volume and pH regulation)
•  Describe how renal enzymes and hormones can control
blood volume and cellularity
•  Describe basic functional anatomy of the ureters and
bladder and explain the basis for urinary continence
The Kidney
Origin, Regions and Maturation
DEVELOPMENT WEEK 5
“sagittal” view of embryo
THE METANEPHRIC AND MATURE KIDNEY
“coronal” view of kidney
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Cortex Medulla –  Pyramids Sinus –  Minor calices –  Major calices –  Renal pelvis Ureter 1x106 nephrons
Establishment of excretory units (nephron)
•  Sieve from blood (glomerulus)
•  Excretory epithelial tube (tubule)
The Nephron-Functional Unit of Kidney
(A Closer Look at Microanatomy and Cell
Types)
REVIEW THE DETAIL
BELOW
AFTER LECTURE
Cells of the Vascular Component
(Endothelium, vascular smooth muscle cells
stretch sensory afferents neurones,
sympathetic fibres pericytes)
Cell of the Tubular Component
(Epithelium, Osmosensory Cells)
Cells of Stromal Component
Mesangial cells
The Renal Tubule Summary of Regions • 
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Proximal convoluted tubule Proximal straight tubule Thick>thin descending limb of Loop of Henle Thin>thick ascending limb of Loop of Henle Distal convoluted tubule ConnecDng tubule CollecDng tubule Functionality Associated With Nephron
(8 KEYWORDS)
The phenomena of FILTRATION,
REABSORPTION and SECRETION
As tuned by INTRINSIC and EXTRINSIC
control mechanisms
Leads to delivery on the key functions of
•  EXCRETION
•  VOLUME REGULATION
•  pH REGULATION
N.B. Two types of nephrons
Cortical (more excretory)
Juxtamedullary (more involved in volume regulation)
The Nature and Selectivity of The
Glomerular Filter
A selectively permeable barrier between blood and tubule lumen is formed
It is essentially 3-layered
1) Endothelial layer 2) Basement membrane and 3) Visceral Epithelium
N.B. Selectivity based on size (4.4nm)
and Charge (-ve species repelled)
The Glomerular Filtration Rate (GFR)
And Its Determinants
The overall GFR is the total volume of fluid filtered by the glomeruli of both kidneys per unit time
NET PRESSURE
(SINGLE NEPHRON)
NET RATE
(GLOBAL RENAL FUNCTION)
Stroke Volume (SV)=70ml
Heart Rate (HR)=72bpm
CO=HR*SV=5040ml/min
Renal Blood Flow(RBF)=20-25% of CO
=Approximately 1L/min
Renal Plasma Flow (RPF)=RBF*1-haematocrit
=1000*0.6
=600ml/min
Presuming pressures detailed on the right
20% of the RPF is subject to filtration
=600*0.2=120ml/min
=180L/day
=Total ECF volume of body is
filtered around 10 times/day!
Alter Arteriolar Calibre-Alter The GFR
Concept Check
What would be the effect on the
GFR of efferent arteriolar
vasoconstriction?
Filtration, Reabsorption and Secretion in
The Tubule
WASTE-Filter or secrete then excrete
(e.g creatinine)
NUTRIENT-Filter and reasorb
(e.g. glucose)
WATER/SALTS/IONS=Filter and fine
tune reclamation
or regulate secretion to
achieve osmotic/volume
and pH balance
Following Reabsorption in The Tubule
Filtrate from Bowman's capsule flows into the proximal
tubule.
Here all of the glucose, and amino acids, >90% of the uric
acid and ~60% of salts are reabsorbed.
A large volume of the water follows them by osmosis
As the fluid flows into the descending segment of the loop
of Henle, water continues to leave by osmosis 25% and
reabsorption of salts (25%) in ascending segment
In the distal tubules, more sodium is reclaimed by active
transport, and still more water follows by osmosis (5%).
Final adjustment of water content of the urine occurs in the
collecting tubules (10% of reabsorption)
Concentration of The Urine Relies on The
Countercurrent Multiplier
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The kidneys filter the blood to rid it of waste and fine tune its composition
Urine is the effluent from this process
Aim is maximum waste removal in minimal volume
180L of filtrate per day-only 1% (1-2L/day) excreted as urine
Key Question-How does the kidney manage to reclaim so much of the filtrate?
From Last Slide
As the fluid flows into the descending segment of the loop of
Henle, water continues to leave by osmosis with exclusive
reabsorption of salts in ascending segment
N.B. Urinary Concentration basically facilitated by
•  The countercurrent arrangement of the limbs of the Loop of
Henle
•  Differential permeability to water therein
•  Arrangement of post-glomerular capillaries in parallel
Visualising The Countercurrent Multiplier
Values are mOsm (measure of osmotic strength)
Example of Nutrient Reabsorption
Glucose Reclamation in The Proximal Tubule
•  Same transport process as that seen in small intestine
•  Saturable
Concept Check
Saturability of renal glucose transport explains the term diabetes mellitus.
Can you make sense of this statement?
Sensing of Filtration Pressure
and Filtered Sodium Load Allow The Kidney
To Monitor and Balance ECF Volume and Tonicity
Imagine an acute decrease in blood volume
1) How will this affect CO?
2) How will this affect pressures in the renal blood vessels?
3) How will that in turn affect GFR?
4) How might the change in GFR affect sodium levels in the forming urine?
•  THE KIDNEY WILL ACT TO NORMALISE BLOOD FLOW AND ENHANCE
RECLAMATION OF SODIUM AND WATER
•  IT DOES SO BY SENSING THESE CHANGES IN SPECIALISED AREAS OF THE
RENAL BLOOD VESSELS AND TUBULE
(THE JUXTAGLOMERULAR APPARATUS-JGA)
•  A MAJOR EFFECTOR OF HOMEOSTATIC CORRECTION
IS THE RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS)
The JGA –RAAS Aldosterone and RenalSoidum
Reabsorption
JGA
RAAS
EFFECT
ALDOSTERONE
In Summary
An acute decrease in circulating blood volume reduces CO and GFR. This reduces stretch of the
afferent arteriole and also reduces delivery of sodium to the macula densa. More generally the
drop in blood pressure has caused a reflex activation of renal sympathetic nerves
All of these changes conspire to induce juxtaglomerular cells to release the hormone renin which
in turn causes generation of AngII. Among the pressor effects of AngII is induction of aldosterone
synthesis and release from the adrenal cortex. This increase distal tubular sodium reabsorption
On the Contrary
•  Increased pressure, GFR and salt delivery to the
macula densa oppose renin release
•  High venous pressure/increased venous return to
heart stretches right atrium wall
•  This releases atrial natriuretic peptide which
effectively opposes everything on last slide
•  Hence promoting urinary sodium loss “natriuresis”
and “depressurising” of the system
The Kidney is An Oxygen Sensor and Influences
Red Blood Cell Production (Erythropoesis)
Renal fibroblasts and oxygen sensing Storage and Expulsion of The Urine
Blood
Tubules
Minor Calyx
Major Calyx
Renal Pelvis
Ureter
Bladder
Urethra
Substances cleared by renal excretion
The Ureters-Location
Muscular tubes taking urine from the kidneys to the bladder
30cm in length, 3mm lumen inside
Retroperitoneal (attached to posterior wall of abdomen)
Structure and Function of The Ureter
Three Layer Structure
1) Transitional epithelium
2) Longitudinal and circular
muscle
3. Adventitia (continuous
with renal capsule)
Function
Pacemaker driven peristalsis
The Uretero-Vesicular Junction
Flap Valve Design to Prevent Reflux
Urine passes out of the ureter into the bladder
Firstly though, the ureter tunnels through the bladder
wall
This causes a flap valve to be made preventing urine from
Refluxing into the ureter from bladder when full or during
pressure increase at urination
The Bladder-Location
Hollow muscular organ for temporary storage of urine
Located medially in the abdomino-pelvic cavity
The Bladder-Gross Anatomy
Ligaments attach
superior part to the
umbilicus
Ligaments attach
inferior,anterior and
posterior parts to the
Pelvic and public bone
URETHRA
The Bladder-Wall Structure
SMOOTH MUSCLE
SKELETAL MUSCLE
Coordination of voluntary and involuntary muscle contraction
required for continence and micturition
Urinary Continence
Shared Learning Objec0ves-­‐Reprise •  Describe the longitudinal and cross-sectional
organisation of the urinary tract
•  Link organisation of the kidney to functional phenomena
(filtration, reabsorption, secretion) to functional endpoints
(excretion, volume and pH regulation)
•  Describe how renal enzymes and hormones can control
blood volume and cellularity
•  Describe basic functional anatomy of the ureters and
bladder and explain the basis for urinary continence
•  Any QuesDons? [email protected]