The Urinary System and Tract
A continued examination
Figure 26.10 Glomerular
Filtration
Figure 26.10a, b
Glomerular filtration rate (GFR)
• Amount of filtrate produced in the kidneys each
minute
• Factors that alter filtration pressure change GFR
Factors controlling the GFR
• A drop in filtration pressure can activate local
mechanisms--results in vasodilation of afferent
arterioles and vasoconstriction of efferent
arterioles----> increase in glomerular (filtration)
pressure
• A drop in filtration pressure stimulates
Juxtaglomerular apparatus (JGA)
– Releases renin and erythropoietin
Figure 26.11 The Response to a
Reduction in the GFR
Figure 26.11a
Figure 26.11 The Response to a
Reduction in the GFR
Figure 26.11b
Sympathetic activation
• Produces powerful vasoconstriction of afferent
arterioles
– Decreases GFR and slows production of filtrate
– Usually in response to big drop in blood pressure
• Changes the regional pattern of blood flow
– Alters GFR
Reabsorption and secretion at the
DCT
• DCT performs final adjustment of urine
– Active secretion or absorption
• Absorption
– Tubular cells actively resorb Na+ and Cl– In exchange for potassium or hydrogen ions
(secreted)
Figure 26.14 Tubular Secretion and
Solute Reabsorption at the DCT
PLAY
Animation: Distal Convoluted Tubule
Figure 26.14
Figure 26.14 Tubular Secretion and
Solute Reabsorption at the DCT
Figure 26.14c
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
Control of urine volume and osmotic
concentration
• Urine volume and osmotic concentration are
regulated by controlling water reabsorption
– Precise control allowed via facultative water
reabsorption
Figure 26.15 The Effects of ADH on
the DCT and Collecting Ducts
Figure 26.15
Figure 26.15 The Effects of ADH on
the DCT and Collecting Ducts
Figure 26.15a, b
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
Summary of renal function:
• Each segment of nephron and collecting system
contribute
–
–
–
–
–
Glomerulus
PCT
Descending limb
Thick ascending limb
DCT and collecting ducts
• Concentrated urine produced after considerable
modification of filtrate
PLAY
Animation: Late Filtrate Processing
Figure 26.16 A Summary of
Renal Function
Figure 26.16a
Figure 26.16 A Summary of
Renal Function
Figure 26.16b
Chapter 26, part 4
The Urinary System
SECTION 26-6
Urine Transport, Storage, and
Elimination
Urine production ends with fluid
entering the renal pelvis
• Rest of urinary system transports, stores and
eliminates
– Ureters
– Bladder
– Urethra
Figure 26.17 A Radiographic View of
the Urinary System
Figure 26.17
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
• Internal features include
–
–
–
–
Trigone
Neck
Internal urethral sphincter
Ruggae
Figure 26.19 Organs for the
Collection and storage of Urine
Figure 26.19a
Figure 26.19 Organs for the
Collection and storage of Urine
Figure 26.19b
Figure 26.19 Organs for the
Collection and storage of Urine
Figure 26.19c
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
Figure 26.20 The Histology of the
Organs that Collect and Transport
Urine
Figure 26.20a
Figure 26.20 The Histology of the
Organs that Collect and Transport
Urine
Figure 26.20b, c
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
Figure 26.21 The Micturition
Reflex
Figure 26.21
Figure 26.21 The Micturition Reflex
Figure 26.21
SECTION 26-7
Aging and the Urinary System
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