Download Lecture 10 urinary system

Lecture 11 Outline
I.
Urinary System I
Overview
A. Body’s purification system
B. Functions
1. Removes wastes and toxic substances
2. Conserves useful substances
3. Regulates blood volume & pressure
4. Regulates blood pH
5. Red Blood Cell Synthesis-secretes erythropoietin
1. Consists of:
 2 kidneys
 2 ureters
 1 urinary bladder
 1 urethra
Kidneys
Size & Shape
 bean-shaped organ, size of fist
 Length = 12 cm, Width = 6 cm, Thick = 3 cm
Location
 Posterior abdominal wall, behind peritoneal cavity = retroperitoneal
 Between T12-L3 vertebrae
 Right kidney slightly lower than left due to liver
Anatomy
 Kidneys are surrounded by thick layer of adipose tissue = perirenal fat
 Renal Capsule = fibrous connective tissue
 Renal cortex = outer layer
 Renal medulla = inner layer
o Renal Pyramids
 Medullary Rays = collecting ducts
 Tip of pyramid = papillae – drains into minor calyx
o Minor Calyx
o Major Calyx = 2-3 per kidney
o Renal Pelvis = enlarged chamber
o Ureter – conveys urine away from kidney

Urine Flow: Renal Pyramid → Papillae → Minor Calyx → Major Calyx → Renal Pelvis → Ureter
Hilum (indentation)
o Entrance for Ureter, Renal Artery, Renal Vein, and nerves
Blood Flow
Arterial:
Abdominal Aorta → Renal Artery → Interlobar Arteries → Arcuate Arteries → Cortical Radiate Arteries
→ afferent arterioles → Glomerulus of nephron
Venous Return:
Efferent Arterioles → Peritubular Capillaries → Cortical Radiate Veins → Arcuate Veins → Interlobular
veins → Renal Vein → Inferior Vena Cava
Renal Arteries = receive 25% of cardiac output
Interlobar arteries = pass between medullary pyramids
Arcuate arteries = incomplete arches along corticomedullary boarder
Cortical Radiate Arteries = radiate into cortex
Afferent Arterioles – lead to nephron
Nephron
I.
Overview
a. Functional unit of kidney
b. Approximately 1 million nephrons per kidney
c. Consists of Renal Corpuscle + Renal Tubules
II.
III.
IV.
Renal Corpuscle
a. Glomerular (Bowman’s) Capsule
b. Glomerulus
Renal Tubules
a. Proximal Convoluted Tubule (PCT)
b. Nephron Loop (Loop of Henle) – descending limb
c. Nephron Loop (Loop of Henle) – ascending limb
d. Distal Convoluted Tubule (DCT)
Collecting Duct
a. Collects filtrate from several nephrons
b. Not part of any nephron
c. Responsible for the striations seen in the medullary pyramids
Urine Formation
I.
3 Steps
a. Glomerular Filtration
b. Tubular Reabsorption
c. Tubular Secretion
II.
Filtration
a. 1st step in urine formation, occurs at renal corpuscle
b. Glomerular Capsule – 2 layers
i. Parietal Layer = outer layer of simple squamous epithelium
ii. Visceral Layer = inner layer of podocytes
 Podocytes
i. Process called Pedicles
ii. Slit pores = openings between pedicles
c. Glomerulus
i. Capillary endothelium resting on basement membrane
ii. contain openings between endothelium, called fenestrae
d. Filtration Membrane = Fenestrae + Basement Membrane + Slit Pores
III.
IV.
Glomerular Filtrate
a. Formed by hydrostatic pressure of blood = Filtration Pressure
b. Filtrate includes:
1. Water
2. Glucose
3. Ions (Na+, K+, Cl-, Ca2+, H+, HCO3-)
4. Amino Acids
5. Urea & Uric Acid
c. Blood cells & proteins are too large to pass membrane
d. Rate of filtration formation = Glomerular Filtration Rate (GFR)
i. 125mL/min = 180L/day (45 gallons/day)
ii. 99% of filtrate is reabsorbed, 1% passes as urine
Autoregulation
a. Maintaining a stable GFR with a wide range of blood pressures
b. GFR is directly proportional to filtration pressure (from blood pressure)
c. GFR is can be controlled by vasoconstriction/vasodilatation of both afferent arterioles &
efferent arterioles
 Vasoconstriction of afferent arteriole (a.a.) decreases GFR
 Vasodilation of efferent arteriole (e.a.) also decreases GFR
 As blood pressure increases a.a. vasoconstrict & e.a. vasodilate to maintain a
stable GFR
Lecture 12 Outline
Urinary System II
Nephron
I.
Overview
a. Functional unit of kidney
b. Approximately 1 million nephrons per kidney
c. Consists of Renal Corpuscle + Renal Tubules
II.
Renal Corpuscle
a. Glomerular (Bowman’s) Capsule
b. Glomerulus
III.
Renal Tubules
a. Proximal Convoluted Tubule (PCT)
b. Nephron Loop (Loop of Henle) – descending limb
c. Nephron Loop (Loop of Henle) – ascending limb
d. Distal Convoluted Tubule (DCT)
IV.
Collecting Duct
a. Collects filtrate from several nephrons
b. Not part of any nephron
c. Responsible for the striations seen in the medullary pyramids
V.
Types of nephron
a. Cortical Nephrons – 80% of nephrons
 located almost entirely within cortex
b. Juxtamedullary Nephrons – 20% of nephrons
 Renal corpuscle positioned near medulla
 Long nephron loops dip far into the medulla
 Minority of nephrons, but important for concentrating urine
Renal Corpuscle
I.
Responsible for filtration
a. Filtration = first step in urine formation
II.
Blood Supply
a. Afferent arteriole – conveys blood to glomerulus
b. Glomerulus – highly permeable capillary network
i. Capillaries have slits, called fenestrae
c. Efferent Arterioles – conveys blood away from glomerulus
III.
Glomerular Capsule
a. Parietal layer
i. Outer layer, composed of squamous cells
b. Visceral layer
i. Inner layer, composed of podocytes
1. Podycytes = foot cell
a. Contains process, called pedicles
b. Spaces between pedicles = filtration slits.
c.
Filtration Membrane
1. Fenestrae of Glomerular capillaries
2. Basement membrane of capillaries
3. Filtration slits between pedicles of podoctyes
IV.
Blood Supply of Nephron
I.
Renal Portal System
a. Afferent Arterioles – convey blood to glomerulus
b. Glomerulus – capillary bed
c. Efferent Arterioles – conveys blood away from glomerulus
d. Peritubular capillaries
 Capillary network surrounding proximal convoluted tubule & distal convoluted
tubule
 Drain into cortical radiate veins
a. Vasa Recta
 Specialized capillary loop that surrounds nephron loops of juxtamedullary
nephrons
II.
Juxtaglomerular Apparatus
a. Regulates blood pressure
 Juxtaglomerular Cells within afferent arterioles
 Macula Densa within Distal Convoluted Tubule
Urine Formation
I.
3 Steps
a. Glomerular Filtration
b. Tubular Reabsorption
c. Tubular Secretion
II.
Filtration
a. 1st step in urine formation
b. occurs at filtration membrane of renal corpuscle
III.
Glomerular Filtrate
a. Formed by hydrostatic pressure of blood = Filtration Pressure
b. Filtrate includes:
1. Water
2. Glucose
3. Ions (Na+, K+, Cl-, Ca2+, H+, HCO3-)
4. Amino Acids
5. Urea & Uric Acid
c. Blood cells & proteins are too large to pass membrane
d. Rate of filtration formation = Glomerular Filtration Rate (GFR)
i. 125mL/min = 180L/day (45 gallons/day)
ii. 99% of filtrate is reabsorbed, 1% passes as urine
IV.
Autoregulation
a. Maintains a stable GFR with a wide range of blood pressures
b. GFR is directly proportional to filtration pressure (from blood pressure)
c. GFR is can be controlled by vasoconstriction/vasodilatation of both afferent arterioles &
efferent arterioles
 Vasoconstriction of afferent arteriole (a.a.) decreases GFR
 Vasodilation of efferent arteriole (e.a.) also decreases GFR
 As blood pressure increases a.a. vasoconstrict & e.a. vasodilate to maintain a
stable GFR
Tubular Reabsorption
I.
Movement of filtrate from tubule into Peritubular capillaries
 Reclaims substances the body needs
II.
Proximal Convoluted Tubule
 H2O (65%) by osmosis
 Glucose
 Amino Acids
 Ions (Na+, Cl-, K+, HCO3-)
III.
Descending Nephron Loop
 Water (15%)
IV.
Ascending Nephron Loop
 Impermeable to water (0% H2O)
V.
Distal Convoluted Tubule & Collecting Duct
 H2O (19%)
i. Requires Antidiuretic Hormone (ADH)
ii. ADH inserts aquaporins (water channels) in collecting ducts
iii. Without ADH, water passes as urine = diabetes insipidus
 Solutes (Na+, K+,Cl-)
Reabsorption at proximal convoluted tubule (65%)
I.
PCT = simple cuboidal epithelium + microvilli
II.
Reabsorption is linked to active transport of Na+ out of the basal surface of tubule and into
Peritubular capillaries
 Na+/K+ pumps: removes Na+ from cells, and creates a large Na+ gradient between
tubular cells & filtrate




Symporters link the transport of glucose, amino acids, K+, ect. to facilitated diffusion of
Na+ into apical surface of cells
Glucose, Na+, amino acids, K+ leave basal surface by facilitated diffusion
Negatively charged ions (Cl-, HCO3-, PO42-) follows positive ions ( Na+ & K+ ) out of
tubules
H2O follows solutes by osmosis
Concentrating Urine – Juxtamedullary Nephrons
I.
Countercurrent mechanism within nephron loop
a. Nephron filtrate flows parallel, but opposite to vasa recta
b. Ascending Nephron Loop flows adjacent to descending vasa recta
 Ascending Nephron Loop (NL) is impermeable to H2O
 As filtrate moves up ascending NL, ions such as Na+, K+, and Cl- are actively
pumped out of ascending NL into descending vasa recta.
 Descending vasa recta becomes more and more hypertonic as it descends,
finally reaching an osmolarity of 1200 at the base.
c. Descending Nephron Loop flows adjacent to Ascending Vasa Recta
 As hypertonic blood (1200mOsm)moves up vasa recta, the high tonicity attracts
water from within the descending nephron loop
 Water leaves descending nephron loop into the ascending vasa recta
 Ascending Vasa recta becomes more isotonic, while descending Nephron Loop
becomes more hypertonic.
i.
Countercurrent multiplier creates a large osmotic gradient for water reabsorption
Reabsorption in DCT & Collecting Duct (19%)
 Na+, K+, Cl- are actively pumped out of collecting duct & flow into descending vasa recta
 Water follows solutes out of filtrate and enter the hypertonic descending vasa recta
o Antidiuretic Hormone (ADH) is required for water reabsorption at collecting ducts
o ADH inserts water channels, called aquaporins into collecting ducts
o Without ADH, water leaves as urine
 Diabetes Insipidus – defective ADH receptors
 Constant thirst, frequent urination
Tubular Secretion
I.
Movement from Peritubular capillaries into nephron tubules
II.
Removes toxic substances quickly from body
III.
a. Secretion in Proximal Convoluted Tubule
i. H+, Uric Acid, Ammonia, some drugs, Bile pigments
b. Secretion in Distal Convoluted Tubule
i. H+, K+
Secretion of H+ helps regulate blood pH.
a. Metabolic acidosis increases H+ secretion
b. Metabolic alkalosis decreases H+ secretion
Juxtaglomerulus Apparatus
 Regulates blood pressure through renin-angiotensin-aldosterone mechanism
 Consists of
1. Juxtaglomerular Cells
a. Within smooth muscles of afferent arterioles
b. Contain renal baroreceptors – detect changes in blood pressure
c. Secretes renin in response to low blood pressure, or high Na+ in filtrate

2. Macula Densa
a. Within Distal Convoluted Tubule
b. Detects changes in [Na+] in filtrate
c. High [Na+] in filtrate stimulates secretion of renin from juxtaglomerular
Cells
Renin-Angiontensin-Aldosterone Pathway
o Renin = converts angiontensinogen into Angiontensin I
o Angiontensinogen = plasma protein produced by liver
o Angiontensin Converting Enzyme (AC) = converts Angiontensin I into Angiotensin II
o Angiontensin II: stimulates Aldosterone secretion from adrenal cortex &
vasoconstriction
o

Aldosterone:
 increases Na+ reabsorption in distal convoluted tubule
 Water follows by osmosis (if ADH is present), increases blood pressure
ACE inhibitors
o Inhibits the actions of ACE, preventing formation of Angiontensin II
o Lowers blood pressure
Antidiuretic Hormone
1. Secreted by posterior pituitary gland
a. Secretion stimulated by low blood pressure – baroreceptors
b. High osmotic pressure “hypertonic” fluid
i. Osmoreceptors in hypothalamus stimulates secretion of ADH
c. Actions of ADH
i. Increase blood pressure by:
1. Vasoconstriction
2. Increases water reabsorption in kidneys
Urine Composition
1. 95% Water
2. Urea
a. Biproduct of amino acid catabolism
b. 80% of urea is recycled
3. Uric acid
a. Byproduct of amino acid catabolism
b. Excess uric acid in plasma is deposited as crystals in joints = gout
4. Electrolytes (K+, H+, PO42-)
Ureters
 25cm length
 Muscles of ureters contract periodically to pass urine (not constant)
Urinary Bladder
 Hollow organ, lined with transitional epithelium that allow bladder to distend.
 Trigone
o On floor of urinary bladder
 Ureters open into posterior, inferior floor of urinary bladder
 Urethra openining positioned on anterior, inferior floor of urinary bladder =
neck
 Detrusor Muscle
o Smooth muscle coat surrounding urinary bladder
o Forms internal urethral sphincter at neck of urinary bladder
o Sustained contractions prevents urination(micturation)
Urethra
 Conveys urine from urinary bladder to exterior
 Opening = external urethral meatus
 External urethral sphincter
o skeletal muscle surrounding urethra


Female urethra = 4cm (1.5 inches)
Male urethra = 19cm (7-8 inches)
o Prostetic urethra – passes through prostate gland
o Membranous urethra – passes through external urethral sphincter (urogenital
diaphragm)
o Penile urethra – passes through corpus spongiosum of penis