Chapter 26 - The Urinary System Flashcards
What does Urinary System consist of?
1- Kidneys
2- Ureters
3- Bladder
4- Urethra
Maintain homeostasis by managing volume and composition of fluid reservoirs, primarily blood
What are Functions of Kidneys?
1- Regulation of blood ionic composition:
Na+, K+, and Cl-
2- Regulation of blood pH:
H+, HCO3-
3- Regulation of blood volume:
H2O
4- Regulation of BP
5- Maintenance of blood osmolarity
6- Production of hormones:
Calcitriol
Erythropoietin
8- Excretion of metabolic wastes and foreign substances (drugs or toxins)
9- Regulation of blood glucose level
What is Kidney?
Retroperitoneal, partly protected by lower ribs
Renal Hilum:
Indented area
Entrance for:
1- Renal Artery
2- Renal Vein
3- Ureter
4- Nerves
5- Lymphatics
What are External Layers of Kidneys?
External Layers:
(Superficial to deep)
1- Renal Fascia:
Anchors to other structures
2- Adipose Capsule:
Protects and anchors
3- Renal Capsule:
Continuous with Ureter
What is Internal Renal Anatomy?
1- Renal Cortex:
Outer layer
2- Renal Medulla:
Inner region
3- Renal Pyramids:
Secreting apparatus and Tubules
4- Renal Columns:
Anchor the Cortex
What is Path of Urine Drainage?
1- Collecting Duct
2- Papillary Duct
3- Minor Calyx
4- Major Calyx
5- Renal Pelvis
6- Ureter
7- Urinary Bladder
What is Kidney Blood Supply?
Receive 20-25% of resting cardiac output
Flow:
1- Renal Artery
2- Segmental Arteries
3- Interlobar Arteries
4- Arcuate Arteries
5- Cortical Radiate Arteries
6- Afferent Arterioles
7- Glomerular Capillaries
8- Efferent Arterioles
9- Peritubular Capillaries
10- Peritubular Venules
11- Cortical Radiate Veins
12- Arcuate Veins
13- Interlobar Veins
14- Renal Vein
What is Kidney Nerve Supply?
Renal Nerves primarily carry Sympathetic outflow
They regulate blood flow through Kidneys
What are Structures of a Nephron?
1- Renal Corpuscle:
Glomerulus
Glomerular Capsule
2- Proximal Convoluted Tubule
3- Nephron Loop:
Descending Limb of Nephron Loop
Ascending Limb of Nephron Loop
4- Distal Convoluted Tubule
What is Renal Corpuscle?
Consists of 2 parts:
1- Glomerulus:
Mass of capillaries
Fed by the Afferent Arteriole
Drains into Efferent Arteriole
2- Glomerular Capsule (Bowman’s Capsule):
Visceral layer of Podocytes which wrap around capillaries
Filtrate is collected between the Visceral and Parietal layers
Glomerular Endothelial Cells have large pores (fenestrations) and are leaky to filter out
Basal Lamina lies between Endothelium and Podocytes
Podocytes form Pedicels, between which are Filtration Slits
What is the Filtration Membrane?
1- Fenestration of Glomerular Endothelial Cell:
Prevents filtration of blood cells
But allows all components of blood Plasma to pass through
2- Basement Membrane of Glomerulus:
Prevents filtration of larger proteins
3- Slit Membrane between Pedicels:
Prevents filtration of medium-sized proteins
What is Cortical Nephron?
80-85% of Nephrons
Renal Corpuscle in outer portion of Cortex
Short Loops of Henle extend only into outer region of Medulla
Create urine with osmolarity similar to blood
What is Flow of Fluid through a Cortical Nephron?
1- Glomerular Capsule (Bowman’s Capsule)
2- Proximal Convoluted Tubule
3- Descending Limb of the Nephron
4- Ascending Limb of the Nephron
5- Distal Convoluted Tubule
Then drains into Collecting Duct, Papillary Duct, Renal Papilla, Minor Calyx, Urine
What is Juxtamedullary Nephron?
Renal Corpuscle deep in Cortex with long Nephron Loops
Receive blood from Peritubular Capillaries and Vasa Recta (where body checks need for ions or not)
Ascending Limb has thick and thin regions
Enables Kidney to secrete very concentrated urine
What is Flow of Fluid through a Juxtamedullary Nephron?
1- Glomerular Capsule (Bowman’s Capsule)
2- Proximal Convoluted Tubule
3- Descending Limb of the Nephron
4- Thin Ascending Limb of the Nephron
5- Thick Ascending Limb of the Nephron
6- Distal Convoluted Tubule
Then drains in Collecting Duct, Papillary Duct, Renal Papilla, Minor Calyx, Urine
What is Juxtaglomerular Apparatus?
The Ascending Loop contacts the Afferent Arteriole at the Macula Densa
The wall of the Arteriole contains smooth muscle cells called Juxtaglomerular Cells (pump blood)
The Juxtaglomerular Apparatus regulates BP in the Kidney in conjunction with the ANS
What is Urine Formation?
Excretion of Solute = Glomerular Filtration + Secretion - Reabsorption
1- Glomerular Filtration:
In Glomerulus, blood plasma and dissolved substances (smaller than most proteins) get filtered into the Glomerular Capsule
2- Tubular Reabsorption:
All along the Renal Tubule and Collecting Duct, water, ions, and other substances get reabsorbed from the Renal Tubule Lumen into the Peritubular Capillaries and ultimately into the blood
3- Tubular Secretion:
All along the Renal Tubule and Collecting Duct, substances such as wastes, drugs, and excess ions get secreted from the Peritubular Capillaries into the Renal Tubule.
These substances ultimately make their way into the Urine
What is Glomerular Filtration?
Driven by BP
Opposed by Capsular Hydrostatic Pressure (How much dissolved in vessel hitting walls) and Blood Colloid Osmotic Pressure (bigger proteins in blood)
Water and small molecules move out of the Glomerulus
In one day, 150-180L of water pass out of the Glomerular Capsule
Net Filtration Pressure = Glomerular Blood Hydrostatic Pressure - Capsular Hydrostatic Pressure - Blood Colloid Osmotic Pressure
NFP = GBHF - CHP - BCOP
What is Glomerular Filtration Rate (GFR)?
Glomerular Filtration Rate (GFR):
Amount of filtrate formed by both kidneys each minute
Homeostasis requires kidneys to maintain relatively constant GFR
If GFR too high:
Substances pass quickly and not reabsorbed, most secreted
If GFR too low:
Nearly all reabsorbed and some waste products not adequately excreted
GFR averages:
1- Males:
125mL/min
2- Females:
105mL/min
GFR is controlled by:
1- Renal Autoregulation
2- Neural Regulation
3- Hormonal Regulation
What is Renal Autoregulation of GFR?
1- Myogenic Mechanism:
Smooth Muscle Cells in Afferent Arterioles contract in response to elevated BP
2- Tubuloglomerular Feedback:
High GFR diminishes reabsorption
Macula Densa inhibits release of NO
Afferent Arterioles constrict
What is Example of Negative Feedback Loop for High GFR?
1- GFR increased
2- Macula Densa Cells of Juxtaglomerular Apparatus detect it
(Detect increased delivery of Na+, Cl-, and water)
3- Juxtaglomerular Apparatus decrease secretion of NO
4- Afferent Arterioles constrict, which decreases blood flow through Glomerulus
5- GFR decreases
What is Neural Regulation of GFR?
Kidneys are richly supplied by Sympathetic fibers
In case of strong Sympathetic stimulation, such as exercise of Hemorrhage:
1- Afferent Arterioles are constricted
2- Urine output is reduced
3- More blood is available for other organs
What is Hormonal Regulation of GFR?
1- Decreased Angiotensin II constricts Afferent and Efferent Arterioles
Therefore decreasing GFR
2- Increased Atrial Natriuretic Peptide (ANP) relaxes Mesangial Cells
Increasing Capillary surface area and GFR
(Have opposite effects)
(ANP secreted in response to stretch of Cardiac Atria)
What is the Effect on GFR from Myogenic Mechanism?
1- Stimulus:
High BP increase stretching of smooth muscle in Afferent Arteriole wall
2- Action:
Stretched smooth muscle contract
Narrowing Lumen of Afferent Arteriole
3- GFR:
Decrease
What is the Effect on GFR from Tubuloglomerular Feedback?
1- Stimulus:
Rapid delivery of Na+ and Cl- to Macula Densa due to high BP
2- Action:
Decreased release of NO by Juxtaglomerular Apparatus causes constriction of Afferent Arterioles
3- GFR:
Decrease
What is the Effect on GFR from Neural Regulation?
1- Stimulus:
Increased level of renal sympathetic nerve impulses release Norepinephrine
2- Action:
Constriction of Afferent Arterioles through increased release of Renin
3- GFR:
Decrease
What is the Effect on GFR from Angiotensin II?
1- Stimulus:
Blood Volume or BP decreases stimulates production of Angiotensin II
2- Action:
Constriction of Afferent and Efferent Arterioles
3- GFR:
Decrease
What is the Effect on GFR from Atrial Natriuretic Peptide (ANP)?
1- Stimulus:
Stretching of Cardiac Atria stimulates secretion of ANP
2- Action:
Relaxation of Mesangial Cells in Glomerulus increases capillary surface area available for filtration
3- GFR:
Increase
What is Tubular Reabsorption and Secretion?
Much of filtrate is reabsorbed, especially water, glucose, AA, and ions
Secretion helps manage pH and rid body of toxic and foreign substances
What is Plasma, Filtrate and Urine Composition of Water?
1- Filtered (enters Glomerular Capsule):
180L
2- Reabsorbed (returned to blood):
178-178.5L
3- Secreted (to become Urine):
1.5-2L
What is Plasma, Filtrate and Urine Composition of Uric Acid?
1- Filtered (enters Glomerular Capsule):
8.5g
2- Reabsorbed (returned to blood):
7.7g
3- Secreted (to become Urine):
0.8g
What is Plasma, Filtrate and Urine Composition of Creatinine?
1- Filtered (enters Glomerular Capsule):
1.6g
2- Reabsorbed (returned to blood):
0g
3- Secreted (to become Urine):
1.6g
What are Reabsorption Routes?
1- Paracellular Reabsorption:
Passive fluid leakage between cells
ex: Tight Junction
2- Transcellular Reabsorption:
Directly through the Tubule Cells
Active Transport
ex: Na+/K+ Pump
(channels receive ions to be reabsorbed)
What are Transport Mechanisms in the Urinary System?
1- Primary Active Transport:
Uses ATP, like Na+/K+ pumps
At rest, accounts for 6% of total body ATP use
2- Secondary Active Transport:
Driven by ion’s electrochemical gradient
Symporters move substances in same direction
Antiporters move substances in opposite direction
What is Water Reabsorption?
1- Obligatory Water Reabsorption:
90%
Water follows the solutes that are reabsorbed
2- Facultative Water Reabsorption:
10%
Regulated by ADH
What is Reabsorption and Secretion in Proximal Convoluted Tubules?
1- Na+/Glucose Symporters
2-Na+/H+ Antiporters
3- Aquaporin-1:
Membrane protein permeable to water
What is Passive Reabsorption in Late Proximal Convoluted Tubules?
1- Diffusion from Lumen in Tubule to Peritubular Capillary:
Cl-
K+
Ca2+
Mg2+
Urea
2- Osmosis of water from Lumen of Tubule to Peritubular Capillary
What is Reabsorption in the Loop of Henle?
1- Relatively impermeable to water, especially the Ascending Limb
2- Little Obligatory Water Reabsorption
3- Na+/K+/2Cl- Symporters
What is Reabsorption in early Distal Convoluted Tubules?
1- Na+/Cl- Symporters reabsorb ions
2- PTH stimulates reabsorption of Ca2+
Also inhibits Phosphate reabsorption in Proximal Convoluted Tubules enhancing its excretion
What is Late Distal Convoluted Tubule and Collecting Duct?
1- Principal Cells:
Na+/K+ Pumps reabsorb Na+
2- Aquaporin-2:
Reabsorb Water
Stimulated by ADH
3- Intercalated Cells:
Reabsorb K+ and HCO3- (Bicarbonate)
Secrete H+
What is Negative Feedback Loop of ADH?
1- Increased Osmolarity of plasma and interstitial fluid
2- Osmoreceptors in Hypothalamus send nerve impulses to Hypothalamus and Posterior Pituitary
3- Hypothalamus increase secretion of ADH through Posterior Pituitary
4- Principal Cells in DCT and Collecting Duct become more permeable to water, which increases Facultative Water Absorption
5- Decrease in plasma Osmolarity
What is Histology of Proximal Convoluted Tubule?
Simple cuboidal epithelial cells
With prominent brush border of Microvilli
What is Histology of Descending Limb of Nephron?
Simple squamous epithelial cells
What is Histology of Thin Ascending Limb of Nephron?
Simple squamous epithelial cells
What is Histology of Thick Ascending Limb of Nephron?
Simple cuboidal epithelial cells
With brush border of Microvilli
What is Histology of most of Distal Convoluted Tubule?
Simple cuboidal epithelial cells
What is Histology of last part of Distal Convoluted Tubule and all of Collecting Duct
Simple cuboidal epithelium
Consisting of Principal Cells and Intercalated Cells
What is Regulation of Tubular Reabsorption and Secretion by Angiotensin II?
1- Stimulus:
Low blood volume or low BP
Stimulates Renin-induced production of Angiotensin II
2- Action:
Stimulates activity of Na+/H+ Antiporters in PCT
3- Effects:
Increase Reabsorption of Na+ and water
Which increases BP and blood volume
What is Regulation of Tubular Reabsorption and Secretion by Aldosterone?
1- Stimulus:
Increased Angiotensin II level and increased level of plasma K+
Promote release of Aldosterone by Adrenal Cortex
2- Action:
Enhance activity of Na+/K+ Pumps in Basolateral membrane
And Na+ Channels in Apical membrane of Principal Cells in CT
3- Effects:
Increase secretion of K+ and reabsorption of Na+
Increase reabsorption of water, which increase blood volume and BP
What is Regulation of Tubular Reabsorption and Secretion by Antidiuretic Hormone (ADH)?
1- Stimulus:
Increased Osmolarity of ECF or decreased blood volume
Promotes release of ADH from Posterior Pituitary Gland
2- Action:
Stimulate insertion of water channel proteins (Aquaporin-2) into Apical membranes of Principal Cells
3- Effects:
Increase Facultative Water Reabsorption
Which decrease Osmolarity of body fluid
What is Regulation of Tubular Reabsorption and Secretion by Atrial Natriuretic Peptide (ANP)?
1- Stimulus:
Stretching of Atria stimulates ANP secretion
2- Action:
Suppresses reabsorption of Na+ and water in PCT and CT
Inhibits secretion of Aldosterone and ADH
3- Effects:
Increase excretion of Na+ in urine (Natriuresis)
Increase urine output (Diuresis)
Thus decrease blood volume and BP
What is Regulation of Tubular Reabsorption and Secretion by PTH?
1- Stimulus:
Decreased level of plasma Ca2+
Promotes release of PTH
2- Action:
Stimulate opening of Ca2+ Channels in Apical membrane of early DCT cells
3- Effects:
Increase reabsorption of Ca2+
What is Urine Production?
Fluid intake is highly variable
Homeostasis requires maintenance of fluid volumes within specific limits
Urine concentration varies with ADH
High intake of fluid results in dilute urine of high volume
Low intake of fluid results in concentrated urine of low volume
What is Formation of Dilute Urine?
Glomerular Filtrate and blood have the same osmolarity (water concentration) at 300mOsm/L
but
Tubular osmolarity changes due to a concentration gradient in the Medulla
When dilute urine is formed, osmolarity in the Tubule:
1- Increases in Descending Limb
2- Decreases in Ascending Limb
3- Decreases more in the Collecting Duct
Thick Ascending Limb:
1- Symporters actively reabsorb Na+, K+, and Cl-
2- Low water permeability
3- Solutes leave, water stays in Tubule
Collecting Duct:
Low water permeability in absence of ADH
What is Formation of Concentrated Urine?
Juxtamedullary Nephrons with long loops
Osmotic gradient is created by the Countercurrent Multiplier
Solutes pumped out of Ascending Limb, but water stays in Tubule
Medulla osmolarity is increased
In presence of ADH, Collecting Ducts become very permeable to water
(more ions, less water)
Tubular fluid becomes very concentrated
Movement of water also carries Urea into the Medulla, contributing to its osmolarity
What is Countercurrent Exchange?
Loop and Duct Cells require nutrients and oxygen from blood supply
Capillaries that feed them (Vasa Recta) form loops like those of Nephron Loops in the Medulla
Incoming and outgoing blood will have a similar osmolarity
This maintains Medulla concentration gradient
1- Symporters in Thick Ascending Limb cause buildup of Na+ and Cl- in Renal Medulla
2- Countercurrent flow through Nephron Loop establishes osmotic gradient
3- Principal Cells in Collecting Duct reabsorb more water when ADH is present
4- Urea recycling causes buildup of Urea in Renal Medulla
What is Evaluation of Kidney Function?
Routine Urinalysis primarily evaluates for the presence of abnormalities in the urine:
1- Albumin
2- Glucose:
Pancreas not secreting Insulin enough
Filtration for urine but still Glucose in urine
Metabolism of Ketones
Ketones acidic
pH of blood decrease
Ketoacidosis
Urine acidic
3- RBC
4- Ketone Bodies
Insulin level low
Glucose out of cells into blood
Starving for glucose
Ketone Bodies breakdown
Elevated Ketone breakdown for energy
Diabetes
5- Microbes
What is Urine Transportation and Storage?
Each Ureter transports urine from a Renal Pelvis by Peristaltic waves, Hydrostatic Pressure, and gravity
No anatomical valve at the opening of the Ureter into Bladder
When Bladder fills, it compresses the opening and prevents backflow
The Bladder is a hollow, distensible, Muscular organ, with a capacity averaging 700-800mL
What is Ureter, Bladder, and Urethra Anatomy?
1- Right and Left Ureters:
Transport urine from Kidneys to Bladder
2- Ureteral Openings:
In Bladder
3- Peritoneum:
Holds Urinary Bladder in place
4- Rugae of Mucosa:
Allow expansion of Urinary Bladder as it fills
5- Detrusor Muscle:
Contracts to push urine into Urethra
6- Trigone:
Triangle area from the 2 Ureteral Openings to the Internal Urethral Orifice
7- Internal Urethral Orifice:
Opening into Urethra
8- Internal Urethral Sphincter:
Involuntary controls opening and closing of Urethra
9- Urethra:
Passageway for discharging urine from body
10- External Urethral Sphincter:
In deep muscles of Peritoneum
Voluntarily controls opening and closing of Urethra
11- External Urethral Orifice:
Opening of Urethra to outside
What is Micturition?
The discharge of urine involves voluntary and involuntary muscle contractions
Stretch Receptors trigger a Spinal Reflex, which we learn to control in childhood
The Urethra carries urine from the Internal Urethral Orifice to the exterior of the body
In males, it discharges Semen as well as urine
What is Urethra in Males?
1- Prostatic Urethra:
Passes through Prostate Gland
Besides urine, it receives secretions containing sperm, sperm motility and viability factors, and substances that neutralize the pH of the Urethra
2- Intermediate Urethra:
Passes through Perineum
Shortest segment
3- Spongy Urethra:
Passes through Penis
Longest segment
Receives secretions including mucus and substances that neutralize the pH of the Urethra
During ejaculation in the male, the semen passes through all segments of the Urethra to the outside
Male vs Female Urethra?
1- Urethra 5x longer in males than females
2- Urethra is divide into 3 segments in males, but only 1 short tube in females
3- Urethra is a common duct for the Urinary and Reproductive systems in males, these 2 systems are entirely separate in females
What is Waste Management?
1- Body buffers
2- Blood
3- Liver
4- Lungs
5- Sweat
6- GIT
What is Development of Urinary System?
During 3rd week of fetal development, a portion of the Mesoderm begins to differentiate inot the Kidneys:
Pronephros
Mesonephros
How does Aging affect Urinary System?
1- Kidneys shrink in size:
Lose about 1/3 their mass
2- Experience a decrease in blood flow:
Glomerular vessels are damaged or decrease in number
3- Experience a decrease in filtration
What are some Urinary System Disorders?
1- Renal Calculi (Kidney stones)
2- Urinary Tract Infection (UTI)
3- Glomerular disease
4- Renal failure
5- Polycystic Kidney disease
6- Urinary Bladder Cancer
7- Kidney transplant
8- Cystoscopy
