Chapter 38 Flashcards
Structure and Function of the Renal/Urologic & Digestive System
What are the primary functions of the Kidney’s?
- Maintain a stable internal environment for optimal cell and tissue metabolism.
- Balance solute and water transport.
- Excrete metabolic waste products.
- Conserve nutrients.
- Regulate acids and bases
What hormones do the kidneys secrete as their endocrine functions?
- Renin: Regulation of blood pressure
- Erythropoietin: Production of erythrocytes
- 1,25-dihydroxyvitamin D3: Metabolism of calcium
Synthesis of glucose from amino acids.
Gluconeogenesis
What substance forms in the kidneys and drains into the bladder?
Urine
Define the structure of the kidneys.
Paired organs located in the posterior region of the abdominal cavity behind the peritoneum (retroperitoneal).
What is a tightly adhering capsule that surrounds each kidney; each kidney is then embedded in a mass of fat.
Renal Capsule
What is the fibrous tissue that attaches each kidney to the posterior abdominal wall?
Renal Fascia
This is where the renal blood vessels, nerves, lymphatic vessels, and ureter enter and exit the kidneys.
Hilum
This is the outer layer of each kidney. It also contains all the glomeruli, most of the proximal tubules, and some segments of the distal tubule.
Renal Cortex
This is the inner part of each kidney that contains tubules and the collecting duct. It also consists of the regions called the pyramids.
Renal Medulla
Extends from the cortex down between the renal pyramids.
Renal Columns
Apexes of the pyramids that projects into a cup-shaped cavity that joins together to form a major calyx?
Minor Calyx
Joins to form the renal pelvis.
Major Calyx
Joins the proximal end of the ureter.
Renal Pelvis
What is the functional unit of the kidney? (Hint, each kidney contains 1.2 million)
Nephron
This makes up 85% of all nephrons, which extend partially into the medulla.
Superficial Cortical Nephrons
These have short or long loops.
Midcortical Nephrons
Lie close to and extend deep into the medulla and are important for the process of concentrating urine.
Juxtamedullary Nephrons
Three main components of the Renal Corpuscle.
- Glomerulus
- Bowman Glomerular Capsule
- Mesangial Cells
Tuff of capillaries
Glomerulus
Bowman space; Circular space between visceral and parietal epithelium
Bowman Glomerular Capsule
- Secrete mesangial matrix; lie between and support the glomerular capillaries. Some of these contracts like smooth muscle cells to regulate glomerular capillary blood flow.
- Have phagocytic properties and release inflammatory cytokines and growth factors.
Mesangial Cells
Filters selected blood components through its three layers
Glomerulus
What are the three layers of the glomerular filtration membrane?
- Inner Capillary Endothelium
- Middle Glomerular Basement Membrane (GBM)
- Outer Layer: Visceral Epithelium that forms the inner layer of the Bowman’s capsule.
- Synthesize Nitric Oxide (a vasodilator)
- Synthesize Endothelin-1 (a vasoconstrictor)
- Regulate glomerular blood flow.
Glomerular endothelial cells
- What part of the Nephron: Is composed of cells bodies called podocytes, which are foot like projections?
- Form an elaborate network of intercellular clefts called filtration slits, modular filtration.
- Supplied by the afferent arteriole and drained by the efferent arteriole.
Visceral Epithelium of the Bowman’s Capsule
What are the two components of the Juxtaglomerular Apparatus?
- Juxtaglomerular Cells
- Macula Densa
These specialized cells are located around the afferent arteriole where the afferent arteriole enters the glomerulus.
Juxtaglomerular Cells
Between the afferent and efferent arterioles of the distal convoluted tubule; sodium-sensing cells.
Macula Densa
What three things are controlled by the Juxtaglomerular Apparatus (JGA) at this site?
- Renal Blood Flow (RBF)
- Glomerular Filtration
- Renin Secretion
This is where substances are reabsorbed from the filtrate or secreted into the filtrate.
Renal Tubules
Is the only surface inside the nephron covered with microvilli?
Proximal Convoluted Tubule
Is a hairpin-shaped loop composed of thick and thin portions of a descending segment that goes into the medulla.
Loop of Henle
Extends from macula densa to collecting duct.
Distal Convoluted Tubule
Descends down the cortex, through the renal pyramids of the inner and outer medullae, draining urine into the minor calyx.
Collecting Duct
Reabsorbs sodium and water and secretes potassium.
Principle Cells
Secretes hydrogen and reabsorb potassium.
Intercalated Cells
Supplies blood to the kidneys.
Renal Arteries
Travel down the renal columns and between the pyramids.
Interlobar Arteries
- Arch over the base of the pyramids and run parallel to the surface of the kidneys.
- Interlobular arteries extend through the cortex toward the periphery of the kidneys and supply the afferent glomerular arterioles.
Arcuate Arteries
- Feed into the efferent Arteriole
- Afferent arterioles subdivide into a fist like structure of four to eight glomerular capillaries.
- Efferent arterioles convoy blood to a second capillary bed
Glomerular Capillaries
Surround the proximal and distal convoluted tubules and loop of Henle.
Peritubular Capillaries
Is a network of capillaries that forms loops and follow loops of Henlel
Vasa Recta
Follow arterial path in reverse direction and have the same names as corresponding arteries, empty into inferior vena cava.
Renal Veins
- Are 30 cm long
- Are long, intertwining smooth muscle Bundles.
- Pass obliquely through the posterior aspect of the bladder
- Peristaltic activity moves urine to the bladder
- Micturition compresses the lower end of this ureter to prevent further urine reflux.
Ureters
Bladder
Detrusor muscle
Transitional epithelium
Trigon
Transitional epithelium
- Internal Urethral Sphincter
*Smooth muscle located at junction of bladder and urethra. - External Urethral Sphincters
*Striated skeletal muscle under voluntary control. - Between 3 and 4 cm long in females
- Between 18 and 20 cm long in males
Urethra
- Parasympathetic Fibers
Bladder and internal urethral sphincter - Skeletal motor Neurons in the pudenda nerve
External Urethral Sphincter
Innervation
Kidneys receive 1000-1200 mL of blood per minute.
Renal Blood Flow
600-700 mL as plasma
Renal Plasma Flow (RPF)
- Filtration of Plasma into the Bowman space.
- 20% of the RPF (120-140 mL/ minute)
- Directly related to the perfusion pressure in the glomerular capillaries.
- If mean arterial pressure decreases or vascular resistance increases then the RBF decreases.
Glomerular Filtration Rate (GFR)
- Strict maintenance of 80-180 mmHg provides constant GFR.
- As the systemic blood pressure increases, afferent arterioles constrict, preventing an increase in filtration pressure.
- Prevents wide fluctuations in the systemic arterial pressure from being transmitted to the Glomerular Capillaries.
- Solute and water excretion is constantly maintained, despite arterial pressure changes. - Myogenic Mechanism (stretch)
- As arterial pressure declines, glomerular perfusion
increases.
- Stretch on the afferent arteriolar smooth
muscle decreases, and the arteriolar relaxes.
- An increase in arteriolar pressure decreases
glomerular perfusion.
- Causes the arteriole smooth muscle to
contract. - Tubuloglomerular feedback (sodium chloride NaCl content)
- When sodium filtration increases, GFR decreases.
- Macula densa cells stimulate afferent arteriolar
vasoconstriction.
- When sodium filtration decreases, the opposite
occurs - GFR increases.
Autoregulation
- Sympathetic nervous system.
- Vasoconstriction diminishes RBF and GFR
- Increases renal tubular sodium and water
reabsorption.
- Increases blood pressure. - Decreased afferent renal sympathetic nerve activity produces opposite effects.
- Renalase: Promotes Metabolism of catecholamines
- Hormonal regulation of renal blood flow.
Neural Regulation
- Increases systemic arterial pressure and increases
sodium reabsorption. - Renin: Enzyme is formed and stored in the afferent
arterioles of the juxtaglomerular apparatus. - Renin helps form angiotensin I (physiologically
inactive). - In the presence of angiotensin-converting enzyme
(ACE), angiotensin I is converted to angiotensin II - Angiotensin II
- Stimulates the secretion of aldosterone by the
- adrenal cortex.
- Is a potent vasoconstrictor.
- Stimulates antidiuretic hormone (ADH) secretion
and thirst.
- Renin-Angiotensin-Aldosterone System (RAAS)
- Atrial natriuretic peptide (ANP) is secreted from myocardial cells in the atria.
- Brain natriuretic peptide (BNP) is secreted from myocardial cells in the ventricles.
- ANP and BNP
- Inhibit sodium and water absorption by kidney
tubules.
- Inhibit secretion of renin and aldosterone.
- Vasodilate the afferent arterioles, constrict the
efferent arterioles.
- Increase urine formation, leading to decreased
blood volume and pressure.
Natriuretic Peptides
- Is secreted from vascular endothelium and in the
nephron. - Causes vasodilation.
C-type Natriuretic Peptide
- Is secreted by the distal convoluted tubules and the collecting ducts.
- Causes vasodilation, increases renal blood flow, and diuretic effects.
Urodilatin
Influences RBF
Hormones and Mediators
- Filters the plasma at the glomerulus.
- Reabsorbs and secretes different substances at
various parts of its tubular structure. - Forms a filtrate of protein-free plasma, called
ultrafiltration. - Regulates filtrate to maintain body fluid volume,
electrolyte composition, and pH with narrow limits.
- Requires tubular reabsorption and tubular
secretion.
Nephron Functions
Movement of protein-free plasma across the glomerular membrane (hydrostatic pressure)
Filtration
Movement of fluid and solutes from tubular lumen to the peritubular capillaries.
Tubular Reabsorption
Transfer of substances from the peritubular capillaries to the tubular lumen.
Tubular Secretion
Elimination of substances in the final urine
Excretion
- Glomerulus is freely permeable to water and
relatively impermeable to large colloids such as
plasma proteins.
- Size and electrical charge are important factors
that affect permeability.
- Positive-Charged particles permeate the
membrane more readily that neutral- or
negative-charged particles.
- Capillary pressure
- Hydrostatic pressure
- Determined by systemic arterial pressure and
resistance to blood flow in the afferent and
efferent arterioles.
Glomerular Filtration
- Is the combined effect of forces favoring and forces opposing filtration.
- Favoring forces: Capillary hydrostatic pressure
- Opposing forces: Oncotic pressure in the capillary
and hydrostatic pressure in Bowman’s capsule - Includes glomerular hydrostatic pressure, capsular
hydrostatic pressure, and blood oncotic pressure.
Net Filtration Pressure
- Total volume of fluid filtered by the glomeruli
averages 180 L/day or approximately 120 mL/minute. - Filtration of plasma per unit of time is directly related
to the perfusion pressure of the RBF. - 99% of the filtrate is reabsorbed into the peritubular
capillaries and returned to the blood.
Filtration Rate
In some molecules, active transport is limited as carrier molecules become saturated: Transport maximum
Active Transport
- Approximately 60% to 70% of filtered sodium and
water and approximately 50% of urea have been
reabsorbed, along with 90% or more of potassium,
glucose, bicarbonate, calcium, phosphate, amino
acids, and uric acid. - Chloride, water, and urea are passively reabsorbed.
Tubular Transport
- Function: Active reabsorption of sodium.
- Promotes the passive diffusion of water.
- Reabsorption of water leaves an increased
concentration of urea.
- Hydrogen ions are actively exchanged for sodium
ions.
- Bicarbonate combines with hydrogen in the tubular
cell and is eventually reabsorbed as carbon dioxide
(CO2) and water.
- Glomerulotubular balance (GTB) - Damaged renal tubules: Metabolic byproducts and
drugs may accumulate, causing toxic levels.
Proximal Convoluted Tubules
- Provides the kidney with the ability to concentrate
urine and conserve water for the body. - Fluid leaving the ascending limb of the loop is
hypoosmotic and is more diluted than the fluid that
entered. - Reabsorb more solute than water into the
interstitium. - Primary function is to establish a hyperosmotic sate
within the medullary interstitial fluid. - Thin, descending segment: Is highly permeable to
water and moderately permeable to sodium, urea,
and other solutes. - Thin, ascending segment: Is highly permeable to
water and moderately permeable to sodium, urea,
and other solutes. - Thick portion of the ascending segment: Is highly
permeable to sodium, potassium, and chloride and
significantly less permeable to water and urea.
Loop of Henle
- Performs the final adjustments in urine composition.
- Convoluted portion of the distal tubule: Is limitedly
permeable to water but readily absorbs ions and
contributes to the dilution of the tubular fluid. - Straight segment of the distal tubule and the
collecting duct: Is permeable to water as controlled
by ADH. - Tamm-Horsfall Glycoprotein (uromodulin)
- Is formed on the epithelial surface of the thick
ascending segment and is the first segment of the
distal tubules.
- Is the most abundant urinary protein.
- Protects against bacterial adhesion and urolithiasis.
Is a renal ligand for lymphokines. - Sodium is readily absorbed by the latter segment of
the distal tubule and collecting duct under the
regulation of aldosterone. - Potassium is actively secreted by the principal cells
and is reabsorbed in lesser amounts by intercalated
cells in these segments; is controlled by aldosterone
and other factors related to the concentration of
potassium in body fluids. - Hydrogen is secreted by the distal tubule; it
combines with non-bicarbonate buffers (ammonium
and phosphate) for the elimination of excess acids in
the urine. - Contribute to the regulation of acid-base balance by
excreting hydrogen ions into the urine and by adding
new bicarbonate to the plasma.
Distal Convoluted Tubules and Collecting Duct
- When GFR spontaneously decreases or increases.
- Renal tubules and, primarily the proximal tubules,
automatically adjust their rate of reabsorption of
sodium and water to balance the change in GFR.
- Constant fraction of filtered sodium and water is
reabsorbed from the proximal tubule.
Glomerulotubular balance
- Are initiated in the thick ascending limb of the loop
of Henle with active transport of chloride and sodium
into the medullary interstitium. - Hyperosmotic interstitium causes water to move out
of descending limb; the remaining fluid becomes
increasingly concentrated. - As fluid enters the ascending limb, sodium and
chloride are removed and water is retained. - Fluid becomes more and more dilute as it enters the
distal tubule.
Water, Sodium, and Chloride
- Is the end product of protein metabolism and the
major constituent of urine. - Approximately 50% of urea is excreted in the urine,
and 50% is recycled in the kidneys.
Urea
- Promote afferent arteriolar vasoconstriction and decrease GFR and RBF.
- Renalase: Is the hormone produced by the kidney that promotes the metabolism of catecholamines and regulates blood pressure.
Catecholamines
- Controls the concentration of final urine.
- Increases water permeability in the last segment of
the distal tubule and along the entire length of the
collecting ducts. - In the presence of ADH, water reabsorption is high,
causing less urine volume.
ADH
Promotes diuresis
Natriuretic peptides
Are the agents that enhance the flow and excretion of urine.
Diuretic Drugs
- Calcitriol (1,25-dihydroxyvitamin D3)
- Is necessary for the absorption of calcium and
phosphate by the small intestine. - Can be obtained in the diet or synthesized by action
of ultraviolet radiation on cholesterol in the skin. - Decreased phosphate levels stimulate calcitriol.
Vitamin D
- Is produced in fetal liver and the adult kidney; is
essential for erythropoiesis. - Chronic renal failure: Causes anemia from reduced
erythropoietin secretion.
Erythropoietin
