Renal Exam 5 Flashcards
Anatomy of the Kidney: Functional portion, functional unit, nephron
Functional portion: Parenchyma
Functional unit: nephron
Nephron: renal corpuscle and renal tubules
Kidneys: Maintenance of homeostasis
Blood ionic composition: Na, K, Ca, Cl, HPO4
Blood pH: Excretion of H+
Blood Volume: Conservation or elimination of water
Blood Osmolarity: Regulating loss of water and solutes in urine
Kidneys: Removal of substances from blood
Metabolic waste and chemicals: urea (aa), creatinine (creatine phosphate in muscle), bilirubin (hemoglobin)
Drugs and metabolites
Kidneys: Regulation of processes
Hormone production: Calcitriol (activate Vit D) and Erythropoietin
Blood Pressure: renin release
Blood Glucose Levels: Gluconeogenesis (Gln)
Functional portion of kidneys contains two distinct regions
Renal cortex (superficial area)
Renal medulla (inner portion)
they constitute the parenchyma or functional portion
Nephrons: location and used for
Located in both cortex and medulla
Used for filtration of blood & reabsorption & secretion of materials
Nephrons: parts and functional units
Parts: renal corpuscle and renal tubule
Functional Units because they: form urine, remove waste from blood, regulate water and electrolyte concentrations
Nephron: Renal Corpuscle
Renal corpuscle is the filtration unit
Composed of: glomerulus, glomerular or Bowman’s capsule
Renal Tubule sections
1: Proximal Convoluted tubule
2: Loop of Henle
3: Distal Convoluted Tubule
Collecting Tubule often is not considered as part of the nephron
Types of Nephrons
Two types based on anatomical location
-Cortical nephrons
-Juxtamedullary nephrons
Cortical Nephrons
Corpuscles located closer to surface of the kidney (renal capsule)
SHORT nephron loops: extend only to outer region of renal medulla
80% of nephrons (near top of cortex)
Juxtamedullary Nephrons
Corpuscles in the cortex but close to renal medulla
Nephron loops extend deep into the renal medulla
20% of nephrons
Important for regulating water
Arterial and Venous blood supply to the kidney
Arterial flow brings blood into the kidney:
-Renal Artery
-Transports O2 blood from heart and aorta to kidney for filtration
Venous flow takes blood out of the kidneys:
-Renal Vein
-Transports filtered and deoxygenated blood from the kidney to the posterior vena cava and then the heart
Arterial blood supply to the kidneys
-Kidney receives blood via renal artery (1)
-Renal artery divides into segmental arteries (2)
-Segmental arteries branch (3)
— enter the parenchyma and pass through renal columns as interlobar arteries
Blood flow from renal column to the renal cortex as follows in the kidney:
-Interlobar arteries arch at the base of the pyramids (between medulla and cortex) forming arcuate arteries
-Arcuate arteries divide producing interlobular arteries
-Interlobular arteries enter the renal cortex and branch off to form afferent arterioles, which supply the nephron
Blood supply to the Glomerulus: Efferent arteriole, afferent arteriole
Afferent arteriole:
-Transports arterial blood to the glomerulus for filtration
-Divides into glomerular capillaries
-Has larger diameter than efferent arteriole
-Passes blood to the efferent arteriole
Efferent arteriole:
-It carries blood out of the glomerulus
-efferent arteriole give rise to capillaries that surround renal tubule
Blood Supply of Renal Tubule of Cortical Nephrons
-Peritubular capillaries originate from efferent arteriole
-Capillaries are low-pressure, porous and adapted for absorption
-They surround the tubules mainly in the renal cortex and the short loop of Henley in the medulla
-They empty into interlobular veins
Blood Supply of Renal Tubule in Juxtamedullary Nephrons
Efferent arteriole originates the vasa recta capillaries
Vasa recta is deep down into the medulla
-parallels the Loop of Henle in juxtamedullary nephrons
-they carry blood at a slow rate
-helps to concentrate the filtrate
Renal Venous System
-Takes blood out of the kidneys
-From the nephron blood enters the interlobular veins
-Blood drains through the arcuate veins
-From arcuate veins blood enters the interlobar veins between the pyramids
-Blood leaves the kidney through a single renal vein
Renal blood supply pathway:
Renal Artery
Interlobar artery
Arcuate artery
Interlobular artery
Afferent arteriole
Glomerulus
Efferent arteriole
Interlobular vein
Arcuate vein
Interlobar vein
Renal vein
Processes of Urine Formation: Reabsorption, Filtration, Secretion
-selective process
-right amount of substances, H2O, electrolytes, glucose enter blood
-waste products and substances in excess are not reabsorbed
Processes of Urine Formation: Filtration
-Water and solutes from blood
-Based on size
Processes of Urine Formation: Secretion
-Removes substances that must be eliminated from the blood
-Lower plasma concentration of undesirable materials
Glomerular Filtration: occurs where, what moves accross capillaries, where does it move
Occurs: in the renal corpuscle
Move freely across glomerular capillaries: Inorganic ions, low molecular weight solutes, and water
From the glomerular capsule, the filtrate moves into the renal tubule
Glomerular Filtration: what are the filtered substances
Commonly filtered substances:
Ions such as Na, K, Cl, HCO3
Natural organic such as glucose and urea
Amino Acids, vitamins, and small proteins are also filtered
Components of Renal Corpuscle: Glomerulus and Glomerular (Bowman’s) capsule
Glomerulus:
site for blood filtration
semi-permeable capillary network - caused by afferent capillaries
filtrate -> product of glomerulus
Glomerular (Bowman’s) capsule:
Epithelial cup or sac surrounding capillaries
Transfer filtrate from glomerulus to Proximal Convoluted Tubule (PCT)
Histology of Bownman’s Capsule: Parietal Layer and Visceral Layer
Parietal Layer:
Outer wall of glomerular capsule
Squamous epithelial cells
Visceral Layer:
Covers glomerulus
Podocytes -> modified squamous cells, component of glomerular filtration barrier
Components of Podocytes
Primary process -> cell surface extensions from cell body
Secondary -> fingerlike extensions aka pedicels
(hand -> fingers (gaps in fingers that water can seep through)
Filtration Membrane or Barrier of Renal: filtration, barrier
Filtration of water and small solutes
Effective barrier for most plasma proteins, blood cells, and platelets
Filtration Membrane: Components (layers)
Podocytes: (outside)
form filtraition slits
Basement Membrane or Basal Lamina:
glycoprotein matrix
collagen and proteoglycans
located between endothelium and podocytes
Endothelial Cells: (inside)
have fenestrations, leaky
Filtration Process forces
Outside: forces opposing filtration
Inside: (in blood) force favoring filtration
Force Favoring Filtration
Glomerular blood hydrostatic pressure (GBHP)
-Blood pressure in the glomerular capillaries
-Generally is high -> efferent arterioles are smaller than afferent arterioles
Forces Opposing Filtration
Capsular Hydrostatic Pressure (CHP)
-Pressure exerted by fluid already in the capsular space and renal tubules
Blood colloid osmotic pressure (BCOP) -> Due to the presence of proteins in plasma
Net Filtration Pressure (NFP)
Glomerular Blood Hydrostatic Pressure (55 mmHg)
Capsular Hydrostatic Pressure (11 mmHg)
Blood Colloid Osmotic Pressure (30 mmHg)
55mg - 15 mmHg - 30 mmHg = 10 mmHg
*filtration ceases when the glomerular blood pressure is 45 mmHg
Control of Glomerular Filtration Rate
-GFR is the volume of fluid filtered from the glomerulus into Bowman’s space per unit time
-GFR can change, but subject to physiological regulation
-Neuronal and hormonal mechanisms are important to maintain a nearly constant glomerular filtration rate
-Regulation of the afferent and/or efferent arterioles adjust blood flow in and out of the glomerulus changing the net GF pressure
Decreased GFR
-Construction of the afferent arterioles
-Decreases the hydrostatic pressure in glomerular capillaries
(smaller AA in front)
-Dilation of efferent arterioles
-Decreases the hydrostatic pressure in glomerular capillaries
(dilate EA in back)
Increased GFR
-Constriction of the efferent arterioles
-Increase the hydrostatic pressure in glomerular capillaries
(Constrict EA in back)
-Dilation of the afferent arterioles
-Increase the hydrostatic pressure in the glomerular capillaries
(dilate AA in front)
Myogenic Mechanism: muscle cells, blood flow
-involves smooth muscle cells in walls of afferent arterioles and prevents increased pressure in the glomerulus
-adjusts blood flow by adjusting the diameter of arterioles
-rapid regulation (works in seconds)
-sympathetic system produces a similar effect
Myogenic Mechanism: Blood Pressure and contraction of smooth muscle
Increased Systemic Blood Pressure
-Increased renal blood flow
-Stretching of arterioles
-protects glomerular capillary from sudden changes in blood pressure w/in seconds
Increased GFR
Contraction of muscle in walls of afferent arterioles (narrows lumen)
-Decrease renal blood flow
-Decrease blood volume
-Decrease glomerular blood pressure
Decreased GFR
Tubular Reabsorption
-Polarized epithelial cells — Apical and basolateral membrane
-Different proteins in each membrane
-Reabsorption removes useful solutes from the filtrate and returns them to blood
-Secretion removes solutes from the blood into filtrate
Characteristics of the Proximal Convoluted Tubule (PCT)
-Originates at the glomerular Bowman’s capsule
-Connects with the loop of Henle
-Lies within the cortex
-Involved in the reabsorption of most of useful solutes and water
-Site for secretion
—Elimination of drugs, waste, and hydrogen ions
Tubular Reabsorption: Paracellular reabsorption, transcellular reabsorption
Paracellular reabsorption:
Passive process that occurs between adjacent tubule cells through tight junctions
Transcellular reabsorption:
-Movement through an individual cell
-Mediated by channels, transporters, or pumps
-Can be active, passive, or facilitated
Function of Sodium/Potassium ATPase in Basolateral Membrane of PCT: Function and Expression
Function:
Ensures one-way process to move substances from apical to basolateral membrane (across cells)
Expression:
-Most abundant cation in filtrate -> cotransport substanses
-Pump is present in basolateral membrane use ATP to move ions
— decreases intracellular Na+ -> maintains a Na+ gradient
PCT Reabsorption
PCT is most active section of the tubule for reabsorption
-Transport of most solutes is facilitated by Na+ concentration gradient established by sodium pump
Secretion of H+ also occurs in the PCT
Amino Acids, glucose and sodium are reabsorbed by ____ ______ -> transport requires _____
Active transport, ATP***
What is needed for glucose reabsorption in PCT (3 things)
In apical membrane
-Na+ glucose symporter
In basolateral membrane
-Na+/K+ - ATPase
-Glucose transporter
Glucose Reabsorption in PCT
Active transport of glucose
-Symporter transports Na+ and glucose into cell
-Na+ is actively transported out of PCT cells by Na/K pump
-Glucose diffuses into the interstitium via facilitated diffusion using glucose transporter
Glucose is _____ absorbed in PCT
100%
What are the two things that are reabsorbed in PCT
Glucose and Bicarbonate
What is needed for Bicarbonate Reabsorption in PCT
Apical Membrane:
Na+/H+ exchanger or antiporter
Basolateral Membrane:
HCO3- transporter
Na+/K+ ATPase pump
What are the two steps in bicarbonate reabsorption in PCT
1: Formation of H2CO3 and then CO2 in the lumen of the tubule
2: Resynthesize bicarbonate in PCT cells, diffusion of bicarbonate into blood vessels
Step 1 Bicarbonate Reabsorption: Na+-H+ antiporter
Na+-H+ Antiporter:
H+ secretion into the tubular fluid -> pH maintenance
Secreted H+ keeps the antiporter running
Carries Na+ inside the cell down its concentration gradient
Step 1 Bicarbonate Reabsorption: Formation of carbonic acid
H+ secretion into the tubule lumen by Na+-H+ antiporter
HCO3- in the filtrate reacts with H+ to form H2CO3
Luminal carbonic acid anhydrase (CA) catalyses the reaction
Step 1 Bicarbonate Reabsorption: Formation of CO2
Dissociation of H2CO3
CO2 diffuses into the PCT
In cells, CO2 also comes form metabolism
Step 2 Bicarbonate Reabsorption: Formation of HCO3- in PTC cells
Hydration of CO2 - carbonic anhydrase (enzyme)
Hydrolysis of H2CO3 forms HCO3- -> H+ production
Step 2 Bicarbonate Reabsorption: Bicarbonate Diffusion
HCO3- leaves the cells by facilitated transport
Diffuses into the capillaries
Na+ is transported out of the cells by Na+/K+ ATPase
(One HCO3- is absorbed for every secreted H+, active process)
Passive Reabsorption of Ions, Cations, and Urea in PCT
Cl- is in high concentration in filtrate
—Cl- diffusion makes interstital fluid more negative
—Promotes diffusion of cations
Passive Diffusion of Cl-, K+, Ca2+, Mg2+ and urea into capillaries
Creation of osmotic gradient promotes reabsorption of water
Water Reabsorption in PCT
Osmosis
-Water will move through the cell into the capillaries following reabsorption of solutes
-Obligatory water reabsorption by cellular or paracellular passive diffusion
Loop of Henle: Basics
-Connects proximal and distal convoluted tubules
-Extends into the medulla
-Has three portions with specific characteristics -> separate functional units
-Creates an hypertonic gradient in the renal medulla
What are the three sections of the Loop of Henle
Descending loop*
Ascending thick limb*
Ascending thin limb
Reabsorption in the Loop of Henle
Lumen -> LOH cell -> interstitial tissue -> blood
H2O, NaCl, K+, Bicarbonate, Ca2+, Mg2+
LOH opposing flow, countercurrent, what is important for water reaborption
-Opposing flows are called countercurrent flow
-Countercurrent system creates a hyperosmotic or concentrated -medullary interstitial fluid -> gradient formed
-Hyperosmotic fluid in medulla is important for water reabsorption in DCT and collecting tubules
Properties of The Descending Limb
Highly permeable to water:
High expression of water channels (aquaporins)
Water moves out by osmosis
—Reabsorption of water from filtrate while concentrating the urine
Impermeable to NaCl:
It does not participate in active solute reabsorption or active transport
Properties of Thick Ascending Loop
Impermeable to Water:
Little or not water is reabsorbed
Permeable to ions:
Na+ and Cl- move out down their concentration gradient
Reabsorption of Na+ from the filtrate by active transport
Presence of Na+/K+/2Cl- symporter on the apical membrane
—Thick loop has high symporter expression
Thin ascending loop has ____ expression of the symporter
Low -> low reabsorption than the thick ascending loop
Mechanism of Na+/K+/2Cl- symporter in Loop of Henle
Na+ and Cl- reabsorption
—Causes build up Na+ and Cl- in renal medulla forming a gradient
K+ rate limiting substrate
K+ recycles by the apical K+ channels -> maintain transporter activity
Movement of K+ and Cl- promotes reabsorption of cations via the paracellular route
Formation of the Osmotic Gradient in the Renal Medulla
-Starts with active transport of Na+ and Cl- from ascending limb into interstitial fluid
-Interstitial fluid surrounding the descending loop becomes more concentrated than tubular fluid
-Higher concentration makes H2O move to interstitial fluid by osmosis from descending limb
-Fluid in the descending limb becomes hypertonic
-Length of LOH, the difference in concentration is multiply as the the fluid goes deeper into the medulla
Fluid Concentration in the LOH
1: Filtrate enters and is isomotic to blood plasma and inter fluid
2: Water moves out concentrating filtrate
3: Filtrate reaches highest concentration at loop bends
4: Na+ & Cl- pumped out of filtrate (increases interstitial fluid osmol)
5: Filtrate most dilute as it leaves loop
Role of Vasa Recta in the Osmotic Gradient
-Is a countercurrent exchanger
-Loop run parallel to LOH
-Maintains gradient set by LOH
—Solutes and water passively exchanged between blood of vasa recta and interstitial fluid of renal medulla
-Supplies renal medulla with O2 and nutrients while preserving osmotic gradient
Descending Limb of Vasa Recta
Blood picks up NaCl
Releases some H2O
Gradual increase of plasma osmolarity
Ascending Limb of Vasa Recta
Blood picks up H2O
-Permits passive H2O reabsorption
-Returns H2O to body
NaCl diffuses out of blood into medulla
-maintain hypertonic medulla
Gradual decrease of plasma osmolarity
Urea recycling and osmotic gradient in medulla
-Helps increase solute concentration and osmolarity in the medulla
-Urea active absorption in collecting tubule under influence of ADH
-Enhances concentration gradient in interstitial fluid in medalla
Distal Convoluted Tubule and Collecting Duct: final adjustments of tubular fluid and volume
Final adjustments in the composition of tubular fluid
-osmotic concentration is adjusted through active transport
Final adjustments in volume
-Exposure to ADH determines final urine concentration
Early Distal Convoluted Tubule
Lumen -> DCT cell -> interstitial tissue -> blood
NaCl, bicarbonate, calcium, H2O
Secreted: H+,K+,NH4+, and drugs
NaCl reabsorption in Early DCT
Active transport of Na+ and Cl-
Apical Membrane:
Na+/Cl- symporter
K+ leaves for lumen
Basolateral Membrane:
Na+/K+ ATPase pump
Cl- leaves for blood
Ca2+ reabsorption in Early DCT
Active transport of calcium in DCT
PTH (thyroid) promotes reabsorption of Ca2+ (Apical Membrane)
Ca2+ reabsorbed passively in the PCT and Loop of Henle
Late Distal Convoluted Tubule and Collecting Duct: Principal and intercalated cells reabsorption & secretion
Principal Cells:
Reabsorption of Na+, Cl-, H2O
Secretion of K+
Intercalated Cells:
Reabsorption of K+
Reabsorption of HCO3-
Secretion of H+
Potassium Secretion in Late DCT
K+ secretion adjusts to dietary intake
Na+/K+ ATPase creates K+ gradient
K+ leakage channels in apical and basolateral membranes
Collecting Tubule: final composition, hormone regulation
Regulates final composition of urine
-Na+, Cl-, H2O reabsorption
-Secretion of K+ and urea
Hormonal regulation of salt and water balance
-Angiotensin 2, ADH, aldosterone, natriuretic peptide
DCT and collecting tubule are impermeable to _______
Water
(Hormones regulate the water permeability)
Principal Cells in CT
Na+ reabsorption and K+ secretion regulated by aldosterone
-Aldosterone regulate body water content by regulating Na+ content
Water reabsorption regulated by vasopressin
-ADH regulates osmolarity by altering water reabsorption
Aldosterone Effect
Modifies membrane permeability to Na+ and K+
-Causes upregulation of Na+ channels, Na+/K+ ATPase and K+ channels
Obligatory Water Reabsorption
Water movement that cannot be prevented
By osmosis -> PCT and LOH
Usually recovers 85% of filtrate volume
Facultative Water Reabsorption
-Controls volume of water reabsorbed along DCT & collecting tubule
-15% of filtrate volume
-Segments semi-impermeable to water -> need hormone regulation
-Final fixes in volume & osmotic concentration of tubular fluid
Vasopressin Effect
ADH increases variable (facultative) H2O reabsorption
Tubules are impermeable to H2O without ADH
ADH activates the insertion of H2O channels in apical membrane
Absence of ADH
H2O is not reabsorbed back into blood
H2O remains in renal tubule giving large urine volume
(clear pee)
Presence of ADH
Increased H2O channels at the membrane
H2O moves into interstitial fluid and then capillaries
Low urine volume (dark pee)
What is the urine drainage system
Papillary duct in renal pyramid -> minor calyx -> major calyx -> renal pelvis -> ureter -> urinary bladder
Acid-Base Balance: regulating H+: Buffer system, exhalation of CO2, kidney excretion of H+
Buffer System:
-phosphate and ammonia
Exhalation of CO2:
-↑ rate & depth of breathing reduce H2CO2
Kidney excretion of H+ or basic ions in urine:
-Secretion of H+ in PCT and collecting tubule
-Intercalated cells of the collecting tubule*
Kidney Excretion of H+: in PCT and collecting tubule
-Only way to eliminate acid load
-Change in rates of H+ and HCO3- secretion or reabsorption by kidneys in response to changes in plasma pH
-In PCT, Na+/H+ antiporters secrete H+ as they reabsorb Na+
-In collecting tubule intercalated cells secrete H+ using proton pump*
Intercalated cells in collecting tubule: Type A and Type B cells
Type A:
Secrete H+
-H+-ATPase and H+/K+ exchanger on APICAL MEMBRANE
Reabsorb HCO3-
-Cl-/HCO3- exchanger BASOLATERAL MEMBRANE
Type B:
Reabsorb H+ basolateral membrane
Secrete bicarbonate apical membrane
Activation of Type A cells: Acidosis
Acidosis -> blood and other body tissues are too acidic
H+ is secreted and HCO3- is reabsorbed
Activation of Type B cells: Alkalosis
Alkalosis -> blood is too alkaline
H+ absorbed and HCO3- secreted
Buffering of H+ in Urine
NH3 -> NH4+
formation of phosphoric acid
