Renal Pt1 Flashcards
Kidneys’ Primary Function
Maintain a stable internal environment for optimal cell and tissue metabolism.
7 ways Kidneys maintain homeostasis
- Electrolyte homeostasis
- Regulation of blood pH
- Regulation of Blood Volume/Blood Pressure
- Osmoregulation
- Hormones Produced by the Kidney
- Excretion of wastes
- Performs gluconeogenesis
Which electrolytes are regulated by the kidneys to maintain homeostasis
Na+, K+, Ca2+, Cl-, HPO42-
Regulation of blood pH by kidneys
1) Removes H+ from blood
2) maintains bicarbonate ions (HCO3-) in blood
Regulation of Blood Volume/Blood Pressure
by kidneys
1) Retention of water = increases BP
2) Elimination of water = decreases BP
Osmoregulation
at 300mOsm/L
Hormones Produced by the Kidney
1) Calcitriol - form of Vitamin D
calcium homeostasis
2) Erythropoietin - RBC production
3) Renin – Blood pressure regulation
Excretion of Wastes
of kidneys
1) Ammonia & Urea (protein metabolism)
2) Bilirubin
3) Creatinine (waste product of creatine phosphate)
4) Uric Acid (purine metabolism – A’s & G’s of DNA)
3) Drugs & toxins
Performs gluconeogenesis
Synthesis of glucose from amino acids
Renal capsule
Tightly adhering capsule covers kidney
Adipose capsule
Fat capsule surrounds each kidney
Renal fascia
Fibrous tissue attaches/suspends kidney
to the posterior abdominal wall
Hilum
Medial indentation where the renal blood vessels, nerves, lymphatic vessels, and ureter enter and exit the kidneys.
Renal cortex
*cortex means outer layer
1) Is the outer layer of each kidney.
2) Contains all of the glomeruli, most of the proximal tubules, and some segments of the distal tubule.
Renal columns
Extend from the cortex down between the renal pyramids.
Renal medulla
1) inner part of each kidney that contains tubules and the collecting duct.
2) Consists of regions called the pyramids.
Minor calyx
1) Receives urine from the collecting ducts through the renal papilla.
2) Apexes of the pyramids project into a cup-shaped cavity that join together to form a major calyx
Major calyx
Joins to form the renal pelvis.
Renal pelvis
Joins the proximal end of the ureter.
A dilated renal pelvis equates to what physiological problem with the kidneys
Hydronephrosis
General location of kidneys
- Left kidney sits higher because Oliver
- Located retroperitoneal at T1 - L3
Protection of kidneys
1) Posteriorly by 11th and 12th rib as well as adipose tissue
2) Anteriorly by adrenal gland and transverse colon
Characteristics of Ureters
1) Are 30 cm long.
2) Are long, intertwining smooth muscle bundles.
3) Pass obliquely into the posterior aspect of the bladder.
4) Peristaltic activity moves urine to the bladder.
5) Micturition compresses the lower end of the ureter to avoid urine reflux.
Bladder Tissue includes?
1) Detrusor muscle (wall)
2) Trigone
3) Transitional epithelium
Characteristics of Urethra
1) Internal urethral sphincter - involuntary (Smooth muscle @ jct. of bladder & urethra)
2) External urethral sphincter (voluntary)
Striated skeletal muscle
3) Between 3 and 4 cm long in females
4) Between 18 and 20 cm long in males
Control of Micturition or urination (voiding) by brain
when volume exceeds 250-300 mL Stretch receptors signal spinal cord and brain
Micturition center in sacral spinal cord triggers reflex:
1) parasympathetic fibers cause detrusor muscle to contract – squeezes out urine and
2) Internal & external sphincter muscles to relax to allow flow
Filling initiates a desire to urinate before the reflex actually occurs
1) conscious control of external sphincter
2) cerebral cortex can initiate micturition or delay it for a limited period of time
Blood flow through the Kidney
Renal arteries»_space;> Segmental arteries »_space;> Interlobar arteries »_space;> Arcuate arteries»_space;> Interlobular arteries »_space;> Afferent arterioles»_space;> Glomerular capillaries»_space;> Efferent arterioles»_space;> Peritubular capillaries »_space;> Vasa recta
Renal arteries
Supply blood to the kidneys
Segmental arteries
branches of the renal artery
Interlobar arteries
Travel between the pyramids
Arcuate arteries
Arch over the base of the pyramids
Interlobular arteries
extend through the cortex toward the periphery of the kidneys and supply the afferent glomerular arterioles.
Afferent arterioles
supply glomerular capillaries
Glomerular capillaries
site of filtration
Efferent arterioles
Convey blood to a second capillary bed
Peritubular capillaries
Surround the proximal and distal convoluted tubules and loop of Henle
Vasa recta
1) Is a network of capillaries for the juxtamedullary nephrons.
2) Influences osmolar concentration of the medullary extracellular fluid, which is important for the formation of a concentrated urine.
Process of Micturition
1) Reflex arc is required for micturition
2) Is stimulated by mechanoreceptors from stretching
3) Bladder fullness is sensed; impulses are sent to the sacral level of the spinal cord
4) When the bladder accumulates 250 to
300 ml of urine, the bladder contracts and the internal urethral sphincter relaxes from activation of the spinal reflex arc (micturition reflex)
5) At this time, the urge to void is felt
6) In older children and adults, reflex can be inhibited or facilitated by impulses coming from brain or voluntary control of micturition
*Mass of kidneys compares to amount of blood received
*Kidneys are less than 0.5% of total body mass, but receive 20-25% of resting cardiac output
Nephron Characteristics
1) 1.2 million per kidney
2) The functional unit of the kidney
3) Contains Superficial cortical nephrons and Juxtamedullary nephrons
Superficial cortical nephrons
Make up 85% of all nephrons, which extend partially into the medulla
Juxtamedullary nephrons
1) Lie close to and extend deep into the medulla and are important for the process of concentrating urine
2) secrete renin
Glomerular filtration
Water & small solutes in blood plasma move across the wall of the glomerular capillaries into glomerular capsule and then renal tubules (PCT –> loop of Henle –> DCT –> Collecting duct)
Tubular reabsorption
As “filtrate” moves along tubule water and many useful solutes reabsorbed = returned to blood
Tubular secretion
“Filtrate” moves along tubule other molecules (wastes, drugs, & excess ions) are secreted into fluid
What happens to Any solutes that remain in the fluid that drains into the renal pelvis
They are excreted as urine
PTH role
PTH stim.s reabsorption of Ca++
Intercalated Cells
Regulates of pH via H+ & HCO3-
Principal cells
regulate ADH and aldosterone
Brush border microvilli
Involved in reabsorption
Proxiamal Tubule Function
Reabsorption of Na, Glucose, Amino acids, Hco3-, PO4, H2O
2) Secretion of H+, and foreign substances
Loop of Henle Function
- Concentration of urine
1) Descending Loop - water reabsorption and Na+ diffuses in
2) Ascending Loop - Na+ reabsorption (active transport) and water stays in
3) Urea secretion in thin segment
Distal Tubule Function
1) Reabsorption of Na+, H2O, and HCO3-
2) Secretion of K+, Urea, H+, NH3, and some drugs
Collecting Duct Function
1) Reabsorption of H20
2) Reabsorption or secretion of Na+, K+, H+, NH3
3) Urea reabsorption in medulla
Tonicity of Fluid within the following Ducts:
1) Proximal Tubule
2) Loop of Henle
3) Distal Tubule
4) Collecting Duct
1) Proximal Tubule - Isotonic
2) Loop of Henle - Isotonic > hypertonic >Hypotonic
3) Distal Tubule - Isotonic or hypotonic
4) Collecting Duct - final concentration
Tubular Reabsorption along the nephron
180 (152) Liters/day of filtrate produced»_space;> Nephron must reabsorb 99% of the filtrate »_space;> Water + Solutes move “Tubules to Peritubular capillaries”
Which cells are mainly responsible for most of the reabsorption that takes place in the nephrons
PCT with microvilli
Mechanism by solutes are reabsorbed
via active transport and passive diffusion
Solutes that are 100% reabsorbed via active transport and passive diffusion in the first half of the PCT
Glucose, amino acids, urea and ions (Na+, K+, Ca2+, Cl-, bicarbonate, phosphate
_____% of water follows by osmosis
65%
Effects of the reabsorption of Na+
Reabsorption of Na+ produces an electrical gradient that caused Cl- to follow by passive transport
Effects accumulation of NaCl outside tubule
Produces an osmotic gradient and helps pull water out of tubule
Desending Limb of Loop of Henle
1) 5% of the filtered water is reabsorbed in the descending limb
2) High solute content of the medulla “pulls” water out
3) Low permeability to solutes = little reabsorption of solutes
Asending Limb of Loop of Henle
1) Variety of transporters reclaim more Na+, Cl-, & K+ ions and other ions by diffusion
2) Thin, ascending segment: Is more permeable to solutes and almost impermeable to water.
3) Thick portion of the ascending segment: Is highly permeable to sodium, potassium, and chloride and significantly less permeable to water and urea.
DCT
1) Moderately permeable to solutes but absorbs about 15% of water
2) reabsorption of Na+ and Cl- continues
3) 15% of water reabsorption by osmosis
4) The DCT serves as the major site where parathyroid hormone stimulates reabsorption of Ca+2.
By end of DCT, ___% of solutes and water have been reabsorbed?
95%
Collecting Duct contains which two kinds of cells that are responsible for making final adjustments
Intercalated and Principal cells
Intercalated Cells Function
1) help regulate pH of body fluids
2) Proton pumps (H+ATPases) secrete protons (H+) into tubule
3) Reabsorb bicarbonate ions (buffers blood pH)
Principle Cells are targeted by which two hormones that promote reabsorption of water and ions
1) ADH - increases water reabsorption (retention)
2) Aldosterone - ↑ reabsorption of Na+ and Cl- and secretion of K+ (adjust for dietary intake of K+)
What is Tubular Secretion
Transfer of materials from blood into filtrate/urine
Where does Tubular Secretion take place?
various locations along the tubule
What is secreted during tubular secretion
1) Hydrogen ions (H+) = to maintain pH
2) K+, ammonia, urea, creatinine to eliminate excess
3) Drugs such as penicillin
5 Hormones responsible for regulation of Tubular reabsorption and tubular secretion
1) Angiotensin II
2) Aldosterone
3) ADH (vasopressin)
4) ANP
5) PTH
Describe the major stimuli that triggers the release of Angitensin II, its MOA, and effect
1) Triggered by - ↓ blood volume, ↓ BP which stimulates renin-induced production of Ang II
2) MOA - Stimulates activity of antiporters in cells of PT
3) Effects -↑ reabsorption of Na+ and H2O
Describe the major stimuli that triggers the release of Aldosterone, its MOA, and effect
1) Triggered by - ↑ Ang II levels and ↑ K+
2) MOA - Enhances activity of Na+/K+ pumps in basolateral membrane and Na+ channels in apical membrane of principal cells in collecting duct
3) Effects -↑ secretion of K+ and reabsorption of H2O
Describe the major stimuli that triggers the release of ADH, its MOA, and effect
1) Triggered by - ↑ osmolarity of elf or ↓ blood volume promotes release of ADH from posterior pituitary gland
2) MOA - Inserts water channel proteins (aquaporins) in apical membranes of principal cells in collecting duct.
3) Effects - ↑ facultative reabsorption of water
Describe the major stimuli that triggers the release of ANP, its MOA, and effect
1) Triggered by Stretching of atria of heart stimulates secretion of ANP
2) MOA - Supresses reabsorption of NA+ and H2O in PT and CD, also inhibits secretion of aldosterone and ADH
3) Effects - ↑ excretion of Na+ in urine (natriuresis)
Describe the major stimuli that triggers the release of PTH, its MOA, and effect
1) Triggered by ↓ Ca2+ which promotes PTH release
2) MOA - Stimulates opening of Ca2+ channels in apical membranes of early DT cells
3) Effects - ↑ Reabsorption of Ca2+
Formation of Dilute Urine
1) Glomerular filtrate and blood have the same osmolarity – 300mOsm/Liter
2) Tubular osmolarity changes due to a concentration gradient in the medulla
Glomerular Filtration Rate
- 105mL(female) to 125mL/min (male) of fluid that is isotonic to blood
- 180L/day in males and 150L/day in females
Substances filtered by the renal corpuscle
1) Water and all solutes present in blood except proteins
2) Ions
3) Glucose
4) Amino acods
5) Creatinine
6) Uric Acid
Approximately how much of renal plasma flow becomes filtrate?
20% (120 to 140mL/min)
The Renal Corpuscle includes:
1) Glomerulus
2) Bowman’s Capsule
3) Mesangial Cells
4) Glomerular Endothelial Cells
5) Visceral Epithelium of Bowman’s Capsule
Glomerulus
- Set of fenestrated capillaries
- Supplied by the afferent arteriole and drained by the efferent arteriole
Bowman’s (glomerular) capsule
Circular space between visceral and parietal epithelium
Mesangial cells
support the glomerular capillaries and respond to ANP to regulate glomerular capillary flow.
Glomerular endothelial cells
- Synthesize nitric oxide (a vasodilator).
- Synthesize endothelin-1 (a vasoconstrictor).
- Regulate glomerular blood flow.
Visceral epithelium of the Bowman capsule
- Is composed of cells called podocytes.
- Are footlike processes.
- Form an elaborate network of intercellular clefts called filtration slits; modulate filtration.
Glomerular filtration membrane
1) Water, Ions, small molecules & small proteins move through the membrane and become “primary urine” or “filtrate”.
2) Blood cells, large/medium sized proteins cannot normally be filtered
3) Negativity of the filtration membrane retard filtration of anionic proteins (prevents proteinuria)
JUXTAGLOMERULAR APPARATUS
Control of renal blood flow (RBF), glomerular filtration, and renin secretion occurs at this site.
Juxtaglomerular cells
These specialized cells are located around the afferent arteriole where the afferent arteriole enters the glomerulus.
Mesangial cells
specialized contractile cells that support glomeruls and help regulate glomerular blood flow; and remove macromolecules from filtration
Macula densa
1) Portion of the distal convoluted tubule with specialized sodium and chloride-sensing cells is located between the afferent and efferent arterioles.
2) Detect high flitrate rate in the DCT which results in a decrease of nitric oxide and vasoconstriction in the afferent arterioles.
Renal Blood Flow
Kidneys receive 1000 to 1200 ml/min of blood (20-25% of CO)
Renal Plasma Flow
of the 1000 to 1200 ml/min of blood the kidneys receive, 600 to 700 ml is plasma
Glomerular Filtration Rate is directly related to the ______ in the glomerular capillaries.
Perfusion pressure
What can cause a decrease in Renal Blood Flow?
If MAP decreases or vascular resistance increases, the RBF decreases.
How is Filtration Fraction (FF) calculated?
GFR/RPF
GFR is regulated by which 3 mechanisms?
1) Autoregulatory
2) Neural
3) Hormonal
2 methods of GFR Autoregulation
1) Myogenic Mechanism (pressure/stretch)
2) Tubular feedback (Sodium chloride content)
Myogenic mechanism (pressure/stretch)
1) If arterial pressure ↑, stretch of the afferent arterioles ↑, smooth muscle contracts to constrict afferent arteriole and perfusion ↓.
2) If arterial pressure declines, stretch of the afferent arterioles ↓, smooth muscle relaxes to dilate afferent arteriole and perfusion ↑.
Tubuloglomerular feedback (sodium chloride content)
1) If sodium filtration increases, GFR decreases.
2) If sodium filtration decreases, the opposite occurs—GFR increases.
______ _______ cells stimulate afferent arterioles vasoconstriction.
Macula densa
3 methods of GFR Neural Regulation
1) SNS - stimulation of A1 receptors cause constriction which ↓ GFR
2) Inhibition of sympathetic nerves causes dilation which ↑ GFR
3) Severe hypoxia which stimulates chemoreceptors and ↓ RBF via sympathetic stimulation
GFR via Hormonal Regulation
1) RAAS - ↑ systemic arterial pressure and increases sodium reabsorption
2) Natriuretic Peptides - ANP and BNP
Where is Renin formed and stored
In the Afferent arterioles of the Juxtaglomerular apparatus
Angitensin II
1) Stimulates the secretion of aldosterone by the adrenal cortex.
2) Is a potent vasoconstrictor. (constricts both afferent & efferent arterioles in kidney; with greater affect on efferent arteriole)
3) Stimulates antidiuretic hormone (ADH) secretion and thirst.
Where are ANP and BNP secreted from
1) ANP is secreted from myocardial cells in the atria
2) BNP is secreted from myocardial cells in the ventricles
ANP and BNP does what?
1) Inhibit sodium and water reabsorption by kidney tubules.
2) Inhibit secretion of renin and aldosterone.
3) Vasodilate the afferent arterioles; constrict the efferent arterioles.
4) Increase urine output, leading to decreased blood volume and blood pressure; promote sodium and water loss.
Myogenic mechanism:
1) Major stimulus
2) MOA
3) Effect of GFR
1) Major stimulus - ↑ stretching of smooth muscle fibers in afferent arteriole walls due to ↑ BP
2) MOA - Stretched smooth muscle fiber contract, thereby narrowing the lumen of the afferent arterioles
3) Effect of GFR - decrease
Tubuloglomerular Feedback:
1) Major stimulus
2) MOA
3) Effect of GFR
1) Major stimulus - Rapid delivery of Na+ AND Cl- to the macula dense due to high systemic BP
2) MOA - ↓ NO release by juxtaglomerular apparatus causes constriction of afferent arteriole
3) Effect of GFR - decrease
Neural Regulation
1) Major stimulus
2) MOA
3) Effect of GFR
1) Major stimulus - ↑ in activity of renal sympathetic nerves release NE
2) MOA - Constriction of afferent arterioles through activation of A1 receptors and ↑ release of renin
3) Effect of GFR - decrease
Ang II
1) Major stimulus
2) MOA
3) Effect of GFR
1) Major stimulus - ↓ blood volume or BP stimulates production of Ang II
2) MOA - Constriction of both afferent and efferent arterioles
3) Effect of GFR - decrease (increase)
ANP
1) Major stimulus
2) MOA
3) Effect of GFR
1) Major stimulus - Stretching of the atria heart stimulates secretion of ANP
2) MOA - Relaxation of mesagial cells in the glomerulus ↑ capillary surface area available for filtration
3) Effect of GFR - increase
Characteristics of Normal Urine
1) One to two liters in 24 hrs
2) Yellow to amber color
3) Turbidity - transparent when freshly voided
4) Odor - Urine mildy aromatic but fruity odor in diabetics
5) pH - ranges 4.6 to 8.0; average is 6.0
6) Specific Gravity - 1.001 to 1.035
Albumin in urine
1) Too large to pass through capillary fenestrations
2) Albuminuria indicates injury or disease or increased BP
Glucose in Urine
Usually indicates diabetes
RBCs in urine
Inflammation of the urinary organs as a result of disease or irritation from kidney stones
Bilirubin in urine is called
bilirubinuria
Urobilinogen in urine is called
Urobilinogenuria
Cats in urine
Tiny masses of material that have hardened and assumed the shape of the lumen of the tubule
Microbes in urine
Indicates specific infection in urinary tract
Types of Renal Function Tests
1) Renal Clearance - determines how much of a substance is cleared from blood in a given unit of time. It is an indirect measurement of GFR
2) Blood Tests
Clearance and GFR
- GFR is the best estimate for the functioning of renal tissue
1) Inulin (a fructose polysaccharide) is often used
2) Creatinine: Provides a good estimate of GFR since only a small amount enters urine.
Clearance and RBF
1) Para-aminohippuric acid (PAH) clearance is used to determine renal plasma flow and blood flow. (renal extraction ratio 0.92, underestimates RPF ~10%)
2) Filtered/Secreted in one circulation through the kidney
3 Blood tests of Renal Function
1) Plasma creatinine concentration
2) Plasma cystatin C concentration
3) Blood urea nitrogen (BUN)
Plasma creatinine concentration
1) By-product produced by muscles.
2) Normal value is 0.6 to 1.2 mg/dl.
3) Is most valuable for monitoring the progress of chronic rather than acute renal disease.
4) Measures progressive renal dysfunction.
Plasma cystatin C concentration
1) Plasma protein is freely filtered at the glomerulus.
2) Normal value is 0.52 to 0.98 mg/L. In kidney failure levels rise.
3) Measures progressive renal dysfunction.
Blood urea nitrogen (BUN)
1) Varies as a result of altered protein intake and protein catabolism.
2) Is a poor measure of GFR.
3) Is a better indicator for hydration status.
Increases in dehydration and kidney failure
4) Adult normal range is 7 to 20 mg/dl.
