Chapter 24 Flashcards
Kidneys
filter blood remove waste products and convert filtrate into urine
Ureters
Transport urine from kidney to urinary bladder
urinary bladder
Stores up to 1 L of urine; expandable muscular sac
urethra
Eliminates urine from the body
8 functions of the kidney
Processes that occur as filtrate is converted to urine:
1. Regulation of total body water volume & solute concentration
2. Regulation of ion levels in extracellular fluid
3. Regulation of acid-base balance
4. Elimination of metabolic wastes, drugs & toxins
5. Production and release of erythropoietin
6. Regulation of blood pressure
7.Formation of active vitamin D (calcitriol)
8. Gluconeogenesis during prolonged fasting
Adrenal glands
small, triangular-shaped glands located on top of both kidneys. Adrenal glands produce hormones that help regulate your metabolism, immune system, blood pressure, response to stress and other essential functions.
hilum
a depressed surface at the center of the medial surface of the lung and lies anteriorly to the fifth through seventh thoracic vertebrae.
Urinary tract
utterers, urinary bladder, urethra
Fibrous capsule
capsule adheres to kidney surface; protects from trauma & infection
Perinephric & paranephric fat
cushions & supports
Renal fascia
anchors kidney to surrounding structures
Innervation of Kidneys
Sympathetic nerves from T10–T12
(renal plexus surround renal artery)
-Blood vessels of kidney and juxtaglomerular apparatus to decrease glomerular filtration rate (GFR)
-Decreases urine production
-Parasympthetic nerve from CN X
Glomerulus
visceral layer: Inner most layer
Parietal layer: middle layer
Capsular space
Capsular space:
the glomerular capsular space (space within the Bowman’s capsule) contains the filtrate (water and solutes) and modifies it to be urine
Renal Corpuscle
sisters blood
Glomerulus
is a knot of fenestrated glomerular capillaries
Visceral layer
the inner layer permeable, podocytes
Parietal layer
Outer layer impermeable s squamous
Renal tubule is specialized for
reabsorbtion and secretion
nephron loop
the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule.
DCT (parathyroid hormone)
End of ascending limb to collecting duct (CD)
Fine-tuned reabsorption; adjusts to body’s needs
Sparse microvilli
Principal cells
maintain H2O Na+ balance more numerous few microvilli, alderstone hormone
ADH
a chemical produced in the brain that causes the kidneys to release less water, decreasing the amount of urine produced.
Intercalated cells
regulate urine and blood by removing acid (h+) Type A and Base (HCO3) type B
Cortical
the renal corpuscle is located in the outer cortex of the kidney; their renal tubules are short and extend through the cortex and dip into the outer medulla.
Juxtamedullary
long loops of Henle that extend deep into the inner medulla. Midcortical nephrons, which have glomeruli located near the midregion of the cortex, may have long or short loops.
renin
Renin is an enzyme made by special cells in your kidneys. It’s part of the renin-angiotensin-aldosterone system — a chain reaction designed to regulate your blood pressure. Specifically, renin controls the production of aldosterone, a hormone made by your adrenal glands.
Aldosterone
A steroid hormone made by the adrenal cortex (the outer layer of the adrenal gland). It helps control the balance of water and salts in the kidney by keeping sodium in and releasing potassium from the body. Too much aldosterone can cause high blood pressure and a build-up of fluid in body tissues.
granular cells
modified smooth muscle cells of afferent arterioles they synthesize, store and release renin
Macula densa
modified epithelial cells of DCT
distal convoluted tubule (DCT)
a short nephron segment, interposed between the macula densa and collecting duct.
Extraglomerular mesangial cells
between arteriole tubule cells, many gap junctions communicate with other cells of JGA
Juxtaglomerular Apparatus (JGA)
consisting of the glomerular afferent and efferent arterioles and the specialized tubular epithelial cells called the macula densa, plays a central role in the regulation of glomerular hemodynamics and renin release.
Two Fluid Flow Patterns in Urine Formation
- Blood flow in & out of the kidney
- Flow of filtrate, tubular fluid & urine through the nephron, collecting ducts, ureters, urinary bladder & urethra
Filtrate, Tubular Fluid & Urine Flow Through Nephrons & Urinary Tract
- capsular space
- proximal convoluted tubule
- descending limb of nephron loop
- ascending limb of nephron loop
- distal convoluted tubule
- Collecting tubules
- collecting duct
- papillary duct
- minor calyx
- major calyx
- renal pelvis
- ureter
- urinary pladder
- urethra
Gomerula filtration
the movement of substances from the blood within the glomerulus into the capsular space
Tubular reabsorption
the movement of substances from the tubular fluid back into the blood
Tubular secretion
the movement of substances from the blood into the tubular fluid
Glomerular filteration
Blood pressure forces H2O & small solutes across a porous, negatively charged filtration membrane
Glomerular filteration 3 layers
- Glomerular endothelium
- Glomerular basement membrane
- Visceral layer of glomerular capsule
Glomerular endothelium
Fenestrated capillaries
Blocks blood cells
Glomerular basement membrane
Blocks everything but the smallest plasma proteins
Visceral layer of glomerular capsule
Blocks passage of most small proteins
Glomerular Mesangial Cells
Modified smooth muscle cells between glomerular capillary loops
Have phagocytic, contractile, and signaling properties
Filtrate can be
Freely filtered
Small substances like water, glucose, amino acids, ions pass through easily
Not filtered
Formed elements & large proteins do not pass
Limited filtration
Proteins of intermediate size
Usually blocked from filtration due to size or negative charge
Glomerular hydrostatic pressure (HPg)
60 mmHg out
Blood colloid osmotic pressure (OPg)
32 mmHg
Capsular hydrostatic pressure (HPc)
18 mmHg
Net filteration pressure (NFP)
Hug - OPg - HPc= 10 mmHg
Variables Influenced by Net Filtration Pressure (NFP)
-Glomerular filtration rate (GFR)
-Increased BP = increased HPg = NFP
-Intrinsic controls (renal autoregulation)
-Extrinsic controls that maintain GFR & BP (JGA)
-Extrinsic controls that change GFR & BP (neural and hormonal)
Glomerular filtration rate (GFR
rate at which the volume of filtrate is formed (mL/min)
Increased Bp means what for GFR
Increases GFR & amount of filtrate formed
Decreases filtrate reabsorption
Increases solutes & water remaining in tubular fluid
Increases substances in urine
Regulation of GFR
Glomerular filtration rate (GFR) is tightly regulated
Helps control urine production based on physiologic conditions (e.g., hydration status)
GFR is influenced by
-Changing luminal diameter of afferent arterioles and altering surface areas of filteration membrane
Intrinsic controls (renal autoregulation)
myogenic response & tubuloglomerular feedback
Tubuloglomerular feedback
an increase in NaCl concentration at the macula densa constricts the glomerular afferent arteriole and thus decreases the single-nephron GFR. Along with the myogenic response, TGF significantly contributes to renal autoregulation.
extrinsic controls vs intrinsic controls
intrinsic controls regulate factors within a local environment; extrinsic controls regulate factors coordinating body systems.
Intrinsic Control of GFR (Renal Autoregulation)
Intrinsic ability of kidney to maintain constant HPg & GFR despite changes in systemic BP between 80-180 mm Hg
Renal regulation
a vital homeostatic mechanism that protects the kidney from elevations in arterial pressure that would be transmitted to the glomerular capillaries and cause injury.
Tubuloglomerular feedback mechanism Intrinsic control of GFR
higher BP = higher NaCl in titular fluid is detected by macula dense of juxtaglomerular apparatus to release signalling molecules
The Juxtaglomerular Apparatus (JGA) Maintains
GFR & Systemic BP
Granular cells detect
decreased stretch in afferent arterioles and decreased BP and GFR
-Cause cells to contract and increase GFR
Macula densa detects
NaCl in tubular fluid of DCT. lower BP = decreased NaCl
decreasing GFR through sympathetic stimulation
Results: vascoconstriction of the afferent arteriole decreases blood flow into the glomerulus and contraction of mesangial cells decrease filtration surface area.
Next effect: GFR decreased and filtrate decreases filtration surface area.
Increasing GFR through atrial natriuretic peptide
Results: Vasodilation of the afferent arteriole increases blood flow into glomerulus and relaxation of mesangial cells increases filtration surface area
Net effect: GFR increased and filtrate increased more fluid eliminated in urine which decreases blood volume
Tubular system reabsorption in PCT
Glucose. protein, amino acids
Transport Maximum (Tm)
maximum amount of a substance that can be reabsorbed across tubule epithelium per unit time
Renal threshold
Maximum plasma concentration of a substance that can be transported in the blood without appearing in the urine (i.e., that does not result in the Tm being exceeded)
Renal threshold for glucose (RTg)
180 mg/dL
at this point transporters are saturated & any elevation will result in excretion in urine
Glucose reabsorbed into tubule PCT transported into tubule cell via
Na+ glucose symporter
-Secondary active transport driven by Na+ gradient maintained by Na+ /K+ pump.
All Proteins & Amino Acids are Reabsorbed in the PCT
Transported into tubule cells by endocytosis
Broken down into amino acids by lysosomes (inside tubule cell)
Amino acids released by exocytosis across basolateral membrane & into blood by facilitated diffusion
Proteins can also be broken down by peptidases at the luminal membrane & moved into the tubular cell by secondary active transport
How much Na is reabsorbed in PCT
65%
How much Na+ is reabsorbed in DCT
5%
How much Na+ reabsorbed in nephron loop
25%
Reabsorption of Sodium (Na+) in PCT
- Na+ is transported out of tubule cell against its gradient by Na+/K+ pump in badolateral membrane
- Na+ passively moves down its gradient across luminal membrane into tubular cell
- na+ enters blood through intercellular clefts in peritubular and vasa recta capillaries.
Aldosterone increased Na+ reabsorption
- Enters principal cells
increased number of Na+ channels & Na+/K+ pumps = faster transport - Na+ moves into blood & H2O follows by osmosis aquaporin
- K+ increases in the tubular fluid
ANP decreased Na+ reabsorption
In PCT and CD
Inhibits aldosterone release
increased Na+ in urine
Increased GFR which increased urine output
Aquaporin
a family of small, integral membrane proteins that are expressed broadly throughout the animal and plant kingdoms.
Obligatory Water Reabsorption in the PCT
Permeability to water changes along nephron
Without regulatory hormones, ascending limb & DCT are impermeable to H2O
180 H2O/day
Pct
a segment of the renal tubule responsible for the reabsorption and secretion of various solutes and water.
PCT reabsorbs
85% of Ca2 and PO43-
Less PO43− in blood to make calcium phosphate = less
deposition in bone = increased blood Ca2+
HCO3− Reabsorption & H+ Secretion in PCT & Nephron Loop
In tubular fluid, HCO3− combines with H+ to carbonic acid (H2CO3) which dissociates to CO2 & H2O
CO2 diffuses into tubule
CO2 combines with H2O to H2CO3 to HCO3− & H+
H+ is secreted into the tubular fluid (will decrease pH of urine if not reabsorbed) & HCO3− is reabsorbed into the blood
Blood [H+] high = pH low
acidosis
Blood [H+] low = pH high =
alkalosis
Acidosis
Type A intercalated cells
H+ is secreted & will be excreted in urine if not reabsorbed
HCO3− is reabsorbed
-Increased blood pH and decreased urine pH
Alkalosis
Type B intercalated cells
H+ is reabsorbed
HCO3− is secreted & will be excreted in urine if not reabsorbed decreased blood pH and increased urine pH
Reabsorption of Urea
Nitrogenous waste product
Urea, molecule produced from protein breakdown
Both reabsorbed and secreted
50% reabsorbed in PCT then secreted back into nephron loop, so 100% of filtered urea is present at DCT
In CD, 50% reabsorbed & 50% is excreted in urine
Helps establish concentration gradient in the interstitial fluid
Excess K+ is secreted into
CD in response to aldosterone when blood K+ is elevated
Hydrogen is secreted at
PCT & thick ascending limb
Secreted at CD by Type A intercalated cells when blood [H+] too high (pH too low; acidosis)
Secretion of nitrogenous wastes
urea, uric acid, creatinine
Drugs and bioactive substances
Penicillin, sulfonamides, aspirin
Urobilin, some hormones (e.g., human chorionic gonadotropin)
Kidneys Create & Use an Osmotic Gradient to
-to Regulate Urine Concentration & Volume
-want to maintain solute concentration of interstitial fluid at 300 mOsm (kidneys make adjustments to maintain this 300)
what are the two countercurrent mechanisms that determine urine concentration and volume
- countercurrent multiplier
- countercurrent exchanger
Countercurrent multiplier
creates osmotic gradient flow of tubular fluid through the ascending and descending limb of nephron
Countercurrent exchanger
preserves osmotic gradient. Flow of blood through ascending and descending portions of the vasa recta
Three Key Players Interact With the Osmotic Gradient
- long nephron loops of juxtamedullary
- vasa recta
- collecting ducts
Long nephron loops of juxtameduallary
create the osmotic gradient & act as countercurrent multiplier
Vasa Recta
preserve the osmotic gradient & act as countercurrent exchanger
Collecting ducts (CD)
use the osmotic gradient to adjust urine
The Countercurrent Multiplier
Depends on 3 properties of nephron loop that establish positive feedback loop to multiply power of salt pumps. Na+, K+, 2Cl-
flow of Countercurrent Multiplier
increased interstitial fluid osomolaity, water leave descending limb, increased osmolatliy of filtrate in descending limb, increased osmolality of filtrate entering the ascending limb, salt is pumped out of the ascending limb
Moving up run pressure
NaCl goes in and H2O goes out
Moving out in pressure
NaCl goers out and H2O goes in
What happens when osmolarity of blood decreases (more Dilute)
-decreased ADH release
-decrease number of aquaporins in CD
-decreased H2O reabsorption from CD
-Pale urine
What happens when osmolarity of blood increases (more concentration)
-increased ADH release
-Increased number oof Aquaporins in CD
-Increased H2O reabsorption from CD
-small volume of concentration dark urine
Urea Recycling Contributes to the Osmotic Gradient
Urea enters tubular fluid in ascending thin loop
In cortical CD, H2O is removed concentrating urea in tubular fluid
In medullary CD, urea moves down its gradient via uniporters into the interstitial fluid
Urea “cycled” between collecting tubule and nephron loop
Renal plasma clearance
volume of plasma that kidneys clear (remove) a particular substance in given time (usually 1 minute) (mL/min)
Kidney Function is Evaluated by Analyzing Blood & Urine = U
concentration of substance in urine (mg/mL)
V=
flow rate of urine formation (mL/min)
P =
concentration of substance in plasma (mg/mL)
Equation for Kidney function by analyzing blood urine
C= UV/P
if substance neither reabsorbed nor filtered (e.g., inulin) what happens to Blood and Urine
C=GFR
If substance reabsorbedwhat happens to Blood and Urine
C is less then GFR
if substance secreted (e.g., creatininewhat happens to Blood and Urine
C is more then GFR
Is urine sterile
yes, until it is contaminated
Chemical composition of Urine
95% H2O, 5% solutes mostly urea
-Salts, nitrogenous wastes (uric acid, creatinine), some hormones, drugs, ketone bodies
-Should NOT have glucose, ketones, protein (trace OK), bilirubin, RBCs, hemoglobin, leukocytes, nitrites or myoglobin
Specificity of urin
1.003 to 1.035 Density of a substance compared to density of water (1.000)
Color and transparency of urine
-clear, cloudy
-higher concentration deeper the colour
-pale to deep yellow
Volume of urine
1-2 L a day
-varies with fluid intake, BP, temp, Diabetes
-Min 0.5L to elicited wastes
-below 0.4L wastes will accumulate in blood
Urinoid
= normal smell of fresh urine
May develop ammonia smell if allowed to stand
Fruity urine smell indicates
smell in diabetes some drug and vegetables
Mucosa:
transitional epithelium & lamina propria
Distensible & impermeable to urine
Muscularis
inner longitudinal & outer circular smooth muscle
Pressure causes peristaltic contraction of smooth muscle
Adventitia
Areolar CT continuous with renal capsule
Urinary Bladder
Expandable, muscular sac posterior to pubic symphysis
Anteroinferior to uterus in females
Anterior to rectum and superior to prostate gland in males
Retroperitoneal: superior surface covered with parietal peritoneum
Trogone
Triangular area of bladder wall
Remains immobile
Directs urine into urethra
(common place for infections)
Four tunics in the urinary bladder
- Mucosa folds
- Submucosa
- Muscular
- Adventetia
Urethra
conveys urine out of the body
What stops release of urine
2 sphincters
Internal urethral sphincter
Involuntary: sympathetic & parasympathetic ANS
Smooth muscle
Neck of bladder
External urethral sphincter
Voluntary: somatic NS
Skeletal muscle
External orifice in females
Membranous urethra in males
Male urethra 3 segments (18 cm) (transports urine and semon)
Prostatic urethra
Membranous urethra
Spongy urethra
Prostate urethra
Runs through prostate gland
Surrounded by 2 smooth muscle bundles
Membranous urethra
Shortest
Surrounded by external urethral sphincter (skeletal muscle)
Spongy urethra
Longest
Encased in cylinder of penile erectile tissue (corpus spongiosum)
Extends to external urethral orifice
3 components of micturition the act of emptying urinary bladder
- Storage reflex
- Micturition reflex
- parasympathetic stimulation
Storage reflex
Sympathetic signals cause
Relaxation of detrusor muscle – allows filling
Contraction of the internal urethral sphincter – prevents urine from leaving bladder
Somatic pudendal nerve continually stimulates external urethral sphincter keeping it closed
Sympathetic stimulation inhibits micturition
Micturition reflex
~300 mL of urine in bladder bladder distends baroreceptors stimulated
Sensory signals micturition center in pons
Micturition center sends signals through parasympathetic pelvic splanchic nerves
Parasympathetic stimulation
Contraction of detrusor muscles in bladder – expel urine
Relaxation of internal urethral sphincter
