Chapter 23 Flashcards
What are the six principal organs of the urinary system?
2️⃣ kidneys
2️⃣ ureters
1️⃣ urinary bladder
1️⃣ urethra
What are two spatial relationships of the urinary tract in males and females?
The urinary tract relates to the vagina and uterus in females and the prostate in males.
Name four functions of the kidneys other than urine formation.
- Filter blood and excrete toxic metabolic wastes
- Regulate blood volume, pressure, and osmolarity
- Regulate electrolyte and acid-base balance
- Secrete erythropoietin for red blood cell production
—————
Here’s a fun and silly mnemonic to help you remember these four kidney functions:
“Funky Rhinos Eat Eggs”
• F = Filter blood and excrete toxic metabolic wastes
• R = Regulate blood volume, pressure, and osmolarity
• E = Electrolyte and acid-base balance regulation
• E = Erythropoietin secretion for red blood cell production
Just imagine some funky rhinos eating giant eggs while wearing sunglasses—because rhinos clearly have awesome kidneys!
What is erythropoietin, and what does it do?
A hormone secreted by the kidneys that stimulates red blood cell production, supporting oxygen-carrying capacity.
—————
Erythropoietin (or EPO for short) is a hormone made by your kidneys. Its main job is to tell your bone marrow (where blood cells are made) to make more red blood cells.
Why is that important? Because red blood cells are what carry oxygen throughout your body. More red blood cells = more oxygen getting to your muscles, brain, and other tissues so they can work properly.
So, if your body senses you don’t have enough oxygen (like if you’re anemic or at a high altitude), your kidneys will release more erythropoietin to make more red blood cells and boost your oxygen levels.
What do the kidneys do to help regulate calcium homeostasis?
They participate in the synthesis of calcitriol.
—————
Your kidneys help regulate calcium levels in your body by helping to make a hormone called calcitriol.
Calcitriol is the active form of vitamin D, and one of its main jobs is to help your intestines absorb more calcium from the food you eat. Without enough calcitriol, even if you eat foods rich in calcium, your body wouldn’t absorb as much of it into your bloodstream.
So, the kidneys are like an assistant chef helping to prepare the final ingredient (calcitriol) that makes sure your body can “digest and use” the calcium properly. This is important for keeping your bones strong and your muscles and nerves working correctly.
Without your kidneys making calcitriol, your calcium levels could drop too low, which could weaken your bones and cause other problems.
What is a metabolic waste?
A waste substance produced by the body during metabolism.
What is the most toxic nitrogenous waste, and how is it handled by the liver?
Ammonia is the most toxic; the liver converts it into urea, which is less toxic.
Name four major nitrogenous wastes and their sources.
- Ammonia (from amino acid deamination)
- Urea (from ammonia and carbon dioxide)
- Uric acid (from nucleic acid metabolism)
- Creatinine (from creatine phosphate breakdown)
—————
“All Ugly Unicorns Can’t-Prance”
• A = Ammonia (from amino acid deamination)
• U = Urea (from ammonia + CO2)
• U = Uric acid (from nucleic acid metabolism)
• C = Creatinine (from creatine phosphate breakdown)
Story to go with it:
“All Ugly Unicorns Can’t-Prance” because they are weighed down by all the waste products they carry around!
What is blood urea nitrogen (BUN) and what can an elevated level indicate?
The level of nitrogenous waste in the blood; elevated BUN may indicate renal insufficiency.
—————
Blood Urea Nitrogen (BUN) is a way to measure how much waste (specifically, urea) is floating around in your blood. Urea is a waste product made when your body breaks down proteins, and your kidneys are responsible for filtering it out and getting rid of it in urine.
If your BUN level is high, it can mean that your kidneys aren’t doing their job well and waste is building up in your blood. This might be a sign of kidney trouble, like renal insufficiency, which means your kidneys aren’t working as well as they should.
—————
Think of your kidneys like garbage collectors for your body. Proteins are like groceries you bring home, but cooking them creates trash (waste) like urea. Normally, the kidneys (garbage collectors) come by and take out the trash (urea) before it piles up.
If your BUN is high, it’s like the garbage collectors are on strike, and now trash is piling up in the streets (your bloodstream). Too much trash = a sign that something is wrong with the garbage service (your kidneys)!
What is excretion?
The process of separating wastes from body fluids and eliminating them.
Name the four organ systems that carry out excretion and what they excrete.
- Respiratory system - CO2, other gases, water
- Integumentary system - water, salts, urea, lactate
- Digestive system - water, salts, lipids, bile pigments, cholesterol, etc.
- Urinary system - metabolic wastes, toxins, drugs, salts, H+ ions, water
—————
Your body has four “clean-up crews” (organ systems) that each help take out different types of “trash” (waste) your body doesn’t need:
- Respiratory system (your lungs): They “breathe out the bad stuff” like carbon dioxide (CO2), extra gases, and some water vapor.
- Integumentary system (your skin): Your skin sweats out water, salt, urea (waste from breaking down protein), and lactate (stuff from muscle activity).
- Digestive system (your intestines): Your poop removes extra water, salts, fats, bile pigments (which help break down fats), cholesterol, and more.
- Urinary system (your kidneys and bladder): Your pee clears out metabolic waste (trash from your cells), toxins, drugs, salts, acid (H+ ions), and water.
Mnemonic:
“Rats In Dark Uniforms”
• R - Respiratory = CO2, gases, water
• I - Integumentary = water, salts, urea, lactate
• D - Digestive = water, salts, fats, bile stuff
• U - Urinary = waste, toxins, drugs, salts, acid, water
Like a squad of sneaky rats in dark uniforms cleaning up your body!
Where are the kidneys located in relation to the vertebrae?
Between vertebrae T12 and L3, with the right kidney slightly lower than the left.
What does “retroperitoneal” mean regarding the kidneys?
The kidneys lie behind the peritoneum along with the ureters, urinary bladder, renal artery and vein, and adrenal glands.
What is the hilum of the kidney?
A slit on the medial surface that admits renal nerves, blood vessels, lymphatics, and the ureter.
Name the three layers of connective tissue protecting the kidney.
Renal fascia, perirenal fat capsule, and fibrous capsule.
What is the renal parenchyma and what does it encircle?
The glandular tissue that forms urine; it encircles the renal sinus.
What are the two zones of the renal parenchyma?
The renal cortex and renal medulla.
What is a renal pyramid and what structure is found at its tip?
A conical structure in the medulla; the renal papilla is found at its tip.
What structures make up a kidney lobe?
One pyramid and its overlying cortex.
What is the flow of urine from the minor calyces to the urethra?
Minor calyx → Major calyx → Renal pelvis → Ureter → Urinary bladder → Urethra.
What is the order of arterial renal circulation starting from the renal artery?
Renal artery → Segmental artery → Interlobar artery → Arcuate artery → Cortical radiate artery → Afferent arteriole → Glomerulus → Efferent arteriole.
What is the glomerulus and where is it located?
A ball of capillaries inside the glomerular capsule.
What two types of nephron microcirculation exist after the efferent arteriole?
Peritubular capillaries (cortical nephrons) and vasa recta (juxtamedullary nephrons).
What is the renal corpuscle made of?
The glomerulus and the glomerular (Bowman) capsule.
What are podocytes and where are they found?
Cells with foot processes (pedicels) found in the visceral layer of the glomerular capsule.
What are the four regions of the renal tubule?
Proximal convoluted tubule (PCT), nephron loop (loop of Henle), distal convoluted tubule (DCT), and collecting duct.
What type of epithelium is found in the proximal convoluted tubule (PCT)?
Simple cuboidal epithelium with prominent microvilli (brush border).
What is the function of the thick and thin segments of the nephron loop?
Thick segment - active salt transport; Thin segment - permeable to water.
Where does the DCT begin and what is its histology?
Begins after the ascending limb reenters the cortex; lined by cuboidal epithelium with smooth cells and few microvilli.
What is the function of the collecting duct?
Receives fluid from multiple nephrons and drains urine into the papillary duct and then the minor calyx.
What is the difference between juxtamedullary and cortical nephrons?
Juxtamedullary nephrons have long loops extending into the medulla, while cortical nephrons have shorter loops that dip slightly into the medulla.
What does the renal plexus do?
Carries sympathetic innervation to regulate blood flow and urine production; also transmits pain signals.
What are the four stages of urine formation?
Glomerular filtration, tubular reabsorption, tubular secretion, and water conservation.
What is glomerular filtrate?
Fluid in the capsular space similar to plasma but with almost no protein.
What is tubular fluid?
Fluid from the proximal convoluted tubule through the distal convoluted tubule, altered by reabsorption and secretion.
What is the filtration membrane composed of?
Fenestrated endothelium, basement membrane, and filtration slits between podocytes.
What types of molecules can pass through the filtration membrane?
Molecules smaller than 3 nm (e.g., water, electrolytes, glucose, amino acids, nitrogenous wastes).
What is proteinuria and hematuria?
Proteinuria: presence of protein in urine; Hematuria: presence of blood in urine.
What is the blood hydrostatic pressure (BHP) in glomerular filtration and why is it high?
About 60 mm Hg, due to the large afferent arteriole and small efferent arteriole.
What is the net filtration pressure (NFP) in the glomerulus?
NFP = 10 mm Hg (60 out - 18 in - 32 in = 10 mm Hg outward pressure).
What is glomerular filtration rate (GFR) in young adult males and females?
Males: ~125 mL/min, Females: ~105 mL/min.
What percentage of filtrate is typically reabsorbed by the kidneys?
99%.
What are the two mechanisms of renal autoregulation?
The myogenic mechanism and tubuloglomerular feedback.
What is the juxtaglomerular apparatus?
A structure where the afferent arteriole contacts the distal tubule at the vascular pole of the renal corpuscle.
What does the macula densa do during tubuloglomerular feedback?
Senses NaCl levels, releases ATP, which is converted to adenosine, leading to vasoconstriction of the afferent arteriole.
What do granular (juxtaglomerular) cells secrete?
Renin, which triggers the renin-angiotensin-aldosterone mechanism.
What does sympathetic control do to GFR during stress or shock?
Constricts afferent arterioles, reducing GFR and redirecting blood to vital organs.
What is the renin-angiotensin-aldosterone mechanism’s main role?
Restores blood pressure and blood volume after a drop in pressure.
What does angiotensin II do?
Potent vasoconstrictor, raises BP, constricts efferent arterioles, and stimulates aldosterone and ADH release.
How does angiotensin II affect the kidneys?
Constricts efferent arterioles to maintain GFR and enhances NaCl and water reabsorption.
What hormones does angiotensin II stimulate?
Aldosterone from adrenal cortex and antidiuretic hormone (ADH) from posterior pituitary.
What percentage of glomerular filtrate is reabsorbed by the proximal convoluted tubule (PCT)?
About 65%.
What is tubular reabsorption?
The process of reclaiming water and solutes from tubular fluid and returning them to the blood.
What are the two routes of reabsorption in the PCT?
The transcellular route (through epithelial cells) and the paracellular route (between epithelial cells).
What is solvent drag?
The process where water carries solutes through the paracellular route into the tissue fluid.
Why is sodium reabsorption key in the PCT?
It creates an osmotic and electrical gradient that drives reabsorption of water and other solutes.
What does the Na+-H+ antiport do?
It reabsorbs Na+ while secreting H+ into the tubular fluid.
What type of transport is Na+-K+ pump an example of?
Primary active transport (ATP-dependent).
What is secondary active transport in the PCT?
Sodium-transporting symports in the apical membrane that depend on the Na+-K+ pump but don’t consume ATP directly.
How do Cl- ions follow Na+ during reabsorption?
They follow due to electrical attraction, primarily via K+-Cl- symport and paracellular route.
What transport protein is responsible for glucose reabsorption in the PCT?
Sodium-glucose transporters (SGLTs).
How does the nephron handle urea?
About 40–60% of urea is reabsorbed, but since 99% of water is reabsorbed, urea concentration in urine is higher.
What nitrogenous waste is not reabsorbed at all in the nephron?
Creatinine.
What channels are responsible for water reabsorption in the PCT?
Aquaporins.
What is obligatory water reabsorption?
The constant reabsorption of water due to osmotic gradients created by solute reabsorption in the PCT.
How does angiotensin II affect tubular reabsorption?
It reduces blood pressure in peritubular capillaries, lowering resistance and enhancing reabsorption.
What is the transport maximum (Tm)?
The maximum rate at which a solute can be reabsorbed due to saturation of transport proteins.
What condition occurs when plasma glucose exceeds its Tm?
Glycosuria.
What are the three purposes of tubular secretion in the PCT and nephron loop?
1) Acid-base balance, 2) Waste removal (urea, uric acid, bile acids, ammonia, creatinine), 3) Clearance of drugs and toxins.
What is the primary function of the nephron loop?
To generate an osmotic gradient to concentrate urine and conserve water.
How much water and salt does the nephron loop reabsorb?
About 25% of Na+, K+, Cl- and 15% of the water.
What is the thick segment of the nephron loop impermeable to?
Water.
What are the two types of cells in the DCT and collecting duct?
Principal cells (salt and water balance) and intercalated cells (acid-base balance).
What does aldosterone stimulate?
Na+ reabsorption and K+ secretion in the nephron loop, DCT, and collecting duct.
What are the effects of natriuretic peptides?
Increase GFR, inhibit renin and aldosterone secretion, inhibit ADH secretion, and inhibit NaCl reabsorption by the collecting duct.
How does ADH affect water reabsorption?
It makes the collecting duct more permeable to water, promoting water reabsorption.
What does parathyroid hormone (PTH) do in the kidney?
Inhibits phosphate reabsorption and increases calcium reabsorption.
Where does the collecting duct begin and what is its role?
The collecting duct begins in the cortex and reabsorbs water while concentrating the urine as it passes through the medulla.
What two factors enable the collecting duct to produce hypertonic urine?
1) The osmolarity of the extracellular fluid (ECF) is four times higher in the medulla than in the cortex.
2) The medullary portion of the CD is more permeable to water than solutes.
What is water diuresis?
A response where a large intake of water results in the production of large volumes of hypotonic (dilute) urine.
How does antidiuretic hormone (ADH) reduce urine output?
ADH makes the collecting duct more permeable to water by triggering aquaporin insertion into the apical membrane, increasing water reabsorption.
What happens to aquaporins when ADH secretion falls?
Aquaporins are removed from the plasma membrane and stored in cytoplasmic vesicles, reducing water reabsorption and producing dilute urine.
What is the countercurrent multiplier?
A mechanism where the nephron loop continually recaptures salt and returns it to the deep medulla, multiplying the osmolarity gradient.
Why is the ascending limb of the nephron loop important in the countercurrent multiplier?
It actively transports Na+, K+, and Cl- into the ECF, making the medullary tissue saltier and contributing to the osmotic gradient.
What is the role of urea in maintaining medullary osmolarity?
Urea cycles from the collecting duct to the nephron loop and back, diffusing into the ECF and contributing about 40% of the high osmolarity in the medulla.
What is the countercurrent exchange system of the vasa recta?
It preserves the osmotic gradient by absorbing water from the medulla without removing significant amounts of salt or urea.
What does the vasa recta do as it flows into and out of the medulla?
On the way in, it loses water and gains salt. On the way out, it reabsorbs water and releases salt back into the medulla.
In a dehydrated state, how does ADH affect the collecting duct?
ADH is secreted, making the medullary part of the CD permeable to water, concentrating urine up to 1,200 mOsm/L.
In a hydrated state, how does the collecting duct behave?
ADH is not secreted; the CD reabsorbs salt but not water, resulting in the excretion of dilute urine.
What is the normal color of urine and what pigment causes it?
Urine normally ranges from almost colorless to deep amber, due to urochrome, a pigment from hemoglobin breakdown.
What might cloudy urine or the presence of blood indicate?
Cloudy urine suggests infection (pyuria); blood in urine (hematuria) may indicate a UTI, trauma, or kidney stones.
What is the typical odor of fresh urine and how can it change?
Fresh urine has a mild odor; bacterial degradation produces ammonia odor; sweet smell may indicate diabetes mellitus.
What is the specific gravity range of urine and what does it estimate?
1.001 to 1.028; estimates grams of solid matter per liter using a constant (e.g., 1.025 x 2.6 = 65 g/L).
What is the osmolarity range of urine and how does it compare to blood?
50–1,200 mOsm/L; blood is ~300 mOsm/L, so urine can be hypo- or hypertonic.
What is the normal pH range of urine?
About 6.0 on average (ranges from 4.5 to 8.2).
What is the average chemical composition of urine by volume?
95% water and 5% solutes, mainly urea, NaCl, KCl, creatinine, and other electrolytes.
What substances should not normally be present in urine?
Glucose, free hemoglobin, albumin, ketones, and bile pigments.
What is considered normal urine output and what is polyuria?
1–2 L/day is normal; polyuria is >2 L/day.
What is oliguria and anuria?
Oliguria: <500 mL/day. Anuria: 0–100 mL/day.
How does diabetes mellitus cause polyuria?
Glucose in the renal tubule retains water osmotically, increasing urine output (osmotic diuresis).
How does diabetes insipidus cause polyuria?
ADH hyposecretion prevents water reabsorption in the collecting duct.
What is renal clearance?
The volume of blood plasma cleared of a particular waste per minute.
What formula is used to calculate renal clearance?
C = UV/P
(U = urine concentration, V = urine output rate, P = plasma concentration)
Why is inulin used to measure GFR?
It is filtered by the glomerulus but neither reabsorbed nor secreted by the tubules.
What is the normal GFR based on inulin clearance?
About 120 mL/min.
Why is creatinine often used to estimate GFR?
Easier to measure and provides a close approximation to GFR.
How does renal clearance of a reabsorbed substance compare to GFR?
It is less than GFR if the substance is reabsorbed (e.g., urea clearance is ~60 mL/min).
What is the function of the ureters?
The ureters transport urine from the renal pelvis to the urinary bladder through peristaltic waves.
What are the three layers of the ureter wall?
The adventitia (connective tissue), muscularis (smooth muscle), and mucosa (urothelium/transitional epithelium).
What prevents urine from backing up from the bladder into the ureters?
A small flap of mucosa acts as a valve at the ureteral openings in the bladder.
What is nephrolithiasis?
The presence of kidney stones (renal calculi) in the renal pelvis or ureter.
What is shock wave lithotripsy (SWL)?
A common treatment for kidney stones that uses shock waves to break stones into smaller fragments that can be passed in urine.
What is the detrusor muscle?
A smooth muscle layer in the bladder wall that contracts during urination to expel urine.
What is the trigone of the bladder?
A smooth triangular area on the bladder floor between the openings of the ureters and urethra; common site for bladder infections.
What is the function of the internal urethral sphincter?
In males, it prevents semen from flowing backward into the bladder during ejaculation.
What is the external urethral sphincter and its function?
A skeletal muscle encircling the urethra, providing voluntary control over urination.
What is the micturition reflex?
A spinal reflex that causes contraction of the detrusor and relaxation of the internal urethral sphincter when the bladder is full.
What provides voluntary control over urination?
The external urethral sphincter, controlled by somatic motor neurons via the pudendal nerve.
What is urinary incontinence?
The inability to control urination, which can result from aging, pregnancy, obesity, or neurological disorders.
What is the Valsalva maneuver?
A technique where abdominal muscles compress the bladder to help initiate the micturition reflex when the bladder isn’t fully distended.
Why are women more susceptible to bladder infections than men?
Because the female urethra is shorter, making it easier for bacteria to reach the bladder.
What is cystitis?
Inflammation of the urinary bladder, often caused by bacterial infection.
What is pyelitis and pyelonephritis?
Pyelitis is infection of the renal pelvis; pyelonephritis is infection that has spread to the renal cortex and nephrons.
How does the urinary system interact with the circulatory system?
The kidneys affect blood pressure and composition, and imbalances can impact cardiac rhythm.
How does the urinary system support skeletal system function?
By synthesizing calcitriol, which is important for calcium and phosphate balance and bone maintenance.
What is renal autoregulation?
The nephron’s ability to adjust blood flow and GFR without external control.
