Chapter 25 Study Guide: Urinary System and Renal Physiology

Comprehensive review flashcards covering Chapter 25: Kidney anatomy, nephron structure and types, the juxtaglomerular complex, the renin-angiotensin mechanism, glomerular filtration, tubular reabsorption and secretion, hormonal regulation, and clinical renal physiology.

What are the major physiological functions of the kidneys?

Regulating blood volume, blood pressure, chemical composition, and pH; excreting nitrogenous wastes; producing hormones (erythropoietin and renin); metabolizing vitamin D; and performing gluconeogenesis if needed during prolonged fasting.

In what anatomical order does urine flow through the organs of the urinary system?

Kidneys $\rightarrow$ Ureters $\rightarrow$ Urinary bladder $\rightarrow$ Urethra.

What are the three main internal regions of the kidney?

1. Renal cortex (superficial outer region)
2. Renal medulla (deep to cortex, containing cone-shaped medullary pyramids)
3. Renal pelvis (funnel-shaped collector continuous with the ureter).

What structures transport urine from the renal papillae to the renal pelvis?

Urine drains from the renal papillae into minor calyces, which empty into major calyces, which then convey urine into the renal pelvis.

How much cardiac output do the renal arteries deliver to the kidneys each minute?

Approximately $1200\,\text{ml}$ of blood per minute (about $20\text{--}25\%$ of resting cardiac output).

What is the structural and functional unit of the kidney, and how many are present per kidney?

The nephron; there are over 1 million nephrons per kidney.

What are the two principal parts of a nephron?

The renal corpuscle and the renal tubule.

What are the two components of the renal corpuscle and their respective functions?

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1. Glomerulus: a tuft of fenestrated capillaries where filtration occurs.

2. Glomerular (Bowman's) capsule: a cup-like sac enclosing the glomerulus that collects the newly formed filtrate.

Where does filtration occur

Glomerulus

Where is filtrate collected

Glomerular capsule

What are the three sections of the renal tubule in sequence before it reaches the collecting duct?

1. Proximal convoluted tubule (PCT)
2. Nephron loop (Loop of Henle)
3. Distal convoluted tubule (DCT).

What structural specializations characterize the cells of the proximal convoluted tubule (PCT)?

Cuboidal epithelial cells with dense microvilli (brush border) that dramatically increase surface area,

abundant mitochondria;

functions primarily in reabsorption and secretion.

Where is the proximal convoluted tubule (PCT) located within the kidney?

Exclusively in the renal cortex.

What are the two limbs of the nephron loop (Loop of Henle)?

1. Descending limb: dives from the PCT down into the renal medulla.
2. Ascending limb: ascends from the medulla back into the cortex to join the DCT.

How do the cells and functions of the distal convoluted tubule (DCT) compare to those of the PCT?

cuboidal with few microvilli;

they perform less overall absorption and are more involved in secretion

reabsorption being hormonally regulated.

What anatomical route do collecting ducts follow to empty urine into minor calyces?

Collecting ducts receive filtrate from many nephrons,

run parallel through the medullary pyramids

fuse near the papillae of the pyramids to deliver urine into the minor calyces.

What percentage of nephrons are cortical nephrons, and what is their defining structural feature?

Cortical nephrons make up $85\%$ of all nephrons; almost the entire nephron resides in the renal cortex, with only a short hairpin loop dipping into the outer medulla.

What are the distinguishing features and primary function of juxtamedullary nephrons?

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They have long nephron loops that extend deep into the renal medulla, are associated with vasa recta, and play a crucial role in establishing the osmotic gradient needed to produce concentrated urine.

Which type of nephron has a vasa recta

Juxtamedullary nephrons

Which type of nephron has the glomerulus and peritubular capillaries

Cortical nephron

Why is blood pressure within the glomerular capillaries unusually high?

Because the glomerulus is both fed and drained by high-resistance arterioles

afferent arteriole has a larger diameter than the exiting efferent arteriole.

What are peritubular capillaries, where do they arise, and what is their role?

Low-pressure,

porous capillary beds found in cortical nephrons that arise from efferent arterioles,

cling to the PCT and DCT,

are adapted for the rapid reabsorption of water and solutes into the blood.

What is the function vasa recta?

maintain the medullary osmotic gradient.

What are the two vital variables regulated by the juxtaglomerular complex (JGC)?

1. Rate of filtrate formation (Glomerular Filtration Rate, GFR)

2. Systemic arterial blood pressure.

How do macula densa cells respond to high GFR?

Chemoreceptors detect high NaCl concentration in filtrate

These cells trigger vasoconstriction in afferent arteriole, reducing filtrate formation rate and reducing GFR

What are granular cells, and what triggers them to secrete renin?

Enlarged smooth muscle cells in the wall of the afferent arteriole acting as mechanoreceptors;

a drop in local arteriolar blood pressure triggers them to release the enzyme renin.

What is the role of extraglomerular mesangial cells in the JGC?

They lie between the arteriole walls and tubule

interconnected by gap junctions

transmit regulatory signals between cells

What enzymatic steps occur in the renin-angiotensin-aldosterone cascade?

Renin converts angiotensinogen into angiotensin I; Angiotensin-Converting Enzyme (ACE) converts angiotensin I into active angiotensin II.

What are the main systemic and renal actions of Angiotensin II?

1. Inc MAP

2. Direct stimulation of renal tubule $\text{Na}^+$ reabsorption

3. Release of aldosterone

4. Stimulates hypothalamus to release ADH and activate thirst

5. Constricts efferent arterioles to increase glomerular pressure and inc fluid reabsorption.

How much fluid is filtered by the kidneys daily, and what volume of urine is actually excreted?

About $180\,\text{liters}$ of fluid is filtered daily, but only about $1.5\,\text{liters}$ ($< 1\%$) is excreted as urine.

How many times per day is the entire plasma volume filtered through the kidneys?

Approximately $60$ times every day.

What is the composition of glomerular filtrate compared to blood plasma?

Filtrate contains all the constituents of plasma except large plasma proteins and blood cells.

What are the three core processes of urine formation?

1. Glomerular filtration (passive, non-selective fluid movement)

2. Tubular reabsorption (selectively returns $~99\%$ of substances to blood)

3. Tubular secretion (selectively moves wastes and drugs from blood into filtrate).

What three layers constitute the filtration membrane of the renal corpuscle?

1. Fenestrated endothelium of glomerular capillaries

2. Fused basement membrane

3. Foot processes (pedicels) of podocytes with filtration slits covered by slit diaphragms.

Is glomerular filtration passive?

Yes

What is the normal Glomerular Filtration Rate (GFR) in healthy adults?

$120\text{--}125\,\text{ml/min}$.

What two routes can solutes and water take across the tubular epithelium during reabsorption?

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1. Transcellular route: across the apical membrane, cytosol, and basolateral membrane of tubule cells, then into peritubular capillary endothelium.

2. Paracellular route: through leaky tight junctions between adjacent tubule cells.

Paracellular route

Fluid and filtrate are returned through leaky tight junctions between adjacent tubule cells.

Transcellular route

Fluid and filtrate are moved across the apical membrane, cytosol, and basolateral membrane of tubule cells, then into peritubular capillary endothelium.

What primary transport mechanism drives the secondary active transport of glucose and amino acids in the PCT?

Secondary active transport with Na

How is water transported in PCT

aquaporins are always present

How is water transported in collecting duct

are inserted only in the presence of ADH

What occurs when the transport maximum ($T_m$) of a renal carrier system is exceeded, such as in diabetes mellitus?

The carriers become saturated, and excess solute cannot be reabsorbed, spilling into the urine (e.g., glycosuria).

What is the full name of ADH, where is it released, and what is its renal effect?

MAYBE SPLIT INTO MULTIPLE QUESTIONS

Antidiuretic Hormone;

released by the posterior pituitary;

it causes aquaporins to insert into collecting duct principal cells, increasing water reabsorption and producing concentrated urine.

What is the target and effect of aldosterone in the nephron?

It targets the DCT and collecting duct principal cells, promoting $\text{Na}^+$ reabsorption; water follows $\text{Na}^+$, expanding blood volume and raising blood pressure.

What is the source and physiological action of Atrial Natriuretic Peptide (ANP)?

Released by atria in response to stretch;

it inhibits $\text{Na}^+$ reabsorption,

promoting $\text{Na}^+$ and water loss,

reducing blood volume and blood pressure.

Where does Parathyroid Hormone (PTH) act in the nephron and what is its specific effect?

distal convoluted tubule (DCT) to increase $\text{Ca}^{2+}$ reabsorption.

What are the major physiological purposes of tubular secretion?

Disposing of protein-bound drugs and metabolites,

eliminating undesirables (like urea and uric acid),

clearing excess $\text{K}^+$

regulating blood pH by secreting excess $\text{H}^+$ or $\text{HCO}_3^-$.

How do ADH levels adjust during overhydration

• Overhydration: ADH release decreases, leading to a large volume of dilute urine.

• Dehydration: maximal ADH is released, causing up to $99\%$ water reabsorption and a small volume of concentrated urine.

What is renal clearance and why is inulin used as the clinical standard to assess it?

The volume of plasma completely cleared of a substance by the kidneys per unit time; inulin is freely filtered by glomeruli but neither reabsorbed nor secreted, making its clearance equal to GFR ($125\,\text{ml/min}$).

What are the GFR thresholds defining Chronic Renal Disease and Renal Failure?

• Chronic Renal Disease: $\text{GFR} < 60\,\text{ml/min}$ for at least 3 months.
• Renal Failure: $\text{GFR} < 15\,\text{ml/min}$ (leads to uremia and requires dialysis or transplant).

What is uremia and what symptoms are typically associated with it?

A toxic clinical syndrome caused by the accumulation of nitrogenous wastes in the blood; symptoms include fatigue, anorexia, nausea, mental status changes, and muscle cramps.

What are the three most abundant nitrogenous wastes found in normal urine?

1. Urea (most abundant, from amino acid breakdown)
2. Uric acid (from nucleic acid metabolism)
3. Creatinine (from creatine phosphate breakdown in skeletal muscle).

What pigment gives normal urine its pale-to-deep yellow color, and what is its source?

Urochrome, a pigment resulting from the body's destruction of hemoglobin (via bilirubin).

What type of epithelium lines the mucosa of the ureters and urinary bladder, and what muscle forms the bladder wall?

Transitional epithelium (allows stretching without tearing); the thick muscular layer is the detrusor muscle (consisting of 3 layers of smooth muscle).

What are the two urethral sphincters and their types of nervous control?

1. Internal urethral sphincter: involuntary smooth muscle at the bladder-urethra junction.
2. External urethral sphincter: voluntary skeletal muscle within the urogenital diaphragm.

What are the anatomical differences between the female and male urethra?

The female urethra is short ($3\text{--}4\,\text{cm}$) and conducts only urine; the male urethra is long ($~20\,\text{cm}$), conducts both urine and semen, and consists of three regions: prostatic, intermediate (membranous), and spongy urethra.

What is stress incontinence and what activities commonly trigger it?

Involuntary leakage of urine caused by an increase in intra-abdominal pressure overcoming weakened pelvic floor muscles; triggered by laughing, coughing, or sneezing.