Urinary system

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Questions and Answers

What type of epithelium lines the collecting duct system?

Stratified cuboidal epithelium

Simple squamous epithelium

Transitional epithelium

Simple cuboidal epithelium (correct)

What is the primary hormonal influence on the light (principal) cells of the collecting duct?

Insulin

Antidiuretic hormone (correct)

Atrial natriuretic peptide

Cortisol

How do dark intercalated cells primarily maintain acid-base balance?

By secreting bicarbonate into the urine

By secreting hydrogen ions and reabsorbing bicarbonate (correct)

By excreting excess sodium directly

By reabsorbing hydrogen ions

What is the effect of aldosterone on the renal collecting duct?

Increases sodium reabsorption Signup and view all the answers

What is the role of aquaporin-2 channels in the principal cells of the collecting duct?

Promoting water reabsorption Signup and view all the answers

Which ion does the thin ascending limb predominantly transport due to Na+/K+/2Cl- cotransporters?

Na+ Signup and view all the answers

What is the primary function of the distal convoluted tubule (DCT)?

Ion resorption Signup and view all the answers

Which hormone is responsible for increasing the absorption of Na+ ions in the distal convoluted tubule?

Aldosterone Signup and view all the answers

What type of epithelium lines the distal convoluted tubule?

Simple cuboidal Signup and view all the answers

Which component is largely impermeable to water in the nephron?

Thin ascending limb Signup and view all the answers

What is the role of uromodulin (Tamm-Horsfall protein) produced by the epithelial cells of the thick ascending limb?

Enhances NaCl reabsorption Signup and view all the answers

Which ion exchange occurs in the distal convoluted tubule with the increase of vitamin D3 production?

Na+ and Ca2+ Signup and view all the answers

What is the role of angiotensin II in the nephron?

Increases Na+ reabsorption Signup and view all the answers

Which structure follows the distal convoluted tubules in the urine passage?

Collecting tubules Signup and view all the answers

What is the effect of antidiuretic hormone (ADH) in the collecting ducts?

Regulates aquaporin channels Signup and view all the answers

What is the primary function of mesangial cells in the glomerulus?

To provide structural support and secrete regulatory molecules Signup and view all the answers

What typically characterizes the initial glomerular filtrate?

Similar in composition to blood plasma with little protein Signup and view all the answers

Which component of the glomerular filtration barrier is responsible for size and charge selectivity?

Filtration slit diaphragms Signup and view all the answers

What can result from damage to the renal glomeruli?

Presence of blood components in urine Signup and view all the answers

What is a common non-inflammatory cause of glomerular damage?

Diabetes Signup and view all the answers

Which molecule does NOT typically cross the filtration barrier during glomerular filtration?

Large proteins Signup and view all the answers

What is the role of angiotensin II receptors in mesangial cells?

Regulate blood flow through the glomerulus Signup and view all the answers

What constitutes the three layered components of the glomerular filtration barrier?

Fenestrated capillaries, glomerular basement membrane, and filtration slit diaphragms Signup and view all the answers

What is a primary characteristic of nephritic syndrome?

Low-level proteinuria Signup and view all the answers

Which part of the nephron is involved in tubular reabsorption?

Proximal convoluted tubule Signup and view all the answers

What describes juxtamedullary nephrons?

Have glomeruli near the corticomedullary junction Signup and view all the answers

What percentage of nephrons are classified as cortical nephrons?

80% Signup and view all the answers

Which part of the Loop of Henle has a larger diameter and thicker walls?

Thick ascending limb Signup and view all the answers

What is the role of glomeruli in cortical nephrons?

Filtration at high pressure Signup and view all the answers

Which segment of the nephron is lined by simple cuboidal epithelium?

Proximal convoluted tubule Signup and view all the answers

What is a potential consequence of untreated glomerular diseases?

Acute or chronic renal failure Signup and view all the answers

What primarily occurs after the ultrafiltrate passes through the glomerulus?

Formation of tubular fluid Signup and view all the answers

What distinguishes nephrotic syndrome from nephritic syndrome?

Generalised edema Signup and view all the answers

What is primarily absorbed in the proximal tubule cells via pinocytosis?

Proteins Signup and view all the answers

How do sodium ions primarily get absorbed in the proximal tubule?

Active transport via Na+ pumps Signup and view all the answers

What characterizes the thin descending limb of the loop of Henle?

Highly permeable to water Signup and view all the answers

What happens to the osmolarity of the ultrafiltrate as it moves through the thick ascending limb of the loop of Henle?

It becomes hyposmotic to plasma Signup and view all the answers

What functions do the basal portions of proximal tubule cells serve?

Energy production and transport of ions Signup and view all the answers

What is the role of aquaporins in the thin descending limb of the loop of Henle?

Facilitate water reabsorption Signup and view all the answers

What substance is primarily recovered in the proximal convoluted tubule besides water?

Sodium Signup and view all the answers

Which segment of the nephron is primarily responsible for the countercurrent exchange system?

Loop of Henle Signup and view all the answers

Which of the following ions is NOT reabsorbed by the proximal tubule?

Calcium Signup and view all the answers

What type of absorption occurs in the proximal tubule for glucose?

Co-transport with sodium Signup and view all the answers

What is one of the primary hormones produced by the kidneys that controls red blood cell production?

Erythropoietin Signup and view all the answers

Which components contribute to the filtration barrier in the kidneys?

Endothelial cells and podocytes Signup and view all the answers

What is one of the functions of the urinary system?

Regulation of blood volume Signup and view all the answers

What type of tissue makes up the capsule covering each kidney?

Smooth muscle and collagen Signup and view all the answers

What structures are responsible for the arrangement of blood vessels in the kidney?

Mesangial cells Signup and view all the answers

In which organ is glucose produced during gluconeogenesis during starvation?

Liver Signup and view all the answers

What characterizes the ureters in the urinary system?

They are paired organs Signup and view all the answers

What role do podocytes play in the kidneys?

They form part of the nephron's filtration barrier Signup and view all the answers

What is the primary role of renin secreted by specific cells?

To regulate blood pressure Signup and view all the answers

How many layers form the transitional epithelium?

Four or five Signup and view all the answers

Which layer is NOT part of the wall structure in urinary passages?

Peritoneum Signup and view all the answers

What distinguishes umbrella cells in transitional epithelium?

They change shape according to organ fullness. Signup and view all the answers

What is the primary muscle layer of the bladder known as?

Detrusor muscle Signup and view all the answers

What is a characteristic feature of nephritic syndrome?

Microhematuria Signup and view all the answers

What structure follows the proximal straight tubule in urine formation?

Descending limb of the Loop of Henle Signup and view all the answers

Which segment of the nephron is primarily involved in maintaining urine osmolarity?

Loop of Henle Signup and view all the answers

What percentage of nephrons are classified as juxtamedullary nephrons?

20% Signup and view all the answers

What characterizes the proximal convoluted tubule (PCT) of the nephron?

Lines with cuboidal epithelium Signup and view all the answers

How much of the ultrafiltrate is typically reabsorbed into the bloodstream?

99% Signup and view all the answers

Which type of nephron has glomeruli located high in the cortex and short loops?

Cortical nephrons Signup and view all the answers

What happens to the osmolarity of the tubular fluid as it passes through the thin descending limb of the Loop of Henle?

Increases Signup and view all the answers

What role do juxtamedullary nephrons primarily serve in the kidney?

Concentration and dilution of urine Signup and view all the answers

What is the space at the hilum of the kidney that accommodates vessels, nerves, and the renal pelvis called?

Renal sinus Signup and view all the answers

What is the primary function of the distal straight tubule (DST)?

Electrolyte balance Signup and view all the answers

Which part of the kidney contains renal corpuscles?

Cortex Signup and view all the answers

What is the primary function of the renal papilla?

To project into a minor calyx Signup and view all the answers

How many nephrons are approximately contained in each kidney?

1 million to 3 million Signup and view all the answers

What structure acts as a double-layered covering for the glomerulus?

Bowman's capsule Signup and view all the answers

What does the area cribrosa refer to at the renal papilla?

The perforated area at the tip of the renal papilla Signup and view all the answers

Which pole of the renal corpuscle is where the afferent and efferent arterioles enter and exit?

Vascular pole Signup and view all the answers

What do renal lobules consist of?

One medullary ray and its surrounding cortex Signup and view all the answers

What is located at the apex of each renal pyramid?

Renal papilla Signup and view all the answers

Which structure does the renal pelvis split into?

Minor calyces Signup and view all the answers

What is a primary characteristic of the distal straight tubule (DST)?

Lined by simple cuboidal epithelium Signup and view all the answers

How does the distal convoluted tubule (DCT) primarily affect the ultrafiltrate?

Decreases ultrafiltrate osmolality Signup and view all the answers

Which ion's reabsorption is primarily influenced by parathyroid hormone (PTH) in the DCT?

Calcium (Ca2+) Signup and view all the answers

What effect does aldosterone have on the distal convoluted tubule?

Promotes sodium reabsorption Signup and view all the answers

What type of transporters are present in the apical cell membrane of the distal straight tubule?

Symporters Signup and view all the answers

What role does the back leak of K+ play in the thin ascending limb?

Induces paracellular reabsorption of ions Signup and view all the answers

Which feature distinguishes the collecting ducts from other tubule segments?

Regulation by antidiuretic hormone (ADH) Signup and view all the answers

What substance is primarily transported by the cotransporters in the thin ascending limb?

Chloride (Cl-) Signup and view all the answers

What is the effect of angiotensin II in the renal system?

Stimulates sodium reabsorption Signup and view all the answers

Study Notes

Glomerular Filtration Barrier

Composed of three layers: fenestrated capillary endothelium, glomerular basement membrane (GBM), and filtration slit diaphragms between pedicels.
Blocks most plasma proteins, but smaller proteins, polypeptide hormones, and amino acids pass into the filtrate.
Size and charge selectivity prevent cells and large or negatively charged molecules (e.g., proteins) from crossing.

Glomerular Filtration

First stage of urine production.
Approximately 20% of blood plasma entering a glomerulus is filtered into the capsular space.
Initial glomerular filtrate is similar to plasma, but with very little protein.

Mesangium

Glomerular capillaries are held together by mesangial cells and their extracellular matrix.
Mesangial cells function similarly to pericytes, embedded in the capillary basal lamina.
Functions include phagocytosis, endocytosis, structural support for podocytes, and secretion of molecules (e.g., IL-1, PGE2, platelet-derived growth factor) involved in glomerular injury response.
Mesangial cells possess angiotensin II receptors and regulate glomerular blood flow.

Glomerular Diseases

Damage disrupts filtration, leading to blood components (proteins and RBCs) in urine.
Often caused by immune-mediated processes (glomerulonephritis) or non-inflammatory causes (e.g., diabetes, amyloidosis).
Present as nephritic syndrome (low-level proteinuria, microhematuria, oliguria, hypertension) or nephrotic syndrome (high-level proteinuria, generalized edema).
Can progress to acute or chronic renal failure; rapid diagnosis and treatment are crucial.

Tubular System

Ultrafiltrate (now tubular fluid) flows through the tubular system after the glomerulus.
Reabsorption and secretion of plasma components occur (approximately 99% of ultrafiltrate is reabsorbed).
Urine concentration follows.
Subsequent stages include tubular reabsorption and secretion.

Tubular Parts

Proximal thick segment: proximal convoluted tubule (PCT), proximal straight tubule (PST).
Thin segment: descending limb, ascending limb.
Distal thick segment: distal straight tubule (DST), distal convoluted tubule (DCT).

Loop of Henle

Consists of the end of the proximal straight tubule, descending limb of the thin tubule, ascending limb of the thin tubule, and distal straight tubule.
Descending limb, loop itself, and part of ascending limb form the thin segment.
Upper part of the ascending limb forms the thick segment.

Types of Nephrons

Cortical nephrons (80%): glomeruli located high in the cortex, short loops, function under high pressure, actively participate in ultrafiltrate formation.
Juxtamedullary nephrons (20%): glomeruli near the corticomedullary junction, long loops extending deep into the medulla, function under low pressure, less critical for filtration, essential for urine concentration and dilution.

Proximal Segment (PCT & PST)

Lined by simple cuboidal epithelium.
Apical cells have microvilli (brush border) increasing surface area.
Basal portions have membrane invaginations and mitochondria (basal striations/labyrinth).
Reabsorbs proteins via pinocytosis, larger proteins cleaved into amino acids.
Glucose and amino acids pass via facilitated diffusion.
Sodium ions absorbed via ion pumps, followed by water.
Tubular secretion of waste products (drugs, creatinine).

Function of Proximal Segment

Major site of reabsorption.
PCT reabsorbs glucose, amino acids, most HCO3-, Na+, Cl-, PO4, K+, H2O, and uric acid.
Isotonic absorption.
PCT recovers most fluid, PST recovers remaining glucose before the thin segment.

Loop of Henle (Detailed)

Part of the countercurrent exchange system concentrating urine.
Thin descending limb: simple squamous epithelium, highly permeable to water (aquaporins), less permeable to Na+ and urea.
Thick ascending limb: taller cells, tight junctions (impermeable to water), highly permeable to Na+ and Cl- (Na+/K+/2Cl- cotransporters).

Differences Between Thin Descending and Ascending Limbs

Thin descending limb: isosmotic ultrafiltrate entry, passively reabsorbs water due to medullary hypertonicity, less permeable to Na+ and urea.
Thin ascending limb: hyposmotic ultrafiltrate exit (more salt than water reabsorbed), highly permeable to Na+ and Cl-, largely impermeable to water, indirectly induces paracellular reabsorption of Mg2+ and Ca2+

Distal Thick Segment (DST & DCT)

Lined by simple cuboidal epithelium without a brush border.
Basal striations present.
DST: part of the ascending limb, transports ions from lumen to interstitium, apical electroneutral transporters for Cl-, Na+, and K+.
DST produces uromodulin (Tamm-Horsfall protein) influencing NaCl reabsorption and urine concentration.

Distal Convoluted Tubule (DCT)

One-third the length of PCT.
Lined by simple cuboidal epithelium without brush border.
Reabsorbs Na+, Cl-, Mg2+, and Ca2+.
Impermeable to water.
Decreases ultrafiltrate osmolality.
PTH increases vitamin D3 production, boosting Ca2+ and Na+ exchange, and Ca2+ reabsorption.
Angiotensin II increases Na+ reabsorption.
ANP and Aldosterone also influence function.
Aldosterone increases Na+ absorption.

Collecting Duct System

Lined by simple cuboidal epithelium (becomes columnar as duct size increases).
Two cell types: light principal cells and dark intercalated cells.

Collecting Duct System (Detailed)

Light/principal cells: electron-lucent cytoplasm, few organelles, aquaporin-2 channels (ADH-sensitive), ANP-sensitive (inhibits Na+ and Cl- reabsorption), aldosterone receptors, reabsorb Na+ and water, secrete K+.
Dark intercalated cells: microvillous surface, abundant mitochondria; α-cells secrete H+, β-cells secrete HCO3-, involved in HCO3- reabsorption (exchanged for Cl-).

Hormonal Regulation - Antidiuretic Hormone (ADH)

Regulates plasma osmolality via V2 receptors, inserting aquaporin channels in principal cells of collecting duct and DCT (increased water reabsorption).
Regulates blood pressure via V1 receptors (vasoconstriction at higher levels).
Increases urea reabsorption in collecting duct, facilitating urine concentration.

Hormonal Regulation - Aldosterone

Binds to mineralocorticoid receptors in distal tubule and collecting duct.
Induces protein synthesis, increasing Na+ reabsorption, water reabsorption, and K+ secretion.
Results in increased blood pressure, hypokalemia, and increased pH.

Stages of Urine Formation (Summary)

Glomerular filtration: transfer of soluble components from blood to glomerulus.
Tubular reabsorption: selective reabsorption of substances from tubular fluid back into blood.
Tubular secretion: selective movement of substances from blood into the tubular fluid.

Kidney Anatomy

Bean-shaped organ enclosed by a capsule of collagen, elastic fibers, and smooth muscle.
Medial border contains the hilum, where vessels and nerves enter.
Renal pelvis connects to the ureter at the hilum.
Renal sinus is the space within the hilum containing vessels, nerves, and the renal pelvis.
Renal pelvis branches into two major calyces, each further dividing into minor calyces.
Minor calyces receive urine from renal papillae (apex of medullary pyramids).
Area cribrosa is the perforated area at the renal papilla due to collecting duct openings.
Renal columns are cortical tissue extending between renal pyramids.
Cortex is the outer region between the capsule and the bases of pyramids.
Renal lobe: one pyramid and overlying cortex.
Renal lobule: a medullary ray and its surrounding cortex.

Nephron Structure and Function

Nephron: functional unit of the kidney (1-3 million per kidney).
Composed of a renal corpuscle and a tubular system.
Renal corpuscle: glomerulus (fenestrated capillaries) and Bowman's capsule (double-layered).
Bowman's space lies between the two layers of Bowman's capsule.
Vascular pole: where afferent and efferent arterioles enter and exit.
Urinary pole: where the proximal tubule exits Bowman's capsule.
Tubular system: proximal convoluted tubule (PCT), proximal straight tubule (PST), thin segment (descending and ascending limbs), distal straight tubule (DST), and distal convoluted tubule (DCT).
Loop of Henle: PST + descending thin limb + ascending thin limb + DST.
Thin segment: narrow, thin-walled; thin ascending limb highly permeable to Na+ and Cl-.
Thick segment: larger diameter, thicker wall.
Cortical nephrons (80%): glomeruli in cortex, short loops of Henle.
Juxtamedullary nephrons (20%): glomeruli near corticomedullary junction, long loops of Henle.

Nephron Tubule Details

Proximal segment (PCT & PST): simple cuboidal epithelium with brush border; actively reabsorbs water, ions, and nutrients.
Thin segment: descending limb permeable to water, ascending limb permeable to Na+ and Cl-.
Distal segment (DST & DCT): simple cuboidal epithelium without brush border; reabsorbs Na+, Cl-, Mg2+, Ca2+; impermeable to water; regulated by hormones (PTH, Angiotensin II, ANP, Aldosterone).
Uromodulin (Tamm-Horsfall protein) produced in the thick ascending limb.

Juxtaglomerular Apparatus (JGA)

Composed of juxtaglomerular cells (granular cells in afferent arteriole, secrete renin) and macula densa (specialized cells in distal tubule, sense NaCl concentration).

Filtration Barrier

Composed of fenestrated endothelium of glomerular capillaries, glomerular basement membrane, and podocyte filtration slits.

Ultrafiltration Factors

Glomerular capillary pressure, Bowman's capsule hydrostatic pressure, and glomerular capillary oncotic pressure.