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Renal > Histology of the Kidney and Urinary Tract > Flashcards

Histology of the Kidney and Urinary Tract Flashcards

1
Q

What is the excretory function of the kidney?

A
  • As the blood passes through the kidney, an ultrafiltrate is produced
  • Excess water and ions, some drugs, toxins and metabolic breakdown products (urea, creatinine) are excreted in the urine
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2
Q

What is the homeostatic function of the kidney?

A
  • **Regulating and maintaining extracellular fluid volume and composition: **
    • selective secretion and re-absorption
      • water, ions, (e.g. Na+, K+, H+, Ca/P04 ) and other compounds
  • Maintenance of acid-base balance
    • generation of bicarbonate
    • selective secretion of H+ ions
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3
Q

What is the endocrine function of the kidney?

A
  • Monitoring the O2 carrying capacity of the blood via erythropoietin
  • Regulating blood pressure through the renin-angiotensin system
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4
Q

Describe the following:

  • Cortex:
  • Medulla:
  • Kidney lobe:
A
  • Cortex:
    • granular in appearance and homogeneous in consistency
    • Medullary Rays: linear arrays of tubules extending into the cortex
  • Medulla:
    • striated appearance and consists of 6-18 Renal Pyramids
    • Renal Papilla: apex or tip of a renal pyramid
  • Kidney lobe:
    • ​macroscopic subdivision consisting of a renal pyramid and its surrounding cortex
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5
Q

Describe the following:

  • Lobule:
  • Caspule:
A
  • Lobule:
    • microscopic subdivision consisting of a medullary ray and the cortical tissue (primarily nephrons) on either side
    • tubules of these nephrons connect with the collecting ducts within the medullary rays
  • Caspule:
    • consists mainly of fibrous connective tissue and surrounds the kidney
      • parenchyma is not subdivided by septa
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6
Q

The total blood volume of the body passes through the kidneys every ….

A

4-5 minutes

  • Note: kidney receives 20-25% of cardiac output
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7
Q

How much fluid is extracted from the blood each minute?

How much is reabsorbed and how much is excreted?

A

125 ml of fluid is extracted from the blood each minute as filtrate [180 L/day]

  • 124 ml is reabsorbed in the kidney tubules
  • 1 ml is excreted as urine
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8
Q

Arterial Supply to the kidney:

A

Renal A ⇒ Lobar A ⇒ Interlobar A ⇒ Arcuate A ⇒ Interlobular A ⇒ Afferent Arteriole

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9
Q

What is the microvasculature of the kidney?

A

Afferent arteriole ⇒ glomerulus ⇒ efferent arteriole

  1. Tubular Plexus
    • supplies tubules of the cortical nephrons
  2. Vasa Recta long capillary loops
    • supplying tubules of juxtamedullary nephrons
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10
Q

What are the components of the nephron? What is the function of the nephron?

A
  1. Components:
    • Renal Corpuscle
    • Renal Tubule
  2. Function: a Filter and a Fluid Modifier (Recycle/Secrete)
    • kidney produces an ultrafiltrate of the blood
    • recycles many components that are in the filtrate
    • other compounds are added to the filtrate as it goes through the tubular system
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11
Q

What is the difference between the developmental and functional viewpoints of the nephron?

A
  1. **Developmental Viewpoint ⇒ **nephron consists of:
    • Renal Corpuscle, Proximal Tubule, Loop of Henle, Distal Tubule [collecting ducts not included]
  2. **Functional Viewpoint **⇒ nephron consists of:
    • Renal Corpuscle, Proximal Tubule, Loop of Henle, Distal Tubule & Collecting Duct
    • Whole structure = Uriniferous Tubule
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12
Q

What are the components of the renal corpuscle?

A
  1. Glomerulus
  2. Visceral Layer of the Renal Capsule (Bowman’s)
  3. Parietal Layer of the Renal Capsule
  4. Mesangium
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13
Q

What can be seen in the renal corpuscle at the EM level?

A
  • spherical, double-layered sac (Renal Capsule) that surrounds a network of capillaries (Glomerulus)
  • Vascular Pole where the arterioles enter and exit
  • Urinary Pole that is continuous with the proximal convoluted tubule
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14
Q

Renal corpuscles are found only in the ______ _____.

A

Renal corpuscles are found only in the kidney cortex

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15
Q

What is the glomerulus? What supplies and drains it?

A
  • a network of capillary loops supplied and drained by an arteriole
  • Afferent (supplying) Arteriole is larger in diameter than Efferent (draining) Arteriole
    • Size difference creates a pressure differential that drives glomerular filtration
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16
Q

Where are podocytes located?

A

visceral layer of Bowman’s capsule

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17
Q

Describe the composition of Bowman’s Capsule:

A
  • a double-layered epithelial sac surrounding the glomerulus
  • Parietal Layer (outer) is a simple squamous epithelium
  • Visceral Layer (inner) a simple epithelium composed of cells called Podocytes
  • Urinary Space: space between the two epithelial layers
    • continuous with the proximal tubule
    • glomerular filtrate enters this space
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18
Q

What makes up the glomerular filtration barrier?

A
  • Capillary Endothelium
    • discontinuous, containing numerous 70-100 nm pores
    • pores are freely permeable to water and solutes ≤ 6-8 kD
    • moderately permeable to molecules 8-16kD
    • luminal surface has a negative charge because it is coated with a glycocalyx
  • Basement Membrane
    • primary barrier that prevents protein from entering the glomerular filtrate
19
Q

What gives podocytes their name?

A

Pedicles: 1° and 2° foot processes

20
Q

The space between pedicles is called the _________ ____.

A

The space between pedicles is called the Filtration Slit.

21
Q

What bridges the Filtration Slit? What is the major protein?

A

Filtration Slit is bridged by an electron dense Filtration Slit Diaphragm, a modified adherens junction consisting of the protein Nephrin

22
Q

What is the function of the glomerular mesangium?

A
  • physical support
  • regulation of glomerular blood flow
  • turnover of glomerular basement membrane
23
Q

What is the role of specialized pericyte/smooth muscle cells?

A

Found in the glomerular mesangium:

  • contain receptors for atrial neuretic peptide (ANP) and angiotensin II
  • secrete endothelin, cytokines and prostaglandins
24
Q
  • Where does the convoluted portion of the proximal tubule begin?
  • What is the function and histology of this portion?
A
  • begins at the urinary pole and located in cortex
  • Function and Histology:
    • substantial reabsorption
    • cuboidal/columnar cells with granular cytoplasm and basal nuclei
    • apical brush border w/glycocalyx obscures lumen
    • lysosomes and apical vesicles
    • numerous mitochondria at base of cell provide energy for transport
    • complex lateral interdigitations between epithelial cells make lateral cell membranes indistinguishable
25
Q
  • What is another name for the straight portion of the proximal tubule?
  • What kind of cells make up this portion?
A

Thick Descending Limb of Henle

  • cuboidal epithelium
26
Q
  • What are the parts of the loop of Henle?
  • Where is it located?
A
  • 4 parts:
    1. straight portion of the proximal tubule (thick descending limb)
    2. thin descending limbs
    3. thin ascending limbs
    4. straight portion of the distal tubule (thick ascending limb)
  • located in the medulla
27
Q

What determines the length of the loop of Henle?

A

Length is determined by the location of its renal corpuscle with respect to the corticomedullary junction

  • Cortical Nephrons
    • external to the juxtamedullary zone
    • short loops
    • only a Descending Thin Limb
  • Juxtamedullary Nephrons
    • long looped
    • Ascending and Descending Thin Limbs
28
Q

What are the major differences between the thick and thin loops?

A
  • thick portions of the loop are lined with cuboidal epithelium
  • thin segments are lined with simple squamous epithelium
  • cell membranes in the ascending thin limb between epithelial cells are interdigitated, resulting in water impermeability
29
Q

What is the function and histology of the straight portion of the distal tubule?

A

Thick Ascending Limb

  • Histology:
    • lined with cuboidal epithelium
    • scant microvilli, efficient tight junctions
    • Lateral & basal membane interdigitations
    • abundant mitochondria
  • Function:
    • Impermeable to water
    • Na+, Cl-, and K+ reabsorbed
    • glucose, amino acids, proteins reabsorbed through facilitated transport
    • H+ ions secreted
30
Q

What is the function and histology of the convoluted distal tubule?

A

Early Distal Tubule

  • Histology:
    • lined with cuboidal epithelium
    • scant microvilli
    • fewer basal interdigitations
    • fewer mitochondria
  • Function:
    • Na+ (Aldosterone responsive), Cl-, K+, HCO3 reabsorbed
    • K+, urate, H+ ions, NH3 secreted
31
Q
  • What is the histology of the collecting tubules?
  • What does the portion repsond to?
A
  • epithelium contains principal cells (cuboidal)
  • transition segment between the nephron and the collecting duct
  • Antidiuretic Hormone (ADH) dependent segment
    • Na+ is reaborbed and K+ is secreted
32
Q

Describe Renal Tubular Disease:

  • Causes
  • Pathophysiology
  • Results in ….
A
  • Caused by toxins, drugs, infections, metabolic disturbances, ischemia
  • Affects reabsorptive and secretory functions resulting in either polyuria or oligo/anuria
  • Renal failure may develop due to accumulation of toxic substances
  • Acidosis results because of failure of H ion excretion
33
Q
  • How are principal cells composed?
  • How do the principal cells respond in the presence of ADH?
  • What happens if there is an absence of ADH?
A
  • Principal Cells:
    • one primary cilium (flow sensor)
    • ADH sensitive AQP-2 water channels
  • In the presence of ADH
    • ​urea and water diffuse out of the collecting duct and into the renal interstitium
    • increases urine tonicity
  • In the absence of ADH
    • ​water is excreted from the collecting ducts
    • leading to Polyuria and hypotonic urine
      • Diabetes Insipidus
34
Q

With regards to principal cells, polycystic kidney disease results from what?

A

defects in Polycystin 1 & 2

  • proteins that mediate the function of the primary cilium
35
Q

Where is the renal interstitium? What are the components?

A
  • interstitial (stromal) tissue is found in the renal cortex & medulla
    • stroma is finer in cortex
  • interstitium components:
    1. interstitial connective tissue
    2. interstitial cells (fibroblasts) in cortex & medulla
36
Q
  • What is the role of the tubular-interstitium-vascular interaction?
  • What are the components?
  • Describe the countercurrent multiplier and counter current exchanger:
A
  • provides a mechanism for modifying and concentrating urine
  • Components:
    1. Collecting ducts
    2. Loops of Henle
    3. Vasa Recta
  • Countercurrent Multiplier
    • urine concentration
  • Countercurrent Exchanger
    • protects ion gradient
37
Q

JG Apparatus Components:

A
  1. Renin producing (JG) cells
    • Specialized smooth muscle cells in the wall of the afferent arteriole
  2. Extraglomerular mesangial (lactis) cells
    • Connected to JG cells via gap junctions
  3. Macula Densa
    • columnar cells of the distal convoluted tubule
    • detects Na+ and Cl- concentration for JG cells resulting in alterations of the filtration rate and auto-regulation of blood volume
38
Q

How can JG aparatus components affect systemic blood pressure and blood volume?

A

JG apparatus components can increase systemic blood pressure (BP) & blood volume (BV) through the angiotensin system

Renin release ⇒ angiotensin conversion ⇒ ↑ in aldosterone secretion ⇒ ↑ Na and water reabsorption

39
Q
  • Describe the role of erythropoiten:
  • What stimulates its production?
A
  • ↑ mitosis of red blood cell precursors
  • ↑ release of red cells from marrow
    • Probably produced by cortical interstitial cells
    • Transported to bone marrow
  • Production stimulated by:
    • high altitude
    • hemorrhage
    • impaired pulmonary function
40
Q
  • What is kidney failure?
  • Acute kidney injury vs. End-stage renal disease:
A
  • Kidney Failure
    • Inability of the kidney to remove accumulated metabolites from blood
  • Acute kidney injury
    • Clinical Picture - oligouria <400ml/day, unexpected weight gain or
      edema, increased toxins in blood
    • Prognosis depends on cause, severity, treatment, age
  • End-stage renal disease
    • Irreversible injury ⇒ end-stage renal disease ⇒ uremia + hematuria
    • Glomerular injury, autosomal dominant polycystic disease, others
41
Q

What are the layers of the ureter?

A
  • Mucosa
    • transitional (uro)epithelium
    • lamina propria contains abundant elastic tissue
  • Muscularis
    • smooth muscle
    • in ureter -2 layers in the upper 2/3 of the ureter; 3 layers lower 1/3 of the ureter
  • Adventitia
    • fibrous connective tissue
42
Q

How is the urinary bladder composed?

A
  • Transitional epithelium
  • 3 layers of smooth muscle
43
Q

What is the difference between the male and female urethra:

A
  1. Male
    • 15-20 cm; 3 parts (prostatic, membranous, penile)
    • Transitional – pseudostratified sq.
    • Shared urinary & reproductive systems
  2. Female
    • 3-5 cm
    • Transitional – pseudostratified sq.
    • Urinary system only
44
Q

What are some common clinical problems leading to obstruction of the excretory passages?

A
  1. Benign Prostatic Hypertropyhy
    • also known as nodular hyperplasia
    • Older males >45 years
    • Can cause urethral obstruction
  2. Renal Calculi (kidney stones)
    • Common in USA (7-21/1000), men, sedintary individual
    • Hereditary disposition
    • Hypercalcemia, pH change, supersaturation of ions enhance stone formation
  3. Bladder Cancer
    • Associated with smoking
    • Majority in US involve the uroepithelium

Renal (17 decks)

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