Histology of the Kidney and Urinary Tract Flashcards
What is the excretory function of the kidney?
- 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
What is the homeostatic function of the kidney?
- **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
-
selective secretion and re-absorption
-
Maintenance of acid-base balance
- generation of bicarbonate
- selective secretion of H+ ions
What is the endocrine function of the kidney?
- Monitoring the O2 carrying capacity of the blood via erythropoietin
- Regulating blood pressure through the renin-angiotensin system
Describe the following:
- Cortex:
- Medulla:
- Kidney lobe:
-
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
Describe the following:
- Lobule:
- Caspule:
-
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
- consists mainly of fibrous connective tissue and surrounds the kidney
The total blood volume of the body passes through the kidneys every ….
4-5 minutes
- Note: kidney receives 20-25% of cardiac output
How much fluid is extracted from the blood each minute?
How much is reabsorbed and how much is excreted?
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
Arterial Supply to the kidney:
Renal A ⇒ Lobar A ⇒ Interlobar A ⇒ Arcuate A ⇒ Interlobular A ⇒ Afferent Arteriole
What is the microvasculature of the kidney?
Afferent arteriole ⇒ glomerulus ⇒ efferent arteriole
-
Tubular Plexus
- supplies tubules of the cortical nephrons
-
Vasa Recta long capillary loops
- supplying tubules of juxtamedullary nephrons
What are the components of the nephron? What is the function of the nephron?
-
Components:
- Renal Corpuscle
- Renal Tubule
-
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
What is the difference between the developmental and functional viewpoints of the nephron?
- **Developmental Viewpoint ⇒ **nephron consists of:
- Renal Corpuscle, Proximal Tubule, Loop of Henle, Distal Tubule [collecting ducts not included]
- **Functional Viewpoint **⇒ nephron consists of:
- Renal Corpuscle, Proximal Tubule, Loop of Henle, Distal Tubule & Collecting Duct
- Whole structure = Uriniferous Tubule
What are the components of the renal corpuscle?
- Glomerulus
- Visceral Layer of the Renal Capsule (Bowman’s)
- Parietal Layer of the Renal Capsule
- Mesangium
What can be seen in the renal corpuscle at the EM level?
- 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
Renal corpuscles are found only in the ______ _____.
Renal corpuscles are found only in the kidney cortex
What is the glomerulus? What supplies and drains it?
- 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
Where are podocytes located?
visceral layer of Bowman’s capsule
Describe the composition of Bowman’s Capsule:
- 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
What makes up the glomerular filtration barrier?
-
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
What gives podocytes their name?
Pedicles: 1° and 2° foot processes
The space between pedicles is called the _________ ____.
The space between pedicles is called the Filtration Slit.
What bridges the Filtration Slit? What is the major protein?
Filtration Slit is bridged by an electron dense Filtration Slit Diaphragm, a modified adherens junction consisting of the protein Nephrin
What is the function of the glomerular mesangium?
- physical support
- regulation of glomerular blood flow
- turnover of glomerular basement membrane
What is the role of specialized pericyte/smooth muscle cells?
Found in the glomerular mesangium:
- contain receptors for atrial neuretic peptide (ANP) and angiotensin II
- secrete endothelin, cytokines and prostaglandins
- Where does the convoluted portion of the proximal tubule begin?
- What is the function and histology of this portion?
- 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
- What is another name for the straight portion of the proximal tubule?
- What kind of cells make up this portion?
Thick Descending Limb of Henle
- cuboidal epithelium
- What are the parts of the loop of Henle?
- Where is it located?
-
4 parts:
- straight portion of the proximal tubule (thick descending limb)
- thin descending limbs
- thin ascending limbs
- straight portion of the distal tubule (thick ascending limb)
- located in the medulla
What determines the length of the loop of Henle?
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
What are the major differences between the thick and thin loops?
- 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
What is the function and histology of the straight portion of the distal tubule?
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
What is the function and histology of the convoluted distal tubule?
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
- What is the histology of the collecting tubules?
- What does the portion repsond to?
- 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
Describe Renal Tubular Disease:
- Causes
- Pathophysiology
- Results in ….
- 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
- 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?
- 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
With regards to principal cells, polycystic kidney disease results from what?
defects in Polycystin 1 & 2
- proteins that mediate the function of the primary cilium
Where is the renal interstitium? What are the components?
- interstitial (stromal) tissue is found in the renal cortex & medulla
- stroma is finer in cortex
- interstitium components:
- interstitial connective tissue
- interstitial cells (fibroblasts) in cortex & medulla
- What is the role of the tubular-interstitium-vascular interaction?
- What are the components?
- Describe the countercurrent multiplier and counter current exchanger:
- provides a mechanism for modifying and concentrating urine
- Components:
- Collecting ducts
- Loops of Henle
- Vasa Recta
-
Countercurrent Multiplier
- urine concentration
-
Countercurrent Exchanger
- protects ion gradient
JG Apparatus Components:
-
Renin producing (JG) cells
- Specialized smooth muscle cells in the wall of the afferent arteriole
-
Extraglomerular mesangial (lactis) cells
- Connected to JG cells via gap junctions
-
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
How can JG aparatus components affect systemic blood pressure and blood volume?
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
- Describe the role of erythropoiten:
- What stimulates its production?
- ↑ 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
- What is kidney failure?
- Acute kidney injury vs. End-stage renal disease:
-
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
- Clinical Picture - oligouria <400ml/day, unexpected weight gain or
- End-stage renal disease
- Irreversible injury ⇒ end-stage renal disease ⇒ uremia + hematuria
- Glomerular injury, autosomal dominant polycystic disease, others
What are the layers of the ureter?
-
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
How is the urinary bladder composed?
- Transitional epithelium
- 3 layers of smooth muscle
What is the difference between the male and female urethra:
-
Male
- 15-20 cm; 3 parts (prostatic, membranous, penile)
- Transitional – pseudostratified sq.
- Shared urinary & reproductive systems
-
Female
- 3-5 cm
- Transitional – pseudostratified sq.
- Urinary system only
What are some common clinical problems leading to obstruction of the excretory passages?
-
Benign Prostatic Hypertropyhy
- also known as nodular hyperplasia
- Older males >45 years
- Can cause urethral obstruction
-
Renal Calculi (kidney stones)
- Common in USA (7-21/1000), men, sedintary individual
- Hereditary disposition
- Hypercalcemia, pH change, supersaturation of ions enhance stone formation
-
Bladder Cancer
- Associated with smoking
- Majority in US involve the uroepithelium
