Human Anatomy: Urinary Bladder and Ureters

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Questions and Answers

What is the primary active process involved in renal cellular transport?

Potassium chloride symport

Sodium-potassium ATPase (correct)

Calcium transport via facilitated diffusion

Sodium-glucose symport

In the proximal tubule, sodium reabsorption primarily occurs through which mechanism?

Diffusion only

Antiport and symport mechanisms (correct)

Active transport without any coupling

Facilitated diffusion using ion channels only

What additional process is required for the effective reabsorption of bicarbonate (HCO3-) in the proximal tubule?

Involvement of carbonic anhydrase (correct)

Active pump transport of chloride ions

Facilitated diffusion through ion channels

Covalent bonding with sodium

What is the outcome of the sodium-potassium exchange mediated by the sodium-potassium ATPase?

Decreased intracellular sodium concentration Signup and view all the answers

What mechanism is primarily responsible for sodium reabsorption across the proximal tubule epithelial cells?

Secondary active transport Signup and view all the answers

Which of the following factors is not involved in the regulation of tubular transport processes?

Nutritional status Signup and view all the answers

What type of epithelium lines the female urethra?

Stratified squamous epithelium Signup and view all the answers

What are umbrella cells and where are they found?

Binucleate cells in the surface layer of the bladder Signup and view all the answers

Which key renal function is primarily associated with the reabsorption of sodium?

Acid-base balance Signup and view all the answers

What occurs when the sodium-potassium pump operates in renal epithelial cells?

A net negative charge develops inside the cell Signup and view all the answers

What unique feature allows the transitional epithelium to accommodate a full bladder?

The ability to stretch and flatten Signup and view all the answers

What structure is formed at the urethra in the urinary bladder?

Internal sphincter Signup and view all the answers

Which of the following describes the arrangement of muscle layers in the urinary bladder?

Longitudinal, circular, and longitudinal Signup and view all the answers

In terms of histology, how does the male urethra differ from the female urethra?

It has segments and modified epithelium types Signup and view all the answers

What role do sensory fibers play in the micturition reflex?

They conduct impulses to the spinal cord Signup and view all the answers

How long is the male urethra on average?

20-25 cm Signup and view all the answers

What is the primary mechanism by which water moves from the interstitial space into blood vessels?

Osmosis Signup and view all the answers

What is the net force moving filtrate into capillaries?

10 mmHg Signup and view all the answers

In which part of the loop of Henle does the reabsorption of sodium mainly occur?

Thick ascending limb Signup and view all the answers

Which mechanism is primarily responsible for sodium reabsorption in the thick ascending limb?

Na+-2Cl--K+ symporter Signup and view all the answers

What occurs in the thin ascending limb of the loop of Henle?

Sodium diffusion out of the tubule Signup and view all the answers

Which of the following ions is primarily reabsorbed across the paracellular pathway in the thick ascending limb due to a positive tubular fluid charge?

Magnesium Signup and view all the answers

What role does Na,K-ATPase play in the thicken ascending limb of the loop of Henle?

Reabsorbs sodium through active transport Signup and view all the answers

Why is the thick ascending limb of the loop of Henle impermeable to water?

Absence of aquaporins Signup and view all the answers

What percentage of the filtered NaCl is reabsorbed by the proximal tubule?

67% Signup and view all the answers

How does sodium primarily enter the renal tubule cells at the luminal membrane?

Through a Na+-H+ antiporter and a Cl- anion antiporter Signup and view all the answers

What effect does the high concentration of Cl- in tubular fluid have on Na+ movement?

Facilitates Na+ movement out of the tubular fluid Signup and view all the answers

What is the primary driving force for water reabsorption in the proximal tubule?

Transtubular osmotic gradient established by solute reabsorption Signup and view all the answers

In what manner is water primarily reabsorbed in the proximal tubule?

Mostly via the paracellular route Signup and view all the answers

What occurs to the osmolality of the tubular fluid during the reabsorption of solutes?

It remains the same as plasma Signup and view all the answers

Which mechanism allows for NaCl reabsorption via a paracellular route?

Electrochemical gradients created by Cl- movement Signup and view all the answers

What type of transporter is involved in sodium leaving the cell at the basolateral membrane?

Na+, K+-ATPase Signup and view all the answers

What stimulates aldosterone secretion?

Angiotensin II Signup and view all the answers

What is the primary mechanism for bicarbonate reabsorption in the proximal tubules?

H+-ATPase and Na+-H+ antiporter Signup and view all the answers

Where is most of the filtered bicarbonate reabsorbed?

Proximal tubules Signup and view all the answers

What is NOT a condition that inhibits aldosterone secretion?

Angiotensin II Signup and view all the answers

What process is primarily responsible for producing new bicarbonate in the body?

CO2 combining with water Signup and view all the answers

How is bicarbonate reabsorbed across the basolateral membrane of the proximal tubule?

Using Na+-HCO3- symporter and Cl--HCO3- antiporter Signup and view all the answers

What percentage of filtered HCO3- is typically excreted?

0.1% Signup and view all the answers

Where does the majority of H+ secreted in the collecting duct combine with urinary buffer?

In the tubular fluid of the collecting ducts Signup and view all the answers

Study Notes

### Bladder

Epithelium is stratified and variable in thickness
2-3 layers in minor calyces, 5-6 layers in bladder
Cells can stretch and shift over each other, accommodating a full bladder
Full bladder appears to have only 2-3 layers of flat cells
Empty bladder:
- Cuboidal basal layer
- Polygonal middle layer
- Convex, often binucleate tall upper layer
Surface has plaques: modified plasma membrane areas that unfold allowing stretching
Umbrella cells of the surface layer can be binucleate and have a refractile border

Ureters

Transitional epithelium with a lamina propria consisting of fibroblasts and connective tissue
Two spirally arranged muscle layers
Third layer towards the urinary bladder
Adventitia and serosa

### Urinary Bladder

Transitional epithelium with 3 spiraled muscle layers: longitudinal, circular, longitudinal
Internal sphincter is formed at the urethra
Sympathetic fibres in the adventitia
Parasympathetic fibres in the adventitia and muscle
These fibres form the efferent fibres of the micturation reflex
Sensory fibres from the bladder muscle to the sacral portion of the spinal cord form the afferent fibres of the micturation reflex

### Female Urethra

Stratified squamous epithelium
Lamina propria: vascular and contains mucous secreting glands
External sphincter of striated muscle from the mid portion of urethra, passes through the striated muscles of the pelvic floor

### Male Urethra

20-25 cm long
Two functions: void urine and final conduit of male reproductive system
Three segments:
- Prostatic: from the neck of the bladder through the prostate
  - Receives the openings of the ejaculatory ducts
  - Many periurethral glands open into it
  - Very thin here
- Membranous: 1 cm long, runs through the pelvic floor
  - External sphincter of striated muscle
- Penile
  - Small mucous glands open into it
Lined with:
- Transitional epithelium
- Stratified columnar epithelium
- Stratified cuboidal epithelium
- Stratified squamous epithelium progressively

### Renal Transport Processes

#### Main Renal Functions

Sodium and water reabsorption
Electrolyte balance
Acid-base balance

#### Basic Elements of the Renal Transport Process

Key element and primary active process is mediated by sodium/potassium ATPase situated at the basolateral membrane
3 Na+ exchanged for 2K+ within the cell, some K+ filters back into the interstitial space, resulting in a net negative charge (-70mv) inside the cell
Sodium/potassium pump maintains decreased cellular sodium concentration, resulting in a favourable gradient for the movement of sodium from the tubular fluid into the cell

### Proximal Tubule

#### First Half

Sodium reabsorption coupled with H+ (antiport mechanism) or organic solutes mainly glucose and amino acids (symport mechanism)
Accompanying filtered anion HCO3- requires a different process involving carbonic anhydrase (CA) for effective reabsorption
Coupled process for Na reabsorption is associated with specific transport proteins (facilitated transport) along concentration and electrochemical gradients (secondary active process)
Transport proteins operate secondarily to Na/K- ATPase situated at the basolateral membrane of the cell, which is the primary source of energy for renal transport processes

#### Second Half

Sodium enters the cell luminal membrane via a parallel operation involving a Na+-H+ antiporter and a Cl—Anion antiporter
Secreted H+ and anion combine in the tubular fluid and re-enter the cell by diffusion, resulting in uptake of NaCl
Sodium leaves the cell via Na/K- ATPase at the basolateral membrane, chloride leaves via a K/Cl- symporter
NaCl is also reabsorbed via a paracellular route
High concentration of Cl- in the tubular fluid in the second half results in a concentration gradient with Cl- in the interstitial space, facilitating movement of Cl- out of the tubular fluid
Loss of Cl- makes the tubular fluid positively charged, facilitating movement of Na+ out of the tubular fluid

#### Overall

67% of filtered NaCl is reabsorbed by the proximal tubule
Two-thirds reabsorbed via a transcellular route and one-third via the paracellular route

#### Water Reabsorption

67% of the water in the filtrate is reabsorbed in the proximal tubule
Driving force is the transtubular osmotic gradient established by solute reabsorption (NaCl, glucose, HCO 3-)
Water moves along the osmotic gradient into the interstitial space mostly via the paracellular route
Reabsorption of water is isosmotic, so the osmolality of the tubular fluid remains the same as plasma in the proximal tubule
Once water has accumulated in the interstitial space by osmosis, it moves by filtration into the blood vessels, dependant on filtration forces

### Loop of Henle

#### Descending Limb

Reabsorption of water but not sodium
Increasing sodium concentration within the tubule

#### Ascending Limb

##### Thin Ascending Limb

Sodium diffuses out along a concentration gradient, impermeable to water
Decreasing osmolality of the tubular fluid

##### Thick Ascending Limb (TAL)

Na/K- ATPase plays the same role in the reabsorption of sodium as it does in the proximal tubule
Sodium reabsorption at the luminal membrane is mediated by the Na+- 2Cl- - K+ symporter, which is the carrier protein inhibited by loop diuretics
Na+- H+ antiporter situated at the apical membrane facilitates the reabsorption of sodium and the secretion of H+ by a secondary active transport process
Reabsorption of HCO3-
Potassium and chloride leave the cell at the basolateral membrane by facilitated diffusion
Tubular fluid in TAL is positively charged due to increased Cl- transport in the second half of the proximal tubule and also within TAL
Positive charge in the tubular fluid causes the reabsorption of cations, mainly Na+, but also Ca++, K+ and Mg++ across the paracellular pathway
TAL is also not permeable to water

### Distal Tubule

Responsible for fine-tuning the reabsorption of sodium, potassium, and calcium
Reabsorption of water is regulated by antidiuretic hormone (ADH)
Na+ reabsorption is stimulated by aldosterone
Reabsorption of water is isosmotic

### Collecting Duct

Reabsorption of sodium and water under the influence of aldosterone and ADH
Reabsorption of potassium is regulated by aldosterone
Reabsorption of water is regulated by ADH

#### Aldosterone Effects

Aldosterone secretion is stimulated by angiotensin II and hyperkalemia
Inhibited by hypervolemia, hypokalemia and natriuretic peptide
Stimulates sodium reabsorption, increasing water reabsorption, plays a critical role in maintaining fluid balance
Reabsorption of water is isosmotic

### Reabsorption of Bicarbonate

Reabsorption of HCO3- requires secretion of H+
H+ secretion is dependent on the actions of a Na+- H+ antiporter and a H+- ATPase at the apical membrane of the proximal tubular cells and on the Na+- H+ antiporter at the apical membrane of TAL tubular cells
H+, K+- antiporter and H+- ATPase at the apical membrane of the Intercalated cell found in the late distal tubules and the collecting ducts
CO2 is produced in the tubular cell as part of normal metabolic processes or diffuses into the tubular cell from the tubular fluid or the interstitium
CO2 combines with H2O catalysed by carbonic anhydrase (CA) to produce carbonic acid
Carbonic acid dissociates into H+ and HCO3-
Bicarbonate exits the cell across the basolateral membrane and returns to the peritubular blood
Exit is mediated by a Na+- 3HCO3- symporter and a Cl- - HCO3- antiporter
Both mechanisms are active in the proximal tubules (85% of filtered HCO 3-) and TAL (10% of filtered HCO3-)
Cl- - HCO3- antiporter is active at the basolateral membrane of the Intercalated cell located in the late distal tubules and collecting ducts (4.9% of filtered HCO 3-)
About 0.1% of filtered HCO3- is excreted

### Urinary Buffering

HCO3- reabsorption does not replenish HCO3- lost during buffering processes in body fluids accompanying metabolism
New HCO3- needs to be produced to maintain acid-base balance
Tubular fluid contains little HCO3- because most of it is reabsorbed in upstream segments of the nephron
H+ secreted into the tubular fluid of the collecting ducts combines with urinary buffer as a consequence
HCO3- produced from endogenous CO2 involving the activity of carbonic anhydrase does not form part of the filtered HCO 3- and represents newly produced HCO3-

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Description

Explore the structure and function of the urinary bladder and ureters in this detailed quiz. Learn about the transitional epithelium, muscle layers, and unique characteristics that allow these organs to accommodate varying volumes. Test your knowledge on how these features contribute to the urinary system as a whole.