Urinary Physiology Overview

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Questions and Answers

What is the primary function of the efferent arteriolar vasoconstrictor mechanism?

To increase both renal blood flow and GFR.

To increase renal blood flow and decrease GFR.

To decrease renal blood flow while maintaining GFR. (correct)

To decrease GFR and increase blood pressure.

What is the main source of energy for primary active transport?

Movement of another substance along its electrochemical gradient.

Hydrolysis of ATP. (correct)

Hydrolysis of ADP into AMP.

Changes in concentration gradient.

In secondary active transport, what provides the energy for moving a substance against its electrochemical gradient?

The passive movement of ions through membrane channels.

The movement of another substance that is moving down its concentration gradient. (correct)

A change in the electrical gradient across cell membranes.

Direct hydrolysis of ATP by transport proteins.

What distinguishes co-transport from counter-transport in secondary active transport?

The direction of movement of the transported substances. Signup and view all the answers

What primarily drives passive transport?

Movement of substance along a concentration gradient Signup and view all the answers

Which of the following is NOT a primary function of the kidney?

Regulating blood glucose levels Signup and view all the answers

The secretion of erythropoietin by the kidney directly stimulates what?

The synthesis of red blood cells Signup and view all the answers

What is a key characteristic of renal circulation that differentiates it from most systemic circulation?

The presence of a portal system with two capillary networks Signup and view all the answers

What is the approximate percentage of glomerular filtrate that is reabsorbed by the renal tubules?

99% Signup and view all the answers

Which of the following is the renal portal vein?

Efferent Arteriole Signup and view all the answers

What is the approximate mean blood pressure in the glomerulus?

60 mmHg Signup and view all the answers

Besides renin, what other hormone is secreted by the juxtaglomerular cells?

Erythropoietin Signup and view all the answers

What percentage of the total cardiac output is received by the kidneys per minute, approximately?

25% Signup and view all the answers

Which mechanism primarily responds to changes in arterial pressure to regulate glomerular filtration rate (GFR)?

Myogenic mechanism Signup and view all the answers

What is the primary factor detected by the tubuloglomerular feedback mechanism?

Concentration of sodium and chloride in the tubular fluid Signup and view all the answers

In the myogenic mechanism, what occurs in response to increased systemic arterial pressure?

Afferent arterioles constrict, decreasing GFR Signup and view all the answers

During hypotension, which substance is released by the macula densa to cause afferent arteriolar dilation?

Nitric oxide (NO) Signup and view all the answers

How does the efferent arteriolar vasoconstrictor feedback mechanism respond to decreased arterial pressure?

By increasing angiotensin II formation to constrict efferent arterioles Signup and view all the answers

What is the main effect of increased sodium and chloride delivery to the macula densa during hypertension?

Afferent arteriolar vasoconstriction Signup and view all the answers

The autoregulation of renal blood flow (RBF) is primarily achieved through which of the following mechanisms?

Afferent arteriolar feedback Signup and view all the answers

What is the effect of increased mean arterial pressure on the concentration of sodium and chloride at the macula densa?

Increased concentration of Na+ and Cl- Signup and view all the answers

What happens to blood flow autoregulation when arterial pressure remains low for more than 10 to 20 minutes?

It disappears Signup and view all the answers

What is the range of mean arterial pressure within which renal blood flow is relatively constant?

70-160 mmHg Signup and view all the answers

What happens to bladder pressure as volume increases from 0 to 50 ml?

Pressure experiences a moderate increase. Signup and view all the answers

At what bladder volume is the first desire for micturition typically felt?

150 ml Signup and view all the answers

What is the fate of the detrusor muscle during the filling phase of the bladder?

It is tonically inhibited to prevent urine voiding. Signup and view all the answers

The sense of bladder fullness that usually initiates micturition reflex is felt at what volume?

400 ml Signup and view all the answers

What triggers the micturition reflex?

Stretch receptors in the bladder wall. Signup and view all the answers

When does a sense of bladder pain begin to occur?

At volumes exceeding 600 ml. Signup and view all the answers

What is the main role of sympathetic discharge during bladder filling?

To mediate relaxation of bladder smooth muscles. Signup and view all the answers

What occurs when bladder volume reaches 700 ml?

Urination becomes obligatory and urgent. Signup and view all the answers

What role do the kidneys play concerning bicarbonate (HCO3) in the body?

They generate bicarbonate to replace what is lost during buffering. Signup and view all the answers

Which buffer is primarily used in the tubular fluid to neutralize excess H+?

Bicarbonate buffer Signup and view all the answers

What is the net effect of the buffering reaction involving sulphuric acid and bicarbonate?

The loss of two HCO3 ions from the body. Signup and view all the answers

What happens to ammonium ions (NH4) after combining with chloride ions?

They form ammonium chloride, which is very weakly acidic. Signup and view all the answers

How does ammonia (NH3) primarily function as a buffer in the kidneys?

By diffusing into the tubular lumen and reacting with H+. Signup and view all the answers

During which condition is the secretion of NH3 increased?

During acidosis. Signup and view all the answers

What is the significance of sodium (Na+) absorption during NH3 buffering?

It helps in the synthesis of new bicarbonate. Signup and view all the answers

What is emphasized by the kidneys to handle the daily addition of fixed acids to body fluids?

The buffering systems provide the immediate defense against H+. Signup and view all the answers

What is the primary role of bicarbonate in the buffer system?

To replace strong bases with weaker bases. Signup and view all the answers

Which body fluid is indicated to have a higher concentration of phosphate buffer system?

Intracellular fluid (ICF) Signup and view all the answers

How does hemoglobin contribute to acid-base balance in the blood?

By binding more H+ ions when deoxygenated. Signup and view all the answers

Why is the pKa of the phosphate buffer system important?

It is closest to the intracellular pH, optimizing buffering capacity. Signup and view all the answers

What occurs when there is an increase in blood CO2 concentration?

The PCO2 in cerebrospinal fluid increases. Signup and view all the answers

What is the effect of sodium hydroxide (NaOH) when added to a bicarbonate buffer solution?

It results in the formation of NaHCO3 and water. Signup and view all the answers

Which statement about the protein buffer system is accurate?

It relies on the ability of proteins to bind to hydrogen ions. Signup and view all the answers

How does the phosphate buffer system respond in kidney tubular fluid?

It manages to buffer due to increased acidic content. Signup and view all the answers

Study Notes

### Urinary Physiology Study Notes

- The urinary system is responsible for maintaining internal bodily balance.
- Kidneys perform homeostatic functions, including regulating water and electrolyte balance, and pH.
   - They also produce hormones.
- Kidneys maintain a stable internal environment through urine excretion.
- Urine contains excess water, electrolytes, acids, and alkalis.
- Kidneys play a role in blood pH, water balance, and electrolyte balance.
- The juxtaglomerular cells (JG cells) secrete renin to regulate blood pressure (ABP).
   - They also produce erythropoietin, which stimulates red blood cell formation. 
- The kidney converts vitamin D3 into its active form (1,25-dihydroxycholecalciferol).
- Kidneys secrete prostaglandins.
- Urine formation happens through three main processes:
   - Filtration (glomerular capillaries to Bowman's capsule)
   - Reabsorption (tubules)
   - Secretion (tubules to capillaries)
- Renal circulation is a portal circulation, involving two capillary networks (glomeruli and peritubular capillaries).
   - The glomerular capillaries drain into arterioles.
- The kidneys have a high blood flow rate, about ¼ of cardiac output.

### Renal Circulation

- The major resistance sites are afferent and efferent arterioles.
- Afferent arteriole blood pressure falls to about 60 mmHg in glomerulus.
- The pressure drops a further 47 mmHg through efferent arterioles.
- The blood pressure at the glomerulus is about 60 mm Hg, leading to rapid fluid filtration into Bowman's capsule.
- The low pressure in peritubular capillaries (about 13 mmHg) facilitates rapid reabsorption of fluid due to high osmotic plasma pressure.
- The high filtration rate related to homeostasis allows high-rate glomerular filtration.


### Glomerular Filtration

- The glomerulus acts as a filter between the blood and the tubule.
- Glomerular capillaries have high permeability which is 100-500 times that of usual capillaries.
- Glomerular filtration is a passive process driven by high capillary blood pressure in the glomeruli.
- Glomerular filtrate is similar to plasma, lacking proteins or colloids (MW > 70,000 daltons).
- Glomerular pressure is approximately 60 mmHg, pressure in Bowman's capsule is 18 mmHg, and colloid osmotic pressure is ~32 mmHg.
- The filtration pressure (net pressure driving filtration) is 10 mmHg (60 - (18 + 32)).
- The filtration coefficient (Kf) is a measure of permeability and surface area of filter, used in calculation of glomerular filtration rate (GFR).
- GFR = Filtration pressure x Kf.

### Factors Affecting GFR

- Renal blood flow is a key factor, increased flow increases GFR.
- Changes in afferent and efferent arteriole diameter affect GFR.
   - Constriction of afferent arterioles decreases GFR, while dilatation increases it.
- Efferent arteriole constriction reduces GFR.
- Sympathetic stimulation constricts afferent arterioles, reducing GFR.
- Renal blood flow is relatively constant between 70-160 mmHg

### Active and Passive Transport

- Active transport: energy-dependent movement of substances across membranes against the electrochemical gradient, requiring carrier proteins. Divided into primary (ATP hydrolysis) and secondary (coupling with other ion's movement).
- Passive transport: movement of substances along the concentration gradient without energy input. Includes simple diffusion, facilitated diffusion with carrier assistance.

### Functions of Proximal Convoluted Tubules

- Reabsorption of glucose, amino acids, sodium, chloride, potassium, water, calcium, bicarbonate, phosphates, and urea occurs here.
- Sodium reabsorption is active, moving Na+ out of the tubule cell.
- Glucose and amino acids are reabsorbed completely through secondary active transport (co-transport with Na+)
- Water reabsorption is osmotic and determined by solute reabsorption from the lumen.

### Water Reabsorption

- Water passively follows the osmotic gradient created from solute reabsorption
- Obligatory water reabsorption is not regulated by hormones.

### Urea Reabsorption
- Urea passively reabsorbed and lost to a lesser extent than water.

### Phosphate Reabsorption

- Phosphate is reabsorbed actively but is regulated by parathyroid hormone (PTH).

### Secretion in Proximal Tubules

- Certain foreign substances (e.g., Diodrast, para-aminohippuric acid) are secreted.
- Most hydrogen ions are actively secreted.

### Loop of Henle Reabsorption

- The descending limb of the loop of Henle is highly permeable to water, causing reabsorption.
- The ascending limb is impermeable to water and actively transports Na⁺, Cl⁻, and K⁺ ions, decreasing the tubular fluid's osmolality.


### Distal Tubules and Collecting Ducts Reabsorption

- Active reabsorption of sodium (8-10%).
- Active secretion of potassium and hydrogen ions regulated by aldosterone.
- Reabsorption of water dependent on ADH.
- Reabsorption of urea from inner medullary part of collecting duct facilitated by ADH.

### Tubular Maximum (Tm)
- Maximum amount of a specific substance the tubules can absorb or secrete per minute. This is a fixed value unique for each individual and substance.
- Glucose tubular maximum (TmG) is the maximum rate of glucose reabsorption possible.


### Countercurrent Mechanism

- Creates progressively increasing osmotic gradient in the renal medulla, crucial for water reabsorption and urine concentration.
- involves the reciprocal flow of fluid in Henle's loop and the vasa recta.


### Dilution Mechanism

- Occurs when ADH is not present in the body fluids.
- Occurs in the late distal tubules and collecting ducts.
- Distal parts of the tubules are impermeable to water, thus allowing urine dilution.


### Osmolality

- Measure of total concentrations of discrete solute particles in solution.
- Normal osmolality of ECF and ICF is about 300 mOsm/kg water.


### Acid Base Balance

- Normal pH of arterial blood is 7.4 ± 0.02.
   - Acidosis occurs when pH falls below 7.35.
   - Alkalosis occurs when pH rises above 7.45.
- Importance of buffering systems (bicarbonate, phosphate, and proteins).
- Regulation by lungs (CO2 excretion) and kidneys (HCO3- regulation).


### Acid Base Disturbances

- Respiratory acidosis: caused by decreased ventilation, leading to increased CO2 and hydrogen ions.
- Respiratory alkalosis: caused by hyperventilation, leading to decreased CO2 and hydrogen ions.
- Metabolic acidosis: caused by increased metabolic acids or bicarbonate loss.
- Metabolic alkalosis: caused by excessive bicarbonate or loss of acids.


### Micturition Reflex

- Involuntary reflex that controls urination.
- Receptors in bladder wall trigger sensation of fullness and initiation of reflex.
- Processes include bladder contraction and relaxation of urinary sphincter.
- Brain can influence the reflex.


### Threats to Acid-Base Balance

- Metabolic processes produce acids (volatile, fixed, and organic).
- Acidosis and alkalosis can severely affect bodily function.

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Description

Explore the essential functions and processes of the urinary system. This quiz covers kidney roles in homeostasis, hormone production, and urine formation, highlighting processes such as filtration, reabsorption, and secretion. Learn about the significance of renal circulation and the kidneys’ impact on blood pressure and electrolyte balance.