Kidney Functions and Regulation Quiz

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Questions and Answers

What is the primary function of the kidneys in the urinary system?

Filtration of oxygen from blood

Excretion of metabolic waste and regulation of blood composition (correct)

Absorption of nutrients from food

Production of hormones

What substance do the kidneys secrete to stimulate the production of red blood cells?

Aldosterone

Insulin

Renin

Erythropoietin (correct)

How do the kidneys help regulate blood pressure?

By excreting or reabsorbing water (correct)

By producing insulin

By increasing heart rate

By filtering out carbon dioxide

Which ion is NOT regulated by the kidneys?

Calcium (Ca2+) Signup and view all the answers

What role does the nephron play in kidney function?

It is responsible for urine production and filtration Signup and view all the answers

What happens to blood pH when more hydrogen ions are excreted by the kidneys?

Blood becomes less acidic (more alkaline) Signup and view all the answers

How often does blood pass through the kidneys in an adult human?

Every 5 minutes Signup and view all the answers

Which blood vessel carries blood towards the kidneys?

Renal artery Signup and view all the answers

What is the primary cause of kidney disease mentioned?

Long term diabetes Signup and view all the answers

What percentage of cardiac output do the kidneys receive in the first pass?

25% Signup and view all the answers

What is the main role of the glomerular capillaries?

Filtration of blood Signup and view all the answers

Which transporter is specifically mentioned as an organic cation transporter?

OCT Signup and view all the answers

What type of substances are reabsorbed passively from renal tubules?

Lipophilic substances Signup and view all the answers

What role do xenobiotic EAlux pumps play in the body?

Transport substances across membranes Signup and view all the answers

Under what condition is the excretion of acids increased?

High urinary pH Signup and view all the answers

What characteristic defines pumps belonging to the ATP-binding cassette superfamily?

Power substrate transport by hydrolyzing ATP Signup and view all the answers

What percentage of glomerular filtrate is typically reabsorbed into the blood?

99% Signup and view all the answers

Which of the following statements is true regarding the filtration membrane in the kidneys?

Small molecules can readily pass into the tubule through its large pores. Signup and view all the answers

Which process allows for the selective secretion of xenobiotics into urine?

Tubular secretion Signup and view all the answers

What is the primary variable that influences glomerular filtration rate?

Size of the molecule and blood flow Signup and view all the answers

What type of diffusion does not require energy to move substances across the renal tubule membrane?

Simple diffusion Signup and view all the answers

Which of the following describes the relationship between pH and the ionization of compounds in renal excretion?

Ionization of compounds may be altered by the pH of the tubular fluid. Signup and view all the answers

What happens to non-ionized compounds in the renal tubule during passive diffusion?

They are easily reabsorbed into the blood. Signup and view all the answers

Which part of the nephron is primarily involved in tubular reabsorption of xenobiotics?

Distal Convoluted Tubule Signup and view all the answers

What class of substances has a bile to plasma ratio nearly equal to 1?

Glucose Signup and view all the answers

Which transport protein primarily facilitates the transport of organic anions into bile?

MRP2 Signup and view all the answers

What is the typical bile to plasma ratio for Class B substances?

Between 10 and 1000 Signup and view all the answers

Which of the following is NOT a symptom of cholestasis?

Increased appetite Signup and view all the answers

Which transporter is primarily responsible for the secretion of bile salts?

BSEP Signup and view all the answers

What effect does amanitin have on mRNA synthesis?

Inhibits RNA polymerase II Signup and view all the answers

Cholestasis can result in the retention of what types of compounds in hepatocytes?

Compounds usually eliminated in bile Signup and view all the answers

What class of substances typically includes arsenic and lead?

Class B Signup and view all the answers

What effect does enterohepatic circulation have on lipophilic xenobiotics?

It increases the retention of xenobiotics. Signup and view all the answers

Which process is primarily responsible for the reabsorption of lipophilic xenobiotics in the intestine?

Passive diffusion Signup and view all the answers

What occurs as a result of liver excretion of lipophilic compounds into bile?

Enhanced enterohepatic cycling Signup and view all the answers

What is the primary role of glucuronic acid in relation to lipophilic xenobiotics?

To promote conjugation for faster clearance Signup and view all the answers

Diethylstilbestrol (DES) is classified as what type of compound?

Endocrine disruptor Signup and view all the answers

What describes the elimination half-life (t1/2) of a xenobiotic?

The time taken to eliminate half of the remaining substance Signup and view all the answers

What is true about lipophilic xenobiotics in terms of elimination?

They tend to be persistent in biological systems. Signup and view all the answers

How does liver metabolism alter lipophilic xenobiotics?

It biotransforms them into conjugated forms. Signup and view all the answers

What is the primary function of active transport in urinary excretion?

Transporting chemicals from the blood to the tubular lumen using energy-dependent carriers Signup and view all the answers

Which factor affects glomerular filtration ability due to plasma protein binding?

Greater binding of compounds to plasma proteins Signup and view all the answers

What effect does alkalinization of urine have on weak acids?

Increases their excretion by maintaining them in the ionized state Signup and view all the answers

Which section of the nephron is responsible for reabsorbing most of the filtrate?

Proximal Tubule Signup and view all the answers

What is the primary characteristic of low Log Kow (hydrophilic compounds)?

Highly water-soluble and likely to remain in the tubular lumen Signup and view all the answers

What drives the hydrostatic pressure in the filtration process of the kidneys?

The heart's pumping action and blood flow Signup and view all the answers

Which substance determines the reabsorption of sodium in the distal tubule?

Aldosterone Signup and view all the answers

How do lipophilic compounds typically behave after filtration in the kidneys?

Decrease renal clearance due to high reabsorption rates Signup and view all the answers

Study Notes

Elimination via the Urinary System

The urinary system consists of four parts: kidneys, ureters, bladder, and urethra
Kidneys have two main functions:
- Excretion of metabolic waste products from the blood
- Regulation of water and ion content in the blood
Kidneys filter blood, excreting dilute solutions (urine) containing urea, mineral ions, water, and xenobiotics.
Kidneys have a large blood supply, ensuring waste materials do not build up. Blood circulates through the kidneys every 5 minutes.
Kidneys play a major role in regulating blood volume by controlling water excretion and reabsorption.
Renal damage can affect blood pressure regulation.
Regulated electrolytes (Na+ and K+) by controlling secretion and reabsorption.
Regulated pH of blood (acid-base balance) by controlling hydrogen ion secretion and reabsorption.

Kidney Nephron System

Glomerular ultrafiltration: approximately 1/3 of blood plasma is filtered by the glomerulus, forming dilute urine (ultrafiltrate).
Tubular secretion: Proximal Convoluted Tubule selectively secretes certain xenobiotics into urine.
Tubular reabsorption: Distal Convoluted Tubule and Collecting Duct reabsorb many xenobiotics into blood passively.

Four Primary Mechanisms of Urinary Excretion

1. Filtration: Blood is filtered at the beginning of the renal tubule. The filtration membrane contains large pores so small molecules easily pass into the tubule. About 99% of the filtrate is reabsorbed into the blood, 1% is excreted as urine. Factors affecting filtration include molecule size and glomerular filtration as determined by blood flow and pressure.
2. Passive diffusion: Substances move across a biological membrane without energy (ATP). Simple diffusion, for small, uncharged, lipophilic molecules.
3. Active transport: Proteins (carrier proteins) are specific for certain weak acids/bases and transfer chemicals from blood to the tubular lumen. These systems may become saturated, limiting the amount of material excreted.
4. Facilitated diffusion: A process that resembles active transport but does not require energy.

Additional Factors Affecting Urinary Excretion

Plasma protein binding: Highly bound compounds have decreased filtration ability, as are actively transported, but are not affected by protein binding.
pH: The excretion of pH-dependent weak acids and bases is affected by pH changes.

Kidney and Liver Clearance

Hydrostatic pressure pushes water and solutes out of the blood.
Oncotic pressure opposes filtration due to plasma proteins.
Filtration pressure is the net pressure favoring filtration.
Substances like glucose, amino acids, sodium, chloride, and water are reabsorbed in the proximal tubule.
The loop of Henle reabsorbs water in the descending limb and ions in the ascending limb.
Ions (sodium, potassium, and water) are fine-tuned in the distal tubule and collecting duct, based on hormone regulation.

Low and High Log Kow Compounds

Low Log Kow (hydrophilic): Highly water-soluble compounds tend to remain in the tubular lumen after filtration and are excreted in urine.
High Log Kow (lipophilic): Highly lipophilic substances are efficiently reabsorbed by passive diffusion in the renal tubules and have low renal clearance. They may require hepatic metabolism for further clearance.

Failure of Homeostasis

Kidney disease can occur caused by long-term diabetes, infections, and chemical poisoning.
Bladder and kidney infections are caused by enteric bacteria entering the urethra.
Kidney stones can form through crystallization of mineral salts and uric acid, blocking the passage of urine.

Kidneys and First-Pass Cardiac Output

Kidneys receive approximately 25% of cardiac output due to their role in filtering blood and homeostasis.
20% is filtered through glomeruli (approximately 25g/day urea).
Glomerular capillaries have large pores, allowing compounds up to 60 kDa (e.g., albumin) to be filtered.
Tubular secretion actively transports acids, bases, and neutrals into renal tubules via organic cation transporters (OCT) and organic anion transporters (OAT).

Tubular Reabsorption and Secretion

Tubular Reabsorption: Passive reabsorption depends on the ionization of xenobiotics. Lipophilic substances are absorbed more than hydrophilic substances. High urinary pH increases acid excretion, while low pH increases base excretion. Active transport via OCTs, peptide transporters (PEP), and MRPs (multidrug-resistant-associated proteins)
Xenobiotic efflux pumps: Specialized proteins actively transport substances (particularly lipophilic compounds) across cell membranes. This is important for detoxification and/or drug resistance. Some belong to ATP-binding cassette (ABC) transporter superfamily - they hydrolyze ATP to power transport. P-gp (a major player in multidrug resistance).
MRP1-7: Multidrug Resistance-Associated Proteins. Contribute to xenobiotic transport. Effective in handling organic anions and overlap in substrates with MDR/P-gp.
OCT: Organic cation transporters; move quaternary ammonium ions, nicotine, cyperquat, dopamine, and MPP+. Other transporters may also move xenobiotics.
OAT: Organic anion transporters move carboxylic acids, metabolites conjugated with glucuronide, glutathione, and sulfate (e.g., E2-SO42-).

Elimination of Xenobiotics

Urine: filtration and excretion.
Feces: via the GI tract or liver, involving metabolism and excretion.
Expired air (in some cases): lungs, involving exhalation.
Excretion in other secretions like breast milk, sweat, and saliva.
Fecal elimination: a significant pathway for xenobiotic excretion.

Biliary Elimination

Biliary elimination is an important pathway for xenobiotic and metabolite excretion.
The liver removes xenobiotics from the blood via the portal circulation.
The liver is the main site for xenobiotic biotransformation.
The resulting metabolites (often more hydrophilic) can be directly excreted into the bile.
Xenobiotics in food and water are carried to the liver via the hepatic portal vein and hepatic artery.
Lipophilic compounds are filtered by the liver into hepatocytes; remaining lipophiles enter the systemic blood-flow via the hepatic vein.
Hepatocytes secrete lipophiles into bile for biliary excretion, carrying these compounds to the gut.

Enterohepatic Cycle

Enterohepatic circulation results in increased retention of xenobiotics if they are deconjugated by glucuronic acid in the intestines, then reabsorbed.
Lipophiles are often difficult to excrete via the kidneys and liver. Persistence is measured by the elimination half-life (t1/2).
Elimination half-life (t1/2) measures the rate of excretion from the body. First-order kinetics means the rate of elimination is proportional to the blood concentration of the xenobiotic. t1/2 is the time taken to eliminate one-half of remaining xenobiotic.
Poor excretion of lipophiles can result in bioaccumulation in the body (i.e., body burden).
Body burden is the concentration of a chemical in different tissues that cannot be directly sampled.

Persistent Organic Pollutants (POPs)

Highly lipophilic organochlorine compounds, such as the Dirty Dozen, tend to remain in the body for a long time (persist).
These chemicals are often bioaccumulative, meaning their concentration increases in the body over time.
They are also toxic, potentially causing various health problems.
Conjugation in the liver is very slow or non-existent for some POPs, which makes excretion through the bile difficult.

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Description

Test your knowledge on the vital roles of the kidneys within the urinary system. This quiz covers their functions such as blood pressure regulation, red blood cell production, and the role of nephron units. Dive into the complexities of kidney operations and their significance in maintaining homeostasis.