Nephron Function and Urine Concentration

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Questions and Answers

What occurs in the first part of the Loop of Henle?

Solute is reabsorbed, while water is not.

Both water and solutes are not reabsorbed into the bloodstream.

Water is reabsorbed into the bloodstream, while solutes are not. (correct)

Both water and solutes are reabsorbed into the bloodstream.

What is the function of parathyroid hormone in the distal convoluted tubule?

To reabsorb sodium ions into the bloodstream.

To enhance the synthesis of transport proteins. (correct)

To excrete bicarbonate ions into the urine.

To reabsorb potassium ions into the bloodstream.

Under what condition would the distal convoluted tubule excrete hydrogen ions and reabsorb bicarbonate into the blood?

When the blood volume is low.

When the blood pH is basic.

When the blood pressure is high.

When the blood pH is acidic. (correct)

What is the function of the collecting ducts?

To reabsorb sodium ions and water into the bloodstream. Signup and view all the answers

What percentage of the cardiac output does the kidneys receive?

20-25% Signup and view all the answers

What percentage of the plasma that flows through the glomerulus is filtered?

20% Signup and view all the answers

What would occur in the collecting ducts if aldosterone is present?

Sodium ions would be reabsorbed into the bloodstream. Signup and view all the answers

What would occur in the distal convoluted tubule if the blood pH is basic?

Bicarbonate ions would be excreted into the urine. Signup and view all the answers

What is a classic sign of kidney dysfunction?

Oliguria-anuria Signup and view all the answers

What type of nephrons are primarily responsible for blood flow to the kidney in a newborn?

Medullary nephrons Signup and view all the answers

Why does an infant produce more dilute urine?

Due to the short loops of Henle in the medullary nephrons Signup and view all the answers

What is the primary reason for an infant's narrow chemical safety margin?

All of the above Signup and view all the answers

At what stage of life does the kidney reach adult size?

Adolescence Signup and view all the answers

What happens to the extracellular fluid volume (ECF) of the newborn infant during periods of rapid growth?

It decreases Signup and view all the answers

What is a consequence of the immaturity of the tubular transport capacity in infants?

Limited ability to buffer hydrogen with ammonia Signup and view all the answers

What can rapidly lead to severe acidosis and fluid imbalance in infants?

Diarrhea, infection, fasting, and poor feeding Signup and view all the answers

What is the primary function of erythropoietin in the body?

Stimulating the bone marrow to produce RBCs Signup and view all the answers

What hormone is responsible for stimulating the renal portion of vitamin D activation?

Parathyroid hormone Signup and view all the answers

What is the primary purpose of renal clearance tests?

To evaluate kidney function for diagnostic and prognostic purposes Signup and view all the answers

What is the result of decreased oxygen delivery to the kidneys?

Stimulation of the bone marrow to produce RBCs Signup and view all the answers

What is the role of Vitamin D in the body?

Aiding in the absorption of calcium in the small intestine Signup and view all the answers

What can renal clearance tests be used to determine?

The glomerular filtration rate (GFR) and renal blood flow (RBF) Signup and view all the answers

What is the primary mechanism of stone formation in the kidney?

Growth into a stone via crystallization Signup and view all the answers

What is the most common cause of uncomplicated urinary tract infections?

Escherichia coli Signup and view all the answers

What is the characteristic presentation of acute glomerulonephritis?

Decreased GFR Signup and view all the answers

What is the primary function of the urethral sphincter?

To maintain continence Signup and view all the answers

What is the term for the inability of the bladder to empty completely despite micturition?

Feeings of incomplete bladder emptying Signup and view all the answers

What is the term for the inflammation of the glomerulus, often related to group A poststreptococcal infection?

Acute glomerulonephritis Signup and view all the answers

What is the term for the excretion of 3.5 g or more of protein in urine?

Nephrotic syndrome Signup and view all the answers

What is the primary mechanism of protection against urinary tract infections in women?

Mucus-secreting glands in the urethra Signup and view all the answers

What is the term for the decline of renal function to approximately 25% of normal?

Renal insufficiency Signup and view all the answers

What is the term for the inflammation of the urinary epithelium following invasion and colonization of a pathogen?

Urinary tract infection Signup and view all the answers

What is the main challenge in controlling dehydration and overhydration in infants?

Higher water exchange rate due to higher water requirements Signup and view all the answers

What is the location of the urethral meatus in hypospadias?

On the ventral side or undersurface of the penis Signup and view all the answers

What is the primary defect in exstrophy of the bladder?

Failure of the abdominal muscles to fuse in the midline Signup and view all the answers

What is the main characteristic of hypoplastic kidneys?

Small kidneys with a decreased number of nephrons Signup and view all the answers

What is the typical presentation of renal agenesis?

Unilateral absence of kidneys, usually on the left side Signup and view all the answers

What is the characteristic feature of renal dysplasia?

Abnormal differentiation of renal tissues Signup and view all the answers

What is the main difference between infants and adults in terms of water exchange?

Infants exchange more water due to higher water requirements Signup and view all the answers

What is the recommended time frame for closing the bladder and pubic defect in exstrophy of the bladder?

Within 72 hours of birth Signup and view all the answers

Study Notes

The Loop of Henle

The descending part of the Loop of Henle reabsorbs additional water into the bloodstream, but not solutes, resulting in a highly concentrated urine.
The ascending part of the Loop of Henle reabsorbs solutes, but not water, resulting in a less concentrated urine.

Nephrons and Distal Convoluted Tubule

From the Loop of Henle, the fluid goes to the distal convoluted tubule.
In the distal convoluted tubule, some Na+ and Ca+ are reabsorbed into the bloodstream.
The calcium is reabsorbed by the effects of parathyroid hormone, which enhances the synthesis of transport proteins in the distal convoluted tubule.
Depending on the pH of the blood, the distal convoluted tubule may:
- Excrete hydrogen ions and reabsorb bicarbonate into the blood.
- Excrete bicarbonate and reabsorb hydrogen ions into the blood.

Collecting Duct

From the distal convoluted tubule, the fluid goes to the collecting duct.
Collecting ducts merge from several different nephrons to form cortical collecting ducts.
The cortical collecting ducts are sensitive to antidiuretic hormone (vasopressin) and aldosterone, allowing for:
- Water and salt reabsorption into the bloodstream if these hormones are present.
- Excretion of sodium, potassium, hydrogen, and bicarbonate into the collecting duct if these hormones are not present.

Renal Blood Flow (RBF)

The kidneys are highly vascular, receiving 20-25% of the cardiac output.
Approximately 20% of the plasma that flows through the kidneys is filtered by the glomerulus.

Erythropoietin

Function: Stimulates the bone marrow to produce RBCs to prevent or correct hypoxia.
Decreased oxygen delivery to the kidneys stimulates the secretion of erythropoietin from the peritubular cells of the kidneys, which then stimulates the bone marrow to produce RBCs.

Tests of Renal Function

Renal clearance tests determine how much of a substance can be cleared from the blood by the kidneys during a given unit of time.
Tests are useful for:
- Evaluating kidney function for diagnostic/prognostic purposes.
- Dosing certain medications like antibiotics.
- Determining if a patient can have a test or procedure.

Renal Stones

Can form in the urinary tract due to changes in temperature and pH.
Types of stones:
- Calcium phosphate stones (alkaline).
- Uric acid stones (acidotic).

Lower Urinary Tract Obstruction

Can be caused by:
- Neurogenic bladder dysfunction.
- Anatomic obstructions (e.g., urethral stricture, prostate enlargement, pelvic organ prolapse).
Manifestations:
- Frequent daytime voiding.
- Nocturia.
- Urgency.
- Dysuria.
- Poor force of stream.
- Feelings of incomplete bladder emptying.

Tumors

Renal adenomas: encapsulated benign tumors usually in the renal cortex.
Renal cell carcinoma (RCC):
- Most common renal cancer (85%).
- Develops from the proximal tubule epithelial cells.
- Risk factors: tobacco use, obesity, long-term analgesic use.
- Manifestations:
  - Asymptomatic early on.
  - Weight loss.
  - Fatigue.
  - Classic triad: hematuria, dull and aching flank pain, and palpable flank mass in thinner individuals.

Urinary Tract Infections

Definition: Inflammation of the urinary epithelium following invasion and colonization of a pathogen.
Most common cause: bacteria.
Classification:
- Uncomplicated UTI: occurs in a healthy individual with a normal urinary tract.
- Complicated UTI: occurs in those with defects in the urinary system or other health problems that compromise their ability to prevent pathogen colonization or fight organisms.
Potential complications:
- Cystitis: inflammation of the bladder.
- Pyelonephritis: inflammation of the upper urinary tracts.
Manifestations:
- Asymptomatic.
- Urinary frequency.
- Dysuria.
- Urgency.
- Flank and/or suprapubic pain.
- Cloudy urine.
- Foul-smelling urine.
- Fever/chills.

Acute Glomerulonephritis

Definition: Inflammation of the glomerulus, most often related to group A poststreptococcal infection.
Mechanism: Antibodies produced against the organism cross-react with the glomerular endothelial cells.
Manifestations:
- Hematuria with red blood cell casts.
- Proteinuria exceeding 3–5 g/day.
- Hypoalbuminemia.
- Edema.
- Decreased GFR.

Chronic Glomerulonephritis

Definition: Glomerular diseases with a progressive course, usually related to a chronic disease, leading to renal failure.
Manifestations:
- Proteinuria.
- Hypercholesterolemia.
Diagnosis: H&P, urinalysis, serum creatinine, creatinine clearance.

Nephrotic Syndrome

Definition: Excretion of 3.5 g or more of protein in urine.
Mechanism: Protein excretion as a result of glomerular injury.
Etiologies: Genetic, rare primary diseases, diabetes mellitus, lupus, amyloidosis, medication-related, HIV, leukemia, lymphoma, vascular disorders.
Manifestations:
- Hypoalbuminemia.
- Edema.
- Oliguria.
- Hypertension.
Diagnosis: H&P, serum albumin level, 24-hour urine protein test.

Classification of Kidney Dysfunction

Acute or chronic; reversible or irreversible.
Renal insufficiency: decline of renal function to approximately 25% of normal.
Renal failure: significant loss of renal function.
End-stage renal failure: less than 15% of renal function remains.

Alterations of Renal and Urinary Tract Function in Children

The kidneys and urologic structures are continuing to develop in children, and dysfunction can look very different to that seen in adults.
Some disorders seen in children are congenital structural issues.
As with adults, renal and urologic conditions can have significant impacts on other systems.
Fluid and electrolyte imbalance:
- Immaturity and smaller tubule surface area diminish the water reabsorption response to antidiuretic hormone (ADH).
- Immature tubular transport capacity.
- Diarrhea, infection, fasting, and poor feeding can rapidly lead to severe acidosis and fluid imbalance.
Congenital abnormalities:
- Hypospadias.
- Epispadias.
- Exstrophy of the bladder.
- Ureteropelvic junction obstruction.
- Bladder outlet obstruction.
- Renal aplasia.
- Hypoplastic kidneys.
- Renal dysplasia.
- Renal agenesis.

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Description

This quiz covers the process of urine concentration and solute reabsorption in the nephrons, specifically in the Loop of Henle and distal convoluted tubule.