Chapter 17 - Kidneys

What is the role of the kidneys in regulating blood plasma volume?

The kidneys regulate the volume of blood plasma, which affects blood pressure.

How does urine travel from the kidneys to the urinary bladder?

Urine made in the kidney nephrons drains into the renal pelvis, then down the ureter to the urinary bladder.

How does urine exit the body?

passes from the bladder through the urethra to exit the body.

How is urine transported through the ureters?

transported using peristalsis.

What are kidney stones made of?

hard objects formed in the kidneys containing crystallized minerals or waste products.

What is the most common type of kidney stone?

About 80% of kidney stones are calcium stones, but they can also be made of magnesium ammonium phosphate or uric acid.

What increases the tendency to form kidney stones?

a person is dehydrated.

What is lithotripsy?

a treatment where shock waves are used to shatter kidney stones.

What connects smooth muscle cells in the detrusor muscle?

Gap junctions connect smooth muscle cells.

How are detrusor muscles innervated?

by parasympathetic neurons, which release acetylcholine onto muscarinic ACh receptors.

What type of muscle makes up the internal urethral sphincter?

smooth muscle.

What type of muscle makes up the external urethral sphincter?

skeletal muscle.

Where do stretch receptors in the bladder send information?

the S2−S4 regions of the spinal cord.

What does the guarding reflex involve?

inhibition of parasympathetic nerves to the detrusor muscles while stimulating somatic motor neurons to the external urethral sphincter.

What is the function of the guarding reflex?

prevents involuntary emptying of the bladder.

Where does information about bladder stretch pass to?

the spinal cord to the micturition center of the pons.

What does the activation of parasympathetic neurons cause in the voiding reflex?

cause detrusor muscles to contract rhythmically.

What happens when sympathetic innervation of the internal urethral sphincter is inhibited?

causes it to relax.

How does a person control urination?

A person feels the need to urinate and can control when with the external urethral sphincter.

What is stress urinary incontinence?

occurs when urine leakage happens due to increased abdominal pressure, as during sneezing, coughing, and laughing.

What causes stress urinary incontinence in women?

occurs when the pelvic floor no longer provides adequate support to the urethra due to childbirth or aging.

How is stress urinary incontinence treated in women?

a sling surgery, in which inserted mesh provides additional support for the urethra.

What is a common cause of urinary incontinence in men?

occurs as a result of treatments for prostate cancer.

What causes overactive bladder?

uncontrolled contractions of the detrusor muscle that produce a great urge to urinate and the leakage of a large volume of urine.

How is urinary incontinence diagnosed?

by urodynamic testing, which includes cystometric tests where bladder pressure and compliance are measured as the bladder is filled with warm water and the subject is asked to say when the urge to urinate appears.

What is the functional unit of the kidney?

The nephron

What is the process that occurs in the nephron?

Blood is filtered, fluid enters the tubules, is modified, and then leaves the tubules as urine.

What surrounds the glomerulus to form the renal corpuscle?

The glomerular (Bowman’s) capsule surrounds the glomerulus, together making up the renal corpuscle.

After the filtrate is produced in the renal corpuscle, where does it pass into?

into the proximal convoluted tubule.

What surrounds the glomerulus and forms the renal corpuscle?

Glomerular (Bowman’s) capsule surrounds the glomerulus. Together, they make up the renal corpuscle.

Where does the filtrate produced in the renal corpuscle pass into?

the proximal convoluted tubule.

After passing through the proximal convoluted tubule, where does the fluid next travel?

Descending and ascending limbs of the loop of Henle

After the loop of Henle, where does the fluid pass into next?

Distal convoluted tubule

After the distal convoluted tubule, where does the fluid pass into?

Collecting duct

After the fluid becomes urine in the collecting duct, where does it drain into?

Minor calyx

Which type of nephron is better at making concentrated urine?

Juxtamedullary

What is the other type of nephron besides the juxtamedullary nephron?

Cortical

What is PKD (polycystic kidney disease)?

A congenital disorder where kidneys are enlarged by fluid-filled cysts

The gene responsible for 85% of autosomal dominant polycystic kidney disease (ADPKD) is located on which chromosome?

Chromosome 16

What protein is coded by the gene on chromosome 16 related to ADPKD?

Polycystin-1

What is a characteristic of the capillaries in the glomerulus?

They are fenestrated with large pores

What is the visceral layer of the glomerular capsule composed of?

Podocytes

What are the extensions of podocytes called?

Filtration slits

What structure serves as the major barrier for the filtration of plasma proteins?

Slit diaphragm pores in the pedicles

A defect in the slit diaphragm pores can cause which condition?

Proteinuria

How does fluid enter the glomerular capsule?

Via hydrostatic pressure, colloid osmotic pressure, and very permeable capillaries

What effect does vasoconstriction or dilation of the afferent arterioles have?

It changes the glomerular filtration rate

What type of regulation involves the sympathetic nervous system affecting the afferent arterioles?

Extrinsic regulation

What is the regulation called when the kidneys themselves send signals to adjust the filtration rate?

Renal autoregulation

During a fight or flight reaction, what happens to the afferent arterioles?

They vasoconstrict

Why does vasoconstriction of the afferent arterioles occur during a fight or flight reaction?

To divert blood to the heart and muscles

What does renal autoregulation maintain at a constant level despite fluctuations in blood pressure?

Glomerular filtration rate (GFR)

What happens to the afferent arterioles if blood pressure drops below 70 mmHg?

They dilate

What is it called when smooth muscle in arterioles senses an increase in blood pressure and responds by constricting?

Myogenic constriction

What is the name of the feedback mechanism where cells sense a rise in water and sodium levels?

Tubuloglomerular feedback

What are the specialized cells in the ascending limb of the loop of Henle that sense changes in water and sodium called?

Macula densa

How much water is filtered per day by the kidneys?

180 L

How much urine is typically excreted per day?

1 to 2 L

Is the reabsorption that occurs in the proximal tubules and descending loop of Henle regulated or unregulated?

Unregulated

What is the osmolality of the filtrate in the glomerular capsule compared to blood plasma?

Isoosmotic

How is Na+ transported in the nephron to set up a concentration gradient for osmosis?

By active transport into the peritubular blood

How are the cells of the proximal tubules joined on the apical side?

By tight junctions

Why do the cells of the proximal tubules have a lower Na+ concentration than the filtrate inside the tubule?

Due to Na+/K+ pumps on the basal side and low permeability to Na+

What happens to Na+ from the filtrate in the proximal tubules?

It diffuses into the cells and is then pumped out the other side

What happens when sodium is pumped into the interstitial space?

It attracts negative Cl− out of the filtrate

Where do the ions and water go after they diffuse into the interstitial space?

They diffuse into the peritubular capillaries

What percentage of salt and water is reabsorbed in the proximal tubule?

65%

What hormone controls the final 15% of water reabsorption in the nephron?

Anti-Diuretic Hormone (ADH)

What is the osmolality of fluid entering the Loop of Henle compared to extracellular fluids?

Isotonic

How is the reabsorption of water through the descending limb of the Loop of Henle regulated?

It is unregulated and happens continuously

Why can't water be actively pumped out of the tubules?

Water will not cross if it is isotonic to extracellular fluid

What is actively pumped into the interstitial fluid from the thick segment of the ascending limb of the Loop of Henle?

Sodium chloride (NaCl)

What powers the secondary active transport of chloride (Cl−) and potassium (K+) in the ascending limb of the Loop of Henle?

The electrochemical gradient of Na+

How is sodium (Na+) moved into the interstitial space from the tubule cells?

Through Na+/K+ pumps

Why can't osmosis occur in the ascending limb of the Loop of Henle?

The walls are impermeable to water

Why is the increased solute concentration of fluid important for the ascending limb?

It enhances salt transport out of the fluid

What is created between the two portions of the loop of Henle?

Positive feedback mechanism

In countercurrent multiplication, what happens as the ascending limb removes more salt?

The fluid entering it becomes saltier

What are the specialized blood vessels around the loop of Henle called?

Vasa recta

How do the vasa recta contribute to the countercurrent system?

By taking in salts in the descending region and losing them in the ascending region

What is one important function of the vasa recta?

They keep salts in the interstitial space

What pulls water into the vasa recta at the beginning of the ascending region?

High oncotic pressure (high salt concentration)

What structures aid the countercurrent exchanges along with the vasa recta?

Urea transporters and aquaporins

What is urea a waste product of?

Protein metabolism

What is the last stop in urine formation impermeable to?

NaCl

What influences water movement in the last part of urine formation?

Hypertonicity of the interstitial space

What does the permeability of the collecting duct to water depend on?

Number of aquaporin channels

What determines the availability of aquaporins in the collecting duct?

Antidiuretic hormone (ADH)

Where is ADH produced and where is it stored and released?

Produced by the hypothalamus, stored and released by the posterior pituitary

What stimulates the release of ADH?

Increase in blood osmolality

What are the main characteristics of diabetes insipidus?

Polyuria, thirst, and polydipsia

What is central diabetes insipidus caused by?

Inadequate secretion of ADH

What causes nephrogenic diabetes insipidus?

Inability of kidneys to respond to ADH

What may cause nephrogenic diabetes insipidus?

Genetic defects in aquaporin channels or ADH receptors

What is a more common cause of nephrogenic diabetes insipidus?

Drug therapy (e.g., lithium for bipolar disorder) or other causes

What treatment can people with central diabetes insipidus use?

Desmopressin when needed

What is the process of removing excess ions and wastes from the blood called?

Renal clearance

What happens during reabsorption?

Substances are returned to the blood, decreasing renal clearance

What increases renal clearance?

Secretion from the peritubular capillaries into the tubules

What is the formula for excretion rate?

Excretion rate = (filtration rate + secretion rate) – reabsorption rate