Exam 3 (Bcmb 230) by Ally

What are the functions of the kidney?

Regulation of the extracellular fluid environment in the body, including:

• Volume of blood plasma (affects blood pressure)

• Waste

• Electrolytes

• pH

• Secrete erythropoietin

What is the process of urine production and secretion?

Kidney → ureter → urinary bladder → urethra → exits the body

How is urine transported?

using peristalsis

peristalsis

the contraction of smooth muscle that pushes the fluid forward

What are the two regions of the kidney?

renal cortex

renal medulla — made up of renal pyramids and columns

How are pyramids drained?

minor calyx → major calyx → renal pelvis

Kidney stones (Nephrolithiasis)

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

what are kidney stones made up of?

80% are made up primarily of calcium, but others can contain magnesium ammonium phosphate or uric acid

Detrusor muscles line the

wall of the urinary bladder

What connects the smooth muscles (detrusor muscles) that line the wall of the urinary bladder?

Gap junctions—the allow them to contract as a single unit

What are the detrusor muscles controlled by?

parasympathetic neurons

What do the parasympathetic neurons that control the detrusor muscles that line the wall of the urinary bladder utilize?

acetylcholine

What surrounds the urethra?

sphincters

What are the two types of sphincters that surround the urethra?

Internal & External

Internal urethral sphincter is made of

smooth muscle

How are internal urethral sphincters controlled?

unconsciously

External urethral sphincter is made of

skeletal muscle

How is the external urethral sphincter controlled?

consciously—you control this

What do stretch receptors in the bladder do?

send information to the spinal cord

What is the process of the stretch receptors sending information to the spinal cord called?

the guarding reflex

What does the guarding reflex do?

it prevents involuntary emptying of the bladder

Stretch of the bladder initiates the ____

voiding reflex

What is the voiding reflex?

information about stretch passes up the spinal cord to the micturition center of the pons

What is the process of urination look like from a neuron perspective

1. Information about stretch passes up the spinal cord to the micturition center of the pons (voiding reflex)

2. Parasympathetic neurons cause detrusor muscles to contract rhythmically

3. Inhibition of the internal urethral sphincter causes it to relax

4. Person feels the need to urinate and can control the urge by contracting the external urethral sphincter

Urinary incontinence

uncontrolled urination due to loss of bladder control and has many possible causes

Stress urinary incontinence

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

How does stress urinary incontinence happen in women?

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?

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

How does incontinence happen in men?

as a result of treatments for prostate cancer.

Overactive bladder involves

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

How can urinary incontinence be diagnosed?

urodynamic testing in which bladder pressure and compliance are measured as the bladder is filled with warm water and the subject is asked to state when the urge to urinate appears.

Renal clearance

excreting waste as urine

What do kidneys remove during renal clearance?

excess ions and wastes from the blood.

What begins the process of filtration?

glomerular capsule

Filtration

water and molecules moving from the blood into the nephron

Reabsorption

returns some substances to the blood (decreases renal clearance)

Secretion

Finishes the process of renal clearance—substances are moved from the nephron to the minor calyx for excretion.

Excretion rate = ….

(filtration rate + secretion rate) — reabsorption rate

What is the excretion rate used to measure?

glomerular filtration rate, an indicator of renal health

What is used to measure GFR and why?

Insulin; it is filtered but not reabsorbed or secreted

What is the function unit of the kidney?

The nephron

Nephron

consists of small tubules and associated blood vessels.

What is the process of filtering in the nephron?

blood is filtered → fluid enters the tubules → fluid is modified → fluid leaves the tubules as urine

What are the two types of nephrons?

Juxtamedullary & Cortical

Juxtamedullary nephrons make up ____ of nephrons

~15%

What do Juxtamedullary nephrons do?

make concentrated urine because they have longer loops of Henle—more water is absorbed!

How is more water absorbed in the Juxtamedullary nephrons?

They set up an osmotic gradient

Cortical nephrons make up ____ of nephrons

~85%

What makes cortical nephrons different from juxtamedullary nephrons?

They are short or no loops of Henle

What is the overall nephron filtration process?

Glomerular capsule → proximal convoluted tubule → descending loop of Henle → Ascending Loop of Henle → distal convoluted tubule → collecting duct

Glomerular capsule in the nephron

filters blood

What structural feature of glomerular capillaries allows filtration to occur?

capillaries are fenestrated—contain small holes

What is the fluid that enters the glomerular capsule called?

filtrate

What is in the filtrate that enters the glomerular capsule?

water, ions, glucose, amino acids, and waste products—but normally does not contain blood cells or large proteins.

What drives water and solutes into the glomerular capsule?

A pressure gradient

Blood pressure in the glomerular capillaries is ____ than the pressure inside the nephron, ____

higher; forcing fluid into the capsule

How does vasoconstriction of blood vessels affect filtration in the glomerular capsule?

reduces filtration/absorption by decreasing the effective pressure pushing fluid into the nephron.

How much filtrate do the glomerular capsules produce daily, and what does this imply?

About 180 liters of filtrate per day are produced, meaning your entire blood volume is filtered roughly every 40 minutes.

What percentage of filtrate is reabsorbed?

99%

What does reabsorption prevent?

excessive fluid loss and allows the body to retain essential substances like glucose and electrolytes.

How much water is typically excreted daily?

1–2 liters of water

How much water is excreted when dehydrated?

~400 mL of water to eliminate waste products (obligatory urine volume).

What is the minimum urine output required to remove metabolic waste?

400 mL/day

How does the sympathetic nervous system affect kidney function during fight-or-flight?

blood is redirected away from the kidneys toward vital organs (heart, lungs, muscles), which decreases urine production.

Why does urine production decrease during sympathetic activation?

Reduced blood flow to the kidneys leads to decreased filtration pressure, resulting in less filtrate formation and therefore less urine output.

Glomerular filtration is a ____

passive process

What type of cell junctions are found in the proximal convoluted tubule?

tight junctions—helps maintain close contact

What important transport mechanism occurs in the proximal convoluted tubule?

sodium/potassium pump

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

65% - 85%

What structure does the proximal convoluted tubule contain that enhances its function?

microvilli—they enhance surface area and improve absorption efficiency

What happens to glucose and amino acids after they enter the glomerular capsule?

they are reabsorbed in the proximal tubule.

How are glucose molecules reabsorbed in the proximal convoluted tubule?

through the cotransporter of sodium and glucose

What does the presence of glucose in urine indicate?

blood glucose levels are too high, and the proximal tubule could not fully reabsorb the glucose.

Why might glucose not be fully reabsorbed in the proximal tubule?

Because all sodium-glucose cotransporters are in use (saturated)

What is reabsorbed in the proximal convoluted tubule?

sodium

When sodium is reabsorbed in the proximal convoluted tubule, what is created?

A concentration gradient

The concentration gradient formed when sodium is reabsorbed in the proximal convoluted tubule forces what?

water to follow and re-enter the blood stream

In the proximal convoluted tubule, what type of transport occurs

Active (sodium) and passive (chlorine)

Glucose and amino acids are reabsorbed in these ____ through ___

proximal convoluted tubule; secondary active transport

What is required for reabsorption of glucose in the proximal convoluted tubule?

glucose transporters

What happens when all glucose transporters are in use?

additional glucose is excreted in the urine.

What condition is indicated by glucose being present in the urine?

diabetes mellitus

How does excess glucose in the filtrate affect water reabsorption?

decreases it

What is a potential consequence of decreased water reabsorption due to excess glucose?

dehydration

What is reabsorbed in the descending loop of Henle

water

water reabsorption in the descending loop of henle is ___

unregulated

What substance is reabsorbed in the ascending loop of Henle?

Sodium

How does the ascending loop of Henle respond to increased sodium concentration in the filtrate?

it sends a message to the capsule, leading to constriction of the blood vessels inside the capsule.

What is the functional significance of the ascending loop of Henle?

it establishes a concentration gradient

What role does urea play in the ascending loop of Henle?

it is reabsorbed and contributes to establishing the concentration gradient.

How is salt transported in the ascending loop of Henle?

it is actively pumped into the interstitial fluid.

How does sodium movement contribute to transport of other ions in the ascending loop of henle?

The movement of Na⁺ down its electrochemical gradient provides energy for secondary active transport of chlorine (Cl⁻) and potassium (K⁺).

What type of mechanism exists between the two portions of the loop of Henle?

positive feedback mechanism

How does salt removal by the ascending loop affect the fluid entering it?

saltier the fluid entering it becomes, due to loss of water in the descending loop.

What role does urea play in the counter current multiplication system (ascending/descending loops)?

establish solute concentration gradients.

How is urea transported in the counter current multiplication system?

transported out of the collecting duct and into the interstitial fluid.

What happens to urea after it enters the interstitial fluid?

diffuses back into the ascending loop and cycles continuously.

What is the overall function of urea cycling in the counter current multiplication system?

helps set up solute concentration gradients, which are essential for the function of the nephron.

Within the nephron, what does the distal convoluted tubule do?

regulates salt and water reabsorption

The collecting duct is the ____ in urine formation

last stop