urinary intro exam questions

what specific type of tissue lines the proximal convoluted tubule? and what special feature is found in the lining of the PCT?

• lined with a simple cuboidal EPI that has very dense microvilli at its apical surface

what are the specific functions of the proximal convoluted tubule (PCT)?

• reabsorbs most of the water (~65%), most of the sodium and chloride, and nearly all the organics

• these substances are moved from inside the tuble to the outside

• they are absorbed by the peritubular capillaries

what type of transport does the PCT use to move Na+ and Cl- outward?

• Na+ is actively transported across the walls of the tubule and eneters the peritubular capillaries

• when Na+ is transported, Cl- follows due to the electrical attraction between oppositely charged ions

what inorganic substances follows the outward moving salts?

• when Na+ and Cl- move outward, water follows

• its basically following the concentration gradient

what are some things that the PCT secretes into the tubule system?

• secretes H+, NH3, creatinine, drugs, and toxins

• it pumps these substances that the body wants to get rid of into the tubular fluid so they go out with the urine (helps control pH)

what types of transport are important in reabsorption and secretion?

• simple diffusion

• osmosis

• carrier proteins (facilitated diffusion, active transport, and others)

would a carrier protein work for just one substance or would it be able to transport a large number of different substances?

• carrier proteins are specific for certain substrates, one works for Na+ and another fo Ca2+

what is meant by saturation of the carrier protein?

• means that a given carrier protein can only transport so fast

• it eventually gets “maxed out“

what is meant by the transport maximum of a carrier protein? What is meant by the renal threshold? Is the renal threshold the same for all solutes?

• transport maximum is the max rate of reabsorption

• renal threshold: the plasma concentration at which a specific solute begins to appear in your urine

• varies for different substances: 65 mg/dL for amino acids ; 180 mg/dL for glucose

what type of meal is likely to result in glucose ending up in the urine?

• Very high in simple carbohydrates (sugars)

  • Sugary drinks (soda, juice)

  • Desserts (cakes, candy)

• Refined carbohydrates with little fiber or protein

  • White bread, pastries, white rice

• Large portion sizes of carbs

where along the nephron does most reabsorption occur?

• proximal convoluted tubule

how would reabsorption of salt change in a person that had a diet high in salt versus person whose diet lacked salt?

• if person ingests too much salt, then reabsorb little, let excess go out in urine

• if person is lacking salt in diet, then reabsorb most to conserve/retain Na+

what substances are usually completely reabsorbed from the tubular fluid?

• glucose

• amino acids

• proteins

• lipids

what substances in the tubular fluid would not be reabsorbed because the body needs to excrete them?

• waste products (urea, creatinine, uric acid, drug metabolites)

give some examples of substances that are secreted into the tubular fluid? What is secretion especially important for?

• essential the reverse of tubular reabsorption

• certain substances are secreted into the renal tubules to be excerted with the urine (H+, NH3, K+, creatinine, drugs, toxins)

• especially important for controlling blood pH and for disposal of substances not already in the filtrate (like drug metabolites)

in terms of the kidneys, why do patients usually have to take repeated doses of penicillin for an extended period?

Penicillin doesn’t stay in the body very long because the kidneys clear it rapidly and efficiently.

why must we reabsorb most of the water and solutes from the tubular filtrate? In other words, what would happen to us if we didn’t reabsorb it?

• most of the water and solutes of the filtrate must be reabsorbed otherwise we would literally urinate to death

what are the 3 major structures in the kidney where water is reabsorbed?

• proximal convulted tubule

• nephron loop (loop of henle)

• collecting duct

what is meant by osmosis?

• the diffuson of water across a selectively-permeable membrane toward areas of high solute concentration

What’s the difference between an isotonic, hypotonic, and hypertonic solution? How would a red blood cell behave in each solution?

• hypotonic - RBC sweels

• isotonic - no change

• hypertonic - RBC shrinks

What is the other name for the nephron loop?

loop of henle

What is the main function of the nephron loop?

• create a gradient of increasing osmolarity from the cortex to the medulla

• create gradient by actively pumping salts into the medulla

Where does this reabsorbed water end up? Does it just stay in the interstitial fluid?

• this allows water to be reabsorbed by osmosis from the descending limb and the collecting duct as they run down into the medulla

Does greater reabsorption of water occur in cortical or juxtamedullary nephrons, why?

Juxtamedullary nephrons are specialized for conserving water and producing concentrated urine, which is why they account for greater water reabsorption overall.

Besides NaCl, what organic contributes greatly to the osmolarity of the deep renal medulla?

• urea

Which part of the kidney allows urea to diffuse out into the interstitial fluid?

• the collective duct is permeable to urea, when the urine gets here, the urea diffuses out into the medulla

In what way is the simple cuboidal epithelium that lines the proximal convoluted tubule different from that of the distal convoluted tubule? What’s the functional significance of this difference? What are the specific functions of the distal convoluted tubule?

• DCT have few microvilli

• does some reabsorption

• it is selective about what it absorbs

• strongly influenced by hormones

• secretes h+, NH3, creatinine, drugs, and toxins into the tubular fluid

Both the distal convoluted tubule and the collecting duct are strongly influenced by which other organ system?

hormones

Describe the specific functions of the collecting duct.

• also reabsorbs water and Na+

• as the collecting duct plunges into the renal medulla, it encounters an increasingly “salty“ interstitial fluid

• secretes K+ and H+

Why is water osmotically drawn out of the collecting duct as it passes down into the renal medulla?

concentrates the urine

Under what conditions would the kidneys excrete a hypertonic urine? A hypotonic urine?

• if we need to conserve water, the kidneys excrete a hypertonic (rich) urine

• if we drink excess water, the kidneys excrete a hypotonic (watery) urine

What two parts of the nephron are always reabsorbing water?

• PCT

• nephron loop

What two parts of the nephron adjust the amount of water they absorb depending heavily on hormone levels in the body?

• collecting duct

• DCT

What is the major function of ADH (antidiuretic hormone)?

stimulates reabsorption of water by the kidneys

Where is ADH produced? Where is it stored?

• produced by the hypothalamus but stored in and secreted by the posterior pituitary

What’s the main stimulus for the increased release of ADH?

• an increase in osmolarity of the blood plasma

• this detected by sensory receptors in the hypothalamus

What are aquaporins? How does ADH influence the aquaporins?

• aquaporins: their epithelial cells contain vesicles (simple membranous sacs) containing water channels

• ADH stimulates these vesicles to fuse with the plasma membrane and thus insert the aquaporins into the plasma membrane

What’s wrong with a Diabetes insipidus patient’s body?

• a condition in which a person doesnt produce ADH

• as result, they constantly excrete a large volume of very dilute urine

• are at risk of severe dehydration and dangerously low blood pressure

What effect does alcohol consumption have on ADH levels? What effect does cold weather have?

• both increase urine volume by inhibiting ADH

Which ion is the major solute in the blood plasma?

sodium ions (Na+)

How would a severe drop in plasma sodium influence blood volume and blood pressure? Explain why.

• when the blood concentration of Na+ falls, so does the osmolarity of the blood

• the drop in osmolarity inhibits ADH secretion with the effect that more water is excreted in the urine…blood volume and blood pressure decline

• a severe drop in Na+ may cause a dangerously low drop in blood pressure

What is the major function of aldosterone?

• secreted by the adrenal cortex of the adrenal gland in response to a decline in the blood Na+ concentration

• stimulates the reabsoption of Na+ in the DCT and the collecting duct in order to maintain homeostasis

• help maintain blood molarity, blood volume, blood pressure

What specific part of the body secretes aldosterone?

adrenal cortex

In general, where is the juxtaglomerular apparatus located? What enzyme does it secrete?

• specialized EPI and smooth muscle cells near the glomerulus

• decreased blood Na+ leads to decreased blood volume and pressure

• brain detects drop in blood pressure and sympathetic nervous system activates juxtaglomerular cells which secrete the enzyme renin into the blood

What is the function of renin? Would it be released in response to high or low blood pressure in the afferent arteriole?

• speeds up the production of angiotensin II

• Trigger: low blood pressure in the afferent arteriole

• Purpose: raise blood pressure and restore perfusion

What are the two major effects of angiotensin II?

• it stimulates blood vessels to constrict

• stimulates the adrenal cortex to secrete aldosterone

What stimulates the release of natriuretic peptides from the heart walls?

• secreted in response to high blood pressure that stretches the heart walls

What is the major function of the natriuretic peptides?

• these hormones oppose the action of aldosterone by inhibiting the reabsorption of Na+ and water

• these hormones thus help reduce blood volume and blood pressure

Describe the structure and function of the ureters

• two muscular tubes that transport urine from kidneys to the bladder

• transports urine toward the urinary bladder

Where is the bladder located and how is its position stabilized?

• hollow, muscular organ that temporarily stores urine

• located inferior to (just below) the peritoneum

• its position is stabilized by tough, fibrous bands (ligaments) that anchor it to the pelvic bones

What did the two lateral umbilical ligaments used to be earlier in life (e.g., in fetus)?

• these ligaments are the vestiges (remainders) of the umbilical arteries which carried “used“ fetal blood to the placenta

Where specifically is the internal urethral sphincter located? Do both men and women have it or just one sex?

• in males, the neck contains the muscle internal urethral sphincter

• below the neck of a male’s bladder

Describe the three layers of the bladder.

• mucosa: innermost layer made of transitional EPI over a layer of reticular tissue

• muscular wall: consists of three irregularly arranged muscle layers

• outermost layer of tough connective tissue

Describe the tissue make-up of the lining of the urethra.

• the lining of the urethra varies from transitional to stratified columnar to stratified squamous at its end

In what sense does the male’s urethra have a dual role?

• in males the urethra also runs though the prostate gland

• dual role: besides conducting urine also serves as a passageway for semen

• urethra is apart of the reproductive system

In males, what are the two “valves” that control micturition? What type of muscle makes up each valve? How is each muscle controlled?

• micturition: the voiding of urine from the body

• internal urethral sphincter: more superior, in neck of bladder ; a smooth muscle, involuntary sphincter

• external urethral sphincter: located more distally around urethra ; skeletal muscle, under voluntary control

Explain in detail the process of micturition, especially the major reflex involved.

• Stretch → contraction → more stretch signaling → stronger contraction

• The micturition reflex is a spinal parasympathetic reflex triggered by bladder stretch

• It causes detrusor contraction and internal sphincter relaxation

• Final control depends on voluntary relaxation of the external sphincter

What is meant by incontinence?

• lack of voluntary control over urination

• normal in children under 3

Why can’t infants control their bladders?

they cant hold their pee

What are some common causes of adult incontinence?

• spinal cord injury, bladder irritability, or trauma to either sphincter