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Anatomy and Physiology > urinary system ii > Flashcards

urinary system ii Flashcards

1
Q

Tubular Reabsorption

A

-Most of tubular contents reabsorbed to blood

Selective transepithelial process

  • almost all organic nutrients reabsorbed
  • water and ion reabsorption hormonally regulated and adjusted

Includes active and passice tubular reabsoption

two routes: trancellular or paracellular

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2
Q

Transcellular tubular reabsobtion

A
  1. transport across apical membrane
  2. diffusion through cytosol
  3. transport across basolateral membrane (often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces)
  4. movement through the interstitial fluid into the capillary
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3
Q

Paracellular route of tubular reabsobtion

A

movement through leaky tight junctions, particularly in the PCT

Movement through the interstitial fluid and into the capillary

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4
Q

Tubular reabsoption of sodium

A

Na+ = most abundant cation in filtrate

Transport across basolateral membrane
-Primary active transport out of tubule cell by Na+-K+ ATPase pump  peritubular capillaries

Transport across apical membrane
-Na+ passes through apical membrane by secondary active transport or facilitated diffusion mechanisms

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5
Q

Reabsoption of nutrients, water, and ions

A

Na+ reabsorption by primary active transport provides energy and means for reabsorbing most other substances by secondary active transport

Creates electrical gradient  passive reabsorption of anions

Organic nutrients reabsorbed by secondary active transport; cotransported with Na+
-Glucose, amino acids, some ions, vitamins

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6
Q

Passive tubular reabsoption of water

A

Movement of Na+ and other solutes creates osmotic gradient for water

Water reabsorbed by osmosis, aided by water-filled pores called aquaporins

Aquaporins always present in PCT  obligatory water reabsorption. If solutes are reabsorbed, water is obliged to follow

Aquaporins inserted in collecting ducts only if ADH present  facultative water reabsorption. Water is reabsorbed only if we need it.

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7
Q

Passive Tubular Reabsorption of Solutes

A

Solute concentration in filtrate increases as water reabsorbed  concentration gradients for solutes 

Fat-soluble substances, some ions and urea, follow water into peritubular capillaries down concentration gradients
– Lipid-soluble drugs, environmental pollutants difficult to excrete

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8
Q

Transport maximum

A

Transcellular transport systems specific and limited
Transport maximum (Tm) for ~ every reabsorbed substance; reflects number of carriers in renal tubules available
When carriers saturated, excess excreted in urine
E.g., hyperglycemia  high blood glucose levels exceed Tm  glucose in urine

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9
Q

Reabsorptive capabilities of PCT

A
  • site of most reabsorption
  • all nutrients (glucos, AA….)
  • 65% of Na and water
  • many ions
  • almost all uric acid; 1/2 of the urea (later secreted back into filtrate)
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10
Q

reabsorptive capabilities of nephron loop

A

Descending limb: water can leave; solutes can’t

Ascending limb: water can’t leave; solutes can

  • thin segment = passive sodium movement
  • thick segment = Na–K–2Cl symporter and Na–H antiporter; some passes by paracellular route
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11
Q

reabsoptive capabilities of DCT and collecting duct

A 
Hormonally regulated
ADH = water
Aldosterone = Na and water
ANP = Na
PTH = Ca
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12
Q

ADH

A

Released by posterior pituitary gland

Causes principal cells of collecting ducts to insert aquaporins in apical membranes  water reabsorption
-As ADH levels increase  increased water reabsorption

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13
Q

Aldosterone

A

Targets collecting ducts (principal cells) and distal DCT

Promotes synthesis of apical Na+ and K+ channels, and basolateral Na+-K+ ATPases for Na+ reabsorption; water follows

 little Na+ leaves body; aldosterone absence leads to loss of 2% filtered Na+ daily - incompatible with life

Functions – increase blood pressure; decrease K+ levels

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14
Q

ANP

A

Reduces blood Na+  decreased blood volume and blood pressure

Released by cardiac atrial cells if blood volume or pressure elevated

Inhibits reabsorption of Na+

Inhibits release of aldosterone and ADH

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15
Q

PTH

A

acts on DCT to increase Ca reabsoption

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16
Q

Tubular secretion

A

Reabsorption in reverse; almost all in PCT

  • Selected substances
  • K+, H+, NH4+, creatinine, organic acids and bases move from peritubular capillaries through tubule cells into filtrate
  • Substances synthesized in tubule cells also secreted – e.g., HCO3-

Disposes of substances (drugs) bound to plasma proteins

Eliminates undesirable substances passively reabsorbed (urea/uric acid)

Rids body of excess K (via aldosterone)

Controls blood pH by altering amounts of H or HCO3 in urine

17
Q

regulation of urine concentration and volume

A

Osmolality of body fluids

  • Expressed in milliosmols (mOsm)
  • Kidneys maintain osmolality of plasma at ~300mOsm by regulating urine concentration and volume
18
Q

Formation of dilute or concentrated urine

A

Osmotic gradient used to raise urine concentration > 300 mOsm to conserve water

Overhydration –> large volume dilute urine

  • ADH production decreases; urine ~ 100 mOsm
  • If aldosterone present, additional ions removed –> ~ 50 mOsm

Dehydration –> small volume concentrated urine

  • Maximal ADH released; urine ~ 1200 mOsm
  • Severe dehydration – 99% water reabsorbed
19
Q

Urea Recycling and the Medullary osmotic gradient

A

Urea helps form medullary gradient:

  • Enters filtrate in ascending thin limb of nephron loop by facilitated diffusion
  • Cortical collecting duct reabsorbs water; leaves urea
  • In deep medullary region now highly concentrated urea –> interstitial fluid of medulla –> back to ascending thin limb –> high osmolality in medulla
20
Q

urinary role in pH balance

A

In tubular cell: that whole carbonic anhydrase reaction happens and H secretion is coupled to Na reabsorption via an antiporter

More H in blood leads to higher H secretion, so you need to buffer the H in the urine with NH3 from tubular cells, HCO3, or HPO4 which is the most important urine buffer

21
Q

Diuretics

A

Chemicals that enhance urinary output

ADH inhibitors, e.g., alcohol

Na+ reabsorption inhibitors (and resultant H2O reabsorption), e.g., caffeine, drugs for hypertension or edema

Loop diuretics inhibit medullary gradient formation

Osmotic diuretics - substance not reabsorbed so water remains in urine, e.g., high glucose of diabetic patient, mannitol

22
Q 
Physical characteristics of urine
transparency
color
ph
specific gravity
A

Clear: if cloudy may indicate UTI

Pale to deep yellow from urochrome –> pigment from hemoglobin breakdown; more concentrated urine –> deeper color

Abnormal color from food, bile pigments, blood, drugs

pH is slightly acidic (4.5-8)

  • acidic diet (protein and whole wheat decreases pH)
  • alkaline diet (vegetarian), vomiting, or UTI increases pH

Specific gravity = 1.001 to 1.035 and is dependent on solute concentration

23
Q

chem comp of urine

A

95% water; 5% solute

Nitrogenous wastes:

  • urea (from AA breakdown) = biggest solute component
  • uric acid (from nucleic acid metabolism)
  • creatine (metabolite of creatine phosphate

other solutes:
Na–K–PO4–SO4–Ca–Mg–HCO3

Too much solute or weird solutes (WBCs, proteins, bile pigments) may indicate pathology

24
Q

Ureters

A

Bring urine from kidney to bladder, starting at L2
Retroperitoneal
Enter at inferior, posterior bladder wall
(as bladder pressure increases, ends of ureters close)

3 layers

  1. mucosa = transitional epithelium
  2. muscularis = smooth muscle sheets which contract in response to stretch and propel urine into bladder
  3. adventitia = outer fibrous CT
25
Q

Bladder definition and m/f dif

A

Muscular sac for temporary storage of urine

Retroperitoneal, on pelvic floor posterior to pubic symphysis

Males—prostate inferior to bladder neck

Females—anterior to vagina and uterus

26
Q

layers of bladder

A

Mucosa - transitional epithelial mucosa

Thick detrusor - three layers of smooth muscle

Fibrous adventitia (peritoneum on superior surface only)

27
Q

bladder: expansion, collapse, size

A

Collapses when empty; rugae appear

Expands and rises superiorly during filling without significant rise in internal pressure

~ Full bladder 12 cm long; holds ~ 500 ml

  • Can hold ~ twice that if necessary
  • Can burst if overdistended
28
Q

Urethra

A

Muscular tube draining urinary bladder

Mostly pseudostratified columnar epithelium, except Transitional epithelium near bladder and stratified squamous epithelium near external urethral orifice

Internal sphincter = smooth muscle which contracts to open

External sphincter = skeletal muscle surrounding urethra as it passes thru pelvic floor

29
Q

Male vs Female urethra

A

Female = 3-4 cm

  • tightly bound to anterior vaginal wall
  • external urethral orifice = anterior to vaginal opening and posterior to clit

Male has 3 parts
Prostatic = 2.5 cm within prostate
Intermediate part of urethra = 2 cm and passes thru urogenital diaphragm
Spongy urethra = 15 cm and passes through penis, opening at external urethral orifice

30
Q

micturition: definition and 3 processes

A

urination or voiding

  1. contraction of detrusor by ANS
  2. opening of internal urethral sphincter by ANS
  3. Opening of external urethral sphincter by somatic nervous system
31
Q

Micturition: reflexive urination (in infants)

A

Distension of bladder activates stretch receptors

Excitation of parasympathetic neurons in reflex center in sacral region of spinal cord

Contraction of detrusor

Contraction (opening) of internal sphincter

Inhibition of somatic pathways to external sphincter, allowing its relaxation (opening)

32
Q

Neural control of micturition

A

Pontine control centers mature between ages 2 and3

Pontine storage center inhibits micturition

  • Inhibits parasympathetic pathways
  • Excites sympathetic and somatic efferent pathways

Pontine micturition center promotes micturition

  • Excites parasympathetic pathways
  • Inhibits sympathetic and somatic efferent pathways

Anatomy and Physiology (50 decks)

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