anatomy 2 content before finals

glomerular filtration rate

amt of filtrate formed by BOTH kidneys per minute, average GFR is 125 mL/min in males and 105 mL/min in females

homeostasis requires kidneys to maintain a relatively constant GFR

high - substance pass too quickly and not reabsorbed

low- nearly all filtrate reabsorbed and some waste not excreted

directly related to pressures that determine net filtration pressure, when system bp rises, net filtration pressure and GFR only increase a little bit

coltrolled by renal autoregulation, neural regulation and hormonal regulation which adjust blood flow into and out of glomeruus and alter glomerular capillary surface available for filtration

renal autoregulation of GFR

keep stable pressure in kidneys and thus- GFR, intrinsic mechanism with the kidneys consisting of the myogenic mechanism and tubuloglomerular feedback

myogenic mechanism- stretching causes contraction of smooth muscle in wall of afferent arteriole

tubuloglomerular feedback- as macula densa provides feedback to the glomerules

• high GFR diminishes reabsorption of Na and Cl

• macula densa inhibits release of nitric oxide

• afferent arterioles contract

neural regulation of GFR

kidneys supplied by sympathetic fibers, excersize and hemorrage trigger sympathetic stimulation and afferent arterioles constricted so urine output is reduced and blood is available for other organs, ANS fibers release norepinephrine on alpha 1 receptors causing vasoconstriction

hormonal regulation of GFR

through the action of angiotensin ll and atrial natriuretic peptide, ANP increases GFR

• ANP secreted in response to stretch of cardiac atria

• increased urine formation leads to decreased blood volume and pressure to promote sodium and water loss

• angiotensin ll constricts afferent and efferent arterioles- decreasing GFR

• RAAS (renin angiotensin aldosterone system)

  • increases systemic arterial presssure and increases sodium absorption

  • renin: enzyme formed and stored in afferent arterioles of the juxtaglomerular apparatus

  • renin helps for angiotensin 1 (physiologically inactive)

  • in presence of angiotensin converting enzyme, angiotensin l converted to ll

regulation of GFR summary

tubular reabsorption and secretion

normal rate of GF is so high that the volume of fluid entering PCT in half an hour is greater than the total plasma volume, much of the filtrate is reabsorbed- esp water, glucose, aa and ions, secretion helps to manage pH and rid the body of toxic and foreign

notes for elena (WHAT WAS NOT ON THE SLIDES)

ex- coffee and tea stimulates reabsorption, 99% of water is reabsorbed

DONT memorise table- will be given, 0 absorbtion of creatinine so it is a good test to see if kidneys are secreting

transcellular is an active process (can passively go into cell, need energy to leave)

when all solutes are reabsorbed- high conc of water left which drives water reabsorbtion

tubular reabsorption

returns more of the filered water and many filtered solutes (glucose, aa, ions) to the bloodstream using passive and active transport

tubular secretion

transfer of materials from the blood and tubule cells into tubular fluid, helps control bood pH and helps eliminate other substance from the body

reabsorption routes

substance being reabsorped in the tubule lumen will take one of 2 routes before entering perirtubular capillary

paracellular reabsorption- passive fluid leakage btwn cells

transcellular reabsorption- directly through tubule cells

what causes transport mechanisms

solute reabsorption drives water reabsorption, mechanisms that accomplish Na+ reabsorption in each portion of renal tubule and collecting ducts recover filtered Na+ and also electrolytes, nutrients and water

Transport Mechanisms

Primary active transport

• uses ATP (Na, K pump)

• energy from ATP used to pump substance across membrane

Secondary active transport

• driven by ions electrochemical gradient

• symporters move substances in same direction

• antiporters move substances in opposite directions

water reabsorbtion

renal tubule and collecting duct use osmosis for water reabsorption, abt 90% of filtered water is reabsorbed by kidneys occurs with reabsorption of solutes (obligatory water reabsorption), reabsorption of final water (facultative water reabsorption) based on need and occurs in collecting ducts and regulated by ADH

reabsorption of PCT

majority of solute and water reabsorption, mostly involves Na, reabsorption of Na and other solutes creates osmotic gradient that promotes reabsorption of water by osmosis

Secretion of PCT

ammonia is waste produced by hepatocytes- convert ammonia to urea, both are filtered at glomerulus and secreted by PCT cells into tubules. PCT cells can produce additional NH3 and NH4+ as needed

reabsorption in the nephron loop

set stage for independent regulation of both the volume and osmolarity of body fluids, relatively impermeable to water esp in the ascending limb, little obligatory water reabsorption

reabsorption and secretion in the DCT and Collecting Duct

Summarise 37, 38

tubular transport summary

homeostatic regulation of tubular reabsorption and secretion

key hormones secreted by renal tubules

RAA- angiotensin ll increases blood volume and pressure, regulated electrolyte reabsorption and secretion along with aldosterone which also increases reabsorption of water in the collecting duct

ADH- antidiuretic hormone, regulated facultative water reabsorption by increasing the water permeability of principal cells

ANP- atrial natriuretic peptide, can inhibit both water and electrolyte reabsorption

PTH- parathyroid hormone, promotes calcium reabsorption

Urine production

fluid intake is highly variable, homeostasis requires maintenance of fluid volumes within specific limits, rate at which water is lost depends on ADH- controls water permeability of principal cells in collecting duct (and in last portion of DCT)

high intake of fluid = dilute urine of high volume

low intake of fluid = concentrated urine of low volume

Urine concentration

formation of dilute urine

when ADH level is very low, kidneys produce dilute urine and excrete excess water- renal tubules absorb more solutes than water, tubular fluid progressively becomes more dilute as it flows- can be as low as 65-70 mOsm/liter

Thick ascending limb

• symporters actively reabsorb Na+, K= and Cl-

• low water permeability

• solutes leave, water stays in tubule

collecting duct

• low water permeability in absence of ADH

Formation of concentrated urine

when ADH level is high, kidneys secrete concentrated urine to conserve water, large volume of water is reabsorped from tubular fluid into interstitial fluid,

ascending limb cells of nephron loop- establish osmotic gradient in renal medulla

collecting ducts- absorbing more water and urea

urea recycling causing a build up of urea in renal medulla

* 2 types of countercurrent mechansims

involves juxtamedullary nephrons with long nephron loops, osmotic gradient created by countercurrent multiplier, colutes pump out of ascending limb but water stays in tubule, medulla osmolarity is increased

in presence of ADH- collecting ducts are very permeable to water- tubular fluid becomes very concentrated

movement of water carries urea to the medulla, contributing to its osmolarity

2 types of countercurrent mechanisms

countercurrent multiplication- progressively increasing osmotic gradient is formed in interstitial fluid of renal medulla as a result of countercurrent flow

countercurrent exchange- solutes and water are passively exchanged btwn blood of vasa recta and interstitial fluid of renal medulla as a result of countercurrent flow

countercurrent exchange

nephron loop and duct cells need nutrients and coygen from blood, capillaries (vasa recta) form loops like those of nephron loops in medulla, solutes and water are passively exchanged btwn blood of vasa recta and interstitial fluid of renal medulla as a result of countercurrent flow

incoming and outgoing blood have similar osmolarity which maintains medulla concentration gradient

urinalysis

an analysis of the volume and physical, chemical and microscopic properties of urine called urinalysis reveals info abt the body, analysed by hospital/clinic lab or using reagent stripts (dipsticks)

ex- color, odor, pH, etc

evalutes for presence of abnormalities: albumin, glucose, rbc, ketone bodies, microbes

normal urinalysis findings

abnormal constituents in urine

blood tests providing info abt kidney function

blood urea nitrogen (BUN)

plasma creatine

blood urea nitrogen test

measures blood nitrogen part of the urea resulting from catabolism and deamination of amino acids, when glomerular filtration rate decreases severly (may occur with renal disease or obstruction of uritnary tract) the BUN rises steeply

varies with protein intake and protein catabolism, better indicator for hydration status (increases in dehydration and kidney failure), adult normal range is 8-26 mg/dl (3.6-7.1 mmol/L)

Plasma creatine

normal value (0.5-1.2 mg/dL or 15.3-76.3 umol/L)

value above 1.5 indicates poor renal function, creatinine produced by muscles, most valuble for monitoring progress of chronic (not so much acute) renal disease, measures progressive renal dysfunction

renal plasma clearance

determines how much of a substance can be cleared from the blood by the kidneys during a given unit of time, permits indirect meaure of GFR, tubular secretion, tubular reabsorption and renal blood flow, clearance in INULIN gives the glomerular filtration rate, clearance of para-aminohippuric acid gives rate of renal plasma flow

GFR vs creatinine clearance

GFR- best estimate for the functioning of renal tissue, uses INULIN (fructose polysaccharide)

Creatinine Clearance- estimate of GFR, only one blood sample is required in addition at a 24 hr volume of urine (normal- 120-140 mL/min)

urine transportation and storage

urine drains through papillary ducts into minor calyces which join to become major calyces that unite to form renal pelvis, then drain into the ureters, then bladder then urethra

ureters

each ureter transports urine from a renal pelvis by peristaltic waves, hydrostatic pressure and gravity, ureters are retroperitoneal and consist of a mucosea, muscularis and adventitia

bladder

no anatomical valve at opening or ureter to bladder, when bladder fills it compresses the opening to prevent backflow, bladder is hollow muscular organ posterior to pubic symphysis (700-800 mL capacity)

floor of bladder is a small smooth triangular area called the trigone, ureters enter bladder near posterior points in trigone, the urethra drains bladder from anterior part of trigone

bladder histology

mucosa (mucuosal folds), lamina propria, muscularis (detrusor muscle) and adventitia/serosa)

area around opening of urethra- the circular fibers of the muscularis form the internal urethral sphincter

below the internal sphincter is the external urethral sphincter, which is composed of skeletal (voluntary) muscle

micturition reflex

urine expelled through bladder by act called micturition (urination or voiding), voluntary and involunatary muscle contractions, when volume reaches 200-400mL- strethc receptors in bladder wall transmit impulses to initiate spinal micturition reflex, older children and adults may initiate or inhibit micturition volunarily

urethra

tube carrying urine from internal urethral orfice to the exterior of body, wall of urethra has 3 coats in females and 2 coats in males, urethra discharges urine as well as duct and ejaculation of semen in males,

waste management in other body systems

buffers- bind H+ to manage acidity

blood- transports waste

liver- metabolic recycling- turns toxic substances less toxic (ammonia and urea)

lungs- CO2, H2O and heat

sweat glands- heat, water, CO2, salts and urea

GI- solid undigested foods, waste, CO2, H2O, salts and heat

aging and urinary system

after 40 effectiveness of kidnyes decreases, kidneys shrink, decrease blood flow to kidneys bc glomerular vessels are damaged or fewer, decrease in filtration, increased bladder symptoms (urgency, frequency, nocturia), decreased elimination of drugs

renal calculi

kidney stones, crystals of calcium oxalate, uric acid, calcium phosphate

glomerular disease

damage to golmerulus and permeability increase: glomerulonephritis (urine contains blood and protein), nephrotic syndrom (urine contains protein)

urinary tract infections

more common in females, painful or burning urination, urgent and frequent urination, low back pain, bed wetting- infections such as urethritis, cystitis, pyelonephritis

renal failure

decrease or cessation of glomerular filtration, acutra renal failure and oliguria/anuria, chronic renal failure, may be caused by low blood volume, decreased cardiac output, kidney stones, contrast dye, NSAIDs, antibiotics, diabetes, liver disease

kidney transplant

kidney from donor to receipent, live or deceased donor, nonfunctioning kidneys left in place

cystoscopy

allow direct examination of urethra, bladder and prostate

body fluids

bodw water + dissolved substances, regulatory mechanisms ensure homeostasis of body fluids since their malfunction may seriously endanger nervous system and organ functioning

body fluid percentages

in adults- 55-60%

infants- 75% (in premature it is higher)

older persons- decreased intracellular fluid

fluid compartments and fluid homeostasis

inside cells (intracellular fluid is called cystol) and outside cells (extracellular fluid is interstitial fliuid (80%) and blood plasma (20%)

selectively permeable membranes seperate fluids

plasma membrane- intracellular fluids from interstitial fluid

blood vessel walls- interstitial fluid from blood plasma

capillary walls- allow exchange of water and solutes btwn blood plasma and interstitial fluid

extracellular fluid

interstitial fluid, intravascular fluid (blood), CSF, pleural, peritoneal, pericardial fluids, sweat, urine, lymph, synovial fluid

fluid balance

means various body compartments contain required amt of water, osmosis is primary way in which water moves in and out of components- determined by solutes, filtratio + reabsorption + diffusion and osmosis allow continous exchange of water and solutes among compartments

solutes in body fluids

mostly electrolytes that dissociate into ions, fluid balance is not just water but also electrolyte balance,

fluid homeostasis

gains water- ingestion and metabolic synthesis

loses water- urination, perspiration, exhalation, feces

osmosis

how water moves btwn intracellular and extracellular fluid compartments

passive transport

occurs when water, solutes and small electrically uncharged molecules move through pores, doesnt require energy, high conc to low conc, osmosis, hydrostatic pressure and diffusion

active transport

larger molecules and molecular complexes, requires energy, moves molecules across concentration gradient, protein mediated, ex- postassium sodium pump

water loss and gain

largest constituent in body, varies from 45-75 percent of body weight depending on age and fat, fluid intake usually equals output so body maintains constant volume

regulation of water gain

metabolic water volume depends mostly on level of aerobic cellular respiration which reflects demand for ATP in body cells, main way to regulate body water balance is by adjusting volume of water intake, when water loss is greater than gain- cause dehydration, stimulation for fluid intake is thirst sensation

thirst sensation

renin angiotensin ll pathway responds to decreased blood volume/pressure and so stimulates the thirst centre in hypothalamus , altered thirst sensation or restricted access to fluids: elderly, infants, confused mental state

dehydration

decrease in volume and an increase in osmolarity of body fluids, triggers osmoreceptors in hypothalamus, volume receptors in atria, baroreceptors in blood vessels, neurons in mouth that detect dryness

regulation of water and solutes lost

mainly depends on urine, amt of urinary salt loss is main factor for determining body fluid volume, main solutes in extracellular fluids are sodium and chloride (wherever solutes go, water follows)

daily water loss

fluid output adjusted by antidiuretic hormone, atrial natriuretic peptide, angiotensin ll and aldosterone,

control Na and Cl: angiotensin ll, aldosterone, ANP

control water loss: ADH

ADH

released when there is an increase in plasma osmolarity or decrease in circulating blood volume, acts on kidney to promote reabsorption of water

Aldosterone

increased reabsorption of sodium by distal tube of kidney

ANP

regulation of water and solute loss summary

movement of fluids btwn body fluid compartments

fluid imbalance btwn intracellular and interstitial fluids can be caused by a change in their osmolarity, most often a change is due to change in Na+ conc.

when extracellular fluid is isotonic to cells of body- cells dont swell or shrink, however changes in the osmolarity can cause shrinking or swelling of cells

edema

accumulation of fluid in interstitial spaces, increased risk for tissue damage, can be in extremities heart or lungs, dependent edema, putting edema

causes: image

water intoxication

when water is consumed faster than kidneys can excrete, water intoxication can occur- when excess body water causes cells to swell dangerously

enema

introduction of solution into the rectum to draw water and electrolytes into the colon osmotically, increased volume increases peristalsis which evacuated feces, used to treat constipation, repeated use of enemas can increase risk of fluid and electrolyte imbalances

electrolytes in body fluids functions

1. many of them, so control osmosis of water btwn body compartments

2. maintain acid base balance for normal cellular activities

3. carry electrical current which allows production of APs and GPs and controls secretion of some hormones and neurotransmitters

4. cofactors needed for optimal activity of enzymes

electrolytes in body fluids

dissolved particles in body fluids, electrically charged, ions with opposite charges attract, (mEq/liter), blood plasma, interstitial fluid and intracellular fluids have different conc of elecrolytes and protiens, (blood plasma has many proteins while interstitial fluid has few

know functions of electrolytes

sodium

kidneys excrete most sodium and conserves it during periods of sodium restriction, controlled by ANP and ADH indirectly,

hyponatremia (less than 136 mEq/L)- caused by fluid loss and causes plasma hypoosmolarity and cellular swelling, hypovolemia

symptoms: muscle weakness, dizziness, headahce, hypotension, tachycardia, shock, mental confusion, stupor, coma

hypernatremia (over 148 mEQ/L)- caused by dehydration, excessive sodium and causes water movement from ICF to ECF (intracellular dehydration)

syhmptoms:intense thirst, hypertension, edema, agitation and convulsions