BIOL: Exam 4

function of kidneys

major excertiry organ, maintain the body’s internal enviornment by:

• regulating total water volume and total solute concentration in water

• regulating ion concentrations in extracellular fluid

• ensuring long-term acid-base balance

• excreting metabolic wastes, toxins, drugs

• producing erythropoietin (RBC production) and renin (blood pressure)

urinary system includes

kidneys

ureters: transport urine from kidneys to urinary bladder

urinary bladder: temporary storage reservoir for urine

urethra: transports urine out of the body

location of kidney

retroperitoneal, in the superior lumbar region

• located between T12 and L3

the right kidney is crowded by the liver, so it is lower than the left

adrenal gland sits atop each kidney

medial surface has renal hilum

• ureters, renal blood vessels, lumphatics, and nerves enter and exit at hilum

kidney damage

upper parts of both kidneys are protected by thoracic cage but lower parts of kidenys are susceptible to blunt trama

• especially right kidney

• ex: falls, motor vehicle accidents, or contact sports injuries

hematuria

blood in urine

it is an important sign of kidney trauma

internal anatomy of kidney

renal cortex: superficial region

renal medulla: deep to cortex, composed of cone-shaped medullary (renal) pyramids

renal pelvis: continuous w/ ureter

• minor calyces: cup-shaped areas that collect urine draining from pyramids

• major calyces: collect urine from minor calyces; empty urine into renal pelvis

urine flow

renal pyramidl→minor cavity→major calyx→ renal pelvis→ ureter

pyelonephritis

infection or inflammation of entire kidney

• infections in females are usually caused by fecal bacteria entering urinary tract

• UTI (E. coli)

Severe cases can cause swelling of kidney and abscess formation, and pus may fil the renal pelvis

If left untreated, kidney damage my result

Normally is sucessful treated with antibiotics

blood supply

kidneys filter blood and adjust its composition, so it has a rich blood supply

renal arteries deliver about ¼ of cardiac output to kidneys each minute

nephrons

are the structural and functional units that form urine

what are the two parts of the renal corpusce

1. glomerulus

   tuft of capillaries

   • highly porous

   • allows for efficient filtrate formation

     • filtrate: plasmaderived fluid that renal tubules process to form water

glomerular capsule

also called bowmans’s capsule; cup-shaped, hollow structure surrounding glomerulus

afferent arterioles

terminal branch of renal artery

brings blood into glomerulus for filtration

Efferent arteriole

recieves substances from blood that now become filtrate

• large macromolecules; proteins, RBCs, WBCs, sigars

• brings back into circulation via peritubular capillaries, renal vein

three major parts of the renal tubule

1. proximal convoluted tubule: closest to renal corpuscle

2. nephron loop: ascending and descending limbs

3. distal convoluted tubule: farthest from renal corpuscle

distal convoluted tubule drains into which duct

collecting duct

peritubular capillaries

low-pressure, porous capillaries adapted from absorption of water and solutes

arise from efferent arterioles

empty into venules

each nephron has how many juxtaglomerular apparatus(s)

1

juxtaglomerular apparatus involves modified portions of

distal convoluted tubule:

• contains macula densa

• controls the salt (NaCl) content of blood/urine

afferent artiole:

• juxtaglomerular cells produce renin

imporant in regulation rate of filtrate formation and blood pressure

physiology of kidney

180L of fluid processed daily, but only 1.5 L of urine is formed

kidneys filter body’s entire plasma volume 60 times each day

consume 20-25% of oxygen used by body at rest

filtrate (produced by glomerular filtration) is basically blood plasma minus proteins

urine is produced from filtrate

• urine

  • <1% of original filrate

  • contains metabolic wastes and unneeded substances

three proceses are involved in urine formation and adjustment of blood composition

1. glomerular filtration: produces filtrate void of cells and proteins

2. tubular reabsorption selectively returns 99% of substances from the filtrate of blood

3. tubular secretion: selectively moves substances from blood to filtrate

   • substance excreted into urine

glomerular filtration

a passive process

hydrostatic pressure forces fluids and solutes through the filtration membrane into the glomerular capsule

• water, glucose, amino acids, nitrogenous wastes are filtered

• proteins and cells cannot pass through (normally)

  • proteins remain in the blood to maintain osmotic pressure

  • whole cells (ex: RBC’s) too big to slip through golmerular capillaries filter

glomerular filtration rate (GFR)

volume of filtrate formed per minute by both kidneys (normal= 120-125 ml/min)

*dont need to memorize number for exam

GFR is directly proportional to

1. net filtration pressure (NFP): primary pressure is glomerular hydrostatic pressure

2. total surface area available for filtration

3. filtration membrane permeability: much more permeable than other capillaries

regulation of glomerular filtration

renin-angiotensin-aldosterone mechansim

• main mechanism for increasing blood pressure

• three pathways to renin release

  1. direct stimulation by the sympathetic nervous system

  2. stimulation by activated macula densa cells when filtrate NaCl concentration is low

  3. reduced stretch of juxtaglomerular cells

anuria

abnormally low urinary output (less than 50ml/day)

may indicate that glomerular blood pressure is too low to cause filtration

renal failure and anuria can also result from situations in which nephrons stop functioning

• ex: acute nephritis, transfusion reactions

tubular reabsorption

quickly reclaims most of the tubular contents and returns them to blood

selective process

• almost all organic nutrients and reabsorbed

  • glucose, amino acids, water, vitamins/minerals

  • key electrolytes: Na+, K+, Ca2+, Mg2+

• water and ion reabsorption is hormonally regulated and adjusted

sodium transport across the membrane

Na+ is most abundant cation in filtrate

Na+-K+ ATPase pumps Na+ into the interstitial space

Na+ is then swept by bulk flow into peritubular capillaries

transport maximum

exists for almost every reabsorbed substance

when carriers for a solute are saturated, the excess is excreted in urine

• ex: hyperglycemia leads to high blood glucose levels that exceed Tm, and glucose spills over into urine

proximal convoluted tubule

site of most reabsorption

• all nutrients, such as glucose and amino acids, are reabsorbed

• 65% of Na+ and water reabsorbed

• many ions

• almost all uric acid

• about half of urea (later secreted back into filtrate)

nephron loop (loop of henle)

descending limb: H2O can return to blood, solutes cannot

ascending limb: H2O stays, solutes diffuse out and return to blood

distal convoluted tubule and collecting duct

reabsorption is hormonally regulated in these areas

antidiuretic hormone (ADH)

released by posterior pituitary gland

causes collecting ducts to insert aquaporins in membranes, increasing water reabsorption

• increased ADH levels cause an increase in water reabsorption

aldosterone

targets collecting ducts and DCT

promotes synthesis of Na+ and K+ channels, and Na+-K+ ATPases for Na+ reabsorption (water follows)

as a result, little Na+ leaves body

without aldosterone, the daily loss of filtered Na+ would be 2%, which is incompatible with life

functions: increase blood pressure and decreases K+ levels

• causes K+ to be excreted more into the urine and lost

ANP (atrial natriuretic peptide)

reduces blood Na+, resulting in decreased blood volume and blood pressure

released by cardiac atrial cells if blood volume or pressure is elevated

PTH (parathyroid hormone)

acts on DCT to increase Ca2+ reabsorption

tubular secretion

reabsorption in reverse

selected substances are moved from peritubular capillaries into filtrate

• K+, H+, NH4+, creatinine, organic acids and bases

tubular secretion is important for…

disposing of substances, such as drugs or metabolites, that are bound to plasma proteins

eliminating undesirable substances that were passively reabsorbed (ex: urea and uric acid)

ridding body of excess K+(aldosterone effect)

controlling blood pH by altering amounts of H+ or HCO3- in urine

regulation of urine concentration and volume

one main function of kidneys is to make any adjustment needed to maintain body fluid osmotic concentration

• osmolaity: number of solute particles in 1kg of H2O

kidneys produce only small amounts of urine if the body is dehydrated or dilute urine if overhydrated

urinalysis

urine is examined for signs of disease

• can also be used to test for illegal substances

assessing renal function requires both blood and urine examination

• ex: renal function can be assessed by measuring nitrogenous wastes in blood and urine are required

• to determine renal clearance, both blood and urine are required

renal clearance

volume of plasma kidneys can clear a particular substance in a given time

renal clearance tests are used to determine GFR =

• to help detect glomerular damage

• to follow progress of renal disease

chronic renal disease

defined as a GFR <60 ml/min for 3 months

• filtrate formation decreases, nitrogenous wastes accumulate in blood, pH becomes acidic

• seen in diabetes mellitus and hypertension

renal failure

defined as GFR <15 ml/min

causes uremia: ionic and hormonal imbalances, metabolic abnormalities, toxic molecules accumulation

symptoms: fatigue, anorexia, nausea, mental changes, cramps

treatement: hemodialysis or transplant

urine

chemical composition: 95% water and 5% solutes

• nitrogenous wastes

  • urea (from amino acid breakdown): largest solute component

  • uric acid (from nucleic acid metabolism)

  • creatinine (metabolite of cretine phosphate)

• other normal solutes found in urine

  • Na+, K+, PO4³-, and SO4²-, Ca²+, Mg²+, and HCO3-

what indicates pathology in urine

abnormally high concentrations of any constituent, or abnormal components such as blood proteins, WBCs, and bile pigments, may indicate pathology

physical characteristcs of urine

color and transparency

• clear

  • cloudy may indicate urinary tract infection

• pale to deep yellow from urochrome (urobilin)

  • pigment from hemoglobin breakdown

  • yellow color deepens with increased concentration

• abnormal color (pinky, brown, smoky)

  • can be caused by certain foods, bile pigments, bloodm drugs

odor of urine

slightly aromatic when fresh

develops ammonia odor upon standing as bacteria metabolize urea

may be altered by some drugs or vegetables (asparagus)

disease may alter smell

• patients with diabetes may have acetone smell to urine

pH of urine

urine is slightly acidic (~pH 6, with range of 4.5 to 8.0)

acidic diet (protein, whole wheat) can cause drop in pH

alkaline diet (vegetarian), prolonged vomitingm or urinary tract infections can cause an increase in pH

ureters

slender tubes that convey urine from kidneys to bladder

• begin as a continuation of renal pelvis

retroperitoneal

enter base of bladder through posterior wall

• as bladder pressure increases, distal ends of ureters close, preventing backflow of urine

renal calculi

kidney stones in renal pelvis

• crystallized calcium, magnesium, or uric acid salts

large stones can block the ureter, obstructing urine flow and causing excruciating pain from the flank to the abdomen

mephrolithiases- stone in kidneys

ureterolithiasis- stone lodged in ureters

most small stones pass without intervention

larger stones or those lodged in the ureter can be removed endoscopically or surgically

many kidney calculi can be treated with lithotripsy

• procedure that uses acoustic wave energy to break stones so they pass more easily

• risk factors: obesity and elevated blood calcium levels

• prevention: adequate hydration

urinary bladder anatomy

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

has openings for ureters and urethra

• trigone

  • smooth triangular area outline by openings for ureters and urethra

  • infections tend to persist in this region

urine stroage capacity

collapses when empty

rugae appear

expands and rises superiorly during filling without a significant rise in internal pressure

moderately full bladder is 5 in long and can hold ~500 ml (1 pint)

• can hold twice that amount if necessary but can burst if overdistended

urethra

muscular tube that frains urinary bladder

the female urethra is only 1-1.5 in long

male urethra carries semen and urine and is about 20 cm (7-8in)

sphincters o the urethra

sphincters

• internal urethral sphincter

  • involuntary (smooth muscle) at bladder-urethra junction

  • contracts to open

• external urethral sphincter

  • voluntary (skeletal) muscle surrounding urethra as it passes through pelvic floor

three regions of the male urethra

prostatic urethra: (2.5cm): within prostate

membranous urethra (2cm): passes through urogenital diaphragm from prostate to beginning of penis

Spongy urethra (15 cm): passes through penis; opens via external urethral orifice

causes of urinary tract infections

improper toilet habits, such as wiping back to front after defecation

• short urethra of females can allow fecal bacteria to easily enter urethra

most UTIs occur in sexually active women

• 40% of women get urinary tract infections

• intercourse drives bacteria fro vagina and external genital region toward bladder

urethritis

inflammation of urethra

cystitis

baldder infection

pyelonephritis

kidney infection

symptoms of urethritis, cystitis, and pyelonephritis

dysturia (painful urination), urinary urgency and frequency, fever, and sometimes cloudy or blood-tinged urine

treatment for urethritis, cystitis, and pyelonephritis

antibiotics can cure most urinary tract infections

micturition

also called urination or voiding

three simultaneous events must occur

• contraction of detrusor muscle by ANS (involuntary)

• opening of internal urethral sphincter by ANS (involuntary)

• opening of external urethral sphincter by somatic nervous system (voluntary)

pontine (pons) control centers mature between ages 2 and 3

urinary incontinence

in adults, usually caused by weakened pelvic muscles

• stress incontinence

  • increased intra-abdominal pressure forces urine through external sphincter

  • laughing, coughing, or sneezing can cause incontinence

• overflow incontinence

  • urine dribbles when bladder overfills

urinary retention

bladder is unable to expel urine

causes;

• common after general anesthesia

• hypertrophy of prostate (benign prostatic hyperplasia- “BPH”)

treatment: catheterization, medications

body water content

infants are 73% or more water (low body fat, low bone mass)

adult males: ~60% water

adult females: ~50% water

• higher adipose content, less skeletal muscle mass (typically)

• adipose tissue is lease hydrated of all

water content declines to ~45% in old age

body fluid compartments

two main fluid compartments

• intracellular fluid (ICF): fluid inside cells (cytoplasm)

  • 2/3 of total body fluid

• extracellular fluid (ECF): fluid outside cells

  • 1/3 of total body fluid

    • plasma (intravascular)

    • intersitiial fluid (IF): in spaces between cells

      • lymph, CSF, eye humor (fluids), synovial fluid, serous fluid, and gastrointestinal secretions

composition of body fluids

water is the universal solvent

solutes are substances dissolved in water

solutes are clasified as non-electrolytes and electrolytes

non-electrolytes: most are organic molecules

• do not dissociate in water

• glucose, proteins and amino acids, lipids, creatine, and urea (waste)

electrolytes

dissociate into ions in water

• inorganic salts, all acids and bases, some proteins

• NaCl → Na+ + Cl-

• KCl → K+ + Cl-

ions conduct electrical current

• greater osmotic power than non-electrolytes

  • water moves to the area with greater solute (electrolyte) concentration

ECF vs ICF

comparison of extracellular and intracellular fluids

• each fluid compartmet has a distinctive pattern of electrolytes

• ECF: electrolyte contents mostly all similar

  • major cation: sodium (Na+)

  • major anion: chloride (Cl-)

  • plasma (diffused from blood): increase protien, decrease Cl-

• ICF: contains more solube proteins than plasma

  • low Na+ and Cl-

  • major cation; potassium (K+)

  • major anion: hydrogen phosphate (HPO4²-)

movement of fluid

regulated by osmotic and hydrostatic pressures

• water moves freely along osmotic gradients

  • toward the area of greater solute concentration

• change in solute concentration of any compartment leads to net water flow

  • increase ECF osmolaroty → water leaves cell into interstitial fluid (IF)

  • decrease ECF osmolarity → water enters cell from interstitial flid (IF)

    • i.e., decrease extracellular sodium (hypoatremia)

water intake and output

water intake must equal water output:

• ~2500ml/day

water intake: most ingested

• some from metabolism (Krebs and electron transport chain (ETC))

water output:

• urine (60%)

• insensible water loss (lost through skin and lungs)

• perspiration (sensible)

• feces

disorders of water balance

dehydration

• ECF water loss due to hemorrhage, severe burns, prolinged vomiting or diarrhea, profuse sweating, water deprivation, diuretic abuse, endocrine disturbances (lack of ADH- “diabetes insipidus)

• signs and symptoms: “cottony” oral mucosa, thirst, dry flushed skin, oliguria

  • oliguria = “reduced or low urine output”

• may lead to weight loss, fever, mental confusion, hypovolemic shock, and loss of electrolytes

edema

atypical accumulation of interstitial fluid resulting in tissue swelling (not cell swelling)

• can impair tissue function by increasing distance from diffusion of oxygen and nutrients from blood into cells

  • could be caused by increased fluid flow out of blood (hydrostatic) or decreased return of fluid (osmotic) to blood