BIOL 204 Flashcards

Flashcards from Urinary System and Fluid, Electrolyte, and Acid-Base Balance Lecture Notes

Urinary System Functions

Maintenance of internal environment, filtering blood, acid/base balance, renin production, erythropoietin production, Vitamin D metabolism.

Organs of the Urinary System

(2) Kidneys (manufacture urine), (2) Ureters (transport urine), (1) Urinary bladder (stores urine), (1) Urethra (carries urine to surface).

Nephron

Functional unit of the kidney; microscopic epithelial tubes that filter blood and manufacture urine; about one million per kidney

Nephron Portions

Glomerulus, Loop of Henle, Glomerular (Bowman's) capsule, Distal Convoluted Tubule, Proximal Convoluted Tubule, Collecting Duct

Renal Corpuscle

Glomerulus + Bowman's capsule

Cortical Nephrons

Glomerulus in cortex, peritubular capillaries, short nephron loop

Juxtamedullary Nephrons

Glomerulus at cortex-medulla junction, vasa recta, long nephron loop; function in concentrating urine

Nephron Functional Anatomy

Renal corpuscle + renal tubule = nephron; Renal tubule consists of PCT, nephron loop, DCT

Urine Formation

1. Glomerular filtration, 2. Tubular reabsorption, 3. Tubular secretion

Glomerular Filtration

Materials are filtered from the blood of the glomerulus into the lumen of the glomerular capsule; driven by glomerular hydrostatic pressure

Filtration Membrane

Plasma filtered from capillary into renal tubule through this membrane; consists of structures of the renal corpuscle; adaptations to promote filtration

Filtrate

Fluid that collects in the lumen of the glomerular capsule as a result of filtration; plasma minus large proteins

Net Filtration Pressure (NFP)

Drives filtration; depends on Glomerular Hydrostatic Pressure (GHP), Blood Osmotic Pressure (BOP), and Capsular Hydrostatic Pressure (CHP). NFP = [HP g] – [OP g + HP c]

Glomerular Filtration Rate (GFR)

Amount of fluid filtered into the glomerular capsule per unit time; influenced by NFP, surface area of filtration membrane, and permeability

Autoregulation of GFR

Protects glomerulus during high blood pressure; maintains GFR during low blood pressure; includes myogenic response and juxtaglomerular feedback mechanism

Myogenic Response

Increased pressure in afferent arteriole leads to vasoconstriction, decreasing NFP and GFR.

Juxtaglomerular Apparatus (or Complex)

Modified ascending tubule & afferent arteriole having granular, macula densa, and mesangial cells; helps regulate GFR and systemic blood pressure

Granular Cells

Modified smooth muscle cells of afferent arteriole; mechanoreceptors that sense BP and secrete renin

Macula Densa Cells

Cells of the ascending limb of the loop of Henle; chemoreceptors for filtrate [NaCl]

Tubuloglomerular Feedback

Macula densa provides feedback to the glomerulus to regulate GFR based on filtrate osmolarity

Renin-Angiotensin-Aldosterone Mechanism

Extrinsic control to maintain systemic blood pressure; stimulus is decreased BP; response is increased BP

Tubular Reabsorption

Filtered substances reabsorbed into peritubular capillaries as filtrate moves through renal tubule

PCT Reabsorption

Most reabsorption takes place here by active (primary/secondary) and passive (diffusion, osmosis) transport

Obligatory Water Reabsorption

Water reabsorption in the PCT (due to aquaporins)

Facultative Water Reabsorption

Water reabsorption in the DCT and CD (no aquaporins normally)

Tubular Secretion

Transfer of molecules from peritubular capillaries to the lumen of the renal tubule

Countercurrent Multiplier Mechanism

Juxtamedullary nephrons helps create urine that is hypertonic to the blood. Osmolarity: The number of particles (ions or intact molecules) per liter of solution

Descending limb of the nephron loop

Water permeable, salt impermeable; H2O moves out of the filtrate into the interstitium

Ascending limb of the nephron loop

Na+ and Cl- are transported into interstitium in the thick segment; not H2O permeable

Vasa Recta

Long, capillary-like vessels that parallel the loops of Henle; permeable to both NaCl and H2O; preserve osmotic gradient of the medulla

Antidiuretic Hormone (ADH)

Triggers the insertion of aquaporin (water channels) into cells of the collecting duct.

Urea Recycling

Urea diffuses out of the terminal portion of the CD into the medulla, then into the ascending limb of loop of Henle; urea permeability is enhanced by ADH in the terminal portion of CD

Normal Urine

Volume: 1-2 liters/day; Color: pale to deep yellow (urochrome); Odor: slightly aromatic; pH: 4.5 – 8 (averages 6); Specific gravity 1.001 – 1.035

Micturition

Detrusor muscle contracts, internal urethral sphincter opens, external urethral sphincter opens to void urine.

Total Body Water

Adult males 57-63%, adult females 50%, infants 73% of weight

Fluid Compartments

Intracellular (2/3 of TBW) and extracellular (1/3 of TBW, includes plasma, interstitial fluid, etc.)

Functions of H2O

Medium for reactions, impacts ion concentration, transports hormones/nutrients/gases/wastes, distributes heat.

Electrolytes

Solutes that dissociate into ions in water (acids, bases, salts, some proteins)

Non-electrolytes

Do not dissociate into ions in water (glucose, amino acids, lipids, vitamins)

Water Intake Regulation

Regulated by thirst mechanism (plasma osmolality, plasma volume, dry mouth)

Sodium (Na+)

Most abundant in ECF; osmotic pressure, neuromuscular function; regulated by aldosterone

Potassium (K+)

Most abundant in ICF; neuromuscular function, protein synthesis, acid-base balance; regulated by aldosterone and pH.

Calcium (Ca2+)

Most in skeleton; skeleton strength, blood clotting, neurotransmitter release, muscle contraction; regulated by parathyroid hormone

Chloride (Cl-)

ECF; activates enzymes, maintains osmotic pressure; regulated by aldosterone

pH Scale

Extends from 0-14, acidity is dependent on concetration of free H+ ions, where 7 is neutral

Acidosis

Plasma pH < 7.35, neurons less excitable, CNS depression

Alkalosis

Plasma pH > 7.45, neurons more excitable, CNS hyperexcitability

Buffer Systems

Prevent rapid pH changes; most are weak acid and anion of that acid; proteins, phosphate, bicarbonate

Ventilation in Lungs and Acid/Base Status

Plasma H2CO3 concentration depends on pCO2: CO2 + H2O ↔ H2CO3

Renal Function and Acid Base Balance

Kidneys alter pH by secreting/reabsorbing H+ and HCO3-

Respiratory Acidosis (Alkalosis)

Lungs control H2CO3

Metabolic Acidosis (Alkalosis)

Kidneys control HCO3-