BSC2086L Lesson 9

urinary system

responsible for removing nitrogenous wastes from body

kidneys

major homeostatic organ of body that filters blood to remove metabolic wastes, toxins, and excess ions

kidney functions

remove nitrogenous wastes from blood stream, maintain fluid balance, maintain electrolyte (ion) balance, maintain acid-base balance

urinary bladder

reservoir for urine until micturition; contains rugae so bladder can stretch as it fills with urine

ureters

transports waste fluids from kidneys to urinary bladder

urethra

connects bladder to external environment

trigone

triangular area delineated by the openings of the ureters and urethra

renal cortex

outer portion of kidney

renal medulla

inner portion of kidney, contains the renal pyramids (papilla/apex faces calyx)

blood flow through kidneys

Descending Aorta → Renal Arteries → Segmental Arteries (enters kidney) → Interlobar Arteries → Arcuate arteries → Cortical Radiate Arteries → Afferent Arterioles (capillary beds where blood filtration occurs) → Cortical Radiate Veins→ Arcuate Veins → Interlobar Veins → Renal Vein

nephrons

function units of kidney that are usually found within cortex (cortical nephrons), but some have parts of the loop of Henle in the medulla (juxtamedullary nephron)

glomerulus

a capillary 'knot' formed by the afferent arteriole where blood is filtered

renal tubule

forms the glomerular (Bowman's) capsule, proximal and distal convoluted tubules, and loop of Henle

Bowman's capsule

surrounds glomerulus; visceral (inner) wall composed of podocytes

podocytes

cells in the Bowman's capsule that form porous membrane so fluid can pass through

collecting duct

fluids/ions pass through when not reabsorbed from renal tubule and dumps urine into calyces and pelvis of kidneys

afferent arteriole

has high pressure/resistance and large diameter

efferent arteriole

draining glomerulus also has high resistance but smaller diameter

net result of glomerulus filtration

high hydrostatic pressure forces fluid and small proteins out of afferent arteriole/glomerulus into glomerular capsule (this fluid is called the filtrate)

peritubular capillary bed

low pressure porous capillary network formed from efferent arteriole that leaves the glomerulus; in close proximity to renal tubule to reabsorb H2O and ions (juxtamedullary nephrons also have vasa recta to help reabsorb fluids/ions)

juxtaglomerular apparatus region

functions to concentrate urine

juxtaglomerular cells

in arteriole walls sense blood pressure

macula densa

area of specialized columnar chemoreceptors cells in distal convoluted tubule

urine formation processes

filtration, reabsorption, secretion

filtration

passive process in glomerulus

reabsorption (tubular)

active & passive (by osmosis) process; 75-80% occurring in proximal convoluted tubule; highly selective (glucose, amino acids and some ions reabsorbed); filtrate components reabsorbed thru tubule wall and into peritubular capillaries

secretion

substances not filtered in glomerulus (left in the blood) are secreted from peritubular capillaries and absorbed into tubules

micturition (emptying bladder) is controlled by:

internal urethral sphincter and external urethral sphincter

internal urethral sphincter

composed of smooth muscles (involuntary)

external urethral sphincter

composed of skeletal muscles (voluntary) - located at the urogenital diaphragm

color of urine

clear/pale yellow to amber (yellow color from urochrome pigment from hemoglobin destruction)

odor of urine

depends on foods, drugs, etc. (diabetes mellitus - urine smells fruity/ acetone-like)

pH of urine

4.5-8.0 depends on diet, disease

specific gravity of urine

1.001-1.030 depends on solutes dissolved in urine

more solutes increase

specific gravity

high specific gravity causes:

kidney stones (renal calculi)

urine concentration caused by:

fever, limited fluid intake, kidney inflammation (pyelonephritis)

solutes in urine

urea (from breakdown of proteins), sodium, potassium, phosphate, and sulfate ions, creatinine (from skeletal muscles), and uric acid (from nucleic acid breakdown)