Urinary System

Intracellular fluid (ICF)

fluid inside the cells, 2/3 of all the water in the body

Extracellular fluid (ECF)

fluid outside of cells, 1/3 od all water in the body, plasma and interstitial fluid, includes plasma, interstitial fluid, lymph, cerebrospinal fluid, etc.

Plasma

liquid part of blood

Interstitial fluid

fluid between all cells

Solutes

particles that dissolve in the fluids of our body; can be electrolytes or nonelectrolytes

Electrolytes

dissociate into charged ions in water

Nonelectrolytes

usually formed by covalent bonds and do not dissociate in fluids

Hydrostatic pressure

pressure of fluid in a system

Osmotic pressure

measure of the tendency of a solvent to move into a more concentrated solution

Osmosis

diffusion of water across a membrane

Aquaporins

protein channels in cell membrane that allow water to flow into/out of the cell

Kidney

regulate body water, the concentrations of solutes in the body, acid/base balance, excrete metabolic wastes and foreign substances, produce hormones, converting vit D to active form

Renal hilum

at the medial edge of the kidney, is the connection point of the ureters/renal artery and vein/lymphatics/ and nerves

Perirenal fat capsule

fatty mass that protects the kidneys

Renal fascia

outer dense fibrous connective tissue anchoring the kidney to surrounding structures

Fibrous Capsule

thin layer of dense regular connective tissue surrounding the kidney

Renal cortex

lighter colored outer layer of the kidney that has a granular appearance

Renal medulla

the inner portions of the kidney that are darker in color

Medullary (renal) pyramids

cone shaped tissue that appear striped due to parallel bundles of urine collecting tubes and capillaries

Renal columns

inward extensions of the cortex separating pyramids

Renal lobes

pyramid surrounded by cortical tissue

Renal artery

the branch of the abdominal aorta that supplies the kidneys with 1/4 of the total CO, branches off into every lobe of the kidney

Renal vein

venous blood collected and brought to the inferior vena cava

Nephron

the basic structural and functional unit of the kidney consisting of 2 parts: renal corpuscle and renal tubule

Renal corpuscle

responsible for filtering the blood and forming preurine

Renal tubule

adjusts contents of preurine to form urine; removes 99% of water, adjusts ion levels, adjusts pH

Major calyces

nephrons empty into collecting ducts, collecting ducts empty into minor calyces which then empty into major calyces

Renal pelvis

the connection point of the ureter to the kidney

Ureter

long muscular tubes that transport urine from the kidneys to the urinary bladder

Urinary Bladder

muscular organ that stores urine

Urethra

tube that transmits urine from the bladder to outside the body

Renal corpuscle

composed of glomerulus and a glomerular capsule

Glomerulus (glomerular capillary)

where blood enters the kidney to be turned into urine; a coiled capillary bed between two arterioles

Glomerular capsule (Bowman’s capsule)

collects what comes out of the glomerulus

Proximal convoluted tubule (proximal tubule, PCT)

the first part of the renal tubule attached directly to the glomerular capsule; fluid flows from the capsule into the tubule

Nephron loop (Loop of Henle)

loop of renal tubule where water and solutes are exchanged as it dips into the medulla

Distal convoluted tubule (distal tubule, DCT)

leads from the nephron loop into the collecting duct

Collecting duct

collects from many nephrons and completes the modification of urine

Cortical nephron

85% of all nephrons, located primarily in the cortex with only part of the nephron loop going into the medulla

Juxtamedullary nephron

15% of all nephrons, renal corpuscle is located near the cortex/medulla junction, primary role is to establish osmotic gradient in kidney to make it possible to concentrate urine

Afferent arteriole

carries blood into the glomerulus

Efferent arteriole

leads out of the glomerulus and drains into the peritubular capillary bed

Peritubular capillary

surrounds the PCT and DCT

Vasa recta

efferent arteriole drains into this and is associated with the nephron loop

Glomerular filtration

dumps cell free and protein free blood filtrate into the container (glomerular capsule)

Filtrate

blood derived fluid that will become urine and leave the body

Tubular reabsorption

reclaims what the body needs to keep moving it from the tubule back into the blood at the peritubular capillary

Tubular Secretion

selectively adds to the filtrate moving from the blood to the tubule at the peritubular capillary

Fenestrated capillary

found at the glomerulus, small holes withing and in between the endothelial cells that allows solutes and water to move across the capillary wall

Parietal layer of Bowman’s capsule

simple squamous epithelium, outer layer

Visceral layer of Bowman’s capsule

composed of podocytes with foot processes, inner layer

Podocyte

cells that make up the inner layer of bowmans capsule

Foot processes

the extensions from podocytes that cover the capillaries in a glomerulus

Filtration slit

spaces between the foot processes that allows fluid/solutes to exit the capillaries and flow into the tubules

Filtration membrane

fenestrated endothelium of glomerular capillary, basement membrane, filtration slits

Ultrafiltrate

anything that is in blood plasma except cells and proteins

Hydrostatic pressure

pressure of fluid against the walls of a vessel

Osmotic pressure

pressure exerted by particles in the blood/fluid which tend to pull water into the vessel or space

Osmolarity

the number of particles or solutes in a given volume of water

Proximal convoluted tubule

majority of tubular reabsorption occurs in here; sodium/glucose/amino acids/urea and water follows by osmosis; some secretion occurs of urea and drugs

Descending limb of nephron loop

dips into the medulla of the kidney; have aquaporins that allow water to leave through osmosis

Ascending limb of nephron loop

goes back up into the cortex of the kidney; impermeable to water, actively transport salts out of the tubule into the interstitial space

Distal convoluted tubule and Collecting duct

makes urine more dilute or more concentrated than blood; changes ion concentrations and adjusts pH

Peritubular capillaries

low pressure capillary beds that surround the OCT and DCT; reabsorb most of the solutes and water from the filtrate back into blood

Vasa Recta

low pressure straight capillaries that follow the nephron loop deep into the medulla; maintains osmotic gradient and makes it possible to concentrate urine

Tubular Reabsorption

reclaims what the body needs to keep (almost everything)

Tubular secretion

selectively adds to the waste from the blood outside the tubule

Simple diffusion

the diffusion of fat soluble molecules directly through the phospholipid membrane; concentration gradient required

Osmosis

the diffusion of water through aquaporins (channel protein) or through the lipid bilayer; concentration gradient required

Aquaporin

water

Facilitated diffusion

molecule specific protein channels that bind to the protein causing it to change shape and move the molecule through the membrane; concentration gradient required but is not active so no ATP needed

Primary active transport

sodium potassium pump; ATP is required and works to move molecules against the concentration gradient

Transcellular pathway for reabsorption

solutes enter the cuboidal cell and exits through the basal layer to exit the tubule

Paracellular pathway for reabsorption

water and small solutes move in between the cells to exit the tubule

Transport maximum

the number of transport proteins available in tubule cell membrane; when proteins are saturated, the substance that cannot bind to them is excreted in the urine

Diabetes mellitus

high blood sugar; if transport maximum is exceeded the glucose is excreted in the urine and urine volume is increased

Medullary osmotic gradient

an increasing osmotic gradient extends through the whole renal medulla

Countercurrent multiplier

creates an osmotic gradient through interactions of the two limbs of the nephron loop; filtrate flows in the opposite direction in the two limbs: salt moving out of the ascending limb causes water to leave the descending limb

Countercurrent exchanger

vasa recta; ensure the medullary gradient doesn't get washed away; as salts move out of the ascending loop water leaves the vasa recta in the same area, as water moves out of the descending loop salts move out of the vasa recta

Ureter

used to transport urine from the kidneys to the bladder; 3 layer wall containing mucosa, muscularis and adventitia

Mucosa

transitional epithelium and lamina propria

Transitional Epithelium

creates a barrier; can stretch or flatten depending on the fullness of the bladder

Muscularis

inner longitudinal and outer circular smooth muscle; extensive smooth muscle layers that contract to void urine

Adventitia

out CT layer holding the ureter in place

Peristaltic waves

contractions of the smooth muscle that propels the urine toward the bladder

Urinary Bladder

stores urine; will stretch/expand when filled with urine; 500 to 1000 mL capacity

Detrusor muscle

smooth muscle in bladder wall stretches and thins allowing for increased storage without increasing internal pressure; ANS controls it

Urethra

carries urine out of the body from the bladder; female 3 to 4 cm long, male 20 cm long

Internal Urethral Sphincter

sphincter composed of smooth muscle controlled by ANS

External Urethral Sphincters

sphincter composed of skeletal muscle, voluntarily controlled by somatic NS

Micturition

the act of emptying the urinary bladder; a spinal reflex with CNS influence

Urinary Incontinence

inability to control urination due to: weak pelvic floor muscles, pressure in pregnancy, stress, nervous system problems

Urinary Retention

bladder is unable to expel urine due to: general anesthesia, hypertrophy of prostate in men

Excretion

the process of eliminating waste

Tubular Secretion

moves substances that we don't want from the peritubular capillaries through the tubule cells into the filtrate mostly occurring in the PCT; includes drugs, urea/uric acid, creatinine, excess K+ and H+

Hormones affecting Kidney

ADH, aldosterone, ANP, and PTH

ADH

stimulates aquaporin synthesis increasing water reabsorption

Aldosterone

stimulates synthesis of Na+ channels and Na/K ATPase increasing Na+ reabsorption

ANP

inhibits Na+ reabsorption (opposes aldosterone)

PTH

increases Ca 2+ reabsorption