Urinary Terms

Kidneys

Major excretory organs

Ureters

Transport urine from kidneys to urinary bladder

Urinary bladder

Temporary storage reservoir for urine

Urethra

Transports urine out of the body

Cortical nephrons

-80% of nephrons

-Located within cortex proper

Juxtamedullary nephrons

-Responsible for osmotic gradient

-Found in border between renal cortex and medulla

-20% of nephrons

Nephrons

-Structural and functional units that form urine

-Composed of renal corpuscle and renal tubule

Renal corpuscle

Composed of glomerulus and glomerular corpuscle

Glomerulus

Tuft of capillaries, fenestrated epithelium, highly porous, allows filtrate formation

Bowman’s capsule

Cup-shaped, hollow structure surrounding glomerulus

Renal tubule

Composed of proximal convoluted tubule, nephron loop, and distal convoluted tubule

Peritubular capillaries

-Low pressure, adapted for absorption of water and solutes

-Arise from efferent arterioles

-Cling to adjacent renal tubules in cortex

-Empty into venules

Vasa recta

-Function in formation of concentrated urine

-Maintain osmotic concentration gradient in renal medulla

-Arise from efferent arterioles serving juxtamedullary nephrons

Glomerular filtration

Produces cell and protein free filtrate

Tubular reabsorption

Selectively returns 99% of substances from filtrate in renal tubules and collecting ducts to blood

Tubular secretion

Selectively moves substances from blood to filtrate in renal tubules and collecting ducts

Glomerular Filtration Rate (GFR)

-Volume of filtrate formed per minute by both kidneys

-Affect systemic blood pressure

-Controlled by glomerular hydrostatic pressure

Nephron Filtration Pressure (NFT)

Primary pressure is hydrostatic pressure in glomerulus

Intrinsic controls

-Maintain GFR in kidney

-Act locally within kidney to maintain GFR

-Renal blood vessels dilated

-Renal autoregulation mechanisms prevail

Extrinsic controls

-Maintain systemic blood pressure

-Nervous and endocrine mechanisms that maintain blood pressure; can negatively affect kidney function

Types of renal autoregulation

Myogenic and tubuloglomerular feedback mechanisms

Myogenic mechanism

A type of intrinsic control that helps maintain Glomerular Filtration Rate (GFR) in the kidney by responding to changes in blood pressure within the renal blood vessels

Tubuloglomerular feedback mechanism

Flow-dependent mechanism directed by macula densa cells; respond to filtrate NaCl concentration to regulate GFR and maintain stable kidney function.

Loops of Henle

Create a concentration gradient in the ECF of the refnal medullar by a countercurrent multiplier mechanism

Vasa recta

-Maintain the osmotic concentration gradient through juxtamedullary nephrons

-Absorb a lot of H2O

Angiotensin II

-Potent vasoconstrictor

-Controls thirst

-Keeps BP elevated

-Tells brain to release ADH and also tells kidney to absorb sodium and water

Vasopressin (ADH)

-Increase water absorption

-Released from posterior pituitary

-Stimulates expression of proteins called aquaporins that serve as water channels in the collecting duct of cell membranes