urinary system

part A

what are the kidneys

• Paired excretory organs

• Make up ~1% of body mass

• Receive 15–30% of cardiac output (high blood flow for filtration)

what are the ureters

• Tubes that transport urine from the kidneys to the bladder

• Located retroperitoneally and surrounded by smooth muscle

what is the urinary bladder

• Muscular storage organ

• Holds urine until it is excreted (voided)

what is the urethra

• Muscular tube

• Carries urine from bladder → outside of the body

what is the job of the renal hilum

serves as the entry and exit point of the kidney

-Indented (concave) area on medial side of kidney

what does the renal vein do at the renal hilum

The renal vein exits the kidney at the hilum and drains deoxygenated blood away from the kidney into the inferior vena cava.

what does the renal artery do around the renal hilum

The renal artery enters the kidney at the hilum and delivers oxygen-rich blood to the kidney for filtration.

the kidneys are retroperitoneal

-behind the digestive cavity (peritoneum)

-no pleura to protect them

what are the 6 functions of the kidney

Regulates body fluids

• Controls volume of body water

• Maintains proper solute concentrations

Regulates ions in ECF (extracellular fluid)

• Balances electrolytes (e.g., Na⁺, K⁺, Ca²⁺)

Maintains acid-base balance

• Keeps blood pH within normal range

Excretes wastes

• Removes drugs and metabolic wastes

• Eliminates byproducts of protein metabolism

Hormone production

• Produces erythropoietin → stimulates red blood cell production

• Produces renin → helps regulate blood pressure

Activates vitamin D

• Converts vitamin D into its active form (calcitriol)

what is the renal pelvis

• Funnel-shaped structure at the start of the ureter

• Collects urine from the calyces(Funnel-shaped structures in the kidney that collect urine from the renal pyramids and direct it into the renal pelvis.)

what is the renal medulla

• The inner part of the kidney beneath the cortex

• Organized into cone-shaped structures called renal pyramids

Concentrates urine by allowing water to be reabsorbed as the filtrate passes through the loops of Henle and collecting ducts.Channels the urine efficiently toward the renal pelvis → ureter → bladder

what does the renal pyramids (renal medulla)

• Tip of each pyramid = renal papilla

• Urine from the nephrons flows toward these papillae

what does the renal papillae do (structure inside renal medulla)n

• Open into minor calyces

• Act like a funnel, directing the concentrated urine from the pyramid into the urinary collecting system

what happens at the renal medulla

body reabsorbs the “good” stuff

-water, glucose, electrolytes

leaves urea inside

what is the Renal cortex

• Outer layer beneath the capsule
  Functions:

  • Filters blood

  • Reabsorbs needed substances

  • Secretes wastes and excess substances

what is the kidneys function?

filter waste, excess water, and impurities from the blood, producing urine

what is the nephron

-structual and functional unit of the kidney

millions of the same structure in the body

what is the renal corpuscle and what does it do

Includes:

• Glomerulus

• Glomerular (Bowman’s) capsule

• Function:

  • Site of blood filtration

  • Produces filtrate (tubular fluid)

  • first part of the nephron

what does the glomerulus do (Renal corpuscle)

• A ball of tiny capillaries (blood vessels)

• Blood flows through here

• This is what actually does the filtering

• Small things pass through (water, glucose, ions)

• Big things stay in blood (RBCs, proteins)

what does the glomerular (Bowmans) capsule do

• A cup-like structure that surrounds the glomerulus

• Catches what gets filtered out of the blood (water, glucose, salts,waste)

what does the paietal layer and visceral layer of tissue do at the glomerulus capsule

parietal:single layer of cells

visceral: touching glomerulus (epithelial cells)

-foot like projections that allow large molecules (glucose) to pass through

-problem with podoyctes if blood/protein in urine

what does the proximal convoluted tubule cells have and help with

has microvilli- larger surface to volume ratio so that our body doesn’t miss anything

what does the proximal convoluted tubule do (what is its 2 main functions)

• Location: Right after the Bowman’s capsule

• Primary role: Reabsorption of most of the filtrate

  • Reabsorbs water, glucose, amino acids, and ions (Na⁺, K⁺, Cl⁻) back into the blood

• Secondary role: Secretion of some wastes

  • Substances like urea, drugs, and H⁺ can be secreted into the tubule

• Big picture: Recovers most nutrients and water that the body needs

what does the nephron loop (loop of henle) do (descending + ascending)

• location: Between PCT and DCT; dips into the renal medulla

• Structure: Has a descending limb and ascending limb

  • Descending limb: Permeable to water, not salts → water leaves, filtrate becomes concentrated

  • Ascending limb: Permeable to salts, not water → salts pumped out, filtrate becomes dilute

• Function: Creates a concentration gradient in the medulla

• Big picture: Allows the kidney to produce concentrated urine when needed

what does the distal convoluted tubule do (2 functions)

• Distal Convoluted Tubule (DCT)

  • Location: After the nephron loop, before the collecting duct

  • Primary role: Secretion of ions and wastes

    • H⁺, K⁺, ammonium ions, and some drugs are secreted into the tubule

  • Secondary role: Fine-tunes reabsorption

    • Sodium and calcium reabsorption can be adjusted based on hormonal signals (e.g., aldosterone, PTH)

  • Big picture: Helps maintain pH, electrolyte balance, and blood pressure

what does the collecting duct do

• Location: Receives filtrate from multiple nephrons

• Primary role: Final adjustment of water and solutes

  • Reabsorbs water under the influence of ADH (antidiuretic hormone)

  • Can also reabsorb or secrete ions under hormonal control

• Function: Delivers urine to the renal pelvis

• Big picture: Determines the final concentration and volume of urine

NOT A COMPONENT OF THE NEPHRON

what is the juxtaglomerular complex

• Where the ascending limb of the nephron loop touches the afferent arteriole (the blood vessel bringing blood into the glomerulus).

• Acts as a control center for filtration and blood pressure.

what do macula dense cells do (JG complex)

• In the ascending limb of the nephron loop.

• Function:

  • Monitor the salt (NaCl) concentration in the filtrate going into the distal convoluted tubule.

  • If salt is high, they signal the arteriole to constrict, lowering GFR so more salt can be reabsorbed.

  • If salt is low, they allow dilation, increasing GFR to bring more filtrate through.

• Analogy: Like a salt sensor checking what’s in the filtrate.

what do granular cells do (JG complex)

• Where: In the wall of the afferent arteriole.

• Function:

  • Sense blood pressure in the kidney.

  • Secrete renin if blood pressure drops → starts the renin-angiotensin-aldosterone system to raise blood pressure.

• Analogy: Like a pressure sensor that also sends out a “help signal” (renin) when BP is too low.

what do mesangial cells do

• Where: Between the capillaries of the glomerulus.

• Function:

  • Support the glomerular structure

  • Keep the filtration apparatus clean by removing debris

• Analogy: Like the maintenance crew keeping the filtration system tidy.

what do cortical nephrons do (85% of a;; nephrons)

• Location: Mostly in the renal cortex

  • Glomerulus is far from the medulla

  • Short nephron loop

• Function:

  • Perform the bulk of reabsorption and secretion

• Blood supply:

  • Efferent arteriole → peritubular capillaries (surround the tubules for exchange)

• Big picture:

  • Focused on processing filtrate and maintaining blood composition, not on concentrating urine as much as juxtamedullary nephrons.