Urinary System: Last Study

The Kidneys

• Filtration of metabolic wastes and toxins

• Hormone production

• Homeostasis of body fluids

• Receives 20-25% of resting cardiac output

What hormones are produced by kidneys?

1. Calicitriol: Works with PTH to increase plasma [Ca+]

2. Erythropoeitin: Increases RBC production

3. Renin (not a hormone) → First step to angiotensin II

Detoxification in detail

When you want to metabolize those amino acids to turn them into glucose or burn them off for ATP, we can deal with the carboxyl group, BUT we need to get rid of the amide group (NH2) because it forms ammonia.

• We convert ammonia to UREA

Nitrogenous wastes

• Urea

  • amino acids → NH₂ removed → forms ammonia → processed by liver and converted to urea

• Uric Acid

  • nucleic acid catabolism

• Creatinine

  • creatine phosphate catabolism

• Renal failure

  • Azotemia: Increased nitrogenous wastes in blood (blood urea nitrogen)

Cortex

Medulla

Filtrate vs Urine

Filtrate can be modified— the ability to gain and lose ions and salts and water. Concentration can be increased or decreased. However as it leaves the renal papilla, draining into the minor calyx/renal pelvis, it becomes URINE.

Blood Flow into the Kidney (Entering cortical nephron)

1. Renal artery

2. Segmental artery

3. Lobar arteries that travel up the pyramid

4. Interlobar arteries bringing them up toward the cortex between lobes

5. Arcuate artery “archs” at the top of the pryamid

6. Cortical radiate arteries radiate from the arcuate

Radiate arteries branch off into the glomerulus → AFFERENT ENTERS the tuft EFFERENT leaves

7. Efferent arterioles then wrap around the peritubular capillaries (tubular network aka “collecting ducts”)

8. Cortical radiate veins, arcuate veins, interlobar veins, and finally the exit at the renal vein

Collecting ducts

• They form that peritubular network that the efferent arteriole wraps around

• They drain into the renal papilla into the minor calyx

Nephron route

• Begins at the renal corpuscle (glomerulus and capsule)

• PCT

• Loop of Henle → Goes into the medulla

• DCT

Juxtamedullary vs Cortical

Cortical:

• Make up 85% of our nephrons

• next to the cortex

• filter and modifies filtrate

Juxtamedullary:

• Make up 15% of our nephrons

• filter and modifies filtrate

• creates a concentration gradient in medulla in order to CONCENTRATE our urine → makes the environment to make concentrated urine

Renal corpuscle

• Bowman’s capsule + glomerulus

• Where filtration occurs (where filtrate is separated into the PCT)

Proximal Convuluted Tubule (PCT)

• Reabsorbing 2/3 of filtrate

• Heavily packed with microvilli for absorption

Decending Loop of Henle

• Allows for water to pass through it— nothing else

Ascending thin loop of Henle

• Only allows salts to move through them— no water

Ascending thick loop of Henle

Distal Convuluted Tubule

• Principal ducts

Collecting Ducts

• Principal and intercalated cells

Vasa recta

• protects the gradient that juxtamedullary nephrons create

Urine Formation Steps

• 1. Filtration

  • occurs in the renal corpuscle; forms filtrate

  • water, ions, small proteins, amino acids, hormones, ect.

• 2. Reabsorption

  • most occurs in the PCT, reclaiming all the good stuff

  • glucose, lipids, amino acids

• 3. Secretion

  • unwanted substances are added to filtrate; occurs throughout the nephron

  • H+, urea, creatinine, uric acid

Renal Corpuscle

• Double layered

  • Parietal layer (outer):

  • Visceral layer (inner): podocytes around the squamous endothelial cells of the glomerulus → these can contract and close pores or relax and open pores

Juxtaglomerular apparatus (JGA)

• the grey cells (mesengial) near vascular pole and orange cells on the walls of the afferent arteriole (where afferent or efferent arterioles come in)

• mesengial cells are smooth muscle cells that relax to create more surface area and increase amount of filtration

  • if reducing filtration, we contract to reduce SA

• How is this regulated?

  • The macula densa cells: Located in the wall of the distal convoluted tubule (where it loops back and touches its own glomerulus), it monitors fluid flow and salt concentration.

  • Macula densa cells sees if things are moving too slow or too fast— it will them take steps to modify the glomerular filtration rate (GFR) by telling these cells to constrict or relax

Glomerular filtration

• driven by hydrostatic pressure inside the glomerular capillaries

• approximately 20% of plasma becomes filtrate

• 180L/day filtered, 0.5-2L is excreted as urine

3 layers:

Innermost → Fenestration of endothelial cell to prevent cells and platelets

Middle → Basal lamina of glomerulus to prevent large proteins

Outer (closest to podocyte) → medium proteins get blocked

small inorganic and organics molecules can pass

Glomerular filtration rate (GFR)

Volume of filtrate produced by both kidneys per minute

eg. 125mL/min (filtrate) x 60 mins