Urinary System

5 functions of kidneys

1. filter the blood
2. produce urine
3. produce renin and erythropoietin
4. fluid and electrolyte balance
5. acid-base balance

3 processes involved in urine formation

1. filtration

2. reabsorption

3. secretion

regions cortex is located

1. renal columns

2. cortical nephrons

regions medulla is located

1. papilla

2. collecting ducts

3. pyramids

regions renal sinus is located

1. renal pelvis

2. minor calyx

3. major calyx

vessels in order that blood encounters them

1. afferent arteriole

2. glomerulus

3. efferent arteriole

4. peritubular capillaries

4 parts of nephron in order

1. bowmans capsule = visceral and parietal layers

2. proximal convoluted tubule = folded + twisted, dense microvilli

3. loop of Henle

4. distal convoluted tubule = folded + twisted

what are nephron structures permeable to

1. proximal convoluted tubule: many compounds including water, electrolytes, glucose, etc.
2. descending loop of Henle: only water
3. ascending loop of Henle: only electrolytes
4. distal convoluted tubule: impermeable

hormones that increase permeability of DCT? compound absorbed?

1. Anti-diuretic hormone (ADH) – permeable to H2O
2. Aldosterone: permeable to Na+, H2O will follow

juxtamedullary nephrons

alters the concentration of the urine

• making it dilute if we are fluid overloaded

• or concentrated if we are dehydrated

filtrate

• fluid inside a nephron

• urine when it enters collecting duct

pathway of urine from kidney to urethra

1. cortical nephron

2. collecting duct

3. pyramid

4. papilla

5. minor calyx

6. major calyx

7. renal pelvis

8. ureter

9. bladder

10. urethra

3 layers of tissue that protects kidneys from innermost to outermost

1. renal capsule

2. adipose capsule

3. renal fascia

process of urine formation

compounds move between the blood and nephron

any compound remains not reabsorbed will?

leave the body in urine

mechanism for moving compounds from blood to nephron

1. filtration

2. secretion

filtration

1. compounds move across filtration membrane from glomerulus into Bowmans capsule

2. hydrostatic pressure gradient moves compounds - drives filtration (55-60 mmHg)

3. passive transport

4. substances the body needs is transmitted to filtrate

reasborption

1. compounds move from the nephron into peritubular capillaries

2. both active and passive transport mechanism used

3. occurs primarily in proximal convoluted tubule

sodium reabsorption

• active transport

• forms electrochemical gradient = anions follow to maintain electronuetrality

• forms osmotic gradient = obligatory H2O reabsorption

• solvent drag = other solutes follow H2O

secretion

• “last chance” to get rid of undesired substanced

• compounds move from the peritubular capillaries into the nephron

• primary site = PCT

excesive ketones in urine indication

• diabetes mellitus or starvation

• also present with ketogenic diets

presence of albumin or other proteins in urine indication

1. severe hypertension

2. kidney failure

3. heart failure

diuretics

caffeine and other substances that increase urinary output

uric acid

breakdown of DNA and RNA

urea

breakdown of amino acids

creatinine

breakdown of creatine phosphate

macula densa cells

• located in the wall of the distal convoluted tubule (DCT) where it is next to the afferent arteriole

• monitors the concentration of NaCl in the filtrate as it passes through

  • Low NaCl levels are associated with decreased blood volume and therefore low blood pressure

• When NaCl levels are low the macula densa cells signal the JG cells

JG Cells

• located in the wall of the afferent arteriole

• When JG cells receive a signal from the macula densa cells or are stimulated by the sympathetic nervous system, they produce and release an enzyme called renin

how is angiotensin II produced

• Renin catalyzes the conversion of angiotensinogen to angiotensin I

• another enzyme called ACE catalyzes the conversion of angiotensin I to angiotensin II:

  • Angiotensinogen ----renin---→ angiotensin I ----ACE---→ angiotensin II

What does angiotensin II do

increases blood pressure using 2 different mechanisms

2 mechanisms used by angiotensin II

• systemic vasoconstriction = almost immediately, dramatically decreases space inside the blood vessels

• stimulates adrenal cortex to release aldosterone

  • Aldosterone causes the DCT to reabsorb more Na+, H2O follows into the bloodstream = blood volume increases

  • takes a little longer, overall effect is dramatic: more blood volume in a smaller space effectively increases blood pressure

ureters

• mostly made of smooth muscle

• transitional epithelium lines inside of ureters

• use peristalsis to move urine from kidneys to bladder

detrusor muscle

• smooth muscle

• wall of urinary bladder contains mainly this muscle

transitional epithelium

• inside lining of bladder

• when bladder is empty bladder will fold (rugae)

trigone

triangular area inside bladder between openings for the urethra and ureters that never displays folding

urethra

transports urine from bladder to the outside of the bladder

2 urethra sphincters

• internal urethral sphincter = located at the proximal end of the urethra just below the bladder, made of smooth muscle (involuntary control)

• external urethral sphincter = more distal, made of skeletal muscle (voluntary control)

micturition

voiding urine

how are aware of our bladders filling with urine

when there is 200 ml of urine in bladder, nerve impulses are sent to cerebral cortex and we become aware of the urge to void

what happens if we choose not to void right away

• ignore + after a minute or two, we are no longer aware of it

• spinal reflexes keep the external urethral sphincter closed.

• fills w 200 ml of urine, nerve impulses sent, cycle repeats until void or max (1L)