Urinary System

major organ of the urinary system

kidney

3 main kidney processes

• filtration: everything goes in

• reabsorption: keeping what's needed

• secretion: eliminating waste

kidneys regulate…

• water

• pH

• salt

kidneys serve as a source of _________ during prolonged fasting

gluconeogenesis

renin

• produced by kidneys

• catalyzes conversion of angiotensinogen to angiotensin I

• activates when low BP/ fluid volume

angiotensin-converting enzyme

• from lungs

• converts angiotensin I to angiotensin II

• then stimulates aldosteron release from the zona glomerulosa of the adrenal cortex

erythropoeitin

• produced by kidneys

• stimulates RBC formation

vitamin D

• activated by kidneys

• crucial for nutrition and calcium metabolism

kidneys are retroperitoneal, which means…

positioned behind the peritoneum and against posterior body wall

renal hilus

internal crook where blood vessels, nerves, and lymphatics enter and exit the kidney

renal capsule

innermost fibrous layer surrounding each kidney

• mainly for protection against infection, not anchoring

adipose tissue capsule

middle layer that helps anchor and cushion the kidneys

renal fascia

outermost layer of dense fibrous connective tissue that wraps around the kidneys, holding them in place

“kidney punch”

blow to the lower back where the kidneys are located

What 3 protective layers anchor the kidneys to the posterior body wall?

• renal capsule

• adipose tissue capsule

• renal fascia

tubular secretion

provides a workaround mechanism for eliminating substances too large to be filtered

• e.g. certain drugs bound to proteins that are too large to pass thru filter

renal cortex

• outer layer of kidney

• lighter color and granular appearance

• where glomeruli are located

substances that cannot pass thru filtration barrier remain…

in the blood

Where are glomeruli located?

renal cortex

renal medulla

• middle region of the kidney

• contains renal pyramids

renal columns

inner extensions of cortical tissue that seperate the pyramids

renal pyramids

corn kernel-shaped structures containing parallel bundles of collecting tubules

collecting tubules

microscopic structures within the pyramids

papillae

drainage points

• located at point of each pyramid

minor calices

collect urine from the papillae

major calices

collect urine from minor calices

renal pelvis

collects urine from major calices

ureters

tubes that carry urine from the renal pelvis to the bladder

urethra

tube that leaves the bladder

nephron

functional units of the kidney

• approx 1 mil per kidney

  • 85% of nephrons are cortical nephrons in the cortex

juxtamedullary nephrons

• remaining ~15% located next to juxta the medulla

• have deep loop of Henle extending into medulla

• play a role in producing really concentrated urine

glomerulus

• where filtration begins

• tuft of fenestrated capillaries

  • allows solute-rich, protein-free filtrate to pass

proximal convoluted tubule

• 1st segment after filtration

  • convoluted b/c wiggles extensively

• performs majority of reabsorption

loop of Henle

• after prox conv tub

  • consists of descending limb and ascending limb

• fine adjestment machanism

descending limb

thin, water movement

ascending limb

thick, sodium movement

distal convoluted tubule

• after loop of Henle

• has cuboidal principal cells w/o microvilli

  • involved in secretion

collecting ducts

• where filtrate moves after distal conv tub

• located in pyramids

• combine at drainage points

high pressure differential

high to low; essential for rapid filtration

• glomerular capillaries must maintain it to fill entire capillary network and drive fluid thru fenestrations

tangled tuft structure of glomerular capillaries

adds resistance, requiring even higher pressure

3 components of filtration

• fenestrated capillaries

• fenestrated endothelium/basement membrane

• podocyte cells

prevent plasma proteins and large anions from passing into the filtrate while allowing water and small solutes thru

fenestrated endothelium/basement membrane

negatively charged basement membrane

• repels large anions including plasma proteins

podocyte cells

have foot processes creating filtration slits that can adjust spacing

adjustable filtration slits

inflating = incr slit width = more leakage

deflating = decr width = less leakage

• dynamically regulate fluid movement out of capillaries

• large molecules (proteins) and blood cells cannot pass thru

mesangial cells

help compress the filtration system

glomerular capillaries

specialized for filtration

• maintains high pressure

peritubular capillaries

responsible for reabsorption

• operates at lower pressure to allow sufficient time for returning needed substances filtered out back into the blood

capillaries

contain only endothelial tissue

• no smooth muscle/elastic tissue

tubular reabsorption

removes “keepers” (water, nutrients, and ions) from the filtrate and returns them to blood

water leaving fluid concentrates it: ______ limb

sodium leaving dilutes it: ________ limb

descending; ascending

tubular secretion

removes substances not already in filtrate

• e.g. drugs bound to proteins and excess potassium

net filtration pressure

= glomerular pressure - osmotic pressure of glomerular blood - hydrostatic pressure of capsule

• e.g. 85 mmHg (glom) - 12 mmHg (osmotic) - 10 mmHg (hydro) = 60 mmHg net filtration pressure

GFR (glomerular filtration rate)

total amount of filtrate formed per minute

• if too high, fluid rushes thru too quickly, preventing adequate tubular reabsorption and causing loss of needed substances in urine

• if too low, extended contact time allows waste products to be absorbed

filtration is super efficient due to…

• fenestrated capillary walls

• highly permeable membranes

• large filtering surface area from tangled capillaries

• high BP

uncontrolled diabetes mellitus

leads to excess glucose in urine b/c kidneys attempt to filter excessive blood glucose, eventually causing kidney disease from overwork

renal autoregulation

keeps GFR constant across normal BP ranges (80-180 mmHg) thru intrinsic mechanisms:

• myogenic control and tubuloglomerular feedback

myogenic control

constricts afferent arterioles when BP incr

• reduces blood flow to glomerular capillaries, maintaining normal filtration rate

• constriction also protects glom capillaries from rupture during high systemic BP

afferent arterioles dilate to maintain normal filtration rate

macula densa cells

on the