Anatomy- Urinary System

Major functions of kidneys- regulation of:

Body fluid osmolarity and volume, electrolyte balance, acid- base balance, blood pressure.

Major functions of kidneys- Excretion of:

Metabolic products, foreign substances, excess substance

Major function of kidneys- secretion of:

Erythropoietin- made in fibroblasts, 1,25- dihydroxy vitamin D3 (vitamin D activation), Renin-made in JG cells

Where are kidneys?

Upper posterior abdominal wall at the level of T1-112, they are asymmetrical (right slightly lower than left)

What covers the kidneys?

Renal/ fibrous capsule, Perirenal fat, Renal fascia, Pararenal fat

What does the major calyces do?

Collect urine draining papillae, Empty urine into the renal pelvis

What do the ureters do?

actively propel urine to the bladder via response to smooth muscle stretch

Ureters have a trilayered wall which means-

transitional epithelial, smooth muscle muscularis, fibrous connective tissue adventitia

What are the three layers of the bladder

Transitional epithelial mucosa, a thick muscular layer, a fibrous adventitia

Trigone

triangular area outlined by the openings for the ureters and the urethra

Main purpose of the Urethra

Drains urine from bladder, conveys it out of body

What keeps the urethra closed when urine isn’t being passed?

Sphincters

What are the different sphincters that keep the urethra closed?

Internal: involuntary sphincter at the bladder- urethra junction, External: voluntary sphincter surrounding the urethra as it passes through the urogenital diaphragm

Cortical Nephron

Glomeruli in outer cortex and short loops of Henle- short distances

Juxtamedullary nephron

Glomeruli in inner part of cortex and long loops of Henle- deep into medulla- blood flow through vasa recta

Glomerular blood pressure drives glomerular filtration, and the filtration barrier is two cells thick-

Squamous cell of the capillary and the podocyte

Podocytes provide an ___ filtration barrier for things like cells and large proteins

extra

Blood pressure in the glomerulus is at an arterial level…

much higher than pressure in typical capillaries

The 4 most important processes- Filtration

-first step in urine formation

-bulk transport of fluid from blood to kidney tubule- isosmotic filtrate, blood cells and proteins don’t filter

result of hydraulic pressure

GFR= 180L/day

The 4 most important processes- Reabsorption

-process of returning filtered material to bloodstream

-99% of what is filtered

-may involve transport protein(s)

-normally glucose is totally reabsorbed

The 4 most important processes- Secretion

-material added to limen of kidney from blood

-active transport (usually) from toxins and foreign substances, but may also include ions

The 4 most important processes- Excretion

-loss of fluid from body in form of urine

Mechanisms of Transport step 1

Primary active Transport: is the actual “pump”, usually against the concentration gradient; needs ATP directly

Mechanisms of Transport step 2

Secondary Active Transport: Move with concentration gradient; needs ATP indirectly (a backdoor pump makes the gradient)

Mechanisms of Transport step 3

Passive Transport: diffusion

Mechanisms of Transport step 4

Pinocytosis: not a major player but useful for reacquiring larger proteins

What are the two pathways?

Transcellular- pathway; across cells, good for both

Paracellular- transport; between cells, good for reabsorption

Hydrogen secretion and bicarbonate reabsorption

-hydrogen secretion can occur through secondary active transport

-mainly at the proximal tubules, loop of henle, and early distal tubule

-more than 90% of the bicarbonate is reabsorbed (passively) in this manner

The Proton pump

-primary active transport

-occurs at the luminal membrane of the tubular cell

-hydrogen ions are transported directly by a specific protein, a hydrogen-transporting ATPase (proton pump)

-accounts for only about 5% of the total hydrogen ion secreted

-Important in forming a maximally acidic urine

-hydrogen ion concentration can be increased as much as 900-fold in the collecting tubules

-tubular fluid pH can drop to about 4.5: the lower limit of pH for normal kidneys

For each molecule of glutamine metabolized in the proximal tubules…

2 NH4+ ions are secreted into the urine and 2 HCO3- ions are reabsorbed into the blood

Renal ammonium-ammonia by this process constitutes __

new bicarbonate

What are the different “limbs” of the Loop of Henle

• Descending limb: permeable to water, not permeable to salts

• Ascending limb: Not permeable to water, but able to actively transport salts out of the tubule fluid and into the ECF of the renal medulla

The collecting tubule can actively transport __ out of the tubule fluid and into the __ of the medulla

Urea, ECF

Water flows from __ concentration to (the tubule fluid) to __ concentration (the medullary ECF)

high, low

Rentention of water is controlled by what?

ADH

Vasoconstrictor does what?

Increases systematic BP and decreases GFR

More aquaporins=

more water reabsorbed

True or false: ADH increases the number of aquaporins incorporated into the membrane of the tubule cells

true

ANP is released by atrium in response to..,

atrial stretching due to increased blood volume

ANP inhibits __ secretion

ADH

Sodium balance is largely controlled by what?

aldosterone

Stimulation of aldosterone release from…

adrenal cortex

Stimulation of ADH/AVP release from..

post pit

Vasoconstriction of many systemic arterioles

increased bp

Vasoconstriction of the afferent arterioles

decreased GFR

Renin is an enzyme that converts __ to __

Angiotensinogen, Agl

Renal mechanism

Macula Densa (content of the Na+ ion in the distal convoluted tubule)

Nervous mechanism

sympathetic nerve stimulation of JG cells

Hormonal mechanism

Epi, prostaglandin stimulation of JG cells

PSNS

• normally maintains internal sphincter tone, so it must be “quiet” during urination

• causes the bladder to contract during urination

SNS

Normally inhibits bladder contraction, so it must be “quiet” during urination

Somatic (vol) motor

Voluntary motor system normally maintains external sphincter tone, so it must be “quiet” during urination

sympathetic promotes urinary __

retention

Parasympathetic promotes urinary __

elimination

⬇GFR to get to ⬆GFR

⬇GFR➡⬇Na+ in DCT➡⬇Na+ in macula➡⬆no release➡VD of afferent arteriole➡⬆GBF➡⬆GFR

⬆GFR to get to ⬇GFR

⬆GFR➡⬆Na+ in DCT➡⬆Na+ in macula➡⬆Adenosine release➡VC of afferent arteriole➡⬇GBF➡⬇GFR

Descending limb of the loop of henle is what

permeable to water not salts

Ascending limb of the loop of henle is what

not permeable to water but can actively transport salts out of the tubule fluid and into the ECF of the renal medulla

What paracrine factor does the macula dense release to cause vasodilation of the afferent arteriole?

NO/Nitric oxide

What effect does vasodilation of the afferent arteriole have on GFR?

increase

What paracrine factor does the macula dense release to cause vasoconstriction of the afferent arteriole?

Adenosine

What affect does vasoconstriction of the afferent arteriole have on the GFR

decrease

What does the ascending limb of the loop transport

salts/solutes

what does the descending limb of the loop transport

water/H2O

what one word best describes the extracellular fluid of the medulla of the kidney

hypertonic/salty

what is the overall purpose of the loop

water reabsorption

Which nervous system causes the bladder to contract

parasympathetic

which nervous system causes the internal urethral sphincter to relax

parasympathetic

which nervous system causes the external urethral sphincter to relax

somatic motor

which hormone helps you reduce sodium levels

ANP

which hormone would help you increase your sodium levels

aldosterone

which hormone helps you reabsorb only water

ADH/AVP

into what structure does the renal pyramid drain

Minor calyx

In what anatomic compartment are the kidneys located

retroperitoneal

what type of epithelium lines are the ureters and bladder

transitional/stratified cuboidal

what is the name of the smooth muscle of the bladder

detrusor

what is the backdoor pump that allows most seoondary active transport on the front door of the tubule cell

Na+/K+ ATPase