Renal

What are the different body fluid compartments?

Extracellular fluid, plasma and intracellular fluid

Kidneys regulate blood vol and pressure via…(2)

• water concentration and fluid vol

• inorganic ion composition

The extracellular compartment has a greater ionic composition of…

Na+, Cl-, and HCO₃

The intracellular compartment has a greater ionic composition of…

K+, Mg+, and P_i

osmolarity

how many solute particles that are dissolved per unit volume of water

Low osmolarity represents

a high water concentration

High osmolarity

a low water concentration

Diffusion

movement of molecules from one location to another as a result of their random thermal motion

osmosis

net diffusion of water across a selectively permeable membrane from a region of high water concentration

osmotic pressure

the pressure necessary to prevent solvent movement

• works against osmosis

Tonicity is determined by the concentration of — of an extracellular solution relative to the intracellular environment of a cell. The solute concentrations may influence —

non-penetrating solutes; changes in cell volume

primary types of tonicity

• isotonic

• hypertonic

• hypotonic

Hypertonic/Hyperosmotic

higher osmolarity than inside the cell

Hypotonic/Hypoosmotic

lower osmolarity than inside the cell

Water flows from — osmolarity to — osmolarity

lower; higher

Normal osmolarity inside a cell is…

~300 mOsm/L

Absorption

Movement of solute/water into the blood (Plasma)

Filtration

Movement of solute/water out of blood (Plasma)

What factors determine fluid movement across blood vessels?

starling forces

The arterial end of the capillary favors…

filtration

The venous end of the capillary favors…

absorption

The kidneys are — in location

Retroperitoneal

Hilum

inner concave part of the kidney

Bladder

storage organ for the formed urine

• ANS innervation

Associated organs of urinary system

• ureter

• bladder

• urethra

Micturition

the process of releasing the urine outside the body i.e. urination

General anatomy of kidney

• outer cortex

• inner medulla

General parts of nephron

• renal corpuscle

• renal tubule

Renal corpuscle is comprised of…(2)

• glomerulus

• bowman’s capsule

Renal tubule is comprised of…(4)

• proximal tubule

• loop of henle (descending + ascending)

• distal tubule

• collecting duct

What is the filtering unit of the kidney?

renal corpuscle

What are the ultra specific structural features that make up the filtering unit?

• afferent/efferent arteriole

• glomerulus

• podocytes

• bowman’s space

• proximal tubule

What is the functional significance of the glomerulus?

it’s where blood first undergoes filtration

Glomerular capillary is comprised of… (3)

• Fenestrated endothelial layer

• basement membrane

• podocytes with filtration slits

Types of Nephrons; Where are they found?

Cortical and Juxtamedullary; In the cortex

Cortical nephron functions

Filtration, reabsorption, secretion

Juxtamedullary nephron functions

Filtration, reabsorption, secretion, regulate concentration of urine

What are the different capillaries that remain associated with nephrons?

• glomerular

• pertibular

• vasa recta

Peritubular capillary

capillaries found around the proximal convoluted tubules → fuse to form renal vein

Vasa recta

capillaries that are found mostly associated with juxtamedullary nephrons in the medullary portion of the kidney

3 basic renal processes involved in urine formation

• Filtration

• Secretion

• Reabsorption

What are the forces involved in the filtration of the plasma through the filtering unit?

• Glomerular capillary blood pressure

• Fluid pressure in Bowman’s space

• Osmotic force due to protein in plasma

Large proteins/albumins are held back (via filtration) because (2)

• pores are too small

• pores and basement membrane repel (-) proteins

— and — are slits in podocytes that remain covered with fine semiporous membrane

Nephrins; Podocins

ultrafiltrate

the protein-free fluid formed as the plasma is filtered at the glomerulus

proteinuria

a condition where some of the proteins that are not supposed to pass through the filtration barrier show up in the filtrate and ultimately in the urine

Net glomerular filtration pressure is always…

positive

What factor would contribute to an increase in the glomerular filtration rate?

High blood pressure

What factor would contribute to a decrease in the glomerular filtration rate?

An increase in the protein concentration in the plasma would increase the protein content in the glomerular capillaries

Filtration fraction

~ 20 % of the plasma that enters into the glomerular capillaries is filtered nto Bowman’s space

Renal fraction

the proportion of blood plasma entering the kidneys that gets filtered into the kidney tubules

What is GFR?

Volume of fluid filtered from the glomerulus into the Bowman’s space per unit time

Factors influencing GFR (4)

• net GF pressure

• neural and endocrine control

• permeability of corpuscular membrane

• surface area available for filtration

What is autoregulation of GFR? How is it achieved?

Maintaining steady blood flow across GFR despite changes in MAP; via myogenic reflex

What is the juxtaglomerular apparatus (JGA)?

A specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole

Glucosuria

glucose appears in the urine

Proteins that play a role in reabsorption of glucose

• SGLT

• GLUT

• Na+/K+/ATPase

transport maximum

all the SGLT proteins that transport glucose from the lumen to the peritubular capillaries are saturated and cannot transport any more glucose

renal threshold

beyond this point, glucose shows up in the urine because transport maximum has been reached

• 300 mg/100 mL

Diabetes mellitus

Capacity to reabsorb glucose is normal (normal SGLT), but filtered load is greatly increased and is beyond the threshold level to reabsorb glucose by the tubules

Renal glucosuria/ benign glucosuria

Genetic mutation of the Na+/glucose cotransporter (SGLT)

Steps for Urea processing by the renal tubules

• Na is reabsorbed by active transport

• electrochemical gradient drives anion reabsorption

• water follows by osmosis (lumen > ecf)

• urea will diffuse down its concentration gradient

Urea reabsorption is dependent on…

water reabsorption

Renal clearance

measures the volume of plasma from which a substance is completely removed from the kidney per unit time

Formula for renal clearance

Inulin

Polysaccharide not found normally in the body used to measure clearance

Creatinine

Product of muscle metabolism; It’s clearance is used to measure GFR (slightly overestimated)

• GFR is inversely proportional to the plasma concentration of the substance

If the clearance of substance X > GFR

X must undergo secretion

If the clearance of substance X < GFR

X must undergo reabsorption

Sources of input maintaining water balance

• ingested liquid

• water from oxidation of food

Sources of output maintaining water balance

• insensible water loss

• sweat

• GI + urinary tract, menstrual flow

Water reabsorption is dependent on…

Na+ reabsorption

Which hormone regulates water reabsorption? Where?

Vasopressin/ADH on AQP2 (luminal side) in the collecting ducts

Water reabsorption occurs through the — portion of the loop of henle, while the — is impermeable to water

thin descending portion; ascending limb

Countercurrent multiplication

process in the Loop of Henle that uses fluid flow in opposite directions to build a salty concentration gradient

What does a long loop indicate about a species’ need to conserve water?

needs to conserve more water; hyperosmolar gradient is greater to conserve more water

Plasma osmolarity is mainly determined by measuring the plasma…

Na+

What cells make ADH?

Neurosecretory cells in the hypothalamus found in supraoptic nucleus (SON)

APQ 2,3,4 are found…

in the collecting ducts

AQPs on the — membranes are not regulated by ADH

basolateral

In the absence of ADH, what happens to collecting ducts?

They become almost impermeable to water, leading to water diuresis

Central diabetes insipidus

Failure to release the ADH from the posterior pituitary

Nephrogenic diabetes insipidus

ADH is secreted in a normal matter from the pituitary but the hormone does not function normally

• ADH is present, body does not respond

When ADH is increased…

AQP-2 levels increase, water reabsorbed (pee less)

When ADH is decreased…

AQP-2 levels decrease, do not conserve water (pee more)

Water diuresis

Only excess water is excreted without excess solute in urine

Osmotic diuresis

Excess solute in urine is always associated with high levels of water excretion

• Uncontrolled diabetes mellitus

— is never secreted into the renal tubules. It is excreted.

Sodium

In regards to low sodium levels, — cells are mechanoreceptors, secreting renin.

— cells are chemoreceptors, sensing NaCl load of the filtrate.

Juxtaglomerular; Macula densa

— stretch (Low circulating volume) stimulates renin release

Decreased

Atrial natriuretic peptide/ANP functions (3)

• regulates GFR

• inhibits Na+ reabsorption

• inhibits aldosterone

ANP source

synthesized and secreted by cardiac atria

Baroreceptors location

• Carotid sinus

• aortic arch

• major veins

• intrarenal (JG cells of JGA)

Aldosterone source + trigger

steroid hormone secreted from the adrenal cortex triggered by low plasma volume associated with low sodium

Aldosterone site of action

Late distal tubule and cortical collecting duct

Renin

enzyme that acts as sensor for low NaCl conc in blood

• Converts angiotensinogen to angiotensin I

What stimulates ANP secretion? (3)

• Increased Na+ concentration

• Increased blood volume

• Atrial distension (!!!)

Aldosterone secretion is directly sensitive to the extracellular — level

K+

An increase in extracellular [K+] results in…

Stimulation of aldosterone production → More [K+] excreted in urine

What is a buffer?

compounds that can bind to H+ and form a hydrogen-buffer conjugate