Exam 3 Systems Physiology

3 processes involved in urine formation and adjustment of blood composition

glomerular filtration

tubular reabsorption

tubular secretion

produces cell- and protein- free filtrate

glomerular filtration

-Selective transepithelial process that returns 99% of substances from filtrate to blood in renal tubules and collecting ducts

tubular reabsorption

selectively moves substances from blood to filtrate in renal tubules and collecting ducts

tubular secretion

Where does filtration occur?

glomerulus

_________ ________ deliver about 1/4 of cardiac output to kidneys each minute.

renal arteries

_________ _________ carries filtered blood away from kidney.

renal vein

The large blood vessel that brings unfiltered blood into the kidneys

renal artery

structural and functional units that form urine

nephron

two main parts of nephron

renal corpuscle

renal tubule

two parts of renal corpuscle

glomerulus

glomerular (Bowman's capsule)

Vessels that carry blood to the glomerulus

afferent arteriole

vessels that carry blood away from glomerulus

efferent arteriole

The network of tiny blood vessels within the glomerulus where filtration happens

Glomerular Capillaries

capillaries that surround the renal tubules and are involved in reabsorption of water and solutes back into the bloodstream

Peritubular Capillaries

plasma-derived fluid that renal tubules process to form urine

filtrate

-cup-shaped, hollow structure surrounding the glomerulus

-contains branching podocytes

-collects the glomerular filtrate

Glomerular (Bowman's) capsule

-tuft of highly porous capillaries

-allows for efficient filtrate formation

-capillary network where filtration of blood occurs

glomerulus

Glomerulus protrudes into a fluid filled capsule called __________.

Bowman's capsule

As blood flows through the glomerulus, about _____% of the plasma filters into the Bowman's capsule.

20%

Filtered blood exits the glomerulus via the efferent arteriole into the ________ _________ for reabsorption and secretion.

peritubular capillaries

What vessels are involved in filtration?

Afferent Arteriole, glomerulus, efferent arteriole

-Site of most reabsorption

-first section of the renal tubule after Bowman's capsule

-what percent of reabsorption?

Proximal convoluted tubule; 65%

What is reabsorbed through the proximal convoluted tubule?

-All nutrients, such as glucose and amino acids

-65% of Na+ and water

-many ions

-almost all uric acid

-half of urea (later secreted back into filtrate)

section of the renal tubule between the loop of Henle and the collecting duct

Distal convoluted tubule

Reabsorption is hormonally regulated in these areas

Distal convoluted tubule and collecting duct

-sharp, hairpin-shaped loop consisting of a descending limb coming from the proximal tubule and an ascending limb leading to the next tubular segment, distal convoluted tube

loop of henle

-H2O can leave, solutes cannot

-Water moves out of the filtrate by osmosis, concentrating the remaining solutes

Descending limb

-H2O cannot leave, solutes can

-dilutes filtrate

-has thin and thick segment

Ascending limb

two parts of loop of henle

ascending and descending limb

Thin segment of ascending limb is passive to _______ movement out of filtrate.

Na+

-Contains Na+−K+−2Cl− symporters that actively transport these ions from the filtrate into the cell

and

-Contains Na+−H+ antiporters that transport Na+ into cell in exchange for hydrogen ions (H⁺) moving into the filtrate

Thick segment of ascending limb

In the thick segment of the ascending limb, some Na+ can pass into the cell by __________ route.

paracellular

final product, urine, is collected in this

collecting duct

each nephron contains this and it is important in regulating rate of filtrate formation and blood pressure

juxtaglomerular complex (JGC)

-Forces that promote filtrate formation

-Chief force pushing water and solutes out of blood

-glomerular blood pressure

outward pressures; hydrostatic pressure in glomerular capillaries (HPgc)

What is the hydrostatic pressure in glomerular capillaries (HPgc)? (number)

55 mm Hg

Pressure seen in most capillary beds? (number)

26 mm Hg

Why is the hydrostatic pressure in glomerular capillaries higher than the pressure in capillary beds?

efferent arteriole is a high-resistance vessel with a diameter smaller than afferent arteriole

-Forces inhibiting filtrate formation

-filtrate pressure in capsule (name and number)

-filtrate that has already entered Bowman's capsule exerts its own pressure, pushing back against the filtration membrane and opposing further filtration

inward pressures; Hydrostatic pressure in capsular space (HPcs); 15 mm Hg

"pulling" force exerted by the proteins that remain in the blood within the glomerular capillaries (name and number)

inward pressures; Colloid osmotic pressure in glomerular capillaries (OPgc); 30 mm Hg

-Specialized cells that make up the visceral layer of Bowman's capsule in the kidneys

-wrap around the glomerular capillaries

podocytes

extensions of the podocytes that interdigitate with each other

foot processes (pedicels)

narrow gaps between foot processes that allow filtrate to pass into capsular space

filtration slits

quickly reclaims most of tubular contents and returns them to blood

reabsorption

Where does reabsorption mostly occur?

Proximal Convoluted Tubule (PCT)

a passive process where water and small solutes in the blood are forced out of the glomerular capillaries and into Bowman's capsule

filtration

reabsorption in reverse; selected substances are moved from peritublar capillaries through tubule cells out into filtrate

secretion

Where does secretion mostly occur?

Distal Convoluted Tubule (DCT)

What type of cells are found within the tubules?

epithelial

-Pressure responsible for filtrate formation

-Main controllable factor determining glomerular filtration rate (GFR)

Net filtration pressure (NFP)

Net filtration pressure (NFP)

-sum of all forces

-55 mm Hg forcing out - 30 mm Hg forcing in - 15 mm Hg forcing in = 10 mm Hg forcing out

What hormone causes water reabsorption by inserting aquaporins?

Antidiuretic hormone (ADH)

What effect does ADH have on the collecting ducts?

It causes principal cells to insert aquaporins in the apical membrane, increasing water reabsorption

Which hormone targets both the collecting duct and the DCT and promotes Na+ reabsorption

Aldosterone

How does aldosterone promote Na⁺ reabsorption?

By promoting synthesis of apical Na⁺ and K⁺ channels and basolateral Na⁺/K⁺ ATPases.

What happens to water when aldosterone increases Na⁺ reabsorption?

Water follows sodium, increasing blood volume

What would happen without aldosterone?

The body would lose about 2% of filtered Na⁺ daily, which is incompatible with life

What are the main functions of aldosterone?

Increase blood pressure and decrease K⁺ levels

ADH and aldosterone act on what part of nephron?

ADH: collecting duct

Aldosterone: collecting ducts and distal convoluted tubule

Acts on DCT to increase Ca2+ reabsorption

Parathyroid hormone

-Reduces blood Na+, resulting in decreased blood volume and blood pressure

-Released by cardiac atrial cells if blood volume or pressure elevated

-Reduces Na⁺ and water reabsorption → increases urine output → lowers blood pressure

Atrial natriuretic peptide

Hormones that regulate formation of urine

ADH

Parathyroid

Aldosterone

Atrial natriuretic peptide

The wall of the afferent arteriole contains secretory cells known as _______ cells.

juxtaglomerular (JG)/granular

an enzyme that influences sodium balance and blood pressure

renin

When is renin secreted?

-When the juxtaglomerular (JG)/granular cells are stimulated by a decrease in stretch

-if NaCl or BP is low

-in the wall of the ascending loop of Henle as it becomes the DCT

-sense changes in the NaCl content of the filtrate and also help to regulate sodium balance and blood pressure

macula densa

combination of macula densa and juxtaglomerular cells is known as the what?

juxtaglomerular apparatus (JGA)

volume of filtrate formed per minute by both kidneys

glomerular filtration rate

Normal glomerular filtration rate value

120-125 ml/min

Why is a constant glomerular filtration rate important?

allows kidneys to make filtrate and maintain extracellular homeostasis

Increased glomerular filtration rate causes _______ urine output.

increased

Increased urine output causes _______ blood pressure.

decreased

Reflects number of carriers in renal tubules that are available

transport maximum

maximum rate at which a substance can be reabsorbed

transport maximum

T/F: Transport maximum (Tm) exists for almost every reabsorbed substance.

True

What happens when transport maximum is reached?

-No more of that solute can be reabsorbed by the nephron

-The excess solute remains in the filtrate and is excreted in urine

Substances reabsorbed in PCT

Na+, HCO3-, water, ions, glucose, amino acids, and other nutrients

Substances secreted in PCT

H+ and NH4+

some drugs

Substances reabsorbed in descending limb

water

substances secreted in descending limb

none

substances reabsorbed in the thin ascending limb

Na+

substances secreted in the thin ascending limb

urea

substances reabsorbed in the thick ascending limb

Sodium (Na⁺)

Chloride (Cl⁻)

Potassium (K⁺)

substances secreted in the thick ascending limb

none

substances reabsorbed in the DCT

Sodium (Na⁺) ----> aldosterone

Chloride (Cl⁻) ----> passively follows Na+

Calcium (Ca²⁺) ----> parathyroid hormone

water

substances secreted in the DCT

Potassium (K⁺) ---> aldosterone

substances reabsorbed in collecting ducts

H2O ---> ADH

Na+ ---> aldosterone; Cl−follows

Urea ---> increased by ADH

substances secreted in collecting ducts

K+ ----> aldosterone

Tubular secretion is important for...

-Disposing drugs or metabolites, that are bound to plasma proteins

-Eliminating undesirable substances that were passively reabsorbed (e.g., urea and uric acid)

-Ridding body of excess K+ (aldosterone effect)

-Controlling blood pH by altering amounts of H+ or HCO3- in urine

Tubular secretion happens mostly in _______.

DCT

Reabsorption or secretion of these substances occur to maintain blood pH

H+, HCO3-, NH4+

Kidneys produce only _______ amounts of urine if the body is dehydrated, or _________ urine if over-hydrated.

small; diluted

Fluid flows in opposite directions in two adjacent segments of same tube with hairpin turn

countercurrent mechanism

Over-hydration produces a _______ volume of diluted urine.

large

What happens to ADH production when over-hydrated?

decreases, reducing water reabsorption

What is the typical urine osmolarity with low ADH?

about 100 mOsm (dilute).

How does aldosterone affect urine during over-hydration?

If aldosterone is present, more ions can be reabsorbed, allowing urine to be even more dilute

What is the lowest possible urine osmolarity in over-hydration (with aldosterone)?

50 mOsm

What hormone is released in high amounts during dehydration and why?

ADH to increase water reabsorption