Filtration, Reabsorption, Secretion

mechanisms of urine formation:

the kidneys filter the body’s entire plasma volume ____ times each day

60

mechanisms of urine formation:

the filtrate contains ______

all plasma components except proteins

mechanisms of urine formation:

the filtrate loses _____ to become urine

water, nutrients, and essential ions

mechanisms of urine formation:

the urine contains _____ and _____

metabolic wastes and unneeded substances

mechanisms of urine formation:

urine formation and adjustment of blood composition involves three main processes

glomerular filtration, tubular reabsorption, secretion

glomerular filtration:

principles of ____ that account for _____ in all capillary beds apply to the glomerulus as well

fluid dynamics, tissue fluid

glomerular filtration:

the glomerulus is more efficient than other capillary beds because (3)

filtration membrane more permeable

higher blood pressure

higher net filtration pressure

glomerular filtration:

______ are not filtered and are used to maintain ______ of the blood

plasma proteins, oncotic pressure

______ is the pressure responsible for filtrate formation

net filtration pressure (nfp)

NFP equals the

glomerular hydrostatic pressure minus the oncotic pressure of glomerular blood combined with the capsular hydrostatic pressure

NFP equation

NFP = HPg - (OPg + HPc)

pressure is the force that drives the movement of water molecules from a region of ____ solute concentration to a ____ concentration

low, high

____ pressure is the force exerted by _____ in the blood that ______ into the blood vessels

oncotic, proteins, draws water

glomerular filtration rate (GFR)

total amount of filtrate formed per minute by the kidneys

factors governing filtration rate at the capillary bed are (3)

total surface area available for filtration

filtration membrane permeability

net filtration pressure

GFR is _____ to the NFP

directly proportional

changes in GFR normally result from changes in _____

glomerular blood pressure

if the GFR is too _____, needed substances cannot be _____ quickly enough and are lost in ____

high, reabsorbed, urine

if the GFR is too _____, everything is _____, including _____ that are normally disposed of

low, reabsorbed, wastes

regulation of glomerular filtration:

three mechanisms control the GFR

renal autoregulation (intrinsic system), neural controls, hormonal mechanism (the renin-angiotensin system)

intrinsic controls:

under normal conditions, _____ maintains a nearly ____ glomerular filtration rate

renal autoregulation, constant

intrinsic controls:

autoregulation entails two types of control

myogenic and flow-dependent tubuloglomerular feedback

intrinsic controls:

myogenic responds to

changes in pressure in the renal blood vessels

intrinsic controls:

flow-dependent tubuloglomerular feedback senses changes in the

juxtaglomerular apparatus

extrinsic controls:

when the sympathetic nervous system is at rest, renal blood vessels are _____

maximally dilated

extrinsic controls:

when the sympathetic nervous system is at rest, _____ mechanisms prevail

autoregulation

extrinsic controls:

under stress, ______ is released by the sympathetic nervous system

norepinephrine

extrinsic controls:

under stress, ____ is released by the adrenal medulla

epinephrine

extrinsic controls:

under stress, ____ constrict and ____ is inhibited

afferent arterioles, filtration

extrinsic controls:

the sympathetic nervous system also stimulates the ____

renin-angiotensin mechainsm

renin-angiotensin mechanism:

triggered when the _____ release renin

JG cells

renin-angiotensin mechanism:

renin acts on _____ to release _____

angiotensinogen, angiotensin I

renin-angiotensin mechanism:

angiotensin I is converted to _____

angiotensin II

renin-angiotensin mechanism:

angiotensin II causes ______ to rise

mean arterial pressure

renin-angiotensin mechanism:

angiotensin II stimulates the _____ to release ____

adrenal cortex, aldosterone

renin-angiotensin mechanism:

as a result, both ____ and ____ rise

systemic and glomerular hydrostatic pressure

renin-angiotensin mechanism flow

enzyme reaction, angiotensin I, enzyme reaction, angiotensin II, stimulates, adrenal cortex to secrete, aldosterone

renin-angiotensin mechanism:

1. ____ releases angiotensinogen into blood

2. macula dense sense ____ or ____

3. juxtaglomerular cells secrete ____

4. ____ releases enzyme renin into blood

5. ____ in pulmonary blood

6. aldosterone stimulates ____ on the apical cell membrane in the ____ and ____

liver

low fluid flow or low Na+ concentration

renin

kidney

angiotensin-converting enzyme

Na+ uptake, distal convoluted tubule, collecting ducts

renin release is triggered by ______ of the granular JG cells

reduced stretch

renin release is triggered by stimulation of the JG cells by

activated macula densa cells

renin release is triggered by direct stimulation of the JG cells via

beta-adrenergic receptors by renal nerves

other factors affecting glomerular filtration:

prostaglandins (PGE₂ and PGI₂) are ______ produced in response to ____ and _____

vasodilators, sympathetic stimulation, angiotensin II

other factors affecting glomerular filtration:

prostaglandins (PGE₂ and PGI₂) are thought to prevent ____ damage when _____ is ____

renal, peripheral resistance is increased

other factors affecting glomerular filtration:

_____ is vasodilator produced by the vascular endothelium

nitric oxide

other factors affecting glomerular filtration:

____ is a vasoconstrictor of renal vasculature

adenosine

other factors affecting glomerular filtration:

endothelin is a powerful _____ secreted by ____

vasoconstrictor, tubule cells

sodium reabsorption is almost always by

active transport

sodium reabsorption:

_____ enters the tubule cells at the _____

Na+, luminal membrane

sodium reabsorption:

is actively transported out of the tubules by a

Na+ K+ ATPase pump

sodium reabsorption:

from there it moves to peritubular capillaries due to (2)

low hydrostatic pressure and high osmotic pressure of the blood

sodium reabsorption:

Na+ reabsorption proves the energy and means for ____

reabsorbing most other solutes

reabsorption by pct cells:

active pumping of Na+ drives reabsorption of

1. water by osmosis, aided by water-filled pores called _____

2. _____ and _____ by diffusion

3. organic nutrients and selected cations by _____

aquaporins

cations and fat-soluble substances

secondary active transport

substances are not reabsorbed if they (3)

lack carriers, are not lipid soluble, are too large to pass through membrane pores

(3) are the most important nonreabsorbed substances

urea, creatinine, uric acid

tubular reabsorption:

all _____ are reabsorbed

organic nutrients

tubular reabsorption:

water and ion reabsorption is _____ controlled

hormonally

tubular reabsorption:

reabsorption may be an ______ or _____ process

active (primary/secondary) or passive

routes of water and solute reaborption

read

tubular secretion:

essentially reabsorption in reverse, where substances move from _____ into _____

peritubular capillaries or tubule cells into filtrate

tubular secretion is important for disposing of

substances not already in the filtrate

tubular secretion is important for eliminating undesirable substances such as

urea and uric acid

tubular secretion is important for ridding the body of

excess potassium ions

tubular secretion is important for controlling

blood pH