Physiology II: The urinary system I - Glomerular Filtration

The kidney maintains … in the body and thus maintains proper … of body fluids

H2O balance, osmolarity

The kidney regulates the quantity and concertation of most …

extracellular fluid ions

The kidney maintains proper …

plasma volume

The kidneys maintain proper … in the body

acid-base balance

The kidneys … the wastes of bodily metabolism and foreign compounds

excrete

The kidneys produce … (2)

Erythropoietin, renin

The kidneys convert … into its active form

vitamin D

…: functional unit of the kidney, smallest unit that can perform all the functions of the kidney, approximately 1 million per kidney

Nephron

Two components of the nephron: …

Vascular, tubular

Two distinct regions of the nephron: …

outer region (renal cortex), inner region (renal medulla)

…: made up of striated triangles called renal pyramids

renal medulla

Two types of nephrons: … they are distinguished by their location and length

juxtamedullary nephrons, cortical nephrons

Vascular component is composed of: … (4)

Afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries

Tubular component is composed of: … (4)

Bowmans capsule, proximal tubule, loop of henle, distal tubule and collecting duct

…: produces substances involved in the control of kidney function (combined vascular/tubular component)

juxtaglomerular apparatus

…: carries blood to the glomerulus

afferent arteriole

…: a tuft of capillaries that filters a protein-free plasma into the tubular component

Glomerulus

…: carries blood from the glomerulus

efferent arteriole

…: supply the renal tissue; involved in exchanges with the fluid in the tubular lumen

peritubular capillaries

…: collects the glomerular filtrate

bowmans capsule

…: uncontrolled reabsorption and secretion of selected substances occur here

proximal tubule

…: establishes an osmotic gradient in the renal medulla that is important in the renal medulla that is important in the kidneys ability to produce urine of varying concentrations

Loop of henle

…: variable, controlled reabsorption of Na+ and H2O and secretion of K+ and H+ occur here; fluid leaving the collecting duct is urine, which enters the renal pelvis

Distal tubule and collecting duct

…: cells of the inner layer of bowman’s capsule lining the glomerular capillaries

Podocytes

Fluid filtered from the glomerulus into bowmans capsule passes through … of the glomerular membrane

three layers

Three layers of the glomerular membrane: …

glomerular capillary wall, basement membrane, inner layer of bowman’s capsule

…: single layer of endothelial cells, more permeable to water and solutes than capillaries elsewhere in the body

Glomerular capillary wall

…: acellular gelatinous layer, composed of collagen and glycoproteins

Basement membrane

…: consists of podocytes that encircle the glomerulus tuft

inner layer of bowman’s capsule

Proteins m.w. > … do not pass through glomerular basement membrane/podocytes

60,000

The final part of the glomerular membrane is a layer of epithelial cells (podocytes) that encircle the … of the capillaries

outer surface

…: the gaps which separate the foot processes, through which the glomerular filtrate moves

Slit pores

The epithelial cells have … provide additional restriction to filtration of plasma proteins

negative charges

…: end feet of the podocyte

pedicles

Slit pore diameter can vary to increase or decrease …

permeability

…: prevents filtration of blood cells but allows all comonents of blood plasma to pass through

fenestration (pore) of glomerular endothelial cell

…: prevents filtration o larger proteins

basal lamina of glomerulus

…: prevents filtration of medium-sized proteins

Slit membrane between pedicles

four basic renal processes: …

Glomerular filtration, tubular reabsorption, tubular secretion, concentration by collecting duct

…: nondiscrimination filtration of a protein-free plasma from the glomerulus into bowman’s capsule

glomerular filtration

…: selective movement of filtered substances from the tubular lumen into the peritubular capillaries

tubular reabsorption

…: selective movement of nonfiltered substances from the peritubular capillaries into the tubular lumen

tubular secretion

Three forces involved in glomerular filtration: …

glomerular capillary bp, plasma-colloid osmotic pressure, bowmans capsule hydrostatic pressure

Force: glomerular capillary bp

Effect: …

Magnitude: …

Favors filtration, 55 mmHg

Force: plasma-colloid osmotic pressure

Effect: …

Magnitude: …

opposes filtration, 30 mmHg

Force: bowmans capsule hydrostatic pressure

Effect: …

Magnitude: …

opposes filtration, 15 mmHg

Force: net filtration pressure

Effect: …

Magnitude: …

favors filtration, 10 mmHg

in severely burned patients there is …

increased GFR

In dehydrating diarrhoea there is …

decreased GFR

Obstructions (kidney stones, enlarged prostates, etc.) can raise … and decrease …

bowman capsule hydrostatic pressure, glomerular filtration

Burns → … → … → …

Loss of plasma proteins, decreased plasma concentration, decreases colloid osmotic pressure

Dehydration → … → … → …

loss of water, increased plasma concentration, increased colloid osmotic pressure

Also in dehydration: … → … → …

decreased plasma volume, decreased MAP, decreased filtration pressure

Kidney obstruction → … → … → … → …

back-pressure, increased bowman capsule pressure, decrease GFR, renal impairment

… causes a decrease in glomerular capillary blood pressure and decreased in net filtration pressure

afferent arteriole vasoconstriction

… causes increase glomerular capillary blood pressure and increased net filtration pressure

afferent arteriole vasodilation

… can be controlled to adjust GFR to suit the body’s needs

glomerular capillary blood pressure

Two major control mechanisms for glomerular filtration rate: …

Autoregulation, extrinsic sympathetic control

…: is aimed at preventing spontaneous changes in GFR

autoregulation

…: aimed at long-term regulation of arterial blood pressure

extrinsic sympathetic control

the … has no influence on the kidneys

parasympathetic nervous system

2 means of GFR autoregulation: …

myogenic mechanism, tubuloglomerular feedback

…: afferent arteriole constriction in response to smooth muscle stretch (arterial bp increases) and relaxation when arterial bp decreases (less stretch)

Myogenic mechanisms

…: a way for the kidney to regulate glomerular filtration rate (GFR) by sensing changes in the salt (NaCl) concentration in the distal tubule and adjusting blood flow accordingly.

tubuloglomerular feedback

three components of the juxtagloomerular apparatus: …

macula densa, granular cells, extraglomerular mesangial cells

…: detect changes in salt level in fluid flowing past within distal ascending loop of henle

macula densa

If … the macula densa sends a signals that GFR is too high and needs to decrease

NaCl is too high

If … the macula densa sends signals that GFR is too low and needs to increase

NaCl is too low

…: cells containing renin-filled secretory granules, located in the afferent arteriole wall

Granular cells

granular cells … when activated by low NaCl or low bp which starts the RAAS system

release renin

…: act as messengers between the macula densa and granular cells

extraglomerular mesangial cells

juxtaglomerular actions are …

paracrine

If there is an increase in bp → increase in GFR and salt delivered to the … → detected by the macula densa cells → release ATP + adenosine → constrict afferent arteriole (thus reducing glomerular blood flow → reduced GFR)

distal ascending loop of henle

Macula densa also exerts fine control by limiting constriction by secreting … (opposing the action of ATP and adenosine)

nitric oxide

The macula densa is a plaque of specialized cells in the wall of the … at the site where the limb attaches to the … of the parent glomerulus

thick ascending limb, extraglomerular mesangium

The cells are anchored to the basement membrane which blends with the matrix of the extraglomerular mesangium, the cells are joined by … with very low permeability and have prominent lateral …

tight junction, intercellular spaces

The most conspicuous immunocytochemical difference between macula densa cells and any other epithelial cell of the nephron is the high content of … and of …

neuronal nitric oxide synthase, cyclooxygenase

Granular cells are assembled in clusters within the terminal portion of the … replacing ordinary … cells

afferent arteriole, smooth muscle

Renin release occurs by … into the surrounding interstitium

exocytosis

Granular cells are connected to the extraglomerular mesangial cells, to adjacent smooth muscle cells, and to endothelial cells by ...

gap junctions

Granular cells are densely innervated by …

sympathetic nerve terminals

Granular cells are …; under conditions requiring enhanced renin synthesis (e.g., volume depletion or stenosis of the renal artery), additional smooth muscle cells located upstream in the wall of the afferent arteriole may transform into granular cells.

modified smooth muscle cells

The basal aspect of the macula densa is firmly attached to the extraglomerular mesangium, which represents a solid complex of cells and matrix that is penetrated neither by … nor by ...

blood vessels, lymphatic capillaries

Like the mesangial cells proper, extraglomerular mesangial cells are ...

heavily branched

extraglomerular mesangial cell processes are interconnected among each other by …, contain prominent bundles of … and are connected to the basement membrane of Bowman's capsule (glomerular mesangium) as well as to the walls of both glomerular arterioles.

gap junctions, microfilaments

The coefficient depends on surface area and the permeability of the glomerular membranes. Both can be modified by … within the membrane

contractile activity

Contraction-relaxation of … varies the size of pores (slits) so influencing permeability

podocyte pedicles