BIOL 230 Lecture Notes - Lecture 14: Renal Blood Flow, Efferent Arteriole, Afferent Arterioles
27 Apr 2018
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Ace inhibitor drugs:
Active reabsorption: takes place if any one of the steps in the transepithelial transport of a
substance requires energy, even if the four other steps are passive.
- Substances that are actively reabsorbed are of particular importance to the body, such
as glucose, amino acids, and other organic nutrients, as well as Na+ and other
electrolytes, such as PO43–
Active secretion:
Afferent arterioles: arterioles which derive from the renal artery and transport blood to each
nephron (more specifically the glomerulus)
Aldosterone: increases Na+ reabsorption by the distal and collecting tubules by promoting the
insertion of additional Na+ channels into the luminal membranes and additional Na+–K+
ATPase carriers into the basolateral membranes of the distal and collecting tubular cells.
Angiotensinogen: an enzyme activated by renin which turns into angiotensin I
Angiotensin I: a plasma protein synthesized by the liver and is always present in the plasma.
When passing throughout he lungs it is converted into angiotensin II by angiotensin-converting
enzyme (found in the pulmonary capillaries)
Angiotensin II: the main stimulus for secretion of the hormone aldosterone from the adrenal
cortex. Additionally:
• Angiotensin II is a potent constrictor of the systemic arterioles, directly increasing blood
pressure by increasing total peripheral resistance
• It stimulates thirst (increasing fluid intake)
• It stimulates vasopressin (a hormone that increases H2O retention by the kidneys)
Angiotensin-converting enzyme: converts angiotensin I to angiotensin II when it passes
throughout the lungs. Enzyme is found in the pulmonary capillaries.
Aquaporins (or water channels): channels water flows through during reabsorption which are
formed by specific plasma membrane proteins in the tubular cells.
Antidiuretic hormone (ADH):
Atrial natriuretic peptide (ANP) inhibits Na+ reabsorption (Fig. 14-17, p. 543): ANP is a
polypeptide hormone which directly inhibits Na+ reabsorption in the distal parts of the nephron.
ANP is released by atrial myocytes (muscle cells) from granules in the atria of the heart in
response to high blood pressure, hypervolemia, and exercise.
⁃ Elevated Na+ concentration, angiotensin II, and endothelin (vasoconstrictor) may also
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stimulate ANP release
⁃ ANP inhibits renin secretion by the kidneys and acts on the adrenal cortex to inhibit
aldosterone secretion.
⁃ ANP also promotes natriuresis and accompanying diuresis by increasing the GFR through
dilation of the afferent arterioles, raising glomerular capillary blood pressure, and by
relaxing the glomerular mesangial cells, leading to an increase in Kf.
Autoregulation:
BUN—blood urea nitrogen: a clinical measurement used to crudely assess kidney function.
⁃ However, the consequences of renal failure are not attributable to the retention of urea,
which itself is not especially toxic, but rather to the accumulation of other substances that
are not adequately excreted because of their failure to be properly secreted—most notably
H+ and K+.
Bowman’s capsule: the start of the tubular system. The Bowman's capsule is an expanded
double-walled invagination that cups around the glomerulus to collect fluid filtered from the
glomerular capillaries.
Collecting tubule (duct):
Cortical nephrons: ~80% of all nephrons are cortical nephrons, which perform excretory and
regulatory functions.
Countercurrent exchange (Fig. 14-28, p. 561): The passive exchange of solutes and H2O
between the two limbs of the vasa recta and the interstitial fluid throughout its hairpin structure.
⁃ It preserves (prevents the dissolution of) the gradient. Because blood enters and leaves the
medulla at the same osmolarity as a result of countercurrent exchange, the medullary
tissue is nourished with blood, yet the incremental gradient of hypertonicity in the medulla is
pre- served.
Countercurrent multiplication:
Distal convoluted tubule:
Diuretics: therapeutic agents used on people with CHF (because of their inappropriate salt
retaining mechanisms) that cause diuresis (increased urinary output) and promote loss of fluid
from the body.
Efferent arteriole: an arteriole that forms from the glomerular capillaries rejoining. Blood that
was not filtered into the tubular component leaves the glomerulus through the efferent
arterioles.
⁃ Only arterioles in the body that drain from capillaries because no O2 or nutrients are
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extracted from the blood at the glomerulus.
Filtration coefficient (Kf): the properties of the glomerular membrane (permeability and surface
area)
- GFR = Kf x net filtration pressure
Filtered load: average 125 mg/min
Filtration fraction: the fraction of plasma flowing through the glomeruli that is filtered into the
tubule. If PAH = plasma flow and inulin clearance = GFR that you can determine the filtration
fraction
Filtration slits: the slits formed between adjacent foot processes of podocytes which filter fluid
that leaves the glomerular capillaries and enters the lumen of the Bowman's capsule.
Glomerular filtration: first step in urine formation where protein-free plasma filters through the
glomerular capillaries into the Bowman's capsule (125 mL/minute or 180 L/day; plasma is
filtered 65 times a day)
⁃ Glomerular filtration is largely an indiscriminate process. With the exception of blood cells
and plasma proteins, all constituents within the blood -- H2O, nutrients, electrolytes, wastes
etc. -- non-selectively enter the tubular lumen as a bulk unit during filtration.
Glomerular filtration rate (GFR): the actual rate of filtration depends on the net filtration
pressure and on how much glomerular surface area is available for penetration and how
permeable the membrane is as well.
Glomerular membrane:
Glomerulus: a ball-like tuft of capillaries which filters part of the water and solutes from blood
passing through. The glomerulus is the dominant part of the nephron's vascular component.
Granular cells: specialized smooth muscle cells within the wall of the afferent arteriole and they
contain many secretory granules.
Hypertonic: when there is a water deficit relative to the solute load and the body fluids are too
concentrated; osmolarity is greater than 300 mosm/litre. Can be brought on by intense exercise
in heat or cold.
Hypotonic: when too much water is present relative to the solute load; body fluids are too dilute
and osmolarity is about less than 300 mosm/litre.
Inulin: a harmless foreign carbohydrate produced by Jerusalem artichokes, is freely filtered and
not reabsorbed or secreted—an ideal substance.
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Document Summary
Active reabsorption: takes place if any one of the steps in the transepithelial transport of a substance requires energy, even if the four other steps are passive. Substances that are actively reabsorbed are of particular importance to the body, such as glucose, amino acids, and other organic nutrients, as well as na+ and other electrolytes, such as po43 . Afferent arterioles: arterioles which derive from the renal artery and transport blood to each nephron (more specifically the glomerulus) Aldosterone: increases na+ reabsorption by the distal and collecting tubules by promoting the insertion of additional na+ channels into the luminal membranes and additional na+ k+ Atpase carriers into the basolateral membranes of the distal and collecting tubular cells. Angiotensinogen: an enzyme activated by renin which turns into angiotensin i. Angiotensin i: a plasma protein synthesized by the liver and is always present in the plasma.
