Physiology 2130 Lecture Notes - Lecture 11: Renal Function, Oncotic Pressure, Interlobular Arteries
11 Feb 2017
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INTRODUCTION
- The renal system includes the kidneys, ureters, bladder and urethra
- Principal function of kidneys: regulation of water balance, electrolyte levels, pH of the blood, and
long term regulation of arterial pressure
FUNCTIONS OF THE KIDNEYS
- Basic function of the kidney:
o Remove nonessential substances from the plasma including waste metabolites,
excess water, and electrolytes
o Recover any essential substance like glucose
- Kidneys play a major role in regulating the water levels, the chemical concentration of the body
fluid compartments, and pH (or acidity) of the blood
- The kidneys DO NOT produce water or electrolytes but only CONSERVE them by reducing the
amount removed from the body
- The elimination of waste or foreign substances is an important function of the kidneys
o Removal of drugs, food additives, and vitamins that are excreted in the urine
- Kidneys act as an endocrine gland, producing hormones or components of hormonal systems
such as erythropoietin, renin, vitamin D, and stanniocalcin
ANATOMY OF THE KIDNEYS
- Kidneys are roughly the size of a fist
- Consist of an outer renal cortex, a middle renal medulla, and inner calyces that drain into a
central renal pelvis
- Renal pelvis then drains into the ureter
- Located within the renal pyramids are the functional units of the kidneys- the nephrons
o Each nephron drains through a collecting duct into a calyx
VIEW THE DIAGRAM
ANATOMY BLOOD SUPPLY OF THE KIDNEYS
- Blood flows to the kidneys through the renal artery
o This large artery branches into several interlobar arteries that, in turn, branch into arcuate
arteries
o The blood in the arcuate arteries flows through the interlobular arteries to supply the
nephron
- The blood supply to the nephron drains into the interlobular vein, the arcuate vein, the interlobar
VEIN and then into the renal vein
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ANATOMY THE NEPHRON
- Nephron is the functional unit of the kidneys
- There are over 1 million nephrons in each kidney whose function is to filter the blood, reabsorb
essential substances, and excrete nonessential molecules and waste
- Each nephron is composed of a highly coiled hollow tube surrounded by a complex blood supply
- The glomerular capsule (Bowman’s capsule) surrounds a very small, highly permeable capillary
bed called the glomerulus
- These structures are often collectively referred to as the renal corpuscle
- The tubular potion of the nephron consists of the following structures in order: the proximal
convoluted tubule (highly coiled portion of the nephron), the descending and ascending limb of
the loop of Henle, the distal convoluted tubule, and the collecting duct
LOOK AT DIAGRAM
ANATOMY BLOOD SUPPLY OF THE NEPHRON
- Blood from the renal artery eventually reaches interlobular artery that drains into the afferent
arteriole
- The afferent arteriole gives rise to the glomerulus (where filtration takes place)
- The blood from the glomerulus enters the efferent artery
- Blood then enters the peritubular capillaries (dense network of capillaries surrounding the tube of
the nephron), which then drains into the interlobular vein and eventually back to the renal vein
THE RENAL CORPUSCLE
- The renal corpuscle is made up of the glomerular capsule (Bowman’s capsule) and glomerulus
o This is the site where the blood is filtered glomerular filtration
- The fluid that is filtered from the blood that enters the glomerular capsule (or capsular space) is
called the filtrate
- Glomerular filtration is facilitated by a highly permeable capillary endothelium that is
surrounded by podocytes
- The larger diameter afferent arteriole and smaller diameter efferent arteriole also enhance
glomerular filtration
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PROCESSES ALONG THE NEPHRON
- Each section of the nephron has different functions
o Filtration, reabsorption, and secretion
- Filtration: movement of fluid through the glomerular capillary due to hydrostatic pressures
- Filtrate: solution created by filtration
o The filtrate is generally composed of water plus all the dissolved solutes in the blood
(except for large proteins that are too big to be filtered)
- Reabsorption: movement of a substance from the lumen of the nephron back into the blood
- Secretion: movement of a substance from the blood into the lumen of the nephron
- Excretion: removal of a substance from the body
- EXCRETION = FILTRATION + SECRETION REABSORPTION
GLOMERULAR FILTRATION
- Glomerular filtration bulk flow of fluid from the blood into the glomerular capsule
o The fluid (filtrate) contains the same substances as plasma with the exception of large
proteins and red blood cells
- Glomerular filtration is affected by the extremely permeable capillaries make up the
glomerulus and Starling forces
- Special epithelial cells called podocytes surround the capillaries
o The podocytes have large filtration slits that are formed between pedicles
o These structural features increase filtration at the glomerulus
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Document Summary
The renal system includes the kidneys, ureters, bladder and urethra. Principal function of kidneys: regulation of water balance, electrolyte levels, ph of the blood, and long term regulation of arterial pressure. Basic function of the kidney: remove nonessential substances from the plasma including waste metabolites, excess water, and electrolytes, recover any essential substance like glucose. Kidneys play a major role in regulating the water levels, the chemical concentration of the body fluid compartments, and ph (or acidity) of the blood. The kidneys do not produce water or electrolytes but only conserve them by reducing the amount removed from the body. The elimination of waste or foreign substances is an important function of the kidneys: removal of drugs, food additives, and vitamins that are excreted in the urine. Kidneys act as an endocrine gland, producing hormones or components of hormonal systems such as erythropoietin, renin, vitamin d, and stanniocalcin. Kidneys are roughly the size of a fist.
