Vocabulary - The Urinary System
Filters the blood and disposes wastes from the body, includes the kidneys, Ureters, Urinary bladder and Urethra.
The medial surface of the kidney that is concave and has a vertical cleft
an outer layer of dense fibrous connective tissue that anchors the kidney and the adrenal gland to surrounding structures
Perirenal fat capsule
a fatty mass that surrounds the kidney and cushions it against blows
a transparent capsule that prevents infections in surrounding regions from spreading to the kidney
The most superficial region of the kidneys, is light in color and has a granular appearance.
Deep to the cortex is the darker, reddish-brown center of the kidney
cone-shaped tissue masses within the renal medulla.
inward extensions of cortical tissue, separate the pyramids
Each pyramid and its surrounding cortical tissue constitutes one of eight lobes.
a funnel-shaped tube, is continuous with the ureter leaving the hilum.
Branching extensions of the renal pelvis
Each one subdivision of a major calyce, cup-shaped areas that enclose the papillae.
deliver one-fourth of the total cardiac output (about 1200 ml) to the kidneys each minute.
five subdivisions of the renal arteries, close to the helum
many subdivisions of the segmental arteries.
Arteries that arch over the bases of the medullary pyramids.
Cortical Radiate Arteries
radiate outward from the arcuate arteries to supply the cortical tissue.
a variable network of autonomic nerve fibers and ganglia, provides the nerve supply of the kidney and its ureter.
are the structural and functional units of the kidneys. Each kidney contains over 1 million of these tiny blood-processing units, which carry out the processes that form urine
(ball of yarn), which is a tuft of capillaries within the Nephron
has a cup-shaped end
(or Bowman’s capsule), which is blind and completely surrounds the glomerulus
collectively, the glomerular capsule and the enclosed glomerulus
plasma-derived fluid is the raw material that the renal tubules process to form urine.
highly modified, branching epithelial cells of the visceral layer, which clings to the glomerular capillaries
Foot Processes – terminations of the octopus
like podocytes , which intertwine as they cling to the basement membrane of the glomerulus.
The clefts or openings between the foot processes. Through these slits, filtrate enters the capsular space inside the glomerular capsule.
Proximal Convoluted Tubule
(PCT) elaborately coiled renal tubule as it leaves the glomerular capsule.
Loop of Henle
the end of the proximal convoluted tube loops around into the distal convoluted tube.
Distal Convoluted Tubule
(DCT) empties into a collecting duct.
each of which receives filtrate from many nephrons, run through the medullary pyramids and give them their striped appearance
Part of the descending limb, is a simple squamous epithelium freely permeable to water.
the epithelium becomes cuboidal or even low columnar in the ascending part of the loop of Henle
represent 85% of the nephrons in the kidneys. Except for small parts of their loops of Henle that dip into the outer medulla, they are located entirely in the cortex.
originate close to the cortex-medulla junction, and they play an important role in the kidneys’ ability to produce concentrated urine. Their loops of Henle deeply invade the medulla, and their thin segments are much more extensive than those of cortical nephrons.
arise from the efferent arterioles draining the glomeruli. These capillaries cling closely to adjacent renal tubules and empty into nearby venules. They are low-pressure, porous capillaries that readily absorb solutes and water from the tubule cells as these substances are reclaimed from the filtrate.
straight peritubular capillaries in the kidneys that are situated parallel to and surrounding the loop of Henle.
where the most distal portion of the ascending limb of the loop of Henle lies against the afferent arteriole feeding the glomerulus
also called juxtaglomerular (JG) cells, which are enlarged, smooth muscle cells with prominent secretory granules containing renin. Granular cells act as mechanoreceptors that sense the blood pressure in the afferent arteriole.
a group of tall, closely packed cells of the ascending limb of the loop of Henle that lies adjacent to the granular cells The macula densa cells are chemoreceptors that respond to changes in the NaCl content of the filtrate.
lies between the blood and the interior of the glomerular capsule. It is a porous membrane that allows free passage of water and solutes smaller than plasma proteins.
contains mostly metabolic wastes and unneeded substances.
is a passive process in which hydrostatic pressure forces fluids and solutes through a membrane
Net Filtration Pressure (NFP)
responsible for filtrate formation, involves forces acting at the glomerular bed
Glomerular hydrostatic pressure (HPg), which is essentially
Glomerular Blood Pressure
is the chief force pushing water and solutes out of the blood and across the filtration membrane. Although theoretically the colloid osmotic pressure in the capsular space of the glomerular capsule “pulls” the filtrate into the tubule, this pressure is essentially zero because virtually no proteins enter the capsule.
The myogenic mechanism reflects the tendency of vascular smooth muscle to contract when stretched. Increasing systemic blood pressure causes the afferent arterioles to constrict, which restricts blood flow into the glomerulus and prevents glomerular blood pressure from rising to damaging levels
Tubuloglomerular feedback mechanism
Autoregulation by the flow-dependent tubuloglomerular feedback mechanism is “directed” by the macula densa cells of the juxtaglomerular apparatus . These cells, located in the walls of the ascending limb of Henle’s loop, respond to filtrate NaCl concentration (which varies directly with filtrate flow rate)
Neural and Hormonal Mechanisms The purpose of the extrinsic controls regulating the GFR is to maintain systemic blood pressure—sometimes to the detriment of the kidneys
Sympathetic nervous system controls
Neural renal controls serve the needs of the body as a whole. When the volume of the extracellular fluid is normal and the sympathetic nervous system is at rest, the renal blood vessels are dilated and renal autoregulation mechanisms prevail. However, during extreme stress or emergency when it is necessary to shunt blood to vital organs, neural controls may overcome renal autoregulatory mechanisms.
The renin-angiotensin mechanism is triggered when various stimuli cause the granular cells to release the hormone renin.Renin acts enzymatically on angiotensinogen, a plasma globulin made by the liver, converting it to angiotensin I. This, in turn, is converted to angiotensin II by angiotensin converting enzyme (ACE) associated with the capillary endothelium in various body tissues, particularly the lungs.
most of the tubule contents are quickly reclaimed and returned to the blood. This reclamation process, is a selective transepithelial process that begins as soon as the filtrate enters the proximal tubules.
Sodium ions are the single most abundant cation in the filtrate, and about 80% of the energy used for active transport is devoted to their reabsorption. Sodium reabsorption is almost always active and via the transcellular route.
Transport Maximum (Tm)
for nearly every substance that is reabsorbed using a transport protein in the membrane. The Tm (reported in mg/min) reflects the number of transport proteins in the renal tubules available to ferry each particular substance.
Passive Tubular Reabsorption
which encompasses osmosis, diffusion, and facilitated diffusion, substances move down their electrochemical gradients without the use of ATP.
transport protiens that form water channels across cell membranes
Obligatory Water Reabsorption
In continuously water-permeable regions of the renal tubules, such as the PCT, aquaporins are constant components of the tubule cell membranes. Because these channels are always present, the body is “obliged” to absorb water in the proximal nephron regardless of its state of over- or underhydration.
essentially, reabsorption in reverse
is the number of solute particles dissolved in 1 kg of water and reflects the solution’s ability to cause osmosis
equal to 0.001 osmol
In the kidneys, the term countercurrent means that fluid flows in opposite directions through adjacent segments of the same tube connected by a hairpin turn
Countercurrent Multiplier system
is a mechanism that expends energy to create a concentration gradient.
maintaining the osmotic gradient established by the cycling of salt while delivering blood to cells in the area and removing reabsorbed water and solutes.
Antidiuretic Hormone (ADH)
Controlling the reabsorption of water from filtrate in the collecting ducts in order to adjust the body’s osmolality
Tubular filtrate is diluted as it travels through the ascending limb of the loop of Henle, so all the kidney needs to do to secrete dilute (hypo-osmotic) urine is allow the filtrate to continue on its way into the renal pelvis
The formation of concentrated urine depends on the medullary osmotic gradient and the presence of ADH.
Facultative Water Reabsorption
depends on the presence of ADH
chemicals that enhance urinary output.
refers to the volume of plasma that is cleared of a particular substance in a given time, usually 1 minute.
volume of plasma that is cleared of a particular substance in a given time, usually 1 minute. Calculated as RC = UV/P
U = concentration of the substance in urine (mg/ml)
V = flow rate of urine formation (ml/min)
P = concentration of the substance in plasma (mg/ml)
Chronic renal disease
defined as a GFR of less than 60 ml/min for at least three months, often develops silently and insidiously over many years. Filtrate formation decreases gradually, nitrogenous wastes accumulate in the blood, and the blood pH drifts toward the acidic range. The leading cause of chronic renal disease is diabetes mellitus
(GFR <15 ml/min), filtrate formation decreases or stops completely. Ionic and pH imbalances build up and wastes accumulate quickly in the blood. At this point, the treatment options are hemodialysis or a kidney transplant.
uses an “artificial kidney” apparatus, passing the patient’s blood through a membrane tubing that is permeable only to selected substances.
responsible for the color of urine, a pigment that results from the body’s destruction of hemoglobin. The more concentrated the urine, the deeper the yellow color.
Composition of Urine
95% water, 5% consists of solutes (urea (derived from the normal breakdown of amino acids. nitrogenous wastes in urine include uric acid (an end product of nucleic acid metabolism) and creatinine (a metabolite of creatine phosphate, which stores energy for the regeneration of ATP and is found in large amounts in skeletal muscle tissue)
slender tubes that convey urine from the kidneys to the bladder
is a smooth, collapsible,muscular sac that stores urine temporarily. It is located retroperitoneally on the pelvic floor just posterior to the pubic symphysis.
thin-walled muscular tube that drains urine from the bladder and conveys it out of the body. The epithelium of its mucosal lining is mostly pseudostratified columnar epithelium. However, near the bladder it becomes transitional epithelium, and near the external opening it changes to a protective stratified squamous epithelium.
Internal Urethral Sphincter
thickening of the detrusor smooth muscle at the bladder-urethra junction
External Urethral Sphincter
surrounds the urethra as it passes through the urogenital diaphragm. This sphincter is formed of skeletal muscle and is voluntarily controlled
External Urethral Orifice
lies anterior to the vaginal opening and posterior to the clitoris.
about 2.5 cm (1 inch) long, runs within the prostate.
which runs through the urogenital diaphragm, extends about 2 cm from the prostate to the beginning of the penis.
about 15 cm long, passes through the penis and opens at its tip via the external urethral orifice.
also called urination or voiding, is the act of emptying the urinary bladder.
involuntary loss of urine, usually a result of emotional problems, physical pressure during pregnancy, or nervous system problems.
the bladder is unable to expel its contained urine.
a slender rubber drainage tube inserted through the urethra to drain urine
During the fourth week of development, the first tubule system formed but quickly degenerates as a second, lower set appears.
that connects it to the cloaca persists and is used by the later-developing kidneys.
the second renal system
the third renal system
(kidney stones) calcium, magnesium, or uric acid salts in urine that have crystallize and precipitate in the renal pelvis
is when body fluids leak into the tubule. Everything except proteins, lipids, and cells can get in, so the urine at this point is very much like plasma. It is called ultrafiltrate.
is when cells of the renal tubule move compounds back into the blood. The cells reabsorb things like glucose, amino acids, and Na+. Water is reabsorbed too, because it follows these solutes by osmosis.
is when cells of the renal tubule move things from the blood into the urine. A good example of secretion is when the Na+/K+ ATPase turns on and moves K+ into the urine.