Urinary System

Filters the blood and disposes wastes from the body, includes the kidneys, Ureters, Urinary bladder and Urethra.

Renal Helum

The medial surface of the kidney that is concave and has a vertical cleft

Renal Fascia

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

Fibrous capsule

a transparent capsule that prevents infections in surrounding regions from spreading to the kidney

Renal Cortex

The most superficial region of the kidneys, is light in color and has a granular appearance.

Renal Medulla

Deep to the cortex is the darker, reddish-brown center of the kidney

Renal Pyramids

cone-shaped tissue masses within the renal medulla.

Renal Columns

inward extensions of cortical tissue, separate the pyramids

Kidney Lobe

Each pyramid and its surrounding cortical tissue constitutes one of eight lobes.

Renal Pelvis

a funnel-shaped tube, is continuous with the ureter leaving the hilum.

Major Calyces

Branching extensions of the renal pelvis

Minor Calyces

Each one subdivision of a major calyce, cup-shaped areas that enclose the papillae.

Renal Arteries

deliver one-fourth of the total cardiac output (about 1200 ml) to the kidneys each minute.

Segmental Arteries

five subdivisions of the renal arteries, close to the helum

Interlobar Arteries

many subdivisions of the segmental arteries.

Arcuate 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.

Renal Plexus

a variable network of autonomic nerve fibers and ganglia, provides the nerve supply of the kidney and its ureter.

Nephrons

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

Glomerulus

(ball of yarn), which is a tuft of capillaries within the Nephron

Renal Tubule

has a cup-shaped end

Glomerular Capsule

(or Bowman’s capsule), which is blind and completely surrounds the glomerulus

Renal Corpuscle

collectively, the glomerular capsule and the enclosed glomerulus

Filtrate

plasma-derived fluid is the raw material that the renal tubules process to form urine.

Podocytes

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.

Filtration Slits

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.

Collecting Ducts

each of which receives filtrate from many nephrons, run through the medullary pyramids and give them their striped appearance

Thin Segment

Part of the descending limb, is a simple squamous epithelium freely permeable to water.

Thick Segment

the epithelium becomes cuboidal or even low columnar in the ascending part of the loop of Henle

Cortical Nephrons

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.

Juxtamedullary Nephrons

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.

Peritubular Capillaries

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.

Vasa Recta

straight peritubular capillaries in the kidneys that are situated parallel to and surrounding the loop of Henle.

Juxtaglomerular Apparatus

where the most distal portion of the ascending limb of the loop of Henle lies against the afferent arteriole feeding the glomerulus

Granular Cells

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.

Macula Densa

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.

Filtration Membrane

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.

Urine

contains mostly metabolic wastes and unneeded substances.

Glomerular filtration

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.

Myogenic Mechanism

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)

Extrinsic Controls

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.

Renin-angiotensin mechanism

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.

Tubular Reabsorption

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 Reabsorption

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.

Aquaporins

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.

Tubular Secretion

essentially, reabsorption in reverse

osmolality

is the number of solute particles dissolved in 1 kg of water and reflects the solution’s ability to cause osmosis

milliosmol (mOsm)

equal to 0.001 osmol

Countercurrent Mechanisms

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.

Countercurrent Exchangers

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

Dilute Urine

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

Concentrated Urine

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

Diuretics

chemicals that enhance urinary output.

Renal Clearance

refers to the volume of plasma that is cleared of a particular substance in a given time, usually 1 minute.

Renal Clearance

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

renal failure

(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.

Hemodialysis

uses an “artificial kidney” apparatus, passing the patient’s blood through a membrane tubing that is permeable only to selected substances.

Urochrome

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)

Ureters

slender tubes that convey urine from the kidneys to the bladder

Urinary 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.

Urethra

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.

Prostatic Urethra

about 2.5 cm (1 inch) long, runs within the prostate.

Membranous Urethra

which runs through the urogenital diaphragm, extends about 2 cm from the prostate to the beginning of the penis.

Spongy Urethra

about 15 cm long, passes through the penis and opens at its tip via the external urethral orifice.

Micturition

also called urination or voiding, is the act of emptying the urinary bladder.

Incontinence

involuntary loss of urine, usually a result of emotional problems, physical pressure during pregnancy, or nervous system problems.

urinary retention

the bladder is unable to expel its contained urine.

Catheter

a slender rubber drainage tube inserted through the urethra to drain urine

Pronephros

During the fourth week of development, the first tubule system formed but quickly degenerates as a second, lower set appears.

Pronephric Duct

that connects it to the cloaca persists and is used by the later-developing kidneys.

Mesonephros

the second renal system

Metanephros

the third renal system

Renal Calculi

(kidney stones) calcium, magnesium, or uric acid salts in urine that have crystallize and precipitate in the renal pelvis

Filtration

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.

Reabsorbtion

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.

Secretion

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.