Introduction to the Urinary System

Introduction to the Urinary System

• The urinary system removes most metabolic wastes produced by the body's cells.
• The kidneys filter metabolic wastes from the circulation.
• The kidneys produce urine.

Organs and Functions of the Urinary System

• The kidneys are paired organs that produce urine.
• The urinary tract eliminates urine.
• The urinary tract includes the ureters, urinary bladder, and urethra.
• The ureters are paired tubes.
• The urinary bladder is a muscular sac.
• The urethra is an exit tube.
• Urination or micturition is the process of eliminating urine.
• Bladder contraction forces urine through the urethra and out of the body

Functions of the Urinary System

• The urinary system performs excretion, eliminating metabolic wastes from body fluids.
• The urinary system performs elimination, discharging the wastes from the body.
• The urinary system performs homeostatic regulation of the blood's volume and solute concentration.

Homeostatic Functions of the Urinary System

• Blood volume and blood pressure are regulated by adjusting water volume lost in urine.
• Erythropoietin and renin are released to help regulate blood pressure.
• Plasma ion concentrations are regulated by controlling sodium, potassium, chloride, etc., lost in urine.
• Calcium ion levels are controlled through the synthesis of calcitriol.
• Blood pH is stabilized by controlling the loss of hydrogen and bicarbonate ions in urine.
• The urinary system conserves valuable nutrients.
• It prevents the loss of nutrients while removing metabolic wastes like urea and uric acid.
• The urinary system assists the liver.
• The liver is assisted in detoxification of poisons, and deamination of amino acids during starvation

Location of the Kidneys

• Situated on either side of the vertebral column.
• The left kidney has a slightly superior location than the right kidney.
• Adrenal gland caps the superior surface.
• The position of the kidneys is maintained by the position of the peritoneum.
• Contact with adjacent visceral organs plays a role.
• Connective tissues help maintain kidney location.

Protection of the Kidneys

• The kidneys are protected and stabilized by 3 layers: Fibrous capsule, Perinephric fat and Renal Fascia
• The fibrous capsule consists of a layer of collagen fibers that cover the outer surface.
• Perinephric fat: A thick layer of adipose tissue surrounds fibrous capsule.
• Renal fascia: A external fibrous layer that anchors kidney to surrounding structures.

Anatomy of the Kidney

• The typical adult kidney is ~10 cm long, 5.5 cm wide, and 3 cm thick weighing ~150 g.
• The hilum is a prominent medial indentation.
• It is the point of entry for the renal artery and renal nerves.
• It has the point of exit for the renal vein and ureter.
• The renal sinus is an internal cavity in the kidney lined by the fibrous capsule.
• A renal sinus is bound to outer surfaces of structures in a renal sinus. The renal sinus stabilizes the positions of the ureter, renal blood vessels, and nerves.
• The renal cortex is the superficial region of the kidney.
• It is in contact with fibrous capsule, and it is reddish-brown and granular.
• Renal pyramids are triangular structures that occur in 6-18 sections.
• The base of each pyramid abuts the cortex.
• The tip which is also called the renal papilla projects into the renal sinus.
• Renal columns consist of bands of cortical tissue that separate renal pyramids. They extend into the medulla and have a granular texture.
• A kidney lobe consists of a renal pyramid, the overlying cortex and adjacent renal columns.

Renal Structures

• Ducts within each renal papilla discharge urine into a minor calyx which is a type of cup-shaped drain.
• Four or five minor calyces form a major calyx.
• The renal pelvis is a large, funnel-shaped chamber.
• The renal pelvis is formed by two or three major calyces and connected to the ureter which drains the kidney.
• It fills most of the renal sinus.

Blood Supply to Kidneys

• The kidneys receive 20–25% of total cardiac output.
• About 1200 mL of blood flow through kidneys each minute.
• Each kidney receives blood through a renal artery.

Key Renal Arteries

• Segmental arteries receive blood from the renal artery.
• Interlobar arteries divide into segmental arteries and radiate outward through renal columns between renal pyramids.
• Arcuate arteries supply blood from interlobar and arch along the space between cortex and medulla of kidney.
• Afferent arterioles - branch from each cortical radiate artery (interlobular artery).
• They Deliver blood to where capillaries supply individual nephrons.
• Cortical radiate veins (interlobular veins) deliver blood to arcuate veins.
• Arcuate veins empty into interlobar veins and drain directly into renal vein.

Renal Nerves

• The renal nerves innervate kidneys and ureters.
• These nerves enter each kidney at the hilum and follow the branches of renal arteries to individual nephrons.
• Sympathetic innervation adjusts the rate of urine formation.
• The sympathetic innervation influences urine composition by stimulating the release of renin.

The Nephron

• Nephrons are the microscopic, function units of the kidneys.
• Each nephron consists of a renal corpuscle and a renal tubule.
• Each renal tubule empties into a collecting system.
• The renal corpuscle is a spherical structure and consists of the Glomerular (Bowman's) capsule, and the Glomerulus (capillary network).

Glomerular Capsule

• It forms the outer wall of renal corpuscle.
• Encapsulates glomerular capillaries and continuous with initial segment of renal tubule.

Glomerulus

• Consists of about 50 intertwined capillaries.
• Blood is delivered by afferent arteriole.
• Blood leaves through efferent arteriole.

Layers of the Glomerular Capsule

• Capsular outer layer - Simple squamous epithelium.
• Visceral layer - covers glomerular capillaries.
• Capsular space.

Podocytes

• Podocytes are large cells of visceral layer.
• They have complex foot processes (pedicels) that wrap around glomerular capillaries.
• They form filtration slits: Narrow (6–9 nm wide) gaps between adjacent foot processes.

Glomerular Capillaries

• Glomerular capillaries are fenestrated capillaries. Their endothelium contains large-diameter pores.
• Intraglomerular mesangial cells are located among glomerular capillaries.
• They are derived from smooth muscle and provide support, filtration, and phagocytosis.
• They also control the diameter of capillaries.

Filtration Membrane

• It consists of Fenestrated endothelium, Basement membrane and the processes (pedicels)
• During filtration in renal corpuscle, blood pressure pushes water and small solutes across the membrane into capsular space.
• Larger solutes do not pass through.
• Solution produced is essentially protein-free filtrate.

Renal Tubule

• It has two convoluted segments named the Proximal convoluted tubule (PCT), and Distal convoluted tubule (DCT).
• Segments are separated by nephron loop (loop of Henle) which consists of a U-shaped tube.
• Extends at least partially into the medulla.
• While traveling along tubule, the tubular fluid (filtrate) gradually changes

Proximal Convoluted Tubule (PCT)

• PCT is the first segment of renal tubule.
• PCT entrance lies opposite of connection of afferent and efferent arterioles with glomerulus.
• Simple cuboidal epithelium with microvilli on apical surfaces.
• Its primary function is reabsorption of ions.

Nephron Loop

• The descending limb which flows towards the renal pelvis.
• Ascending limb flows towards the renal cortex.
• Segments of limbs have thick or thin epithelia: Descending thin limb (DTL), Ascending thin limb (ATL) and Thick ascending limb (TAL).

Distal Convoluted Tubule (DCT)

• The third segment of the renal tubule.
• Initial portion of loop passes between afferent and efferent arterioles.
• Smaller luminal diameter than PCT.
• Epithelial cells lack microvilli.
• The primary function is to reabsorb water and selected ions, and actively secrete the secretion of undesirable substances.

The Juxtaglomerular complex (JGC)

• JGC helps regulate the blood pressure and filtrate formation
• Consists of Macula densa, Juxtaglomerular cells and Extraglomerular mesangial cells.

Juxtaglomerular Complex

• Macula densa have cells of DCT, near renal corpuscle. Function as chemoreceptors or baroreceptors.
• Juxtaglomerular cells: smooth muscle cells of afferent arteriole, function as baroreceptors and secrete renin.
• Extraglomerular mesangial cells are located between afferent and efferent arterioles and provide feedback control.

Collecting System

• Has a series of tubes that carries tubular fluid away from the kidney's nephrons.
• The collecting ducts receive fluid from many nephrons.
• Each collecting duct carries fluid to a papillary duct, which carries and drains into a minor calyx.
• It transports tubular fluid from nephrons to renal pelvis, adjusts fluid composition and determines final osmotic concentration and volume of urine.

Types of Nephrons:

• Cortical nephrons: makes up 85% of all nephrons. Located mostly within superficial cortex of kidney, they have a Nephron loop that is relatively short.
• The Efferent arterioles deliver blood to a network of peritubular capillaries
• Juxtamedullary nephrons: 15 % of nephrons, the Nephron loop extends deep into medulla.
• Efferent arterioles connect to vasa recta.

Urine Production

• Goal of urine production is to stay homeostatically balanced.
• Kidneys regulate the volume and composition of blood and excretes metabolic wastes.

Metabolic Wastes

• Three Main Wastes: Urea, Creatinine, and Uric Acid
• Urea, which is the most abundant organic waste product produced.
• Creatinine, is produced from breakdown of creating phosphate in muscles.
• Urid acid from recycling of nitrogenous bases.
• Organic wastes like urea, creatinine and uric acid are dissolved in the bloodstream and can only be eliminated when dissolved in urine.
• Waste removal is accompanied by water loss.

Kidney Function in Producing Urine

• Kidneys can usually produce concentrated urine ( 1200 mOsm/L which is what is needed.
• Kidney concentrates and contains filtrate.
• When filtrate is not concentrated, the failure leads to fatal dehydration within hours.
• kidney can reabsorption and retain valuable materials.
• For example, sugars and amino acid are reabsorbed so they are not excreted in the urine.

Basic Processes of Urine Function

• Filtration, during glomerular capillaries.

• Reabsorption, during movement of water and solutes.

• Secretion, Transport of solutes from peritubular flues to tubular fluid

Glomerular Filtration

• Its driven by a hydrostatic pressure.
• It involves passage across a filtration membrane that allows small solute molecules to pass through, but restricts the larger items such as material and solutes.
• This passage involves three components of membrane being fenestrated endothelium, basement membrane, foot pressure of podocyte

Glomerular Capillaries

• Made up of fenestrated endothelium with small pores, Prevent passage of blood cells and allow diffusion of solutes
• Basement membrane, contains more selective allowance through and can also allow for small proteins to past
• Glomerular filtration is governed by balance between:
  • Hydrostatic pressure (fluid pressure)
  • Colloid osmotic pressure (of materials in solution) On each side of capillary walls

Glomerular Hydrostatic Pressure

• Blood pressure in glomerular capillaries.
• Blood leaving glomerular capillaries- Flows into efferent arteriole with luminal diameter smaller than that of afferent.
• Tends to push water and solutes in certain direction depending where it is in respect to a certain area through its filtration.

Capsular Hydrostatic Pressure vs Colloid Osmotic Pressure

• Capsular Hydrostatic pressure is what opposes hydrostatic pressure (the flow of water and solutes in certain direction) within the process.
• Blood Colloid Osmotic Pressure is the same as the pressure due to osmosis that draws water molecules to other solutes

Fluid Pressure

• Net Hydrostatic Pressure Difference between glomerular hydrostatic pressure, capsular hydrostatic pressure
• Fluid is measured through mm of mercury: GHP – CsHP = NHP -> 50 mm Hg –15 mm Hg = 35 mm Hg

Net Filtration Pressure

• It refers to the average pressure forcing water and dissolved substances, which is out the capillaries, and that in the end, makes a solution.
• Its found my the difference through,Net pressure - colloid Osmotic pressure.
• To show the pressure, NHP – BCOP = NEP. 35 mm HG - 25mm HG = 10 mm HG.

Glomerular Filtration Rate

• There is an amount of filtrate that kidneys produce for minutes averages, and it averages to 125 mL/min.

• About 10 percent of fluid delivered to kidneys leaves bloodstream and enters a filtration-based system.

• Each Glomeruli (or glomerulus) generates about 180 liters of filtrate per day.

• It makes about Approximately 70 times of plasma volume, and determined thought the overall filtration

GFR Regulation

• Its controlled is 3 levels, 1) Autoregulation (local level 2) Hormonal regulation (initiated by kidneys and. 3) Autonomic regulation (by the sympathetic division of the ANS).

Auto-regulation

• Maintains adequate GFR despite changes in local blood flow
• Involves changing of luminal diameters.

Hormonal Regulation

• Happens through Two systems Renin-angiotensin-aldosterone system and. 2) Natriuretic peptides

Renin System

• Is where three stimuli that cause the JGC where releases renin to release aldosterone.
• Decrease the pressure at the glomerulus due to lowering in blood volume – Stimulation of kidney cells by sympathetic innervation
• Decrease concentration in tubular blood fluid

Regulation

• Renin converts inactive angiotensinogen to inactive angiotensin | , angiotension| will then release it after.
• Angiotensin I gets releases in Angio tension II through angiotensin | converting and what produces that, is where it all starts and happens where is primary capalaries

Effects of Angiotensin

• Overall all these functions of angiotensin will increase increase overall pressures .
• Contraction of muscular structure to deliver increase of secretions by adrenal glands Na+
• Increased of artery levels Stimulation of Thirst Centers . increased production and the overall is to increase to the system

Hormonal GFR

• Where blood is involved automatically increases the GFR for for flow to occur more quickly . If increase in blood in the volume is severe hormonal factors would rise.

Natriuretic peptides

• It involves the released through the heart in respond to the blood volume and pressures
• Triggers dilations of afferent arteriole where an Increase in glomerular pressures which ANP also does
• Net reabsorption increased urine production volume

GFR Autonomic Regulation

• Autonomic- Mostly consists to the sympathetic postganglionic that slow filtrate as result can stabilize
• Constricting: Glomerular
• Decrease rates of productions

Filtration

• It is Passive because It has solutes that have to get through with the help on capsule and its space, a glucose, or any metabolic waste products that are also extra.

Useful Materials

• The Kidney then puts the useful things back for distribution

Renal Tubules

• There is 3 functions which include useful organic reoccurring that didn’t glomerular
• Also reabsorbtion to prevent that also did not start glomerular

Fluid in Renal Function

• During the bodies, the reabsorption returns fluid to the blood stream in general that 99 of volume goes through with the transport of the tubes
• The main function of blood is to add components in which adds to blood in the tubular

Kidney

• Has channels that reabsorpt it helps. Has a singular system
• Membrane contains many proteins

Maximum of transport maximum

• As the transports gets its, that reabosorptive can be saturated to nephron it depends with concentrations and reabosrobtive

Reabsorptions

• Can be in the renal threshold and what goes in and the kidney is to prevent to allow to function. The kidneys help in the control

Osmotic Function

• Its concentration (osmolarity) in which Is defined it number of particles . the units, can vary in a lot of different types of measuring.

Normal Reabsorption System Revert

• There three layers that all have a transport. There is Reabsorbtion which are the fluids .
• Second are the secretions And the transports which are the mechanisms

Functions of the Sodium:

• Its reabosrobtion within a process, that helps sodium, and to also take of excess hydrogen and other things it needs

Sodium and Reabsorption in Limbs

• As it makes, its limb, the water begins at a low
• As it reabosros, its half the ions
• Very juxmmedula

DCT

-Only 15-20 percent of initial filtrate volume reaches, when the volume is high the body has time to reabsorb from there. The concentration in their electrosluts

DCT Processes

• Active Secretion transport and toxins that need to not cross.
• As its primary function with its electrolyte

Reabsorption Function

• Cell activity transports + in tubular and also. Contain ion pumps where it is in its exahcnge to go another direction

Aldosterone

• Can create that of a home produced by the adrenal cortex function that stimulates its own production and to prevent that which does create a lot. The system in there

Hypokalemia

• The production would prolonged and in turn could be damaged

ATriai peptide

• To counter that is oppose secretion of it would hurt with such a

Secretion

• Rate falls then it be high in fluid to take its own space back

Hyrogen:

• Is the exchange for the sodium

Acidity and PTT

• Causes and increases from blood flow and can speed in to.

Damage and High Levels

• Can leads so and it

Collecting

• They come together near their renal space through each that is is what controls those. And also then can leads to water if necessary the levels also help. And is another

Reabsorption

• Sodium is exchanged Bicarbonate:
• Is helped to transfer back with another. And so will be what is left as a final end product. Final the product will all head so a way to test it is through which is measured by a process.

Reabsorption

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Urea

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Function Tests

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