Urinary System: Functions and Anatomy

Urinary System Overview

• The urinary system removes most metabolic wastes.
• Kidneys produce urine, eliminating metabolic waste from the bloodstream.
• Organs of the urinary system include paired kidneys which produce urine, the urinary tract which eliminates urine via the ureters, the urinary bladder, and the urethra.
• Urination/micturition is the process of eliminating urine; contraction of the bladder forces urine through the urethra.

Functions of the Urinary System

• Excretion involves removing metabolic wastes from fluids in the body.
• Elimination involves discharging waste products from the body.
• Homeostatic regulation balances the volume and the solute concentration of blood.

Homeostatic Functions

• Regulates blood volume and blood pressure by adjusting water loss in urine and releasing erythropoietin and renin.
• Regulates plasma ion concentrations by controlling the quantities of sodium, potassium, chloride, and other ions lost in the urine, also synthesizing calcitriol to control calcium ion levels.
• Stabilizes blood pH by controlling hydrogen and bicarbonate ion loss in urine.
• Conserves nutrients by preventing their loss while removing metabolic wastes like urea and uric acid.
• Assists the liver in detoxification of poisons, and deamination of amino acids during starvation.

Kidneys

• The Kidneys are located on either side of the vertebral column, with the left kidney slightly superior to the right.
• The superior surface is capped by the adrenal gland.
• The Kidneys' position is maintained by the peritoneum, contact with visceral organs, and connective tissues.
• Kidneys are protected and stabilized by three layers:
  • Fibrous capsule: Collagen fiber layer covering the outer surface.
  • Perinephric fat: Thick adipose tissue surrounding the fibrous capsule.
  • Renal fascia: Dense outer layer anchoring the kidney to surrounding structures.

Kidney Structure

• Typical adult kidneys are 10 cm long, 5.5 cm wide, 3 cm thick, and weigh about 150 g.
• The hilum is a medial indentation that serves as the point of entry for the renal artery and nerves and the exit point for the renal vein and ureter.
• The renal sinus is an internal cavity within the kidney lined by the fibrous capsule and stabilizes the ureter, blood vessels, and nerves.
• Renal cortex is the superficial region of the kidney in contact with the fibrous capsule (reddish-brown and granular)
• Renal pyramids are 6-18 triangular structures in the renal medulla, the base abuts the cortex, and the tip (renal papilla) projects into the renal sinus.
• Renal columns are bands of cortical tissue separating renal pyramids, extending into the medulla, granular texture.
• Each Kidney lobe consists of a renal pyramid, the overlying cortex, and adjacent tissues of the renal columns and produces urine.
• Ducts within the renal papilla discharge urine into minor calyx and a major calyx is formed by four or five minor calyces.
• The renal pelvis is a large funnel-shaped chamber formed by two or three major calyces, fills most of the renal sinus, connects to the ureter and drains the kidney.

Blood Supply

• Kidneys receive 20-25% of total cardiac output, about 1200 mL of blood per minute through the renal artery.
• Segmental arteries receive blood from the renal artery and divide into interlobar arteries, which radiate through renal columns between renal pyramids.
• Interlobar arteries supply blood to arcuate arteries that arch along the cortex/medulla boundary.
• Afferent arterioles branch from each cortical radiate artery and deliver blood to capillaries supplying individual nephrons.
• Cortical radiate veins (interlobular veins) deliver blood to arcuate veins, which empty into interlobar veins, ultimately draining into the renal vein.

Renal Nerves

• Innervate the kidneys and ureters, entering each kidney at the hilum, then follow the branches of the renal arteries to the individual nephrons.
• Sympathetic innervation adjusts the rate of urine formation by changing blood flow at the nephron. It also influences urine composition by stimulating the release of renin.

Nephrons

• Nephrons are microscopic functional kidney units and consist of a renal corpuscle and renal tubule.
• The renal tubule empties into the collecting system.
• Renal Corpuscle: Spherical structure consists of glomerulus and glomerular capsule.
  • Glomerular capsule: Outer wall of renal corpuscle, encapsulates glomerular capillaries, and has simple squamous epithelium and visceral layer.
  • Glomerulus: A capillary network with about 50 intertwined capillaries, delivered blood by afferent arteriole and blood exits via efferent arteriole.

Glomerular Capsule Structure

• The capsular outer layer has simple squamous epithelium.
• Visceral layer covers glomerular capillaries.
• Capsular space separates two layers.
• Podocytes are large cells of the visceral layer with complex foot processes (pedicels) wrapping around glomerular capillaries.
• Filtration slits are 6–9 nm wide gaps between adjacent foot processes.

Glomerular Capillaries & Filtration

• Glomerular capillaries are fenestrated, preventing passage of blood cells but allowing diffusion of solutes, including plasma proteins.
• Intraglomerular mesangial cells are specialized. They are found among glomerular capillaries, are derived from smooth muscle, provide support/filtration/phagocytosis, and control capillary diameter.
• The filtration membrane consists of fenestrated endothelium, the basement membrane, and foot processes.
• Filtration involves blood pressure forcing water and small solutes across the membrane into the capsular space, creating a protein-free filtrate.

Renal Tubule Structure & Function

• Has two segments: a proximal tubule (PCT) and a distal tubule (DCT) which are seperated by the nephron loop.
• While traveling along the tubule tubular fluid (filtrate) changes in its composition due to substances being reabsorbed/secreted within the nephron.
• The PCT is the initial segment of the tubule, opposite from the afferent and efferent arteriole connect to the glomerulus, lining with simple cuboidal epithelium and microvilli on apical surfaces performing main function = reabsorption of ions.
• Nephron loop flow: fluid towards renal pelvis to ascending.
• Thin epithelia segments that have thick: Descending, ascending and Thick (TAL)

Distal Convoluted Tubule (DCT)

• It's the third segment of the renal tubule where the initial section passes through afferent and efferent arterioles.
• The Epithelial cells do not have microvilli.
• The DCT active function revolves around reabsorbing water and undesirable elements.

Juxtaglomerular Complex & Filtration

• The JGC regulates blood pressure and filtrate formation.
• It consists of macula densa, juxtaglomerular cells, and mesangial cells.
• Macula densa epithelial cells contain chemoreceptors or baroreceptors near the renal corpuscle.
• Juxtaglomerular cells are smooth muscle cells lining afferent arteriole that serves as both baroreceptors & secrete renin.
• Extraglomerular mesangial cells are located between arterioles that assist in feedback management.

Collecting System

• The collecting system carries away the tube fluid through a series of channels.
• Many neurons supply the collecting ducts.
• They descends into the medulla then travels through the cortex. The small calyx, which is a minor calyx, collects fluid after being carried by a duct.
• This structure allows to carry tubular fluid for the distal nephrons in order to make/adjust renal pelvis.

Types of Nephrons

• Cortical Nephrons: 85% of them, short nephron, that's delivers their blood to capillaries.
• Juxtamedullary Nephrons: 15%, with long blood, and the Efferent connects to Vasa.

Renal Physiology

• The goal is to assist the elimination of wastes and assist concentrating filtrate by dehydration to hours.
• Useful materials examples is sugars and amino acids.
• Basic Process:

1. Filtration: blood pressuring pushes against walls, and glomerular capillaries;
2. Reabsorption - where fluid moves from the filtrate to peritublar peritublar.
3. Secretion - fluid transports solutes.

Solute/Filtrate Processing & Composition

• There are three metabolic wastes: Urea, Creatinine, and Uric Acid; which only dissolves if accompanied with fluid water lost as the process progress.
• The three items in urine is: H20, Salt, Urea
• Filtrate consist of solutes, and some blood contents without Red Blood Cells, Albumins & Proteins in the urine.

Glomerular Filtration

• Hydro-static pressures determines glomerular filtration, the small the more passage of solutes. Also three components are used in this process: "fenestrated"; basemental and "podocytes".
• Filtration rates averages out to be 125 ml/min Regulation is accomplished by 3 ways that either: 1) Autoregulation; 2) Hormonal; 3) Autonomic.

Autonomic of Glomerular

• Autonomic: Constricts, Decreases with sympathetic activation.
• Hormonal: Blood Volume = GFR and to promotes fluid.

RAAS (Renin-angiotensin-aldosterone system) in Kidneys

• It results from decreased pressures to glomerulus. This causes the release of renin, triggering hormone for ADH that influences blood pressure.
• Angiotensin Effects: Contractions, secretion by the adrenal glands and blood fluid increased.

Net Filtration Pressure

• Colloid forces/dissolves solute, and is hydrostatic balance/filtrate.
• Blood Hydrostatic pressure, Capsular hydrostatic pressure and NHP will assist blood and solutes out which would be an average.

Natriuretic Peptides

• Stretched walls resulting from increased GFR, by Aniral peptide and the atria.
• Constricting leads pressuring to volume.

Autonomic

• It's sympathetic with the sympathetic activation, filtrate in short, decreasing and constricting everything.

Reabsorption & Secretion

• Happens when blood cells is in the capsules with metabolic wastes, acids etc.
• Everything useful will be reabsorbed!
• It is in the tubles, and collection via diffusion & osmosis
• It does that when:
  1. reaborbs organic;
  2. greater with the 90% of water and then secretion of elements not filtered.

PCT

• This segment can absorb 60/70 as it reabsorbs then diffues the capilaires. Also it actively reabsorbs or passively. The same principles applies with water.
• Sodium plays role as its in the body w/channels and to the tubules when the solutes in the body are.

Nephron

• 60 and 70% of fluids are looped inside of each segments with reabsorption that assists with filtration. This descending part consist reabsorbing while the latter ascends impermeable.
• Re/secretion distal occurs when 15/20 percent which consists of electrolytes as a priority.

Distal Tubule

• Main Processes involved: Reaborbing the sodium and calcium ions with H20, to the selective of fluid in it.
• Secretions of Ions, and Acid. By the sodium, calcium, tube into of it with ions.

Juazta Cells

• Located in between and control feedback, with extra being there as a back.
• For Macula it has chemo and baro
• In relation to blood or Renin with hormones in charge of that.

Collecting System

• It gets from many Nephrons while hormones is on duty to: a) control + b) water ADH influences permeability.

DCT

15.20 percent + It is reabsorbed with the concentration that makes up of H20. Hormone = Aldos with that with the Sodium levels. Hypokalemia from blood stimulations and Parathyroid hormone in there.

Hydrogen

• This acidifies and it causes for elevations for blood with pH in blood increasing the metabolic acidosis.

Tubular Fluids

• Aids to blood pH level and Bicarbonoates that comes blood.

Reabsorption & Secretion in the Renal/Collecting System

• Collecting Ducts:* Receive tubular fluid from nephrons and carry it toward the sinus.
• Hormonal Regulation:* Aldosterone controls the sodium pumps while ADH affects permeability of it, to either an opposed and/or a suppressed.
• Ion Process:* Is through Sodium and Bicarbonoates levels then Urea's.

CounterCurrent

• It can exchange or multiplies fluid, with a "Descending fluid and the limbs". The limb is either water relative with an element. This effect has different permeability charareristics: Water and Solutes with transport mechanisms.

Transport with Rate Transports & Osmotic

1: As the sodium and the chloride with fluid. 2: Distal = 1.3 + there a process of concentration with the Urea in the duct. Papillary is involved with the Urea concentration levels.

Homeostasis Volume with Urine

• Water in control with reabsorption through either a Proximal segment tub or Descending with short volumes either controlled, or influenced in volume.

Urea In Lumen

• Its' purpose helps with levels.
• If Water is high with Osmosis can results in two items. Which is water, and tubular can also increases the concentration of it. Oblibatory in it helps prevent the percentage from happening with water. The same concept can helps with the volume, a 27I can cause a segment to be water with ADH on duty. The blood level is the main aspect that will results in the number needed with Osmosis.

Urine Compostions

• It filters with some being able to excrete or not, the goal is to reabsorb the elements.

Normal Levels

• Urine is always as a clear or sterile.

Clearence

• It test how much Creatinine the body is taking and it gets the GFR. Is Inulin if GFR test accurate?. The Urea test helps determine the amount.

Urine

• It's only modified if entering pelvic is present. Then the process will starts with bladders, uteral as an example. Image assists during administration. Then will begin when you need the toilet for the process. They is a slit. This contractions repeats.

Bladder & Tissue Description

• It helps support ligaments bands from with a pair with the tubes for either storing or conducting these.
• Layers involved Mucosa, Submu, detrusor then tissue layer connects. The triangular (three side point structure that funnel) is for contracting. It must relaxed during this time.
• There to be internal/external control as this system involves, in males, in a urethra tube.

Male Anatomy

• Extends for the neck all the way, the prostatic passes when the member assist with the perinal muscles.

Outside Female

• Female member is usually short as the area assists with veins.

External (Muscle) Anatomy

• It valves with a voluntary control + resting levels + pelvic's ground.