Urinary System Flashcards

Urinary System: Organs and Functions

• Composed of:
  • Kidneys
  • Ureters
  • Urinary bladder
  • Urethra
• Functions:
  • Removal of waste products from blood
  • Storage and expulsion of urine
  • Regulation of blood volume, erythrocyte production, ion levels, and acid-base balance

Removal of Waste Products

• Kidneys filter blood plasma to remove waste products.
• Filtrate is converted into urine.

Storage and Expulsion

• Ureters transport urine from kidneys to urinary bladder.
• Urine is stored in the urinary bladder.
• Urethra transports urine from the urinary bladder and expels it from the body through micturition (urination).

Regulation of Blood

• Kidneys regulate:
  • Blood volume: controlled by hormones, influencing blood pressure (BP). Changes in blood volume lead to changes in BP.
  • Erythrocyte production: kidneys release erythropoietin (hormone) when oxygen levels in blood are low, stimulating red blood cell (erythrocyte) production.
  • Ion levels: control levels of ions (sodium, potassium, calcium, phosphate) by removing them as needed.
  • Acid-base balance: control hydrogen and bicarbonate ion levels, regulating blood's acid-base balance.

The Kidneys

• Paired retroperitoneal organs in abdominal cavity.
• Located approximately between T12 and L3.
• Right kidney is slightly lower than left kidney due to the liver.
• Adrenal (suprarenal) glands sit on superior aspect; also retroperitoneal.
• Hilum (medial border):
  • Renal artery, renal vein, renal pelvis (continuous with ureter), lymphatics, and nerves enter or exit.
• Function: regulate blood and remove waste products to produce urine.

Tissues Covering Kidneys

• Renal Fascia:
  • Anterior and posterior layers.
  • Dense irregular connective tissue.
  • Anchors kidney to posterior abdominal wall.
• Perirenal Fat Capsule:
  • Adipose connective tissue.
  • Provides support, helping to keep kidney in place.
• Fibrous Capsule:
  • True capsule.
  • Dense irregular connective tissue.
  • Maintains kidney shape.
  • Provides protection from traumatic injury, helps prevent infections.

Internal Anatomy of the Kidneys

• Renal Cortex: outer region.
• Renal Medulla: inner region.

Renal Pyramid

• Structures in renal medulla.
• 8-15 renal pyramids per kidney.
• Base faces renal cortex; apex points towards hilum.

Renal Column

• Extensions of renal cortex projecting into renal medulla between renal pyramids.

Renal Papilla

• Apex of the renal pyramid.

Renal Lobe

• Region of a kidney consisting of a renal pyramid and its surrounding cortical tissue.

Minor Calyx

• Each renal papilla projects into a funnel-shaped space called a minor calyx.
• Each kidney has 8-15 minor calyces.

Renal Pelvis

• Several minor calyces merge to form a single space called the renal pelvis, which is continuous with the ureter.
• Structures collect urine produced in the kidney and drain it into the ureter.

Renal Sinus

• Hilum continuous with renal sinus within each kidney.
• Renal calyces, renal pelvis, renal artery, renal vein, lymphatic vessels, nerves, and adipose tissue occupy this space.

Blood Supply of Kidneys

• Renal artery (branch of abdominal aorta) for each kidney.
• Arteries enter at hilum and renal sinus, branching to form afferent arterioles.
• Afferent arterioles: blood vessel delivers blood to nephron (functional unit of kidney).
• Nephron filters blood plasma to produce urine.
• Afferent arterioles form glomerulus (capillary network within nephron).
• Filtration of blood plasma occurs at the glomerulus.
• Remaining blood flows out of glomerulus into efferent arterioles.
• Efferent arterioles branch into capillary networks, draining into renal vein.
• Renal vein exits kidney at hilum and drains into inferior vena cava.

The Nephron

• Functional unit of the kidneys; produces urine via:
  • Filtration: substances in blood plasma (water and some solutes) are filtered out to produce filtrate.
  • Reabsorption: substances in filtrate (most water and essential solutes) are returned to blood; filtrate becomes tubular fluid.
  • Secretion: solutes (waste products) are removed from blood into tubular fluid.
• 2 main parts: renal corpuscle and renal tubule.

Renal Corpuscle

• Filtration of blood plasma occurs.
• 2 components: glomerulus and glomerular (Bowman’s) capsule.

Renal Tubule

• Reabsorption and secretion occur.
• 3 components: proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Renal Corpuscle Details

• Filtration of blood plasma occurs; located in renal cortex with vascular pole (afferent/efferent arterioles) and tubule pole (proximal convoluted tubule).
• Blood flows in via afferent arteriole, is filtered to produce filtrate, and exits via efferent arteriole.

Glomerular (Bowman’s) Capsule

• Double-layered epithelial capsule surrounding glomerulus.
  • Outer parietal layer: simple squamous epithelium.
  • Inner visceral layer: specialized cells called podocytes.
• Visceral layer covers glomerulus; filtration slits between podocytes allow small substances to filter out to become filtrate.
• Larger substances (most plasma proteins) are left behind.
• Capsular space between parietal and visceral layers collects filtrate before flowing into proximal convoluted tubule.

Renal Tubule Details

• Receives filtrate produced in renal corpuscle and modifies it to produce tubular fluid.
• Begins in renal cortex, extends into renal medulla, before returning to renal cortex.

Distal Convoluted Tubule

• 3rd part of renal tubule; continuation of ascending limb of loop of Henle in renal cortex; simple cuboidal epithelium with few short microvilli.
• Lumen does not appear fuzzy.
• Lighter staining than proximal convoluted tubule.

Loop of Henle

• Descending limb (continuation of proximal convoluted tubule) extends into renal medulla, and an ascending limb, returning back to renal cortex.
• Each limb has thick & thin portions lined by simple squamous epithelium - involved in reabsorption of water & essential solutes back into blood & some secretion of hydrogen ions into tubular fluid

Collecting Tubules, Collecting Ducts, & Papillary Ducts

• Tubular fluid exits nephron and drains into collecting tubules in renal cortex.
• Collecting tubules are lined by simple cuboidal epithelium and form main components of medullary rays.
• Collecting tubules move into renal medulla and form collecting ducts.
• Collecting ducts are lined by simple columnar epithelium and have larger lumens than collecting tubules.
• Collecting ducts are the last structures where tubular fluid can be modified (reabsorption of water and sodium to conserve water).
• Collecting ducts > papillary duct (located at renal papilla of each renal pyramid).
• Once tubular fluid drains into a pillar ducts it is called urine fails into a minor calyx, then flows into ureter.

Ureters

• 3 layers: inner mucosa, middle muscularis, & outer serosa or adventitia
• Tubes that transport urine from kidneys to urinary bladder.
• Sit directly against posterior abdominal wall; retroperitoneal.
• Originate from renal pelvis as it exits hilum of kidney & terminates by entering urinary bladder

Mucosa

• Composed of transitional epithelium with underlying lamina propria made of fibroelastic CT - allows ureters to stretch when they fill with urine
• Mucosa is folded, giving ureters a star-shaped lumen.
• Folds allow lumen to increase considerably when ureters are stretched.

Muscularis

• Consists of 2 smooth muscle layers - inner longitudinal layer & outer circular layer
• Opposite arrangement to GI tract

Adventitia

• Outer layer of ureters is an adventitia composed of areolar CT, as ureters are retroperitoneal - helps anchors ureters to posterior abdominal wall

Urinary Bladder

• Muscular sac that stores urine until it is ready to be expelled.
• Located in pelvic cavity directly posterior to pubic symphysis - can ascend slightly into abdominal cavity when full
• Male urinary bladder sits directly anterior to rectum & superior to prostate gland
• Female urinary bladder sits anterinferior to uterus & directly anterior to vagina
• When empty, urinary bladder is shaped like upside-down pyramid - has an apex that points anteriorly & a base which is directly posteriorly
• Ureters enter at its two posterolateral angles - neck of urinary bladder is located inferiorly & is where it drains urine into urethra to be expelled from body
• Internally on posterioniferior aspect, there is a triangular region called trigone which is defined by 2 ureteric openings in superior corners & the urethra opening in the inferior corner
• This area is smooth, unlike the rest of internal surface which has mucosal folds called rugae
• Muscle in the wall of urinary bladder is called detrusor muscle

Mucosa

• Composed of transitional epithelium with underlying lamina propria - folded to form rugae, which increases distensibility of urinary bladder - rugae flatten out when bladder fills w/ urine, the mucosa lacks these folds in the area of the trigone

Muscularis

• Consists of smooth muscle called detrusor muscle that is arranged in 3 layers: inner longitudinal, middle circular & outer longitudinal- addition of 3rd layer allows urinary bladder to squeeze urine out when detrusor muscle contacts during micturition

Adventitia/Serosa

• Outer layer is mostly adventitia composed of areolar CT, as it lies outside of peritoneal cavity. It’s superior surface is covered by parietal peritoneum, making thr outer layer in this region a serosa composed of simple squamous epithelium w/ underlying areolar CT

Urethra

• Tube that transports urine from urinary bladder to expel it.
• Originates at neck of urinary bladder, where a circular thickening of the detrusor muscle forms a structure called the internal urethral sphincter.
• Involuntary sphincter that keeps urethra closed when urine is not being expelled.
• Guarded by another sphincter (external urethral sphincter) - located in sheet of muscle called urogenital diaphragm - voluntary sphincter composed of circulatory arranged skeletal muscle fibres
• Both internal & external urethral sphincters relax during micturition, allowing urine to be expelled from the body
• Opens to exterior body at an opening called external urethral orifice

Female Urethra

• Guarded by involuntary internal urethral sphincter at its origin. from the neck of urinary bladder & by another sphincter at its inferior end called external urethral sphincter.
• Voluntary sphincter composed of circularly arranged skeletal muscle fibres located in urogentiial diaphragm.
• Prevents urine from being expelled in body until voluntarily decided to

Male Urethra

• 2 functions - transport urine out of body during micturition & conduct semen during ejaculation
• Important to note it does not carry these at the same time
• Divided into 3 regions named to structures they pass through
  • Prostatic urethra: first part that passes z prostate gland, which sits directly inferior to urinary bladder
  • Membranous urethra : 2nd part - passes through membrane-like urogenital diaphragm (aka. intermediate urethra)
  • Spongy urethra : 3rd & longest - passes through penis. Passes through specific mass of erectile tissue in the penis called the corpus spongiosum