Urinary System

John Minor and Jeremiah Shaw

What are the major parts of the urinary system?

Diagram of Urinary System

Esophagus (cut)

Celiac trunk

Left adrenal gland

Left kidney

Left renal arteryLeft renal vein

Superior mesenteric artery

Ureter

Left common iliac artery

Urinary bladder

Rectum (cut)

Gonadal artery and vein

Quadratuslumborum muscle

Psoas majormuscle

Right adrenalgland

Right kidney

HilumAorta

Iliacus muscle

Inferior vena cava

Diaphragm

Anterior view

Parts of Urinary System

• Kidneys – organs that have excretory functions and produce urine

• Ureters – tubes leading from the kidneys to the urinary bladder

• Urinary Bladder – a muscular sac for temporary storage of urine

• Urethra – a tube that conducts urine to the exterior

What are the functions of the Urinary System?

Functions of Urinary System

• Regulation of blood pressure

• Regulation of concentrations of ions in plasma

• Stabilizing blood pH

• Conserving valuable nutrients

• Assisting liver in detoxifying poisons

What is the anatomy of the kidney?

Minor calyx

Renal pyramid

UreterRenal capsule

(a)

Major calyx

Connection to minor calyx

Hilum

Renal pelvis

Medulla

Renal sinus

Adipose tissuein renal sinus

Renal papilla

Renal columns

Minor calyx

Renal pyramids

UreterRenal papilla

Renal lobe

(b)

Renal pelvis

Renal capsuleCortex

Hilum

Medulla

Renal sinus

Major calyx

Renal lobe

Structure of the Kidney

Anatomy of Kidneys

• The kidneys lie on each side of the vertebral column between T12 and L3

• Surrounded by three layers of connective tissue: renal capsule, adipose capsule and the renal fascia

• Average kidney: 10cm x 5.5cm x 3cm, weighing 150g

• Left kidney lies slightly superior to the right kidney

Anatomy of Kidneys (cont.)

• Hilum: entry for the renal artery and nerves and an exit for renal vein and ureter

• Renal sinus: internal cavity within the kidney

• Renal Pyramids: Triangular structures with bases at the cortex and tips at the renal sinus

• Renal Medulla: structure containing 6 - 18 renal pyramids

• Renal Columns: bands of tissue that separate renal pyramids

Anatomy of Kidney (cont.)

• Cortex – superficial part of kidney

• Renal Papilla – the tip of each renal pyramid

• Renal Lobe – consists of a renal pyramid, the overlying renal cortex and adjacent columns

• Renal Pelvis – a large funnel that drains the kidneys

How does blood flow through the kidney?

Blood flow of kidney

Interlobararteries

Interlobarveins

Interlobulararteries

Interlobularveins

Arcuate veins

Arcuate arteries

Renalartery

Renalvein

Suprarenalartery

Segmentalartery

(a)

(b)

Interlobar artery

Interlobar vein

Interlobularartery

Interlobularvein

Nephron

Afferentarterioles

Arcuate vein

Arcuate artery

Renalpyramid

Renal arteryRenal vein

Segmental arteries

Interlobar arteries

Arcuate arteries

Interlobular arteries

Afferent arteriolesVenules

Interlobular veins

Arcuate veins

Interlobar veins

NEPHRONS

Efferentarteriole

GlomerulusPeritubularcapillaries

(c)

Blood flow of kidney

• The kidney receives blood from the renal artery and blood is removed by the renal vein

• Through a system of various types of arteries and veins blood enters and exits the kidney

• At the lowest level the blood is passed through the nephron which starts urine production

What is the anatomy of the nephron?

Secretion of ions, acids, drugs, toxinsVariable reabsorption of water, sodium ions, and calcium ions (under hormonal control)

COLLECTING SYSTEM

Ascending limb

Thick ascending limb

Ascending limb of loop ends

Descendinglimb of loop

begins

Descendinglimb

NEPHRON

Renaltubule

Minorcalyx

Thindescending

limb

Water

Solutes

Filtrate

Variable reabsorption or secretion

KEY

Glomerulus

Capsular space

Bowman’s capsule

Afferent arteriole

Efferent arteriole

Variable reabsorption of water and reabsorption or secretion of sodium, potassium, hydrogen, and bicarbonate ions

Delivery of urine to minor calyx

Reabsorption of water, ions, and all organic nutrients

Production of filtrate

Further reabsorption of water (descending limb) and both sodium and chloride ions (ascending limb)

Proximal convoluted tubule Distal convoluted tubule

Renal corpuscle

Collecting duct

Papillary duct

Loop of Henle

Anatomy of the nephron

• The nephron consist of two parts, the renal corpuscle and the renal tubule

• The renal tubule is a long tubular passage way measuring about 50mm

• The renal corpuscle is a spherical structure consisting of the Bowman’s capsule and the glomerulus

• The renal tubule consist of the proximal convoluted tubule (PCT), distal convoluted tubule (DCT), and the Loop of Henle

Anatomy of the Nephron (cont.)

• Glomerulus – system of about 50 intertwining capillaries

• Bowman’s Capsule – a chamber that holds the glomerulus with a visceral epithelium

How is urine produced?

Filtration

• The renal corpuscle is the site where filtration occurs

• Blood pressure forces water and other solutes out of the glomerular capillaries

• This process produces a primarily protein free solution called filtrate

Entry into the renal tubule

• After filtrate is formed it enters the renal tubule

• As filtrate travels through the renal tubule it becomes tubular fluid with more of the characteristics of urine

• The renal tubule has 3 major functions:- Reabsorbing all useful organic nutrients in the filtrate- Reabsorbing more than 90% of water in the filtrate- Secreting any waste products that failed to enter the

renal corpuscle through filtration

The Proximal Convoluted Tubule (PCT)

• The PCT is the first segment of the renal tubule

• The lining of the PCT is a simple cuboidal epithelium whose surface bears microvilli

• Reabsorption is the main function of the PCT and it reabsorbs organic nutrients, ions, water and plasma proteins (if present)

Loop of Henle

• The second part of the renal tubule is the Loop of Henle

• The Loop of Henle is divided into the descending limb and ascending limb

• The descending limb flows toward the renal pelvis and is lined with a cuboidal epithelium

• The ascending limb flows toward the renal pelvis and is lined with a squamous epithelium

Distal Convoluted Tubule (DCT)

• The third part of the renal tubule is the DCT

• It is lined with a cuboidal epithelium that is not lined with microvilli

• The DCT is necessary for three vital processes- Selective reabsorption of Na and Ca ions- Active secretion of ions, acids, drugs and toxins- Selective reabsorption of water

The Collecting System

• The last segment of the nephron is the collecting system

• The nephron drains into a collecting duct, which drains into a larger papillary duct, which empties into the minor calyx

• Final osmotic pressure and urine volume is determined by the collecting system

General Characteristics of Urine

• pH range: 4.5 – 8.0 (average 6.0)

• Specific Gravity: 1.003 – 1.030

• Water Content: 93 - 97%

• Color : Clear yellow

• Odor: Varies with composition

Organic Waste Products

• Urea – most abundant organic waste, generate from the breakdown of amino acids (21g)

• Creatinine – generated in skeletal muscle through the breakdown of creatine phosphate (1.8g)

• Uric Acid – waste product from recycling the nitrogenous base in RNA molecules (.48g)

Basic Processes of Urine Formation

• Filtration – blood pressure forces water from the blood across the walls of the glomerular capillaries

• Reabsorption – the removal of water and solutes from the filtrate and their movement across the tubular epithelium

• Secretion – the movement of solutes from the outside of the tubular epithelium (peritubular fluid) to the inside

Glomerular Filtration Rate (GFR)

• GFR is the amount of filtrate produced each minute

• On average a GFR is about 125ml a minute, that is around 180 liters of filtrate a day

• About 99% of filtrate is then reabsorbed by the renal tubules

• One can test GFR with a creatinine clearance test

• The GFR can be regulate automatically or with the use of hormones

What is the anatomy of the urinary bladder?

Urinary BladderMiddle umbilical

ligament

Rugae

Center of trigone

Prostate gland

Neck

Membranous urethra

Internalurethral

sphincter

Ureteralopenings

Ureter

Lateralumbilicalligament

Prostatic urethra

External urethralsphincter (in

urogenitaldiaphragm)

Anatomy of the urinary bladder

• The urinary bladder is a hollow muscular organ that is a temporary reservoir for urine

• The superior surface of the bladder is covered with a peritoneum and is stabilized by the middle umbilical ligament and lateral ligaments

• The interior surface of the urinary bladder is thrown into folds called rugae

• The ureters enter the bladder through ureteral openings and meets the center of trigone

• The center of trigone lies superior to the neck which opens to the urethra

Anatomy of urinary bladder (cont.)

• Internal Urethral Sphincter – (sphincter vesicae) an involuntary sphincter that allows urine to leave the bladder to the urethra.

• External Urethral Sphincter – a circular band of muscles that is under voluntary control to allow for urination

Histology of the urinary bladder

• The wall of the urinary bladder has three layers: mucosa, submucosa and muscularis

• Muscularis layer has two layers, longitudinal smooth muscular and circular muscle

• The two muscle layers form the detrusor muscle, which contracts to expel urine out the urethra

What is the anatomy of the ureters?

Anatomy of the ureters

• The ureters are a pair of muscular tubes that extend from the kidneys to the urinary bladder

• They are approximately 12in. in length

• The ureters are made from three tissues:

- An inner transitional epithelium layer

- A middle muscle layer made up of circular and longitudinal layers

- An outer connective tissue in conjunction with the renal capsule

Micturition Reflex

• The process of urination is coordinated by the micturition reflex

• The urge to urinate arises when the urinary bladder contains around 200ml of urine

• Nerves receive the signal that the bladder is expanding

• The detrusor muscle contracts causing relaxation of the internal and external urethral sphincters

What are the complications that occur with the urinary system?

Urinary issues

• Aminoaciduria – amino acid loss in the urine

• Calculi – insoluble deposits that form within the urinary tract

• Glomerulonephritis – an inflammation of the renal cortex

• Hematuria – the presence of blood in urine

• Polycystic Kidney Disease – an inherited abnormality that affects the development of the kidney tubule

• Proteinuria – the presence of protein in urine

• Renal failure – an inability for kidneys to function to maintain homeostasis

• Urinary obstruction – a blockage of the urinary tract

Aging on the Urinary System

• A decline in the number of functional nephrons, 30 -40% between 25 – 85

• A reduction in the GFR due to a lack of renal blow flow and fewer glomeruli

• Reduced sensitivity to ADH, a hormone that reduces the amount of water lost in urine

Professions

• Urologist – a doctor that specializes in urinary diseases and function

• Urology Oncologist – a doctor that specializes in the cancers of the urinary system

• Nephrologist – a doctor that specializes in the kidneys