The Urinary System

• Anterior view

• KIDNEY

• Produces urine

• URETER• Transports urine toward • the urinary bladder

• URINARY BLADDER• Temporarily stores urine • prior to elimination

• URETHRA

• Conducts urine to exterior

Figure 26-1: An Introduction to the Urinary System

5 Functions of the Urinary System

1.Regulating blood volume and blood pressure: adjusts volume of water lost in urine, and releasing erythropoietin and renin.

2.Regulating concentrations of certain ions (sodium, potassium, etc.) in plasma: controls quantities lost in urine

5 Functions of the Urinary System

3.Helps maintain blood pH: controlling loss of hydrogen and bicarbonate ions in urine.

4. Conserving nutrients: by preventing excretion in urine

5.Assist liver: helps to detoxify poisons

Anatomy of the Kidney

• Veins and arteries: The Renal vein and artery are the main blood suppliers for the kidney and enter at the hilium

• Calyxes: Cup shaped drains for urine, multiple minor calyxes join to form a major calyx.

• Cortex: superficial portion of kidney

Anatomy of the Kidney

• Renal Capsule: layer of collagen fibers that covers the entire outer surface of the kidney

• Renal Pelvis: The major calyxes of the kidney combine to form the renal pelvis, which drains into the ureters.

• Medulla: the medulla contains 6-18 renal pyramids, which are one of the base functional structures of the kidney.

• Minor calyx

• Renal • pyramid

• Ureter• Renal capsule

• (a)

• Major calyx

• Connection • to minor calyx

• Hilum

• Renal pelvis

• Medulla

• Renal sinus

• Adipose tissue• in renal sinus

• Renal papilla

• Renal columns

• Minor calyx

• Renal pyramids

• Ureter• Renal papilla

• Renal lobe

• (b)

• Renal pelvis

• Renal capsule• Cortex

• Hilum

• Medulla

• Renal sinus

• Major calyx

• Renal lobe

Renal Pyramid

• The base connects to the cortex and the tip (renal papilla) connects to a renal sinus or calyx.

• A Renal Lobe contains a renal pyramid, the cortex connected to it, and the adjacent renal tissues.

• The base functional part of a kidney is the nephron, the nephron is supplied with blood by means of the afferent arterioles.

The Nephron

• The basic functional unit of the kidney • Chief function- filter the blood

• Secretion of ions, acids, • drugs, toxins

• Variable reabsorption • of water, sodium ions, and • calcium ions (under • hormonal control)

• COLLECTING SYSTEM

• Ascending • limb

• Thick • ascending • limb

• Ascending • limb of loop • ends

• Descending• limb of loop

• begins

• Descending• limb

• NEPHRON

• Renal• tubule

• Minor• calyx

• Thin• descending

• 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

Figure 26-6: The Functional Anatomy of a Representative Nephron and the Collecting System

The Nephron

• Consists of the renal tubule– Long tubular passageway

AND

•Renal corpuscle- spherical structure-contains bowman’s capsule which contains the glomerulus ( a capillary network)

Where it Begins

• Blood arrives at the renal corpuscle• Delivered into the glomerulus • Glomerulus is where filtration occurs

Distalconvoluted

tubule

Parietalepithelium

Capsularspace

Efferentarteriole

Glomerularcapillary

Bowman’s capsule

Juxtaglomerular cells

Macula densa

Juxtaglomerularapparatus Afferent arteriole

Proximalconvoluted

tubule

Visceral epithelium

Capillary endothelial cell

RBC

Supporting cell

Pores

PodocyteNucleus

Lamina

Capsular epithelium

Capsular space

Pedicels

Pedicels

Filtrationslits

(a) (b)Figure 26-8: The Renal Corpuscle

Filtration

• Blood pressure forces water and dissolved solutes out of the glomerular capillaries into the capsular space

• Filtration produces a protein free solution, filtrate

The Renal Tubule

• Major Functions:-Reabsorbing the useful organic nutrients in the filtrate -Reabsorbing most of the water in the filtrate-Secreting any leftover waste products into the tubule

The Renal Tubule has Two Segments

• The proximal convoluted tubule • The distal convoluted tubule• Separated by the Loop of Henle

• Filtration

• Water reabsorption

• Solute reabsorption

• Secretion

• Variable rate

• KEY

• Glomerulus

• Urine storage• and elimination

• Proximal convoluted tubule

• Loop of Henle

• Distal convoluted tubule

• Collecting duct• Bowman’s capsule

The Proximal Convoluted Tubule

• Contain microvilli• Reabsorption water, ions and other organic

nutrients• Release into the peritubular fluid, the

interstitial fluid surrounding the renal tubule

The Distal Convoluted Tubule

• Secretion of wastes • Some selective reabsorption under hormonal

control • No microvilli

The Loop of Henle

• Further absorption of water and both sodium and chloride ions

• Creates a concentration gradient in the medulla

Tubular Fluid

• Once the filtrate passes through the renal corpuscle and the renal tubule, it is called tubular fluid

The Collecting System

• Series of tubes that carry tubular fluid away from the nephron

The Collecting Duct

• Shared by many nephrons • Responsible for final reabsorption of water • Secretion of sodium, potassium, hydrogen and

bicarbonate ions

The Collecting Duct

• Determines final osmotic concentration and volume of urine

• Then empties into the minor calyx

The Function of the Nephron Video

• http://www.youtube.com/watch?v=glu0dzK4dbU

Basic Processes of Urine Formation

The goal of urine production is to maintain homeostasis involving the

excretion of solutes

Three Distinct Processes

• Filtration• Reabsorption• Secretion

Filtration

• Blood pressure: Forces water and solutes across capillary walls and into capsular space.

• Solute molecules: If small enough to pass through filtration membrane, they are carried by surrounding water molecules.

• Ex: coffee filter

• Pores in endothelium

• Lamina• densa

• Pedicels• of podocytes

• Capillary• lumen

• Glomerulus

• Filtration slit• Capsular space• (a)

• Small solute• particles

• Filtrate in• capsular• space

• Plasma protein• Blood

• Filtration pressure =• 10 mm Hg

• Filtration• slit

• (b)

Figure 26-10: Glomerular Filtration

Reabsorption

• Occurs after the filtrate has left renal corpuscle (beginning of nephron).

• Removal of water and solutes from the filtrate and into the peritubular fluid

• Most reabsorbed materials are nutrients the body can use.

• Different from filtration: Selective process that is not based on size of solutes.

Secretion

• The transport of solutes from peritubular fluid to tubular fluid.

• Tubular fluid lowers plasma concentration of unwanted materials further after the filtration process.

• Happens primarily at proximal and distal convoluted tubules.

• Normal kidney function can only continue if these three processes function within narrow limits

Organic Waste Products in Urine

• Urea– The most abundant organic waste– Generated through the breakdown of amino acids

• Creatinine – Generated in skeletal muscle tissue by breakdown

of creatine phosphate• Uric Acid– Formed through the recycling of nitrogenous

bases from RNA molecules

Accessory Organs of the Urinary System

Urine Transport, Storage, and Elimination

• The ureters, urinary bladder, and urethra are responsible for the transport, storage, and elimination of urine.

The Ureters

• A pair of muscular tubes that extend from the kidneys to the urinary bladder (about 12 in. long)

• They extend inferiorly and medially, passing over the anterior surfaces of the psoas major muscles

The Ureters

• The paths of ureters in men and women are different, due to variations in the nature, size, and position of the reproductive organs

• In males:- The base of urinary bladder lies between the

rectum and the pubic synthesis• In females:- The base sits inferior to the uterus and anterior

to the vagina

The Ureters

• The ureteral openings are slit-like rather than rounded

• This shape helps to prevent backflow of urine toward the ureter and kidneys when the urinary bladder contracts

Histology of the Ureters

• The wall of each ureter consists of 3 layers:1. An inner mucosa2. A middle muscular layer3. An outer connective-tissue layer

The Urinary Bladder

• A hollow, muscular organ that functions as a temporary reservoir for the storage of urine

• Can contain as much as 1 liter of urine

The Urinary Bladder

• The mucosa lining the urinary bladder is thrown into folds, or rugae

• The triangular area bounded by openings of the ureters consists of a region called trigone

- The trigone acts as a funnel that channels urine into the urethra

• Middle umbilical• ligament

• Rugae

• Center • of trigone

• Prostate • gland

• Neck

• Membranous • urethra

• Internal• urethral• sphincter

• Ureteral• openings

• Ureter

• Lateral• umbilical• ligament

• (c) Urinary bladder in male

• Prostatic • urethra

• External urethral• sphincter (in• urogenital• diaphragm)

Figure 26-18c: Urinary Bladder – Male

Histology of the Urinary Bladder

• The wall of the urinary bladder contains mucosa, submucosa, and muscularis layers

The Urethra

• Extends from the neck of the urinary bladder to the exterior of the body

• In males the distance is around 7-8 in.• The male urethra is subdivided in 3 portions:1. Prostatic urethra2. Membranous urethra3. Spongy urethra

• (a)• Male

• External• urethral• orifice

• Urogenital • diaphragm

• Prostate gland

• Rectum• Peritoneum

• Urinary• bladder

• Pubic• symphysis

• External• urethral• sphincter

• Spongy• urethra

• Urethra [see part (c)]

• Ureter

Figure 26-18a: Urine Conduction and Storage – Male

The Urethra

• In females, the urethra is very short, extending around 1-2 in. from the bladder to the vestibule. Uterus

(b)Female

Peritoneum

Urinarybladder

Pubicsymphysis

Urethra

Vestibule

Vagina

Rectum

External urethralsphincter (in

urogenital diaphragm)

Histology of the Urethra

• The urethral lining consists of stratified epithelium

• The lamina propria is thick and elastic • The mucous membrane is thrown into

longitudinal folds

The Effects of Aging on the Urinary System

• Decline in number of working nephrons: Drops by 30-40% after age 25

• Reduced sensitivity: Reabsorption of water and sodium ions happens at a slower rate.

• Incontinence: The sphincter muscles become weaker. May cause a slow leak of urine.

• The Micturition reflex is compromised: diseases and age may affect urinary retention, or the ability to control urination.

Diseases of the Urinary System

• Nephrolithiasis- Kidney stones may form from calcium deposits or uric salts.

• Cystocele- Occurs in women when something like a hernia occurs and calls the bladder to sag into the vagina.

• Neurogenic Bladder- Muscles around the bladder that help with urine retention do not function properly.

• Urinary Tract Infection (UTI)- when bacteria from waste cling to the walls of the urethra and cause irritation, prominent in women but common in everyone.

Occupations Involving the Urinary System

• Urologist: doctors who diagnose and treat diseases involving the urinary system (i.e. kidney stones, urinary tract infections)

• Urology Oncologist: a doctor who diagnoses and treats cancer of the urinary system

• Nephrologist: a doctor who specializes in kidney care and the treatment of diseases of the kidney

Kidney Dissection Tutorials

• http://www.nationalstemcentre.org.uk/dl/f7b08d6454e976cc2dae61953710575536a67f8b/21054-letsdissectkidneytutor.swf