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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
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