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55 Cards in this Set
- Front
- Back
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Major Function of Urinary System
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Helps maintain homeostasis in the body
Works with other organs in the body to regulate the composition & volume of interstitial fluid Main function is to control blood volume & composition This is done by filtering the blood to remove waste products, salts & water These are secreted in the form of urine |
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Urinary System Structure
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The structure of the urinary system consists of:
Two kidneys Two ureters Urinary bladder Urethra |
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The Kidneys
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Paired organ
Bean shaped 12.5 cm long, 6cm wide & 3cm thick Lie on posterior abdominal wall Behind the peritoneum (retroperitoneal) Either side of the vertebral column Right kidney lower than left due to the space taken up by liver above right kidney Protected by the ribs |
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Tissue Layers of Kidney
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Three tissue layers surround the kidney
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Renal Capsule:
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Renal Capsule: a thin tough fibrous connective tissue surrounding each kidney
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Renal Fat Capsule:
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Renal Fat Capsule: a dense deposit of adipose tissue that surrounds the renal capsule
Protects kidney from trauma & shock Holds the kidney in place |
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Renal Fascia:
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Renal Fascia: connective tissue that anchors the kidney & adipose tissue to abdominal wall
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Renal Hilum
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The Renal Hilum is a vertical fissure
Positioned in the middle of the concave portion of the kidney Exit and entry point for blood & lymphatic vessels and nerves Exit point for the ureter Renal Hilum opens internally into kidney to a cavity called the renal sinus Renal sinus is filled with fat and connective tissue |
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Vessels Entering Hilum
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Renal Vein
Renal Artery Renal Hilum Ureter |
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Internal Anatomy of the Kidney
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Internally each kidney has a
Cortex Medulla Pelvis |
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Internal Anatomy cont
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If the kidney is sliced lengthways, two distinct regions are visible
Renal Cortex Superficial region Smooth textured Light colour Renal Medulla Inner region Deep reddish brown |
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Renal Cortex
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Extends from the renal capsule to the base of the renal pyramids
Tissue of the renal cortex extends into the spaces between the renal pyramids These extensions are called the Renal Columns |
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Renal Medulla
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Triangular cone shaped pyramids
8-18 renal pyramids occur in each kidney Striped in appearance The base of a renal pyramid faces the renal cortex The apex (tip) of the pyramid points toward the renal hilum Renal columns separate the renal pyramids |
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Kidney Parenchyma
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Functional part of the kidney
Is made up of the renal cortex and renal pyramids of the medulla Within this region there are 1 million microscopic structures called nephrons & numerous blood vessels Both contribute to the kidney parenchyma |
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Nephrons
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Are basic functional units of the kidney
Constant from birth, not replaced if injured Injury not evident unless function declines by 25% If one kidney removed the other enlarges until it can filter at 80% of normal rate of both kidneys A constant internal environment is maintained by balancing & maintaining fluid & solute levels Nephrons play a major role in this |
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Function of the Nephron
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The Nephrons purpose is to produce urine through 3 basic functions:
filtration reabsorption secretion Urine is produced by the nephron as a result of the substances that are filtered and secreted into the nephron less the substances that are reabsorbed out of the nephron |
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Filtration, Reabsorption & Secretion
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Filtration A portion of blood plasma is filtered across the filtration membrane due to pressure in the glomerulus
Filtrate is the plasma that enters nephron Reabsorption is the movement of substances out from the filtrate in nephrons into the interstitial fluid & back into blood vessels Secretion is the active transport of substances from blood vessels across interstitial fluid & into the nephron to be excreted in urine |
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The Nephron
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Consists of two parts
Renal Corpuscle Bowmans Capsule Glomerulus Renal Tubule Proximal convoluted tubule Loop of Henle Distal convoluted tubule |
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Renal Corpuscle: Bowmans Capsule
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Proximal enlarged end of the nephron
Doubled walled concave C shaped chamber Main function is filtration Surrounds a network of capillaries called the glomerulus Consists of an inner visceral layer: covers the capillary network outer parietal layer: lines the inside of capsule |
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Renal Corpuscle: Glomerulus
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Is a network of capillaries
Glomerulus sits inside the Bowmans Capsule These both lie in the renal cortex Blood plasma is filtered from the capillaries between the parietal and visceral layers of the Bowmans Capsule through a filtration membrane Glomerular filtrate then passes through the capsular space into the renal tubules |
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Glomerular Filtration
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Is influenced by blood pressure
The blood vessel leaving the glomerular capillary (efferent arteriole) has a smaller diameter than the blood vessel entering (afferent arteriole) which causes an ↑ in pressure Plasma, glucose, urea & other smaller molecules are forced through the filtration membrane The filtration membrane prevents larger molecules such as RBC’s, WBC’s & proteins passing through into the capsular space |
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Amount of Filtrate Produced
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Kidney receives 20-25% of resting cardiac output
Receives of 1200ml / min, (1728Litres / day) 125ml / min, (180Litres / day) becomes filtrate Amount of filtrate formed / min is called GFR 99% of filtrate is reabsorbed & 1% becomes urine = approx 1ml / min of urine is produced |
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Renal Tubules
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The main function of the Renal Tubules is reabsorption with some secretion
Proximal Convoluted Tubule (PCT) Attached to the Bowmans Capsule Lies in renal cortex Loop of Henle (LOH) Consists of a thin and thick portion Dips into the renal medulla Distal Convoluted Tubule (DCT) Last portion of renal tubule Returns to renal cortex area Several DCT from other nephrons empty into a single collecting duct |
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Tubular Reabsorption
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Proximal Convoluted Tubule
Filtrate leaves the Bowmans capsule & flows into proximal convoluted tubule PCT are permeable to H2O & filtration occurs by osmosis 100% of protein, amino acids, lactic acid, glucose, 90% of HCO3, Ca++, Mg & PO4, 65% Na+, K+, & 50% of Clˉ are actively transported from nephron to the interstitial space surrounding nephron 65% of total reabsorption occurs in PCT |
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Tubular Reabsorption
Loop of Henle |
Highly permeable to H2O, occurs by osmosis
Moderately permeable to Na+, Urea (50% reabsorbed), and other ions Concentration of solutes in renal medulla surrounding LOH is high, so H2O moves readily out of thin segment of the LOH Ascending LOH is impermeable to H2O Na+, K+ and Cl ˉ are actively transported into interstitial fluid surrounding LOH Filtrate reduced by a further 15% |
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Tubular Reabsorption
Distal Convoluted Tubule |
Permeability to H2O is controlled by ADH
Causes the DCT and collecting duct become permeable to H2O No ADH DCT are impermeable to H2O & H2O remains in the nephron 15% of filtrate reabsorbed in DCT (when ADH present) Na+, Clˉ & ions actively transported out of DCT PTH also stimulates Ca++ reabsorption Impermeable to urea so urea concentration ↑ |
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Tubular Secretion
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Secretion into the nephron occurs along the renal tubules which removes substances from blood
Substances such as: By products of metabolism: waste & excess ions Drugs Molecules not normally produced by the body Can be active or passive H+ secreted in PCT, DCT & collecting duct, helps control the pH of blood K+ actively secreted into DCT & collecting duct Penicillin actively secreted into PCT |
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Collecting Duct
Reabsorption & Secretion |
By the end of DCT 95% of solutes & H2O have been reabsorbed & returned to blood stream
Cells in collecting duct make the final adjustments (4%) Na+, HCO3, & K+ are reabsorbed K+ & H+ are secreted Reabsorption of H2O influenced by ADH & Aldosterone |
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Collecting Ducts
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Last section of kidney parenchyma in medulla
Several nephrons drain urine into one collecting duct within medullary pyramids Large numbers of collecting ducts merge at base of pyramids to form a renal papilla Each renal papillae empties into a cuplike structure called minor calyces Urine then tips into larger shared cups called major calyces These open into a wider space called the renal pelvis Renal pelvis acts like a funnel draining urine out of kidney & into the ureters The ureters empty urine into the urinary bladder |
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Hormone Regulation
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Four hormones affect fluid and solute filtration, reabsorption & secretion
ADH Angiotensin II Aldosterone Atrial Natriuretic Peptide |
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Anti Diuretic Hormone
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ADH also called vasopressin (potent vasoconstrictor)
Released by posterior pituitary gland to adjust body’s fluid levels If there is an ↑ in plasma osmolarity & ↓ in blood volume ADH is released Which ↓ fluid loss by ↓ sweat gland activity Causes constriction of smooth muscle in arterioles Causes DCT & collecting duct to be permeable to H2O H2O is reabsorbed resulting in ↑ blood volume Urine therefore becomes more concentrated In the absence of ADH urine output ↑ |
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Renin-Angiotensin-Aldosterone system
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Cells in the kidney secrete renin if BP is low in afferent arteriole or Na+ concentration low in DCT
Renin causes production of angiotensin II Angiotensin II is a potent vasoconstrictor Smooth muscle in afferent & efferent arterioles are constricted ↑ peripheral resistance occurs & BP is ↑ Angiotensin II stimulates adrenal glands to secrete Aldosterone |
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Aldosterone
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Promotes reabsorption of Na+ in the DCT and collecting duct
H2O follows Na+ by osmosis Blood volume ↑ & therefore ↑ BP ↑ K+ in blood also stimulates aldosterone release Aldosterone ↑ secretion of K+ & H+ into urine |
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Atrial Natriuretic Peptide
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ANP is a cardiac hormone
Stored in cells of atria and released when pressure in atria ↑ due to ↑ blood volume Shuts off Renin-angiotensin-aldosterone system ↑ glomerular filtration ↓ ADH release Water is not reabsorbed ↑ urine excretion ↓ blood volume Causes vasodilation ↓ vascular resistance |
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Production of Concentrate Urine
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Occurs when the body needs to conserve H2O
Decreased fluid intake or excessive sweating ADH is released when osmolarity of blood ↑ DCT & collecting duct become permeable to H2O H2O is reabsorbed Urine becomes concentrated |
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Production of Dilute Urine
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Increased fluid consumed
Fluid needs to be excreted without loosing excessive electrolytes ADH release is ↓ due to a ↓ in osmolarity Low levels of ADH causes the DCT & collecting duct to be impermeable to H2O H2O is therefore not reabsorbed Renal tubules absorb more solutes than H2O Urine therefore becomes dilute |
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Renal Blood Supply
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Blood is supplied to the R&L kidneys by the R&L Renal Arteries
They branch off the abdominal aorta The renal artery enters at the Renal Hilum & further divides into arteries They divide & pass through renal columns between renal pyramids & arch over the base of the renal pyramids They branch from here & project into renal cortex & branch into arterioles |
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Blood Supply within the Kidney
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One arteriole enters each nephron at the Bowmans Capsule & is called the afferent arteriole
The afferent arteriole divides into a tangled capillary network called the glomerulus The capillary network supply the Bowmans Capsule with plasma for production of filtrate |
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Capillary Network in the Kidney
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One arteriole leaves the Glomerulus at the end of the capillary network & is called the efferent arteriole
The efferent arteriole then leads into a capillary network called peritubular capillaries which surround the tubules of the nephron in the renal cortex Renal capillaries play a part in reabsorption and secretion processes of the nephron Branching from efferent arterioles are also the vasa recta which surround the tubules in renal medulla The peritubular capillaries lead into the venous system and join up with the renal vein The renal vein carries blood that has reabsorbed H2O & solutes away from the nephrons and back into circulation The renal vein exits at the Renal Hilum Substances from the renal tubule are reabsorbed into the blood via the peritubular capillaries & vasa recta Substances from blood in the peritubular capillaries are secreted into the renal tubules |
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Renal Nerve Supply
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Derived from the renal plexus
Enters kidney along with the renal artery Sympathetic division of the ANS innervates smooth muscle in renal arterioles causing vasodilation or vasoconstriction both efferent and afferent arterioles are innervated equally minimally innervated at rest so arterioles are maximally dilated regulates blood flow by altering the renal resistance to blood flow Can affect glomerular filtration rate (GFR) |
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Urine Production Review
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Blood flows into kidney via renal artery
Which divides into afferent arterioles that supply individual nephrons The head of the nephron is a C shaped capsule called the Bowmans Capsule The afferent arteriole leads into a capillary network called the glomerulus & sits inside the Bowmans capsule Plasma is forced out of the glomerulus across a filtration membrane into the capsular space The efferent arteriole leaves the glomerulus & becomes the peritubular capillaries surrounding tubules in the renal cortex & vasa recta surrounding tubules in the medulla The filtrate enters renal tubules at the PCT PCT: 65% of H2O & solutes are reabsorbed into interstitium & into peritubular capillaries 100% of glucose Filtrate then flows into the loop of Henle LOH: 15% H2O, Na+ & urea are reabsorbed into interstitium & into vasa recta Filtrate then travels to the DCT DCT & Collecting Duct: 19% H2O & solutes reabsorbed in presence of ADH Several nephrons tip urine into one collecting duct Collecting Duct: Na+, HCO3 & K+ are reabsorbed K+, H+ and other substances are secreted Final adjustments are made here with H2O reabsorption which is influenced by ADH Urine then flows from many collecting ducts into the renal papillae From there urine flows into cups called minor calyces & onto larger cups called major calyces The major calyces open into a larger cavity called the renal pelvis The renal pelvis acts as a large funnel tipping urine into the ureters The ureters leave the kidney’s via the hilus and extends down to the urinary bladder Urine is stored here until it is excreted |
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Anatomy of Ureters
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Each kidney has a single ureter
They are retroperitoneal Exit kidney via Renal Hilum & extend down to urinary bladder Transports urine from the renal pelvis to urinary bladder 10 to 12 in long Vary in diameter from1mm - 10 mm along their course to the bladder |
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Anatomy of Ureters
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Enters posterior wall of bladder
Where the ureters meet the bladder a physiological valve exists As the bladder fills it compresses the ureteric openings which prevents backward flow of urine up ureters Flow of urine through the ureters results from peristalsis, gravity & hydrostatic pressure Walls of ureters consist of 3 layers: Mucosal, muscularis & adventitia layers |
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Layers of the Ureters
Mucosa |
Inner layer made up of:
transitional epithelium (which is able to stretch to accommodate variable volumes of fluid) Underlying lamina propria layer Mucous membrane that secretes mucous from goblet cells Mucus prevents the epithelial cells from being in contact with urine |
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Muscularis
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Muscle fibers consist of inner longitudinal & outer circular smooth muscle layer
Last 1/3 has an additional longitudinal layer Peristalsis of muscularis contributes to urine flow |
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Adventitia
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Coat of loose fibrous connective tissue
Contains lymphatic & blood vessels to supply ureters Anchors ureters in place |
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Bladder Anatomy
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Hollow muscular organ
Situated in the pelvic cavity posterior to the symphysis pubis Folds of peritoneum holds bladder in place The empty bladder is 5 - 7.5cm long There are thick folds (rugae) on the inner walls which thin and flatten as the bladder fills with urine |
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Bladder Trigone
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Floor of urinary bladder contains a small, smooth triangular area called the trigone
The trigone has three openings The ureters enter the urinary bladder near two posterior points in the triangle The urethra drains the urinary bladder from an anterior point of the triangle |
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Bladder Anatomy
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In females bladder is anterior to vagina & inferior to uterus
In males bladder lies anterior to rectum Average bladder capacity 400-600 ml Bladder Wall consists of 3 layers Mucosal Muscularis Adventitia |
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Mucosa
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Inner layer of bladder
Has two layers transitional epithelium underlying lamina propria Folds (rugae) in epithilium allow for expansion as organ must inflate & deflate Mucus secreted by goblet cells prevents the cells from being in contact with urine |
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Muscularis
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Known as detrusor muscle
Consists of 3 layers of smooth muscle inner longitudinal middle circular outer longitudinal Circular smooth muscle fibers around opening of urethra form internal urethral sphincter Inferior to internal sphincter is a circular skeletal muscle which forms the external urethral sphincter situated in the pelvic floor |
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Adventitia
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Layer of loose fibrous connective tissue
Continuous into adventitia of the ureters Coating the superior surface of bladder is a layer of visceral peritoneum (serosal layer) Contains blood vessels |
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Micturition Reflex
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Micturition, urination, voiding are terms used for describing excretion of urine from bladder through urethra to external environment
The bladder stretches as the volume of urine increases & exceeds 200-400 mL Stretch receptors send signals to micturition center spinal cord (S2 and S3) A reflex is triggered called the micturition reflex PSNS fibers cause bladder detrusor muscle to contract & external & internal sphincter muscles to relax Filling causes a sensation of fullness that initiates a desire to urinate before the reflex actually occurs Micturition is a reflex however we learn as children to initiate or stop the reflex Through conscious control of the external sphincter & muscles of the pelvic floor the cerebral cortex is able to delay its occurrence for a limited time |
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Urethra
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Small tube leading from urethral orifice of bladder to exterior of the body
Ends the passage of urine from the body In females the urethra is Posterior to symphysis pubis 4cm long Opens between the clitoris & vaginal opening |
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In the male the urethra is
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15 to 20cm long
The male urethra is divided into three regions prostatic urethra: section of urethra passing through the prostrate membranous urethra: section of urethra passing through the perineum spongy urethra: section of urethra passing through the penis Passage of sperm also passes through urethra |
