presentation urinary system

7/30/2019 Presentation Urinary System

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The Urinary System

Chapter 23


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Introduction

Kidneys - maintain purity and chemical constancyof blood and other extracellular body fluids

- filters liters of fluid sending toxins, metabolic wastes,

excess water, and excess ions out in urine

- while returning needed substances from the filtrate to theblood

Main waste products are 3 nitrogenous compounds

1) urea derived from breakdown of amino acids

2) uric acid results from the turnover of nucleic acids

3) creatinine formed by the breakdown of creatine

phosphate, molecule in muscle that stores energy for

manufacture of ATP


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Kidneys also regulate the volume and chemical

makeup of the blood- maintains the proper balance of water and salts and of

acids and bases

Other organs of the urinary system include:- the paired ureters(pertaining to urine), tubes that carry

urine from the kidney to the bladder

- urinary bladder, temporary storage sac for urine

- urethra, a tube that carries urine from the bladder to thebody exterior


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Organs of the Urinary System

Kidneys

Ureters

Urinary

bladder Urethra

Fig 23.1a


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Location and External

Anatomy of Kidneys

Bean-shaped kidneys lie retroperitoneal - lateral

to T11,12 - L3 vertebrae

- right kidney crowded by the liver lies slightly inferior to

the left kidney

- on superior part of each kidney is the suprarenal gland

Average kidney 12cm tall, 6cm wide, 3cm thick

- lateral surface, is convex; medial surface is concave- with a vertical cleft, the renal hilum where vessels,

ureters, and nerves enter and leave the kidneys


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Several layers of supportive tissue surround each

kidney

Fibrous (renal) capsule surrounds the kidney

surface

- maintains its shape and forms a barrier that can inhibit

the spread of infection from surrounding regions

Perirenal and pararenal fat layers - cushion and

help hold the kidneys in place

- perirenal fat capsule lies external to the renal capsule- external to that is an envelope of renal fascia

- pararenal fat lies external and mostly posterior to the

renal fascia


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Relationship of the Kidneys

to Vertebra and Ribs

Figure 23.1b


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Kidneys within

the Posterior

Abdominal Wall

Figure 23.2a


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Internal Gross Anatomy

Frontal section through the kidney reveals 2distinct regions:

- superficial renal cortex, lighter in color with a granular

appearance

- deeperrenal medulla, darker color consists of cone-

shaped masses called renal pyramids

- renal pyramids contain parallel bundles of tiny urine-

collecting tubules

- pyramids apex orpapilla points internally

- renal columns, inward extensions of the renal cortex,

separate adjacent pyramids


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Internal Anatomy

of the Kidneys

Figure 23.3b


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Kidney lobes a single renal pyramid + the

cortical tissue that surrounds that pyramid

- 5 to 11 lobes and pyramids in each kidney

Renal sinus large space within the medial part

opening to the exterior through the renal hilum

- filled space, contains the renal vessels and nerves, somefat, and the urine-carrying tubes

Renal pelvis flat, funnel-shaped tube

- expanded superior part of the ureter- branching extensions form 2 or 3 majorcalices (sing.

calyx= cup), each divide to form several minor calices

- calices collect urine draining from the papillae, empty it

into the renal pelvis

urine flows into the ureter

bladder


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Gross Vasculature & Nerve Supply

About 1/4 of the hearts systemic output reachesthe kidneys via the large renal arteries

- divide into 5 segmental arteries that enter the hilum

- within the renal sinus, each segmental artery divides into

interlobararteries

- at the medulla-cortex junction, interlobar arteries branch

into arcuate(shaped like a bow) arteries

- radiating outward from arcuate arteries are the small

cortical radiate arteries (supply the cortical tissue)

- give rise to the glomerulararterioles, which feed into the

peritubularcapillaries


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Veins trace the pathway of the arteries in reverse

except there are no segmental veins

Nerve supplyrenal plexus (offshoot of the

celiac plexus)

- a network of autonomic fibers and autonomic ganglia on

the renal arteries

- supplied by sympathetic fibers from the inferior thoracic

splanchic and 1st lumbar splanchnic nerves, and other

sources

- fibers control the diameters of the renal arteries and

influence the urine-forming functions of the uriniferous

(urine-carrying) tubules


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Summary of Blood Vessels

Supplying the Kidney

Figure 23.3c


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Mechanisms of Urine Production

Uriniferous tubule - main structural and functional

unit of the kidney- more than a million within each kidney

3 interacting mechanisms: filtration, resorption,

secretion

- in filtration, a filtrate (similar to blood plasma) leaves the

kidney capillaries, it is processed into urine by resorption

and secretion

- during resorptionm nutrients, water, and essential ions

are recovered and returned to the blood via tissue

capillaries, remaining waste contribute to urine

- secretion, removes additional undesirable molecules into

the tubule


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Uriniferous Tubules

2 major parts:1) urine-forming nephron, where filtration,

resorption, and secretion occur, and

2) a collecting duct, concentrates urine byremoving water

Uriniferous tubule is lined by simple epithelium,

one cell thick, adapted for urine production


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Figure 23.4


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Nephrons

Composed of the renal corpuscle and a tubular

section- proximal convoluted tubule, loop of Henle, distal

convoluted tubule

Renal corpuscle (1st

part of the nephron)located in the cortex, where filtration occurs

- consist of a tuft of capillaries called the glomerulus(ball

of yarn) surrounded by the glomerular capsule

(Bowmans capsule)- glumerulus is supplied by an afferent arteriole and

drained by an efferent arteriole


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- endothelim is fenestrated, allowing large quantities of fluid

and small molecules to pass from the capillary blood into

the capsular space- about 20% of the fluid leaves the glomerulus and enters

the capsular space; 80% remains in the blood within the

capillary

- parietal layer of the capsule contributes only to thestructure

- visceral layer consists of branching epithelial cells called

podocytes(foot cells), end in pedicels, foot processes

that interdigitate

- filtrate passes into the capsular space through thin clefts

between the podocytes called filtration slits orslit pores


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Uriniferous Tubule Figure 23.5a


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Filtration Membrane

Filtration barrier - lies between the blood in the

glomerulus and the capsular space Consists of 3 layers

1) fenestrated endothelium of the capillary

2) filtration slits between the pedicels- each covered by a thin slit diaphragm

3) intervening basement membrane

- consists of the fused basal laminae of the endothelium and

the podocyte epithelium

- capillary fenestration restrict passage of the largest

molecules (blood cells)

- basement membrane & slit diaphragm allow small proteins

and molecules (water, ions, glucose, amino acids, urea)


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Renal Corpuscle and the Filtration Membrane

Fig 23.6a


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Fig 23.6c

Renal

Corpuscle and

the FiltrationMembrane


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Tubular Section of the Nephron

After formation in the renal capsule the filtrateproceeds into the long tubular section:

Proximal convoluted tubule (renal cortex), is

most active in resorption and secretion- walls are cuboidal epithelial cells with long microvilli on

the exposed luminal surface

- contain many mitochondria and a highly infolded

basolateral membrane with- many ion-pumping enzymes responsible for resorbing

molecules from the filtrate


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U-shaped loop of Henle (the nephron) consists

of a descending limb and ascending limb

Descending limb, continuous with the proximal

tubule (has a similar structure)

- rest of the descending limb, the thin segment, is thenarrowest part of the nephron with walls of permeable

simple squamous epithelium, continues into the

- ascending limb, joining the thick segment orthick

ascending limb, cell structure resembles the distal

convoluted tubule


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Distal convoluted tubule (in the renal cortex)

selective secretion and resorption of ions

- walls of simple cuboidal epithelium

- less active in resportion, cells do not have abundant

microvilli

- but do have many mitochondria and infoldings of the

basolateral membrane (typical of all ion-pumping cells in

the body)


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2 classed of nephrons

1) Cortical nephrons (85%) almost entirelywithin the cortex

- loops of Henle dip only a short distance into the medulla

2)Juxtamedullary (near the medulla) nephrons

(15%) renal corpuscles lie near the cortex-

medulla junction

- loops of Henle deeply invade the medulla

- thin segments are much longer- long loops of Henle, with nearby collecting ducts,

contribute to production of concentrated urine


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Fig 23.8

Collecting tubules - receive urine from distal convoluted tubules


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Collecting Ducts

Receive urine from several nephrons runsstraight through the cortex into the deep medulla

- adjacent collecting ducts join to form larger papillary

ducts that empty into the minor calices

- most important role to conserve body fluids is sharedwith the distal tubules

- pituitary gland secretes ADH, increases permeability of

the collecting ducts and distal tubules to water;

- water is resorbed from the filtrate into the surroundingBVs, decreasing the total volume of urine produced

Note: Alcohol inhibits the release of ADH, reduced water

resorption from the renal tubules results in copious amounts

of dilute urine


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Microscopic Blood Vessels

Nephrons are associated with 2 types of capillarybeds (a portal system): glomerulus and the

peritubular capillaries

Juxtamedullary nephrons also associate with thecapillary-like vasa recta


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Micrograph through the Renal Medulla

Figure 23.7


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Glomeruli

Capillaries produce the filtrate that moves

through the uriniferous tubule to become urine

Both fed and drained by an afferent arteriole and

an efferent arteriole (respectively)

- high-resistance vessels, the efferent arteriole isnarrower than the afferent arteriole

BP is high for a capillary bed and easily forces the

filtrate out of the blood and into the glomerular capsule

Kidneys generate 1 L of filtrate every 8 minutes only 1% ends up as urine

- 99% resorbed by the uriniferous tubule, and returned to

the blood in the peritubular capillary beds


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Peritubular Capillaries

Or intertubular capillaries - arise from the efferent

arterioles draining the cortical glomeruli

- lie in the interstitial CT of the renal cortex, areolar CT

surrounds the uriniferous tubules- capillaries cling closely to the convoluted tubules and

empty into nearby venules of the renal venous system

- are adapted for absorption: low-pressure porous

capillaries readily absorb solutes and water- all molecules secreted by the nephrons into the urine are

from the blood of peritubular capillaries


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Vasa Recta (straight vessels)

Located in the deepest part of the renal cortex

efferent arterioles from the juxtamedullary glomeruli

continue into these thin-walled looping vessels

- part of the kidneys urine-concentrating mechanism


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Classes of Nephron

Fig 23.9a


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Juxtaglomerular Apparatus

Near the glomerulus functions in the regulation

of blood pressure

- area of specialized contact between the terminal end of

the ascending limb and the afferent arteriole- within the apparatus, structures of both the tubule and

the arteriole are modified

- granular cells (juxtaglomerularcells), modified smooth

muscle cells (mechanoreceptors) secrete renin inresponse to falling blood pressure in the afferent arteriole


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Macula densa(dense spot) the terminal portion

of the loop of Henle

- tall, closely packed epithelial cells, act as chemo-

receptors, monitor solute concentrations in the filtrate

- level of solute concentration drops, cells signal the

granular cells to secrete renin

- renin initiates the renin-angiotensin mechanism that

results in secretion ofaldosterone from the adrenal cortex

- aldosterone increases Na+ resorption, water follows along

the osmotic gradient, causing blood volume and BP to rise

- extraglomerular mesangial cells interact with cells of the

macula densa and granular cells to regulate blood pressure


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Figure 23.10


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Ureters

Slender tubes ~25cm (10in) long carry urine from

the kidneys to the urinary bladder

- begins superiorly at L2 as a continuation of the renal pelvis

- descends retroperitoneal through the abdomen, enters the

true pelvis into the posterolateral corner of the bladder

- runs medially within the posterior bladder wall before

opening into the bladders interior

- oblique entry into the bladder prevents backflow of urine

Innervated by both sympathetic and parasympatheticnerve fibers

- although neural control of peristalsis is insignificant

compared to local stretch response of smooth muscle


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Histology of ureter 3 basic layers:

Mucosa lining of transitional epithelium thatstretches when the ureters fill with urine

- and a lamina propria composed of fibroelastic CT with

patches of lymphoid tissue

Muscularis consists of 2 layers

- inner longitudinal layer

- outer circular layer

Adventitia in the inferior 1/3 of the ureter is an

external longitudinal layer of muscularis

- typical CT

Mi i


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Microscopic

Structure of the

Ureter

Figure 23.12


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Urinary Bladder

Collapsible

muscular sac- stores and

expels urine

Full bladder

spherical- expands into

the abdominal

cavity

Empty bladder lies entirely

within the

pelvis

Figure 23.13


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Figure 23.14

Urinary Bladder

Urachus

closed remnant

of the allantois

Prostate gland

- in males

- lies directly

inferior to the

bladder

- surrounds theurethra


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Bladder wall has 3 layers:

Mucosa distensible transitional epithelium and a

lamina propria

Thick muscular layer, the detrusor (to thrust out)

muscle intermingled smooth muscle fibers

- arranged in inner and outer longitudinal layers and amiddle circular layer

- contraction squeezes urine from the bladder

Fibrous adventitia (except on the superior surfacewhich is covered by parietal peritoneum)

Basic pyramidal shape contains little urine

- walls are thick and mucosa thrown into folds, or rugae

Hi t l f th U i Bl dd


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Histology of the Urinary Bladder

Fig 23.15a, b

U i Bl dd d U th


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Urinary Bladder and Urethra

Trigone (triangle) openings for both the ureters

and urethra

- defines a triangular region on the posterior wall

Urethra thin-walled tube

- drains urine from the bladder, conveys it out of the body

Internal urethral sphincter involuntary smooth

muscle at the bladder-urethra junction

External urethral sphincter surrounds the urethra

- lies within the urogenital diaphragm muscle

- voluntary skeletal muscle inhibits urination until the proper

time, relaxes when one urinates

M l U i


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Fig 23.16a

Male Urinary

Bladder and

Urethra

Long urethra of the male

has 3 regions:

Prostatic passes

through the prostate

gland

Membranous through

the urogenital diaphram

Spongy (penile)

passes through the

length of the penis

M l U i Bl dd d U th


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Fig 23.16b

Male Urinary Bladder and Urethra

In females length of 3-4 cm


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Urethra

Transitional epithelium at the proximal end (near

the bladder)

Stratified and pseudostratified columnar mid

urethra (in males)

Stratified squamous epithelium at the distal

end (near the urethral opening)

Mict rition


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Figure 23.17

Micturition


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Disorders of the Urinary System

UTI urinary tract infections,more common in

females

- burning sensation during micturition

Renal calculi kidney stones

Bladder cancer 3% of cancers, more common

in men

Kidney cancer- arises fro epithelial cells of uriniferous tubules

Urinary System Throughout Life


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Embryo develops 3 pairs of kidneys:

pronephros, mesonephros, metanephros

- only metanephros persists to become the adult kidneys

- metanephric kidney produces urine by fetal month 3- contributes to the volume of amniotic fluid


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Development of the

Urinary Organs

Figure 23.18a,b


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Figure 23.18c, d

U i S Th h if


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Kidney and bladder function declines with

advancing age

Nephrons decrease in size and number

Tubules less efficient at secretion andreabsorption

Filtration declines

Recognition of desire to urinate is delayed Loss of muscle tone in the bladder

presentation urinary system

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