Urinary System

Urinary System

• The urinary system (excretory system) is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder, the urethra, and two sphincter muscles.

Kidney

The kidneys are bean-shaped organs with several functions, such as :

Regulation of electrolytes (e.g. sodium, potassium and calcium)

Regulation of blood pressure (via maintaining salt and water balance)

Serve the body as a natural filter of the bloodResponsible for the reabsorption of water, glucose,

and amino acidsProduce hormones including calcitriol,

erythropoietin, and the enzyme renin.

• kidney is divided into two major structures: superficial is the renal cortex and deep is the renal medulla.

Ureters

• 2 muscular tubes that propel urine from the kidneys through renal pelvis to the urinary bladder

URINARY BLADDER• a distensible reservoir for urine• located in the pelvis, posterior to pubis

symphysis• Size & shape change as it fills• Contains three openings:

• two for ureters (Ureteric orifices)• One for urethra (Internal urethral

orifice)• The triangular region defined

by these three openings is called Trigone

Urethra• A fibro muscular tube that conveys

urine from the urinary bladder to the exterior through “external urethral orifice”

•  In males, the urethra travels through the penis, and carries semen as well as urine

•  In females, the urethra is shorter and emerges above the vaginal opening.

Kidney

Renal capsule

• Tough capsule made of collagenous fibers and connected on the kidney by areolar tissue

• As it proceeds medially towards the hilum, it connects with the connective tissue of the vessels which are entering kidney.

• Perirenal fascia (or renal fascia envelope), encloses the kidneys and the suprarenal glands and contain the perirenal fat as cushioning for these structures.

Cortex• It is brownish-red in color, 1 cm wide and lies beneath

fibrous renal capsule. Medullary rays penetrate the cortex,

Medulla

• It consists of several large pyramids. Their apices (papillae) point towards the renal pelvis. It can be distinguished in 2 zones:

• the reddish external zone (with internal and external striations);

• the pale internal zone.

Lobules of kidney The renal lobe is a portion of a kidney consisting of renal

pyramid and the renal cortex above it. The kidney is made up of 10-18 lobes.

The bases of the renal pyramids are enveloped by a cortex. Its apices are called renal papilla.

Renal papilla open to the renal pelvis via a branch of a renal pelvis called a calyx.

Cortex contain renal corpuscles , proximal & distal parts of tubules.

• A cortical lobule (or renal lobule) is a part of a renal lobe. It consists of the nephrons grouped around a single medullary ray and draining into a single collecting duct.

* Medullary ray

Is the middle part of the cortical lobule or renal lobule, consisting of a group of straight tubes to the collecting ducts.

- Their name is potentially misleading – the "modullarly" refers to their destination, not their location.

Nephrons

Structure of nephron Nephron: Is the basic structural and functional unit of the kidney.

• chief function is to regulate the concentration of water and soluble substances and to eliminate wastes from the body.

• In humans, a normal kidney contains 800,000 to 1.5 million nephrons.

PARTS OF NEPHRON Subsections of Nephrons:

1.Renal corpuscle (glomerulus)

2.Proximal tubule

a. Proximal Convoluted Tubule (PCT)

b. Proximal Straight Tubule (PST) 3.Loop of Henle

a. Descending Thin Limb (DTL)

b. Ascending Thin Limb (ATL)

c. Thick Ascending Limb (TAL)

4. Distal tubule

a. Thick Ascending Limb (TAL)

b. Macula densa

c. Distal Convoluted Tubule (DCT)

5. Collecting Duct (CD)

PARTS OF NEPHRON

Podocytes:

* Podocytes are highly specialized cells

* envelope the glomerular capillaries with foot projections.

* The podocytes are thus the visceral layer of the Bowmann's capsule and part of the filtration barrier of the glomerular filtration.

Functions

• reabsorption and secretion of various solutes such

as ions (e.g., sodium), carbohydrates (e.g.,

glucose), and amino acids (e.g., glutamate).

• Fluid in the filtrate entering the proximal

convoluted tubule is reabsorbed into the peritubular

capillaries, including approximately two-thirds of

the filtered salt and water and all filtered organic

solutes (primarily glucose and amino acids).

* The loop of Henle(nephron loop)- a U-shaped tube

that extends from the proximal tubule. It consists

of a descending limb and ascending limb. It begins

in the cortex, receiving filtrate from the proximal

convoluted tubule, extends into the medulla as the

descending limb, and then returns to the cortex as

the ascending limb to empty into the distal

convoluted tubule.

* The primary role of the loop of Henle is to

concentrate the salt in the interstitium, the tissue

surrounding the loop.

Section of Nephron Function Histology

Bowman’s Capsule Filter Blood from arteries in glomerulus

Double-layered epithelial cap

Proximal Convoluted Tubule (PCT)

Reabsorbs 2/3 of filtrate: water, Na, Cl, KReabsorbs virtually all glucose and amino acids that are filtered

Acidophilic, cuboidal epithelium, prominent brush border.

Loop of Henle

Thick Descending Segment (pars recta)

Thin Segment (descending and ascending)

Thick Ascending Segment

1. Descends to medulla, not much absorption  2. Passive transport of Na and water 3. Reabsorbs NaCl WITHOUT WATER

1. Looks like PCT   2. Simple squamous epithelium 3. Simple cuboidal epithelium, NO brush border, extensive mitochondria

Section of Nephron Function Histology

Macula Densa (part of the distal straight ascending tubule)

Monitors NaCl concentration in afferent arteriole and regulates release of renin from juxtaglomerular cells (JG cells)

Narrower and taller than DCT cells, concentrated nuclei

Distal Convoluted Tubule (DCT)

Reabsorbs 5% of NaCl WITHOUT WATER

Simple cuboidal epithelium, NO brush border, extensive mitochondria

Macula Densa (part of the distal straight ascending tubule)

Monitors NaCl concentration in afferent arteriole and regulates release of renin from juxtaglomerular cells (JG cells)

Narrower and taller than DCT cells, concentrated nuclei

Section of Nephron Function Histology

Collecting Duct Final regulation of Na, Cl, K, protons, water, urea

Regulates acid-base balance

Pale staining columnar cells, apex of cells tends to bulge into the lumen (dome-shaped apical surface), intercellular boundaries are evident

Types of Nephrons

1. Juxtamedullary nephrons

2. Cortical nephrons

Juxtamedullary nephrons

Located in the coticomedullary junction.

These have long loops of Henle that extend deep into the inner zone of the medulla.

Responsible for the production of concentrated urine.

Cortical nephrons

85% of nephrons. Located in the renal

cortex Have shorter loops of

henle that extends only up to the outer zone of the medulla.

Renal Interstitium

Renal InterstitiumIs the Connective Tissue of the kidney parenchyma that

surrounds the nephrons, ducts, and blood and lymph vessels.

Its volume, in the cortex, is relatively small, but increases in the medulla.

It includes fibroblast-like cells, mononuclear cells, and small bundles of collagen fibers in a highly hydrated proteoglycan matrix.

Fibroblast-like cells Location: Cortex of the Kidney Have long, tapering processes that are in contact with processes of like

cells. Cytoplasm contains occasional small lipid droplets and dilated cisternae of

rough E.R. that may contain flocculent material of low electron density. These interstitial cells are believed to produce the fibrous and amorphous

components of the extracellular matrix.

Mononuclear cells Location: Cortex of the Kidney More or less spherical in shape Have a large heterochromatic nucleus surrounded by a relatively thin rim of

cytoplasm. It is likely that they are early stages of monocyte-macrophage lineage.

• ***Both of these cells synthesize and secrete collagen and glycosaminoglycans of the extracellular matrix.

Renal Cortical interstitial cells

Renal Medullary interstitial cells

Location: Medulla of the KidneyFibroblast-like cells that differ from those of

the cortex in their orientation and in their ultrastructure.

Highly pleomorphic cellsPresence of multiple lipid dropletsHave endocrine function in the regulation of

systemic blood pressure.Secretes Medullipin-I that is

antihypersensitive.

Histophyisiologyof the Kidney

• Vasa recta containing descending arterioles and ascending venules act as countercurrent exchangers

• Interaction between collecting ducts, loops of Henle, and vasa rectae is required for concentrating urine by the countercurrent exchange mechanism

Histophysiology of the Kidney

AREA PROCESS HISTOLOGY, ETC.

Afferent Arteriole Vasodilates in autoregulation w/low b.p.Vasoconstricts in autoregulation w/ high b.p.

Juxta-glomerular apparatus connection

Glomerus filtration of water and dissolved substances out of the blood

Fenestrated capillaries

Efferent arteriole vasoconstricts due to angiotensin II

renin from Juxta-glomarular cells

Bowman’s capsule filtrate begins in capsular space visceral layer podocytes parietal layer simple squamous

proximal convoluted tubule reabsorbs 65% of water, all glucose and amino acids, Na+Cl- secretion of toxins, drugs, K+, H+, NH4

+

Cuboidal cells with microvilli

Descending limbs of loop of Henle

reabsorption of water due to counter- current mechanisms

thin segment with specialized simple squamous cells

AREA PROCESS HISTOLOGY, ETC.

Ascending limb of loop of Henle reabsorption of Na+Cl- to produce hypertonic medulla

Thick segment cuboidal cells

Descending limb of vasa recta

picks up salt from hypertonic medulla

thick segment cuboidal cells

Ascending limb of vasa recta releases salt back into medulla

thick segment cuboidal cells

Distal convoluted tubule Na+ reabsorbed under control of aldosterone/ some secretion here

cuboidal epitheliummacula densa cells

Peritubular capillaries reabsorbs 65% of water, all glucose and amino acids, Na+Cl- secretion of toxins, drugs, K+, H+, NH4

+

cuboidal epitheliummacula densa cells

Collecting duct facultative water reabsorption under control of ADH active transport of K+, H+, NH4

+, HCO3

-, Cl-

Cuboidal cells

Urinary System

Ureters, Urinary Bladder and Urethra

Ureters…

Ureters• Lined by “Transitional Epithelium

(UROTHELIUM)” in the luminal surface of it’s wall

• Smooth Muscle and CT in the remainder wall.

Inner : longitudinal layerMiddle : circular layerOuter : longitudinal layer – – only at distal end of ureter

Ureters• Consists of 3 major layers

of tissue:

Mucosa Muscular coat Fibrous coat or

Adventitia

Mucosa• Inner layer• Consists of :• EPITHELIUM

• transitional type, avascular and w/out lymphatics

• LAMINA PROPRIA• w/ areolar CT and vascular

Mucosa• The urinary sites have no muscularis

mucosae, and therefore, the lamina propria and the submucosa tend to merge. Sometimes the connective tissue closest to the mucularis is called the submucosa. There is no distinct submucosa

Mucosa

LP

Mucosa

LP

Muscular Coat • “Muscularis”• Consists of Smooth Muscle

• Main function is peristalsis – –propel urine

Inner : longitudinal layerMiddle : circular layerOuter : longitudinal layer – – only at distal end of ureter

Muscular Coat • In contrast to the muscularis of the intestinal tract,

this muscular coat of UT is not arranged in clearly defined longitudinal and circular layer. Instead, it is made up of anastomosing bundles of muscle fibers of varying orientation.

• Although the inner bundles are predominantly of both layers, they grade with each other with no clearly defined boundary.

Fibrous Coat • “Adventitia” or “serosa”• Supporting layer of Fibrous CT• With Adipose tissue, vessels an nerves

Urinary Bladder

URINARY BLADDER WALL

has the same tissue layers as the renal pelvis and ureter: Mucosa Muscularis Serosa

URINARY BLADDER WALL: MUCOSA

MUCOSA

Empty bladder Numerous folds

Full (distended bladder)

Folds disappear

* innermost portion of the urinary bladder is the mucosa.

• Layers you will found in Mucosa

1.Transitional Epithelium2.Lamina Propria

2.1. subepithelial region

2.2. Deeper zone

URINARY BLADDER WALL: MUCOSA

1. Transitional Epithelium

Empty bladder

•Cuboidal and columnar•Bulge into lumen•“dome-shaped” cells because of the curvature at the apical surface

Full (distended bladder)

•squamous•Stretched, flatten and unfold to accommodate the increasing surface area

URINARY BLADDER WALL: MUCOSALayers in mucosa:

2. Lamina Propria

- wider in urinary bladder than in ureter

- have two zones:

- subepithelial region

- deep zone

URINARY BLADDER WALL: MUCOSALayers in mucosa:

• Lamina Propria: Subepithelial Region

- denser with fine fibers- numerous fibroblasts

• Lamina Propria: Deeper Zone

- Typical loose or moderately dense irregular connective tissue, which extends between the muscle fibers as interstitial connective tissue

URINARY BLADDER WALL: MUCOSA

• similar to those in the ureter except for its thickness

• A smooth muscle• smooth muscle of the bladder is

called the detrusor muscle•Contraction of this muscle expels urine from the bladder.

URINARY BLADDER WALL: MUSCULARIS

• Muscularis is subdivided into three layers of anastomoting smooth muscle(that’s why they can’t be clearly

separated from each other), namely: a.) inner longitudinal layerb.) middle circular layer - thickestc.) outer longitudinal layer – most prominent and compact on the dorsal and ventral surfaces of bladder

• The interstitial connective tissue(loose connective tissue) merges with the connective tissue of serosa

URINARY BLADDER WALL: MUSCULARIS

URINARY BLADDER WALL: SEROSA• Located at the superior surface of the

bladder• composed of a simple squamous epithelium

overlying a small bit of connective tissue• Have two layers:

• Superficial connective tissue• Peritonel mesothelium (outermost layer)

• Beyond the serosa, covering the bladder is perivesical fat.  This is a layer of fat surrounding bladder

Internal urethral sphincter

• toward the opening of urethra, the muscle fibers form the involuntary internal urethral sphincter

• A ring-like arrangement of muscle around the opening of urethra, in the region of trigone at the base of bladder

Urethra…

Urethra• Urine flow is controlled by two

uretheral sphincters: Internal urethral sphincter o start of the urethrao composed of smooth muscle

External urethral sphincter.  o composed of skeletal muscle

Male Urethra• longer than the urethra of

females• About 20 cm long • divided into three

sections: a. prostatic urethra

b. membranous urethra

c. spongy (penile) urethra.

Prostatic Urethra• First portion• 3 to 4 cm from the neck of the bladder

to the prostate gland• Lined with transitional epithelium

(urothelium)

Prostatic Urethra• There are several openings:

a. ejaculatory duct - receives sperm from the vas deferens and ejaculate fluid from the seminal vesicle

b. prostatic ducts - where fluid from the prostate enters and contributes to the ejaculate,

c. prostatic utricle- which is merely an indentation.

• These openings are collectively called the “verumontanum”

• Transitional epithelium is the lining proximal to the ejaculatory duct and distal to this, it becomes psuedostratified or stratified columnar epithelium with occasional mucus-secreting goblet cells.

• Most of the cells in the lumen are polygonal in outline with abundant microvilli. These microvilli tend to confine at the periphery, leaving the central area smooth.

Membranous Urethra• Second part (shortest)• 1 cm from the apex of the prostate

gland to the bulb of the penis• It passes through external urethral

sphincter, which is composed of skeletal muscles(voluntary)

• Lined with pseudostratified columnar epithelium

Spongy(penile) Urethra• Third part (longest)• About 15 cm through the length of the

penis and opens on the body surface of the glands penis

• Surrounded by spongy tissue called “corpus spongiosum”

• Lined with pseudostratified columnar epithelium except at the distal part where it is lined with stratified squamous epithelium

Spongy(penile) Urethra• Ducts of the “bulbourethral glands

(cowper’s glands)” and the mucus-secreting “urethral glands (glands of Littré)” empty into this area.

*Bulbourethral glands (cowper’s glands)- small exocrine glands present in

the reproductive system of human males*Urethral glands (glands of Littré)

- glands secrete mucus, which is incorporated into the semen, and are most numerous in the section of the urethra that runs through the penis

Female Urethra• Short• 3 to 5 cm in length from the bladder to

the vestibule of the vagina• Lined by stratified squamous

epithelium before it terminates • Psuedostratified columnar epithelium

at the midportion

Female Urethra• In the lumen, there are openings of

numerous small urethral glands • Other glands, paraurethral glands

secreting alkaline secretion opens in each side of external urethral orifice.

• Lamina propria is highly vascularized layer of loose CT with abundant elastic fibers

• Urethral sphincter (voluntary) is composed of striated muscles.

Female Urethra• Short• 3 to 5 cm in length from the bladder to

the vestibule of the vagina• Lined by stratified squamous

epithelium before it terminates • Psuedostratified columnar epithelium

at the midportion