The Urinary System (Lecture)

The Urinary System

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The Urinary System

Paired kidneys

A ureter for each kidney

Urinary bladder

Urethra

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Main Functions of Urinary System

Kidneys filter blood to keep it pure Toxins Metabolic wastes Excess water Excess ions

Dispose of nitrogenous wastes from blood Urea Uric acid Creatinine

Regulate the balance of water and electrolytes, acids and bases

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Kidneys are retroperitoneal organs (see next slide) Superior lumbar region of posterior abdominal wall

Lateral surface is convex Medial surface is concave

Hilus* is cleft: vessels, ureters and nerves enter and leave Adrenal glands* lie superior to each kidney

(the yellow blob in pic)

**

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Transverse sections show retroperitoneal position of kidneys

Note also: liver, aorta muscles on CT

Note layers of adipose (fat), capsule, fascia

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Kidney has two regions Cortex: outer

Columns of cortex divide medulla into “pyramids” Medulla: inner

Darker, cone-shaped medullary or renal pyramids Parallel bundles of urine-collecting tubules

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The human kidney has lobes Pyramid and cortical tissue surrounding it 5-11 per kidney

Renal pelvis (=basin) Expanded, funnel shaped, superior part of ureter Branches to form two or three major calices (seen best on right pic below) Each of these divides again, minor calices: collect urine from papillae of

pyramids

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The ArteriesAorta gives off right and left renal arteries

Renal arteries divides into 5 segmental arteries as enters hilus of kidney

Segmentals branch into lobar arteriesLobars divide into interlobarsInterlobars into arcuate in junction of medulla and cortexArcuates send interlobular arteries into cortexCortical radiate arteries give rise to glomerular arterioles

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Vasculature of the kidney

The glomerular capillary bed is unusual in having arterioles going both to it and away from it (afferent and efferent), instead of a vein going away as most

It is also unusual in having two capillary beds in series (one following the other)

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Uriniferous tubule is the main structural and functional unit

To left is a single, generalized uriniferous tubule

More than a million of these tubules act together to form the urine

Three main mechanismsa. Glomerular filtrationb. Tubular reabsorptionc. Tubular secretion

Two major parts1. A urine-forming nephron2. A collecting duct which

concentrates urine by removing water from it

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Outline

Uriniferous tubule (anatomical unit for forming urine) Nephron

Renal corpuscle (in cortex)– Glomerulus (tuft of capillaries)– Glomerular (Bowman’s) capsule

Tubular section– Proximal convoluted tubule– Loop of Henle– Distal convoluted tubule

Collecting duct

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Outline Uriniferous tubule (anatomical unit for

forming urine) Nephron

Renal corpuscle (in cortex)– Glomerulus (tuft of capillaries)– Glomerular (Bowman’s) capsule

Tubular section– Proximal convoluted tubule– Loop of Henle– Distal convoluted tubule

Collecting duct

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Understand at least this much:

Filtrationa. Fluid is squeezed out of

the glomerular capillary bed

Resorptionb. Most nutrients, water ad

essential ions are returned to the blood of the peritubular capillaries

Secretionc. Moves additional

undesirable molecules into tubule from blood of peritubular capillaries

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Nephron Renal corpuscle Tubular section

Renal corpuscle: only in cortex Tuft of capillaries called

glomerulus Surrounded by cup-shaped,

hollow glomerular (Bowman’s) capsule


Renal corpuscle (in cortex) Glomerulus (tuft of capillaries) Glomerular (Bowman’s) capsule

Tubular section Proximal convoluted tubule Loop of Henle Distal convoluted tubule

Collecting duct

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(refer to this (refer to this pic as we go)pic as we go)

Visceral layer of capsule has podocytes Unusual branching

epithelial cells Foot processes with

slit processes between them

-------------------

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Scanning EM of podocytes clinging to capillaries (left) and filtration membrane diagram (right) The capillary pores (fenestrations)

restrict the passage of the largest elements such as blood cellsThe basement membrane and slit diaphragm hold back all but the smallest proteins while letting through small molecules such as water, ions, glucose, amino acids, and urea

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Nephron

Renal corpuscle Tubular section

(processes the filtrate)

Proximal convoluted tubule

Loop of Henle Distal convoluted

tubule

(ends by joiningcollecting duct)




Collecting duct

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Proximal convoluted tubule

Confined to renal cortex

Cuboidal epithelial cells with long microvilli (fuzzy appearance in pics)

Resorption of water, ions and solutes




Collecting duct

*

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Loop of Henle

Descending limb

Thin segment

Thick ascending limb




Collecting duct

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Distal convoluted tubule

Confined to the renal cortex

Simple cuboidal epithelium

Selective secretion and resorption of ions




Collecting duct

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Classes of nephrons

Cortical nephrons 85% of all

nephrons Almost entirely

within cortex Juxtamedullary

nephrons Renal corpuscles

near cortex-medulla junction

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Collecting Ducts Each receives

urine from several nephrons

Run straight through cortex into the deep medulla




Collecting duct

Collecting Duct

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Collecting Ducts

At papilla of pyramid* ducts join to form larger papillary ducts

Empty into minor calices

Role: conserve body fluids

Uriniferous tubules1. Nephron 2. Collecting ducts

*

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The collecting ducts

The most important role is to conserve body fluids

When the body must conserve water, the posterior pituitary gland secretes ADH (antidiuretic hormone)

ADH increases the permeability of the collecting tubules and distal tubules to water so more is reabsorbed

This decreases the total volume of urine Alcohol inhibits the release of ADH, so less

water is reabsorbed producing copious amounts of dilute urine (can cause dehydration)

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Vessels Afferent and efferent arterioles associated with glomerular capillaries

Allows high pressure for forcing filtrate out of blood About 20% of renal plasma flow is filtered each minute (125 ml/min): this is the

glomerular filtration rate (GFR), an important clinical measure of renal function This is about one liter every 8 minutes (only 1% ends up as urine)

Peritubular capillaries arise from efferent arterioles Absorb solutes and water from tubule cells

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The Vasa recta is a portion of the peritubular capillary system which enters the medulla where the solute concentration in the interstitium is high. It acts with the loop of Henle to concentrate the urine by a complex mechanism of counter current exchange using urea. If the vasa recta did not exist, the high concentration of solutes in the medullary interstitium would be washed out.

____vasa recta

(vessels, continued)

The Vasa recta

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Histology

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Juxtaglomerular apparatus Regulation of blood pressure Granule (jg cells) – modified muscle cells secreting renin in response to

falling blood pressure in afferent arteriole Macula densa – chemoreceptors which secrete renin if solute concentration

falls

Renin-angiotensin mechanism: Sequence of reactions resulting in aldosterone secretion from adrenal cortex: increases sodium resorption from distal convoluted tubules: water follows, blood volume increases and blood pressure increases

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For studying

Parts of the kidney:1. Renal pyramid2. Efferent vessel3. Renal artery4. Renal vein5. Renal hilum6. Renal pelvis7. Ureter8. Minor calyx9. Renal capsule10. Inferior renal capsule11. Superior renal capsule12. Afferent vessel13. Nephron14. Minor calyx15. Major calyx16. Renal papilla17. Renal column

http://en.wikipedia.org/wiki/Renal_pyramid

http://en.wikipedia.org/wiki/Efferent_vessel

http://en.wikipedia.org/wiki/Renal_artery

http://en.wikipedia.org/wiki/Renal_vein

http://en.wikipedia.org/wiki/Hilum_of_kidney

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The Ureters Slender tubes about

25 cm (10 “) long leaving each renal pelvis

One for each kidney carrying urine to the bladder

Descend retroperitonealy and cross pelvic brim

Enter posterolateral corners of bladder

Run medially within posterior bladder wall before opening into interior

This oblique entry helps prevent backflow of urine

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Ureters play an active role in transporting urine (it’s not just by gravity)

Three basic layers Transitional epithelium

of mucosa stretches when ureters fill

Muscularis Inner longitudinal, outer

circular layers Inferior 3rd with extra

longitudinal layer) Stimulated to contract

when urine in ureter: peristaltic waves to propel urine to bladder

Adventitia (external)

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Urinary Bladder Collapsible muscular sac

Stores and expels urine

Lies on pelvic floor posterior to pubic symphysis Males: anterior to

rectum Females: just

anterior to the vagina and uterus

See also brief atlas

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If full: bladder is spherical and extends into abdominal cavity (holds about 500 ml or 1 pt)

If empty: bladder lies entirely within pelvis with shape like upside-down pyramid

Urine exits via the urethra Trigone is inside area between ureters and

urethra: prone to infection (see slide 38)

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Bladder wall has three layers (same as ureters) Mucosa with distensible transitional epithelium and

lamnia propria (can stretch) Thick muscularis called the detrusor muscle

3 layers of highly intermingled smooth muscle Squeezes urine out

Fibrous adventitia

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The Urethra Smooth muscle with inner mucosa

Changes from transitional through stages to stratified squamous near end Drains urine out of the bladder and body

Male: about 20 cm (8”) long Female: 3-4 cm (1.5”) long

Short length is why females have more urinary tract infections than males - ascending bacteria from stool contamination

Urethra____

urethra

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Urethral sphincters Internal: involuntary sphincter of smooth muscle External: skeletal muscle inhibits urination voluntarily

until proper time (levator anni muscle also helps voluntary constriction)

Males: urethra has three regions (see right)

1. Prostatic urethra__________

2. Membranous urethra____

3. Spongy or penile urethra_____

_________trigone

female

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With all the labels

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Micturition AKA: Voiding Urinating Emptying the bladder

(See book for diagramexplanation p 701)

KNOW:Micturition center of brain:

pons(but heavily influenced by

higher centers) Parasympathetic: to voidSympathetic: inhibits

micturition

Science

The Urinary System (Lecture)