1. The Urinary System

2. The Urinary System

Paired kidneys

A ureter for each kidney

Urinary bladder

Urethra

3. 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

4.

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)

* * 5. 6. 7. Transverse sections showretroperitonealposition of kidneys Note also: liver, aorta muscles on CT Note layers of adipose (fat), capsule, fascia 8. 9.

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

10.

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

11. The Arteries

Aortagives off right and left renal arteries

Renalarteries divides into 5 segmental arteries as enters hilus of kidney

Segmentalsbranch into lobar arteries Lobarsdivide into interlobars Interlobarsinto arcuate in junction of medulla and cortex Arcuatessend interlobular arteries into cortex Cortical radiatearteries give rise toglomerular arterioles 12. 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 unusualin having two capillary beds in series (one following the other)

13.

Uriniferous tubuleis 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 mechanisms

Glomerular filtration

Tubular reabsorption

Tubular secretion

Two major parts

A urine-forming nephron

A collecting duct which concentrates urine by removing water from it

14. Outline

Uriniferous tubule (anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

15. Outline

Uriniferous tubule (anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

16. Understand at least this much:

Filtration

• a.Fluid is squeezed out of the glomerular capillary bed

Resorption

• b.Most nutrients, water ad essential ions are returned to the blood of the peritubular capillaries

Secretion

• c.Moves additional undesirable molecules into tubule from blood of peritubular capillaries

17. Nephron

Renal corpuscle

Tubular section

Renal corpuscle: only in cortex

• Tuft of capillaries calledglomerulus

• Surrounded by cup-shaped, hollowglomerular (Bowmans) capsule

Uriniferous tubule (anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

18. (refer to thispic as we go)

Visceral layer of capsule haspodocytes

• Unusual branching epithelial cells

• Foot processes with slit processes between them

------------------- 19.

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 cells The 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 20. Nephron

Renal corpuscle

Tubular section

(processes the filtrate)

• Proximal convoluted tubule

• Loop of Henle

• Distal convoluted tubule

• (ends by joining

• collecting duct)

Uriniferous tubule(anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

21. Proximal convoluted tubule

Confined to renal cortex

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

Resorption of water, ions and solutes

Uriniferous tubule(anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

* 22. Loop of Henle

Descending limb

Thin segment

Thick ascending limb

Uriniferous tubule(anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

23. Distal convoluted tubule

Confined to the renal cortex

Simple cuboidal epithelium

Selective secretion and resorption of ions

Uriniferous tubule(anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

24. Classes of nephrons

Cortical nephrons

• 85% of all nephrons

• Almost entirely within cortex

Juxtamedullary nephrons

• Renal corpuscles near cortex-medulla junction

25. Collecting Ducts

Each receives urine from several nephrons

Run straight through cortex into the deep medulla

Uriniferous tubule (anatomical unit for forming urine)

• Nephron

• • Renal corpuscle (in cortex)

• • • Glomerulus (tuft of capillaries)

• • • Glomerular (Bowmans) capsule

• • Tubular section

• • • Proximal convoluted tubule

• • • Loop of Henle

• • • Distal convoluted tubule

• Collecting duct

Collecting Duct 26. Collecting Ducts

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

Empty into minor calices

Role: conserve body fluids

Uriniferous tubules 1. Nephron2. Collecting ducts * 27. The collecting ducts

The most important role is to conserve body fluids

When the body must conserve water, the posterior pituitary gland secretes ADH ( a nti d iuretich ormone)

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

This decreases the total volume of urine

Alcoholinhibits the release of ADH, so less water is reabsorbed producing copious amounts of dilute urine (can cause dehydration)

28. 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 (125ml/min): this is theglomerular 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

29.

TheVasa rectais 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 30. Histology 31. 32. 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 33. 34. For studying Parts of the kidney: 1.Renal pyramid 2.Efferent vessel 3.Renal artery 4.Renal vein 5.Renalhilum 6.Renal pelvis 7.Ureter 8.Minor calyx 9.Renal capsule 10.Inferior renal capsule 11.Superior renal capsule 12.Afferent vessel 13.Nephron 14.Minor calyx 15.Major calyx 16.Renal papilla 17.Renal column 35. 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

36. Ureters play an active role in transporting urine (its not just by gravity)

Three basic layers

Transitional epithelium of mucosa stretches when ureters fill

Muscularis

• Inner longitudinal, outer circular layers

• Inferior 3 rdwith extra longitudinal layer)

• Stimulated to contract when urine in ureter: peristaltic waves to propel urine to bladder

Adventitia (external)

37. 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 38. 39. 40. 41.

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 theurethra

Trigoneis inside area between ureters and urethra: prone to infection (see slide 38)

42.

Bladder wall has three layers (same as ureters)

• Mucosa with distensible transitional epithelium and lamnia propria (can stretch)

• Thick muscularis called thedetrusor muscle

• • 3 layers of highly intermingled smooth muscle

• • Squeezes urine out

• Fibrous adventitia

43. 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 44.

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 45. With all the labels 46.

Micturition

AKA:

• Voiding

• Urinating

• Emptying the bladder

• (See book for diagram

• explanation p 701)

KNOW:

Micturition center of brain: pons

(but heavily influenced by higher centers)

Parasympathetic: to void

Sympathetic: inhibits micturition