1. Chapter 25 The Urinary System

2. Urinary System Organs Kidneys are major excretory organs
Urinary bladder is the temporary storage reservoir for urine
Ureters transport urine from the kidneys to the bladder
Urethra transports urine out of the body
Kidneys filter 200 liters of fluid from the blood a day removing toxins, waste, and excess ions

3. Kidney Functions
Removal of toxins, metabolic wastes, and excess ions from the blood
Regulation of blood volume, chemical composition, and pH
Gluconeogenesis during prolonged fasting
Endocrine functions
Renin: regulation of blood pressure and kidney function
Erythropoietin: regulation of RBC production
Activation of vitamin D

4. Kidney Anatomy Retroperitoneal, in the superior lumbar region
Right kidney is lower than the left
Convex lateral surface, concave medial surface
Renal hilum leads to the renal sinus
Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilum

5. Layers of supportive tissue
Kidney Anatomy
Layers of supportive tissue
Renal fascia-outer layer
The anchoring outer layer of dense fibrous connective tissue
Perirenal fat capsule-surrounds the kidney
A fatty cushion
Fibrous capsule-transparent capsule
Prevents spread of infection to kidney
Renal ptosis-if fatty layer is lost, kidney may drop lower and cause a kink in the ureter; this can prevent the urine from draining-can lead to hydronephrosis or backup and pressure of urine in the kidney

6. Internal Anatomy Renal cortex Renal medulla Lobe
A granular superficial region
Renal medulla
The cone-shaped medullary (renal) pyramids separated by renal columns
Lobe
A medullary pyramid and its surrounding cortical tissue

7. Internal Anatomy Papilla Renal pelvis
Tip of pyramid; releases urine into minor calyx
Renal pelvis
The funnel-shaped tube within the renal sinus

8. Internal Anatomy Major calyces Urine flows from the pelvis to ureter
The branching channels of the renal pelvis that
Collect urine from minor calyces
Empty urine into the pelvis
Urine flows from the pelvis to ureter
Pyelitis-infections of the renal pelvis or calyces
Pyelonephritis – infections of the entire kidney; in females usually caused by fecal bacteria (may come from other bacteria traveling)-in severe cases it causes the kidney swells, abscesses form, and the pelvis fills with pus

9. Blood and Nerve Supply
Renal arteries deliver ~ 1/4 (1200 ml) of cardiac output to the kidneys each minute
Arterial flow into and venous flow out of the kidneys follow similar paths
Nerve supply is via sympathetic fibers from the renal plexus
Renal artery from the abdominal aorta (right renal artery is longer than left because aorta lies to the left of the midline)
Divides into 5 segmented arteries which then branch into 5 interlobar arteries (the arcurate arteries)
Cortical radiate arteries branch from the interlobar arteries

10. Cortical radiate artery
Aorta
Inferior vena cava
Renal artery
Renal vein
Segmental artery
Interlobar vein
Interlobar artery
Arcuate vein
Cortical radiate
vein
Arcuate artery
Peritubular
capillaries
and vasa recta
Cortical radiate artery
Afferent arteriole
Efferent arteriole
Glomerulus (capillaries)
(b) Path of blood flow through renal blood vessels
Figure 25.4b

11. Nephrons Structural and functional units that form urine
Two main parts
Glomerulus: a tuft of capillaries
Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus
~1 million per kidney
Renal tube comes from Bowman’s capsule

12. Nephrons Renal corpuscle Fenestrated glomerular endothelium
Glomerulus + its glomerular capsule
Fenestrated glomerular endothelium
Allows filtrate to pass from plasma into the glomerular capsule

13. Renal Tubule Proximal convoluted tubule (PCT)
Cuboidal cells with dense microvilli and large mitochondria
Functions in reabsorption and secretion
Confined to the cortex
After the renal tube leaves the glomerulus it has three parts which are about 3 cm long

14. Renal Tubule Loop of Henle with descending and ascending limbs
Thin segment usually in descending limb
Simple squamous epithelium
Freely permeable to water
Thick segment of ascending limb
Cuboidal to columnar cells

15. Renal Tubule Distal convoluted tubule (DCT)
Cuboidal cells with very few microvilli
Function more in secretion than reabsorption
Confined to the cortex

16. Collecting Ducts Receive filtrate from many nephrons
Fuse together to deliver urine through papillae into minor calyces
Give kidneys their striped appearance
Two types of cells in the collecting ducts
Intercalated cells
Cuboidal cells with microvilli
Function in maintaining the acid-base balance of the body
Principal cells
Cuboidal cells without microvilli
Help maintain the body’s water and salt balance

17. Cortical nephrons—85% of nephrons; almost entirely in the cortex
Juxtamedullary nephrons
Long loops of Henle deeply invade the medulla
Extensive thin segments
Important in the production of concentrated urine

18. Nephron Capillary Beds
Glomerulus
Afferent arteriole  glomerulus  efferent arteriole
Specialized for filtration
Blood pressure is high because
Afferent arterioles are smaller in diameter than efferent arterioles
Arterioles are high-resistance vessels
Differs from all capillary beds because it is fed and is drained from arterioles
High blood pressure easily forces fluid and solutes out of the blood int the glomerular capsule-about 99% is reabsorbed by the renal tubule and returned to the blood in the peritubular capillary beds

19. Nephron Capillary Beds
Peritubular capillaries
Low-pressure, porous capillaries adapted for absorption
Arise from efferent arterioles
Cling to adjacent renal tubules in cortex
Empty into venules

20. Nephron Capillary Beds
Vasa recta
Long vessels parallel to long loops of Henle
Arise from efferent arterioles of juxtamedullary nephrons
Function information of concentrated urine

21. Juxtaglomerular Apparatus (JGA)
One per nephron
Important in regulation of filtrate formation and blood pressure
Portion of the ascending limb of the Loop of Henle comes into contact with the afferent arteriole
Important in the regulation of renin and monitoring NaCl content of filtrate

22. Kidney Physiology: Mechanisms of Urine Formation
The kidneys filter the body’s entire plasma volume 60 times each day
Filtrate
Blood plasma minus proteins
Urine
<1% of total filtrate
Contains metabolic wastes and unneeded substances
1200 ml of blood passes the glomeruli each minute-650 ml is plasma and about 1/5 ( ml) is forced into renal tubules-equivilant to filtering entire plasma 60 times a day
Kidneys account for 1% of total body weight, but consume about 20-25% of all oxygen used by the body at rest
Kidneys process about 180 L (47 gallons) of blood derived fluid daily-of this less than 1% leaves the body (1.5 L) as urine-rest returns to circulation

23. Mechanisms of Urine Formation
Glomerular filtration
Tubular reabsorption
Returns all glucose and amino acids, 99% of water, salt, and other components to the blood
Tubular secretion
Reverse of reabsoprtion: selective addition to urine
Glomerular Filtration
Passive mechanical process driven by hydrostatic pressure
The glomerulus is a very efficient filter because
Its filtration membrane is very permeable and it has a large surface area
Glomerular blood pressure is higher (55 mm Hg) than other capillaries
Molecules >5 nm are not filtered (e.g., plasma proteins) and function to maintain colloid osmotic pressure of the blood

24. Glomerular Filtration Rate (GFR)
Volume of filtrate formed per minute by the kidneys (normal: 120–125 ml/min)
Governed by (and directly proportional to)
Total surface area available for filtration
Filtration membrane permeability
Net Filtration Pressure (NFP) - The pressure responsible for filtrate formation (10 mm Hg)
Glomerular capillaries have the surface area of the skin
This means huge amounts of filtrates can be produced even with the low NFP-flip side is a drop of only 18% stops filtration completely
Any factors that change NFP will directly affect GFR

25. Extrinsic Controls: Sympathetic Nervous System
Under normal conditions at rest
Renal blood vessels are dilated
Renal autoregulation mechanisms prevail
Under extreme stress
Norepinephrine and epinepherine are released
Both cause constriction of afferent arterioles, inhibiting filtration and triggering the release of renin

26. Effects of Angiotensin II
Constricts arteriolar smooth muscle, causing MAP to rise
Stimulates the reabsorption of Na+
Acts directly on the renal tubules
Triggers adrenal cortex to release aldosterone
Stimulates the hypothalamus to release ADH and activates the thirst center
Release of renin creates a cascade of events that ultimately leads to the production of angiotensin II
Aldosterone promotes the conservation of sodium and excretion of potassium
This works in conjunction with ADH to promote water conservation

27. Effects of Angiotensin II
Constricts efferent arterioles, decreasing peritubular capillary hydrostatic pressure and increasing fluid reabsorption
Causes glomerular mesangial cells to contract, decreasing the surface area available for filtration
Easiest way to remember the effect of angiotensin II is to remember its job is to restore blood volume and blood pressure-all the hormones and changes will promote the return of water to the blood system and not into the urinary system for excretion

28. A selective transepithelial process
Tubular Reabsorption
A selective transepithelial process
All organic nutrients are reabsorbed
Water and ion reabsorption are hormonally regulated
Na+ (most abundant cation in filtrate)
Other ions also reabsorbed – Ca2+, Mg2+, K+
All of the total plasma volume filters into the renal tubules about every 22 minutes

29. Reabsorptive Capabilities of Renal Tubules and Collecting Ducts
PCT
Site of most reabsorption
65% of Na+ and water
All nutrients
Ions
Small proteins

30. Reabsorptive Capabilities of Renal Tubules and Collecting Ducts
Loop of Henle
Descending limb: H2O
Ascending limb: Na+, K+, Cl

31. Reabsorptive Capabilities of Renal Tubules and Collecting Ducts
DCT and collecting duct
Reabsorption is hormonally regulated
Ca2+ (PTH)
Water (ADH)
Na+ (aldosterone and ANP)

32. Tubular Secretion Reabsorption in reverse
K+, H+, NH4+, creatinine, and organic acids move from peritubular capillaries or tubule cells into filtrate
Disposes of substances that are bound to plasma proteins

33. Importance of Tubular Secretion
Eliminates undesirable substances that have been passively reabsorbed (e.g., urea and uric acid)
Rids the body of excess K+
Controls blood pH by altering amounts of H+ or HCO3– in urine

34. Formation of Dilute Urine
Filtrate is diluted in the ascending loop of Henle
In the absence of ADH, dilute filtrate continues into the renal pelvis as dilute urine

35. Formation of Concentrated Urine
Depends on the medullary osmotic gradient and ADH
ADH triggers reabsorption of H2O in the collecting ducts
Facultative water reabsorption occurs in the presence of ADH so that 99% of H2O in filtrate is reabsorbed

36. Diuretics Chemicals that enhance the urinary output
Osmotic diuretics: substances not reabsorbed, (e.g., high glucose in a diabetic patient)
ADH inhibitors such as alcohol
Substances that inhibit Na+ reabsorption and obligatory H2O reabsorption such as caffeine and many drugs
Loop diuretics – Lasix
Acts on the ascending loop of Henle to prevent the medullary gradient from forming

37. Volume of plasma cleared of a particular substance in a given time
Renal Clearance
Volume of plasma cleared of a particular substance in a given time
Renal clearance tests are used to
Determine GFR
Detect glomerular damage
Follow the progress of renal disease

38. Physical Characteristics of Urine
Color and transparency
Clear, pale to deep yellow (due to urochrome)
Drugs, vitamin supplements, and diet can alter the color
Cloudy urine may indicate a urinary tract infection

39. Physical Characteristics of Urine
Odor
Slightly aromatic when fresh
Develops ammonia odor upon standing
May be altered by some drugs and vegetables

40. Physical Characteristics of Urine
Slightly acidic (~pH 6, with a range of 4.5 to 8.0)
Diet, prolonged vomiting, or urinary tract infections may alter pH
Specific gravity
1.001 to 1.035, dependent on solute concentration

41. Chemical Composition of Urine
95% water and 5% solutes
Nitrogenous wastes: urea, uric acid, and creatinine
Other normal solutes
Na+, K+, PO43–, and SO42–,
Ca2+, Mg2+ and HCO3–
Abnormally high concentrations of any constituent may indicate pathology
Urea is the highest component by weight besides water
Blood or proteins may indicate a problem

42. Ureters Convey urine from kidneys to bladder Retroperitoneal
Enter the base of the bladder through the posterior wall
As bladder pressure increases, distal ends of the ureters close, preventing backflow of urine

43. Three layers of wall of ureter
Ureters
Three layers of wall of ureter
Lining of transitional epithelium
Smooth muscle muscularis
Contracts in response to stretch
Outer adventitia of fibrous connective tissue

44. Kidney stones form in renal pelvis
Renal Calculi
Kidney stones form in renal pelvis
Crystallized calcium, magnesium, or uric acid salts
Larger stones block ureter, cause pressure and pain in kidneys
May be due to chronic bacterial infection, urine retention, Ca2+ in blood, pH of urine

45. Urinary Bladder Muscular sac for temporary storage of urine
Retroperitoneal, on pelvic floor posterior to pubic symphysis
Males—prostate gland surrounds the neck inferiorly
Females—anterior to the vagina and uterus

46. Urinary Bladder Trigone
Smooth triangular area outlined by the openings for the ureters and the urethra
Infections tend to persist in this region

47. Urinary Bladder Layers of the bladder wall Collapses when empty
Transitional epithelial mucosa
Thick detrusor muscle (three layers of smooth muscle)
Fibrous adventitia (peritoneum on superior surface only)
Collapses when empty
Expands and rises superiorly during filling without significant rise in internal pressure

48. Urethra Muscular tube Thin-walled muscular tube
Drains urine from bladder out of body
Females 3-4 cm
Males 20 cm
Female urethra (3–4 cm):
Tightly bound to the anterior vaginal wall
External urethral orifice is anterior to the vaginal opening, posterior to the clitoris
Male urethra
Carries semen and urine
Three named regions
Prostatic urethra (2.5 cm)—within prostate gland
Membranous urethra (2 cm)—passes through the urogenital diaphragm
Spongy urethra (15 cm)—passes through the penis and opens via the external urethral orifice

49. Urethra Sphincters Internal urethral sphincter
Involuntary (smooth muscle) at bladder-urethra junction
Contracts to open
External urethral sphincter
Voluntary (skeletal) muscle surrounding the urethra as it passes through the pelvic floor

50. Three simultaneous events
Micturition
Urination or voiding
Three simultaneous events
Contraction of detrusor muscle by ANS
Opening of internal urethral sphincter by ANS
Opening of external urethral sphincter by somatic nervous system