** Digestive System (cont’d) **Lecture Notes Pages 110-111

Urinary System ILecture Notes Pages 122-140

2

Lecture Overview• CHO, protein, lipid metabolism

• Urinary System– Overview– Gross anatomy/blood supply of kidney– The nephron, its blood supply; fluid flow– Urinary elimination system– Urine formation

• Filtration• Reabsorption/Secretion• Countercurrent multiplier and water conservation

– Renin-angiotensin pathway

3

Pyruvate is a Key Junction in Metabolism

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Pyruvate is used to synthesize amino acids and Acetyl CoA

Pyruvate can also be used to synthesize glucose via gluconeogenesis.

*

Lipolysis

Lipo-

genesis

GlycogenesisGlycogenolysis

Carbohydrate Metabolism

4

Protein Metabolism

5

Very toxic even in small quantities Ketone bodies

- acetoacetic acid- betahydroxybutyric acid- Acetone

Lipid Metabolism

6

(lipogenesis)

(Ketone body)

The Urinary SystemLecture Notes Pages 122-140

8

Functions of the Urinary System

• Make urine

• Regulate blood volume and blood pressure

• Regulate plasma concentrations of Na+, K+, Cl-, HCO3

-, and other ions

• Help to stabilize blood pH

• Conserve valuable nutrients

• Assist the liver in detoxification and deamination

9

Urinary System

Kidneys receive about 1.2 L of blood per minute and filter nearly 180 L of fluid from the bloodstream every day!

Figure from: Hole’s Human A&P, 12th edition, 2010

10

Location of Kidneys

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Located retroperitoneally from T12 to L3

Left kidney is slightly higher than right kidney

Adrenal glands sit on the medial and superior part of kidneys

Nephro(s) = kidney

11

Location of Kidneys

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Helps maintain position of kidney

12

Gross Anatomy of the Kidneys

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Renal capsule is tough, fibrous capsule (tunica fibrosa)

Hilus is entry point for renal artery, vein, and nerve (mostly sympathetic fibers)

Bases of renal pyramids face the cortex, apices face the renal pelvis and end at renal papillae

[Pyel(o)-]

( 2-3 per kidney)

( 8-14 per kidney)

[p. 123-124]

13

Overview of the Nephron

Nephrons are the structural and functional units of the kidney

About 1 million nephrons/kidney

(80%)

(20%)

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 124;128]

tubule (CT)

14

The Nephron

1. PCT – simple cuboidal with a brush border

2. Thin segment of the descending nephron loop - simple squamous epithelium

3. Thick ascending nephron loop - cuboidal/low columnar

4. DCT/CT - simple cuboidal with no microvilli

(PCT)

(DCT)

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 125-127]

(JGA)

(Bowmans’s capsule - BC)

(EA)

(AA)

(Loop of Henle - LoH)

(CT; in renal pyramids)

To papillae of renal pyramid, then minor calyx (NOW IT’S URINE!)

Note: CT is not part of nephron

15

Renal Blood Vessels

Figures from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Nerves, mainly sympathetic postganglionic fibers of the ANS, follow arteries to nephrons

[p. 129]

16

Blood Vessels of the Nephron

The capillary loop of the vasa recta is a type of capillary that is closely associated with the nephron loop of juxtamedullary nephrons

Medulla

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 125-127]

tubule

17

Blood Flow Through Kidney and Nephron

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 129]

18

Elimination of Urine

• nephrons• collecting ducts• renal papillae• minor and major calyces• renal pelvis• ureters• urinary bladder• urethra• outside world

Flow of Urine

Know this…

19

Ureters

• 25 cm long• extend downward posterior to the parietal peritoneum• parallel to vertebral column• in pelvic cavity, joins urinary bladder• peristaltic contractions

Mucous coat – transitional epithelium continuous with linings of the renal tubules and urinary bladderMuscular coat – smooth muscle in longitudinal and circular bundles; carries out peristalsis to move urine toward bladderFibrous coat (adventitia)– CT layer continuous with the renal capsule and peritoneum

Walls of the ureters:

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 130]

20

Urinary Bladder [Cyst(o)]

Four layers:

1. Mucous layer; (transitional epi., with rugae)

2. Muscular coat (detrusor; 3 layers)

3. Serous layer (adventitia)

Temporary reservoir for storage of urine

Note the internal sphincter at neck of bladder

Frontal section, anterior posterior

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 130]

21

Micturition (Urination) Reflex

• trigger = bladder distention & stimulation of stretch receptors• micturition center activated in sacral portion of spinal cord

• parasympathetic nerve impulses cause detrusor muscle to contract (short reflex) and internal urethral sphincter to open• need to urinate is sensed (spinal cord -> thalamus - > cortex) - urge to urinate at about 150-200 ml of urine - discomfort at about 300 ml of urine - maximum capacity of bladder is about 600-1000 ml

• voluntary (tonal) contraction of external urethral sphincter prevents urination and also closes the internal sphincter

• when decision is made to urinate, external and internal urethral sphincters relax, detrusor muscle contracts, and urine is expelled

[p. 131]

22

Urinary Bladder and Urethra - Male

Base of the urinary bladder lies between the rectum and pubis symphysis.

Pelvic region, midsagittal section

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

[p. 131]

23

Urinary Bladder and Urethra - Male

Note the long urethra (about 18-20 cm). There are three sections to the male urethra:

- Prostatic urethra - Membranous urethra - Penile (cavernous) urethra

Urethra in males serves 2 functions:

1)urination

2)passage of semen (ejaculation)

Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

[p. 131]

24

Urinary Bladder and Urethra - Female

Urinary bladder is inferior to the uterus and is separated from the rectum by the vagina.

Note the short urethra (about 4 cm)

Proximity of urethra to anus, and short length of the urethra in females may make it easier for women to get UTIs.

Pelvic region, midsagittal section

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

[p. 132]

25

Simplified Overview of Urine FormationRenal corpuscle – provides the raw materials to the nephron for processing

PCT – reclaims those substances the body can use; gets rid of some things

DCT – gets rid of those substances the body doesn’t want or need; reabsorbs some more Na+, Ca2+

Collecting tubule (duct) – provides the OPTION of reclaiming H2O or letting it pass out of the body

Characteristics of urine

Volume – about 1,500 ml/day (95% H2O)

Color – clear (dilute) to amber (conc.)

Specific gravity – 1.0002 – 1.04

pH – 4.8 – 7.5 (avg ~ 6.0)

Smell – nearly odorless to characteristic; ammonia smell if standing [p. 132-133]

26

Urine Formation

• Glomerular Filtration (GF) *Adds to volume of urine produced• substances move from blood to glomerular capsule

• Tubular Reabsorption (TR) *Subtracts from volume of urine produced• reabsorbs 168,500 ml of filtrate and returns to IVF (plasma)!• substances move from renal tubules into blood of peritubular capillaries• glucose, water, urea, proteins, creatine• amino, lactic, citric, and uric acids• phosphate, sulfate, calcium, potassium, and sodium ions

• Tubular Secretion (TS) *Adds to volume of urine produced• substances move from blood of peritubular capillaries into renal tubules• drugs and ions, urea, uric acid, H+

Urine formation = GF + TS - TR

About ~120-125 ml/minute (170,000-180,000 ml/day) of the total 1200 ml/min of blood that passes through the glomerulus becomes filtrate

[p. 133]

27

Overview of Reabsorption and Secretion

Figure from: Hole’s Human A&P, 12th edition, 2010

28

Renal Corpuscle (Glomerulus + Capsule)

Notice that the efferent arteriole is smaller than the afferent arteriole

This creates a high hydrostatic pressure (~55-60 mm Hg) in the glomerular capillary bed

Filtrate in capsular space

Figure from: Hole’s Human A&P, 12th edition, 2010

Tubular fluid in PCT up to minor calyx

[p. 133-134]

(Bowman’s)

29

Visceral Glomerular Epithelium

Material passing out of the blood must be small enough to fit through the filtration slits (slit pores)

Figure from: Hole’s Human A&P, 12th edition, 2010 [p. 133-134]

30

Glomerular Filtrate and Urine Composition

Glomerular filtrate is about the same composition as plasma: H2O, glucose, amino acids, urea, uric acid, creatine, creatinine, Na, Cl, K, HCO3

-, PO43-, SO4

2-. But notice how different the composition of urine is. Additionally, note that protein is not normally present in urine.

(1.69 L/day)

[p. 134]

31

Sodium and Water Filtration, Reabsorption, and Excretion

Because of the large volumes involved, small changes in tubular reabsorption amount to LARGE changes in excretion of Na+ and H2O (since “water follows salt (solute)”)

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 134]

33

Glomerular Filtration Rate (GFR)

Net filtration pressure is normally positive, i.e., favors the movement of fluid out of the glomerular capillaries

GFR = amount of filtrate produced each minute (~120-125 ml/min)

Net Filtration Pressure = force favoring filtration – forces opposing filtration (*glomerular capillary ( capsular hydrostatic pressure hydrostatic pressure) + glomerular capillary osmotic pressure )

NFP = HPg – (HPc + OPg)

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 134]

34

Afferent/Efferent Arterioles – Effect on GFR

• Afferent arteriole (AA)– Δ radius GFR radius GFR; radius GFR

• Efferent arteriole (EA)– Δ radius 1/GFR radius GFR; radius GFR

AA and EA Innervated by sympathetic nerves

35

Amounts of Glomerular Filtrate and Urine

average amounts over a 24 hour period

Glomerular Filtration Rate (GFR) is directly proportional to the net filtration pressure

GFR 120-125 ml/min (168,500 ml/day)

This means that all of the plasma is filtered ~ 60x every day (How did we get this number?)

Notice that urine output is only 600 – 2,500 ml per day (an average of about 1,500 ml, or about 1% of glomerular filtrate); 99% of filtrate is reabsorbed!!

Figure from: Hole’s Human A&P, 12th edition, 2010

[p. 134]

36

Glomerular Filtration Rate (GFR)

Net filtration pressure, although normally positive, is relatively low ( 10 mm Hg)

Glomerular hydrostatic pressure is the blood pressure in the glomerular capillaries, and is usually higher than other capillary pressures

Capsular hydrostatic pressure tends to push water and filtrate BACK into the capillaries

Anything that alters the filtration pressures will alter GFR

* Blood pressure is the most important factor altering the glomerular hydrostatic pressure (and NFP).

A MAP fall of 10% will severely impair glomerular filtration; a fall of 15-20% will stop it.

[p. 134]

37

Summary of Factors Affecting GFRFactor Effect

Vasoconstriction (↑ Sympathetic stimulation)

Afferent arteriole GFR

Efferent arteriole ↑ GFR

Vasodilation ( Sympathetic stimulation)

Afferent arteriole ↑ GFR

Efferent arteriole GFR

Increased capillary hydrostatic pressure ↑ GFR

Increased colloid osmotic pressure GFR

Increased capsular hydrostatic pressure GFR

[p. 134]