Pages 965-1008

C h a p t e r

26

The Urinary System

PowerPoint® Lecture Slides prepared by John L. Wilson

Copyright © 2009 Pearson Education, Inc.,publishing as Pearson Benjamin Cummings

Elimination of metabolic wastesWastes mostly from catabolism of

moleculesThese molecules excreted by various

systems

Excretion Defined

Systems Involved in Excretion

Urinary system_____

Respiratory system____________

Digestive system_____

Integumentary system_____

Carbon dioxide

Feces

Sweat

Urine

Functions of the Urinary System

Excretion of metabolic wastes Regulates fluid and electrolyte balanceRegulates blood pH Produces hormones

Calcitriol (vitamin D) helps regulate calciumErythropoietin regulates RBC formation

Regulates blood pressure by enzyme renin

Nephron

Microscopic filtering units of kidneys composed of renal tubules and a blood supply

Called functional units – make most of urine

About 1.25 million per kidneyMostly in renal cortex with some tubules

extending into renal pyramids of medulla

Nephron Anatomy

Bowman’s CapsuleGlomerulusDistal Convoluted Tubule

(end of nephron)Proximal Convoluted Tubule

Collecting Duct

Descending limb of Henle Ascending limb of Henle

Papillary Duct

Renal Papilla

Renal Corpuscle Anatomy

Renal Corpuscle Glomerulus – the

capillaries beneath

the podocytes

PCT

Afferent arteriole

Efferent arterioleDCT

Capsular space

Bowman’s Capsule

Nephron Blood Supply

Afferent arteriole

Efferent arteriolePeritubular capillaries

Vasa Recta

Physiology of the Urinary System

2 31

•Three processes required for urine formation

1. Filtration from the glomerulus to Bowman's capsule

2. Tubular reabsorption from renal tubules to blood of peritubular capillaries

3. Tubular secretion from blood of peritubular capillaries into the renal tubules

Urine

Afferent arteriole

Efferent arteriole

peritubular capillaries

Glomerulus

Bowman’s capsuleRenal Tubules

Filtration

Water and many different solutes pass from glomerulus to the Bowman’s capsule

Resulting fluid in capsular space called filtrate

Filtrate contains Wastes such as urea and uric acid that must be

eliminated in the urine

Useful (vital) substances such as water, organic nutrients and electrolytes that must be kept

Filtrate Formation

High glomerular blood hydrostatic pressure forces water and solutes through filtration membrane into the capsular space, then into the PCT

Capsular space

Filtration membrane

PCT

Filtration Continued

Amount of blood flow through kidneys in one minute = renal blood flow (RBF) About 1200 mL/minute

Amount of filtrate formed in one minute = glomerular filtration rate (GFR)Between 105 and 125 mL/minute

So, around 10% of RBF becomes filtrate

Tubular Reabsorption

Most of the filtrate is taken back into the blood from the nephron tubules by various methods Most Water, organic nutrients and electrolytes are kept Wastes and some water remain in filtrate and become

urine Most reabsorption in proximal convoluted tubule

Blood of peritubular capillaries

Tubular Reabsorption Continued

Water reabsorbed by osmosisSolutes reabsorbed by diffusion,

active transport, cotransport, countertransport and pinocytosis

Reabsorption Continued

Most actively transported substances have a transport maximum (Tm)The Tm refers to how much of a substance

(in milligrams) the nephron tubules can reabsorb in a minute

When Tm is exceeded, substance shows up in urine

Reabsorption Continued

Renal threshold is the maximum blood concentration at which a substance begins to appears in the urine when transport maximum (Tm) is exceeded

Renal threshold for glucose 180 milligrams per 100 mL (deciliter), and above that amount, glucose will appear in the urine

Can you think of what might cause the RT of glucose to be exceeded?

Tubular Secretion

Some solutes move from the blood of the nephron capillaries into the filtratePotassium, ammonium, hydrogen and

bicarbonate ions are secreted into filtrateHelps regulate acid-base balance and

electrolyte concentrationsBlood of peritubular capillaries

Water Reabsorption

Each day we lose about as much water as we gain

If loss exceeds gain, become dehydrated If gain exceeds loss, become over-

hydratedControlled by reabsorption of varying

amounts of water

Water Reabsorption Continued

Each day, between 150-180 L of filtrateEach day, 1-2 L of urine What does this tell you?

Types of Water Reabsorption

Obligatory water reabsorption In PCT and descending LOH More constant

Facultative water reabsorption In DCT and CDVariable, depending on degree of hydrationThis reabsorption controlled by hormones,

particularly the antidiuretic hormone (ADH)

Amounts of H2O Reabsorbed

65% in proximal convoluted tubules15% in descending limbs of HenleNone in ascending limb of Henle10-15% in distal convoluted tubulesRemainder in collecting ductsNext slide illustrates these amounts

Water Reabsorption Drawing

H2O-65%

H2O-15% from descending LOH

ISF and Blood

More salt and urea

Less salt and urea

Facultative Reabsorption-remainder of H2O reabsorptionis from the DCTand CD; variable, depending on water balance – mostly controlledby hormone ADH.

Obligatory Reabsorption – about 80 percent of H2Oreabsorbed at a more constant rate in PCT and descending LOH

No water reabsorbedby thick ascending LOH,it reabsorbs only salt(NaCl)

ISF and Blood

Concentration and Dilution of Urine

When water loss exceeds water gain, our kidneys can increase facultative water reabsorption Results in a smaller volume of a darker urine Our kidneys are thus concentrating our urine

When water gain exceeds water loss, our kidneys can decrease facultative water reabsorption Results in a larger volume of a lighter-colored

urine Our kidneys are thus diluting our urine

Steps in Concentration of Urine

1. As water loss exceeds gain, hypothalamus stimulates secretion of antidiuretic hormone (ADH) from the posterior pituitary

2. ADH makes the cells of the DCT and CD more permeable to water – adds water pores

3. More water leaves the DCT and CD and enters concentrated interstitial fluid and blood of the pyramid

Steps in Concentration of Urine

4. Concentrated interstitial fluid and blood take more water out of the filtrate and concentrate the urine

5. Result is less of a darker, concentrated urine Also, aldosterone from adrenal cortex

increases salt reabsorption from tubules and thus helps to concentrate urine How does this work?

Concentration of Urine-ADH Present

ADH

ADH

DCT and CD more permeable to water thus more water reabsorbed and urine is concentrated

Steps in Dilution of Urine

1. As water gain exceeds loss, hypothalamus stops secreting ADH

2. DCT and CD become less permeable to water – water pores decrease

3. Less water is reabsorbed

4. More water stays in filtrate and urine

Steps in Dilution of Urine

5. Results in more of a dilute urine

6. Adrenal cortex decreases aldosterone

secretion, thus less salt is reabsorbed

from tubules and this helps to dilute

urine

Dilution of Urine–ADH Absent

No ADH, so DCT and CD less permeable to water, thus less water reabsorbed and urine is diluted

Urine composition

95% H2O

5% solutes (solids) ElectrolytesNitrogenous wastes such as urea, creatinine

and uric acidUrea from __________________Creatinine from ________________Uric acid from ____________________

protein metabolism

muscle metabolism

nucleic acid metabolism

Characteristics of Urine

Color

Turbidity

Specific gravity

pH

Clinical Terms

Glomerulonephritis – page 1030

Acute and Chronic Renal failure – page 1030  Hemodialysis (kidney dialysis) –page 1022

Renal Calculi – page 1030 

Polycystic Disease – page 1030&1031

Cyst-------------

Incurable, kidney disease in which cysts form in kidney, and destroy it. Cysts can be clearly seen in kidney below; it weighed 17 pounds.