I. Functions of the Urinary System Regulate plasma ionic composition Regulate plasma volume Regulate plasma osmolarity Regulate plasma pH Remove metabolic.

I. Functions of the Urinary System

• Regulate plasma ionic composition

• Regulate plasma volume

• Regulate plasma osmolarity

• Regulate plasma pH

• Remove metabolic waste products and foreign substances from plasma as urea and uric acid.

Other Functions of the Kidneys

• Secrete erythropoietin which stimulate erythropoeisis so there is anemia in kidney diseases

• Secrete renin- angiotensin mechanism which regulates ABP

• Activate vitamin D3 to calcitriol

• Help in controlling Ca and PO4 levels as it is responsible of formation of 1-25 dihydrocholecalciferol.

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Anatomy of the Kidney

Figure 18.2

Physiological anatomy of the kidney

*In adult ,each kidney weights about 150 gm

*The kidney is composed of 6-18 lobes ,each lobe consists of a pyramid of medulla covered with cortex

*The cortex (granular &deep in color) consists of glomeruli, convoluted tubules, cortical collecting tubules and B.V

*The medulla has striated appearance &pale as it contains loop of Henle, collecting ducts and blood vesseles

*Nephron is the functional unit of the kidney ,there are one million nephrons in each human kidney The nephron consists of renal (Malpigian corpuscle) and renal tubule

*Renal (Malpigian corpuscle is formed of glomerulus and Bowman capsule.

*Renal tubule is divided into proximal convoluted tubule, Loop of Henle and distal convoluted tubule.

Physiological anatomy of the kidney(continued)

*There are two types of nephrons: cortical nephrons(75%) and juxtaglomerular nephrons(25%)

*There are two capillary beds associated with nephrons .• 1- Glomerular capillary arises from afferent arteriole ,capillary pressure equal

60 mm Hg . Plasma is filtered• 2- Peritubular capillary Arises from efferent arteriole.Capillary pressure equal

13 mm Hg. Filterate is reabsorbed

Urine Drainage through the Kidney and body

• From papillary duct• Minor Calyx• Major Calyx• Ureter• Urinary Bladder• Urethra:

Figure 26.7a

Cortical and Juxtamedullary Nephrons

• Cortical Nephrons:80 to 85% of nephrons. Have short Loops of Henle that lay mainly in the cortex

• Juxtamedullary Nephrons:15 to 20% of nephrons. Have long Loops of Henle that extend into the deepest regions of the medulla. Produce the most concentrated urine.


Anatomy of the Nephron

Figure 18.3

• Subdivision of a Nephron:

1. Renal Corpuscle2. Proximal Convoluted

tubule3. Descending Loop of

Henle4. Ascending Loop of

Henle5. Distal Convoluted

tubule6. Collecting duct7. Papillary duct


Nephron Blood Supply

Figure 18.6b


Juxtaglomerular Apparatus

Figure 18.5

Basic Functions of a Nephron and urine formation process

Basic processes of urine formation

Glomerular filteration

Glomerular filterate:It is the fluid that filters through glomeruli into Bouman capsule

Glomerular filteration rate:Is the amount of glomerular filterate that formed each minute in all

nephrons of both kidneys. It equals 125 ml/min- 180 lit/day.

Glomerular filterate:Is an ultrafilterate of plasma through glomerular capillary

membrane i.e. material of colloid size (plasma protein )or more are not filtered ,only substances of small MW are present in filterate in the same concentration as plasma

Glomerular capillary membrane

It is formed of 3 layers.1- Capillary endothelium:Which have wide pores called fenestrata 70-90- mm in diameter (not

barrier of plasma protein)

2- Basment membrane:Which has no pores and is composed of collagen and

proteoglycan. It is negatively charging forming anionic sites that repel anions of plasma (plasma protein).

3- Bowman capsule epithelium:Formed of podocytes.


Glomerular Filtration Rate

Figure 18.9b

Glomerular filtration

• Filtration : Is the process by which a fluid is forced through a membrane due to difference ion hydrostatic pressure on either sides

• Filtration fraction: It is the fraction of renal blood flow that becomes glomerular filtrate.

• Plasma is filtered through fenestrated epithelium

• Filtrate = plasma - proteins

• About 2 liters of urine produced per day

Determination of GFR

• By inulin clearance testA large dose of inulin is injected intravenouslyInulin is * A polymer of fructose MW=5200 * Neither reabsorbed or secreted by renal tubule i.e amount filtered=amount excreted *Non toxic *Non metabolized * Not stored by kidney and not affect GFR *Can be easily measured in urine and plasma *since it is neither reabsorbed nor excreted so amount filtered= amount excreted

C X P = U X V C = The vol of glomerular filteration P = The concentration of plasma which is equal to that in urine U= Is the concentration in urine V= Is the volume of urine / min GFR= U XV / P = 30 X 1 / 0.25 = 120 ml/min


Effect of MAP on GFR

Figure 18.10

Regulation of glomerular filtration rate (GFR)

• the GFR can be regulated by constriction or dilation of the afferent arterioles.

• Sympathetic innervation causes constriction of the afferent arterioles under the control of: Epinephrine/Norepinephrine from the ANS

• . • Intrinsic mechanisms help

to autoregulate the rate of renal blood flow and the GFR.

Renal Control of Electrolyte by aldosterone hormone

• Aldosterone secretion is stimulated directly by

a rise in blood potassium and indirectly by a fall in blood sodium. • Decreased blood flow through the kidneys

stimulates the secretion of the enzyme renin from the juxtaglomerular apparatus.

• Renin catalyzes the formation of angiotensin I, which is then converted to angiotensin II.

• Angiotensin II stimulates the adrenal cortex to secrete aldosterone.

M.O.A. of aldosterone

1. Aldosterone stimulates sodium reabsorption and potassium secretion in the distal convoluted tubule

2. Aldosterone stimulates the secretion of H+, as well as potassium, into the filtrate in exchange for sodium.


Figure 26.11a

The Response to a Reduction in the GFR


Angiotensin II Effect on MAP

Figure 19.16

Adrenal cortexSystemic arterioles Posterior pituitary Hypothalamic neurons

Aldosterone secretion

Sodium reabsorptionin late distal tubulesand collecting ducts

Water reabsorptionin late distal tubulesand collecting ducts

Extracellular fluidosmolarity

Thirst stimulationADH secretionVasoconstriction

MAP

Plasma volume

Kidneys

Angiotensin II


Response: Decrease in Blood Volume

Figure 19.12

Proximal convoluted tubule

• The proximal tubule is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle

• Proximal Convoluted Tubule (PCT)• A thick, constantly actively segment of the nephron

that reabsorbs most of the useful substances of the filtrate: sodium (65%), water (65%), bicarbonate (90%), chloride (50%), glucose (nearly 100%!), etc.

• The primary site for secretion (elimination) of drugs, waste and hydrogen ions


Reabsorption: Proximal convoluted tubule (PCT)

1. Glucose, amino-acid, sodium will be reabsorped

2. Chloride will follow sodium3. Water will move into the

peritubular space because of osmosis

4. Some compounds present in high concentration in the filtrate but low in the blood can move through diffusion

Reabsorption: Proximal convoluted tubule (PCT)

• 70% of sodium and water are reabsorbed in PCT

• Amino-acids, glucose should be 100% reabsorbed at the end of the PCT

• The filtrate, at the end of the PCT should be iso-osmolar to the filtrate at the beginning

• Reabsorption is not regulated

Reabsorption: Loop of Henle

• Characteristics of Loop of Henle:

-- Descending tubule: permeable to water has no sodium pumps

-- Ascending loop: thick epithelium is impermeable to water but has many sodium pumps

Reabsorption in this segment is also (like PCT) not regulated

Reabsorption: Loop of Henle

• Additional filtrate is reabsorbed

• The filtrate is concentrated as it travels through the loop but returns to a concentration similar to the other end.

• Reabsorption in this segment is also (like PCT) not regulated

So, why is the loop of Henle useful?

اإلبل)) • إلى ينظرون أفال)) خلقت كيف

• Loop of Henle establishes conditions necessary to concentrate urine

• Minimizes water loss

• The longer the loop, the more concentrated the filtrate

Desert animals have long nephron Loop More H2O is reabsorbed

DCT

• It is partly responsible for the regulation of potassium, sodium, calcium, and pH. How?

• it regulates pH by absorbing bicarbonate and secreting protons (H+) into the filtrate, or by absorbing protons and secreting bicarbonate into the filtrate.

• Sodium and potassium levels are controlled by secreting K+ and absorbing Na+. Sodium absorption by the distal tubule is mediated by the hormone aldosterone. Aldosterone increases sodium reabsorption.

• It also participates in calcium regulation by reabsorbing Ca2+ in response to parathyroid hormone.


Reabsorption and secretion along the collecting system

• Water and solute loss is regulated by aldosterone and ADH

• Reabsorption• Sodium ion, bicarbonate, and urea are reabsorbed

• Secretion • pH is controlled by secretion of hydrogen or

bicarbonate ions

Water reabsorption

About 180 litre /day of fluid is filtered by both kidney& urine volume is about 1 litre /day.i.e. 179 litre of water are reabsorbed/day(99%)

Reabsorption in kidney is of 2 typesA- obligatory about 70% .It occurs secondary to solute reabsorbed e.g.

Na .It has no effect on urine concentrationB- Facultative It is variable and not Na dependant .It can affect urine

concentration Reabsorption of water in different tubular segments:1- PCT:70% is obligatory reabsorbed secondary to active transport of solutes as

Na,cl,glucose and amino acids2-Loop of henle:15% of water is reabsorbed by descending limb3-DCT:5% of water is reabsorbed4- Late distal tubule and collecting duct: variableUnder effect of ADH.

Nephron-Tubular System

1. Proximal convoluted tubule

2. Descending loop of Henle

3. Ascending loop of Henle

4. Distal convoluted tubule

5. Collecting duct

35


Secretion

• Solute moves from peritubular capillaries into tubules

• Barriers same as for reabsorption

• Transport mechanisms same but opposite direction


Secretion

• Secreted substances

• Potassium

• Hydrogen ions proton

• Choline

• Creatinine

• Penicillin

Summary of urine formation

Blood enters the kidney through the renal artery at the site of the hilum

The renal artery divides in to ever smaller arteries and arterioles

Afferent arterioles take blood to the glomerulus to be filtered

Once blood is filtered efferent arterioles take blood away from the glomerulus

The glomerulus is a network of capillaries which filters the blood

Products which are filtered out: water, mineral salts, amino acids, glucose, hormones, urea, toxins

Products which do not filter and remain in the blood: Leukocytes, erythrocytes, platelets, plasma proteins

The filtered substances move into the proximal convoluted tubule

The PCT is concerned with reabsorption- organic nutrients are reabsorbed and water follows because there is a concentration gradient

The remaining filtrate moves into the descending loop of henle. This is lined with thin cells so water moves out

Because water has been reabsorbed the concentration of the filtrate is not very high

The walls of the ascending loop of henle are lined with thicker cells, so water can’t pass in or out. Instead sodium and chloride is pumped out actively

The filtrate now enters the distal convoluted tubule- is it now only 20% of what it originally was.In the DCT the volume and

composition of the filtrate can be adjusted but this is controlled by hormones

From the DCT the filtrate now passes into the collecting duct.

A number of other nephrons join up to the collecting duct which travels through the medulla to the renal papilla where the filtrate is emptied in the minor calyx

4-5 minor calyces join up to make a major calyx

2-3 major calyces join up to form the renal pelvis

The renal pelvis joins the ureter at the hilum

The ureter transport the filtrate/urine from the kidney to the bladder

SECTION 26-6: Urine Transport, Storage, and Elimination

• Urine production ends with fluid entering the renal pelvis

• Ureters: Pair of muscular tubes

• Extend from renal pelvis to the bladder

• Peristaltic contractions force urine toward the urinary bladder

• Bladder

• Urethra

• Hollow, muscular organ • Reservoir for the storage of urine

• Contraction of detrusor muscle voids bladder

• Internal features include• Trigone

• Neck

• Internal urethral sphincter

• Ruggae

The urinary bladder

Micturition

• Desire is felt when urine is 150 ml ,marked at 400 ml

• Controlled by the sacral parasympathetic NS

• Stretch sensors in the bladder wall send impulses to the sacral spine

reflex opening of the urethral smooth muscle

• Impulses also sent to the cortex to notify the brain of the need to urinate

if the moment is OK, the person will go to the bathroom (hopefully!), and will open the skeletal (voluntary) muscle of the urethral sphincter the person will be able to urinate

Dialysis Therapy

The most common form of dialysis is hemodialysis which uses a machine to transfer patient’s blood through a semipermeable tube that is permeable only to selected substances. The dialysis machine contains an appropriate dialysis fluid that produces a diffusion gradient. This gradient allows abnormal substances to diffuse from the patient’s blood and produce a “cleaning” effect.

Dialysis Therapy

Some key aspects of hemodialysis are: - blood is typically transferred from an arm artery - after dialysis, blood is typically returned to an arm vein - to prevent clotting, blood is typically heparinized - dialysis sessions occur about three times a week - each dialysis session can last four to eight hours! - long term dialysis can lead to thrombosis (fixed blood clots), infection and death of tissue around a shunt (the blood access site in the arm)

Disorders of the Urinary System

• Incontinence• caused by loss of the ability to control voluntary

micturition (releasing urine from the bladder) due to age, emotional disorders pregnancy, damage to the nervous system, stress, excessive laughing and coughing

• leads to wetting of clothing and discomfort.


• Glomerulonephritis ( Bright’s Disease)• caused by inflammation of the glomeruli due to

an abnormal immune response (autoimmune, streptococcal antibody complexes).

• Inflammation of the glomeruli leads to faulty filtration (passage of blood cells and proteins) and possible kidney failure.


• Cystitis• Inflammation of the urinary bladder• typically caused by bacteria from the anal

region, but, can also be caused by sexually transmitted diseases and various chemical agents

• can lead to inflammation, fever, increased urgency and frequency of urination and pain


• Renal Calculi (kidney stones)• caused by the crystallization of calcium,

magnesium or uric acid salts that precipitate in the renal pelvis.

• If the calculi become large and travel down the ureter, they can cause excruciating pain which radiate from the flank to the anterior abdominal wall on the same side.

Urine Volume

• Normal volume - 1 to 2 L/day• Polyuria > 2L/day• Oliguria < 500 mL/day• Anuria - 0 to 100 mL/day

• Diuretics• Effects• urine output

• Uses• hypertension and congestive heart failure

Animation web site

• www.as.wvu.edu/~sraylman/physiology/renal_processes1_ct.swf


I. Functions of the Urinary System Regulate plasma ionic composition Regulate plasma volume Regulate plasma osmolarity Regulate plasma pH Remove metabolic.

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