unit 1 1 urinary system

Human Anatomy and Physiology II

Biology 1414

Unit 1

The Urinary System

Objective 1

List the functions of the urinary system and explain how they

contribute to homeostasis.

Unit 1 - Objective 1

Functions of the Urinary System

• Filtration of the blood– Occurs in the glomerulus of the kidney

nephron

– Contributes to homeostasis by removing toxins or waste



• Reabsorption of vital nutrients, ions and water– Occurs in most parts of the kidney

nephron

– Contributes to homeostasis by conserving important materials



• Secretion of excess materials– Assists filtration in removing material

from the blood

– Contributes to homeostasis by preventing a build-up of certain materials in the body such as drugs, waste,etc.



• Activation of Vitamin D– Vitamin D made in the skin is converted

to Vitamin D3 by the kidney

– Active Vitamin D (D3) assists homeostasis by increasing calcium absorption from the digestive tract



• Release of Erythropoietin by the kidney– Erythropoietin stimulates new RBC

production

– New RBC’s assist homeostasis by insuring adequate Oxygen and Carbon Dioxide transport



• Release of Renin by the kidney– Renin stimulates the formation of a

powerful vasoconstrictor called Angiotensin II

– Angiotensin II assists homeostasis by causing vasoconstriction which increases blood pressure



• Release of Prostaglandins– Prostaglandins dilate kidney blood

vessels

– Dilated blood vessels contribute to homeostasis by maintaining blood flow in the kidneys



• Secretion of H (+1) and reabsorption of HCO3 (-1)– Eliminates excess hydrogen ions and

conserves buffer material such as bicarbonate

– Contributes to homeostasis by controlling acid/base conditions in body fluids


Objective 2

Given a diagram of the Urinary System, you will recognize and label the following parts: kidney, ureters, bladder, urethra, internal and external sphincters.


Urinary System

Renal arteryKidney

Ureter

Urinary Bladder

Renal Vein

For sphincters, see next slide

Urinary System

Internal urethral sphincterExternal Urethral Sphincter

Male Sphincters Female Sphincters

Objective 3

Given a diagram of the kidney you will label and give the functions of the following structures: renal vein, renal artery, capsule, cortex, medulla, pyramids, renal papilla, calyx, pelvis, ureter, renal column and nephron


Kidney Diagram

Capsule

Renal VeinRenal ArteryCortex

Pyramid

PapillaCalyx

Pelvis

Ureter

Column

Medulla

Nephron

Functions of Kidney Structures

Examine the kidney structures in the following slides and note the particular functions.



• The Renal Artery– Transports oxygenated blood from the

heart and aorta to the kidney for filtration



• Renal Vein– Transports filtered and deoxygenated

blood from the kidney to the posterior vena cava and then the heart



• Renal Column– A passageway located between the renal

pyramids found in the medulla and used as a space for blood vessels



• Nephron– The physiological unit of the kidney used

for filtration of blood and reabsorption and secretion of materials



• Capsule– The outer membrane that encloses,

supports and protects the kidney



• Cortex– The outer layer of the kidney that contains

most of the nephron; main site for filtration, reabsorption and secretion



• Medulla– inner core of the kidney that contains the

pyramids, columns, papillae, calyces, pelvis and parts of the nephron not located in the cortex; used for salt, water and urea absorption



• Renal Pyramids– Triangular shaped units in the medulla that

house the loops of Henle and collecting ducts of the nephron; site for the counter-current system that concentrates salt and conserves water and urea



• Renal Papilla– The tip of the renal pyramid that releases

urine into a calyx



• Calyx– A collecting sac surrounding the renal

papilla that transports urine from the papilla to the renal pelvis



• Renal Pelvis– Collects urine from all of the calyces in

the kidney



• Ureter– Transports urine from the renal pelvis to

the bladder


Objective 4

Given a diagram of a Nephron you will label and give the functions of the structures: afferent arteriole, efferent arteriole, glomerulus, Bowman’s capsule, proximal convoluted tubule, decending limb and ascending limbs of the loop of Henle, vasa recta, distal convoluted tubule, peritubular capillaries and the collecting duct.


Diagram of Kidney Nephron

Efferent arteriole

Afferent arteriole

Bowman’s capsule

Collecting duct

Proximal convoluted tubuleGlomerulus

Peritubular capillaries

Vasa recta

Decending limb of loop of Henle

Ascending limb of loop of Henle

Distal convoluted tubule


Functions of Nephron Structures

• AfferentArteriole– Transports arterial blood to the

glomerulus for filtration



• Efferent Arteriole– Transports filtered blood from the

glomerulus , through the peritubular capillaries and the vasa recta, and to the kidney venous system



• Glomerulus– The site for blood filtration

– operates as a nonspecific filter; in that, it will remove both useful and non-useful material

– the product of the glomerulus is called filtrate



• Bowman’s Capsule– A sac that encloses Bowman’s Capsule and

transfers filtrate from the glomerulus to the Proximal Convoluted Tubule (PCT)



• 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



• Decending Limb of the Loop of Henle– A part of the counter current multiplier

– freely permeable to water and relatively impermeable to solutes (salt particles)

– receives filtrate from the PCT, allows water to be absorbed and sends “salty”filtrate on the the next segment. “Saves water and passes the salt”



• Ascending Limb of the Loop of Henle– a part of the counter current multiplier

– impermeable to water and actively transports (reabsorbs) salt (NaCl) to the interstitial fluid of the pyramids in the medulla. “Saves salt and passes the water.”

– the passing filtrate becomes dilute and the interstitium becomes hyperosmotic



• Distal Convoluted Tubule (DCT)– receives dilute fluid from the ascending limb

of the Loop of Henle

– Variably active portion of the nephron

– When aldosterone hormone is present, sodium is reabsorbed and potassium is secreted. Water and chloride follow the sodium.



• Collecting Duct– receives fluid from the DCT

– variably active portion of the Nephron

– when antidiuretic hormone (ADH) is present, this duct will become porous to water. Water from the collecting duct fluid then moves by osmosis into the “salty” (hyperosmotic) interstitium of the medulla.

– The last segment to save water for the body



• Peritubular Capillaries– transport reabsorbed materials from the

PCT and DCT into kidney veins and eventually back into the general circulation

– help complete the conservation process (reabsorption) that takes place in the kidney


Objective 5

Identify the parts of the Nephron responsible for Filtration, Reabsorption and Secretion, and describe the Mechanisms underlying each of these functional processes.


Site of Filtration

• Glomerulus– the Glomerulus is the site of filtration

– the filtration mechanism is sieve-like and consists of fenestrated glomerular capillaries, podocytes and a basement membrane that allows free passage of water and solutes smaller than plasma proteins


Location of the Glomerulus

Afferent Arteriole

Efferent Arteriole

Bowman’s Capsule

Proximal Convoluted Tubule

Glomerulus

Glomerular Filtration Mechanism

Bowman’s Capsule

Glomerulus

Fenestrated Capillary

Podocyte with Basement Membrane

Objective 6

Describe the Juxtaglomerular Apparatus and how it maintains renal blood pressure


The Juxtaglomerular Apparatus

• Description– the juxtaglomerular apparatus consists of

specialized macula densa cells that develop in the distal convoluted tubule (DCT) and specialized granular juxtaglomerular (JG) cells that develop mainly in the afferent arteriole. See following diagram.



Afferent Arteriole

Efferent Arteriole

DCT

Macula Densa Cells

Granular Juxtaglomerular (JG) Cells

PCT

Bowman’s Capsule


• Used in maintaining blood pressure– if the blood pressure drops, the granular JG

cells release renin

– renin converts the blood protein angiotensinogen into angiotensin I which converts to angiotensin II

– angiotensin II acts as a vasoconstrictor to raise blood pressure. Continued on next slide.



• Used in maintaining blood pressure continued:– Angiotensin II also stimulates the release of

aldosterone hormone from the adrenal cortex

– aldosterone stimulates the DCT to reabsorb salt (NaCl). Continued on next slide.



• Used in maintaining blood pressure continued:– salt reabsorption attracts water to the blood

by osmosis and raises blood volume, as well as, contributing to the increase in blood pressure. Continued on next slide.



• Used in maintaining blood pressure continued:– the macula densa cells monitor the salt

content of the blood

– if the blood salt content gets too high, the macula densa cells begin to inhibit the granular cells and suppress renin release



• Used in maintaining blood pressure continued:– suppression of renin acts as a negative

feedback mechanism to prevent further increases in angiotensin II, Aldosterone and blood pressure



• Use in maintaining blood pressure continued:– eventually the blood pressure will come back

down

– the “push/pull” action of the granular cells and macula densa cells provide an effective mechanism for regulating blood pressure in the kidney


Objective 7

Discuss the functioning of the counter current mechanism through which the kidneys excrete a concentrated urine by indicating the role of the following: sodium chloride, posterior pituitary, ADH, hypothalamus, collecting duct, active transport, osmosis, interstitial fluid, vasa recta, diffusion, loop of Henle and urea


The Counter Current Mechanism

Compare to the Nephron and recall parts


?

?

?

?


Were you able to locate the decending limb of the Loop of Henle, the ascending limb of the Loop of Henle, the collecting duct and the vasa recta in the previous diagram? Be able to explain these components in your discussion of this mechanism.



We will begin our discussion of the counter current mechanism with the ascending limb of the loop of Henle (ALLH). This portion of the nephron reabsorbs chloride by active transport. As chloride moves from the filtrate it pulls along sodium into the interstitium of the medulla. The medulla then becomes very hyperosmotic



As salt (NaCl) leaves the ALLH, the osmolarity of the fluid decreases from 1,200 to 100 milliosmoles/L (mOSM/L). This happens because the ALLH is impermeable to water. The net effect of this activity is to remove salt from the kidney filtrate and transfer it into the medulla where it can be saved for use by the body.



The accumulated salt in the interstitium of the medulla acts as an osmotic force which can be used to “draw” and conserve water from other parts of the nephron: the decending limb of the Loop of Henle (DLLH) and the collecting duct. The DLLH is a thin passive segment that is permeable to water, but, impermeable to salt.



As the DLLH gives up water to the medullary interstitium, the osmolarity of the fluid changes from 300 to 1,200 mOSM/L. The net effect of this process is to conserve water for the body. Thus, the loop of Henle actively transfers salt back into the kidney which can be used to save water osmotically. A remarkable process!



The hyperosmotic interstitium of the medulla will also “pull” and conserve water from the collecting duct, but, on a variable basis depending on the availibility of ADH. As water moves from the collecting duct, urea will follow. Thus, as water is conserved at this level, a certain amount of urea is also conserved. The urea contributes to the high osmolarity of the medulla



The availibility of Antidiurectic Hormone (ADH) is determined by dehydration and thirst. Under these conditions, the hypothalamus makes extra ADH and stores it in the posterior pituitary where it can be released. The increased release of ADH causes the “water pores” of of the collecting duct to open and allow water to move from the urine to the medulla.



As water leaves the collecting duct, the urine becomes progressively more concentrate. The osmolarity of the collecting duct fluid will increase from about 150-300 to 1,200 mOsm/l. under these conditions. If ADH is not present, water is not conserved and is lost as part of a dilute urine (100 mOsm/l).



The vasa recta is made up of a group of capillary like vessels and is freely permeable to salt and water. The vessels of the vasa recta roughly flow counter to the loop of Henle and acts as a counter current exchanger. As blood flows through the vasa recta it picks up water and leaves behind salt. Thus, the vasa recta returns conserved water back to the body and leaves the salt which maintains the hyperosmotic medulla.


Objective 8

Given the value for two of the following, you will compute the value for the third:

Amount Filtered, Amount Reabsorbed and Amount Excreted.


Objective 8

The relationship between the variables of Objective 8 is as follows:

Amount Excreted = Amount Filtered - Amount Reabsorbed

This equation signifies that if we take the difference between the filtration and reabsorption rate, we can determine how much of a substance the kidneys eliminate per unit of time.


Objective 8

If the kidneys filter 16 grams of NaCl per day and then reabsorb 14 grams of NaCl per day, then 2 grams of NaCl would be excreted or eliminated by the kidneys per day as part of the urine.

Amount Excreted = Amount Filtered - Amount Reabsorbed

2 g NaCl/day = 16 g NaCl/day - 14 g NaCl/day


Objective 8

Examine the following and find the missing value: Amount Excreted = Amount Filtered - Amount Reabsorbed

1) ? = 100 g of glucose - 100 g of glucose

2) 100 g of glucose = ? - 300 g of glucose

3) 100 g of glucose = 400 g of glucose - ?

Answers: (1)equals zero; (2) equals 400; (3) equals 300


Objective 9

Given the concentration of a substance in the plasma and the amount of the substance excreted in the urine per minute, you will compute the plasma clearance rate.


Plasma Clearance

Plasma clearance is defined as the amount of plasma that is cleared or “cleansed” of a particular substance in one minute. The kidneys will carry out this clearance process through the use of filtration, reabsorption and secretion.


Plasma ClearanceFiltration will directly affect clearance. As filtration increases, more material will be removed from the blood plasma. Reabsorption will indirectly affect clearance. As reabsorption increases, less material will be removed from the blood plasma. Secretion will directly affect clearance. As secretion increases, more material will be removed from blood plasma.


Plasma Clearance

The formula used to calculate plasma clearance is: C = V x U/P

C = plasma clearance rate in ml/min

V = urine production rate in ml/min

U = the concentration of a substance in the urine in mg/ml

P = the concentration of a substance in the plasma in mg/ml

As you track the units in the equation, you will notice that mg/ml cancel out, leaving ml/min.


Plasma Clearance

Let us practice calculating plasma clearance using the clearance equation. In all your calculations, assume that the urine production rate (V) is 2 ml/min. Let’s start with the substance inulin (not insulin!). If after a dose of inulin, your urine has 30 mg/ml and your plasma has 0.5 mg/ml of this substance, what is the inulin clearance rate? If you got 120ml/min, you are correct!


Plasma Clearance

If you did not get 120ml/min, look at the following calculation and recheck your work.

120 ml/min = 2 ml/min x 30 mg/ml/ 0.5 mg/ml


Plasma ClearanceTest your ability to conduct further calculations by calculating the clearance rate for the following substances:Substance Urine concentration Plasma concentration

Urea 7.0 mg/ml 0.2 mg/ml

Glucose 0.0 mg/ml 1.0 mg/ml

Penicillin 298 mg/ml 0.7 mg/ml

Remember that the urine production rate (2ml/min) will be the same for all of the above calculations. The clearance rate for each of the above substances will be: Urea = 70 ml/min; Glucose = 0 ml/min; Penicillin = 851 ml/min. Were you able to get the right answers? If not, go back and restudy the clearance process.


Objective 10

Give the cause and describe the disease process for the following: renal calculi (kidney stones); cystitis; gout; Glomerulonephritis (Bright’s Disease); incontinence.


Disorders of the Urinary System

• 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.



• Cystitis– 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



• 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.



• 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, discomfort and embarassment


Objective 11

Describe the process involved in dialysis therapy.


Dialysis Therapy

Dialysis is a process that artificially removes metabolic wastes from the blood in order to compensate for kidney (renal) failure. Kidney failure results in the rapid accumulation of nitrogen waste (urea, etc.) which leads to azotemia. Uremia and ion disturbances can also occur. This condition can cause acidosis, labored breathing, convulsions, coma and death.


Dialysis TherapyThe 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 TherapySome 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)


unit 1 1 urinary system

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