URINARY SYSTEM - Science at Yorkdale with Jessica! · URINARY SYSTEM • Let’s take a look at the anatomy first! URETERS: tubes the conduct the urine from the kidneys to the bladder

URINARY SYSTEM

Sunday, July 17, 2011

URINARY SYSTEM• Let’s take a look at the anatomy first!

KIDNEYS: are complex reprocessing centers where blood is filtered through and waste products are removed. Wastes and extra water become urine.

Blood is carried to the kidneys via the RENAL ARTERIES and blood leaves the kidneys via the RENAL VEINS.

The kidney’s may hold 25% of the body’s blood at one time!


URINARY SYSTEM• Let’s take a look at the anatomy first!

URETERS: tubes the conduct the urine from the kidneys to the bladder.

BLADDER: is a hollow muscular organ which collects urine prior to its excretion.

URETHRA: tube that carries urine from the bladder to the exterior of the body.


URINARY SYSTEM• OMG! I’M GOING TO PEE MY PANTS!

The bladder is a muscular organ which can expand slightly as it fills and which can contract in order to expel urine. Voluntary control comes from the muscular urinary sphincters at the base of the bladder.

200 mL of urine = bladder stretches slightly, nerve signal sent to the brain

400 mL of urine = more stretch receptors activated, signal becomes more urgent!

600 mL of urine = voluntary control will be lost – sphincters relax and urine is voided.


URINARY SYSTEM• Let’s look at a cross section of the kidney!

The CORTEX is the outer layer of connective tissue that surrounds the kidney.

The MEDULLA is the inner layer, underneath the cortex.

A hollow cavity called the RENAL PELVIS joins the kidney with the ureter.


URINARY SYSTEM• The functional unit of the kidney is called

the NEPHRON!!!!The kidneys are made up of approximately one million nephrons!!!!


URINARY SYSTEMSmall branches from the renal artery supply the nephron with blood – these are called AFFERENT ARTERIOLES.

The afferent arterioles branch into a capillary bed called the GLOMERULUS.

GLOMERULUS = high-pressure capillary bed that is the site of filtration. The glamorous does not transfer blood to a venule – it leaves by way of EFFERENT ARTERIOLES.


URINARY SYSTEMAFFERENT ARTERIOLES = blood in

GLOMERULUS = capillary bed = site of filtration

EFFERENT ARTERIOLES = filtered blood out

The glomerulus is surrounded by a funnel-like part of the nephron called the BOWMAN’S CAPSULE

Path of blood through the nephron

PERIUBULAR CAPILLARIES = site of gas exchange


URINARY SYSTEMThe BOWMAN’S CAPSULE, AFFERENT and EFFERENT ARTERIOLES are all located within the CORTEX of the kidney.

Fluids to be processed into urine enter the Bowman’s capsule from the blood.

Urine that results from filtration in the bowman’s capsule enters the PROXIMAL TUBULE.


URINARY SYSTEM

PROXIMAL TUBULE

LOOP OF HENLE

DISTAL TUBULE

COLLECTING DUCTS

Path of urine through the nephron


FORMATION OF URINE• Urine formation depends on 3 major

functions:

» FILTRATION – accomplished by the movement of fluids from the blood into the Bowman’s capsule

» REABSORPTION – involves the transfer of essential solutes and water from the nephron back into the blood

» SECRETION – involves the movement of materials from the blood back into the nephron


FORMATION OF URINE• http://www.youtube.com/watch?

v=aQZaNXNroVY


FILTRATIONThe GLOMERULUS is considered to be a high pressure capillary bed.

Pressure inside the GLOMERULUS is about 65mmHg.

Since particles want to move from high to low pressure, solutes within the blood will move from the high pressure glomerular capillary bed into the BOWMAN’S CAPSULE of the nephron.

Note: each nephron has its own individual blood supply, so filtration occurs at each nephron for each afferent arteriole.


FILTRATIONMaterials that get filtered:

- Water

- sodium chloride (NaCl)

- glucose

- amino acids

- hydrogen ions

Some molecules are TOO LARGE to move through the walls of the glomerulus. PLASMA PROTEINS, BLOOD CELLS and PLATELETS are

too large and do not get filtered!!!!


FILTRATIONFollowing filtration, the FILTRATE enters the PROXIMAL TUBULE.

The filtered blood leaves through the EFFERENT ARTERIOLES.

On average, about 600 mL of fluid flows through the kidneys every minute! Approximately 20% of that fluid is filtered into the nephron – this

means 120 mL of fluid is filtered EVERY MINUTE!!!!…this is why we need the next step: REABSORPTON!!


REABSORPTION• For every 120 mL of fluid filtered into the

nephron, approximately 119 mL of fluids and solutes are reabsorbed.

• In the PROXIMAL TUBULE, selective reabsorption occurs.

» selective reabsorption occurs via passive and active transport

» numerous mitochondria supply the energy for active transport


REABSORPTIONPassive Transport:

H3O-, NH3, H2O and K+ ions are all able to move via passive transport.

Active Transport:

Glucose and amino acids are shuttled out of the nephron and back into the blood by specific carrier molecules.

NaCl and H+ ions are also actively transported across the membrane.

*NOTE* Reabsoprtion occurs only until the THRESHOLD LEVEL (in the blood) of a substance is reached. Excess will

remain in the urine to be excreted with the urine.


REABSORPTIONThe active transport of solutes OUT of the nephron and back into the blood creates an OSMOTIC GRADIENT.

Recall that OSMOSIS refers to the movement of water from an area of high water concentration to an area of low water concentration.

OR

Movement of water from an area of low solute concentration to an area of high solute concentration.


REABSORPTION• The osmotic gradient is created by the

solutes that were actively transported back into the blood as well as the proteins in the blood that were never filtered out.

» Thus, as filtrate descends the LOOP OF HENLE, water is absorbed from the filtrate, into the blood.

The absorption of water into the blood causes remaining solutes in the filtrate to become more concentrated – leading to their diffusion back into the blood, although less is reabsorbed this time than was originally filtered.



SECRETION• Occurs in the DISTAL TUBULE

» involves the movement of wastes from the blood back into the nephron

» Cells loaded with mitochondria line the distal tubule to function in active transport of these wastes back into the blood.

» wastes like: nitrogen-containing wastes, excess H+ ions, and minerals such as K+.


FORMATION OF URINE• http://www.youtube.com/watch?v=uo-NOr-

P49I

• **REVIEW: Table 2 on page 351 in your textbook for a step-by-step breakdown of urine formation.


http://www.youtube.com/watch?v=uo-NOr-P49I




WATER BALANCE• The body adjusts for increased water intake

by increasing urine output.

• The body adjusts for increased exercise or decreased water intake by reducing urine output. These adjustments involve the interaction of the body's two

communication systems: THE NEVERVOUS SYSTEM & THE ENDOCRINE SYSTEM.

Hormone involved = ANTIDIURETIC HORMONE (ADH)


WATER BALANCE• Antidiuretic hormone (ADH) = helps to

regulate the osmotic pressure of body fluids by causing the kidneys to increase water reabsorption.

ADH is released more water is reabsorbed in the kidneys urine produced is more concentrated

ADH is stored and released by the PITUITARY GLAND its release is signalled by the HYPOTHALAMUS


WATER BALANCE• specialized cells called OSMORECEPTORS,

located in the hypothalamus will detect changes in the osmotic pressure of the blood and surrounding extracellular fluids.

A loss of body water resulting from decreased water intake

OR excessive sweating

= blood solutes become more concentrated

= INCREASED OSMOTIC PRESSURE OF BLOOD.

An increase in body water resulting from a greater volume

of water being consumed

= blood solutes become more diluted

= DECREASED OSMOTIC PRESSURE OF BLOOD.


WATER BALANCEA loss of body water resulting

from decreased water intake OR excessive sweating

= blood solutes become more concentrated

= INCREASED OSMOTIC PRESSURE OF BLOOD.

An increase in body water resulting from a greater volume

of water being consumed

= blood solutes become more diluted

= DECREASED OSMOTIC PRESSURE OF BLOOD.

ADH is releasedMore water is reabsorbed by the

kidneys

Less ADH is releasedless water is reabsorbed by the

kidneys


WATER BALANCE

Water balance in the body using ADH is an example of a negative feedback loop.


KIDNEYS AND BLOOD PRESSURE

• the kidneys also play a role in the maintenance of blood pressure by adjusting blood volumes.

» the hormone involved in this feedback loop is ALDOSTERONE

ALDOSTERONE = is produced in the cortex of the adrenal glands and acts on the kidneys by increasing Na+ reabsorption from the distal tubule and collecting duct.


KIDNEYS AND BLOOD PRESSURE

Increased fluid loss causes a decrease in blood pressure, reducing oxygen delivery to tissues.

This is detected by specialized receptors and leads to the release of RENIN.

Renin is an enzyme which converts angiotensinogen, a plasma protein, into angiotensin.

Angiotensin has two functions. It will cause vasoconstriction of blood vessels and signals the relase of aldosterone from the adrenal gland.


KIDNEYS AND pH BALANCE

• read pg. 355 in your textbook about the kidneys and pH balance.


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URINARY SYSTEM - Science at Yorkdale with Jessica! · URINARY SYSTEM • Let’s take a look at the anatomy first! URETERS: tubes the conduct the urine from the kidneys to the bladder