Excretory Systems 1 Ch. 38 - Excretory Systems & Body Fluid Regulation.

1Excretory SystemsCh. 38 - Excretory Systems & Body Fluid Regulation

2Excretory Systems

Body Fluid Regulation

An excretory system regulates body fluid concentrations. It does this by:•Retaining or eliminating certain ions & water

Dependent upon concentration of mineral ions such as: Na+, Cl-, K+, & HCO3

- Water can enter the body through:

Drink, food & metabolism

Water can leave the body through:Evaporation, feces formation, excretion (urine)

3

Excretory Functions

4Excretory Systems

Osmoregulation

When there are differences in osmolarity (solute concentration) between two regions, water tends to move from regions with the greatest water concentration into regions with the lowest water concentration Thus, water moves to the region with the highest amount of ions

Marine Environment = high in salts -Promotes osmotic loss of water & gain of ions by animals Fresh Water Environment = low in salts -Promotes osmotic gain of water & loss of ions by animals

•Terrestrial Environments -Animals tend to lose both water and ions to environment

5Excretory Systems


Marine InvertebratesLike mollusks (squid) & arthropods (lobsters)Have body fluids that are ~ isotonic to seawaterThese organisms have little difficulty maintaining normal salt and water balance (osmotic balance)Thus, they have no special mechanisms

6Excretory Systems


Cartilaginous fishes (Elasmobranchs)Like sharks & raysHave body fluids that are ~ isotonic to seawaterThese organisms have little difficulty maintaining normal salt and water balance (osmotic balance)They do NOT have the same amount of mineral ions as seawater like the marine invertebrates Instead, their blood contains a high concentration of urea (a nitrogen waste product). This level would be toxic to other vertebrates but is not to these fish.

7Excretory Systems

Osmoregulation in Cartilaginous Fishes

8Excretory Systems


Bony Marine FishesBody fluids of bony fishes have less salt than the surrounding seawater. Thus they are hypotonic to their surroundings.They continually lose water through their gills & thus risk dehydrationMust constantly drink seawater to compensateThe excess salt intake is counteracted by actively transporting salt ions out into seawater through the gillsThey produce small amounts of isotonic urine

9Osmoregulation in Bony Fishes

10

Excretory Systems


Freshwater Bony FishesThe body fluids of freshwater bony fishes are hypertonic to fresh water but not as concentrated as seawaterWater tends to rush into their bodies through gills.They never drink waterEliminate excess water by producing large quantities of dilute, hypotonic, urineThis causes them to lose salt, so they actively transport salts into the blood through their gills

11

Osmoregulation in Bony Fishes

12

Excretory Systems


Terrestrial animals •Lose water through excretion, respiration, sweat & feces •Most must drink water to make up for loss.

(Exception is kangaroo rat)Some reduce excretory loss by excreting nitrogen as relatively insoluble uric acid

Marine birds & reptiles drink seawater & need to excrete excess salts. They have salt glands located above each eye

Certain animals, camels & kangaroo rats, also have a highly convoluted nasal passage with a mucous membrane surface

13

Excretory Systems

Terrestrial Animal Osmoregulation

14

Excretory Systems

Nitrogenous Waste Products

Catabolism of amino acids and nucleic acids results in nitrogenous wastes since the NH2 has to be removed (deamination)

There are 3 forms that may be excreted: 1. Ammonia (NH3)

Little or no energy needed to create It is very toxic; needs a great deal of water to wash it from the body

High solubility in water permits it to be excreted directly by many aquatic animals

Excreted by bony fishes, marine invertebrates & aquatic amphibians whose gills & skin are in direct contact with water

15

Excretory Systems


2. Urea Terrestrial animals must convert ammonia to urea or uric acid since they don’t have a watery environment

Much less toxic than ammonia Requires the expenditure of energy. Liver changes ammonia into urea by adding CO2

Excreted by terrestrial amphibians and mammals Can be excreted in a moderately concentrated solution Urea allows water to be conserved but there is still a loss of

significant water Thus, most amphibians & mammals must drink water

16

Excretory Systems


3. Uric Acid Not very toxic Requires large amounts of energy to produce Relatively insoluble in water; leads to water conservation Uric acid requires much less water per unit of nitrogen

excreted Allows invasion of drier habitats far from standing water

Excreted by reptiles, birds & insects, -Especially good in desert areas

- Also very useful for egg-laying animals. Insoluble wastes are stored in shell until hatching & don’t poison the embryo

inside

17

Nitrogenous Wastes

18

Excretory SystemsOrgans of Excretionin Invertebrates

Various mechanisms have evolved in different animal groups to cope with fluid balance.

1. Flame Cells in Planarians Set of tubules & bulblike flame cells rid body of

excess water & wastes

2. Nephridia in EarthwormsIn every segment of body there is a pair of these excretory structures that creates urine from blood in surrounding capillaries.

3. Malpighian Tubules in InsectsLong thin tubes attached to gut. Uric acid leaves through anus.

19

Excretory Organs in Animals

Flame Cells in Planaria

Nephridia in Earthworms

Malpighian tubules in Ant

20

Excretory Systems

Urinary System in Humans

Human kidneysLocated on either side of vertebral column, just below the diaphragmEach connected to a tube called a ureterUreters conduct urine from the kidney to the urinary bladder

Urine leaves bladder through tube called the urethra In males, the urethra passes through the penis & shares functions with reproductive system In females, there is no connection between excretory & reproductive systems

21

The Human Urinary System

22

Excretory Systems

Functions of Human Kidneys

The kidneys have various functions:Removal of urea from blood into urineRegulation of water balanceElimination of excess moleculesRegulation of ionic balance (Na+, Cl-, H+, K+, etc.)

23

Excretory Systems

Kidneys

The parts of the kidney:1. Renal cortex

Outer region with granular appearance

2. Renal medulla Inside of cortex; cone-shaped renal pyramids

3. Renal pelvisHollow-chambered innermost part of the kidney

24

Macroscopic & MicroscopicAnatomy of the Kidney

25

Excretory Systems

Nephrons

Each kidney composed of over 1 million tubular nephrons

Each nephron is composed of several parts:Glomerular capsule (Bowman’s capsule)GlomerulusProximal convoluted tubuleLoop of HenleDistal convoluted tubeCollecting duct

26

Nephron Anatomy

27

Excretory Systems

Nephrons

Each nephron has its own blood supply:Aorta branches off to renal artery which branches into

renal arterioles which branch into an afferent arteriole which divides to form the

glomerular capillary bed (glomerulus) (bed #1)Glomerulus drains blood into efferent arteriole which branches into

A second capillary bed, the peritubular capillary bed (bed #2)

The capillaries lead to venules which join theThe renal vein which brings blood back to vena cava

28

Nephron Anatomy

29

Excretory Systems

Urine Formation

Urine production requires three distinct processes:Glomerular filtration in glomerular capsuleTubular reabsorption at the proximal convoluted tubule

Tubular secretion at the distal convoluted tubule

30

Processes in Urine Formation

31

Excretory Systems

Glomerular Filtration

Occurs at glomerulus & Bowman’s capsuleBlood pressure forces large percentage of molecules to move out of capillaries of glomerulus & into the Bowman’s capsule. Walls of glomerulus are 100 times more permeable than most capillaries in body.Water, nutrients, salts & urea move out of blood & into capsule and end up in tubules of nephronPlasma proteins & blood cells are too large & remain behind in the blood that flows into efferent arterioleFluid in capsule is now called filtrate. 180 liters produced per day.

32

Excretory Systems

Tubular Reabsorption

Takes place when substances move across the walls of the tubules into the peritubular capillaries.Kidneys produce only about 1-2 liters of urine per day

99% of water must be reabsorbed into blood or humans would die of dehydration

100% of glucose is reabsorbed into blood or we could die of starvation

Plentiful carrier molecules actively reabsorb glucose through walls of tubules.

In diabetes mellitus, abnormally large amounts of glucose are in blood & cannot be completely reabsorbed.

99% of salts are reabsorbed into blood

33

Excretory Systems


How does tubular reabsorption occur?1. Proximal convoluted tubuleNa+ is actively transported out of tubule & back into peritubular capillaries

Cl- follows passively Water then follows by osmosis.

~60-70% of salt & water are thus reabsorbed right away.

- Nutrients, like glucose & amino acids, are returned to blood here

- Filtrate is now isotonic to blood in surrounding capillaries & to the fluids in the surrounding kidney tissues

34


35

Excretory Systems


2. Descending Loop of HenleThis side of loop is permeable to water & NOT permeable to salts

-Water will leave the descending limb along its entire length due to an increasing concentration gradient in the surrounding kidney tissues (more on how this was created soon)

-By the time the filtrate reaches the bottom of the loop of Henle, it is very concentrated in solutes

-Much of the water that was in the filtrate has now been reabsorbed back into the blood

36


37

Excretory Systems


3. Ascending Loop of HenleThis side of loop is impermeable to water & permeable to salts

-Salt passively diffuses out of the lower portion of the ascending loop

-The upper portion actively transports Na+ out of the loop tubule & into the surrounding kidney tissues

-Less & less salt is available for transport as the fluid moves up the ascending loop.

An osmotic concentration gradient is set up within the tissues of the renal medulla.

***This allows the increasing amount of water to diffuse out of the descending loop which is

permeable to H2O***

38


39

Excretory Systems


The innermost portion of inner medulla has the highest concentration of solutes

-Due to the leakage of urea from the lower portion of ascending loop of Henle

Countercurrent Multiplier Mechanism •The combined effects of:

1. the active transport of salts from the ascending limb 2. the leakage of urea from lower end of ascending

loop 3. and the passive transport of water out of the descending loop

set up an increasing solute concentration gradient from the renal cortex down to the medulla

40


41

Excretory Systems


Countercurrent Multiplier Mechanism (continued) •As water diffuses out of descending limb the

remaining fluid in the tubule encounters outside kidney tissues of an even higher concentration

•So water continues to flow out of the descending limb all the way to the bottom.

•This maximizes the amount of water that can be diffused out of the filtrate at this point.*** The longer the loop of Henle, the greater the concentration gradient will become & the more concentrated the urine that can

be produced***The kangaroo rat has an extremely long loop of Henle which

allows it to produce almost no urine & thus conserve so much water it usually doesn’t drink water in the desert

42

Countercurrent Mechanism

43

Excretory Systems


4. Distal Convoluted TubuleThe fluid that enters this tubule is actually hypotonic compared to the renal cortex surrounding it

-The distal tubule is now permeable to water again-Salts are actively transported out of this tubule-Water will follow passively by osmosisFluid that exits the distal tubule is isotonic to surrounding cortex tissue

44


45

Excretory Systems


5. Collecting Duct (Tubule)The fluid that enters this tubule is actually isotonic compared to the renal cortex surrounding it

-This tubule goes down through the renal medulla once again through the same increasing concentration gradient as the loop of Henle

-Tubule is usually permeable to water; but not to salt-Water will flow out passively by osmosis as tubule passes through the concentration gradient

Fluid becomes hypertonic to blood plasma by the time it reaches the renal pelvis

46


47

Excretory Systems

Tubular Secretion

Tubular secretion is the second way that substances are removed from blood & added to filtrate

•Excess ions and other substances like uric acid, ammonia, creatinine, histamine & penicillin move from the capillaries into the tubules, most often at the distal convoluted tubule

●The body can get rid of substances like drugs & other foreign substances in this step.

-This is how athletes get caught when they are taking steroids & have to produce urine to be

tested

48


49

Excretory Systems

Urine Formation and Homeostasis

Humans are capable of excreting hypertonic urineAs water flows down the collecting duct towards the renal medulla it is going through the external concentration gradient & the filtrate will continue to lose water to blood capillaries as long as the collecting tubules are permeable to water.

Permeability of collecting duct can be changed:

The hormone, antidiuretic hormone (ADH), produced by the posterior lobe of the pituitary gland, regulates the permeability of collecting duct

50

Excretory Systems

Urine Formation and Homeostasis

How does ADH work? When ADH is present, more water will be reabsorbed into blood capillaries from tubule

-This will tend to occur when you are slightly to greatly dehydrated & need to conserve water

-A decreased amount of urine will be formed & its color will be a darker yellow

When ADH is NOT present, the collecting tubules become impermeable to water & it does not reabsorb the water into capillaries (alcohol & caffeine can cause this)

-This will tend to occur when you drank a lot of water & need to get rid of the excess water

-An increased amount of urine will be formed & its color will be a lighter yellow

51

Excretory SystemsMaintenance ofpH and Osmolality

Reabsorption of sodium at the distal convoluted tubule is regulated by hormonesAldosterone – promotes excretion of K+ & reabsorption of Na+

Renin – secreted when blood volume & pressure is low. Helps to increase both

Atrial Natriuretic Hormone (ANH) – secreted by atria of heart when stretched by large blood volume. It inhibits secretion of aldosterone & decreases blood volume & pressure

52

Excretory Systems

Kidney Dialysis

Kidney dialysis might be needed if your kidneys are temporarily or permanently damaged

Basically it is an artificial kidney that will cleanse the blood of urea & helps to create a proper salt & water balance

Blood is pumped from an artery through a series of permeable tubes that are surrounded by dialysis solution.

Urea & other wastes will diffuse out; salts & water will come into homeostasis with the dialysis solution

Then blood is returned to the patient’s body

Excretory Systems 1 Ch. 38 - Excretory Systems & Body Fluid Regulation.

Documents

Transcript of Excretory Systems 1 Ch. 38 - Excretory Systems & Body Fluid Regulation.