Regulating the Internal Environment

Animals need to regulate:1. Water/solute concentration of body fluids

– Body fluids-total amount of fluids in the body

• Intracellular-amount of fluids found inside the cells, blood cells, and other tissue

• Extracellular-amount of fluids found outside of the cells

– Plasma-extracellular fluids found in the circulatory system

– Interstitial fluid-fluids found between the cells outside the circulatory system

2. pH

3. temperature

• The excretory system is a regulatory system that helps to maintain homeostasis within the body

• Homeostasis is the dynamic constancy of the internal environment

• The excretory system eliminates wastes and functions in osmoregulation.

• Osmoregulation is the control of salt and water balance

• Osmoconformers– Do not actively adjust their internal osmolarity

• Osmoregulators– Animals whose body fluids are not isotonic with

the external environment must manipulate solute concentrations in their body fluids

Osmoregulation involves:

1.Osmosis-diffusion of H2O across a membrane due to a concentration gradient

• remember, hyper/hypo/isotonic

2. Excretion- process of an organism ridding their bodies of metabolic wastes. This process also helps regulate Salt Balance.

Animals have to get rid of nitrogen

• The metabolism of proteins and nucleic acids produces toxic by-products ammonia

• Ammonia:– a small and very toxic molecule– can be transported and excreted only in a very

dilute solution• Many animals convert ammonia to urea (mammals

and amphibians) or uric acid (birds and reptiles), which are much less toxic, but require ATP to produce

Maintaining Extracellular Fluid• Urinary/Excretory system:

– keeps volume and composition of extracellular

fluid within tolerable ranges

– regulates solute movement between internal

fluids and the external environment

• interacts with the digestive, respiratory, and

circulatory systems to fulfill these tasks

Urinary System Interactionsfood, water intake oxygen intake

DIGESTIVE SYSTEM

RESPIRATORY SYSTEM

elimination of carbon dioxide

CIRCULATORY SYSTEM

URINARY SYSTEM

oxygen carbon dioxide

water, solutes

nutrients, water, salts

elimination of food residues

rapid transport to and from all living cells

elimination of excess water, salts, wastes

Aquatic animals: -excrete ammonia which can readily cross membranes and then be flushed from the body

1. Many Marine invertebrates - lack a specialized excretory system, most waste diffuses across a membrane. The sea is an isotonic solution so salt balance is no problem EXCEPT if the organism is put in fresh water or a hypotonic solution. The animal most likely will lose salts and fluids and die

2. Marine fish - their body fluids are diluted (or hypotonic) in comparison to their environment (sea water)

-Marine fish tend to lose water to their environment

-Compensation

1. Marine fish drink water to replace H2O loss

2. Gills secrete ammonia not urine

Gain of water andsalt ions from foodand by drinkingseawater

Osmotic water lossthrough gills and other partsof body surface

Excretion ofsalt ionsfrom gills

Osmoregulation in a saltwater fish

Excretion of salt ions and small amountsof water in scantyurine from kidneys

3. Fresh water fish – their body fluids are concentrated (or hypertonic) in comparison to their environment

- Fresh water fish tend to gain water from their environment

- Compensation

- almost never drink H2O

- Fish excrete a dilute urine, therefore keeping more salts in the body

Excretion oflarge amounts ofwater in diluteurine from kidneys

Osmotic water gainthrough gills and other partsof body surface

Osmoregulation in a freshwater fish

Uptake ofsalt ionsby gills

Uptake ofwater and someions in food

Terrestrial animals:

**must fight desiccation (drying out)

-compensation

1. drinking H2O

2. food with H2O

3. H2O is a by product respiration

-Mammal and amphibians form Urea and finally urine

-Birds and reptile form uric acid which is insoluble and less H2O is needed for excretion. Also will not toxify embyos in eggs.

Nitrogenous bases

Nucleic acids

Amino acids

Proteins

—NH2

Amino groups

Most aquatic animals, including most bony fishes

Mammals, most amphibians, sharks, some bony fishes

Many reptiles (including birds), insects, land snails

Ammonia Urea Uric acid

Ammonia• Animals that excrete nitrogenous wastes as

ammonia need lots of water

• They release ammonia across the whole body surface or through gills

Urea• The liver of mammals and most adult amphibians

converts ammonia to less toxic urea

• The circulatory system carries urea to the kidneys, where it is excreted

Uric Acid• Insects, land snails, and many reptiles,

including birds, mainly excrete uric acid • Uric acid is largely insoluble in water and can

be secreted as a paste with little water loss

Excretory Processes

• Most excretory systems produce urine by refining a filtrate derived from body fluids

• Key functions of most excretory systems:– Filtration: pressure-filtering of body fluids– Reabsorption: reclaiming valuable solutes– Secretion: adding toxins and other solutes from

the body fluids to the filtrate– Excretion: removing the filtrate from the system

Protonephridia: Flame-Cell Systems - flatworms

• A protonephridium is a network of dead-end tubules lacking internal openings

• The smallest branches of the network are capped by a cellular unit called a flame bulb

• These tubules excrete a dilute fluid and function in osmoregulation

LE 44-10

Protonephridia(tubules)

Tubule

Nephridioporein body wall

Flamebulb

Interstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)

Tubule cell

Cilia

Nucleusof cap cell

Metanephridia• Each segment of an earthworm has a pair of

open-ended metanephridia

• Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion

LE 44-11

Collectingtubule

Nephridio-pore

Capillarynetwork

Coelom

Bladder

MetanephridiumNephrostome

Malpighian Tubules• In insects and other terrestrial arthropods,

Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation

• Insects produce a relatively dry waste matter, an important adaptation to terrestrial life

LE 44-12

Salt, water, andnitrogenous

wastes

Digestive tract

Midgut(stomach)

Malpighiantubules

RectumIntestine Hindgut

Reabsorption of H2O,ions, and valuableorganic molecules

Malpighiantubule

HEMOLYMPH

Anus

Rectum

Feces and urine

The Vertebrate Excretory System

• Kidneys (function in both excretion and osmoregulation), ureters, urinary bladder, urethra, renal artery, renal vein

• Also…– Lungs: excrete carbon dioxide– Skin: excretes water, salts, and a small

amount of urea (in sweat)

Water Gains and Losses

Water Gains

• Absorption from

gut

• Metabolism

Water Losses

• Urination

• Cell secretions

• Sweating

• Water in feces

Solute Gains and Losses

Solute Gains

• Absorption from

gut

• Cell secretions

• Respiration

• Metabolism

Solute Losses

• Urinary

excretion

• Respiration

• Sweating

Controlling Water Gain & Loss

• Urinary excretion provides the

most control over water loss

• Concentration of urine can be

varied

Components of Urinary System

• Pair of kidneys

• Pair of ureters

• Urinary bladder

• Urethra

• Anytime you see the terms “nephr” or renal it has something to do with the kidneys

Urinary Excretion

• Urine flows from each kidney to a ureter

• Ureters deliver urine to bladder

• Contraction of the smooth muscle of the bladder forces urine out of the body into the urethra

• Skeletal muscle surrounds urethra; allows voluntary control of urination

Function of Kidneys

• Filter water, mineral ions, wastes from

the blood

• Adjust filtrate concentration and return

most to blood

• Remaining water and solutes in filtrate

constitute urine

Structure of Kidney

• Renal capsule surrounds kidney

• Two regions – Outer renal cortex– Inner renal medulla

• Renal pelvis collects urine and funnels it to ureter

Figure 42.4aPage 747

Excretory organs and major associated blood vessels

RenalmedullaRenalcortex

Renalpelvis

Section of kidney from a ratKidney structure

Ureter

Kidney

Glomerulus

Bowman’s capsule

Proximal tubule

Peritubular capillaries

Afferentarteriolefrom renalartery

Efferentarteriole from glomerulus

Distaltubule

Collectingduct

SEM20 µm

Branch ofrenal vein

Filtrate and blood flow

Vasarecta

Descendinglimb

Ascendinglimb

LoopofHenle

Renalmedulla

Nephron

Torenalpelvis

Renalcortex

Collectingduct

Juxta-medullarynephron

Corticalnephron

Posterior vena cava

Renal artery and vein

Aorta

Ureter

Urinary bladder

Urethra

Nephron

• Functional unit of

the kidney

• Each consists of

a renal tubule and

associated

capillaries

Bowman’s capsule (red)

proximal tubule

distal tubule

loop of Henle

collecting duct

Figure 42.4cPage 747

Humans - There are over 1,000,000 nephrons in each kidney. 1,100-1,200 L of blood flows through the kidneys each day.

-blood is delivered via an efferent arteriole to a capillary bed called the glomerulus.

-The blood leaves the glomerulus via the afferent arteriole forming a second capillary bed called the peritubular capillaries that surrounds the nephron. --The blood then leaves the nephron via the a venule.

-

Urine Formation

Filtration

Tubular reabsorption

Tubular secretion

Hormone action

Excretion

Figure 42.5 Page 748

Leaky Glomerular Capillaries

• Glomerular capillaries

have large pores

• Fluid leaks from

glomerular capillaries

into kidney tubules

Figure 42.5Page 748

Renal corpuscle (Bowman’s capsule + glomerular capillaries)

Filtration Rate Varies

• Increased blood pressure increases

glomerular filtration

• Flow volume to kidneys changes in

response to neural, endocrine, and local

changes

Most Filtrate Is Reabsorbed

• Each day, about 180

liters of filtrate flows out

of glomerulus into

tubules

• 1 to 2 liters excreted

• Most filtrate is

reabsorbed into blood

peritubular capillaries

Tubular Reabsorption

• Ions move from the filtrate in tubule lumen into the interstitial fluid

• Sodium ions are actively pumped out of the proximal tubule into the interstitial fluid

• Chloride ions follow; they are passively transported

Tubular Reabsorption

• Ion flow creates an osmotic gradient; it is saltier outside the tubule than inside

• Water flows down the osmotic gradient, from the tubule lumen into the interstitial fluid

• Peritubular capillaries pick up the water and ions from the interstitial fluid

Amino acids, vitamins, proteins, and glucose are reabsorbed in the PCT.

Tubular Reabsorption

peritubular capillary

sodium pump

Na+

Na+

Na+

Na+

Cl-

H2O

interstitial fluid filtrate in tubule

Na+

Na+

Figure 42.6Page 749

Tubular Secretion

• The opposite of reabsorption

• Molecules are transported out of the

peritubular capillaries, through tubule

cells, and into the filtrate

• Eliminates H+ ions, metabolites, and

toxins

Filtrate

H2O

Salts (NaCl and others)

HCO3–

H+

Urea

Glucose; amino acids

Some drugs

Key

Active transport

Passive transportINNERMEDULLA

OUTERMEDULLA

NaCl

H2O

CORTEX

Descending limbof loop ofHenle

Proximal tubule

NaCl Nutrients

HCO3–

H+

K+

NH3

H2O

Distal tubule

NaCl HCO3–

H+K+

H2O

Thick segmentof ascendinglimb

NaCl

NaCl

Thin segmentof ascendinglimb

Collectingduct

Urea

H2O

INNERMEDULLA

OUTERMEDULLA

CORTEX

Osmolarity ofinterstitial

fluid(mosm/L)

NaCl

Urea

H2O

Activetransport

Passivetransport

300300

300 100

100

400 200H2O

H2O

H2O

H2O

H2O

H2O

600 400

900 700

1200

300

400

H2O

600

12001200

600

900

300

400NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

UreaH2O

UreaH2O

H2O

H2O

H2O

H2O

Urine Formation

Filtration

Tubular reabsorption

Tubular secretion

Hormone action

Excretion

Figure 42.5 Page 748

• http://www.biologymad.com/resources/kidney.swf

Regulation of Kidney Function• The osmolarity of the urine is regulated by

nervous and hormonal control of water and salt reabsorption in the kidneys

Hormones:

1.Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney making urine more concentrated and conserving water– Acts on collecting ducts; makes walls more

permeable to water

Osmoreceptorsin hypothalamus

Hypothalamus

ADH

Pituitarygland

Increasedpermeability

Distaltubule

Thirst

Drinking reducesblood osmolarity

to set point

Collecting duct

H2O reab-sorption helpsprevent further

osmolarityincrease

Homeostasis:Blood osmolarity

STIMULUSThe release of ADH istriggered when osmo-receptor cells in the

hypothalamus detect anincrease in the osmolarity

of the blood

2. The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis controlling blood pressure and volume

• If low blood volume or low blood pressure:

a) Aldosterone - Stimulates reabsorption of sodium (H2O follows) in the Distal Convoluted Tubule , increasing blood volume and therefore pressure

b) Kidneys can also secrete an enzyme (resin) which is converted to Angiotensin which helps control blood pressure by causing arterioles to constrict

Distaltubule

Aldosterone

Homeostasis:Blood pressure,

volume

STIMULUS:The juxtaglomerular

apparatus (JGA) respondsto low blood volume or

blood pressure (such as due to dehydration or

loss of blood)

Increased Na+

and H2O reab-sorption in

distal tubules

Reninproduction

Arterioleconstriction

Adrenal gland

Angiotensin II

Angiotensinogen

JGA

Renin

Thirst

• Osmoreceptors detect changes

• Activate thirst center in hypothalamus

and ADH-secreting cells

• Angiotensin II acts on brain to promote

thirst and ADH secretion

3. Another hormone, atrial natriuretic factor (ANF), opposes the RAAS

• The walls of the atria of the heart release ANF in response to increase in blood volume and pressure.

• ANF inhibits the release of rennin from the JGA and inhibits NaCl reabsorption by the collecting ducts

Variation in Urinary Systems

• Structure of vertebrate urinary systems varies in details

• Adapted to particular habitats

• Freshwater fish must deal with continuous influx of water by osmosis

• Marine fish must deal with continuous loss of water

Length of Loop of Henle

• Longer loop of Henle allows an organism to

produce a very steep osmotic gradient and the

more water that is conserved or retained by the

body

• Kangaroo rats have very long loops of Henle.

Kidney Disorders

• Glomerulonephritis

– Infection of glomeruli leads to chronic

inflammation that damages kidney

• Kidney stones

– Uric acid and calcium salts settle out of

urine, form hard deposits that can lodge in

ureter or urethra

Renal Failure

• Both kidneys are damaged to the point where they are nonfunctional

• Fatal if not treated

• Dialysis is used to restore normal solute balances temporarily

• Transplant is only way to fully restore function

Acid-Base Balance

• Kidneys work in concert with

buffering systems to keep pH in

normal range

• Normal range is 7.37 to 7.43

• Normal metabolism produces an

excess of H+

Buffer Systems

• Weak acid and weak base that can

reversibly bind and release ions

• Bicarbonate-carbon dioxide buffer

system can neutralize excess H+

Regulating Blood pH (1)

• Involves secretion of H+ and reabsorption

of HCO3- (bicarbonate)

• HCO3- in filtrate combines with H+ to form

carbonic acid (H2CO3)

• H2CO3 becomes CO2 and H2O, which are

reabsorbed into blood from filtrate

Regulating Blood pH (2)

• In blood, HCO3 dissociates to form

HCO3- and H+

• The H+ can be secreted into proximal tubule, while the HCO3

- remains in

blood, thus increasing blood pH

• H+ can also combine with K+ or ammonia and leave body in urine

Core Temperature

• Internal temperature of an animal’s body

• Must be maintained within a narrow range for

normal enzyme function

– Human body temp is 37C or 98.6F on average

• Heat gains and losses must be kept in

balance

THERMOREGULATION• Thermoregulation – homeostatic process

where body temperature is maintained

• VASOCONSTRICTION & VASODILATION – making blood vessels smaller or larger to shunt blood to areas of the body

ENDOTHERM METHODS• Shivering – involuntary muscle contraction

that generates heat

• Goose bumps – muscles at base of hairs raise hairs off of skin creating a pocket of warmer air near skin

• Sweating – water evaporating removes heat energy from the skin

• Panting – loss of body heat as water evaporates from moist surfaces of resp. tract (birds, dogs, bears)

Maintaining Temperature

• Peripheral thermoreceptors in skin

• Thermoreceptors deeper in body

• Feed input to hypothalamus

• Hypothalamus sends messages to

effectors by way of nervous system

Response to Heat Stress

• Peripheral vasodilation

• Sweating

• Panting

Response to Cold

• Peripheral vasoconstriction

• Pilomotor response –moving the hairs

• Shivering response

• Nonshivering heat response

Fever

• Part of response to tissue damage

• Hypothalamus resets body thermostat

at higher temperature

• Moderate fever can promote healing

and need not be suppressed

ECTOTHERM METHODS• CONDUCTION – direct transfer of heat

between molecules of objects in contact (lizard on a hot rock)

• CONVECTION – transfer of heat by movement of air or liquid past a surface – blood moving heat from extremities to the core

• RADIATION – sun

• EVAPORATION – cooling effect