2d2 digestive systems, respiratory systems (gas exchange), blood/osmolarity/osmotic balance, urinary...

2D2

Digestive systems, Respiratory systems (gas exchange), Blood/Osmolarity/Osmotic Balance, Urinary systems (removal of nitrogen wastes)

Types of Digestive Systems

• Heterotrophs are divided into three groups based on their food sources1. Herbivores are animals that eat plants

exclusively2. Carnivores are animals that eat other animals3. Omnivores are animals that eat both plants and

other animals

2


• Single-celled organisms and sponges digest their food intracellularly

• Other multicellular animals digest their food extracellularly– Within a digestive cavity

• Cnidarians and flatworms have a gastrovascular cavity – Only one opening, and no specialized

regions

3


• Specialization occurs when the digestive tract has a separate mouth and anus– Nematodes have the most primitive digestive tract

• Tubular gut lined by an epithelial membrane

– More complex animals have a digestive tract specialized in different regions

4

Gas Exchange

• One of the major physiological challenges facing all multicellular animals is obtaining sufficient oxygen and disposing of excess carbon dioxide

• In vertebrates, the gases diffuse into the aqueous layer covering the epithelial cells that line the respiratory organs

• Diffusion is passive, driven only by the difference in O2 and CO2 concentrations on the two sides of the membranes and their relative solubilities in the plasma membrane

5

Gas Exchange

• Rate of diffusion between two regions is governed by Fick’s Law of Diffusion

• R = Rate of diffusion • D = Diffusion constant• A = Area over which diffusion takes place• Dp = Pressure difference between two sides• d = Distance over which diffusion occurs

6

R =DA Dp

d

Gas Exchange

• Evolutionary changes have occurred to optimize the rate of diffusion R– Increase surface area A– Decrease distance d– Increase concentration difference Dp

7

Gas Exchange• Gases diffuse directly into unicellular organisms• However, most multicellular animals require system adaptations

to enhance gas exchange• Amphibians respire across their skin• Echinoderms have a poorly developed respiratory system. They

use their tube feet to take in oxygen and pass out carbon dioxide• Insects have an extensive tracheal system throughout their

bodies. It is a complex network of tubes with openings called spiracles.

• Fish use gills• Mammals have a large network of alveoli

8

Blood

• Type of connective tissue composed – Fluid matrix called plasma– Formed elements

• Functions of circulating blood1. Transportation2. Regulation3. Protection

9

Blood plasma

• 92% water• Contains the following solutes

– Nutrients, wastes, and hormones– Ions– Proteins

• Albumin, alpha (a) and beta (b) globulins • Fibrinogen

– If removed, plasma is called serum

11

Formed elements

• Red blood cells (erythrocytes)– About 5 million per microliter of blood– Hematocrit is the fraction of the total blood

volume occupied by red blood cells– Mature mammalian erythrocytes lack nuclei– RBCs of vertebrates contain hemoglobin

• Pigment that binds and transports oxygen

12

Osmolarity and Osmotic Balance

• Water in a multicellular body distributed between– Intracellular compartment– Extracellular compartment

• Most vertebrates maintain homeostasis for– Total solute concentration of their extracellular

fluids– Concentration of specific inorganic ions

13


• Important ions– Sodium (Na+) is the major cation in extracellular

fluids– Chloride (Cl–) is the major anion– Divalent cations, calcium (Ca2+) and magnesium

(Mg2+), the monovalent cation K+, as well as other ions, also have important functions and are maintained at constant levels

14

15

Animal body

H2O(Sweat)

CO2 and H2O

O2 Solutesand H2O

Solutesand H2O

Solutesand H2O

Solutesand H2O

Solutesand H2O

Solutesand H2O

CO2 and H2O

FoodandH2O

External environment

Urine (excess H2O) Waste

Extracellular compartment(including blood)

O2

IntracellularcompartmentIntracellular

compartment

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.


• Osmotic pressure– Measure of a solution’s tendency to take in water by

osmosis

• Osmolarity – Number of osmotically active moles of solute per liter of

solution

• Tonicity – Measure of a solution’s ability to change the volume of a

cell by osmosis– Solutions may be hypertonic, hypotonic, or isotonic

16


• Osmoconformers– Organisms that are in osmotic equilibrium with their

environment

• Among the vertebrates, only the primitive hagfish are strict osmoconformers

• Sharks and relatives (cartilaginous fish) are also isotonic

• All other vertebrates are osmoregulators– Maintain a relatively constant blood osmolarity despite

different concentrations in their environment

17


• Freshwater vertebrates– Hypertonic to their environment – Have adapted to prevent water from entering

their bodies, and to actively transport ions back into their bodies

• Marine vertebrates– Hypotonic to their environment– Have adapted to retain water by drinking seawater

and eliminating the excess ions through kidneys and gills

18


• Terrestrial vertebrates– Higher concentration of water than surrounding

air– Tend to lose water by evaporation from skin and

lungs– Urinary/osmoregulatory systems have evolved in

these vertebrates that help them retain water

19

Osmoregulatory Organs

• In many animals, removal of water or salts is coupled with removal of metabolic wastes through the excretory system

• A variety of mechanisms have evolved to accomplish this– Single-celled protists and sponges use contractile

vacuoles– Other multicellular animals have a system of

excretory tubules to expel fluid and wastes

20


• Invertebrates– Flatworms

• Use protonephridia (All except the simplest flatworms have nephridial tubules, called protonephridia, usually distributed throughout the body. Such structures consist of an external opening and a tubule that branches internally, terminating in a number of blind, bulb-shaped structures called flame bulbs, which bear tufts of cilia.) They probably function as excretory and osmoregulatory organs which branch into bulblike flame cells

• Open to the outside of the body, but not to the inside

– Earthworms• Use nephridia• Open both to the inside and outside of the body

21


• Insects– Use Malpighian tubules

• Extensions of the digestive tract

– Waste molecules and K+ are secreted into tubules by active transport

– Create an osmotic gradient that draws water into the tubules by osmosis

– Most of the water and K+ is then reabsorbed into the open circulatory system through hindgut epithelium

24


• Vertebrate kidneys– Create a tubular fluid by filtering the blood under

pressure through the glomerulus– Filtrate contains many small molecules, in addition

to water and waste products– Most of these molecules and water are

reabsorbed into the blood• Selective reabsorption provides great flexibility

– Waste products are eliminated from the body in the form of urine

26

Evolution of the Vertebrate Kidney

• Made up of thousands of repeating units – nephrons

• Although the same basic design has been retained in all vertebrate kidneys, a few modifications have occurred

• All vertebrates can produce a urine that is isotonic or hypotonic to blood

• Only birds and mammals can make a hypertonic urine

27


• Kidneys are thought to have evolved among the freshwater teleosts, or bony fishes

• Body fluids are hypertonic with respect to surrounding water, causing two problems1. Water enters body from environment

• Fishes do not drink water and excrete large amounts of dilute urine

2. Solutes tend to leave the body• Reabsorb ions across nephrons• Actively transport ions across gills into blood

29


• In contrast, marine bony fishes have body fluids that are hypotonic to seawater

• Water tends to leave their bodies by osmosis across their gills

• Drink large amounts of seawater• Eliminate ions through gill surfaces and urine• Excrete urine isotonic to body fluids

30

31



• Cartilaginous fish, including sharks and rays, reabsorb urea from the nephron tubules

• Maintain a blood urea concentration that is 100 times higher than that of mammals

• Makes blood isotonic to surrounding sea• These fishes do not need to drink seawater or

remove large amounts of ions from their bodies

32


• Amphibian kidney is identical to that of freshwater fish

• Kidneys of reptiles are very diverse– Marine reptiles drink seawater and excrete an

isotonic urine• Eliminate excess salt via salt glands

– Terrestrial reptiles reabsorb much of the salt and water in their nephron tubules• Don’t excrete urine, but empty it into cloaca

33


• Mammals and birds are the only vertebrates that can produce urine that is hypertonic to body fluids

• Accomplished by the loop of Henle • Birds have relatively few or no nephrons with

long loops, and so cannot produce urine as concentrated as that of mammals

• Marine birds excrete excess salt from salt glands near the eyes

34

35


Nitrogenous Wastes

• When amino acids and nucleic acids are catabolized, they produce nitrogenous wastes that must be eliminated from the body

• First step is deamination– Removal of the amino (―NH2) group

– Combined with H+ to form ammonia (NH3) in the liver

• Toxic to cells, and thus it is only safe in dilute concentrations

36

Nitrogenous Wastes

• Bony fishes and amphibian tadpoles eliminate most of the ammonia by diffusion via gills

• Elasmobranchs, adult amphibians, and mammals convert ammonia into urea, which is soluble in water

• Birds, reptiles, and insects convert ammonia into the water-insoluble uric acid– Costs most energy, but saves most water

37

Nitrogenous Wastes

• Mammals also produce uric acid, but from degradation of purines, not amino acids

• Most have an enzyme called uricase, which convert uric acid into a more soluble derivative called allantoin

• Humans lack this enzyme• Excessive accumulation of uric acid in joints

causes gout

38

The Mammalian Kidney

• Each kidney receives blood from a renal artery• Produces urine from this blood• Urine drains from each kidney through a

ureter into a urinary bladder• Urine is passed out of the body through the

urethra

40


• Within the kidney, the mouth of the ureter flares open to form the renal pelvis

• Receives urine from the renal tissue• Divided into an outer renal cortex and inner

renal medulla

41

42



• The kidney has three basic functions– Filtration

• Fluid in the blood is filtered out of the glomerulus into the tubule system

– Reabsorption• Selective movement of solutes out of the filtrate back

into the blood via peritubular capillaries

– Secretion• Movement of substances from the blood into the

extracellular fluid, then into the filtrate in the tubular system

43


• Each kidney is made up of about 1 million functioning nephrons– Juxtamedullary nephrons have long loops that dip deeply

into the medulla – Cortical nephrons have shorter loops

• Blood is carried by an afferent arteriole to the glomerulus

• Blood is filtered as it is forced through porous capillary walls

45


• Blood components that are not filtered drain into an efferent arteriole, which empties into peritubular capillaries– Vasa recta in juxtamedullary nephrons

• Glomerular filtrate enters the first region of the nephron tubules – Bowman’s capsule

• Goes into the proximal convoluted tubule• Then moves down the medulla and back up

into cortex in the loop of Henle46


• After leaving the loop, the fluid is delivered to a distal convoluted tubule in the cortex

• Drains into a collecting duct • Merges with other collecting ducts to empty

its contents, now called urine, into the renal pelvis

47

Reabsorption and Secretion

• Approximately 2000 L of blood passes through the kidneys each day

• 180 L of water leaves the blood and enters the glomerular filtrate

• Most of the water and dissolved solutes that enter the glomerular filtrate must be returned to the blood by reabsorption

• Water is reabsorbed by the proximal convoluted tubule, descending loop of Henle, and collecting duct

49

Reabsorption and Secretion

• Reabsorption of glucose and amino acids is driven by active transport and secondary active transport– Maximum rate of transport– Glucose remains in the urine of untreated

diabetes mellitus patients• Secretion of waste products involves transport

across capillary membranes and kidney tubules into the filtrate– Penicillin must be administered several times a

day50

Excretion

• Major function of the kidney is elimination of a variety of potentially harmful substances that animals eat and drink

• In addition, urine contains nitrogenous wastes, and may contain excess K+, H+, and other ions that are removed from blood

• Kidneys are critically involved in maintaining acid–base balance of blood

51

Transport in the Nephron

• Proximal convoluted tubule– Reabsorbs virtually all nutrient molecules in the

filtrate, and two-thirds of the NaCl and water– Because NaCl and water are removed from

the filtrate in proportionate amounts, the filtrate that remains in the tubule is still isotonic to the blood plasma

52


• Loop of Henle – Creates a gradient of increasing osmolarity from

the cortex to the medulla – Actively transports Na+, and Cl– follows from the

ascending loop • Creates an osmotic gradient

– Allows reabsorption of water from descending loop and collecting duct

– Two limbs of the loop form a countercurrent multiplier system

• Creates a hypertonic renal medulla53


• Distal convoluted tubule and collecting duct– Filtrate that enters is hypotonic – Hypertonic interstitial fluid of the renal medulla

pulls water out of the collecting duct and into the surrounding blood vessels

• Permeability controlled by antidiuretic hormone (ADH)

– Kidneys also regulate electrolyte balance in the blood by reabsorption and secretion

• K+, H+, and HCO3–

55

Hormones Control Osmoregulation

• Kidneys maintain relatively constant levels of blood volume, pressure, and osmolarity

• Also regulate the plasma K+ and Na+ concentrations and blood pH within narrow limits

• These homeostatic functions of kidneys are coordinated primarily by hormones

57


• Antidiuretic hormone (ADH)– Produced by the hypothalamus and secreted by

the posterior pituitary gland– Stimulated by an increase in the osmolarity of

blood – Causes walls of distal tubule and collecting ducts

to become more permeable to water• Aquaporins

– More ADH increases reabsorption of water• Makes a more concentrated urine

58


• Aldosterone – Secreted by the adrenal cortex– Stimulated by low levels of Na+ in the blood – Causes distal convoluted tubule and collecting

ducts to reabsorb Na+

– Reabsorption of Cl– and water follows– Low levels of Na+ in the blood are accompanied by

a decrease in blood volume• Renin-angiotensin-aldosterone system is activated

60


• Atrial natriuretic hormone (ANH)– Opposes the action of aldosterone in promoting

salt and water retention– Secreted by the right atrium of the heart in

response to an increased blood volume– Promotes the excretion of salt and water in the

urine and lowering blood volume

62

Formed elements

• White blood cells (leukocytes)– Less than 1% of blood cells– Larger than erythrocytes and have nuclei– Can migrate out of capillaries into tissue fluid– Types

• Granular leukocytes– Neutrophils, eosinophils, and basophils

• Agranular leukocytes– Monocytes and lymphocytes

63

Formed elements• Platelets

• Cell fragments that pinch off from larger cells in the bone marrow

• Function in the formation of blood clots

64

Formed elements

• All develop from pluripotent stem cells• Hematopoiesis is blood cell production• Occurs in the bone marrow• Produces 2 types of stem cells

– Lymphoid stem cell Lymphocytes– Myeloid stem cell All other blood cells

• Erythropoietin stimulates the production of erythrocytes (erythropoiesis)

65

Invertebrate Circulatory Systems

• Sponges, Cnidarians, and nematodes lack a separate circulatory system

• Sponges circulate water using many incurrent pores and one excurrent pore

• Hydra circulate water through a gastrovascular cavity (also for digestion)

• Nematodes are thin enough that the digestive tract can also be used as a circulatory system

67


• Nature of the circulatory system in multicellular invertebrates is directly related to the size, complexity, and lifestyle of the organism

• No circulatory system– Sponges and most cnidarians utilize water from the

environment as a circulatory fluid• Gastrovascular cavity

– Nematodes• Use the fluids of the body cavity for circulation• Small or long and thin

68


• Larger animals require a separate circulatory system for nutrient and waste transport

• Open circulatory system– No distinction between circulating and extracellular fluid– Fluid called hemolymph

• Closed circulatory system– Distinct circulatory fluid enclosed in blood vessels and

transported away from and back to the heart

69

Vertebrate Circulatory Systems

• Fishes– Evolved a true chamber-pump heart – Four structures are arrayed one after the other to

form two pumping chambers• First chamber – sinus venosus and atrium• Second chamber – ventricle and conus arteriosus

– These contract in the order listed• Blood is pumped through the gills, and then to

the rest of the body

71

72



• Amphibians– Advent of lungs required a second pumping

circuit, or double circulation– Pulmonary circulation moves blood between the

heart and lungs – Systemic circulation moves blood between the

heart and the rest of the body

73


• Amphibian heart– 3-chambered heart

• 2 atria and 1 ventricle

– Separation of the pulmonary and systemic circulations is incomplete

– Amphibians living in water obtain additional oxygen by diffusion through their skin

– Reptiles have a septum that partially subdivides the ventricle, thereby further reducing the mixing of blood in the heart

74


• Mammals, birds, and crocodilians– 4-chambered heart– 2 separate atria and 2 separate ventricles– Right atrium receives deoxygenated blood from

the body and delivers it to the right ventricle, which pumps it to the lungs

– Left atrium receives oxygenated blood from the lungs and delivers it to the left ventricle, which pumps it to rest of the body

76

78


Lancelets Fish Mammals TurtlesAmphibians CrocodiliansSquamates Birds

4-chamberheart4-chamber

heart

3-chamberheart

2-chamberheart

The Cardiac Cycle• Heart has two pairs of valves

– Atrioventricular (AV) valves• Maintain unidirectional blood flow between atria and

ventricles• Tricuspid valve = On the right• Bicuspid, or mitral, valve = On the left

– Semilunar valves• Ensure one-way flow out of the ventricles to the arterial

systems• Pulmonary valve located at the exit of the right ventricle• Aortic valve located at the exit of the left ventricle

79

The Cardiac Cycle

• Valves open and close as the heart goes through the cardiac cycle

• Ventricles relaxed and filling (diastole) • Ventricles contracted and pumping (systole) • “Lub-dub” sounds heard with stethoscope

– Lub – AV valves closing– Dub – closing of semilunar valves

80

Right ventricle

1. The atria contract.

Diastole

“Lub” “Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve

2. “Lub”: The ventriclescontract, theatrioventricular (AV)valves close, andpressure in theventricles builds

up until the aortic and pulmonary valves open.

3. Blood is pumped outof ventricles andinto the aorta andpulmonary artery.

5. The ventricles fill with blood.

4. “Dup”: The ventriclesrelax, the pressure inthe ventricles falls atthe end of systole, and since pressure is now greater in the aorta and pulmonary artery, the aortic and pulmonary valves slam shut.

Time (seconds)

65 mL

130 mL

81


Right ventricle


Diastole

“Lub” “Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve






pressure inleft ventricle

Time (seconds)

65 mL

130 mL

82


Right ventricle


Diastole

“Lub”

1.

“Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve







Time (seconds)

65 mL

130 mL

83


Right ventricle


Diastole

“Lub”

1. 2.

“Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve







Time (seconds)

65 mL

130 mL

84


Right ventricle


Diastole

“Lub”

1. 2.

3. “Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve







Time (seconds)

65 mL

130 mL

85


Right ventricle


Diastole

“Lub”

1. 2.

3.

4.

“Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve







Time (seconds)

65 mL

130 mL

86


Right ventricle


Diastole

“Lub”

1. 2.

3.

4.5.

“Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve







Time (seconds)

65 mL

130 mL

87


Right ventricle


Diastole

“Lub”

1. 2.

3.

4.5.

“Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve







pressurein aorta

Time (seconds)

65 mL

130 mL

88


Right ventricle


Diastole

“Lub”

1. 2.

3.

4.5.

“Dup”

DiastoleSystole

Pres

sure

(mm

Hg)

0

25

0.10 1.00.90.80.6 0.70.50.40.30.2

50

75

100

125

Pulmonaryvalve

Rightatrium

AVvalves

Leftventricle

Leftatrium

Aorticvalve







pressurein aorta

Time (seconds)

65 mL

130 mL

volume inleft ventricle


89

The Cardiac Cycle

• Heart contains “self-excitable” autorhythmic fibers

• Most important is the sinoatrial (SA) node– Located in wall of right atrium– Acts as pacemaker– Autonomic nervous system can modulate rate

90

The Cardiac Cycle

• Each SA depolarization transmitted– To left atrium– To right atrium and atrioventricular (AV) node

• AV node is only pathway for conduction to ventricles– Spreads through atrioventricular bundle– Purkinje fibers– Directly stimulate the myocardial cells of both

ventricles to contract

91

The Cardiac Cycle

• Electrical activity can be recorded on an electrocardiogram (ECG or EKG) – First peak (P) is produced by depolarization of

atria (atrial systole)– Second, larger peak (QRS) is produced by

ventricular depolarization (ventricular systole)– Last peak (T) is produced by repolarization of

ventricles (ventricular diastole)

92

Seconds

R

T wave

1 sec

+1

-1

0

Purkinje fibers

Left atriumRight atrium

Purkinje fibers

AV bundle

SA node(pacemaker)

AV node

AV bundleInterventricularseptum

Left and rightbundle branches

1. The impulse begins at the SA node and travels to theAV node.

InternodalpathwayAV

2. The impulse is delayed at the AV node. It then travels to the AV bundle.

P wave

Mill

ivott

s

QS


93

Seconds

R

T wave

1 sec

+1

-1

0

Purkinje fibers

AV bundle

Interventricularseptum

3. From the AV bundle, the impulse travelsdown the interventricular septum.

Left and rightbundle branches

5. Finally reaching the Purkinje fibers, the impulse is distributed throughout the ventricles.

4. The impulse spreads to branches from the interventricular septum.

P wave

Mill

ivott

s

94


QS

The Cardiac Cycle

• Right and left pulmonary arteries deliver oxygen-depleted blood from the right ventricle to the right and left lungs

• Pulmonary veins return oxygenated blood from the lungs to the left atrium of the heart

95

The Cardiac Cycle

• Aorta and all its branches are systemic arteries, carrying oxygen-rich blood from the left ventricle to all parts of the body– Coronary arteries supply oxygenated blood to the

heart muscle• Blood from the body drains into the right

atrium– Superior vena cava drains upper body– Inferior vena cava drains lower body

96

The Cardiac Cycle

• Arterial blood pressure can be measured with a sphygmomanometer

• Systolic pressure is the peak pressure at which ventricles are contracting

• Diastolic pressure is the minimum pressure between heartbeats at which the ventricles are relaxed

• Blood pressure is written as a ratio of systolic over diastolic pressure

97

Characteristics of Blood Vessels

• Blood leaves heart through the arteries• Arterioles are the finest, microscopic branches

of the arterial tree • Blood from arterioles enters capillaries• Blood is collected into venules, which lead to

larger vessels, veins• Veins carry blood back to heart

99

Gills

• Specialized extensions of tissue that project into water

• Increase surface area for diffusion• External gills are not enclosed within body

structures– Found in immature fish and amphibians– Two main disadvantages

• Must be constantly moved to ensure contact with oxygen-rich fresh water

• Are easily damaged

103

Gills

• Branchial chambers– Provide a means of pumping water past stationary

gills– Internal mantle cavity of mollusks opens to the

outside and contains the gills• Draw water in and pass it over gills

– In crustaceans, the branchial chamber lies between the bulk of the body and the hard exoskeleton of the animal

• Limb movements draw water over gills

104

Gills

• Gills of bony fishes are located between the oral (buccal or mouth) cavity and the opercular cavities

• These two sets of cavities function as pumps that alternately expand

• Move water into the mouth, through the gills, and out of the fish through the open operculum or gill cover

105

106

Gills

Gills

• Some bony fish have immobile opercula– Swim constantly to force water over gills– Ram ventilation

• Most bony fish have flexible gill covers• Remora switch between ram ventilation and

pumping action

107

Gills

• 3–7 gill arches on each side of a fish’s head • Each is composed of two rows of gill filaments• Each gill filament consist of lamellae

– Thin membranous plates that project into water flow

– Water flows past lamellae in 1 direction only

108

Gills

• Within each lamella, blood flows opposite to direction of water movement– Countercurrent flow– Maximizes oxygenation of blood– Increases Dp

• Fish gills are the most efficient of all respiratory organs

110

Gills

• Many amphibians use cutaneous respiration for gas exchange

• In terrestrial arthropods, the respiratory system consists of air ducts called trachea, which branch into very small tracheoles – Tracheoles are in direct contact with individual

cells– Spiracles (openings in the exoskeleton) can be

opened or closed by valves

112

Lungs

• Gills were replaced in terrestrial animals because– Air is less supportive than water– Water evaporates

• The lung minimizes evaporation by moving air through a branched tubular passage

• A two-way flow system – Except birds

113

Lungs

• Air exerts a pressure downward, due to gravity• A pressure of 760 mm Hg is defined as one

atmosphere (1.0 atm) of pressure• Partial pressure is the pressure contributed by

a gas to the total atmospheric pressure

114

Lungs

• Partial pressures are based on the % of the gas in dry air

• At sea level or 1.0 atm– PN2 = 760 x 79.02% = 600.6 mm Hg– PO2 = 760 x 20.95% = 159.2 mm Hg– PCO2 = 760 x 0.03% = 0.2 mm Hg

• At 6000 m the atmospheric pressure is 380 mm Hg– PO2 = 380 x 20.95% = 80 mm Hg

115

Lungs

• Lungs of amphibians are formed as saclike outpouchings of the gut

• Frogs have positive pressure breathing– Force air into their lungs by creating a positive

pressure in the buccal cavity• Reptiles have negative pressure breathing

– Expand rib cages by muscular contractions, creating lower pressure inside the lungs

116

Lungs

• Lungs of mammals are packed with millions of alveoli (sites of gas exchange)

• Inhaled air passes through the larynx, glottis, and trachea

• Bifurcates into the right and left bronchi, which enter each lung and further subdivide into bronchioles

• Alveoli are surrounded by an extensive capillary network

118

119

Lungs

Lungs

• Lungs of birds channel air through very tiny air vessels called parabronchi

• Unidirectional flow• Achieved through the action of anterior and

posterior sacs (unique to birds)• When expanded during inhalation, they take

in air• When compressed during exhalation, they

push air in and through lungs120

Lungs

• Respiration in birds occurs in two cycles– Cycle 1 = Inhaled air is drawn from the trachea

into posterior air sacs, and exhaled into the lungs– Cycle 2 = Air is drawn from the lungs into anterior

air sacs, and exhaled through the trachea• Blood flow runs 90o to the air flow

– Crosscurrent flow– Not as efficient as countercurrent flow

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Lungs

Gas Exchange

• Gas exchange is driven by differences in partial pressures

• Blood returning from the systemic circulation, depleted in oxygen, has a partial oxygen pressure (PO2) of about 40 mm Hg

• By contrast, the PO2 in the alveoli is about 105 mm Hg• The blood leaving the lungs, as a result of this gas

exchange, normally contains a PO2 of about 100 mm

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Lung Structure and Function

• Outside of each lung is covered by the visceral pleural membrane

• Inner wall of the thoracic cavity is lined by the parietal pleural membrane

• Space between the two membranes is called the pleural cavity– Normally very small and filled with fluid– Causes 2 membranes to adhere– Lungs move with thoracic cavity

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• During inhalation, thoracic volume increases through contraction of two muscle sets– Contraction of the external intercostal muscles

expands the rib cage– Contraction of the diaphragm expands the volume

of thorax and lungs• Produces negative pressure which draws air

into the lungs

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• Thorax and lungs have a degree of elasticity• Expansion during inhalation puts these

structures under elastic tension• Tension is released by the relaxation of the

external intercostal muscles and diaphragm• This produces unforced exhalation, allowing

thorax and lungs to recoil

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• Tidal volume– Volume of air moving in and out of lungs in a person at rest

• Vital capacity– Maximum amount of air that can be expired after a

forceful inspiration• Hypoventilation

– Insufficient breathing– Blood has abnormally high PCO2

• Hyperventilation– Excessive breathing– Blood has abnormally low PCO2

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• Each breath is initiated by neurons in a respiratory control center in the medulla oblongata

• Stimulate external intercostal muscles and diaphragm to contract, causing inhalation

• When neurons stop producing impulses, respiratory muscles relax, and exhalation occurs

• Muscles of breathing usually controlled automatically– Can be voluntarily overridden – hold your breath

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• Neurons are sensitive to blood PCO2 changes • A rise in PCO2 causes increased production of carbonic

acid (H2CO3), lowering the blood pH• Stimulates chemosensitive neurons in the aortic and

carotid bodies • Send impulses to respiratory control center to

increase rate of breathing• Brain also contains central chemoreceptors that are

sensitive to changes in the pH of cerebrospinal fluid (CSF)

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Respiratory Diseases

• Chronic obstructive pulmonary disease (COPD)– Refers to any disorder that obstructs airflow on a

long-term basis– Asthma

• Allergen triggers the release of histamine, causing intense constriction of the bronchi and sometimes suffocation

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• Chronic obstructive pulmonary disease (COPD) (cont.)– Emphysema

• Alveolar walls break down and the lung exhibits larger but fewer alveoli

• Lungs become less elastic• People with emphysema become exhausted because

they expend three to four times the normal amount of energy just to breathe

• Eighty to 90% of emphysema deaths are caused by cigarette smoking

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• Lung cancer accounts for more deaths than any other form of cancer

• Caused mainly by cigarette smoking• Follows or accompanies COPD• Lung cancer metastasizes (spreads) so rapidly that it

has usually invaded other organs by the time it is diagnosed

• Chance of recovery from metastasized lung cancer is poor, with only 3% of patients surviving for 5 years after diagnosis

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• Ingested food may be stored or first subjected to physical fragmentation

• Chemical digestion occurs next– Hydrolysis reactions liberate the subunit

molecules• Products pass through gut’s epithelial lining

into the blood (absorption) • Wastes are excreted from the anus

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Vertebrate Digestive Systems

• Consists of a tubular gastrointestinal tract and accessory organs

• Mouth and pharynx – entry• Esophagus – delivers food to stomach• Stomach – preliminary digestion• Small intestine – digestion and absorption• Large intestine – absorption of water and minerals• Cloaca or rectum – expel waste

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• Accessory organs– Liver

• Produces bile– Gallbladder

• Stores and concentrates bile– Pancreas

• Produces pancreatic juice• Digestive enzymes and bicarbonate buffer

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• Gastrointestinal tract is layered– Mucosa – innermost

• Epithelium that lines the interior, or lumen, of the tract

– Submucosa• Connective tissue

– Muscularis• Circular and longitudinal smooth muscle layers

– Serosa – outermost • Epithelium covering external surface of tract

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Mouth and Teeth

• Many vertebrates have teeth used for chewing or mastication

• Birds– Lack teeth– Break up food in a two-chambered

stomach– Gizzard – muscular chamber that

uses ingested pebbles to pulverize food

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• Carnivores – pointed teeth that lack flat grinding surfaces

• Herbivores – large flat teeth suited for grinding cellulose cell walls of plant tissues

• Humans have carnivore-like teeth in the front and herbivore-like teeth in the back

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Mouth and Teeth

• Inside the mouth, the tongue mixes food with saliva– Moistens and lubricates the food– Contains salivary amylase, which initiates the

breakdown of starch– Salivation is controlled by the nervous system

• Tasting, smelling, and even thinking or talking about food stimulate increased salivation

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Mouth and Teeth

• Swallowing– Starts as voluntary action

• Continued under involuntary control

– When food is ready to be swallowed, the tongue moves it to the back of the mouth

– Soft palate seals off nasal cavity– Elevation of the larynx (voice box) pushes the

glottis against the epiglottis• Keeps food out of respiratory tract

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Mouth and Teeth

2d2 digestive systems, respiratory systems (gas exchange), blood/osmolarity/osmotic balance, urinary...

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