1. Circulation and Gas Exchange Chapter 42 (all)

2. Overview: Trading with the Environment
Every organism must exchange materials with its environment (whether it be nutrients or gases (oxygen and carbon dioxide)
And this exchange ultimately occurs at the cellular level

3. In unicellular organisms
These exchanges occur directly with the environment across the cell membrane. Diffusion is adequate for necessary rapid exchange.
For most of the cells making up multicellular organisms direct exchange with the environment is not possible because diffusion distances are too great! Therefore specialized exchange and transport systems have evolved!

4. Gills as exchange sites in aquatic animals!
The feathery gills projecting from a salmon
Are an example of a specialized exchange system found in animals
Figure 42.1
Gill arch with filaments which have lamellae on both sides!
Surface area of gill equal body skin surface area!

5. Transport systems
Functionally connect the organs of exchange with the body cells where nutrients and oxygen required!
Most complex animals have internal transport systems providing a conduit between the evironment and the cell cytoplasm!

6. Invertebrate Circulation
The wide range of invertebrate body size and form is paralleled by a great diversity in circulatory systems. Water vascular system in star fish, open circulatory systems in insects and closed circulatory systems in earth worms and squids.

7. Gastrovascular Cavities
Simple animals, such as cnidarians
Have a body wall only two cells thick that encloses a gastrovascular cavity (recall sea anemone sac with a mouth!)
The gastrovascular cavity
Functions in both digestion and distribution of substances throughout the body. Also gas exchange for cells lining the cavity.

8. Some cnidarians, such as jellies
Have elaborate gastrovascular cavities with canals radiating off the central sac!
Figure 42.2
Circular canal
Radial canal
5 cm
Mouth

9. Open and Closed Circulatory Systems
More complex animals
Have one of two types of circulatory systems: open or closed
Both of these types of systems have three basic components
A circulatory fluid (blood)
A set of tubes (blood vessels)
A muscular pump (the heart)

10. Open circulatory systems
In insects, other arthropods, and most molluscs
Blood bathes the organs and tissues directly in an open circulatory system
Heart
Hemolymph in sinuses surrounding ograns
Anterior vessel
Tubular heart
Lateral vessels
Ostia
(a) An open circulatory system
Figure 42.3a
Valves in heart so blood flow is unidirectional
No interstitial space or fluid!

11. Closed Circulatory System
In a closed circulatory system
Blood is confined to vessels and is distinct from the interstitial fluid
Figure 42.3b
Interstitial fluid
Heart
Small branch vessels in each organ
Dorsal vessel (main heart)
Ventral vessels
Auxiliary hearts
(b) A closed circulatory system
Closed systems
are more efficient at transporting circulatory fluids to tissues and cells.
Earthworm an annelid is the first time we see a closed circulatory system!

12. Survey of Vertebrate Circulation
Humans and other vertebrates have a closed circulatory system often called the cardiovascular system.
Blood flows in a closed cardiovascular system consisting of blood vessels and a two- to four-chambered heart.
Arteries carry blood from heart to capillaries
The capillaries are the sites of chemical exchange between the blood and interstitial fluid
Veins collect blood from capillaries and return blood to the heart.
Types of hearts!

13. REPTILES (EXCEPT BIRDS) Pulmocutaneous circuit
Vertebrate circulatory systems
FISHES
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Systemic capillaries
Lung capillaries
Lung and skin capillaries
Gill capillaries
Right
Left
Systemic circuit
Pulmocutaneous circuit
Pulmonary circuit
Systemic circulation
Vein
Atrium (A)
Heart: ventricle (V)
Artery
Gill circulation A V
Systemic aorta
Right systemic aorta
Figure 42.4

14. Fishes- two chambered heart!
A fish heart has two main chambers
One ventricle and one atrium and blood pumped from the ventricle through the gills
where it is loaded with oxygen and unloadsf CO2. It then travels through the dorsal aorta to the organs and tissues thru capillary beds and is returned to the heart as venous blood. Where does heart get its oxygen? Enough remains in the venous blood. In some active species (Tuna fishes) a branch off the ventral aorta supplies oxygenated blood to the heart.

15. Amphibians
Frogs and other amphibians have a three-chambered heart, with two atria and one ventricle
The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous circuit (lung and skin) and the systemic circuit. Thus a certain amount of mixing of oxygenated and oxygen poor blood occures.

16. Reptiles (Except Birds)
Reptiles have double circulation
With a pulmonary circuit (lungs) and a systemic circuit
Turtles, snakes, and lizards
Have a three-chambered heart.

17. Mammals and Birds In all mammals and birds
The ventricle is completely divided into separate right and left chambers
The left side of the heart pumps and receives only oxygen-rich blood
While the right side receives and pumps only oxygen-poor blood

18. A powerful four-chambered heart
Was an essential adaptation of the endothermic way of life characteristic of mammals and birds. Reason is because of metabolism being almost 10 times greater than the ectotherms!

19. Heart valves dictate a one-way flow of blood through the heart.
A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds. Reason is because of metabolism being almost 10 times greater than the ectotherms!
Double circulation in mammals depends on the anatomy and pumping cycle of the heart (Good model).
Heart valves dictate a one-way flow of blood through the heart.
Blood begins its flow
With the right ventricle pumping blood to the lungs
In the lungs
The blood loads O2 and unloads CO2

20. Oxygen-rich blood from the lungs
Enters the heart at the left atrium and is pumped to the body tissues by the left ventricle
Blood returns to the heart
Through the right atrium

21. The mammalian cardiovascular system
See text for description of sequential events
Pulmonary
vein
Right atrium
Right ventricle
Posterior
vena cava
Capillaries of
abdominal organs
and hind limbs
Aorta
Left ventricle
Left atrium
artery
Capillaries
of left lung
head and
forelimbs
Anterior
of right lung
Figure 42.5 1 10 11 5 4 6 2 9 3 7 8

22. The Mammalian Heart: A Closer Look
A closer look at the mammalian heart
Provides a better understanding of how double circulation works
Figure 42.6
Aorta
Pulmonary veins
Semilunar valve
Atrioventricular valve
Left ventricle
Right ventricle
Anterior vena cava
Pulmonary artery
Posterior vena cava
Right atrium
Left atrium
In fetus ductus artieriosus shunts blood from pulmonary artery into the aorta. Closes off at birth when the lungs inflate!

23. The heart contracts and relaxes
In a rhythmic cycle called the cardiac cycle
The contraction, or pumping, phase of the cycle
Is called systole
The relaxation, or filling, phase of the cycle
Is called diastole

24. The cardiac cycle: filling of chambers longest!
Figure 42.7
Semilunar valves closed
AV valves open
AV valves closed
Semilunar valves open
Atrial and ventricular diastole 1
Atrial systole; ventricular diastole 2
Ventricular systole; atrial diastole 3
0.1 sec
0.3 sec
0.4 sec

25. The heart rate, also called the pulse The cardiac output
Is the number of beats per minute
The cardiac output
Is the volume of blood pumped into the systemic circulation per minute and depends on the rate of contraction and the stroke volume (how much blood is “loaded” into the ventricle during diastole).

26. Maintaining the Heart’s Rhythmic Beat
Some cardiac muscle cells are self-excitable (myogenic)
Meaning they contract without any signal from the nervous system (heart transplant).
A region of the heart called the sinoatrial (SA) node, or pacemaker sets the rate and timing at which all cardiac muscle cells contract
Impulses from the SA node spread across the atria to the atrioventricular (AV) node
At the AV node, the impulses are delayed and then travel down bundle fiber to the the Purkinje fibers that make the ventricles contract

27. The impulses that travel during the cardiac cycle
Can be recorded as an electrocardiogram (ECG or EKG)

28. The control of heart rhythm
The impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (EKG)
Figure 42.8
SA node (pacemaker)
AV node
Bundle branches
Heart apex
Purkinje fibers 2
Signals are delayed
at AV node. 1
Pacemaker generates wave of signals in the atria to contract. 3
Signals pass
to heart apex. 4
Signals spread
throughout ventricles.
ECG

29. The pacemaker is influenced by
Nerves, hormones, body temperature, and exercise

30. Blood Circulation
The same physical principles that govern the movement of water in plumbing systems
Also influence the functioning of animal circulatory systems.
Structure of circulatory system is a network of vessels that are differ in structure to accommodate function.

31. The velocity of blood flow varies in the circulatory system
And is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area
Figure 42.11
5,000 4,000
3,000
2,000
1,000
Aorta
Arteries
Arterioles
Capillaries
Venules
Veins
Venae cavae
Pressure (mm Hg)
Velocity (cm/sec)
Area (cm2)
Systolic pressure
Diastolic pressure
50 40 30 20 10 80 60 40

32. All blood vessels Are built of similar tissues
Have three similar layers
Basement membrane composed of mucopolysaccharides and collagen fibers. Not a barrier to diffusion of molecules.
Figure 42.9
Artery
Vein
100 µm
Arteriole
Venule
Connective tissue
Smooth muscle
Endothelium
Valve
Basement membrane
Capillary
Arteries have thicker walls to accommodate the high pressure of blood pumped from the heart. Veins thinner walls.

33. In the thinner-walled veins
Blood flows back to the heart mainly as a result of muscle action
Figure 42.10
Direction of blood flow in vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)

34. Blood Flow Velocity
Physical laws governing the movement of fluids through pipes
Influence blood flow and blood pressure

35. Blood pressure Systolic pressure Diastolic pressure
Is the hydrostatic pressure that blood exerts against the wall of a vessel
Systolic pressure
Is the pressure in the arteries during ventricular systole
Is the highest pressure in the arteries
Diastolic pressure
Is the pressure in the arteries during diastole
Is lower than systolic pressure

36. Blood pressure Can be easily measured in humans Figure 42.12 Artery
Rubber cuff inflated with air
Artery closed
120
Pressure in cuff above 120
Pressure in cuff below 120
Pressure in cuff below 70
Sounds audible in stethoscope
Sounds stop
Blood pressure
reading: 120/70
A typical blood pressure reading for a 20-year-old is 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high. 1
A sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure in an artery. The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery. 2
A stethoscope is used to listen for sounds of blood flow below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure. 3
The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed. 4 70

37. Blood pressure is determined partly by cardiac output
And partly by peripheral resistance due to variable constriction of the arterioles (anaphylactic shock).
For high blood pressure try and reduce peripheral resistance using smooth muscle relaxants!

38. Capillary Function
Capillaries in major organs are usually filled to capacity
But in many other sites, the blood supply varies. Homeostatic mechanisms involved to keep blood pressure constant!

39. Control of Blood Flow Through Capillaries
Two mechanisms
Regulate the distribution of blood in capillary beds
In one mechanism
Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel

40. In a second mechanism
Precapillary sphincters control the flow of blood between arterioles and venules
Figure a–c
Precapillary sphincters
Thoroughfare
channel
Arteriole
Capillaries
Venule
(a) Sphincters relaxed
(b) Sphincters contracted
(c) Capillaries and larger vessels (SEM)
20 m

41. The critical exchange of substances between the blood and interstitial fluid
Takes place across the thin endothelial walls of the capillaries

42. Arterial end of capillary
The difference between blood pressure and osmotic pressure
Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end
At the arterial end of a
capillary, blood pressure is
greater than osmotic pressure,
and fluid flows out of the
capillary into the interstitial fluid.
Capillary
Red
blood
cell
15 m
Tissue cell
INTERSTITIAL FLUID
Net fluid
movement out
movement in
Direction of
blood flow
Blood pressure
Osmotic pressure
Inward flow
Outward flow
Pressure
Arterial end of capillary
Venule end
At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.
Figure 42.14
Osmotic pressure in capillary due to plasma proteins!

43. Fluid Return by the Lymphatic System
Returns fluid to the body from the capillary beds
Aids in body defense because it passes through lymph nodes where white blood cells take out any pathogens or foreign material!
Fluid reenters the circulation
Directly at the venous end of the capillary bed and indirectly through the lymphatic system

44. Number per L (mm3) of blood
The cellular elements of mammalian blood
Cellular elements 45%
Cell type
Number per L (mm3) of blood
Functions
Erythrocytes (red blood cells)
5–6 million
Transport oxygen and help transport carbon dioxide
Separated blood elements
Leukocytes (white blood cells)
5,000–10,000
Defense and immunity
Lymphocyte
Basophil
Eosinophil
Neutrophil
Monocyte
Platelets
250,000 400,000
Blood clotting
Figure 42.15

45. Plasma Blood plasma is about 90% water Among its many solutes are
Inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes

46. Substances transported by blood
The composition of mammalian plasma
Plasma 55%
Constituent
Major functions
Water
Solvent for
carrying other
substances
Sodium
Potassium
Calcium Magnesium
Chloride
Bicarbonate
Osmotic balance
pH buffering, and
regulation of
membrane
permeability
Albumin
Fibringen
Immunoglobulins
(antibodies)
Plasma proteins
(blood electrolytes)
Osmotic balance,
pH buffering
Substances transported by blood
Nutrients (such as glucose, fatty acids, vitamins)
Waste products of metabolism
Respiratory gases (O2 and CO2)
Hormones
Defense
Figure 42.15
Separated blood elements
Clotting

47. Erythrocytes Red blood cells, or erythrocytes
Are by far the most numerous blood cells
Transport oxygen throughout the body
Platelets function in blood clotting

48. Blood Clotting A cascade of complex reactions
Converts fibrinogen to fibrin, forming a clot
Platelet plug
Collagen fibers
Platelet releases chemicals that make nearby platelets sticky
Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K)
Prothrombin
Thrombin
Fibrinogen
Fibrin
5 µm
Fibrin clot
Red blood cell
The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Platelets
adhere to collagen fibers in
the connective tissue and release a substance that
makes nearby platelets sticky. 1
The platelets form a plug that provides
emergency protection
against blood loss. 2
This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via a multistep process: Clotting factors released from the clumped platelets or damaged cells mix with clotting factors in the plasma, forming an activation cascade that converts a plasma protein called prothrombin to its active form, thrombin. Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM). 3
Figure 42.17
A baby aspirin per day makes the platelets lazy!
Hemophiliacs