Gastrovascular Cavities

1. Gastrovascular Cavities • Simple animals, such as cnidarians, have a body wall only two cells thick that encloses a gastrovascular cavity • This cavity functions in both digestion and distribution of substances throughout the body • Some cnidarians, such as jellies, have elaborate gastrovascular cavities

2. Circular canal Radial canal Mouth 5 cm

3. Open and Closed Circulatory Systems • More complex animals have either open or closed circulatory systems • Both systems have three basic components: • A circulatory fluid (blood or hemolymph) • A set of tubes (blood vessels) • A muscular pump (the heart)

4. In insects, other arthropods, and most molluscs blood bathes the organs directly in an open circulatory system • There is no distinction between blood and interstitial fluid, and this general body fluid is more correctly called hemolymph • In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid • Closed systems are more efficient at transporting circulatory fluids to tissues and cells

5. Heart Heart Hemolymph in sinuses surrounding organs Interstitial fluid Small branch vessels in each organ Lateral vessel Anterior vessel Ostia Dorsal vessel (main heart) Tubular heart Auxiliary hearts Ventral vessels An open circulatory system. A closed circulatory system.

6. 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 to capillaries, the sites of chemical exchange between the blood and interstitial fluid • Veins return blood from capillaries to the heart

7. LE 42-4 FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS Gill capillaries Lung and skin capillaries Lung capillaries Lung capillaries Pulmocutaneous circuit Pulmonary circuit Gill circulation Pulmonary circuit Right systemic aorta Artery Heart: Ventricle (V) Left systemic aorta A A A A A A Atrium (A) V V V V V Right Left Left Right Right Left Systemic circulation Systemic circuit Systemic circuit Vein Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries Systemic circuits include all body tissues except lungs. Note that circulatory systems are depicted as if the animal is facing you: with the right side of the heart shown at the left and vice-versa.

8. Mammalian Circulation: The Pathway • 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 • 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

9. Capillaries of head and forelimbs Anterior vena cava Pulmonary artery Pulmonary artery Aorta Capillaries of right lung Capillaries of left lung Pulmonary vein Pulmonary vein Right atrium Left atrium Left ventricle Right ventricle Posterior vena cava Aorta Capillaries of abdominal organs and hind limbs

10. Pulmonary artery Aorta Anterior vena cava Pulmonary artery Right atrium Left atrium Pulmonary veins Pulmonary veins Semilunar valve Semilunar valve Atrioventricular valve Atrioventricular valve Posterior vena cava Left ventricle Right ventricle

11. The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle • The contraction, or pumping, phase is called systole • The relaxation, or filling, phase is called diastole • The heart rate, also called the pulse, is the number of beats per minute • The cardiac output is the volume of blood pumped into the systemic circulation per minute

12. The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract • Impulses from the SA node travel to the atrioventricular (AV) node • At the AV node, the impulses are delayed and then travel to the Purkinje fibers that make the ventricles contract • Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)

13. The pacemaker is influenced by nerves, hormones, body temperature, and exercise Signals pass to heart apex. Signals are delayed at AV node. Pacemaker generates wave of signals to contract. Signals spread throughout ventricles. SA node (pacemaker) AV node Bundle branches Purkinje fibers Heart apex ECG

14. Vein Artery 100 µm Endothelium Valve Basement membrane Endothelium Endothelium Smooth muscle Smooth muscle Capillary Connective tissue Connective tissue Vein Artery Venule Arteriole

15. Blood Vessel Structure and Function • Structural differences in arteries, veins, and capillaries correlate with functions • Arteries have thicker walls that accommodate the high pressure of blood pumped from the heart • In the thinner-walled veins, blood flows back to the heart mainly as a result of muscle action

16. Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed)

17. Blood Flow Velocity • Physical laws governing movement of fluids through pipes affect blood flow and blood pressure • Velocity of blood flow is slowest in the capillary beds, as a result of the high resistance and large total cross-sectional area

18. 5,000 4,000 3,000 Area (cm2) 2,000 1,000 0 50 40 Velocity (cm/sec) 30 20 10 0 120 Systolic pressure 100 80 Pressure (mm Hg) 60 Diastolic pressure 40 20 0 Venae cavae Aorta Capillaries Venules Veins Arterioles Arteries

19. Blood Pressure • Blood 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; it is the highest pressure in the arteries • Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure • Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles

20. Blood pressure reading: 120/70 Pressure in cuff below 120 Pressure in cuff below 70 Pressure in cuff above 120 Rubber cuff inflated with air 120 120 70 Sounds audible in stethoscope Sounds stop Artery closed Artery

21. Capillary Function • Capillaries in major organs are usually filled to capacity • Two mechanisms regulate distribution of blood in capillary beds: • Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel • Precapillary sphincters control flow of blood between arterioles and venules

22. Thoroughfare channel Precapillary sphincters Venule Arteriole Capillaries Sphincters relaxed Venule Arteriole Sphincters contracted

23. The critical exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries • The difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end

24. Tissue cell INTERSTITIAL FLUID Net fluid movement out Net fluid movement in Capillary Capillary Red blood cell 15 µm Direction of blood flow Blood pressure Osmotic pressure Inward flow Pressure Outward flow Arterial end of capillary Venous end

25. Fluid Return by the Lymphatic System • The lymphatic system returns fluid to the body from the capillary beds • This system aids in body defense • Fluid reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system

26. Blood Composition and Function • Blood consists of several kinds of cells suspended in a liquid matrix called plasma • The cellular elements occupy about 45% of the volume of blood

27. Plasma • Blood plasma is about 90% water • Among its solutes are inorganic salts in the form of dissolved ions, sometimes called electrolytes • Another important class of solutes is the plasma proteins, which influence blood pH, osmotic pressure, and viscosity • Various plasma proteins function in lipid transport, immunity, and blood clotting

28. Plasma 55% Cellular elements 45% Constituent Major functions Cell type Number Functions Water Solvent for carrying other substances per µL (mm3) of blood Erythrocytes (red blood cells) Ions (blood electrolytes) 5–6 million Transport oxygen and help transport carbon dioxide Sodium Potassium Calcium Magnesium Chloride Bicarbonate Osmotic balance, pH buffering, and regulation of membrane permeability Separated blood elements Leukocytes (white blood cells) Defense and immunity 5,000–10,000 Plasma proteins Osmotic balance, pH buffering Albumin Lymphocyte Basophil Fibrinogen Clotting Defense Immunoglobulins (antibodies) Eosinophil Substances transported by blood Monocyte Neutrophil Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O2 and CO2) Hormones Platelets 250,000– 400,000 Blood clotting

29. Cellular Elements • Suspended in blood plasma are two types of cells: • Red blood cells (erythrocytes) transport oxygen • White blood cells (leukocytes) function in defense • Platelets, a third cellular element, are fragments of cells that are involved in clotting

30. Red blood cells, or erythrocytes, are by far the most numerous blood cells • There are five major types of white blood cells, or leukocytes: monocytes, neutrophils, basophils, eosinophils, and lymphocytes • They function in defense by phagocytizing bacteria and debris or by producing antibodies • Erythrocytes, leukocytes, and platelets all develop from a common source, pluripotent stem cells in the red marrow of bones

31. Pluripotent stem cells (in bone marrow) Myeloid stem cells Lymphoid stem cells Basophils B cells T cells Lymphocytes Eosinophils Neutrophils Erythrocytes Platelets Monocytes

32. Blood Clotting • When the endothelium of a blood vessel is damaged, the clotting mechanism begins • A cascade of complex reactions converts fibrinogen to fibrin, forming a clot

33. Endothelium of vessel is damaged, exposing connective tissue; platelets adhere Platelets form a plug Seal is reinforced by a clot of fibrin Collagen fibers Fibrin clot Red blood cell Platelet plug 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

34. Connective tissue Smooth muscle Endothelium Plaque 50 µm Normal artery Partly clogged artery 250 µm

35. Cardiovascular Disease • Hypertension, or high blood pressure, promotes atherosclerosis and increases the risk of heart attack and stroke • A heart attack is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries • A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head

36. Gas exchange occurs across specialized respiratory surfaces • Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide • Animals require large, moist respiratory surfaces for adequate diffusion of gases between their cells and the respiratory medium, either air or water

37. Respiratory medium (air or water) Respiratory surface O2 CO2 Organismal level Circulatory system Cellular level Energy-rich fuel molecules from food ATP Cellular respiration

38. Gills in Aquatic Animals • Gills are outfoldings of the body surface specialized for gas exchange • In some invertebrates, gills have a simple shape and are distributed over much of the body • Many segmented worms have flaplike gills that extend from each segment of their body • The gills of clams, crayfish, and many other animals are restricted to a local body region

39. Gills Coelom Tube foot Sea star

40. Parapodia Gill Marine worm

41. Gills Scallop

42. Gills Crayfish

43. Effectiveness of gas exchange in some gills, including those of fishes, is increased by ventilation and the countercurrent flow of blood and water

44. Oxygen-poor blood Lamella Oxygen-rich blood Gill arch Blood vessel Gill arch 15% 40% 70% Water flow 5% 30% Operculum 60% 100% 90% Water flow over lamellae showing % O2 O2 Blood flow through capillaries in lamellae showing % O2 Gill filaments Countercurrent exchange

45. Tracheal Systems in Insects • The tracheal system of insects consists of tiny branching tubes that penetrate the body • The tracheal tubes supply O2 directly to body cells

46. Tracheae Air sacs Spiracle

47. Body cell Air sac Tracheole Trachea Air Body wall Mitochondria Tracheoles Myofibrils 2.5 µm

48. Lungs • Spiders, land snails, and most terrestrial vertebrates have internal lungs • An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea

49. Mammalian Respiratory Systems: A Closer Look • A system of branching ducts conveys air to the lungs • Air inhaled through the nostrils passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs

50. Branch from pulmonary artery (oxygen-poor blood) Branch from pulmonary vein (oxygen-rich blood) Terminal bronchiole Nasal cavity Pharynx Alveoli Larynx Left lung Esophagus 50 µm Trachea Right lung 50 µm Bronchus Bronchiole Diaphragm Heart Colorized SEM SEM