Comparative Animal Physiology--------Review for Exam IV & Final--------Fall, 2004

---make sure you have all four essay questions, listed at the end of this review sheet.

********* note the addition of the following essay question….

Section 1 of 5-note essay questions for this last set of material and the 'makeup' essay questions are at the end of the review material.

Section 2 of 5 ***General Information for the last exam: Recall that this last exam will cover the last set of material and there will be additional questions that are considered the final exam.

Section 3 of 5 ***Review material for exam 4.

I.Hb-Hemoglobin Monomer: a 17,000 dalton amino acid sequence [about 150 aa] with a heme group binding a ferrous [Fe⁺⁺] iron.

1)This molecule has the ability to reversibly interact [bind] molecular oxygen [O₂].

2)What determines binding/release of O₂? The PO₂ in the environment immediately adjacent to the respiratory pigment.

3)Hb-O₂ affinity - To express how readily the respiratory pigment binds O₂ we use the term P₅₀ which, defined is the PO₂ to just 50% saturate the respiratory pigment with O₂.

4)Key point - When O₂ links to the respiratory pigment it is NOT an oxidation/reduction reaction. Molecular O₂ is rather loosely linked to the respiratory pigment. So Hb without O₂ is deoxyhemoglobin and Hb with O₂ is oxyhemoglobin. However, Fe⁺⁺ may be oxidized to Fe⁺⁺⁺! Hb with Fe⁺⁺⁺ is nonfuntional - it cannot bind O₂! This form of Hb is called methemoglobin. An enzyme in red blood cells [methhemoglobin reductase or glutathione reductase] converts Fe⁺⁺⁺ back to Fe⁺⁺ restoring the functional capacity of Hb.

1)Subunit cooperativity - The O₂ binding curve of Hb is hyperbolic [be able to draw this for Hb or Mb - myoglobin]. The curve for Hb₄ is sigmoid ['S'-shaped]. This O₂-binding curve results because the first O₂ linkage is 'difficult'' [requires a large PO₂ change]. But, linking the first O₂ increases the affinity of the Hb₄ for additional O₂ so with much smaller changes in O₂ additional oxygen will be bound to/released from Hb₄. The phenomenon of cooperativity results in the oxygen-buffer/reserve function of Hb₄.

2)Hb₄-ligands - The tetrameric form of Hb links several molecules/elements [ligands] that alter the way the respiratory pigment functions. The all operate by i)changing the P₅₀ of the molecule increasing the Hb₄ affinity to physiological levels and ii)modulating Hb₄ funtion under altered environmental conditions [hypoxia, etc]. These ligands and there actions are:

a.CO₂ (carbamino Hb₄) - binds to amino terminal groups and holds Hb₄ in its low O₂ affinity [tense] state.

b.H⁺ - binds at several sites on molecule and holes Hb₄ in its low O₂ affinity [tense] state.

c.Organophosphates [ATP(fish), 2,3-diphosphoglycerate(amphibians, mammals), inositol pentaphosphate or IP₅(birds)] bind to amino terminal groups and hold Hb₄ in its low O₂-affinity [tense] state.

These ligands also compete with each other which creates a complex set of interactions between Hb₄ and O₂.

3)Bohr Effect - Under physiological conditions we expect O₂ high and CO₂ low in lungs but O₂ low and CO₂ high in tissues. These different levels of ligands promote O₂ loading in lungs and O₂ unloading in tissues, the Bohr effect or Bohr shift.

III. Carbon dioxide transport in blood. CO₂ is transported in several forms:

a.molecular or physical solution [dissolved].

b.carbamino or attached to Hb₄

c.bicarbonate [all forms, but mainly - HCO₃^-]

I.There are several general plans for circulations [pgs p 473-476, fig 12-1]. You should have an idea of 'open' versus 'closed' circulatory systems. Know the major requirements for a circulatory system; pressure-pressure-pressure. Also know how the requirements are similar/differ for the right/left sides of the avian/mammalian circulatory systems. From the handout know the basic design features of the: fish/amphibian/reptilian/avian/-mammalian circulatory systems.

II.Functional characteristics of the Mammalian/Avian Circulatory system.

Provide an adequate "flow-of-Blood" to a set of organ systems whose needs: a)differ from each other and where the needs of any individual organ b)changes with time due to changes in the internal/external conditions and where the different organs are at c)different elevations from the pump [heart].

Components: The circulatory system is made up of: a heart [responsible for flow to blood vessels arranged in-parallel], arteries [pressure conduits], arterioles [resistance vessels], capillaries [exchange vessels], veins [capacitance vessels], lymph vessels [dead-end, tissue fluid].

The key to understanding everything there is to know about circulatory systems = pressure! In our class we will begin with a nominal mean-systemic-arterial blood pressure value of 100 mmHg [this holds for a reasonable number of mammals] with a systolic pressure of 120 mmHg and a diastolic pressure of 80 mmHg. This is blood pressure measured at the heart-level. What is arterial pressure in the feet or in the head?

Why is pressure so important? Two reasons: a)w/o pressure it is not possible to have organs 'uphill' from the heart and b)w/o pressure redistribution of flow is inefficient. If pressure is so important for insuring blood flow uphill [to the head] then how can giraffes have such long necks, how could diplodocus have an even longer neck and why don't amphibians have any neck?

How is pressure generated? Pressure = Flow x Resistance or P = F x R. Where is flow generated? The left-heart which at rest generates a flow of about 5 liters of blood per min! Where is resistance generated? The arterioles [small arteries just preceding each capillary bed, sometimes called resistance vessels]! Circulatory function then is a balance of heart activity [F] against arteriole activity [R].

What homeostatic mechanisms insure pressure? We will talk about two mechanisms. First, there is the Windkessel effect where the elastic properties of large arteries (aorta) store energy during heart contraction and release it [runoff pressure] when the heart is refilling. Second, The central nervous system regulates pressure by: a)The sympathetic portion of the nervous system activates smooth muscle constrictors around the arterioles to maintain resistance. b)Baroreceptors in the aortic arch further activate sympathetic outflow in responses to reductions in blood pressure.

If arterioles are normally constricted to preserve blood pressure [resistance] then how do capillary beds [tissues] increase flow during times of increase needs? When a given tissue becomes active it produces a substance nitric oxide [NO]. NO in turn relaxes the smooth muscle wraps around the arteriolar resistance vessels leading to that tissue thereby increasing flow.

If arterioles are normally constricted aren't capillary pressures fairly low? Yes, capillary pressures in head/feet/in-between all average about 30 mmHg at the arterial end and 20 mmHg at the venous end. Is the difference important? Yes! Recall that plasma osmotic pressure is about 25 mmHg. Thus there is net outward filtration at the arterial end and net inward filtration at the venous end of capillaries! Overall, there is a slight net outward filtration = tissue fluid. If there is continual accumulation of tissue fluid via filtration how is it returned to the circulation? Via the lymphatic system.

If capillary pressure is so low then aren't venous pressures really low and if so how is blood returned to the heart? Yes, venous pressures are about 5 mmHg! Venous return occurs because veins have a)one-way valves and b)deep veins run between muscles that act as pumps. What is orthostatic hypotension and why do people faint?

III. Evolutionary Development of the circulatory system in Vertebrates - another element of the Aquatic-Terrestrial transition (see handouts of arterial trees and hearts). One of the points made in this class is that evolution is NOT normally built around the appearance of new/novel features. Instead most of evolutionary change comes via modification of existing parts. This is true of the circulatory changes associated with the transition from breathing water (gills) to breathing air (lungs). As a result we can trace the elements/blood vessels in our circulatory system to those in other vertebrates. Driving force for the changes seen in the circulatory system. Fish exchange gases via the gills. Blood can be pushed through the gills under pressure. Hence gills/body capillaries can be arranged in series. Amphibian gas exchange is via lungs. Blood cannot be pushed through the lungs under pressure. With a single ventricular chamber [pump] systemic pressure must be reduced to a level that can be tolerated by the lungs. By separating pulmonary from systemic circuits/pumps the pulmonary circuit can be operated as a low-pressure/low-resistance circuit while the systemic circuit can be operated as a high-pressure/high-resistance circuit [see top figure on the back of the handout].

Find the following features of the heart/arterial tree in the handout figures. These are the principle features leading from water breathing to air breathing.

1)Teleost [bony fish] arterial tree is paired [right/left sides] see fig 330 D. From a two chambered heart [heart figure] blood is pumped into a single aorta which feeds paired ventral aortas. This blood feeds into four arotic arches containing the gills. From the gills blood passes to dorsal aortae and then to the head and body. Note that this is a circulation in series (pump-vessels-gill capillaries-vessels-systemic capillaries).

2)Amphibian [salamander] see fig 330 E and heart figure. The atrium of the heart is partitions = 3 chambered heart [note however, spongy tissue in ventricle. The gills are gone and a branch from Arch VI feeds the lungs. The single aorta is becoming branched by virtue of splitting of the aortic-arch vessels. Arch VI is now called the pulmo-cutaneous vessel [how does an amphibian exchange gases?]. Note also 'cd' which stands for carotid duct. This vessel is diminishing in size = separation of head/body blood flows. Key functional features: a)partitioning oxy/deoxy bloods, shunts.

3)The reptile [lizard] see fig 330 F and heart figure. The changes noted in amphibia become more exaggerated; aortic vessels further partitioned, ventricular chamber 'partially' partitioned, pulmonary branch of pulmocutaneous vessel enlarged. Key features = same as amphibian.

4)Birds/mammals - fig 330 G/H and heart figure. Arch VI now separated all the way to the heart as a pulmonary artery. Heart ventricle fully partitioned to a four-chambered pump. One set of the branched vessels disappears [note that in birds the left disappears and in mammals the right set disappears - see fig 330 G/H]. This reduction in vessel number is a design efficiency step. What is 'da' why does it exist and what does it 'tell-us' about evolutionary change?

5)Summary - Essentially all of the changes in the evolutionary development of the avian/mammalian circulatory system can be traced to modifications of existing vessels found in fish-amphibians-reptiles.

IV.Design-handout: Know the central features of our 'generic' avian/mammal [closed] circulatory system [text pgs 473-476, fig12-3 and handout figure]. Be able to draw the figure [including the enhancements as given in lecture]. You may be asked to draw the fig on the exam and/or to label the parts [showing only 3 capillary networks- uphill, level, downhill relative to the heart], as well as to describe "how" the system works. Know that pressure is the central item regulated, how it is regulated, have representative pressures for a supine/upright person [pgs 512-519, fig 12-42], know how these pressures would be different in a mouse-giraffe-brontosaurus and why [pgs 504-505, fig 12-33]. Why does a mouse have a blood pressure similar to a humans? How do right/left cardiac outputs/ pressures/ resistances differ/compare. Some terms are: baroreceptors/resistance vessels/ nitric oxide/capacitance vessels/CNS/ sympathetic outflow tracts/valves/muscle pumps [pgs 516 - 519, fig 12-45].

V.Hemodynamics - You should have a pretty good idea of the importance of vessel branching to velocity flow and surface area [pgs 497-504, figs 12-25, 12-26, 21-27]. You should know the importance of Poiseuille's law- and what it means to Flow/Resistance: You should know that flow ~ r4/resistance ~ r-4[equation 12-3, pg 498]. Know what we can conclude about flow through tubes of different dimensions from these relations. You should be especially interested in the resistance to flow as a function of tube radius [What happens to flow if tube radius is reduced by 1/2? What does this tell us about how sensitive flow may be to changes in the size of 'resistance' vessels?]. You should also know what is the origin and fate of tissue fluid-hint lymph and lymphatic system. terms: capillary-osmotic pressures,hydrostatic pressures, plasma, interstitial,filtration, reabsorption), lymphatic capillaries.

VI. Circulatory Patterns (handouts, pgs 488-495, fgs 12-16, 12-17, 12-18, 12-20, 12-22): You will want to know the basic design features of the fish-to-bird/mammal aortic arches and hearts. There are many key points that are summarized in the handouts. Terms include: sinus venosus and its fate, series to parallel circuits, functional-to-physical separation of venous-and-arterial blood, shunts, portal, pulmocutaneous, right/left systemic arches, Foramen of Panizzae, spiral fold, incomplete ventricular septum, cavum venosum, foramen ovale, ductus arteriosus/carotid duct, shunts. You should also know how the information in these figures and the handout gives us a clue about the complex array of vasculatures in the vertebrates especially as is associated with the aquatic-terrestrial transition and the unique requirements of the pulmonary circuit.

VII.The heart: You should have a detailed understanding of the path flow of blood through the vertebrate hearts, what determines one-way flow of blood and relative pressures in the various chambers of the heart and vessels attached to the heart. Based on the mammal heart [figs 12-4, 12-22] you should also have an good working knowledge of the relationships between electrical and mechanical events in the heart to generate blood pressure/flow [pgs 476-488, fgs 12-8, 12-12]. Terms: electrocardiogram, ejection, isovolumetric contraction/relaxation,relationships between pressures/flows, phonocardiogram. Also know when valves open/close and what produces these events. In the heart electrical activity you should know sinoatrial node, atrioventricular node (conduction delay), bundle of His Purkinje fibers (right/left bundles), pacemaker, parasympathetic/sympathetic, cardiac output, heart rate/stroke volume (which changes during exercise?), pericardium.

Section 4 of 5 ***Possible exam questions: Expect to answer two of the following essays

2)Draw a figure showing the major features of a mammal/bird circulatory system. Label the key parts. Explain how it works to insure a)needs of organs with different demands, b)needs changing over time, c)a long neck and upright posture.

3) Draw a figure of one [I select which one] of a [fish, amphibian, reptile, mammal] heart and/or arterial tree. Label the parts and explain how it works.

4) Draw a figure that illustrates the cardiac cycle. Describe how it works to insure blood flow against a resistance.

Section 5 of 5 ***Exam questions for final: Two of these questions will be asked.

1.What is dormancy? Why does it occur? Select one example of dormancy [a specific animal] and explain the process.

2.Draw a vertebrate hair cell with associate afferent-efferent neurons. Label and explain how it works.

3.Draw a juxtamedullary nephron. Explain how this structure achieves clearance with minimum water loss.