Animal physiology:organ systems and internal environment

© Dr. Regis FerriereDepartment of Ecology & Evolutionary Biology

University of Arizona

ECOL 182 - Spring 2008Lecture 3

What are the key terms?

• Multicellular animals• Organs• Internal environment• Homeostasis• Hormones• Circulatory system• Heart• Blood• Gas exchange

How are cells organizedin our body?

• In multicellular animals cells are organized

in tissues, tissues make up

organs, interacting organs

form organsystems.

“Internal environment”? “Homeostasis”?

• Cells, tissues, organs, organ systems are surroundedby extra-cellular fluid.This is the internal environment.

• Organs and organ systems provide physiologicalcontrol and regulation to maintain stability orhomeostasis of the internal environment.

• The regulation of physiological systems is mostlythrough negative feedback regulation.Feedforward information functions to change set

points.

How does homeostasis work for temperature?

• Endotherms do regulate theirinternal temperature!Ectotherms are animals

whose body temperaturesare determined by externalsources of heat.

• Endotherms thermoregulationis achieved by producing heatand/or regulating heat loss.

• Control of blood flow to the skinis a very important forregulating heat loss.

How do endothermsproduce heat?

• Energy is required. The rate atwhich an animal consumesenergy is called metabolic rate.

• Most nonshivering heatproduction occurs in aspecialized adipose tissue:brown fat.Specialized cells

that release heatby consumingmetabolic fuelswithoutproducing ATP!

How do cells, tissues and organs exchangeinformation about the internal environment?

• Control and regulation require information.Most information transmitted as electrical

signals and as chemical signals.Chemical signals are hormones.

• There are many hormones that all play crucial rolesin physiology, reproduction, development andbehavior.

How do hormones work?(1/4)

• Hormones are released byendocrine cells into internalenvironment, where theydiffuse to nearby cells or intoblood.Some hormones are

released by groups ofaggregated endocrinecells called endocrineglands.

• Target cells have receptorson their surface or in theircytoplasm.

How do we hormoneswork? (2/4)

• Hormones often occur ininfinitesimal quantities.

• Immunoassays areperformed to detect andmeasure hormoneconcentrations.

How do hormones work? (3/4)

• A hormone can act through many receptors.Affinity chromatography and genomic analysis to

identify receptors and discover new ones.• Receptors can be upregulated or downregulated.

This will change the sensitivity to the hormone.

How do hormones work? (4/4)

• A hormone can act throughdifferent signal transductionpathways.For example, norepinephrine

(produced by adrenal gland)binds to a cell-surface G-protein receptor. The receptorcan be of two kinds thatconnect to different pathwayswithin cells.

• Signaling pathways often involvecascades in which each stepamplifies the signal.

The internal environment of animals is networked• Two networks: circulatory system and nervous system.

Here we focus on the former.• The circulatory system networks cells, tissues and organs by

moving extracellular fluid around the body.Extracellular fluid transports heat, hormones, respiratory

gases, nutrients and wastes.• Circulatory systems consist of a pump (heart) and an open

or closed system of vessels through which is pumped a fluid(blood) that transports substances and heat.

• Some animals do not have circulatory systems. Vertebrate,annelids and some other invertebrates have closedcirculatory systems.The vascular system keeps circulating blood separate from

the interstitial fluid.

How are vertebrate circulatory systems organized?

• Vertebrates have closed circulatorysystems and hearts have evolvedfrom two to four chambers.When a heart chamber contracts,

arteries and arterioles carryblood from the heart. Capillariesare the site of exchange betweenblood and interstitial fluid. Venulesand veins carry blood back to theheart.

• In birds and mammals, pulmonarycircuit (from heart to lungs and backto heart) and systemic circuit arecompletely separate.

How does blood flow through the human heart?

• Blood flows from right heart to lungs to left heart to body.

What is the cardiac cycle?

• Both sides of the heart contract at the same time. Thecontraction of the two atria, followed by the contraction ofthe two ventricles, is the cardiac cycle.

• Cardiac cycle divided into two phases:systole, when ventricles contract.diastole, when ventricles relax.

• Cardiac muscle has unique adaptationsthat enable it to function as a pump!

• Cardiac muscle cells are in electric contactwith one another - enable action potentialsto spread rapidly.This results in large groups of cells

contracting in unison.• Some cardiac muscle cells are pacemaker

cells - can fire action potentials withoutstimulation from nervous system.Special behavior of ion channels in their

membranes.Two clusters: sinoatrial node and

atrioventricular node.

Where does the heartbeatcome from?

• Blood consists of plasma (complex aqueoussolution), and cells and cell fragments.Hematocrit measures cellular proportion.

What’s in the blood?

• Red cells contain huge numbers of hemoglobin proteins.Hemoglobin molecule has 4 heme groups - iron-containing

ring stuctures that can reversibly bind a O2 molecule.

How does blood transport oxygen?

• Because of positivecooperativity, hemoglobinaffinity for O2 depends on P(O2)experienced by hemoglobin.Hemoglobin picks up O2 as it

flows through respiratoryexchange structures & givesup O2 in metabolically activetissues.

How do capillaries work?• Capillaries have tiny holes (not in brain: blood-brain barrier).

Small enough for water, some ions, small molecules but not proteins.• Arterioles branch into many capillaries, hence blood pressure drops.• Starling’s model: blood volume maintained in capillary beds by a

changing balance between blood pressure and the colloidal osmoticpressure (maintained constant by proteins that cannot leave capillaries).

Suggested readings

Madigan, M. T. and B. L. Marrs. 1997. Extremophiles. Scientific American,April. A discussion of the adaptations of many microorganisms that enable themto live in extremely hot, cold, acidic, basic, or salty environments.

Storey, K. B. and J. M. Storey. 1990. Frozen and alive. Scientific American,December. An explanation of the adaptations of some ectotherms (those thatfreeze solid in winter and survive) that cause ice to form between rather thanwithin cells, thus protecting cell organelles from damage.

Atkinson, M. A. and N. K. MacLaren. 1990. What causes diabetes? ScientificAmerican, July. A discussion of how malfunctions of the immune system causeinsulin-dependent diabetes, a major disease that involves a hormone deficiency.

Cabe, D. K. 2000. Saving hearts that grow old. Scientific American, June. Anexplanation of how better understanding of atherosclerosis-the inflammation andbuildup of fatty deposits in blood vessels-has triggered new approaches totreating the nation's leading causes of death.

Perutz, M. F. 1978. Hemoglobin structure and respiration. Scientific American,December. An authoritative article on hemoglobin structure and function by theman who received the Nobel Prize for his work on the subject.