ECOL 182 - Spring 2008 Lecture 3

Animal physiology: organ systems and internal environment © Dr. Regis Ferriere Department of Ecology & Evolutionary Biology University of Arizona

What are the key terms? • • • • • • • • •

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

How are cells organized in our body? • In multicellular animals  cells are organized in tissues,  tissues make up organs,  interacting organs form organ systems.

“Internal environment”? “Homeostasis”? • Cells, tissues, organs, organ systems are surrounded by extra-cellular fluid.  This is the internal environment. • Organs and organ systems provide physiological control and regulation to maintain stability or homeostasis of the internal environment. • The regulation of physiological systems is mostly through negative feedback regulation.  Feedforward information functions to change set points.

How does homeostasis work for temperature? • Endotherms do regulate their internal temperature!  Ectotherms are animals whose body temperatures are determined by external sources of heat. • Endotherms thermoregulation is achieved by producing heat and/or regulating heat loss. • Control of blood flow to the skin is a very important for regulating heat loss.

How do endotherms produce heat? • Energy is required. The rate at which an animal consumes energy is called metabolic rate. • Most nonshivering heat production occurs in a specialized adipose tissue: brown fat.  Specialized cells that release heat by consuming metabolic fuels without producing ATP!

How do cells, tissues and organs exchange information 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 roles in physiology, reproduction, development and behavior.

How do hormones work? (1/4) • Hormones are released by endocrine cells into internal environment, where they diffuse to nearby cells or into blood.  Some hormones are released by groups of aggregated endocrine cells called endocrine glands. • Target cells have receptors on their surface or in their cytoplasm.

How do we hormones work? (2/4) • Hormones often occur in infinitesimal quantities. • Immunoassays are performed to detect and measure hormone concentrations.

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 through different signal transduction pathways.  For example, norepinephrine (produced by adrenal gland) binds to a cell-surface Gprotein receptor. The receptor can be of two kinds that connect to different pathways within cells. • Signaling pathways often involve cascades in which each step amplifies 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 closed circulatory systems.  The vascular system keeps circulating blood separate from the interstitial fluid.

How are vertebrate circulatory systems organized? • Vertebrates have closed circulatory systems and hearts have evolved from two to four chambers.  When a heart chamber contracts, arteries and arterioles carry blood from the heart. Capillaries are the site of exchange between blood and interstitial fluid. Venules and veins carry blood back to the heart. • In birds and mammals, pulmonary circuit (from heart to lungs and back to heart) and systemic circuit are completely 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. The contraction of the two atria, followed by the contraction of the two ventricles, is the cardiac cycle. • Cardiac cycle divided into two phases:  systole, when ventricles contract.  diastole, when ventricles relax.

Where does the heartbeat come from? • Cardiac muscle has unique adaptations that enable it to function as a pump! • Cardiac muscle cells are in electric contact with one another - enable action potentials to spread rapidly.  This results in large groups of cells contracting in unison. • Some cardiac muscle cells are pacemaker cells - can fire action potentials without stimulation from nervous system.  Special behavior of ion channels in their membranes.  Two clusters: sinoatrial node and atrioventricular node.

What’s in the blood? • Blood consists of plasma (complex aqueous solution), and cells and cell fragments.  Hematocrit measures cellular proportion.

How does blood transport oxygen? • 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. • Because of positive cooperativity, hemoglobin affinity for O2 depends on P(O2) experienced by hemoglobin.  Hemoglobin picks up O2 as it flows through respiratory exchange structures & gives up O2 in metabolically active tissues.

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.

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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 osmotic pressure (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 them to 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 that freeze solid in winter and survive) that cause ice to form between rather than within cells, thus protecting cell organelles from damage. Atkinson, M. A. and N. K. MacLaren. 1990. What causes diabetes? Scientific American, July. A discussion of how malfunctions of the immune system cause insulin-dependent diabetes, a major disease that involves a hormone deficiency. Cabe, D. K. 2000. Saving hearts that grow old. Scientific American, June. An explanation of how better understanding of atherosclerosis-the inflammation and buildup of fatty deposits in blood vessels-has triggered new approaches to treating 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 the man who received the Nobel Prize for his work on the subject.