animal_systems

                         Animal Systems Unit Objectives

 Chapter 40: Animal Form and Function

1. Animal exchange of nutrients and gases occurs as substances dissolved in an
   aqueous medium move across the plasma membrane of each cell. Rate of exchange
   is proportional to surface area; the amount of material that must be
   exchanged is proportional to volume. For this reason, animals try to maximize
   the surface area to volume ratio of their exchange surfaces. Once absorbed,
   circulatory fluids can carry the materials around the body.

2. Table 40.1 lists ten animal organ systems: digestive, circulatory,
   respiratory, immune and lymphatic, excretory, endocrine, reproductive,
   nervous, integumentary, skeletal, and muscular.

3. Animal tissues are organized into four groups: epithelial tissue (like simple
   columnar or simple squamous), connective tissue (like cartilage, blood, and
   bone), muscle tissue (skeletal, cardiac, or smooth), and nervous tissue
   (neurons).

4. Animal homeostasis relies largely on negative feedback loops. When a variable
   such as body temperature or solute concentration fluctuates away from the set
   point, a receptor triggers a response that helps return the variable to the
   set point.
   
   Animals use energy harvested from the food they eat to fuel metabolism and
   activity. Food is digested by enzymes in the gut, and nutrients are
   absorbed by body cells. Most energy-containing molecules are used in cellular
   respiration to generate ATP, which then powers cellular work.

5. See the handout.


 Chapter 41: Animal Nutrition

1. As far as diet goes, herbivores dine mainly on plants or algae, carnivores on
   other animals, and omnivores on some combination of the two. As far as
   denition goes, herbivores usually have teeth with broad, ridged surfaces,
   carnivores generally have pointed incisors and canines, and, again, omnivores
   have some combination of the two.

2. The four stages of food processing are ingestion, digestion, absorption, and
   elimination.

3. A gastrovascular cavity (found in cnidarians and flatworms) is lined with
   both specialized gland cells that secrete digestive enzymes as well as cells
   that then engulf the digested particles. In animals with a gastrovascular
   cavity, food is eaten through the same hole that later excretes the waste.
   
   An alimentary canal (found in the other phyla) is much fancier. Since food
   passes through it in only one direction, it can have specialized compartments
   that carry out digestion and nutrient absorption in a stepwise fashion.
   Animals with an alimentary canal can therefore eat dinner while still
   digesting lunch.

4. The human digestive organs include the mouth, which contains teeth that mash
   and grind the food to increase its surface area and make it easier to
   swallow; the salivary glands, which release, among other things, an enzyme
   called amylase that hydrolyzes starch and glycogen in the food, and a
   glycoprotein called mucin that lubricates the food for easier swallowing; the
   pharynx and esophagus, which transport the food to the stomach; the stomach,
   which secretes hydrochloric acid and pepsin that help break down proteins in
   the food; the pancreas, liver, and gallbladder, which release a mixture of
   digestive enzymes and chemicals into the small intestine; the small
   intestine, in which digestion is completed and through the walls of which
   the food particles get absorbed; and finally the large intestine, comprising
   the colon, which helps to reabsorb water, the cecum, important for fermenting
   ingested material, and the rectum, which stores feces until they can be...
   eliminated.

5. The major digestive enzymes are salivary amylase, secreted by the
   salivary glands into the mouth, which hydrolyzes starch, glycogen, sucrose,
   and lactose; pepsin-in-the-stomach, which hydrolyzes proteins; peptidase,
   which breaks down polypeptides in the small intestine into amino acids;
   pancreatic lipase, which breaks down fat droplets in the small intestine into
   glycerol, fatty acids, and monoglycerides; pancreatic nuclease, which works
   in the small intestine to get nucleotides out the DNA and RNA in food; and
   finally nucleotidases, nucleosidases, and phosphatases, which operate at the
   epithelium of the small intestine to further digest nucleotides into their
   constituent nitrogenous bases, sugars, and phosphates.

6. What ensures that we do not inhale our food? The esophageal reflex, which
   works like this: when a bolus of food enters the pharynx, the epiglottis
   covers the glottis and the esophageal sphincter relaxes. Now the esophagus is
   open and it happily accepts the bolus. Wavelike contractions then move the
   food down the esophagus to the stomach, and the epiglottis moves up anew.

7. The herbivore's alimentary canal has several digestive chambers containing
   bacteria that aid digestion of plant material, gastric ceca that function in
   digestion and absorption, and a lengthy cecum that helps ferment the plant
   material. The carnivore's alimentary canal has a much shorter intestine and
   the cecum is short and to the point.


 Chapter 42: Circulation and Gas Exchange

1. A closed circulatory system (found in annelids, cephalopods, and vertebrates)
   has branching vessels filled with blood. Gas and nutrients in the blood
   diffuse through the vessel wall into the interstitial fluid, which surrounds
   the cell. The heart pumps continuously, moving blood in a one-way circuit
   around the body.

   An open circulatory system (found in arthropods and most mollusks) has,
   instead of blood and interstitial fluid, a single fluid called hemolymph.
   Contraction of the heart pumps the hemolymph through vessels into the sinuses
   that surround the organs; relaxation of the heart pulls the hemolymph back to
   the heart through pores in the sinus walls.

2. In mammals, the heart continuously beats, pumping blood around the body. As
   the blood passes through the capillary beds, the blood spreads out and slows
   down, helping nutrients and gases in the bloodstream diffuse across the thin
   capillary wall and into the interstitial fluid, and vice versa.

3. In fish, the heart consists of two chambers: the blood passes through the
   gills on the way to the body; that is, the oxygenated blood doesn't first
   return to the heart. Amphibians have a three-chambered heart, and two
   circuits of blood flow: pulmocutaneous and systemic. Reptiles also have a
   three-chambered heart, but with a septum partially dividing the single
   ventricle. Mammals and birds have a four-chambered heart.

4. In vertebrates with double circulation (all but fish), blood is pumped
   first through the pulmonary circuit, which carries deoxygenated blood to the
   lungs and back to the heart, where the oxygenated blood is then pumped around
   the body via the systemic circuit.

5. There was once a red blood cell who was sad because its hemoglobin was
   terribly lonely. So, being a kind-hearted creature, and one who hated
   indecision, the red blood cell, without a second thought, set out to find
   some oxygen to keep its hemoglobin company. She left the left atrium and blew
   into the left ventricle. He was the owner of a prominent nightclub in
   Amorita, and so she had hoped to find some oxygen hidden, perhaps, in his
   nightstand, or under his floorboards, but after snooping around for a good
   twenty minutes and then nearly getting caught when he finally emerged from
   the bathroom (without flushing), she wisely decided that it was far too
   risky (she was already on parole for attempting to blow up a public plaque),
   and so she left. Outside it was getting dark. The sky was fiery red in the
   afterglow of what, she imagined, must have been quite the sunset. Far away,
   she could hear the beating of drums... or was it a Chinese boy dropping
   stones into a pond? On and on she walked, humming Catholic hymns and
   thinking to herself. 'How is my dear Mr. Hemoglobin doing?' she suddenly said
   out loud, 'And will I ever be able to help him? Oh, I love him so... I do
   hope so.' Just then, she rounded a giant curve and the road split into a
   million tiny paths. She picked one at random and it led her straight into a
   tiny glass bubble (she had to crawl it was so small) that Joy to the world!
   had oxygen straws. She stepped back a few paces, got a running start, and
   impaled herself right onto one of the straws. Nobody knows if it was the
   terrific pain or simply her weariness after a day of walking that caused her
   to feint, but in any case, just then, an old, Victorian-looking lady dressed
   in green, spotted her lifeless body and dragged her onto a train that was
   headed to Grand Central Station. She woke up a few hours later in the right
   ventricle. He was in a foul temper and screamed so loud that the poor blood
   cell nearly began to cry. But she held herself together -- one hand clutching
   the puncture wound -- and, holding her head high, walked out his front door,
   on which hung a large sign that read "aorta". It was a blustery day, but the
   wind was only picking up.  Because a moment after her floral, straw hat was
   carried away in the breeze, she felt a stirring in her soul and, before she
   knew it, she had been picked up by the heel of her lambskins and was spinning
   out of control like a leaf in the atmosphere. Our story ends here. For
   chronicles of her later travels, see Volumes 2 and 3, coming soon -- maybe.