Lab #9: Digestive and Urinary Systems
All animals are heterotrophs, which means that they must acquire food from other organic sources. These
heterotrophs are characterized by the type of food that they consume.
1. Herbivores-eat exclusively plants
2. Carnivores-eat other animals
3. Omnivores- eat both plants and other animals
To allow sustainability of the environment and to reduce competition in the animal Kingdom, animals
have evolved certain preferences in the foods they eat as well various mechanisms for acquiring and
digesting their foods, such as developing the specialized mouth parts seen ingestive feeders, for example
beaks (e.g birds and squids), teeth (humans, and other chordates), and sucking mouth parts seen in some
arthropods such as aphids and butterflies.
Digestion is simply the mechanical and chemical breaking down of food into smaller components, so that
it can be absorbed. Digestion can take place intracellularly or extracellularly.
1. Intracellular digestion- digestion within vacuoles in cells. The vacuoles protect the cells from the
enzymes used to break down foods. Sponges and other single-celled organisms use this method
exclusively.
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2. Extracellular digestion- digestion takes place outside the cell in a specialized gastrovascular
cavity.
There are two types of gastrovascular cavities:
o Incomplete digestive tracts (single opening) –mouth and “anus” is in the same place e.g.
hydras and flatworms
Raven P, Johnson G, Losos J, Mason K, Singer S.2008. Biology. Eight Edition. McGraw Hill, NY New York
o Complete digestive tracts (two openings) -food proceeds from mouth to anus eg. Most
higher animals such as vertebrates, annelids and crustaceans.
Raven P, Johnson G, Losos J, Mason K, Singer S.2008. Biology. Eight Edition. McGraw Hill,
NY New York.
The digestive process can be organized into different stages.
1. Mechanical
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Food is physically broken down into smaller pieces, either due to the chewing action by teeth in the
mouths (exhibited in many vertebrates), or by the grinding action of pebbles found in specialized
organs called gizzards (seen in birds, as well as some reptiles, earthworms, mollusks, and insects)
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Food is also moved through the digestive system under involuntary control which uses peristaltic
contractions
2. Chemical
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Food is broken down into their smaller subunit molecules by digestive juices. The digestive juices are
enzymes that are released by secretory sytems found in the digestive tract or by accessory digestive
organs such as the liver, gallbladder and the pancreas. The digestive juices are secreted in response to
a specific stimulus; for example entry of food into the stomach stimulates secretion of HCl and
pepsinogen.
The following table gives examples of enzymes that we will focus on in the lab.
Location
Salivary Glands
Stomach
Pancreas
Enzymes
Amylase
Pepsin
Lipase
Substrates
Starch,glycogen
Proteins
Triglycerides
Digestion Products
Disaccharides
Short peptides
Fatty acids
3. Absorption
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The food is broken down into its molecular components during chemical digestion to allow the
molecules to be able to cross the plasma membrane and enter the circulatory system so that the
nutrients can be distributed to the rest of the body.
4. Elimination
- Any undigested food molecules are considered waste products. These wastes are excreted or
defecated from the anus.
The digestive tracts of the animal kingdom vary in its complexity, mainly due to the types of food that are
consumed (See Figure 48.16 in text book). Four organs are subject to specialization in the Kingdom
Animalia.
1.
The first organ is the tongue which is only present in the phylum Chordata.
2.
The second organ is the esophagus. The crop is an enlargement of the esophagus in birds, insects and
other invertebrates that is used to store food temporarily.
3.
The third organ is the stomach . In addition to a glandular stomach (proventriculus), some animlas
such as birds and earthworms have a muscular "stomach" called the ventriculus or "gizzard." The
gizzard is used to mechanically grind up food.
Raven P, Johnson G, Losos J, Mason K, Singer S.2008. Biology. Eight Edition. McGraw Hill, NY New York.
Furthermore some animals have multi-chambered stomachs (eg. Ruminants), while some animals'
stomachs contain a single chamber (eg.humans).
N.B. A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially
softening it within the animal's first stomach, known as the rumen, then regurgitating the semi-digested
mass, now known as cud, and chewing it again. The process of rechewing the cud to further break down
plant matter and stimulate digestion is called "ruminating". Ruminating mammals include cattle, goats,
sheep, giraffes, deer, camels.
4.
The fourth organ is the large intestine. An outpouching of the large intestine called the cecum is
present in non-ruminant herbivores such as rabbits. It aids in digestion of plant material such as
cellulose.
- in most vertebrates (except mammals) waste products leave the large intestine into a cavity called the
cloaca. The cloaca also receives products from the urinary and reproductive systems. In mammals
however there is a specialized urogenital system that separates urinary wastes from fecal matter.
We still start of by looking at the human digestive system, and then look at how simpler organisms
compare and at some other variations. Therefore we can first understand the general parts and
mechanisms.
THE HUMAN DIGESTIVE SYSTEM
Raven P, Johnson G, Losos J, Mason K, Singer S.2008. Biology. Eight Edition. McGraw Hill, NY New York.
Feeding begins in the oral cavity and ends at the anus. parts include:
1. Mouth
- Ingestive eaters, the majority of animals, use a mouth to ingest food.
- vertebrates such as reptiles, and mammals have teeth for tearing, grasping and cutting their food, while
birds possess beaks, arthropods have highly modified mandibles for sucking or chewing
- The tongue manipulates food during chewing and swallowing. It mixes food with saliva and then forms
the mixture into a bolus in preparation for swallowing
- In humans the digestion of starch also begins in the mouth due to chemical breakdown of starch by
production of salivary amylase from the salivary glands. The exocrine glands send their juices by way of
ducts to the mouth.
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2. Pharynx
Swallowing moves food from the mouth through the pharynx into the esophagus.
3. Esophagus
The esophagus is a muscular tube leading from the pharynx to the stomach whose muscular
contractions (peristalsis) propel food to the stomach
4. Stomach
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During a meal, the stomach gradually fills to a capacity of 1 liter, from an empty capacity of 50-100
milliliters.
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Epithelial cells line inner surface of the stomach, and secrete about 2 liters of gastric juices per day.
Gastric juice contains hydrochloric acid, pepsinogen, and mucus; ingredients important in digestion.
Secretions are controlled by nervous (smells,thoughts, and caffeine) and endocrine signals.
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Hydrochloric acid (HCl) lowers pH of the stomach so pepsin is activated (and pH kills most bacteria).
Pepsin is an enzyme that controls the hydrolysis of proteins into peptides. Mucus protests the wall of
the stomach from HCl.
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The stomach also mechanically churns the food. Chyme, the mix of acid and food in the stomach,
leaves the stomach and enters the small intestine.
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5. Small Intestine
Receives bile from the gall bladder and secretions from the pancreas, chemically breaks down chyme,
absorbs nutrient molecules, and transports undigested material to the large intestine.
o Liver and Gall Blladder- Bile, a watery greenish fluid is produced by the liver and
secreted via the hepatic duct and cystic duct to the gall bladder for storage, and thence on
demand via the common bile duct to an opening near the pancreatic duct in the duodenum.
It contains bile salts, bile pigments (mainly bilerubin, essentially the non-iron part of
hemoglobin) cholesterol and phospholipids. Bile salts and phospholipids emulsify fats, the
rest are just being excreted.
o Pancreas- produces pancreatic juice which contains sodium bicarbonate (basic) and
neutralizes the acidity of the chyme as it enters the duodenum.
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6. Large Intestine
The large intestine is made up by the colon, cecum, appendix, and rectum.
Material in the large intestine is mostly indigestible residue and liquid.
Movements are due to involuntary contractions that shuffle contents back and forth and propulsive
contractions that move material through the large intestine.
Secretions in the large intestine are an alkaline mucus that protects epithelial tissues and neutralizes
acids produced by bacterial metabolism.
Water, salts, and vitamins are absorbed, the remaining contents in the lumen form feces (mostly
cellulose, bacteria, bilirubin).
o Absoption in the large intestine due to the presence ofvilli (fingerlike projections that line
the lumen)
http://pharyngula.org/~pzmyers/MyersLab/teaching/Bi104/l05/img/villi.jpg
http://nbhcl.neurobio.ucla.edu/campbell/epithelium/wp_images/107%20villi.jpg
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Bacteria in the large intestine, such as E. coli, produce vitamins (including vitamin K) that are
absorbed.
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7. Anus
The rectum opens at the anus where defecation, (expulsion of feces) occurs. Feces contains
nondigestible remains, bile pigments (give color), and bacteria (give smell).
GUIDE TO BIOMOLECULES FOR ENZYME TESTS
Carbohydrates:
→Most monosaccharides are reducing sugars, therefore they possess a free aldehyde (-CHO) or ketone (C=O) groups. These groups are free to reduce weak oxidizing agents such as copper in Benedict’s
reagent.
→Therefore Benedict’s reagent is used to test for the presence of reducing sugars in compounds. The
reducing sugars reduce the cupric ions in Benedict’s solution to cuprous oxide at basic (high) pH. The
sugars themselves then become oxidized. The Benedict’s solution then turns from blue to green to reddish
orange.
Test For Sugar: Reagent=Benedict’s Solution
Negative: Blue
Positive: Green (low concentration)
Yellow (low concentration)
Orange (more concentration)
Red (high concentration)
→An iodine test using iodine-potassium iodide I2KL is used to test specifically for the carbohydrate,
starch. Starch unlike monosaccharides, disaccharides, and other polysaccharides has a coiled structure.
When iodine interacts with this coiled structures its natural brown/yellow color becomes bluish/black.
Proteins:
→ Biuret test is used to test for the presence of proteins. Peptide bonds in proteins complex with the
cupric ions in Biuret reagents to produce a pinkish/purple/violet color. The intensity of the color relates to
the number of peptide bonds that react.
Test For Proteins: Reagent=Biuret reagent
Negative: Blue
Positive: Purple (presence of protein)
Pink/pink purple (protein digestion/peptides)
OSMOREGULATION AND URINARY SYSTEMS
Osmoregulation is the active regulation of the osmotic pressure of bodily fluids to maintain the
homeostasis of the body's water content; that is it keeps the body's fluids from becoming too dilute or too
concentrated.
Simple organisms such as an amoeba make use of contractile vacuoles to collect excretory waste, such as
ammonia, from the intracellular fluid by both diffusion and active transport. As osmotic action pushes
water from the environment into the cytoplasm, the vacuole moves to the surface and disposes the
contents into the environment.
Higher animals such as vertebrates have developed urinary systems to control water osmoregulation and
the excretion of nitrogenous wastes. This excretory system consists of a series of tubes and the kidneys
that filter the blood of nitrogenous wastes.
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Ammonia is a toxic by-product of protein metabolism and is generally converted to less toxic
substances after it is produced then excreted; mammals convert ammonia to urea, whereas birds and
reptiles form uric acid to be excreted with other wastes via their cloacas.
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Other animals such as some invertebrates, which include annelids, arthropods and mollusks have a
rudimentary excretory system which consists of nephridia. These nephridia are excretory glands that
consist of funnel type tube that are lined with cells, and function as kidneys.
http://images.search.yahoo.com/images/view?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fei%3DUTF8%26p%3Dearthworm%2520nephridia%26rs%3D0%26fr2%3Dtab-web%26fr%3Dyfp-t-501&w=487&h=381&imgurl=www.biologie.unihamburg.de%2Fb-online%2Flibrary%2Fonlinebio%2Fannelidbody.gif&rurl=http%3A%2F%2Fwww.biologie.uni-hamburg.de%2Fbonline%2Flibrary%2Fonlinebio%2FBioBookDiversity_8.html&size=35.3kB&name=annelidbody.gif&p=earthworm+nephridia&type=gif&oid=e8
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Nephridia in Earthworms
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In some arthropods such as Uniramia (Insects and Myriapoda), arachnids and tardigradeswe also see
the development of malphigian tubes to aid in osmoregulation.
o Malpighian tubule system consists of branching tubules extending from the alimentary
canal that absorbs solutes, water, and wastes from the surrounding hemolymph. The wastes
then are released from the organism in the form of solid nitrogenous compounds.
MalphigianTubules in the grasshopper
http://images.search.yahoo.com/images/view?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fei%3DUTF8%26p%3Dmalpighian%2520tubules%26y%3DSearch%26SpellState%3Dn-1501296073_qig3t1M3yMlK9EYy1.alDzwAAAA%2540%2540%26rs%3D0%26fr2%3Dtab-web%26fr%3Dyfp-t501&w=800&h=366&imgurl=www.bio200.buffalo.edu%2Flabs%2Fimages%2Fgrasshopper.JPG&rurl=http%3A%2F%2Fwww.bio200.buff
alo.edu%2Flabs%2Fgrasshopperpic.html&size=190.4kB&name=grasshopper.JPG&p=malpighian+tubules&type=JPG&oid=a8d0a74810a4a
7d4&no=11&tt=66&sigr=11msth99m&sigi=11i2ftr14&sigb=15edghgdn
References
Abraham L. Kierszenbaum (2002). Histology and cell biology: an introduction to pathology. St. Louis: Mosby.
Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David
LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall.
http://www.angelfire.com/sc/mrcomeau/digestivenotes.html
Raven P, Johnson G, Losos J, Mason K, Singer S.2008. Biology. Eight Edition. McGraw Hill, NY New
York.