Biol 2: Digestive Systems
accessory organs
- 3 pair of salivary glands (secrete digestive chemicals that enter alimentary canal through ducts) - liver - gallbladder - pancreas
How fats break down
- EMULSIFICATION - insoluble in water and tend to clump together in large globules - bile salts separate and coat smaller fat droplets, process called emulsification - when there are many small droplets a larger surface area of fat is exposed to lipase, a pancreatic enzyme that breaks fat molecules down into fatty acids and glycerol
steps of food moving through the human esophagus
- Esophageal opening is normally closed off by sphincter, air enters your larynx (voice box) flows past your vocal cords and through the trachea (windpipe) - When you start to swallow the tongue pushed a bolus of food into the pharynx, triggering the swallowing reflex - Movement of the trachea tips the epiglottis flap over the opening to the trachea closing it making sure food goes down the esophagus - Esophageal sphincter relaxes, and the bolus enters the esophagus - The esophageal sphincter then contracts above the bolus and the epiglottis tips up again reopening the breathing tube
overall steps of the human digestive system
- Ingest and chew food in your oral cavity and use your tongue to push the food into your pharynx - Once you swallow muscles propel the food through alimentary canal by peristalsis - Sphincters regulate the food into and out of the stomach, sphincter controlling passage out of the stomach keeps food in there for about 2-6 hours for stomach acids and enzymes to begin digestion - Final steps of digestion and nutrient absorption occur in the small intestine over period of 5-6 hours - Undigested material moves slowly through the large intestine over a period of 12-24 hours - Feces are stored in the rectum and then expelled through the anus
parts of the alimentary canal
- Oral cavity - Tongue - Pharynx - Esophagus - Small intestine - Large intestine - Anus
_______ digestion occurs in the stomach
- Some - the stomach secretes a digestive fluid called gastric juice, made up of a protein-digesting enzyme, mucus, and strong acid - one function of the acid is to break apart the cells in food and denature proteins
Definition and function of a food vacuole
- a cellular organelle in which enzymes break down food - after a cell engulfs food by phagocytosis newly formed food vacuole fuses wit lysosome - as food digests food molecules pass through the vacuole membrane into the cytosol
the appendix
- a small finger like extension of the cecum, contains a mass of white blood cells that make a minor contribution to immunity - if the junction between the appendix and the rest of the large intestine becomes blocked, appendicitis -- bacterial infection of the appendix -- may result - if this occurs emergency surgery is usually required to remove the appendix and prevent the spread of infection
How does the food move from the stomach to the intestine?
- about every 20 seconds, your stomach muscles contract, churning and mixing the contents of your stomach - what entered the stomach as food soon becomes an acidic, nutrient-rich broth known as chyme - the sphincter between the stomach and the small intestine regulates the downstream passage of chyme which leaves the stomach and enters the small intestine a squirt at a time - usually takes 2-6 hours for the stomach to completely empty after a meal
mechanical digestion
- begins in the mouth - food mechanically broken into smaller pieces increasing the surface area available for chemical processes
The liver also converts many of its nutrients it receives into new substances
- blood leaving the liver may have a very different nutrient makeup than the blood that entered - ex: liver cells synthesize many essential proteins, such a plasma proteins important in blood clotting and in maintaining the osmotic balance of the blood, and lipoproteins that transport fat and cholesterol to body cells
chemical digestion (hydrolysis)
- breaks down polymers into monomers to be resembled into the body's own molecules - needed because animals cannot directly use the big 4 macromolecules, they are too large to pass through into cells - once they are broken down they're used to make specific large molecule the animal needs through dehydration synthesis - proteins are split into amino acids, - polysaccharides / disaccharides split into monosaccharides - nucleic acids split into nucleotides - fats into glycerol and fatty acids
wastes of the digestive system
- called feces, become increasingly solid as water is reabsorbed and they move along the colon by peristalsis - takes around 12-24 hours for material to travel the length of the colon - the feces consist mainly of indigestible plant fibers and enormous numbers of prokaryotes that normally live in the colon - some colon bacteria, such as E. coli, products important vitamins, including several B vitamins and vitamin K - these substances are absorbed into the bloodstream and supplement your dietary intake of vitamins
undigested lactose
- cannot be absorbed so it passes into the large intestine - there prokaryotes consumed into lactose, reeling gases such as methane - this produces the uncomfortable symptoms that are associated with lactose intolerance, such as painful bloating
suspension feeders
- capture food particles from the surrounding medium - manta rays, sponges
Steps of a hydra digesting a water flea
- cells lining the gastrovascular cavity - enzymes break down the food into smaller particles - other cells engulf these particles - digestion is complete in cellular food vacuoles - undigested material expelled back out single opening
Functions of a crop vs a stomach or gizzard
- crop: food is softened and stored - stomach/gizzard: muscular organs that churn and grind food and may store food temporarily as well
Most digestion is completed in the ______________
- duodenum - main function of the rest of the small intestine (jejunum and ileum) is to absorb nutrients
the first 25 cm (10 in) of the small intestine
- duodenum - where chyme squirted from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and gland cells in the intestinal wall - the pancreas produces pancreatic juice, a mixture of digestive enzymes and an alkaline solution that neutralizes the acidity of the chyme as it enters the small intestine - in response to chyme the hormones produced by the duodenum stimulate the release of bile from the liver and gallbladder as well as digestive juices from the pancreas
simple steps of the digestive system
- food entering the mouth passes into the pharynx, or throat - depending on species, the esophagus may channel food to a crop, stomach, or gizzard - chemical digestion and nutrient absorption occur mainly in the intestine - undigested materials are expelled through the anus
omnivores
- generally eat both plants and animals -humans, crows, roaches
carnivores
- generally eat other animals - lions, spiders, whales
herbivores
- generally eat plants and algae - cattle, gorillas, and snails
bulk feeders
- ingest large pieces of food - heron, whale
four main stages of food processing
- ingestion - digestion - absorption - elimination
substrate feeders
- live in or on their food source and eat their way through it - leaf miner caterpillar, maggots, earthworms
How carbohydrates breakdown
- maltose splits maltose (disaccharide) into glucose (monosaccharides) - sucrase hydrolyzes table sugar (sucrose) - lactase digests lactose
in rabbits and some rodents, cellulose-digesting bacteria live in the large intestine as well as in the cecum
- many of the nutrients produced by these microbes are initially lost in the feces because they do not go through the small intestine - they recover these nutrients by eating some of their feces, thus passing the food through the alimentary canal a second time - the feces from the second round of digestion, rabbit "pellets" are more compact and are not re-ingested
The oral cavity is where we ingest food and begin to digest it
- mechanical digestion begins - incisors: biting - canine: riping - premolars/molars: grinding and crushing
respiratory mishaps
- mishaps like not chewing enough, eating too fast, or swallowing an object too big to pass could lead to a blocked pharynx or trachea which could prevent air flow of trachea causing them to choke - if breathing is not restored within minutes, brain damage or death will result
Gastric glands have three types of cells that secrete different components of gastric glands
- mucous cells: secrete mucous which lubricated and protects the cells lining the stomach - parietal cells: secret hydrogen and chloride ions, which combine in the stomach to form hydrochloric acid (HCl) - chief cells: secrete pepsinogen, an inactive form of the enzyme pepsin
Saliva contains substances that are important in food processing
- mucus: protects the soft lining of your mouth and lubricates food for easier swallowing - buffers: neutralize food acids, helping prevent tooth decay - antibacterial agents: kill many of the bacteria that enter your mouth with food - digestive enzyme, amylase: begins chemical digestion of starches
How nucleic acids break down
- nucleases hydrolyzes nucleic acids - nucleases from the pancreas split DNA and RNA into their component nucleotides - the nucleotides are then broken down into nitrogenous bases, sugars, and phosphates by other enzymes
How is active pepsin formed?
- pepsinogen and HCl are secreted into the stomach - the HCl converts some pepsinogen into pepsin - pepsin itself than helps activate more pepsinogen, starting a chain reaction
liver
- removes excess glucose from the blood and converts it into glycogen ( a polysaccharide) which is stored in liver cells - in balancing the storage of glycogen with the release of glucose to the blood, your liver plays a key role in regulating metabolism - given its central location it can modify and detoxify substances absorbed by the digestive tract before the blood carries these materials to the rest of the body
Barry Marshall and Robin experiment (1982)
- reported that infection by an acid- tolerant bacterium called Helicobacter pylori causes ulcers - Marshall proved this by drinking beef soup laced with H. pylori and soon developed gastritis - eventually H. pylori was found to be involved in 90% of ulcer and gastritis cases - awarded 2005 Nobel Prize
The most elaborate adaptations for an herbivorous diet have evolved in the mammals called
- ruminants - ex: cattle, sheep, deer
What prevents gastric juice from digesting away the stomach lining
- secreting pepsin in the inactive form of pepsinogen helps protect the cells of the gastric glands - mucus helps protect the stomach lining from both pepsin and acid - epithelium of the stomach is constantly eroded but new cells replace your stomach lining every three days
GERD
- some people suffer from acid reflux more frequently and severely enough to harm the lining of the esophagus, a condition called GERD (gastroesophageal reflux disease) - to treat GERD, its recommended to stop smoking, avoid alcohol, lose weight, eat small meals, refrain from lying down after eating, and sleep with the head of the bed raised - medication to treat GERD include antacids (reduce stomach acidity) and drugs like Pepcid AC and Prilosec (stop the production of acid) or surgery
Heimlich maneuver needs to be done to dislodge any foreign object in/blocking the throat
- stand behind victim and place arms around their waist - make a fist with one hand and place it against the victim's abdomen with a quick upward thrust - place other hand over fist and press into the victims abdomen with a quick upward thrust - when donee properly the diaphragm is forcibly elevated, pushing air into the trachea - created by Dr. Henry Heimlich in the 1970s
fluid feeders
- suck nutrient rich liquids from a living host - aphids, mosquitoes, hummingbird
4 major types of feeding mechanisms
- suspension - substrate - fluid - bulk
Gastric ulcers, open sores, can develop in the stomach wall
- symptoms: gnawing pain in the upper abdomen, often occurring a few hours after eating - doctors mistakenly thought that excess acid secretion due to psychological stressed caused these, which Barry Marshall and Robin Warren disproved - Gastric ulcers develop when pepsin and hydrochloric acid destroy cells faster than cells can regenerate - usually respond to combination of antibiotics and bismuth (active ingredient in Pesto-Bismol) which eliminates the bacteria and promotes healing
ingestion
- the act of eating - the first stage of food processing
digestion
- the breakdown of food into molecules small enough for the body to absorb - chemical and mechanical
Feces are stored in
- the final portion of the colon, called the rectum, until they can be eliminated - contractions of the colon create the urge to defecate - two rectal sphincters, one voluntary and one involuntary, regulate the opening of the anus - when the voluntary sphincter is relaxed, contractions of the rectum expel feces
Structure and function of the small intestine
- the inner wall of the small intestine has large circular folds with numerous small, finger-like projections called villi - each of the epithelial cells on the surface of a villus has many microscopic projections called microvilli and each villus is surrounded by a network of capillaries - many nutrients including amino acids and sugars pass out of the intestinal epithelium, through the thin walls of the capillaries, and into blood by simple diffusion - other nutrients are pumped against concentration gradients into the epithelial cells - after fatty acids and glycerol are absorbed by an epithelial cell, these building blocks are recombined into fats which are then coated with proteins and transported into lymph vessel and eventually go into the blood - this combination of folds and projections greatly increases the surface area across which nutrients are absorbed - lining of the small intestine has a surface area of roughly 300 m^2
How can bacteria cause ulcers
- the low pH of the stomach kills most microbes but not H. pylori - this species burrows underneath mucus and releases harmful chemicals - growth in this species seems to result in a localized loos of protective mucus and damage to the cells lining the stomach - numerous white blood cells move into the stomach wall to fight the infection and their presence is associated with gastritis
The esophagus is a muscular tube conveying food from the pharynx to the stomach
- the muscles at the top are under voluntary control (swallowing) - then involuntary contractions of smooth muscles (peristalsis) in the rest of the esophagus take over (move bolus into the stomach, then continues when reaches intestines)
How proteins breakdown
- the pancreas and the duodenum produce enzymes that completely dismantle polypeptides into amino acids - enzymes trypsin and chymotrypsin break polypeptides into smaller polypeptides - several types of enzymes called peptidases then split off one amino acid at a time from these small polypeptides
Structure and function of a ruminant
- the stomach of a ruminant has four chambers containing symbiotic microbes - a ruminant such as a cow periodically regurgitates food from the first two chambers and "chews its cud" exposing more plant fibers to its microbes for digestion - the cud is then swallowed and moves to the final stomach chamber where digestion is completed - the cow actually obtains many of its nutrients by digesting the microbes along with the nutrients they produce - the microbes reproduce so rapidly that their number remain stable despite this constant loss
Gastric glands don't secrete acidic gastric juice constantly
- their activity is regulated by a combination of nerve signals and hormones - when you see, smell, or taste food a signal from your brain stimulates your gastric glands - as food arrives in your stomach it stretches the stomach walls and triggers the release of the hormone gastrin - gastrin circulates in the bloodstream returning to the stomach where it stimulates additional secretion of gastric juice
absorption
- when the cells lining the digestive tract take up the products of digestion, small molecules like amino acids and simple sugars - nutrients travel in the blood to body cells where they are used to build a cell's large molecules or are broken down further to provide energy
What prevents gastric juice from being secreted?
- when the stomach contents become too acidic, the release of gastrin is inhibited - lower level of gastrin in the blood cause gastric glands to secrete less gastric juice
gallstones
- within the gallbladder, bile sometimes crystallizes to form these which can cause pain by obstructing the gallbladder of its ducts - often the only cure is surgical removal is the gallbladder which usually has no long-lasting effect on digestion
What is the size of the large intestine?
1.5m (5 feet) long and 5cm in diameter (twice as wide as the small intestine)
each day we consume about __ L of water and secrete __ L of digestive juices into the alimentary canal
2 , 7
What is the pH of gastric juice?
2, acidic enough to dissolve iron nails and kill ,out bacteria and microbes swallowed with food
More than __ % of this water is absorbed back into the blood via osmosis by the small intestine, most of the rest is recovered by the colon
90
Enzymatic digestion of nucleic acids
DNA and RNA -nucleases nucleotides -other enzymes nitrogenous bases, sugars, and phosphates
If you add pepsinogen to a test tube containing protein dissolved in distilled water, not much protein will be digested. What inorganic chemical could you add to the tube to accelerate protein digestion? What effect will it have?
HCl or some other acid will convert inactive pepsinogen to active pepsin which will begin digestion of the protein and also activate more pepsinogen
Astronauts working on the International Space Station have to eat their meals in zero gravity. Under these conditions, how does the food get from the mouth into the stomach?
Peristalsis propels the food along the esophagus without any need for gravity
__________ are the only animals that digest their food entirely in food vacuoles
Sponges
by the time your snack has reached the large intestine most of its nutrients have been _________, is processes whatever remains
absorbed
Structurally the small intestine is well suited for its task of ______________ _______________
absorbing nutrients
Pepsins begins the chemical digestion of proteins and works best under ________ conditions
acidic
Most animals have a(n) ___________ ___________, also called a _____
alimentary canal, gut : a digestive tube extending between two openings, mouth and anus
What is an advantage of an alimentary canal compared to a gastrovascular cavity?
an alimentary canal has specialized regions that can carry out digestion and absorption sequentially
What is happening in the trachea when food "goes down the wrong pipe"?
an incorrectly position epiglottis lets food enter the trachea rather than the esophagus which triggers a strong couch reflex
The ___________ or ___________ of food stimulates three pairs of salivary glands to deliver saliva through the ducts to the oral cavity
anticipation, presence
Herbivores have special changes that house large numbers of ____________ and __________, form of mutualistic symbiosis
bacteria, protists - because animals lack enzymes needed to digest the cellulose in plants - microbes break down cellulose to simple sugars, which the animals then absorb or obtain by digesting microbes - many herbivorous mammals (horses, elephants, koalas) house cellulose-digesting microbes in a large cecum
The liver produces a chemical mixture called
bile
The tongue manipulates food and helps shape it into a ball called a _________
bolus
At the T-shaped junction of the small and large intestines, a sphincter controls passage into a small pouch called the
cecum - compared to other mammals, humans have a small cecum
the main portion of the large intestine is the
colon - one major function of the colon is to complete reabsorption of water that was begun in the small intestine
structure and function of bile
contains bile salts, which act as emulsifiers (detergents) that break fats into small droplets, making the fats more susceptible to attack by digestive enzymes
In an animal that eats more than the body immediately needs, the nutrient molecules are _______________________________.
converted to fat for storage
At what point to food molecules actually enter the body's cells?
during absorption into the epithelial cells lining the villi and the small intestine
The liver converts toxins such as alcohol and other drugs into inactive products that are ...
excreted in the urine - the urine tests for various drugs check for these breakdown products - as liver cells detoxify alcohol or process some over-the-counter and prescription drugs, however they can be damaged - the combination of alcohol and certain drugs, such as acetaminophen, is particularly harmful
The evolution found in most animal species is the chemical digestion of food within the tissues of the body. True or false?
false, chemical digestion of food happens within specialized compartments - these compartments can be within cells (vacuoles) or extracellular
In general herbivores and omnivores have shorter alimentary canals relative to their body size than do carnivores. True or false?
false, they have much longer alimentary canals relative to their body size than do carnivores - plant matter, which contains cell walls, is more difficult to digest than meat; a longer canal provides more time for digestion and more surface area for the absorption of nutrients - ex: intestines of a typical cow are about 7 times longer than yours
If your diet includes too many calories the liver converts the excess into _______, which is stored in your body
fat
Enzymatic digestion of fats
fat globules -biles salts fat droplets -lipase fatty acids and glycerols
What stores and concentrates bile until it is needed in the small intestine?
gallbladder
Animals with relatively simple body plans guest food within a ___________ _____________
gastrovascular cavity
capillaries from the small and large intestines converge into veins that lead into the ___________ ___________ ___________
hepatic portal vein
How may diarrhea result?
if the lining of the colon is irritated -- by a viral or bacterial infection -- the colon is less effective in reclaiming water
The hepatic portal vein
is a large vessel that transports blood to the liver, giving the liver first access to nutrients absorbed in the intestines
name two advantages of a long alimentary canal in herbivores
it provides increased time for the processing of difficult-to-digest plant material and increased surface area for the absorption of nutrients
The liver is between the _______ and the _______
liver, heart
the small intestine is the __________ organ in the alimentary canal
longest, 6m (20 feet) but only 2.5cm wide
What are two types of. digestion that take place in your mouth?
mechanical and chemical breakdown
Name one structure in the oral cavity that participates in mechanical digestion and one that participates in chemical digestion
mechanical: teeth chemical: salivary glands
Most bacteria in the human digestive tract illustrate the principle of __________ ____________
mutualistic symbiosis ex: some intestinal bacteria produces vitamins and regulate the development of the intestinal epithelium, the bacteria in turn obtain a steady supply of nutrients and a stable host environment
The prevention of too much gastric juice being secreted is an example of a __________ feedback system
negative
Red pandas munch large quantities of bamboo, but also eat small mammals, birds, eggs and berries. Name their diet category and type of feeding mechanism.
omnivore, bulk feeder
In contrast to most microbes, the species that causes ulcers thrives in an environment with a very low ______
pH
Enzymatic digestion of proteins
polypeptides -trypsin, chymotrypsin smaller polypeptides -various peptidases amino acids
Enzymatic digestion of carbohydrates
polysaccharides -pancreatic amylase maltose (and other disaccharides) -maltase, sucrase, lactase, etc. monosaccharides
How active pepsin is formed is an example of a ___________ feedback system.
positive
explain why treatment with antibiotics for an extended amount of time may cause vitamin K deficiency
the antibiotics may kill the bacteria that synthesize vitamin K in the colon
What is acid reflux?
the back flow of chyme into the lower end of the esophagus that causes the feeling we call heartburn
The pharynx opens to two passageways
the esophagus and trachea
Between which two body systems does the liver act as a go between?
the liver processes blood received from the digestive system and releases into the circulatory system
During the Heimlich maneuver what causes food to dislodge from the throat?
the pressure of air being expelled from the lungs
What organ is the master organ for chemical digestion and for absorption of nutrients into the bloodstream?
the small intestine
Most animals eat outside of there standard diets. True or false?
true, ex: deer are mainly herbivores but will consume bird eggs sometimes
Interior surface of the stomach wall is highly folded and is dotted with pits leading to ________ _________ ________
tubular gastric glands
elimination
undigested material passing out of the digestive system
How may constipation occur?
when peristalsis moves the feces along too slowly; the solon reabsorbs too much water, and the feces become too compacted - often occurs from a diet that does not include enough plant fiber
