Digestion Flashcards
Why do animals eat?
As heterotrophs, they eat for energy.
Why is food broken down as it goes through the body?
Food is too bulky to be absorbed directly by the body’s cells
Digestion
The process of breaking down food into molecules that are small enough to be absorbed
Mechanical digestion
The physical breakdown of food through non-chemical processes
Chemical digestion
The process of breaking down food with enzymes and chemicals
Describe intracellular digestion
Food particle is enclosed by cell membrane through phagocytosis, digestion of food takes place in the digestive vacuole, products of digestion are absorbed into the cell, waste products are removed by exocytosis
Sponges are … (and what 3 cells)
Suspension feeders who use intracellular digestion exclusively. They have no mouth or gut. choanocytes, archaeocytes, pinacocytes
Extracellular digestion process
Digestion occurs within gut and not within cells
What does extracellular digestion require?
A digestive tract and cells that secrete digestive enzymes into the gut
Advantages of extracellular digestion?
Larger food masses can be ingested, cells lining the gut can become specialized for secreting particular enzymes or for absorption of nutrients
Two types of digestive tracts
alimentary canal - mouth and anus (2 separate openings), gastrovascular cavity- mouth and anus (1 opening)
Most animals with an incomplete gut use what form of digestion?
Intracellular and extracellular
Disadvantage of an incomplete gut?
Newly ingested food is mixed with previous ingested food and waste
Alimentary canal allows for
continuous and sequential processing of food, regional specialization of gut
What animals have a complete gut?
vertebrates and other chordates
Region 1 name and funtion
Region of reception - mouthparts for mechanical digestion such as jaws with teeth or beaks, mandibles. Mouth (buccal) cavity with salivary glands and tongues, pharynx
What has a tongue?
vertebrates only
Salivary glands function
Lubrication of food, secrete toxins to incapacitate prey, secrete salivary amylase (only in primate mammals, herbivorous molluscs, and some insects
Functions of tongue
Mixing food with salivary gland secretion, capturing prey, detection of prey or conspecifics
What animals use tongue for prey capture?
Frogs, salamanders, chameleons, anteaters, woodpeckers
Tongues are used for chemoreception in all snakes and lizards to ____
detect prey, detect conspecifics (see if they are of the same species)
Pharynx extends from what to what
Back of buccal cavity to the beginning of the esophagus
In terrestrial vertebrates, the pharynx is what?
the passages for air and food cross
Describe how a food bolus travels through the pharynx via (what is the food reflex?)
Swallowing reflex. Soft palate is pressed back against the pharynx to close the nasopharynx off, then the epiglottis tips down to close the trachea, and food travels downward via peristalsis and the epiglottis raises again so the trachea can reopen
Region 2 name and function
Region of conduction and storage. Esophagus serves in conduction, crop serves for storage, peristalsis propels food toward stomach
What layer of muscle is responsible for peristalsis mainly?
Inner circular muscles
What allows food to enter the stomach?
The cardiac sphincter relaxes and allows food in.
Function of the crop?
Food storage prior to the initiation of chemical digestion?
Avian crop (5)
Present in most birds,
allows for excess food storage temporarily,
allows for ingestion of large quantities of abundant food,
allows for parent to store and regurgitate food for younglings,
well-developed in seed and grain-eating species to allow food to be softened prior to chemical digestion in stomach
Bird stomach is called ____
proventriculus
The gizzard is also known as the
ventriculus
Region 3 name and function
Region of Early digestion and storage (and grinding),
Stomach serves in early digestion of proteins
Gizzard is not found in all animals, but it serves for grinding of food for it to absorbed
What juice does the stomach produce and what are the 3 cells and their function? (4)
Gastric juice
parietal cells secrete hydrochloric acid and look like crab claws
Chief cells secrete pepsinogen which reacts with HCl to produce pepsin (which breaks down proteins) and they are located near the base of the structure
Surface mucous cells produce mucus that coats the stomach lining so that the hydrochloric acid does not break down stomach lining and are located near the top of the structure
Rugae
Smooth muscle folds in the stomach that churn the food
What sphincter releases food to the duodenum?
Pyloric sphincter
Why doesn’t absorption of nutrients occur in the stomach?
It has not been digested enough
Region 4
Region of terminal digestion and absorption
Duodenum function
Duodenum receives bile from the liver and pancreatic juice to break down food.
Bile
A fat emulsifier, which increases the surface area of fat
Pancreatic juice composition and function of each enzyme (6)
Introduced in the duodenum
3 proteases
Trypsin, chymotrypsin, carboxypeptidase - break down smaller proteins into even smaller proteins
Pancreatic Lipase - turns fats into fatty acids and glycerol which can then be absorbed
Pancreatic amylase - turns starch into maltose
Nucleases turn DNA/RNA into nucleotides which can then be absorbed
Gastric bypass surgery
Staples are used to permanently close off part of the stomach and this small pouch is attached directly to the jejunum.
As a result this bypasses a large part of the stomach and the entire duodenum.
How does gastric bypass result in weight loss?
The stomach is smaller, so the feeling of hunger will be satiated by less food. Also, food is not digested as entirely by the time it reaches the region of terminal digestion and absorption.
Enzymes secreted by the epithelial cells lining the small intestine (5)
Aminopeptidase - turns even smaller proteins into amino acids, which can be absorbed
Maltase - turns maltose into glucose, which can be absorbed
Sucrase - turns sucrose into fructose and glucose, which can both be absorbed
Lactase - turns lactose into galactose and glucose, which can be absorbed
Alkaline phosphatase - breaks down a variety of phosphate compounds, e.g ATP, which can be absorbed
How has the surface area adapted? (5)
Increased length
Coiling
Folding - spiral folds (sharks) or longitudinal folds (lampreys)
Villi: tissue-level fingerlike projections from epithelial tissue
Microvilli : Cellular-level fingerlike projections from the cell membrane
Surface area of a cylinder is equal to what equation
2 pi r squared + 2 pi r h
Mammalian small intestine is very ___ and shows ____
small; extensive coiling
Sharks and rays increase the surface area available for absorption through___
Spiral valves in their intestines
Microvilli and villi increase the surface area more than ____ compared to a smooth cylinder the same diameter
1000 ; the surface area of the inner lining of the small intestine is that of a football field (4500 square meters)
Fatty acids and glycerol are transported from the lumen across the cell membrane into epithelial tissue via ___
simple diffusion
Describe how simple sugars and amino acids are transported from the lumen across the cell membrane of epithelial tissue.
If concentration in lumen is higher, then it is done via facilitated diffusion via protein channels down the concentration gradient. If the concentration in the lumen is lower, then it is done via active transport via protein channels against the concentration gradient.
Where do fats go from the epithelial cells of the small intestine?
Into lacteals, a part of the lymphatic system. This is done via simple diffusion. Fats pass through the thoracic duct into the circulatory system.
Where do amino acids and simple sugars go from the epithelial cells of the small intestine?
They diffuse into blood capillaries and enter the circulatory system via facilitated diffusion down the concentration gradient.
Region 5 name
Region of water absorption and concentration of solids
Large intestine is the site of (3)
reabsorption of water
reabsorption of salts
considerable microbial activity (bacteria comprises 1/3 of dry weight of feces, bacteria degrade organic wastes, bacteria synthsize vitamin k and b, which are absorbed)
Specialization of herbivores (3)
Herbivores have longer guts
Herbivores cannot digest cellulose directly,
which leads to a direct relationship with microbes that can produce cellulase
Frogs in relation to digestion (4)
Most tadpoles are herbivorous and eat primarily algae.
After metamorphosis, the frogs shift to a carnivorous diet consuming insects
Dietary shift is reflected in differences between the digestive tracts of tadpoles and frogs.
Their gut goes from a long spiral in a tadpole to a tube that does not take up as much space.
Three major strategies of herbivorous animals (3)
Large, 4-chambered stomachs, coupled with rumination - in cows, deer, bison
Large multi-chambered stomachs, usually without rumination - sloth, some marsupials
Enlarged caecum - Seen in herbivorous non-ruminants, such as horses, rabbits, rodents
4 chambers and their function in rumination species
Rumen - house microbes and digest cellulose
Reticulum - House microbes and digest cellulose
Omasum - absorption of water and minerals
Abomasum - Functions in early digestion of proteins
Rumination
Chewing the cud, which is partly digested food from the first stomach of ruminants to the mouth for further chewing
Large multi-chambered stomachs without rumination resemble ____
The stomach of ruminants
Enlarged caecum strategy (2)
Enhances digestion of plant matter
Coprophagy - Keeps balance of flora in the gut as well as introduces another source of nutrients that are created in the lower large intestine and passed in the dung
Is the ruminant herbivore or non-ruminant herbivore more efficient?
The nonruminant herbivore is more efficient since their strategy does not rely on regurgitation of cud and simply passes through their gut. The enlarged cecum strategy is inefficient as it requires coprophagy but is still more efficient than ruminant behaviors.
