Digestion Flashcards
1
Q
What is digestion?
A
the mechanical & chemical breaking down of ingested food into particles, then into molecules small enough to move through epithelial cells and into the internal enviornment
2
Q
What is absorption?
A
the movement of digested nutrients from the gut lumen into the blood or lymph, which distributes them through the body
3
Q
What is elimination?
A
the expulsion of indigestible residues from the body
4
Q
What happens during the digestion process overall?
A
- food is mechanically and chemically broken down into these molecules during digestion by using amino acids, fatty acids, & glucose, after which they can be taken up by body cells through the separate process of absorption
- during digestion, proteins are broken down into amino acids, carbs into glucose, fat to glycerol & fatty acids, nucleic acids to nucleotides
- food travels in one-way from mouth to esophagus to stomach o small intestine to large intestine to anus
- digestion is an extracellular process; it occurs within the gut(a tube that runs from mouth to anus)
5
Q
Describe the mouth
A
- where digestion begins
- receives food, chews it up, moistens it, and starts to digest any starch in the food
- divided into an anterior hard palate and a posterior soft palate, and the end of the soft palate is the uvula which is the thing that hangs down in the back of the throat
- the sense of hunger is due to combined sensations of smelling and tasting of food; olfactory(scent receptors) in the nose and taste buds on the tongue, remind you that you’re hungry
6
Q
What are the three salivary glands and what are their functions?
A
- the 3 salivary glands are parotoid(below ears), sublingual(below tongue), and submandibular(under lower jaw)
- saliva moistens and lubricates food
- saliva contains water, mucus, and salivary amylase, a hydrolytic enzyme that breaks down starch in the pressure of water
- starch is broken down into maltose which is later broken down to glucose in the intestine
7
Q
Describe the swallowing process
A
- after food has been chewed, it’s then passed through the back of the mouth when you swallow
- it first enters the pharynx(which is the region between mouth & esophagus where swallowing takes place
- swallowing is a reflex action(requires no conscious thought)
- in order to prevent food from going down the air passages, the soft palate moves back to cover openings to nose
- trachea moves up and is covered by the epligottis
- food then has to go down the esophagus
8
Q
Describe the esophagus
A
- a long muscular tube that extends from pharynx to stomach and is made of several types of tissue
- the inner surface is lined with mucus membranes, and is attached by connective tissue to a layer of smooth muscle containing both circular and longitudinal muscle
- food moves through the esophagus through peristalsis(contractions of the esophagus muscles)
- when food reaches the end of the esophagus, it arrives at the cardiac sphincter connecting to the stomach
9
Q
What is the cardiac sphincter?
A
- function like valves
- made of muscles that encircle tubes and they open them when they relax and close them when they contract
- the sphincter usually prevents food from moving up out of stomach but when vomiting occurs, a reverse peristaltic wave causes the sphincter to relax and the contents of the stomach are propelled outward
10
Q
Describe the stomach
A
- the stomach is a thick-walled, J-shaped organ that lies on the left side of the body beneath the diaphragm
- there are 3 layers of muscle contract to churn and mix its contents
- the mucus lining of the stomach contains gastric glands which produce gastric juice which contains pepsinogen and HCl; when the two combined, pepsinogen forms pepsin, a hydrolytic enzyme that breaks down proteins into peptides
- HCl gives stomach a pH of 2, and that kills bacteria in food and helps break it down
- inner wall of stomach is protected by a thick layer of mucus secreted by mucosal cells to prevent the stomach from digesting itself
- after 2-6 hours, the food has been turned into a semi-liquid food mass called acid chyme, and the stomach empties into the first part of the small intestine; this emptying is controlled by the pyloric sphincter at the bottom of the stomach
11
Q
What are stomach ulcers?
A
- if HCl does penetrate, pepsin starts to digest the stomach lining which forms an ulcer(an open sore on the wall of the stomach)
- too much gastric juice can cause ulcers, as can too much nervous stimulation(stress), since this will cause over-secretion of gastric juices
- however, the #1 cause of ulcer is actually a bacterial infection that impairs the ability of cells to produce mucus
12
Q
Describe the small intestines
A
- most digestion and absorption of nutrients occur in the small intestine
- divided into 3 zones: duodenum, jejunum, and ilium
- about 6m long
- long with convoluted walls to increase surface area
- lined with millions of interstitial glands that produce juices containing enzymes that finish digesting protein & starch
- digestive enzymes secreted from the interstitial glands include peptidase to digest peptides to amino acids, maltase to digest maltose to glucose, lactase to digest lactose, etc.
13
Q
What is the function of duodenum?
A
- plays a major role in digestion
- secretions of the duodenum itself also breaks down other nutrients(peptides to amino acids, maltose to glucose, sucrose to glucose & fructose, and lactose to glucose)
- bile sent from the gall bladder emulsifies fat to fat droplets
- secretions from pancreas also arrive at the duodenum; they contain trypsin which breaks down proteins into peptides, pancreatic amylase which digests starch to maltose, and lipase which breaks lipids to glycerol and fatty acids
14
Q
What are villi?
A
- further increase the surface area of the small intestines; has finger-like shape and have microvilli to further increase the surface area so nutrients are absorbed easily
- interstitial glands are at the base of each villi
- lined with columnar cells coated microvilli
- each villi contains blood vessels and lymph vessels(lacteal)
- absorption of nutrients takes place across the wall of each villu; this can happen passively or actively
- the blood vessels from the villi in the small intestine merge to form the hepatic portal vein which leads to the liver
- contain lots of mitochondria to facilitate the active uptake of digested materials; otherwise there are pinocytotic vesicles to take material away from the lumen of the intestine to the villi cells
15
Q
Describe the large intestine
A
- consists of the colon & rectum; the opening of rectum is called the anus
- the colon has 3 parts: ascending, transverse, and descending
- main function of large intestine is the reabsorption of water from indegestible food matter(feces) and the absorption of certain vitamins
- although feces contain bile pigments, heavy metals, and E. coli(parasites), E.coli breaks down some indigestible food, and in the process produce some vitamins, amino acids, and other growth factors, that are in turn absorbed by the axon
