Download Understanding Digestion: Mechanical and Chemical Processes and more Schemes and Mind Maps Human Biology in PDF only on Docsity!
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..! .,,.-!n14;: ,,gl$*1^ i: i"+ .$ :-: '-'l-.^ ii:;-;..-.. (^) - t" k' (^) Ifl-:t'ff'E:1'rl I-.-Y: ldentify As^ you^ read, undertine the ways that your^ body uses n utrients.
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The Stomach
6 lnfer The stomach tining is made up of deep muscutar
grooves. (^) How do you (^) thinl< these structures help the stomach to breal< down food? Sa SA ln (^) t- grir ln th are I ffiFrcm$" $s (^) &fu* #$gms€Erus*= sgss€+=rceH Your cells need a lot of energy for their daily activities. Cells
use nutrients, which are substances in^ food,^ for^ energy,^ growth,
maintenance, and repair.^ The^ digestive system^ breaks^ down the food
you eat into nutrients that can be used as building materials^ and
that can provide^ energy^ for^ cells. The digestive system interacts rvith other body^ systems^ to obtain and use^ energy^ from^ food. Blood,^ part^ of the^ circulatory
system, transports nutrients to other tissues. In order to extract
energy from nutrients,^ cells need oxygen.^ The respiratory^ system is responsible for obtaining this oxygen from the environment. The nerr.ous system^ controls^ and regulates^ the^ functioning^ of the digestive system. W$#mH #Fjffi €"fu E+-s+^ Epsg"Btrs #,$^ €€$g*sE:E+src.i- Digestion is the process of breaking down^ food into^ a^ form that can pass from the digestive system into the bloodstream. There are two types of digestion: mechanical and chemical. 48 Unit^ l^ Human Body Systems -T
.lechanical digestion is the breaking, crushing, and mashing of
-.od. Chewing^ is^ a type of mechanical digestion. Chewing creates .nrall pieces (^) of food that are easier to (^) swallow and digest than large :Leces are. Mechanical digestion increases the surface (^) area of food
. (^) .,r the action of chemical digestion.
-hernical digestion^ is^ the^ process^ in which^ large^ molecules^ of
,-,od are broken down into smaller molecules so that they can pass
.rto the bloodstream. An enzyme (EN.zym) is a chemical that the
-.odr. uses^ to break down^ large^ molecules into smaller molecules. -nzymes (^) act like (^) chemical scissors. They'tut (^) up" large molecules .nto smaller pieces. Mechanical digestion breaks up food (^) and -ncreases surface area so that enzymes can (^) break nutrients into
.r-naller molecules. Without mechanical digestion, chemical
Jigestion (^) would take days instead of hours!
7 Categorize Decide whether (^) each of these steps in (^) digestion is an example of mechanicat (^) digestion or chemical digestion. (^) Then put (^) a checl< in (^) the correct box.
In your mouth, teeth grind food. ffmechanicat
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Salivary glands^ release a tiquid called saliva, which helps to break food down.
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ffchemicat ln the stomach, (^) muscles contract to grind food into (^) a pulpy mixture.
Mmechanicat
n chemicat
In (^) the smal[ intestine, most nutrients are broken down (^) by enzymes.
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t .# Lesson 4 The Digestive and Excretory S@'ems (^49)
The stomach is a muscular bag that crushes food and contains acids
and enzymes for^ killing^ bacteria^ and^ breaking down proteins. The
walls of the stomach contain layers of muscle so the stomach walls
can churn and mix food. This is the final^ step^ in^ the process^ of
mechanical digestion of the food you^ have eaten. Tiny glands in the stomach release^ a^ special^ type of^ acid^ that
is so harsh that it kills most bacteria that might be swallowed with
your food. A coating of thick mucus protects the^ stomach^ lining
from the acid. The glands in the stomach also release enzymes that begin the process of breaking down proteins. The^ enzymes^ that
break down proteins^ can^ function only in^ the acidic^ environment^ of
the stomach.
After a few^ hours^ in^ the^ stomach,^ food^ is
reduced to a soupy mixture called chyme (kym). (^) Chyme leaves the stomach and moves into the small intestine. The smatl intestine is^ a muscular tube where most chemical digestion takes place and most nutrients are absorbed.
After food moves^ through^ the
small intestine, it moves to the large intestine. In^ the^ large intestine, water and nutrients are absorbed. Most of the solid material remaining is waste, which is compacted and stored.
Eventually it is eliminated from
the body.
Leqson 4 The Digestive and Excretory Systems 51
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The digestion of nutrients in^ the small intestine^ takes place^ with
the help of three organs that attach to the small intestine. These organs are the pancreas,liver,^ and gall bladder. The pancreas (PANG.kree.uhz)^ makes fluids that break down
eyery type of material found in foods: proteins, carbohydrates, fats,
and nucleic acids. The tiver makes and releases a mixture called bile that is then stored in the gail bladder. Bile breaks up iarge fat droplets into very small fat droplets.
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After nutrients are broken down, they are absorbed into the bloodstream and used by the body's cells. The inside wall of the small intestine
has three features that allorv it to absorb nutrients
efficiently: folds, villi, and microvilli.
First, the walls of the small intestine have many folds. These folds increase the surface area inside the intestine wall, creating more room for nutrients to be absorbed. Each fold is
covered with tiny fingerlike projections called
villi (YIL.eye). In turn, the villi are covered with
projections called microvilli. Microvilli increase
the surface area of the villi. Villi contain blood
and lymph vessels that absorb nutrients from
food (^) as it passes (^) through the small intestine.
T'he large intestine removes water from mostly- digested food,^ absorbs vitamins,^ and^ turns food
waste into semi-solid waste called feces.
Some parts of food,^ such as the^ cell^ walls^ of
plants, cannot be absorbed by the body. Bacteria live in the large intestine that feed off of this undigested food. The bacteria produce vitamins that are absorbed by the large intestine along
with most of the water in the undigested food.
The rectum is the last part of the large
intestine. The rectum stores feces until it can
be expelled. Feces pass to the outside of the body through an opening called the anus.It
takes about 24 hours for a meal to make the full
journey through a person's digestive system.
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10 Relate How is the structure and function of this sponge similar to that of the smatt intestine? *rt r *-l :lc
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Small intestine
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This (^) natvral sTonge has many c?evattet,which incrLase its (^) sur{ace area.
ffi.^ e# ;#r:' Vlli^ eoverthe sur{ace o{ the^ small inferline.
