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Biology 12
The Human Digestive System Notes
A. Digestive System
 Digestion occurs within the ______________ which is a long tube
beginning at the _______ and ending at the _________
B. Functions of Digestive System

 Digest food to small molecules that can cross plasma membranes

 Eliminate indigestible wastes
C. Parts of the Digestive System
1. Mouth

 Breaks food down into smaller pieces with help of teeth to facilitate
swallowing


 Food and saliva rolled into ball called ______ with help of tongue
 Food is tasted using ______ ______ on tongue

 Taste also determined by olfactory (smell) receptors in nose (IOlfactory nerve)
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2. Teeth


 ___________ (hardest substance in body) covers crown
 Underneath enamel is bone-like ________ and inner pulp containing
nerves and blood vessels
 ____________ _____________ between root and gum lines tooth
socket and holds tooth in place
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Diseases of teeth
 ___________________—cavities caused by bacteria that metabolize
sugars and produce acids
 _____________—inflammation of gums that can lead to...
 __________________—infection of the periodontal ligaments and
loosening of the teeth
3. Roof of Mouth (Hard Palate)

 Consists of the anterior _____ _________ made of several hard bones
 Also consists of the posterior ______ ________ mostly made of muscle
 Soft palate ends in the ___________
4. Tonsils


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5. Salivary Glands





______ ________—sides of face below and in front of ears
____________ _________—beneath tongue
____________ ________—beneath tongue on floor of mouth
Glands release saliva through ducts in the mouth
Enzyme in saliva (_________________) begins digestion of starch
6. Pharynx

 Divided into ____________, _____________ and _______________
 Muscular tube


 In swallowing, tongue pushes bolus back to ________ → soft palate
moves back to block off _____________ → epiglottis (flap covering
glottis—i.e. opening to the larynx) blocks glottis → bolus enters
_________________
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Cross Section of Upper Digestive System
7. Esophagus

 Transports bolus from pharynx to stomach
 Accomplishes this through _____________—rhythmic contractions of
muscles lining esophagus
 Esophagus made up of different layers:
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Esophageal Layers:
Layers of the digestive tract
(i)
Mucosa

 epithelial lining of the inner part of esophagus

 in other parts of digestive system, find digestive glands
located in this layer
(ii)
Submucosa

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(iii) Muscularis mucosa

(iv) Serosa

 not found in esophagus!
 Esophagus is covered by a loose connective tissue layer
called _____________ layer
 Band of circular muscle at base of esophagus called ________ sphincter
acts as valve and prevents backflow of stomach acids into esophagus
 Heartburn
 ___________ results from contraction of abdominal muscles and
diaphragm to squeeze stomach contents up into esophagus and
through mouth
8. Stomach

 Has deep folds (________) that disappear as stomach fills (≈ 2L)
 Functions:
 Some absorption occurs in the stomach such as alcohol but no other
food substances
 Inner walls of stomach lined with columnar epithelial cells containing
___________ ________
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Diagram of stomach:
 Gastric pits lead to gastric glands which secrete the following:
a) Pepsin—
b) ______________ acid—strong acid that kills bacteria, breaks down
connective tissue in meat and activates pepsin (produced by
___________ cells)
c) _____ secreted by ________ cells that protect stomach lining
 The mixture of gastric juices and food is called ________

 Chyme leaves stomach via the pyloric sphincter and enters the
duodenum of the small intestine

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Ulcers:

 Caused by stress, oversecretion of gastric juice, bacterium Helicobacter
pylori
9. Small Intestine
 4-6 m long tube with a small diameter (2.5 cm) relative to large
intestine
 Divided into three sections—the ________, __________ & _______

 The last two sections are made of the jejunum and ileum respectively
and form the largest portion of the small intestine (about 6 m in length)
 ________________ receives chemicals from ducts coming from
pancreas and liver

Functions of the small intestine:
a)
b) Absorption of products of digestion
c)
Wall of small intestine contains folds analogous to the gastric rugae in the
stomach. In the small intestine these folds are called _________ ______ or
_________ _________. These folds contain smaller folds or finger-like
projections called ______ which:
a)
b)
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c) Layer of columnar epithelial cells lining villus contain __________
that further increase the surface area for final digestion and
absorption of nutrients
d) Microvilli give cells a fuzzy brush look called a _______________
e)
f) ____________ (small vessel containing lymph) found in villi returns
lymph fluid back to veins after absorbing fats
Diagram of internal anatomy of small intestine:
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Diagram of an intestinal villus with accompanying vessels:
10. Regulation of Digestive Secretions

 This led to the idea that the _________ ________ was involved in
digestion→ the thought of food caused the nervous system to
stimulate secretion of digestive juices
 __________ also cause secretion of digestive juices
For example:
a) In response to protein, stomach produces _________ hormone →
b) Cells in the wall of the duodenum produce hormone __________ in
response to acidic chyme in duodenum→ secretin enters blood
causing pancreas to increase secretions of pancreatic juices
containing bicarbonate;
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secretin also stimulates bile production by liver as well as slowing
down stomach motility and inhibiting gastric juice secretions which
slow down digestion in stomach and stomach emptying.
c) _________ (cholecystokinin) is also released by cells lining duodenal
wall in response to protein and fat which causes liver to increase
output of bile and for gall bladder to contract; CCK also increases
the secretion of pancreatic enzyme into the duodenum to facilitate
digestion of fats, proteins and carbohydrates.
d) Duodenal wall also produces ______ (gastric inhibitory peptide)
which works opposite to gastrin; GIP also stimulates insulin
secretion from pancreas. GIP released when glucose enter
duodenum
11. Large Intestine

 Diameter of 6.5 cm
 Function:
 Made up of cecum, colon, rectum and anal canal
Diagram of Large Intestine:
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 Cecum contains ________ _________—function unkown

 If allowed to burst →can lead to infection of abdominal lining
and peritonitis—this can result in death

 The colon can be divided into the following parts: ascending
colon, transverse, descending colon and sigmoid colon—last 20
cm that connect to rectum)
Nervous Control of Defecation

 Can also be under conscious control via brain

 Efferent nerves from spinal cord send messages to rectal muscles to
contract and for anal sphincter muscles to relax

 Result is defecation

 Brown colour of feces due to bacterial breakdown of bilirubin
(component of heme)

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Diseases of Colon
Polyps:

 Can be benign or malignant

 Diets rich in fiber decrease the likelihood of colon cancer since they
facilitate the passage of material in colon and create bulk to decrease
concentration of fats
Diarrhea

 If due to infection, irritation of intestinal wall occurs and this reduces
reabsorption of water→ facilitates the flushing out of contaminants

 Prolonged diarrhea is dangerous as loss of water and electrolytes
occurs → can lead to heart problems
Constipation

 Variety of causes: e.g. training bowels to eliminate feces less
frequently or too little roughage among other things

 Prolonged constipation can result in haemorrhoids → inflamed
blood vessels surrounding anus
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Accessory Organs of the Digestive System
12. Pancreas

 Has both endocrine and exocrine role

 Enzymes are used for digestion of fats, carbohydrates and proteins

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13. Liver

 Internally, liver also made up of many lobules

 At each vertex of the lobule is found a triad of vessels:
a) Branch of __________________________ (80% of blood supply to liver
lobules: brings in blood from digestive system)
b) Branch of ___________________ (20% of oxygenated blood from heart)
Note: both above mix in sinusoids where interact with cells of liver →
transported to central vein which joins hepatic vein and then to inferior
vena cava to heart
c) Branch of ________ _______ (collects bile from liver cells and carries it to
gall bladder)
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Drawing of Liver Lobule:
Functions of Liver:


 Makes plasma proteins (albumin, fibrinogen, etc.)

 Converts glycogen to glucose between meals

 Converts haemoglobin from worn out rbc’s to ____________ and
____________ which are excreted with bile
 Produces bile →
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Diseases of Liver
1. Hepatitis

 Can be viral (Hep A, B, C )

 Can also be caused by toxins
2. Cirrhosis

 Get much fatty tissue in liver

 Scar tissue is ineffective in liver function
3. Jaundice
 Results from high concentrations of __________ in blood which is
deposited in skin and whites of eyes
 Can result from ____________ jaundice—rbc’s broken down in large
quantities (sickle cell anemia, malaria, etc.)
 Can result from ____________ jaundice—bile ducts are blocked or liver
cells damaged; can result from gallstones
14. Gallbladder

 Stores excess bile produced by liver

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Drawing of biliary system:
15. Digestive Enzymes

 Use water to break apart lipids, proteins and carbohydrates

1. Mouth
a. Salivary amylase

 Breaks down starch to ________
Note: only glucose can be absorbed by intestine
___________________________________________
2. Stomach
a. HCl


____________________________________________
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b. Pepsinogen/Pepsin

 Converted to pepsin by HCl in stomach

 Peptides are smaller bits of proteins
Note: only amino acids can be absorbed by intestine
______________________________________
3. Pancreatic Enzymes

a. Sodium bicarbonate (NaHCO3)

b. Pancreatic amylase

___________________________________
c. Trypsin

 Secreted by pancreas as trypsinogen but converted to trypsin in
duodenum
____________________________________
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d. Lipase

 These compounds will rejoin again in microvilli to become fats and then
enter lacteals
_______________________________________
4. Duodenal Enzymes
a. Peptidases

 Amino acids are small enough to enter cells in small intestine and then
to capillaries in the villi
_______________________________________
b. Maltase

 Glucose small enough to enter villi and then to capillaries
________________________________________
c. Lactase

 Lactose intolerant individuals lack this enzyme

_________________________________________
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Digestion Experiment on page 213
 Notice how the right substrate, the right enzyme and right conditions (pH)
must be present for digestion to occur
 See table 12.2 on major digestive enzymes and the conditions they need
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