Ms. Ghtaura 1

The Digestive System

Human Biology

Ms. Ghtaura 2

What’s happening?• INGESTION:

– the process of taking a (food) into the or

• DIGESTION: – the and breaking down of ingested food into

particles, then into small enough to move through cells and into the environment.

• ABSORPTION: – the passage of digested nutrients from the gut lumen into the blood or lymph,

which distributes them through the body.

• ELIMINATION: – the of residues from the body.

Ms. Ghtaura 3

physical breakdown

Ms. Ghtaura 4

• 3 salivary glands in the mouth– Parotid glands– Sublingual glands– Submandibular glands

• Mouth food• Tongue: has taste

buds so we can enjoy our food

• Teeth: for chewing or so

food is convenient for

.– After mastication,

our food form into a mass called

Ms. Ghtaura 5

• Pharynx – region the mouth and the esophagus made of a long tube

• Epiglottis – flap of elastic cartilage tissue attached to the entrance of the

– Glottis is the opening to the larynx

• Esophagus – bolus is passed into this tube from the

to stomach

Ms. Ghtaura 6

Swallowing and Peristalsis

Ms. Ghtaura 7

Stomach• Stomach – a thick walled, J-

shaped organ which food until ready to enter the

• Entrance of food from the esophagus to stomach is marked by sphincter– Sphincter – muscles that

encircle tubes and act as valves (saloon doors)

• Churning – muscular walls of the stomach , mixing the food with juice

Ms. Ghtaura 8

peristalsis happens throughout the gut

• Chemical digestion is aiding in the overall digestion of food as discussed in the next section

• As this is happening, food is being pushed along the digestive track (small and large intestine) rhythmic muscle movements

• The bolus leaves the stomach in the form of ‘chyme’

• Chyme is squeezed through the pyloric sphincter to the duodenum of the small intestine

Ms. Ghtaura 9

chemical breakdown

Ms. Ghtaura 10

Salvia• First chemical breakdown

occurs in the mouth as food turns into bolus

• 3 salivary glands in the mouth–

glands–

glands–

glands• Salivary glands are exocrine glands that produce (neutral pH)• Saliva is made up of an enzyme called and water• Amylase breaks down polysaccharides into

(disaccharide)

Salivary amylase

+ H20

Ms. Ghtaura 11

Stomach• The stomach contains millions of gastric glands which make gastric juices• Gastric juice is made up of pepsinogen, HCl and mucus.• A think layer of mucus protects the lining of the stomach from HCl

– If the HCl penetrates this lining an ulcer can result• HCl in the stomach has two primary roles:

– Activates pepsinogen into pepsin (a protease) • This happens since active pepsin may destroy proteins in the gastric cells, so its important

that it remains in the form on pepsinogen until it is secreted out of the gastric cells

– Keeps the environment of the stomach at pH 2 to kill bacteria present in most food

• Pepsin breaks down proteins in the following manner:

Pepsin Protein + H20 Peptides

Ms. Ghtaura 12

In the Duodenum

• As the chyme is being pushed into the duodenum, pancreatic juices (pH 7.5 to 8.5), and bile are also being secreted into the

• Hence, the duodenum is the site for many chemical breakdowns during digestion

Ms. Ghtaura 13

Liver

bile salts

Fat Fat Droplets

• Largest gland in the body• Produces (which contains

bilirubin and bile salts)• Bile is stored in the • Bile fat into fat

droplets in the duodenum• Fat droplets have a larger surface

area available to be further

Ms. Ghtaura 14

Pancreas

• Is an organ in the digestive system• Is an and

gland• Secretes the enzymes: ,

, and • These enzymes are produced in

the pancreas and are released into the duodenum as pancreatic juice

• Pancreatic juice is also known to contain basic sodium bicarbonate ( ) which functions in:– acidic chyme– Providing a basic pH for optimal

pancreatic enzyme function

Ms. Ghtaura 15

Pancreas• Pancreatic amylase breaks down

polysaccharides into molecules

• Since the salivary amylase may have not this breakdown in the mouth (depends on how long you chew your food) the pancreatic amylase makes up for this by completing the same digestion in the .

Pancreatic amylase

polysaccharide + H20 disaccharides

Ms. Ghtaura 16

Pancreas• Pancreatic trypsin (

) also breaks down proteins into

• Since the pepsin may have not completed this breakdown in the

the pancreatic trypsin makes up for this by completing the same digestion in the .

• Trypsin exists in the pancreatic cells as trypsinogen. Upon being release into the duodenum, it is activated into trypsin so it can break down proteins

Pancreatic trypsin

+ H20

Ms. Ghtaura 17

Pancreas• Pancreatic lipase further breaks

down fat • Bile helps break down fats into

fat , which exposes more surface area for to act on

• Each triglyceride molecule (neutral fat) in a fat droplet is then broken down into 3 fatty acids and a 1 glycerol molecule

• These broken down triglycerides are small enough to be

into the small intestine.

Pancreatic lipase

+ H20 +

Ms. Ghtaura 18

Small Intestine• Primary functions:

– absorption of nutrients into the and systems.– Further chemical breakdown of proteins and carbohydrates

• Named for its diameter (though it is longer in length than the large intestine)

• The inside of the small intestine has like projections called which increase the surface area for of nutrients

• Each villus is lined with epithelial cells, which have microvilli structures on their

Ms. Ghtaura 19

Small Intestine• The small intestine is made up of the:

– Duodenum – – Jejunum – – Ileum –

• Chemical break down continues in the duodenum while the rest of the small intestine is involved primarily in

Ms. Ghtaura 20

Small intestine

Light micrograph of small intestine

• Peptidases are also a type of which

complete the digestion of proteins to

• Peptidases are found in the cell membrane of the epithelial cells lining the

• As the cross into cells, the break them down into

• Then, the amino acids enter the cells

+ H20 acids peptidase

Ms. Ghtaura 21

Small intestine

Light micrograph of small intestine

• Maltase is an enzyme which completes the digestion of maltose into to glucose molecules

• Maltases are found in the cell membrane of the cells lining the

• As the maltose molecules try to cross into , the maltase breaks them down into two glucose

• Glucose then enters the cells

+ H20 2 maltase

Ms. Ghtaura 22

Monosaccharides form disaccharides

There are many enzymes that break down disaccharides into monosaccharaides other than maltase. One example is , which breaks down lactose into galactose and glucose

Ms. Ghtaura 23

Absorption• Glucose and amino acids are directly absorbed into the blood capillaries and

eventually the blood stream• acids and reforms into neutral fats upon entering the epithelial

cells and then enter the

Ms. Ghtaura 24

Large Intestine

• The large intestine is also known as the colon

• The ascending colon is the junction point between the small and large intestine

• The cecum, , rectum and anal canal are all a part of the

intestine

Ms. Ghtaura 25

Large Intestine - Appendix

• Some doctors argue that the appendix plays a role in human

while others say its function has been lost over

• It is attached to the .• The appendix is subject to

(injury or obstruction of fecal matter)

• During inflammation, if the fluid content increases enough, it can burst.

• A deadly infection (peritonitis) can result after the appendix bursts causing hemorrhage of all organs

Ms. Ghtaura 26

Large Intestine

• The colon absorbs , salts, and some • Inside the large intestine, there are

anaerobic bacteria which break down material

• Anaerobic bacteria also produce and other molecules that can

be absorbed and used by us. • The rectum stores non-digestible

material until it is ready to be

• The sigmoid colon enters the rectum• Rectum is the last of the large

intestine• The rectum opens at the anus, where

(expulsion of feces) occurs

Ms. Ghtaura 27

Major functions of the Liver• Detoxifies blood by and poisonous• Stores and fat soluble A, D, E, and K• Makes plasma proteins such as and from amino acids• Removes (derived from the breakdown of hemoglobin

molecules) and excretes it in bile – hence the yellowish-green colour• Helps regulate blood level, converting some cholesterol into

salt• Stores glucose as after a meal and breaks down glycogen into

glucose to help maintain the glucose concentration of blood between periods

• If glycogen is not available, it converts amino acids and glycerol (from fats) into glucose. The liver produces urea after breaking down amino acids

Ms. Ghtaura 28

Blood glucose levels• The pancreas has an

function, where it secretes insulin directly into the blood stream to control levels.

• Insulin is a hormone which causes cells (ex: liver or muscle cells) to take up from the blood.

• In the liver, glucose is taken up and is stored as until needed by the body

Ms. Ghtaura 29

By the end of this section, you should be able to:

• Identify and give a function for each of the following:

– mouth– tongue– teeth– salivary glands– pharynx– epiglottis– esophagus– cardiac sphincter– stomach– pyloric sphincter– duodenum

– liver– gall bladder– pancreas– small intestine– appendix– large intestine (colon)– rectum– anus

Ms. Ghtaura 30

• describe swallowing and peristalsis• identify the pancreas as the source gland for insulin, and

describe the function of insulin in maintaining blood sugar levels

• list at least six major functions of the liver• explain the role of bile in the emulsification of fats• describe how the small intestine is specialized for chemical

and physical digestion and absorption• describe the structure of the villus, including microvilli, and

explain the functions of the capillaries and lacteals within it• describe the functions of anaerobic bacteria in the colon

Ms. Ghtaura 31

• relate the following digestive enzymes to their glandular sources and describe the digestive reactions they promote:

– salivary amylase– pancreatic amylase– proteases (pepsinogen, pepsin, trypsin)– lipase– peptidase– maltase

• describe the role of water as a component of digestive juices• describe the role of sodium bicarbonate in pancreatic juice• describe the role of hydrochloric acid (HCl) in gastric juice• describe the role of mucus in gastric juice• describe the importance of the pH level in various regions of the

digestive tract

Ms. Ghtaura 32

Mandatory Vocabularyabsorption, anaerobic bacteria, anus, appendix, bile, capillary, cardiac sphincter, chemical digestion, digestive enzyme, digestive tract, duodenum, emulsification, epiglottis, esophagus, gall bladder, gastric juice, hydrochloric acid (HCl), insulin, intestinal juice, lacteals, large intestine (colon), lipase, liver, maltase, microvillus, nuclease, pancreas, pancreatic amylase, pancreatic juice, pepsin, pepsinogen, peptidase, peristalsis, pH, pharynx, physical digestion, protease, pyloric sphincter, rectum, salivary amylase, salivary gland, salivary juice/saliva, small intestine, sodium bicarbonate, stomach, swallowing, trypsin, villus