digestive system

Question 1

Why do we digest?

Answer 1

We have to breakdown nutrients in foods into a form that is:
Small enough to fit into our cells
Usable by the cells

Question 2

What are the 4 steps of the digestive system?

Answer 2

Ingestion - getting the food in
Digestion - breaking it down
Egestion - getting rid of indigestible or unusable food
Absorption - the absorption of nutrients into the blood stream

Question 3

Types of digestion

Answer 3

Mechanical digestion = the physical breakdown of food into smaller pieces to ensure a larger surface area for the action of digestive enzymes (chemical digestion)

Chemical digestion = the chemical breakdown of food; the hydrolysis of large molecules into smaller, usable molecules using enzymes in chemical reactions

Question 4

Mouth palates

Answer 4

• Begins mechanical digestion (chewing) and chemical digestion of carbohydrates
• Hard Palate
  Bony structure – the roof of the mouth.
  Separates the nose area from the mouth.
  Important for chewing and talking
• Soft Palate
  Behind the hard palate
  Ends in the uvula

Question 5

Teeth

Answer 5

• mechanically digest food/break food apart into smaller pieces to increase SA allowing for quicker chemical reaction rate, allowing for chemical digestion to occur quicker
• incisors cut food/canines tear food/premolars and molars grind food

Question 6

Salivary glands

Answer 6

Submaxillary Glands
– at the base of the jaw

Sublingual Glands
– under the tongue

Parotid Glands
– below the earlobes, get infected when you have mumps

Question 7

Saliva

Answer 7

Saliva (pH 6.5-7.5) is produced under the control of the autonomic nervous system and therefore does not require conscious control. It is an autonomic nervous response to a stimulus.

The saliva is made up of water, mucus & enzymes:

the water moistens dry food & makes it easy to swallow and puts the food into solution

the mucus binds loose crumbs into a ball and makes the food slippery enough to swallow & slide down the esophagus.

the enzymes called amylase (a carbohydrase) starts breaking down starch (a polysaccharide) into disaccharides.

Question 8

Esophagus

Answer 8

The Esophagus:

Hollow tube lined with mucus-secreting cells called mucosa
Lines with involuntary smooth muscles
Moves food along by rhythmic wave-like contraction called peristalsis
Esophagus connects the pharynx and stomach

Question 9

THE STOMACH

Answer 9

The food enters the stomach by the cardiac sphincter, a circular muscle, but not back up
The stomach is a J-shaped sac
Mechanical digestion takes place 🡪 churn the food
Mucous cells secrete a bicarbonate-rich mucous onto the surface of the gastric mucosa to protect it from the acidic contents of the stomach.
The mucosa form folds called rugae

Question 10

pancreatic juice enzymes (chemical digestion)

Answer 10

The enzymes in pancreatic juice are able to breakdown 3 major components of foods – proteins, carbohydrates and lipids.

Proteases - breaks down protein into amino acid:
Amylase - further breakdown of polysaccharides into maltose (disaccharides).
Lipase – breakdown of fats into glycerol & 3 fatty acids

Answer 11

Sac-like organ that produces pancreatic juice secreted into the duodenum
The pancreatic juice contains enzymes and sodium bicarbonate

HCl enters duodenum
🡪 Prosecretin in duodenum gets converted to Secretin
🡪 Secretin is absorbed by blood stream & carried to pancreas
🡪 signals pancreas to release HCO3- solution into duodenum
🡪 pH increase from pH 2 to pH 8 before lowering slightly
🡪 basic pH inactivates pepsin

The above mechanism protects the linings of small intestine.

Question 12

MORE STOMACH

Answer 12

The two types of glands exist in the gastric mucosa that aid in chemical digestion: oxyntic glands and pyloric glands.

Pyloric glands:
primarily located in the pyloric region of the stomach (the lower portion)
produce mucus - helps lubricate and protect the stomach lining from the acidic environment and digestive enzymes present in gastric juice
secrete hormones such as gastrin - stimulates the secretion of gastric acid → promotes the contraction of the pyloric sphincter, → controls flow of chyme through pyloric sphincter

Oxyntic (Gastric) glands:
found in the body and fundus regions of the stomach (the upper portion) and contain parietal cells and chief cells
responsible for producing gastric juice, a mixture of hydrochloric acid (HCl), pepsinogen, and intrinsic factor for absorption of vitamin B12 in small intestine

Question 13

MORE STOMACH

Answer 13

a) Chief Cells - secrete pepsinogen, an inactive precursor of the enzyme pepsin.

b) Parietal cells - secrete hydrochloric acid into the lumen of the stomach; concentrated to approximately 160 mmol/L and a pH of 0.8.

Hydrochloric acid secreted by the parietal cells serves three main functions:
To create a hostile environment for pathogenic microorganisms taken in through the mouth,
To denature proteins and make them more accessible for enzymatic degradation by pepsin, and
To activate the pepsinogen to its active form, pepsin.
The food and gastric juice = chyme
The pyloric sphincter allows food into small intestine
No digestion of carbohydrates occurs in the stomach

Question 14

liver

Answer 14

The biggest gland
Converts glucose into glycogen and stores it
Produces bile which is stored in the gallbladder
Bile contains bile salts which can emulsify fats.
Release of bile salts is triggered by presence of fats in the duodenum

Question 15

see slide 33

Answer 15

fat enters duodenum and cck is triggered, cck is carried by bloodstream and enters gallbladder, cck triggers release of bile salts, bile enters small intestine and begins to emulsify fats

Question 16

small intestine

(bile, pancreas)

Answer 16

About 6 m long (about 20 ft)
Average pH ranges from 7.2-7.5 except in the duodenum
The mucosa is folded into finger-like projections called villi 🡪 absorption of a very large amount of food molecules is permitted as surface area is increased
Lining up each villus are microvilli – actin filaments covered by a plasma membrane – which further increases absorption surface area (0.5 to 1 micrometer)
Uses peristaltic movements
The majority of chemical digestion occurs in the small intestine

Question 17

villi

Answer 17

Secrete enzymes and mucus, aiding in digestion and lubrication of the intestinal contents.
Contain blood vessels and lacteals (lymphatic vessels) that transport absorbed nutrients (carbs and amino acids) to the bloodstream and lymphatic system.

Question 18

duodenum

Answer 18

Duodenum
average pH 5.8 - 8.0
Short, wide U-shaped section, approx. 25-30 cm long.
The bile and pancreatic juice enter duodenum through ducts
Duodenum produces enzymes like peptidase 🡪 break peptides into amino acids.
Amylase - produced by the pancreas enters the small intestine to assist in digestion by hydrolyzing complex carbohydrates; ionized calcium is required for this process.
Lipases - produced and secreted by the pancreas that breaks down triglycerides into free fatty acids and glycerol by catalyzing the hydrolysis of the ester bonds in triglycerides

Question 19

jejunum

Answer 19

2. Jejunum
   Coiled part of the small intestine
   Absorption of small molecules (nutrients)occurs

Question 20

ileum

Answer 20

absorption occurs by diffusion ad active transport

Question 21

large intestine

Answer 21

Average pH 7.9 - 8.5
Only about 2 m long but wider than the small intestine
Absorption of water and salts occurs here
Prepares wastes for elimination
Anaerobic bacteria in colon produces vitamins (folic acid, various B vitamins & vitamin K) that gets absorbed into the bloodstream
Uses peristaltic movements

Question 22

rectum and anus

Answer 22

The Rectum:
Storage of solid indigestible waste

The Anus:
Elimination of waste