Digestion and Nutrition

Question 1

Identify all digestive system organs & their functions?

Answer 1

-Mouth:
-Pharynx
-Stomach
-Small Intestine
-Large Intestine

Question 2

Describe the major layers of the walls of the digestive tract & briefly their functions?

Answer 2

Mucosa
Mucous membrane – epithelium, lamina propria, muscularis mucosae.
Secretion/absorption/folding.
Submucosa
Binds mucosa to muscularis externa.
Contains nerves network (ENS).
Muscular Layer (Muscularis externa)
Smooth muscle – patterns of contraction & relaxation.
Important for movement of substances (peristalsis & segmentation).
Serosa
Membrane allowing attachment to abdominal walls.

Question 3

Explain the 6 main digestive functions?

Answer 3

1. Ingestion:
   -Material enters digestive tract via mouth.
2. Propulsion (peristalsis):
   -Movement of food along the GIT.
3. Mechanical breakdown/processing (segmentation):
   -Easier to propel along tract.
   -Increases surface area to allow easier breakdown.
4. Chemical Digestion:
   -Chemical breakdown of food for absorption.
   -Large molecules (e.g. starch) broken down small molecule (e.g. absorbable sugars).
5. Absorption:
   -Movement of substrates, electrolytes, vitamins and water across epithelium into interstitial fluid.
6. Defecation:
   Removal of indigestible waste products from body.

Question 4

What are the two main types of intestinal movement?

Answer 4

Peristalsis:
Waves of muscular contraction.
Circular muscles – push forward.
Longitudinal muscles – shorten.
Propels bolus forward at different speeds.
E.g. Moves along SI in approx. 90-120 min.
Segmentation:
Cycles of contraction.
Churn and fragment bolus.
Mix with intestinal secretions.
Ensure contents comes into contact with absorptive layer.
Not directional.

Question 5

Explain the role of the divisions of ANS on digestive control?

Answer 5

-Both parasympathetic and sympathetic divisions of ANS control digestion.
-Act on enteric nervous system (ENS) in the wall of the digestive tract.
—Controls local secretion and motility.
-Parasympathetic (rest and digest) typically stimulates.
-Sympathetic (fight or flight) typically inhibits.
—-GIT not required in ‘stressful’ situations.

Question 6

Identify the role and functions of the oral cavity & saliva?

Answer 6

-Sensory analysis of material before swallowing.
—Tongue
-Mechanical processing.
—-Teeth, tongue and palatal surfaces.
—-Mastication (chewing).
-Lubrication:
—-Mixing food with mucus and saliva.
-Limited digestion:
—-Mechanical processing
—-Chemical digestion - carbohydrates & lipids.
———Salivary amylase & lingual lipase.
-Salivary glands
—-Lubrication of mouth and pharynx (mucins).
—-Cleanse mouth and teeth.
—-Moistening food.
—-Dissolve food and chemicals (stimulate taste buds).
—–Begins chemical digestion.

Question 7

Explain the process of swallowing?

Answer 7

1.Buccal Phase:
-The Upper Esophageal Sphincter is contracted (closed).
-The Tongue presses against the Hard Palate, forcing the food bolus into the oropharynx
. Pharyngeal-esophageal phase begins:
-the tongue blocks the mount
-the soft palate and its uvula rise, closing off the nasopharynx
-The larynx rises so that the epiglottis blocks the trachea.
-The upper esophageal sphincter relaxes food enters the esophagus
3. Pharyngeal-esophageal phase continues (3-5):
-the constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly.
-The upper esophageal sphincter contracts after food enters.
4: Peristalsis moves food through the esophagus to the stomach
5: The Gastroesophageal sphincter surrounding the cardial orifice opens. After food enters the stomach, the sphincter closes, preventing regurgitation

Question 8

Explain the functions of the stomach?

Answer 8

Function
1. Mechanical breakdown:
Mixing waves every 15-25 sec.
Forms chyme (partially digested semi-fluid material).
Forces chyme into duodenum.
2. Chemical digestion:
HCl
Denatures (unravels) proteins.
Pepsinogen
Converted to pepsin (HCl and already converted pepsin).
Hydrolyses peptide bonds.
Gastric lipase
Hydrolyses triglycerides.

Question 9

how gastric activity is regulated?

Answer 9

-Cephalic phase:
Sight, smell, taste or thought of food.
Prepares stomach for arrival of food.
↑ gastrin secretion.
-Gastric phase:
Arrival of food into stomach.
Stretch receptors and chemoreceptors (pH).
Enhanced secretion (gastrin, pepsinogen, HCl).
Maintains gastric secretion and motility.
-Intestinal phase:
Chyme enters duodenum (small intestine).
Enhanced secretion.
Secretin (reduces gastric secretion).
Cholecystokinin (CCK) (inhibits gastric emptying).
Gastric Inhibitory Peptide (GIP) (inhibits gastric emptying and secretions).
Slows exit of chyme from stomach.

Question 10

Explain briefly how we control feelings of hunger and fullness (satiety)?

Answer 10

-Ghrelin - appetite stimulant.
Acts as a ‘dinner bell’ to tell the body it’s ready for a meal.
-Leptin - appetite suppressant.
Secreted by adipose tissue when fat stores increase.
Acts by inhibiting appetite stimulant neuropeptide Y (NPY).
-Insulin and CCK are released during food absorption.
Act as satiety signals (feelings of fullness) to depress hunger.

Question 11

Explain the functions of the pancreas?

Answer 11

Exocrine cells:
-Acinar glands secrete pancreatic juice.
-Digestive enzymes and buffers.
Endocrine cells:
-Pancreatic islet cells.
-Secrete insulin and glucagon into bloodstream.
-1000 mL pancreatic secretions released per day.
-Controlled by duodenal hormones.

Question 12

Describe the main functions of the liver?

Answer 12

Metabolic regulation:
-Carbohydrate, Lipid & Protein metabolism.
-Waste removal.
-Store vitamins and minerals.
-Process drugs (metabolism/inactivation).
Haematological regulation:
-Removal of bacteria and old RBC, WBC.
-Make plasma proteins.
-Removal of hormones and antibodies.
-Removal or storage of toxins .
-Activation of vitamin D.
Bile production:
-Synthesis and secretion of bile into duodenum.
-Excrete bilirubin.
Liver failure – build up of hormones and toxins.

Question 13

Name the key functions of pancreatic juices?

Answer 13

Pancreatic secretions:
-Water, Salts, Bicarbonate & Phosphate buffers.
-Enzymes to digest key nutrients.
-Carbohydrates
–Pancreatic alpha-amylase
-Proteins
–Proteolytic enzymes (Trypsin)/Proteases
-Triglycerides (complex lipids)
–Pancreatic lipase
-RNA and DNA
–Nucleases

Question 14

What is the role of bile in the digestive system?

Answer 14

Aids digestion of lipids.
-Lipids are not water soluble.
Mechanical processing in stomach creates large drops containing lipids.
Pancreatic lipase is not lipid soluble.
-Interacts only at surface of lipid droplet.
Bile salts break droplets apart (emulsification).
-Increases surface area exposed to enzymatic attack.
-Creates tiny emulsion droplets coated with bile salts.
-Promote absorption of the lipids by epithelium.

Question 15

Explain the main functions of the gallbladder?

Answer 15

Stores bile.
Concentrates bile.
-Water absorbed, bile salts and solutes concentrated.
Releases bile into duodenum.
-Under stimulation of CCK.

Question 16

Describe the small intestine functions and anatomy?

Answer 16

Digestion and absorption of nutrients.
90% of nutrient absorption.
Length (approx. 6 m) - large surface area.
-Further increased by:
–Circular folds (plicae circulares) – many present, mix chyme.
–Villi – capillaries and lacteals.
–Microvilli – brush border.

anatomy:
Duodenum (25cm)
-Receives chyme from stomach.
-Mixes with digestive enzymes from pancreas.
-Neutralises acids:
–Avoid damage to absorptive surfaces.
–Avoid inactivating digestive enzymes.
Jejunum (2.5m)
-Chemical digestion and nutrient absorption!
Ileum (3.5m)
-Nutrient absorption.
–Vitamin B12, bile salts, leftover undigested products.
-Controls flow of from ileum to large intestine.

Question 17

What are the classes of digestive enzymes?

Answer 17

Carbohydrases (amylases):
-Break bonds between simple sugars (carbohydrates).
Proteases/Peptidases:
-Break bonds between amino acids (proteins).
Lipases:
-Separate fatty acids from glycerides (lipids).
Nucleases:
-Break nucleotides into:
–Sugars, Phosphates and Nitrogenous bases.
Brush border enzymes:
-Disaccharidases, peptidases and nucleases (and some lipases).

Question 18

How does the large intestine’s structure differ from the small intestine?

Answer 18

-Small intestine absorb the nutrients from the digested food. Large intestine helps in the absorption of water and electrolytes and in production of vitamins

Question 19

What are the main functions of the large intestine?

Answer 19

-Reabsorption of water.
-Compaction of intestinal contents into feces.
-Absorption of important vitamins produced by bacteria.
-Breakdown of some remaining products for removal.
-Storage of fecal material prior to defecation.

Question 20

Can you describe the two final stages of digestion (mechanical and chemical) that take place in the large intestine?

Answer 20

Mechanical digestion:
-Movement of LI begins when substances pass ileocaecal sphincter.
-Peristalsis slower than SI.
-Haustral churning (segmentation).
–Initiated by distension of haustra as chyme enters LI.
-Mass movement:
–Strong peristaltic wave beginning in transverse colon that drives contents into rectum.
–Occurs during or immediately after meal when food enters stomach!
–Causes defecation reflex.
Chemical digestion:
-Final stage of digestion occurs through activity of bacteria.
-Produces gases and other by-products.
–Vitamin K, biotin, pantothenic acid
–Organic waste products
–Short chain fatty acids
–Toxins
-Bacteria produce necessary enzymes that humans don’t have genetic capacity to produce.
–Able to digest complex polysaccharides (indigestible carbohydrates).

Question 21

Describe the defecation reflex and why it is necessary?

Answer 21

-Mass movement into rectum initiates defecation reflex.
-Parasympathetic reflex causing colon and rectum to contract, and internal anal sphincter to relax.
-Faeces forced into anal canal.
External sphincter under voluntary control.

Question 22

Identify the different nutrients our body requires to function?

Answer 22

-Fruits
-Vegetables
-Grains
-Protein
-Dairy
-water

Question 23

Explain why obesity is an issue in Australia and briefly how it happens?

Answer 23

Obesity is an issue in Australia due to people relying on prepared meals. lack of nutritional diversity and hidden calories. Obesity happens when you take in more calories then your body is burning throughout the day.

Question 24

Carbohydrates
Approx. daily requirements?
General sources?
Uses in the body?

Answer 24

130g/day = 45-65% of total
Dietary sources – primarily from plants
-Starch (complex) in grains and vegetables
-Sugars (simple) in fruits, sugarcane, sugar beets, honey and milk/dairy
-Insoluble fiber - cellulose in vegetables; not digested
-Soluble fiber - pectin in apples and citrus fruits; reduces blood cholesterol levels

Uses in body
Glucose - fuel used by cells to make ATP
-Some cells use fats for energy
–Neurons and RBCs rely entirely on glucose
–Neurons die quickly without glucose
-Excess glucose converted to glycogen or fat and stored

Question 25

Lipids
What types of lipids, good vs bad?
General sources?
Uses in the body?

Answer 25

20% of total nutrients (maximum)
Triglycerides (neutral fats)
-Saturated fats in meat, dairy foods, and tropical oils; hydrogenated oils (trans fats)
-Unsaturated fats in seeds, nuts, olive oil, and most vegetable oils
Essential fatty acids
-Linoleic and linolenic acid, found in most vegetable oils

Uses in body
-Phospholipids essential in myelin sheaths and all cell membranes
-Adipose tissue  protection, insulation, fuel storage
-Prostaglandins  smooth muscle contraction, BP control, inflammation
-Help absorb fat-soluble vitamins (e.g. the antioxidants A,E and D)

Question 26

Proteins
Approx. daily requirements?
General sources?
Uses in the body?

Answer 26

Variable, dependent on age, size, metabolic rate, nitrogen balance
Average is 0.8g/kg (56g/70kg)

Dietary sources
-Eggs, milk, fish, most meats, soybeans contain complete proteins
–Contain all needed amino acids
-Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids – usually lysine and isoleucine)
-Legumes and cereal grains together contain all essential amino acids
-Varied diets cover all amino acids

Uses in body
-Structural materials
–Keratin (skin); collagen and elastin (connective tissue); muscle proteins
-Functional molecules
–Enzymes, some hormones
-Amino acids can be burned for energy

Question 27

What are the key water and fat soluble vitamins and how do we use them?

Answer 27

Water soluble vitamins
B complex and C are absorbed with water
B12 absorption requires intrinsic factor
Not stored in the body ** (exception is B12 – stored in liver)
Any not used within one hour is excreted (megadosing useless)

Fat-soluble vitamins
A, D, E, and K absorbed with lipid digestion products
Stored in body, except for vitamin K
Pathologies due to excess

Question 28

What are some of the key minerals we require?

Answer 28

Calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium