Digestion

Purpose of digestion

To break down nutrients (macromolecules) from food into smaller forms so that our cells can use it to maintain life

Carbohydrates

Macromolecules composed of Carbon, Hydrogen and Oxygen in 1:2:1 ratio

What macromolecule is the primary fuel source of the body

Carbohydrate

3 types of carbohydrates

Monosaccharides (simple sugar)
disaccharides (double sugars
Polysaccharides (complex sugars

monosaccharide

Single sugar group with formula C6H12O6

3 types of monosaccharides

Glucose
Fructose
Galactose

Where are the monosaccharide sugars from? (3)

Glucose - from animals and plants
Fructose - fruits and honey
Galactose - milk sugar

Types of Disaccharides

Sucrose (table sugar)
Maltose (grain sugar)
Lactose (milk sugar)

What is a disaccharide

Sugar made of 2 monosaccharides, one is alway a glucose molecule

Formula for each disaccharide sugar

Sucrose = glucose + fructose
Maltose = glucose + glucose
Lactose = glucose + galactose

Polysaccharides

Complex sugars made of 100s-1000s of sugar monomer, they are long chain polymers used for energy storage

Types of polysaccharides and uses

Starch - stored in plant cells
Cellulose - stored in plant cell walls
Glycogen - stored in animal cells
Chitin - insect and crustacean exoskeletons

Example of protein function

Antibodies - defense OR
myosin - movement OR
enzymes - control chemical reactions

What are proteins made of?

Amino acids

What is the chemical makeup of amino acids?

Amino + acid + variable ‘R’ group

What is a chain of amino acids called?

Polypeptides

What is the function of amino acids

They link together to form proteins (sequences are determined by DNA)

How many amino acids cannot be made by the human body?

8

Lipids

Concentrated source of energy storage

T/F - lipids are soluble in water

F

What are the main functions of lipids

Aid in absorption of fat soluble vitamins
Insulate the body
Cushion the organs

Types of lipids

Fats
Phospholipids
Steroids
Waxes

Fats

Solid lipids - composed of triglycerides

Triglyceride

1 glycerol + 3 fatty acids

2 types of fats

Saturated and unsaturated fats

Difference between saturated and unsaturated fats

Saturated: straight chemical shape (single bonds), difficult to digest, should be limited, solid at room temp
Unsaturated: liquid at room temp, have double bonds which create ‘kinking’ and make molecule easier to break down

2 types of unsaturated fats

Cis fats: 👍 molecule is bent
Trans fats 👎 kinks lock with e/o and are the hardest to break down

Example of saturated and unsaturated fat

Saturated: beef, pork, cheese fats
Unsaturated: corn, olive oils

Phospholipids

Main component of cell membrane

Steroids example

Cholesterol and sex hormones

Waxes

Firm yet pliable fats like beeswax

What proportion of the human body is made up of water

2/3

What are the functions of water in the body

1. Transporting nutrients to cells (through blood)
2. Transports waste (urine and sweat)
3. Lubricates tissues and joints
4. Major component of blood and mucus (eliminating toxins)
5. Regulating body temp

Vitamins

Organic molecules typically count on foods, only small amount needed to change food into energy

Which vitamins are soluble in what?

A,D,E,K = fat soluble
B1, B2, C = water soluble

Minerals

Found in inorganic nutrients/elements, variety needed in diet
Excessive amts can be just as harmful as not enough

Examples of minerals

Ca, Fe, P, K, Na, I

Alimentary canal

“Tube within a tube” which allows digestive processes to be separated into different regions

Do herbivores or carnivores have longer alimentary canals?

Herbivores - cellulose from plant walls take longer to break down

stages of food processing

1. Ingestion - taking in or eating food
2. Digestion - breakdown of food physically and chemically by enzymes
3. Absorption of nutrients in small intestine
4. Egestion (excretion) of undigested solid waste

Digestive enzymes

Proteins that break down complex molecules

digestive enzymes each have an optimum…

Temperature and pH

Where is pepsin found? + ideal pH

Stomach, opt pH 2-3

Where is amylase found + ideal pH

Oral salive, opt pH 7

Where is trypsin found + ideal pH

Small intestine, opt pH 9-10

Mouth

Where digestion begins, food is broken down mechanically (chewing) and chemically (saliva)

Bolus

Ball of food formed by the tongue

Saliva

Does chemical digestion in the mouth. Dissolves food particles, activates taste buds, lubricates food contains enzyme amylase

Salivary glands

Submandible, sublingual, parotid

Amylase

Enzyme found in saliva, breaks down carbs/starch to sugar

Pharynx

Short tube shared by digestive and respiratory tract, the throat

Epiglottis

a flap of cartilage that covers the trachea to prevent food entering airway while swallowing

Esophagus

Section of digestive tract responsible for pushing bolus and fluid into the stomach,
Made of smooth muscle that contracts to push food down

Peristalsis

Involuntary muscle contractions of the alimentary canal (notably in the esophagus) which pushed food along

Stomach

J shaped organ hat churns and stores food
Takes part in chemical (stomach acid) and physics (pummeling) digestion

Capacity of human stomach

1-1.5L

Chyme

Acidic nutrient rich liquid formed by the stomach churning a bolus

T/F, the stomach help absorbs nutrients

False! The stomach CANNOT absorb nutrients as they are still too large at that point of digestion
it CAN absorbs water, glucose, salts and alcohol through the membrane directly into the bloodstream

How long does the stomach take to empty after a meal?

2-6hrs

Parts of the stomach

(Esophagus)
1. Fundus
2. Body
3. Pylorus
(Duodenum)

sphincters of the stomach region

1. Cardiac sphincter- between esophagus and stomach
2. Phyloric sphincter -between pylorus and duodenum

Cells lining the stomach

Parietal cells
Chief cells
Mucus

Parietal cells

Secrete HCl (stomach acid) to
a) destroy bacteria in food
b) convert pepsinogen into pepsin

Pepsin

Enzyme that digests proteins into amino acids

Chief cells

Found in stomach, Secrete pepsinogen (broken down into pepsin by parietal cells)

Mucus

Secreted in the stomach to protect stomach lining and prevent ulcers from occuring

Small intestines

7m long tube (in humans) responsible for absorbing nutrients into the bloodstream through villi

Regions of the small intestine + lengths

1. Duodenum (0.3m)
2. Jejunum (2.7m)
3. Ileum (4m)

Villi

Finger-lined tubes in small intestine used to absorb nutrients into the bloodstream

Microvilli

Small villi lining the villi of the small intestine

Purpose of villi

Increase surface area for absorption of nutrients (allows faster absorption)

Core of villus

Lymph vessels (lacteal)
Access the bloodstream to distribute nutrients throughout the body

Why are the large and small intestine named as such?

The large intestine has a larger diameter, though not length

Is the small or large intestine smooth?

Small intestine - the large intestine is puskered and ridged

Length of the human large intestine

1.5m

Sections of the large intestine

1. Caecum
2. Ascending colon
3. Transverse colon
4. Descending colon
5. Sigmoid colon
6. Rectum

Functions of the large intestine

1. Absorb water, minerals, and vitamins
2. House E. coli bacteria that use waste to make vitamins
3. Form feces
4. Move feces for excretion

Where is it healthy to find E. Coli bacteria in the body?

Large intestine - uses waste to make vitamins

Accessory organs

Organs which aid in digestion and are outside the alimentary canal

Ducts

Used by accessory organs to secrete their contents into the alimentary canal

Pancreas

a large ‘cottage cheese’ like gland located behind the stomach; secretes pancreatic juice and insulin

Pancreatic juices

Released into duodenum via pancreatic duct: Neutralizes stomach acid and contains digestive enzymes

Endocrine gland

secrete directly into the bloodstream

exocrine gland

a gland that secretes externally through a duct (not into the bloodstream)

Enzymes contained in pancreatic juices + functions

Amylase (turns carbs into sugars
Lipase (turns lipids into fatty acids + glycerol)
Trypsin (turns proteins into amino acids)

Insulin

hormone secreted by the pancreas; regulates blood-glucose levels

Liver functions

1. Forms bile
2. Converts glucose to glycogen
3. Detoxifies blood
4. Breaks down hemoglobin from red blood cells

What gives feces their colour and consistency

Colour: combination of broken down hemoglobin from RBCs and green bile colour
Consistency: how much water is absorbed in the large intestine

Gall bladder

Stores reserve supply of bile when the stomach is empty

Bile

Greenish fluid that contains cholesterol and bile salts
Responsible for breaking down fat into small droplets through emulsification

Gall stones

Large crystals of cholesterol which accumulate, only become problematic when they block gall bladder duct

Emulsification

Physical process whereby fat molecules are broken down into smaller droplets, increasing surface area for the lipase enzyme to work

Stages of emulsification

1. Body recognizes fats present in small intestine
2. Gall bladder releases bile
3. Bile salts break down large globs of fat

Where do the accessory structures feed into?

The duodenum

Formula for total energy in food

(g fat) x 37kJ + (g protein) x 17kJ + (g carbs) x 17 kJ

What percentage of energy should you get from fat?

No more than 30%

How much total energy intake should be from protein?

15%

How much of your daily energy intake should be made of carbs?

50-55%

Fats, proteins and carbs yield how much energy per gram?

Fats: 37kJ
Proteins: 17kJ
Carbs: 17kJ

Metabolism

Chemical reactions used to maintain life