Human Nutrition - Chp 28

Nutrition

is the process by which an organism takes in and uses food necessary for metabolism and continuity of life

Autotrophic

organism that makes its own food, eg plants using photosynthesis

Heterotrophic

organism that cannot make its own food, must obtain it from another source, eg animals

Saprophytic organism

lives on dead organisms, eg rhizopus (bread mould)

Parasitic organism

lives in or on another living organism causing harm, eg streptococcus (causes strep throat)

Carnivores

eats animals only

Herbivore

eats plants only

Omnivore

eats plants and animals

Digestion

the breakdown of food into particles that are small enough to pass into body cells

Mechanical digestion

breaking down food physically
chewing and grinding of teeth, breaks down food into smaller particles to give enzymes a larger surface area to react on

Chemical digestion

the breakdown of food using enzymes
saliva, softens and dissolves food, amylase only acts for a short time as it is inhibited by the acid in the stomach

Digestive system

it is made up of the alimentary canal, which is a long tube starting at the mouth and ending at the anus

What are the 3 glands associated with the digestive system?

salivary glands, liver, pancreas

What are the 5 stages of human nutrition?

Ingestion - taking food into the digestive system at the mouth
Digestion - breaking down food into molecules so it can be absorbed into the bloodstream
Absorption - digested food is absorbed into the bloodstream at the small intestine
Assimilation - the way the body uses the absorbed food
Egestion - getting rid of unused, unabsorbed or undigested food through the large intestine

What are the 4 types of teeth + their functions?

Incisors - chisel shaped, cut and slice food
Canines - sharp, pointed, grip and tear food
Premolars - projections on the surface called cusps, chew and grind food
Molars - large, flat surfaces, chew and grind food

What are deciduous teeth?

adult teeth

What is the dental formula for adults?

What is a bolus?

food is formed into a ball which is pushed back into the oesophagus

What is the epiglottis?

is a flap of muscle that closes off the trachea and ensures the bolus passes down the oesophagus

What is the function of the oesophagus?

carries food from the mouth into the stomach by muscular contractions (peristalsis)

Peristalsis

involuntary wave of muscular contractions that push food along the alimentary canal in one direction only

Why is fibre good for the digestive system?

• stimulates peristalsis in the alimentary canal
• fibre absorbs and stores water, the expansion stimulates the muscles of the intestines to work
• prevents constipation, moves food along

Describe the structure of the stomach?

• j-shaped muscular bag
• the lining of the stomach, called the mucosa, is a heavily folded tissue
• the folds form millions of gastric glands which produce gastric juice
• cardiac sphincter muscle is a round muscle that opens and closes, keeps the food and stomach acid from coming back up into the oesophagus
  gastric juice = water + mucous + hydrochloric acid + pepsinogen

How does the stomach protect itself from self digestion?

• mucous which is alkaline, coats inside of the stomach, reduces acidity near the stomach wall

• pepsinogen is an enzyme that is released by the stomach glands in its inactive form, and therefor cannot digest its own cells, it is only converted into its active form pepsin by the HCl in the stomach

• cells that line the stomach are tightly packed and can be replaced rapidly

What is the function of HCl in the stomach?

• gives the stomach a pH of 2

• kills bacteria

• softens food

• activates pepsinogen

What is chyme?

thick mixture of semi-digested food

What is the digestive function of the pancreas?

• secretes pancreatic juice
• sodium bicarbonate salts neutralise chyme from the stomach in the duodenum
  pancreatic juice = sodium bicarbonate + enzymes (eg amylase, lipase)

How does pancreatic juice enter the alimentary canal?

enters the duodenum through the pancreatic duct

What is the function of the liver?

— deamination: break down of excess amino acids to form urea
— storage of vitamin D
— storage of minerals, iron, copper, zinc
— converts glucose to glycogen for storage
— converts excess carbohydrates to fat
— detoxifies the body by breaking down poisons such as alcohol or drugs
— making bile, cholesterol and plasma proteins

What is bile?

— a yellow/green viscous liquid, partly formed from the remains of red blood cells
bile = water + bile salts + bile pigments

Where is bile stored?

gallbladder

How does bile enter the alimentary canal?

enters the duodenum through the bile duct

What is the function of bile?

— emulsify lipids, breaks apart large fats and oils, more surface area for digestion
— neutralises chyme from the stomach
— secretes pigments (bilirubin + biliverdin) which help with iron content

What is the function of the duodenum?

• further digestion
• cells lining the duodenum produces a range of digestive enzymes

What is the pH of the duodenum?

pH 7-9

What is the function of the ileum?

• to absorb nutrients
• food is almost fully digested

What is the digested product of a carbohydrate?

monosaccharide

What is the digested product of a protein?

amino acids

What is the digested product of a lipid?

fatty acids and glycerol

Summary of digestion for amylase:

• made in salivary glands + pancreas
• active in mouth + duodenum
• substrate is starch
• product is maltose

Summary of digestion for pepsin (a protease/protein digesting enzyme):

• made in the stomach lining
• active in the stomach
• substrate is protein
• product is peptides

Summary of digestion for hydrochloric acid:

• made in the stomach lining
• active in the stomach
• substrate is bacteria and fibrous foods
• product is dead bacteria and softened food

Summary of digestion for sodium hydrogen carbonate (salts):

• made in the pancreas
• active in the duodenum
• substrate is acid in the chyme
• product is neutralised acid

Summary of digestion for lipase:

• made in the pancreas
• active in the duodenum
• substrate is lipid
• product is fatty acids + glycerol

Summary of digestion for bile salts:

• made in the liver
• active in the duodenum
• substrate is lipids
• product is lipid droplets (allows more surface area for digestion)

What is the structure of the lining of the small intestine?

• contains many infoldings called villi
• each villus has many microvilli
• intestinal glands are located between the villi, produce a range of enzymes and intestinal juices

What are the adaptations of villi to carry out their function?

Microvilli - large numbers of villi and microvilli increase the surface area for digestion in the duodenum and absorption in the ileum
Rich blood supply - abundant capillaries absorb water and soluble nutrients (glucose, amino acids, vitamins, minerals), then carry nutrients to the hepatic portal vein and to the liver
One cell thick - allows easy diffusion
Lacteals - carries away the fats

What is the function of a lacteal?

• lacteal contains a liquid called lymph
• fats are absorbed and passed into the lymph in the lacteals

Where is the caecum found?

found under the junction where the small and large intestine meet

What is the function of the appendix?

• function in humans not fully understood
• in some animals, they contain enzymes for the digestion of cellulose

What is a vestigial organ?

An organ which has lost their former function in humans

What is the function of the colon?

reabsorb water from unabsorbed waste, forming faeces

What are the functions of the rectum and anus?

• the rectum stores faeces
• the anus egests faeces

When does diarrhoea occur?

• when unabsorbed material moves too rapidly through the colon
• less water is reabsorbed

When does constipation occur?

• when unabsorbed material moves too slowly through the colon
• too much water is reabsorbed

What is symbiosis?

when one living thing lives off another living thing with mutual benefit

What are the benefits of symbiotic bacteria in the colon?

• feed on waste and produce vitamin B and K
• compete with pathogenic bacteria

Balanced diet

contains all the nutrients in the correct amounts for the needs of the body

What influences the total amount of food/energy a person needs?

• age
• activity level
• gender
• occupation
  = health