Biology - Chapter 28: Human Nutrition

autotroph

type of nutrition where an organism makes its own food

heterotroph

type of nutrition where an organism cannot make its own food

herbivores

animals that feed only on plants

carnivores

animals that feed on other animals

omnivores

animals that feed on both plants and animals

saphrophytes

feed on dead/decaying matter

parasites

feeds on live hosts

digestion

the physical and chemical breakdown of food into soluble particles small enough to pass into cells in the body

need for digestion

to break down large food particles until they are small enough to pass into body cells

physical digestion

mechanical breakdown of food into smaller pieces (occurs in mouth and stomach)

chemical digestion

the breakdown of food into smaller molecules through enzymes (occurs in mouth, stomach and small intestine)

ingestion

food is taken into the alimentary canal through the mouth

digestion

food is broken down into smaller, soluble pieces

absorption

the movement of digested food from the alimentary canal into the bloodstream

egestion

removal of unabsorbed material in the form of faeces through the anus

excretion

removal of metabolic waste such as urine and CO2

the mouth

mechanical digestion: chewing and grinding action of the teeth on food takes place

chemical digestion: occurs in the mouth by the action of salivary amylase (an enzyme)

salivary amylase

• converts starch into maltose

• it’s produced by 3 pairs of salivary glands

incisors

located in front of the mouth - they cut and slice food

canines

long, fang-like teeth, used to grip and tear food

premolars

have large flat surfaces to crush and grind food

molars

located at the back of the jaw to chew and grind food

dental formula

2( I 2/2 C 1/1 P 2/2 M 3/3 )

epiglottis

flap that closes over trachea to ensure that food is passedd down through the oesophagus

peristalsis

the wave of muscular action in the walls of the alimentary canal that moves the contents along

role of fibre

stimulates peristalsis

physical digestion in the stomach

• occurs when the stomach churns the food

• helps to turn the food into chyme

• increases the surface area of the food so that enzymes can digest the food more easily

chemical digestion in the stomach

• occurs due to action of a number of enzymes

• stomach juice contains electrolytes, HCL and multiple enzymes

• pepsinogen activated to form pepsin

pepsinogen and pepsin

• pepsinogen is an inactive enzyme formed by glands within the mucus lining of the stomach

• it is activated to form pepsin by HCL

• pepsin becomes active only when it mixes with proteins to digest it

• pepsin is a protease: a protein-digesting enzyme

stomach

• mucus lines the stomach to prevent self-digestion

• HCl kills many bacteria, loosens fibrous and cellular foods, activates pepsinogen and denatures salivary amylase

pancreas

• secretes the hormone insulin and enzymes such as amylase and lipase (flows down in pancreatic duct and acts in duodenum)

• it neutralises the chyme from the stomach

• pancreaticamylase has same functions as salivary amylase (replaces it due to denaturation in the stomach)

lipase

converts lipids to fatty acids and a glycerol

amylase

converts starch into maltose

liver

only organ that receives blood from the hepatic artery + hepatic portal vein

functions:

• makes bile

• breaks down toxins in the body

• deamination

• converts glucose into glycogen (which is stored)

• converts excess carbohydrates into fat

• stores excess fat-soluble vitamins and excess minerals

• makes plasma proteins

• makes cholesterol

• heat production

bile

• emulsifies lipids to increase surface area for enzyme digestion

• neutralises chyme

• to excrete pigments - bilverdin and bilirubin

deamination

excess protein turned into urea

urea

converted ammonia into much less toxic substances

small intestine

contains 2 parts - duodenum and ileum (lining of both of these contains many villi)

duodenum - carries out digestion

ileum - site of absorption

chyme from the stomach moves to the SI

duodenum

• the first 25cm of SI

• food is forced forwards and backwards through the duodenum due to peristalsis

• its lining produces a large range of enzymes

• its function is digestion → most digestion takes place here

• products of liver and pancreas entre the duodenum through the pancreatic duct

ileum

• aka jejeneum

• has numerous infoldings called villi to increase surface area for absorption

absorption in the ileum:

• occurs in the bloodstream

• glucose and amino acids pass through villi walls into the bloodstream through diffusion and are then carried to the liver by the hepatic portal vein

• fatty acids and glycerol enclosed in coverings and pass into lacteals

• fatty acids and glycerol also carried by lymph vessels and pas into the bloodstream near the neck - coating is removed and the fats pass into body cells

• part of the lymphatic system

adaptations of small intestine

• made of muscle to allow peristalsis

• duodenum produces many enzymes

• contains villi and microvilli for improved absorption

• each villus has a lymph supply (lacteal) to carry away the fats

villi

• adaptions: large numbers of villi and microvilli to increase surface area + walls are only 1 cell thick + they have a rich blood supply

• inside contains a lacteal, which contains a liquid called lymph

• they reform into fats that are coated with protein and pass into the lymph in the lacteals, which are transported by the lymph to be carried into the bloodstream in lymph vessels

large intestine

functions: reabsorbs water, produces -group vitamins, digest cellulose

these functions are carried out by symbiotic bacteria

caecum and appendix

these are vestigial organs, meaning that they have lost their former use

colon

its function is to reabsorb water

symbiotic bacteria in the colon

makes vitamins and digest cellulose, break down cellulose, prevent the growth of disease-causing organism

rectum

stores faeces

balanced diet

contains all the necessary food types in the correct proportions

enzymes

1. salivary amylase: starch → maltose

2. pepsin: protein → peptides

3. pancreatic amylase: lipids → fatty acids and a glycerol

4. lipase: lipids → lipid droplets

nutrition

the way in which an organism gets its food