Human Nutrition.

balanced diet

Provides sufficient energy. Provides molecules for metabolism and nutrients in correct quantities.

necessary food groups

• carbohydrates

• lipids

• proteins

• water

• dietary fibre

• minerals

• vitamins

food functions funcitons

• carb - Source of energy. Provide energy for respiration in cells

• protein - growth and repair of tissues

• lipid - insulation and energy storage

• vitamins - needed in small quantities to maintain health

• minerals - needed in small quantities to maintain health

• fibre - provides bulk/roughage and helps food to move through the stomach and intestines

• water - needed for chemical reactions to take place. regulates body temperature.

vitamin C

forms an essential part of collagen protein, which makes up skin, hair, gums and bones

maintains healthy skin and gums

deficiency of VC is called scurvy

vitamin D

helps the body absorb calcium and so required for strong teeth and bones

deficiency of vitamin D is called rickets. rickets causes weak and soft bones, as well as deformities

calcium

essential for strong bones and teeth and involved of the clotting of blood

can lead to osteoporosis later in life if u dont have enough calcium

iron

required to make haemoglobin

for transport of oxygen

prevent iron-deficient anaemia

stages of digestion

* ingestion - taking in of substances * digestion - breakdown of food * absorption -  the movement of nutrients (small food molecules and ions) from the wall of the intestine into the blood * assimilation - uptake and use of nutrients by cells * egestion - the removal of undigested food from the body as faeces

mouth and salivary glands in digestive system role

The teeth in the mouth break down food into smaller pieces. This is to increase the food's surface area for the action of of amylase enzymes in chemical digestion. The salivary glands produce amylase, which breaks down starch into maltose. The tongue shapes the food into a bolus and is lubricated by saliva, so it is easier to swallow.

oesophagus

Tube that connects the mouth and stomach.

Uses wave-like contractions/peristalsis to push the food down without relying on gravity.

stomach

• The stomach mechanically digests food by churning actions. The muscles in the lining of the stomach contract to physically squeeze and mix the food with hydrochloric acid. This breaks it down into smaller pieces and liquefies it.

• chemically digests food using pepsin enzymes, which chemically digest proteins

• hydrochloric acid killing harmful microorganisms in food and denatures enzymes in bacteria

• providing an acidic pH for optimum enzyme activity

small intestine

duodenum (first section) - where food coming out of the stomach finishes being digested by enzyme secreted here and from the pancreas.

the pH here is alkali. 8-9

ileum (second section) - where absorption of food molecules take place. long and lined with villi to increase the surface area over which food absorption can take place

large intestine

water is absorbed from the remaining material to produce faeces

faeces is stored in the rectum and removed through the anus

pancreas

produces all three digestive enzymes; amylase, lipase. protease

secretes an alkaline fluid (pancreatic juice) to raise the pH of the small intestine and provide an optimum pH for enzymes there

liver

produces bile which emulsifies fats.

bile raises the pH of the small intestine

amino acids not used to make proteins r broken down here (deamination) this produces urea

gallbladder

stores bile and releases it into the small intestine/duodenum as required

mechanical digestion

the breakdown of food into smaller pieces without chemical change to the food molecules

what does physical digestion do?

increase the surface area of food for the action of enzymes in chemical digestion

teeth

incisor - chisel shaped for biting and cutting

canines – pointed for tearing, holding and biting

premolars and molars – larger, flat surfaces with ridges at the edges for chewing and grinding up food

structure of teeth

chemical digestion

breakdown of large insoluble molecules into smaller soluble ones

role of chemical digestion

producing small soluble molecules that can be absorbed

carbohydrases

amylase - breaks down starch into simpler reducing sugars

produced in the salivary glands and pancreas. acts in the mouth

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maltase breaks down maltose to glucose on the membranes of the epithelium lining the small intestine

proteases

proteases break down proteins into amino acids.

pepsin breaks down protein in the acidic conditions of the stomach

trypsin breaks down protein in the alkaline conditions of the small intestine

produced by the pancreas - trypsin

lipases

breaks down lipids into fatty acids and glycerol

produced in the pancreas and acts in the duodenum

bile role in chemical digestion

neutralises the acidic mixture of food and gastric juices entering the duodenum from the stomach, to provide a suitable pH for enzyme action

where r nutrients absorbed?

small intestine

most of the water is

most water is absorbed from the small intestine (the ileum) but that some is also absorbed from the colon

how r villi adapted for absorption

• microvilli on the surface of the villi further increase the surface area for the absorption of nutrients. to increase rate of absorption of nutrients

• the wall of each villus is one cell thick. this reduces the diffusion pathway and there is a short distance for active transport

• lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph

• Well supplied with a network of blood capillaries to maintain good concentration gradient. Capillaries absorb glucose and amino acids.

• (For structure diagrams say:

• Thin epithelium. One cell thick to reduce diffusion pathway and increase diffusion rate. Epithelium has microvilli to increase surface area for absorption)

lacteal functions

absorbs, fatty acids (and glycerol)

transports, fats / fatty acids, into, lymph(atic) vessels

importance of microvilli

large surface area

allow, increased rate of / fast, absorption of nutrients