Chapter 6:Nutrition in Humans

6.1 Holozoic Nutrition

Nutrition is the intake of food and processes of converting food substances into living matter

Plants manufacture their own food – autotrophic

Animals cannot manufacture their own food, dependent on eating plants or other animals – heterotrophic

Mode of feeding organic matter is known as holozoic nutrition

6.1 Holozoic Nutrition Heterotrophic Nutrition Ingestion/Feeding – Taking food into body Digestion

Mechanical – chopping and grinding food with teeth and muscular churning of food, in stomach

Chemical – breaking large insoluble molecules into small, soluble ones (using enzymes)

Absorption – taking digested food into bloodstream Assimilation – using absorbed food in metabolic

processes Any food which cannot be digested/absorbed is

passed out of the gut during egestion

6.2 Mammalian Digestive System Consist of the gut (alimentary canal) and

glands associated with it (9m long) Includes mouth, pharynx, oesophagus,

stomach, small intestine and large intestine Other structures include salivary glands,

pancreas, liver and gall bladder

6.2 Mammalian Digestive SystemThe Mouth and buccal cavity Opening where food is ingested into buccal

cavity (mouth cavity) Buccal cavity processes food:

Teeth mechanically digest the food (increase surface area for enzymes to act on)

Salivary glands secrete saliva containing enzyme salivary amylase to digest starch into maltose

Tongue rolls the food into balls or boli (bolus) and pushes them to the back of the buccal cavity for swallowing

6.2 Mammalian Digestive SystemPharynx Pharynx is the part of

the gut leading from mouth to oesophagus and windpipe

Larynx (voice box) which lies below pharynx has a slit-like opening called glottis

Pharynx is a passage for both food and air

6.2 Mammalian Digestive SystemPharynx Food entering windpipe is prevented by a piece

of flap-like cartilage called epiglottis Epiglottis is above larynx just behind root of

tongue During swallowing, larynx moves up to be

covered by epiglottis and thus preventing food from entering windpipe

If small particles get into the larynx or windpipe, violent coughing results to force them out and prevent choking

6.2 Mammalian Digestive SystemOesophagus (Gullet) Muscular tube connecting mouth cavity and

stomach Wall of the oesophagus is made up of 2

layers of muscles These muscles are present along the gut

from the oesophagus to rectum

6.2 Mammalian Digestive SystemOesophagus (Gullet) > Peristalsis The two layers of muscles cause rhytmic,

wave-like contractions of the gut walls. This movement is known as peristalsis This process enables:

Enables food to be mixed with the digestive juices Moves the food along the gut

The circular and longitudinal muscles are antagonistic muscles (one set of muscles contracts, other set relaxes)

6.2 Mammalian Digestive SystemOesophagus (Gullet) > Peristalsis When circular muscles contract, longitudinal

muscles relax wall of gut constricts becoming narrower and longer Food in gut is squeezed/pushed forward

When longitudinal muscles contracts, circular muscles relaxes Wall of gut dilates becoming wider and shorter Widens lumen for the food to enter

6.2 Mammalian Digestive SystemOesophagus (Gullet) > Peristalsis

6.2 Mammalian Digestive SystemStomach Distensible muscular bag with thick and well

developed muscular walls Peristalsis of stomach wall churns

(mechanical digestion) food for up to 4 hours to mix with gastric juices

Mucous coat of stomach wall has numerous pits that secrete gastric juices.

Gastric juice consists of concentrated hydrochloric acid (pH2) and enzymes (rennin and pepsin)

6.2 Mammalian Digestive SystemStomach > Hydrochloric Acid Hydrochloric acids:

Stops action of salivary amylase Changes inactive forms of enzymes in gastric

juice to the active forms Provides an acidic medium suitable for the action

of the gastric enzymes Kills germs and certain potential parasites in food

6.2 Mammalian Digestive SystemStomach Partly digested food

becomes liquefied, forming chyme

Chyme passes in small amounts through a ring of muscle called the pylorus / pyloric sphincter, which relaxes to allow the food to enter the duodenum

6.2 Mammalian Digestive SystemSmall Intestine Final place of digestion Place where absorption of nutrients take

place Consists of: Duodenum, Jejunum, ileum

6.2 Mammalian Digestive SystemSmall Intestine > Duodenum U-shaped First part of small intestine (most digestion

occurs here) About 30m long Receives bile (produce by liver) via bile duct

from gall bladder (stores bile) Receives pancreatic juice from pancreas,

through pancreatic duct Releases digestive juice from its walls

6.2 Mammalian Digestive SystemSmall Intestine > Duodenum Chyme stimulates intestinal glands to secrete

intestinal juice Food comes in contact with pancreatic juice,

bile and intestinal juice All 3 fluids are alkaline which neutralize the

acidic chyme and provide suitable alkaline medium for the action of pancreatic and intestinal enzymes

6.2 Mammalian Digestive SystemSmall Intestine > Duodenum Pancreatic juice contains pancreatic

amylase, pancreatic lipase and protease (trypsinogen)

Intestinal juice contains enterokinase, erepsin (peptidase), maltase, sucrase, lactase, intestinal lipase

6.2 Mammalian Digestive SystemLarge Intestine 1.5 m long Consists of : Colon, Rectum (stores faeces

temporarily) Absorbs water and mineral salts No digestion takes place here

6.2 Mammalian Digestive SystemOrgans and glands related gut > Liver Largest gland Dark red with 5 lobes Attached with 3 blood vessels

Hepatic portal vein: Transport digested products from intestines to liver

hepatic vein: carries deoxygenated blood away hepatic artery: carries oxygenated blood to liver

Secretes bile (alkaline greenish-yellow fluid)

6.2 Mammalian Digestive SystemOrgans and glands related gut > Gall Bladder Stores bile temporarily Greenish yellow bag attached to liver Contracts to release bile via bile duct into

duodenum

Connected to duodenum via pancreatic duct Produces pancreatic juice (Digestive

enzymes) Pancreatic amylase Pancreatic lipase Trypsinogen

Secretes hormones insulin and glucagon

6.2 Mammalian Digestive SystemOrgans and glands related gut > Pancreas

A process where large insoluble molecules are broken down to smaller, soluble and diffusible molecules.

It can be broken down as: Physical/Mechanical Chemical

6.3 Digestion

Mechanical breakdown of food in: Mouth by the action of teeth (chewing) Stomach by churning of food

Increase surface area to volume ratio for enzyme to acts on.

6.3 DigestionPhysical Digestion

Breakdown of food involving hydrolytic reactions catalysed by enzymes

Takes place in Mouth, Stomach, Small Intestine (SMS)

6.3 DigestionChemical Digestion

Mouth Both Physical and chemical process Physical – chewing by teeth to increase surface area

for enzyme to act on Food In mouth stimulates salivary glands to secrete

saliva Salivary glands secrete saliva containing enzyme

amylase to digest starch into maltose and protein mucin

Mucin is sticky thus binding food together and lubricates it

pH 7

6.3 Digestion: The Digestive Process

Oseophagus No digestion occurs here Peristalsis and gravity help to push food down to

stomach.

6.3 Digestion: The Digestive Process

Stomach Physical churning of food Chemical digestion (Digestion of proteins starts) Digested by proteases - rennin and pepsin Carbohydrates digestion stops

Stomach contains gastric juice and it contains: Pepsin = digest proteins to polypeptides Rennin which clots or curdles milk proteins by

converting soluble protein caseinogens into casein dilute hydrochloric acid

6.3 Digestion: The Digestive Process

Stomach > Hydrochloric Acid Stops action of salivary amylase by denaturing it Changes inactive forms of enzyme pepsinogen and

prorennin in gastric juice to active forms pepsin and rennin respectively.

Partly digested food in stomach is called chyme Chyme passes into the duodenum when they pyloric

sphincter relaxes and opens

6.3 Digestion: The Digestive Process

Small Intestine Chyme stimulates the release of 3 fluids into the

duodenum: Pancreas secretes pancreatic juice into pancreatic duct Intestinal glands secrete intestinal juice Gall bladder releases bile into bile duct

Digestion of Carbohydrate and protein continues Fat digestion starts

6.3 Digestion: The Digestive Process

Pancreatic Juice Pancreatic amylase which digests starch to maltose Trypsin which digests proteins to polypeptides. Trypsin is produced as inactive trypsinogen are converted to the

active trypsin by intestinal enetrokinase Lipase which digests fats to fatty acids and glycerol

Intestinal Juice Maltase which digests maltose to glucose Enterokinase – Converting inactive trypsinogen to active trypsin Erepsin – digest polypeptides to amino acids Lipase – digest fats to fatty acids and glycerol

Bile Emulsify (breaking down into smaller molecules) fats

6.3 Digestion: The Digestive Process

6.3 Digestion : Carbohydrates

Starch

Maltose

Maltose(in small intestine)

Glucose

Pancreatic Amylase

Salivary Amylase(In Mouth)

No digestion of starch in stomach (amylase are denatured)

6.3 Digestion : Proteins Starts in stomach : acidic – pH2 Enzymes pepsin and rennin – pH 7 Continues in small intestine : alkaline- pH9

Trypsinogen Trypsinenterokinase

Proteins PolypeptidesTrypsin

Polypeptides Amino acidsErepsin

InSmall intestine

6.3 Digestion : Fats Starts in small intestine

Bile emulsifies fats, i.e.: lowers the surface tension of fats and breaks them up into smaller fat globules

Surface area increased for action of lipases

Fats + Bile Emulsion

Fatty Acids + GlycerolGall bladder

secretes

6.4 Absorption

Occurs in ileum Active transport takes place (requires energy) Rate of absorption depends on:

Length of Small Intestine Inner wall of intestine has numerous folds Presence of villi (singular: villus) Presence of microvilli on villi

6.4 Absorption Villi have thin wall (one

cell thick) Absorbed nutrients

transported away quickly resulting in concentrating gradient

All these speeds up diffusion for efficient absorption.

6.4 Absorption Sugar, amino acids and mineral salts pass

into blood capillaries via process of active transport

Glycerol and fatty acids enters into epithelium before combining into minute fat globules

Fat globules enters the lacteals/ lympathic capillary.

6.4 AbsorptionUndigested and unabsorbed materials Stored temporarily in rectum Discharged as faeces through anus Process of removal is known as egestion /

defacation

6.5 Functions of Liver Regulate blood glucose level Production of bile Iron storage Protein synthesis Deamination of amino acids Detoxification

6.5 Function of Liver Regulate blood glucose level

When blood glucose is too high (especially after meal), liver alerts pancreas

Islets of langerhans in pancreas will produce insulin

Insulin convert glucose into glycogen.

6.5 Function of Liver Regulate blood glucose level

After Lunch

Blood Glucose High

Liver

Pancreas

Islets of Langerhans

InsulinGlucose

Glycogen

Stored in Liver and Muscles

High Blood Glucose Concentration

6.5 Function of Liver Regulate blood glucose level

Liver (Low blood glucose)

Pancreas Islets of Langerhans

Glucagon GlucoseGlycogen

Low Blood Glucose Concentration

6.5 Function of Liver Production of Bile

Helps in digestion fats (emulsifies fats) Stored temporarily in gall bladder

Protein Synthesis Forms amino acids Albumins, globulins, fibrinogen found in blood

plasama

6.5 Functions of LiverIron Storage Spleen (near liver) Destroys red blood cells Haemoglobin in red blood cells destroyed by

liver > Storing of Iron Bile pigments also formed during haemoglobin

breakdown.

6.5 Function of Liver Deamination of Amino Acids

Amino Acids

Deamination

Carbon ResidueAmino Group

GlucoseAmmonia

GlycogenUrea

converted

converted

converted

converted

6.5 Functions of LiverDetoxification Converting harmful substances in harmless

ones. Example: Alcohol dehydrogenase (a type of

enzyme) breaks down acetaldehyde in alcohol

Alcohol stimulates secretion of stomach acid which may lead to stomach ulcers

Prolonged alcohol abuse may lead to cirrhosis (Damage of liver cells)