Chapter 6:Nutrition in Humans
IntroductionPeristalsisProcess of DigestionAbsorptionAssimilationThe Liver
NUTRITION is the intake of food and the processes that convert food substances into living matter.
Nutrition comprises of the following:-
FEEDING: the intake of food into the body
DIGESTION: the process whereby large food molecules are broken down into soluble and diffusible molecules that can be absorbed into the body cells.
ABSORPTION: the process whereby digested food materials are taken into the body cells.
ASSIMILATION: the process whereby some of the absorbed food materials are converted into new protoplasm or used to provide energy
INTRODUCTION
PHYSICAL vs. CHEMICAL DIGESTION
Physical digestion:
Mechanical breakdown of food into small particles
Increases the surface area to volume ratio of the ingested food so that digestive enzymes can act on the food more efficiently.
Occurs in the mouth, when you chew food using your teeth and in the stomach, where churning of the stomach walls breaks up the food particles and mixes them with digestive enzymes.
Chemical digestion:
Enzymatic hydrolysis (recall Chap 4) of large food molecules into small soluble molecules which can be absorbed.
Achieved by the digestive enzymes found in the mouth,
stomach, duodenum and ileum.
The Human Alimentary Canal
You must be able to identify and label all structures!
Definition:
The rhythmic, wave-like contractions of the gut walls caused by the action of 2 antagonistic muscles.
Functions:
1. Moves the food along the gut
2. Mixes the food with digestive enzymes
Part of the gut wall
circular muscles
longitudinal muscles
What is Peristalsis?
The wall of the oesophagus is made up of 2 layers of muscles.
These muscles are present along the gut from the oesophagus to the rectum.
Part of the gut wall
layers of muscles
Antagonistic Muscles
The two layers of muscles are:
1. Longitudinal muscles on the outside of the gut; and
2. Circular muscles on the inside of the gut.
They are antagonistic = 2 muscles opposes the action of one another to bring about movement. (When 1 muscle contracts, the other relaxes and vice versa.)
circular muscles
Part of the gut wall
LABEL YOUR DIAGRAM NOW!
longitudinal muscles
Antagonistic Muscles
circular muscles constrict the lumen
longitudinal muscles dilates the lumen
Contraction of the circular muscles always constricts the lumen (becomes narrower and longer)
Contraction of the longitudinal muscles always dilates/ expands the lumen (becomes widen and shorter).
lumen
What is Peristalsis?
food mass is pushed forward
wall constricts to push food forward
circular muscles contract
longitudinal muscles relax
Contraction of Circular muscles
• When the circular muscles contract, the longitudinal muscles relax.
• The diameter of the gut decreases lumen constricts (becomes narrower and longer)
• Food is squeezed forward from original position.
food mass enters
circular muscles relax
longitudinal muscles contract
wall dilates to allow food to enter
Contraction of Longitudinal muscles
• When the circular muscles relax, the longitudinal muscles contract.
• The diameter of the gut increases lumen dilates/ expand (becomes widen and shorter)
• Food enters the lumen created.
Both food and air must pass through the pharynx when they enter the body. pharynx
What happens during breathing & swallowing?
pharynx
trachea (windpipe)
oesophagus
Normally, air passes into the trachea (windpipe) while food passes into the oesophagus.
air
What happens during breathing & swallowing?
trachea (windpipe)
glottis
During breathing, the larynx is lowered and the glottis is open.
pharynx
oesophagus
larynx (voice-box)
air
What happens during breathing & swallowing?
During swallowing, the larynx is raised and the glottis is covered by the epiglottis. This prevents food particles from entering the trachea.
pharynx
trachea (windpipe)
oesophagusglottis
epiglottis
food particles
larynx (voice-box)
What happens during breathing & swallowing?
trachea (windpipe)
Food particles then pass down the oesophagus by peristalsis.
pharynx
oesophagusglottis
epiglottisfood particles
larynx (voice-box)
What happens during breathing & swallowing?
Occasionally, small particles of food or water may get into the larynx or trachea.
trachea (windpipe)
larynx (voice-box)
food particles
What happens during breathing & swallowing?
This automatically induces violent coughing to force the food particles or water out and to prevent choking.
trachea (windpipe)
larynx (voice-box)
food particles
What happens during breathing & swallowing?
How is food digested in our body?
Stations: Mouth Oesophagus Stomach Small Intestines Large intestines Anus
Food enters the mouth.food
THE PROCESS OF DIGESTION
salivary gland
saliva
Food in the mouth stimulates the salivary glands to secrete saliva.
Saliva is mixed with the food. Mucin in saliva helps to soften the food.
Saliva contains an enzyme called salivary amylase which digests starch to maltose.
STATION 1: MOUTH
salivary gland
saliva
Chemical digestion in the mouth:
Action of salivary amylase:
Starch maltose
The pH of saliva is neutral (around pH 7). Salivary amylase is active at this pH.
Physical digestion in the mouth:
Chewing by teeth breaks the food up into smaller pieces. This increases the surface area to volume ratio for salivary amylase to work on.
STATION 1: MOUTH
The tongue rolls the food into small, slippery, round masses or boli (singular: bolus).
bolus
STATION 1: MOUTH
The boli are swallowed and pass down the oesophagus via the pharynx.
Peristalsis in the walls of the oesophagus pushes each bolus of food down into the stomach. Gravity also helps the food to pass down the oesophagus.
No digestion occurs here. bolus
STATION 2: OESOPHAGUS
Food passes into the stomach. bolus
stomach
STATION 3: STOMACH
The presence of food in the stomach stimulates the gastric glands to secrete gastric juice into the stomach cavity.
Peristalsis in the stomach wall churns and breaks up the food. Peristalsis also mixes the food well with gastric juice.
gastric juice
gastric gland
food
STATION 3: STOMACH
protein
Gastric juice is a dilute solution of hydrochloric acid (about pH 2) and two enzymes, pepsin and rennin.
curdled milk protein
milk protein pyloric sphincter
pepsin
polypeptide
rennin
STATION 3: STOMACH
protein
The dilute hydrochloric acid:1. stops the action of
salivary amylase by denaturing it;
2. changes the inactive forms of the enzymes, pepsinogen and prorennin, in the gastric juice, to the active forms, pepsin and rennin respectively;
3. provides a slightly acidic medium suitable for the action of the gastric enzymes; and
4. kills certain potentially harmful microorganisms in food.
curdled milk protein
milk protein pyloric sphincter
pepsin
polypeptide
rennin
STATION 3: STOMACH
protein
The proteases pepsin and rennin act on proteins.
Action of Pepsin: proteins polypeptides
Action of Rennin: caseinogen casein
Rennin clots or curdles milk proteins by converting the soluble protein caseinogen into insoluble casein. This is necessary because milk proteins would pass through the the duodenum as easily as water and would not be digested by pepsin. Insoluble casein remains long enough in the stomach to be digested by pepsin.
curdled milk protein
milk protein pyloric sphincter
pepsin
polypeptide
rennin
STATION 3: STOMACH
Food normally remains in the stomach for about three to four hours. The partly digested food becomes liquefied, forming chyme.
stomach
chyme
STATION 3: STOMACH
Chyme passes in small amounts into the duodenum when the pyloric sphincter relaxes and opens.
Structure:
Around 6m long!!!
It consists U-shaped duodenum (first part of small intestine), jejunum and the much coiled ileum.
pyloric sphincter
stomach
chyme
STATION 4: SMALL INTESTINES
STATION 4: SMALL INTESTINES
3 types of digestion occurs here:
1. Carbohydrate digestion (continues from the mouth)
2. Protein digestion (continues from the stomach)
3. Fat digestion (1st time digestion!)
3 other organs associated with digestion here:
1. Liver – produces bile and store in gall bladder
2. Gall bladder – releases the bile
3. Pancreas – secretes pancreatic juice
Chyme enters the small intestine. It stimulates:
1. Intestinal glands to secrete intestinal juice.
2. Pancreas to secrete pancreatic juice. The pancreatic juice passes through the pancreatic duct into the duodenum.
3. Gall bladder to release bile. Bile does not contain enzymes. Bile passes through the bile duct into the duodenum.
bile
intestinal juice
pancreatic duct
pancreatic juicebile duct
STATION 4: SMALL INTESTINES
During digestion in the small intestine,the chyme stimulates:
Intestinal glandsTo Secrete…
PancreasTo Secrete…
Gall bladderTo Release…
Intestinal juice:1. Enterokinase2. Erepsin3. Maltase4. Sucrase5. Lactase6. Intestinal lipase
Pancreatic juice:1. Pancreatic
amylase2. Pancreatic lipase3. Trypsinogen
Bile (passes through bile duct)
STATION 4: SMALL INTESTINES
STATION 4: SMALL INTESTINES
Intestinal juice is secreted by intestinal gland.
Intestinal juice consists of 6 digestive enzymes:
1. Enterokinase: inactive trypsinogen active trypsin
2. Maltase: maltose glucose + glucose
3. Lactase: lactose glucose + galactose
4. Sucrase: sucrose glucose + fructose
5. Erepsin: polypeptides amino acids
6. Intestinal lipase: fats fatty acids + glycerol
STATION 4: SMALL INTESTINES
Pancreas secretes PANCREATIC JUICE.
Pancreatic juice consists of 3 digestive enzymes:
1. Pancreatic amylase: starch maltose
2. Pancreatic lipase: fats fatty acids + glycerol
3. Trypsin: protein polypeptides
STATION 4: SMALL INTESTINES
Liver produces bile and stores in the gall bladder.
Gall bladder releases the bile via the bile duct.
Bile is not an enzyme!
Bile is an alkaline greenish-yellow liquid containing bile salts and bile pigment.
Function of bile:
Bile emulsifies fats breaks up fat into minute fat globules thereby increasing the surface area of the fat molecules for lipase to act on.
In the small intestine, bile salts emulsify fats.
They lower the surface tension of the fats, that is, they reduce the attractive forces between the fat molecules.
This causes the fats to break into tiny fat droplets suspended in water, forming an emulsion.
Note that this is just a physical break-up, but no chemical digestion of fat molecules has occurred.
big drop of fat
Bile salts emulsify fats into tiny fat droplets.
+
bile salts
tiny fat droplets
More about fat digestion…
Emulsification increases the surface area to volume ratio of the fats, speeding up their digestion by lipase.
Emulsified fats are digested by lipases (pancreatic and intestinal lipases) to fatty acids and glycerol.
fatty acids + glycerol
+
lipase
Bile salts emulsify fats into tiny fat droplets.
tiny fat droplets
More about fat digestion…
All three fluids (intestinal juice, pancreatic juice & bile) are alkaline.
The alkalis:
1. Neutralise the acidic chyme
2. Provide a suitable alkaline medium for the action of the pancreatic and intestinal enzymes.
bile
intestinal juice
pancreatic duct
pancreatic juicebile duct
STATION 4: SMALL INTESTINE
The digested food (simple sugars, amino acids, fatty acids & glycerol) are absorbed by the villi of the small intestine, especially of the jejunum & the ileum.
Water and mineral salts are absorbed from the undigested food material.
STATION 4: SMALL INTESTINES
Structure:
• Consists of the colon & rectum (muscular tube).
Processes:
• No digestion occurs here.
• Water and mineral salts are absorbed from the undigested food material. (same as the small intestines!)
• Faeces are stored temporarily in the rectum.
STATION 5: LARGE INTESTINES
• Faeces are egested through the anus.
• This is the last station. All food particles, please alight via the anus. We thank you for traveling with us.
STATION 5: THE ANUS
How is food absorbed by our body?
Definition of absorptionEnd products of digestionAdaptation of the small intestinesStructure of the villusHow are nutrients absorbed?
Absorption is the process whereby digested food is taken into the body cell.
Definition of Absorption
Carbohydrates:
• Simple sugars (glucose, galactose & fructose)
Protein:
• Amino acids
Fats:
• Fatty acids + glycerol
End products of Digestion
1. INCREASES THE SURFACE AREA FOR ABSORPTION
The inner walls of the small intestine are thrown into numerous transverse folds and furrows.
The small intestine also has numerous minute finger-like projections called villi projecting into the intestinal cavity.
These villi further increase the surface area; the epithelial cells of the villi, in turn, bear numerous microvilli
2. REDUCES BARRIER TO DIFFUSION
Villi have thin walls epithelium is only ONE cell thick.
How is the small intestine adapted for absorption?
3. PROVIDES SUFFICIENT TIME FOR ABSORPTION
The length of the small intestine is around 6m which is long enough to provide sufficient time for absorption.
4. CARRIES AWAY ABSORBED FOOD SUBSTANCES + CONTINUAL REMOVAL MAINTAINS A CONCENTRATION
GRADIENT FOR ABSORPTION
The villi of the small intestine are richly supplied with blood capillaries and lymphatic capillaries (lacteal).
How is the small intestine adapted for absorption?
Structure of the Villi
Structure of the Villi
Between the bases of the villi are the minute openings of the intestinal glands that secrete intestinal juice.
The intestinal wall and the villi are richly supplied with blood vessels & lymphatic vessels to carry away the absorbed substances.
In each villus is a lacteal or lymphatic capillary by blood capillaries.
The lymphatic capillaries of the villi transport fats while the blood vessels transport sugars and amino acids away from the intestine.
The Structure of the Villi
Adaptation of the villus for absorption
Minute/ small opening at the base of the villi helps in the production of intestinal juice that contains enzymes.
Each villi has its own blood capillary system aids in the absorption of amino acids and simple sugars
Each villi has its own lacteal system fatty acids and glycerol can be absorbed easily
Finger-like projections Allows for more efficient rate of absorption
Simple Sugars & Amino acids
Absorbed into blood capillaries of the villus
via diffusion or active transport
Glycerol & fatty acids
Absorbed into the lacteal (lymphatic capillaries) of the villus
via diffusion
Mineral salts
Absorbed into blood capillaries of the villus
via diffusion or active transport
How are nutrients absorbed into the body?
Assimilation
Definition of assimilation
How simple sugars, amino acids and fats are transported?
The Liver
Definition: The transport, modification and utilization of
absorbed food
Simple sugars and amino acids are transported by the hepatic portal vein to the liver.
Fats are transported by the lymphatic system to empty directly into the heart.
Assimilation
The largest gland in the body.
Refer to Pg 5 of your notes :
Match the following functions of the liver to their respective descriptions and construct a mind map
titled “the Liver”.
Metabolism of glucose Deamination of amino acids Detoxification Protein synthesis Iron storage Heat production Bile production
The Liver (Group work)