chapter 6: nutrition in humans. a balanced diet is a diet which contains all the essential nutrients...

Chapter 6: Chapter 6: Nutrition in Nutrition in

HumansHumans

Chapter 6: Chapter 6: Nutrition in Nutrition in

HumansHumans

• A balanced diet is a diet which contains all the essential nutrients (carbohydrates, fats, proteins, vitiamins, minerals, water and dietary fibre) in the right proportions.

I need more proteins to synthesize new cells so

that I can grow big and tall.

• The nutrients required vary among individuals. For example, a growing child requires more protein than an older person to make new cells and teenagers require more carbohydrates for energy than an older person.

Nutrition• Nutrition is the process of taking in food and

converting it into living matter.

• In animals, nutrition consists of:

Ingestion (Taking in food)Digestion (Breaking down food)Absorption (Absorbing digested food into cells)Assimilation (Making use of absorbed food)Egestion (Removing undigested food)

INGESTION

DIGESTION

ABSORPTION

ASSIMILATION

EGESTION

Taking in food

Breakdown of complex food substances into smaller

soluble food substances

Digested food is absorbed Into body cells

Absorbed food is use to provide energy or form

new protoplasm

Removal of undigested food

Case Study 2:• The burger you ate yesterday

would like to travel from your stomach to your muscles. How would it go about

doing so?

The Digestive System

Consists of:

1) The gut or alimentary canal (9 m) from mouth to anus.

2) Glands (A cell, tissue, or organ that secretes a chemical substance).

3) Associated organs.

MOUTH(Buccal Cavity) PHARYNX

OESOPHAGUS(GULLET)

STOMACH

RECTUMANUS

ALIMENTARY CANAL

LARGEINTESTINE

SMALLINTESTINE

The Alimentary Canal

Overview

• Mouth & Buccal Cavity → Pharynx →

Oesophagus → Stomach → Small Intestine

→ Large Intestine → Anus.

LIVERGALL

BLADDERPANCREAS

THE ASSOCIATED ORGANS

Mouth & Buccal Cavity

The Mouth & Buccal Cavity

Buccal Cavity

The Mouth & Buccal Cavity

• Food enters through the mouth. This process is called ingestion.

• Teeth cuts food into small pieces. This increases surface area to volume ratio for enzyme to act more efficiently.

The Mouth & Buccal Cavity

• Salivary glands produce saliva to moisten food.

• Saliva also contains salivary amylase to break down starch to maltose.

• pH of saliva is neutral (around pH 7).

The Mouth & Buccal Cavity

Salivary Glands

The Mouth & Buccal Cavity

Starch Maltose Salivary Amylase

Salivary amylase is active at pH 7.

The Mouth & Buccal Cavity

• Tongue rolls food into boli.

• Food is swallowed and enters the pharynx.

Pharynx

Pharynx & Oesophagus

Pharynx

A common passage

for food & air.

Pharynx

• Connects buccal cavity to oesophagus.

• When swallowing, epiglottis (a flap-like tissue) covers wind pipe preventing entry of food into wind pipe.

Oesophagus

• 2 layers of muscles:

• Outer layer: Longitudinal muscles

• Inner layer: Circular muscles

• Longitudinal and circular muscles present throughout the wall of alimentary canal from oesophagus to rectum.

• Food moves along the alimentary canal by peristalsis.

Peristalsis

• A rhythmic, wave-like contractions of the gut wall.

• Caused by alternate contractions of the longitudinal & circular muscles.

• It helps to move food along the gut & mix food with digestive juices.

Peristalsis

• A muscular bag that can be stretched or expanded.

The Stomach

Walls of Stomach

Gastric Glands

Gastric Glands

•Walls of stomach contain gastric glands which secrete gastric juice.

•Food in stomach stimulates gastric glands to produce gastric juice.

The Stomach

• Peristalsis mixed food with gastric juice.

• Gastric juice contains:

1) Proteases (Pepsin & Rennin)

2) Dilute hydrochloric acid

Protein Digestion in Stomach

• Pepsin digests proteins to polypeptides.

Proteins PolypeptidesPepsin

Digestion of Milk Proteins

• Milk contains soluble protein caseinogen.

• Caseinogen passed through stomach too quickly for pepsin to digest.

• The protease, rennin curdles milk by converting soluble caseinogen to insoluble casein.

Caseinogen Casein (Soluble) (Insoluble)

Rennin

Casein Polypeptides(Insoluble)

Pepsin

The Stomach

Insoluble casein stays in stomach long enough for pepsin to act on.

The Stomach

• Peristalsis mixed food with gastric juice.

• Gastric juice contains:

1) Proteases (Pepsin & Rennin)

2) Dilute hydrochloric acid

Dilute Hydrochloric Acid

• Create pH 2 environment in stomach.

• Stops activity of salivary amylase.

• Activate proteases pepsin and rennin.

• Provide pepsin with a suitable pH environment to work in.

• Kills bacteria in food.

The Stomach

Oesophagus

Pyloric Sphincter

Partially digested food in stomach is called chyme. (acidic)

Small Intestine

Small Intestine

• Around 6 m long.

• Divided into 3 parts:

- Beginning part: duodenum

- Middle part: jejunum

- Last part: ileum

• Presence of chyme in duodenum stimulates release of 3 substances:

- Pancreatic juice

- Intestinal juice

- Bile

• All these fluids are alkaline. They neutralise the acidic chyme.

Pancreatic Juice

• Produced by pancreas.

• Passed through pancreatic duct into duodenum.

Pancreatic Juice

Contains the following enzymes:

• Pancreatic amylase

(Digests starch to maltose)

• Trypsin

(Digests proteins to polypeptides)

• Lipase

(Digests fats to fatty acids & glycerol)

Pancreatic Juice In Duodenum

Starch Maltose Pancreatic Amylase

Proteins PolypeptidesTrypsin

Fats Fatty acids + GlycerolLipase

Intestinal Wall

Intestinal glands

Intestinal Juice

• Intestinal glands produce intestinal juice, which contains:

• Maltase (Digests maltose to glucose)

• Erepsin (Digests polypeptides to

amino acids)

• Lipase (Digest fats to fatty acids & glycerol)

Intestinal Juice In Duodenum

Maltose Glucose Maltase

Polypeptides Amino acids

Fats Fatty acids + GlycerolLipase

Erepsin

Intestinal juice also contains sucrase and lactase.

Bile

An alkaline greenish-yellow fluid.

Bile• Bile is produced

by liver cells.

• It is stored in the gall bladder.

Liver

• Bile passed through the bile duct into duodenum.

Bile

Bile

• Bile does not contain enzymes.

• Bile is made up of bile pigments and bile salts. Bile pigments give bile its colour.

• Bile salts help in the digestion of fats.

Bile Salts Emulsify Fats

Large fat drop

+ Bile Salts

Tinyfat droplets

• By breaking fats into smaller droplets (Emulsification), bile salts increase surface area to volume ratio of fats for digestion by lipase.

Tinyfat droplets

Bile Salts Emulsify Fats

MOUTH(Buccal Cavity) PHARYNX

OESOPHAGUS(GULLET)

STOMACH

RECTUMANUS

ALIMENTARY CANAL

LARGEINTESTINE

SMALLINTESTINE

1. MOUTH•MASTICATION•SALIVARY GLANDS secrete saliva (ph 7) - MUCIN MOISTEN FOOD - Salivary amylase : Starch MALTOSE

2. OESOPHAGUS•No digestion

3. STOMACH ( acidic pH)• gastric Glands produce gastric juice - Hydrochloric Acid : kills bacteria, activate protease - Pepsin : - Renin :

Protein Polypeptide

Caseinogen Casein (Insoluble) (soluble)

INTESTINAL GLANDS

4. SMALL INTESTINE

BILEPANCREATIC

JUICEINTESTINAL

JUICE

PANCREAS LIVER via Bile duct

Pancreatic Amylase

Trypsin

Pancreatic Lipase

Maltase, Sucrase, Lactase

Erepsin (Peptidase)

Intestinal Lipase

Quiz on Digestion

• 1. Involuntary muscle contractions which

move a bolus through the gastrointestinal

tract are called ____________________

• 2. Hydrochloric acid is secreted in the

_____________________.

• 3. Polypeptides is broken down into amino

acids by the enzyme ___________ found in

intestinal juice.

• 4. Name the 2 proteases found in the

stomach.

• 5. Which organ produces bile?

• 6. How does bile aids in digestion of food?

INGESTION

DIGESTION

ABSORPTION

ASSIMILATION

EGESTION

Taking in food

Breakdown of complex food substances into smaller

soluble food substances

Digested food is absorbed Into body cells

Absorbed food is use to provide energy or form

new protoplasm

Removal of undigested food

Absorption of digested food substances

• End products of digestion are simple molecules

-Simple sugars (glucose, fructose and galactose)

-Amino acids -fatty acids & glycerol.

• Main site of absorption – ileum of small intestine

How is the small intestine adapted for absorption?

VIDEO

To increase the surface area for absorption:

• The inner walls of the small intestine have numerous foldings.

Villi

• Inner walls of small intestine is lined with finger-like projections called villi.

• Villi help to increase surface area for absorption of digested food substances.

One-cell Thick Epithelium

• Epithelium – The surface layer

• The villi have epithelium that is very thin (only one-cell thick).

• This allows digested food substances to pass through easily.

Microvilli

• The epithelial cells (cells on the surface) of the villi have microvilli.

• This further increases surface area for absorption.

Figure 14.9Slide 14.10ACopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

The Wall of the Small Intestine

The small intestine is well supplied with blood capillaries and lacteals to carry the absorbed food substances.

This helps maintain the concentration gradientfor absorption of digested food substances.

Amino acids and glucose enters blood capillaries of the villi.

Fatty acids and glycerol diffuses into villi and enter lacteals as fat molecules.

Blood capillaries

Lacteal

Small intestine is long enough ( 6 m ) to provide sufficient time for absorption.

The Large Intestine

Most water is absorbed in ileum.

Colon absorbs water and mineral salts.

Egestion

• Undigested materials are stored temporarily in rectum and will be egested through the anus.

Transport and Assimilation of Food Substances

Hepatic Portal Vein

• Sugars and amino acids absorbed into small intestine will be transported to the liver via the hepatic portal vein.

Functions of The Liver

In Liver,

• Liver converts Excess Sugar to glycogen for storage.

• Some of the glucose leave the liver and distributed around the body.

•

• When concentration of glucose in blood is high,

Pancreas will produce the hormone insulin: causes the liver to convert glucose to glycogen.

• Blood glucose concentration returns to normal.

• When the concentration of glucose in blood is low,

Pancreas will produce the hormone glucagon which causes the liver to convert glycogen to glucose.

• Glucose enters blood, blood glucose concentration returns to normal.

1) Liver regulates the concentration of glucose in blood.

AMINO ACID

NH2 COOH

R

C

H

Amino group

Acidic group

Hydrocarbon side chain

2) Deamination of Amino Acids

• Excess amino acids are broken down in liver.

• Amino group → ammonia (toxic to cells) → Urea (non-toxic, removed in urine).

• This process is called deamination.

• Remaining amino acid molecule is converted into glucose and stored as glycogen in the liver and muscles.

Functions of Liver

3) Produces bile for the emulsification of fats.

4) Worn out red blood cells are destroyed in spleen and the haemoglobin is transported to the liver. Liver breaks down haemoglobin and stores the iron released.

5) Detoxification - Breaks down alcohol.

Effects of excessive alcohol consumption:

• Alcohol stimulates acid production in stomach, increasing risk of gastric ulcers.

• Alcoholic cirrhosisCirrhosis is a condition where normal liver tissue is replaced by scar (fibrous) tissue. The scar tissue affects the normal structure and re-growth of liver cells. Liver cells become damaged and die as scar tissue gradually develops. So, the liver gradually loses its ability to function. Prolonged alcohol abuse destroys liver cells, causing bleeding in liver resulting in liver failure and death.

Jigsaw Puzzle