Chapter 6: Nutrition in Humans

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 RECTUM ANUS ALIMENTARY CANAL LARGE INTESTINE SMALL INTESTINE

The Alimentary Canal Overview Mouth & Buccal Cavity → Pharynx → Oesophagus → Stomach → Small Intestine → Large Intestine → Anus.

LIVER GALL BLADDER PANCREAS 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

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 Polypeptides Pepsin

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

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 Polypeptides Trypsin Fats Fatty acids + Glycerol Lipase

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 + Glycerol Lipase 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 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 Tiny fat droplets

By breaking fats into smaller droplets (Emulsification), bile salts increase surface area to volume ratio of fats for digestion by lipase. Tiny fat droplets Bile Salts Emulsify Fats

MOUTH (Buccal Cavity) PHARYNX OESOPHAGUS (GULLET) STOMACH RECTUM ANUS ALIMENTARY CANAL LARGE INTESTINE SMALL INTESTINE

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 BILE PANCREATIC JUICE INTESTINAL 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 14.9 Slide 14.10A Copyright © 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 gradient for 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 NH 2 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 cirrhosis Cirrhosis 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