Nutrition in Humans Chapter 6 Learning Objectives Questions

Nutrition in Humans Chapter 6

Learning Objectives Questions to answer! 1. What is nutrition? 2. Which parts of the body are involved in digestion? 3. What is digestion? 4. What happens to the food after digestion?

What is Nutrition? Objective 1: State the definition of nutrition.

What is Nutrition? Definition of Nutrition is the process of taking in food and converting it into living matter. Animals feed by taking in complex organic matter – HOLOZOIC NUTRITION

What is Nutrition? 5 Processes of Nutrition 1. Feeding or ingestion: food is taken into the body. 2. Digestion: large food molecules are broken down into smaller soluble molecules that can be absorbed into the body cells. 3. Absorption: digested food substances are absorbed into body cells. 4. Assimilation: some of the absorbed food substances are converted into new protoplasm or used to provide energy. 5. Egestion: undigested food is being passed out of the body via the anus.

Which parts of the body are involved in digestion? Objective 2: Describe the functions of the main regions of the alimentary canal.

Which parts of the body are involved in digestion? The Digestive System • Consists of the alimentary canal and the glands and organs associated with it. • The alimentary canal is like a tube that extends from the mouth to the anus. • Most of its length is coiled in the abdominal cavity.

Which parts of the body are involved in digestion? mouth teeth The Digestive System salivary gland pharynx oesophagus stomach liver Gall bladder pancreas pyloric sphincter duodenum ileum ascending colon caecum appendix descending colon rectum anus

The Digestive System - Mouth • Food enters the body through the mouth. • The mouth leads to the buccal cavity.

The Digestive System - Mouth What do you find in the mouth? : • Teeth: chewing action (mastication) breaks down large mouth pieces of food into smaller pieces. This increases surface area to volume ratio of the food for enzyme action. • Salivary glands: secrete saliva teeth into the mouth via ducts. • Tongue: helps to mix food with saliva. Taste buds help one to identify and select suitable foods. Process of salivary gland

The Digestive System - Pharynx • Connects the buccal cavity to the oesophagus and larynx (voice box). • Leads to the trachea. • Both food and air must pass through the pharynx then they enter the body. • Air will pass to the trachea, while food will go into the oesophagus.

The Digestive System - Pharynx • The epiglottis is above the larynx, and it prevents food from going the wrong way. • During swallowing, the larynx moves up and the epiglottis moves downwards so that the epiglottis covers the larynx. • If food or water enters the trachea, it induces coughing to force the food/water particles out and prevent choking.

The Digestive System - Oesophagus • Also known as the gullet. • A narrow, muscular tube. • Passes through the thorax (chest) and the diaphragm to join the stomach.

The Digestive System - Oesophagus • Made up of 2 layers of muscles, present from the oesophagus to the rectum: – Longitudinal muscles (outer layer) circular – Circular muscles (inner muscles layer) • These muscles are antagonistic muscles – when one contracts, the other relaxes longitudinal muscles Part of the gut wall

The Digestive System - Oesophagus • The muscles cause peristalsis – rhythmic, wavelike contractions of the gut walls. • It helps to move food along circular the gut while mixing the muscles food with digestive juices. longitudinal muscles Part of the gut wall

Which parts of the body are involved in digestion? mouth teeth oesophagus The Digestive System salivary gland

The Digestive System - Oesophagus PERISTALSIS • When circular muscles contract, longitudinal muscles relax. The gut wall constricts (becomes narrower and longer). Food is squeezed or pushed forward. • When longitudinal muscles contract, circular muscles relax. The gut wall dilates (becomes wider and shorter). This widens the lumen for food to enter. wall dilates to allow food to enter circular muscles longitudinal muscles food mass wall constricts to push food forward

The Digestive System - Oesophagus PERISTALSIS • When circular muscles contract, longitudinal muscles relax. The gut wall constricts (becomes narrower and longer). Food is squeezed or pushed forward. • When longitudinal muscles contract, circular muscles relax. The gut wall dilates (becomes wider and shorter). This widens the lumen for food to enter. Process of

Which parts of the body are involved in digestion? Objective 2: Describe the functions of the main regions of the alimentary canal.

The Digestive System - Stomach • The stomach is a distensible (muscular) bag. • The muscles of the stomach wall are thick and welldeveloped. • When fully stretched, it sends signals to the brain to indicate that it is full.

The Digestive System - Stomach • The stomach wall has many pits which lead to gastric glands. • They secrete gastric juices into the stomach. What is one enzyme found in gastric juice? pits

The Digestive System - Stomach Where else can we find circular • The stomach stores food for a few muscles? hours. It digests food to become chyme. • Food stays in the stomach because of the pyloric sphincter – a ring of circular muscle located between the stomach and duodenum. – Contracts: stomach exit closes – Relaxes: stomach exit opens, food leaves the stomach. Process of

The Digestive System – Small Intestine • Consists of 3 parts: – Duodenum progressively – Jejunum more coiled – Ileum

The Digestive System – Small Intestine • Wall of small intestine has 2 functions: – Contains glands which secrete intestinal juice. It contains digestive enzymes. – Wall is adapted to absorb digested food products and water. Process of

The Digestive System – Large Intestine large intestine • The large intestine is about 1. 5 m long – Shorter and wider than the small intestine • Consists of 2 parts: – Colon – Rectum colon rectum small intestine

The Digestive System – Large Intestine • Only undigested food enters the colon. • It absorbs water and mineral salts from the food. • No digestion occurs in the colon

The Digestive System – Large Intestine • The rectum temporarily stores faeces. • When it contracts, faeces is expelled through the anus. rectum

The Digestive System – Large Intestine • Between the small and large intestines lie the caecum and appendix. • The caecum has no function in humans. • The appendix contains bacteria that are useful to the body. caecum Process of appendix

Which parts of the body are involved in digestion? The Digestive System

Which parts of the body are involved in digestion? Objective 3: Describe the functions of the organs associated with digestion.

Which parts of the body are involved in digestion? mouth teeth The Digestive System salivary gland pharynx oesophagus stomach liver Gall bladder pancreas pyloric sphincter duodenum ileum ascending colon caecum appendix descending colon rectum anus

The Digestive System - Liver • The largest internal organ in the body • There are 3 important blood vessels attached to the liver: – Hepatic vein – Hepatic artery – Hepatic portal vein

The Digestive System - Liver liver • It is also the largest Whygland in the body. alkaline – Secretes bile into? the duodenum • Properties of bile: – Alkaline – Greenish-yellow – Contains bile salts and bile pigments – Produced in the liver, stored in the gall bladder bile duct

The Digestive System - Liver liver • Functions of bile: – – Neutralize acid in chyme Activate intestinal enzymes Speed up fat digestion Gives faeces its colour • When the gall bladder contracts, bile is secreted into the duodenum via the bile duct. Process of gall bladder bile duct

The Digestive System - Pancreas • Connected to the duodenum via the pancreatic duct • Secretes pancreatic juice which contains digestive enzymes. • Also secretes hormones which control blood glucose level. Process of

What is Digestion? Objective 4: State the definition of digestion.

What is Digestion? Definition of Digestion is the process by which the body breaks down carbohydrates, fats and proteins into simpler substances that cells can absorb and use. Physical digestion The mechanical break up of food into small particles. Chemical digestion The breaking down of large molecules in food into small, soluble molecules which can be absorbed. Chemical digestion involves hydrolysis catalyzed by digestive enzymes.

What is Digestion? Objective 5: Describe the process of digestion in the alimentary canal and the functions of digestive enzymes.

What is Digestion? Physical Digestion • Physical digestion breaks down food into smaller particles. • Purpose: to increase surface area to volume ratio of the food to aid enzyme action. • Food substances are not chemically changed during physical digestion. • Where does physical digestion occur? – In the mouth chewing / mastication – Along the alimentary canal peristalsis – Physical digestion of fats in the small intestine emulsification

What is Digestion? Physical Digestion EMULSIFICATION • Fats do not dissolve in water – they tend to clump together. • This reduces the surface area for enzymes to work, slowing down fat digestion. • Bile molecules place themselves in between the fat and water – half the molecule is hydrophilic, half is hydrophobic. • This prevents the fat from clumping together. • Surface area of fat molecules is increased, speeding up enzyme action. Picture taken from http: //www. colorado. edu/eeb/web_resources/carto ons/bile. html

Chemical Digestion What is Digestion? • Breaking down of large molecules in food (starch, protein, fats) into small soluble molecules which can be absorbed. • Hydrolytic reactions – catalysed by ENZYMES • Three groups of enzymes: Carbohydrases Lipases Proteases • Chemical digestion occurs mainly in 3 parts of the alimentary canal: – Mouth, stomach, small intestine

What is Digestion? Chemical Digestion In the mouth. . . • Food in the mouth stimulates the salivary glands to secrete saliva. • Saliva is mixed with food. Mucin in saliva softens the food. • Salivary amylase is found in saliva: – Digests to maltose is p. H 7. • The optimum p. Hstarch of salivary amylase – The p. H of saliva is neutral. • The tongue rolls the food into small, slippery, round masses called boli (singular: bolus). • The boli are swallowed and passed down into the oesophagus.

What is Digestion? Chemical Digestion In the stomach. . . The presence of food in the stomach stimulates the gastric glands to secrete gastric juice into the stomach. Gastric juice contains 3 substances: – Hydrochloric acid – Pepsinogen – Prorennin

What is Digestion? Chemical Digestion In the stomach. . . Action of Pepsinogen is activated to pepsin by hydrochloric acid. Pepsin then digests protein to polypeptides. pepsinogen proteins hydrochloric acid pepsin polypeptides

Chemical Digestion What is Digestion? In the stomach. . . Action of Rennin Prorennin is activated to rennin by hydrochloric acid. Rennin curdles milk proteins by converting soluble protein caseinogen into insoluble casein. – Soluble caseinogen would pass through the stomach as easily as water and not be digested. – Insoluble casein can remain in the stomach to be digested. hydrochloric acid rennin caseinogen rennin casein pepsin polypeptides prorennin

What is Digestion? Chemical Digestion In the stomach. . . Purpose of Hydrochloric Acid Stops the activity of salivary amylase by denaturing it Activates pepsinogen and prorennin to form pepsin and rennin respectively Provides acidic medium for the action of pepsin and rennin Kills harmful microorganisms in food

What is Digestion? Chemical Digestion In the small intestine. . . When chyme enters the small intestine, it stimulates 3 glands: – Intestinal glands secrete intestinal juice, which contains enzymes sucrase, maltase, intestinal lipase, lactase, enterokinase, and erepsin. SMILEE! – Pancreas secretes pancreatic juice, which contains pancreatic amylase, pancreatic lipase, and ALT trypsinogen. – Gall bladder releases bile. It does not contain enzyme

What is Digestion? Chemical Digestion In the small intestine. . . All 3 fluids are alkaline: – Neutralize acidic chyme – Provide suitable p. H for the action of pancreatic and intestinal enzymes

What is Digestion? Chemical Digestion In the small intestine. . . Carbohydrate digestion starch pancreatic amylase maltose maltase glucose lactase glucose + galactose sucrase glucose + fructose

What is Digestion? Chemical Digestion In the small intestine. . . Protein digestion trypsinogen enterokinase trypsin proteins trypsin polypeptides erepsin amino acids

Chemical Digestion What is Digestion? In the small intestine. . . Fat digestion fats lipase fatty acids + glycerol Recall: What process speeds up fat digestion in the small intestine?

What is Digestion? Digestive Enzymes small intestine mouth Carbohydrate digestion starch salivary amylase maltose starch pancreatic amylase maltose maltase glucose lactase glucose + galactose sucrase glucose + fructose

Digestive Enzymes What is Digestion? small intestine stomach Protein digestion hydrochloric acid rennin caseinogen rennin casein pepsin polypeptides prorennin trypsinogen enterokinase trypsin proteins trypsin polypeptides erepsin amino acids

What happens to the food after digestion? Objective 6: Describe how digested food is absorbed.

What happens to food after digestion? Absorption • Where does absorption occur? ü In the small intestine and large intestine • What nutrients are being absorbed? ü Simple sugars ü Amino acids ü Fatty acids and glycerols ü Water and mineral salts

What happens to food after digestion? Absorption How does absorption take place in the small intestine? • Glucose and amino acids: – Absorbed by diffusion into blood capillaries of the villi. – Absorbed by active transport when there is lower concentration of digested food substances in the small intestine than in the blood capillaries. • Fatty acids and glycerol: – Absorbed by diffusion into the epithelium – Combine to form fat globules which enter the lacteals • Water and mineral salts: small intestine – Absorbed by the and colon – Most of the water is absorbed by the ileum

What happens to food after digestion? Absorption: Small Intestine Adaptations of the Small Intestine for Absorption • The rate of absorption of digested food substances depends on 3 factors: 1. Surface area 2. The thickness of 3. cell membranes 3. Concentration gradient

What happens to food after digestion? Absorption: Small Intestine 1. Surface Area • The surface area of the small intestine is increased for absorption in 4 ways: 1. Inner walls have folds 2. The surface of the folds are lined with numerous villi (singular: villus), which are minute finger-like projections. 3. The epithelial cells of the villi have numerous microvilli. 4. The small intestine is long, providing large surface area and ample time for absorption.

What happens to food after digestion? Absorption: Small Intestine

What happens to food after digestion? Absorption: Small Intestine

What happens to food after digestion? Absorption: Small Intestine 2. Thickness of Cell Membranes • The villi have very thin membranes: the epithelium is only one-cell thick. 3. Concentration Gradient • In each villus is a lacteal (lymphatic capillary) surrounded by blood capillaries. • The lacteal continually transports fats away from the villus, while the blood capillaries transports sugars and amino acids away. • This maintains the concentration gradient needed for the absorption of food substances.

What happens to food after digestion? Egestion • Some food substances cannot be digested and remain unabsorbed in the large intestine. • These are stored temporarily in the rectum. • When the rectum is full, they are discharged as faeces through the anus. • This process is known as egestion or defecation.

What happens to the food after digestion? Objective 7: Describe how digested food is assimilated.

What happens to food after digestion? Transport and Assimilation Transport of Simple Sugars • After absorption, the blood in the villi is rich in sugars. • Blood capillaries unite to form the hepatic portal vein. • The hepatic portal vein transports sugars to the liver.

What happens to food after digestion? Transport and Assimilation of Simple Sugars • In the liver, most sugars are converted to glycogen and stored. • Glucose leaves the liver and is distributed around the body by the bloodstream. – Used during respiration to provide energy for cells. • Excess glucose is returned to the liver – Hormone insulin (produced by Islets of Langerhan in the pancreas) stimulates the liver to convert glucose to glycogen for storage. – When more glucose is required, the liver will convert glycogen back to glucose.

What happens to food after digestion? Transport and Assimilation of Amino Acids • Amino acids pass through the liver before they are transported to the rest of the body. • How are amino acids used? – Converted to protoplasm by cells, used for growth and repair of body parts – Used to form enzymes and hormones • Excess amino acids are deaminated.

What happens to the food after digestion? Objective 8: State the functions of the liver.

What happens to food after digestion? Functions of the Liver The Liver has 7 Functions 1. Regulation of blood glucose concentration 2. Production of bile 3. Protein synthesis 4. Iron storage 5. Deamination of amino acids 6. Detoxification 7. Heat production

What happens to food after digestion? Functions of the Liver 1. Regulation of Blood Glucose Concentration • Blood normally contains about 70 -90 mg of glucose per 100 cm 3 of blood. • After a meal: – Amount of glucose in the blood rises – Stimulates Islets of Langerhans in the pancreas to secrete insulin into the bloodstream – Insulin is transported to the liver. – Insulin stimulates liver to convert excess glucose to glycogen for storage. – Blood leaving the liver contains a constant amount of glucose. What about adrenaline? ?

What happens to food after digestion? Functions of the Liver 1. Regulation of Blood Glucose Concentration • When body cells need glucose: – Glucose level in the blood drops. – Islets of Langerhan are stimulated to secrete hormone glucagon. – Glucagon stimulates liver to convert stored glycogen to glucose. – Glucose enters the blood; blood glucose level returns to normal.

What happens to food after digestion? Functions of the Liver 1. Regulation of Blood Glucose Concentration • If we have not eaten for a long time: – Glucose level in the blood drops below average. – Blood that is low in glucose reaches the hypothalamus in the brain. – Brain sends signals to the stomach. – This causes strong contractions and we feel hunger pangs. – After eating, the blood glucose level rises. The hypothalamus signals to the stomach to stop contracting.

What happens to food after digestion? Functions of the Liver 1. Regulation of Blood Glucose Concentration high blood glucose concentration pancreas secretes insulin converts glucose to glycogen pancreas secretes glucagon low blood glucose concentration converts glycogen to glucose normal blood glucose concentration

What happens to food after digestion? Functions of the Liver 2. Production of Bile • The liver produces bile which is stored in the gall bladder before use. • Bile is used in the emulsification of fats. 3. Protein Synthesis • Blood plasma contains amino acids from the diet. • The liver synthesizes these amino acids to form proteins, e. g. : – Albumins, globulins, fibrinogen (for blood clotting)

What happens to food after digestion? Functions of the Liver 4. Iron Storage • Red blood cells contain a iron, which is involved in the transportation of oxygen around the body. • These cells become worn out after some time. • They are destroyed in the spleen, a gland near the liver. • Haemoglobin from red blood cells is brought to the liver. • Haemoglobin is broken down, forming iron and bile. • Iron is stored in the liver.

What happens to food after digestion? Functions of the Liver 5. Deamination of Amino Acids • Excess amino acids are transported to the liver. • The amino groups are removed and converted to urea. • Urea leaves the body in urine. • The remains of the amino acid are converted into glucose. • Excess glucose is converted to glycogen.

What happens to food after digestion? Functions of the Liver 6. Detoxification • This is the process of converting harmful substances into harmless ones. • Breaks down alcohol to acetaldehyde by the action of alcohol dehydrogenase • Acetaldehyde can be broken down to compounds which can be used in respiration. • Excessive alcohol consumption stimulates acid secretion in the stomach, increasing the risk of gastric ulcers.

What happens to food after digestion? Functions of the Liver 6. Detoxification • Prolonged alcohol use can lead to cirrhosis of the liver. – Liver cells are being destroyed and replaced with fibrous tissue – Cells are less able to function – Can lead to liver failure and death

What happens to food after digestion? Functions of the Liver 7. Heat Production • There are many chemical reactions taking place in the liver. • Heat is produced from these reactions. • The heat is distributed by the blood to other parts other body. • Helps to maintain body temperature.

Pure Biology Chapter 6 Nutrition Alimentary Canal consists of Organs and Glands In digestion consists of Ingestion Mouth Teeth consists of Tongue Liver Pharynx Salivary glands Pancreas contains leads to secretes Gall bladder Oesophagus stores Digestion Pancreatic amylase Bile secreted into Hormones consist of Stomach Duodenum Insulin Small intestine Absorption Colon Jejunum Ileum Hepatic portal vein walls have Large intestine unite to form Folds Assimilation Glucagon Rectum Anus Simple sugars Villi via Amino acids Microvilli Egestion absorbs Fats via Blood capillaries Lacteals

Pure Biology Chapter 6 Nutrition Alimentary Canal consists of Organs and Glands In digestion consists of Mouth Teeth consists of Tongue Pharynx Salivary glands contains leads to secretes Gall bladder stores Pancreatic amylase secreted into consist of Hepatic portal vein Colon Hormones Glucagon walls have unite to form Folds Rectum Simple sugars Anus via Amino acids Microvilli absorbs Fats via