Mammalian Digestive System Notes

The Mammalian Digestive System

Key Knowledge, Learning Intentions, and Success Criteria

Key Knowledge:

• Specialization and organization of animal cells into tissues, organs, and systems with specific functions, focusing on the digestive system.

Learning Intentions:

• Understanding the terms ingestion, digestion, and egestion.

• Differentiating between mechanical and chemical digestion.

• Identifying the roles of different enzymes in the digestive system.

• Understanding the structure and function of different organs in the human digestive system.

• Understanding the structure and role of villi in the absorption of nutrients.

Success Criteria:

• Explaining the difference between mechanical and chemical digestion.

• Identifying different enzymes, their location, and the organic molecules they act upon.

• Identifying and labeling the different parts of the digestive system.

• Explaining the role of each organ in digestion and nutrient absorption.

• Explaining the structure and role of villi in food absorption.

Marshmallow Activity

• A marshmallow is made up of gelatine (a protein), water, vanilla essence, lemon juice, and sugar (carbohydrate).

• Consider what happens to the marshmallow as it is eaten and over the next 24 hours.

• Questions to consider:

  • What happens in the mouth?

  • What does the top of your throat feel like as you swallow?

  • Where does it go after the mouth, and what organs does it pass through?

  • What happens to the protein, sugar, lemon juice, vanilla essence, and water?

  • Where do the nutrients leave the system?

  • Where do the nutrients go, and how do they get there?

  • What are the nutrients for?

  • What happens to excess nutrients that we eat?

  • What happens to indigestible food?

Organs of the Digestive System

• Liver: The largest organ inside the body. It makes bile (fluid that helps break down fats), changes food into energy, and cleans alcohol, some medicines, and poisons from the blood.

• Gallbladder: Stores the bile made in the liver and empties it to help digest fats.

• Large Intestine (Colon): Absorbs water and sodium from stool.

• Appendix: A pouch attached to the first part of the large intestine; its function is not well understood.

• Esophagus: Carries food from the mouth to the stomach.

• Stomach: The organ where digestion of protein begins.

• Pancreas: A gland that makes enzymes for digestion and the hormone insulin to help the body turn food into energy.

• Small Intestine: The organ where most digestion occurs.

• Rectum: The lower end of the large intestine, leading to the anus.

• Anus: The opening at the end of the digestive tract where bowel movements leave the body.

Digestion

• Occurs in the digestive system (gastrointestinal tract, alimentary canal, digestive tract, or gut).

• Ingest: Take in food.

• Digest: Break food down.

• Egest: Removal of indigestible matter.

• Involves the breakdown of large, insoluble food molecules into smaller, soluble molecules which can be absorbed by the bloodstream through:

  • Mechanical digestion

  • Chemical digestion

Mechanical Digestion

• Physical breakdown of food into smaller pieces.

• Increases surface area and mobility of food particles.

• Teeth: Mastication (biting, chewing, and grinding).

• Muscles contracting

• Tongue and jaws

• Peristalsis and Segmentation (small intestine).

• Stomach churning

Chemical Digestion

• Breaking the chemical bonds in the three main macromolecules:

  • Carbohydrates

  • Proteins

  • Lipids (fats and oils)

• Chemicals produced by various organs to help:

  • Acids

  • Enzymes

  • Bile (emulsifier of fats)

Chemical Digestion - Enzymes

• Enzymes are chemical catalysts.

• Speed up the rate of reactions (do not actually take part).

• Work under very specific conditions and will only work with one type of substance (substrate) – lock and key mechanism.

• Different enzymes are produced in different areas of the gut to breakdown the different food nutrients (biomacromolecules) – carbohydrates, proteins & lipids.

Chemical Digestion - Enzymes (Carbohydrates)

• The body produces a variety of enzymes which can break apart the long chains of sugars which make carbohydrates. These are often broadly classified as amylases.

• E.g. Starch is broken down to maltose by amylases in the mouth, then Maltose is broken down to glucose in the small intestine by maltase.

Chemical Digestion - Enzymes (Proteins)

• Proteins are made up of long chains of amino acids. The enzymes which can break apart these chains are generally called proteases.

• Protein digestion starts in the stomach and continues in the small intestine with gastric juices and with help from the pancreas.

Chemical Digestion - Enzymes (Lipids)

• Lipids (fats and oils) are broken down into smaller fatty acid chains and glycerol by Lipases.

• Lipid digestion starts in the mouth with lingual lipase that helps breakdown triglycerides and continues in the small intestine.

• Fats also need to be emulsified by bile salts before these enzymes will act on them.

Chemical Digestion - Enzyme Table

Parts of the Mammalian Digestive System

• Mouth and salivary glands

• Esophagus

• Stomach

• Liver

• Gallbladder

• Pancreas

• Duodenum

• Jejunum

• Ileum

• Ascending colon

• Transverse colon

• Descending colon

• Sigmoid colon

• Cecum

• Appendix

• Rectum

• Anus

Student Activities

• Label Diagram 3.8 The Human Digestive System on page 67 of your Skills Workbook using the diagram on page 101 of your textbook

• 3.2.1 Mechanical Digestion on page 66 and Figure 3.9 on page 68 of your Skills workbook using the following Slides or your Textbook pages 100-109 to explain the structure and contents of each part of the digestive system

• 3.2.2 Chemical Digestion on page 68 of your Skills Workbook

• 3.2.3 Digestive Enzymes page 70-72 of the Skills Workbook

Mouth

• Food is ingested.

• Spends up to 1 minute here

• Mechanical breakdown by tongue and teeth.

• Chemical breakdown by saliva produced by salivary glands (high in rER, ribosomes & golgi bodies).

• Salivary amylase breaks down starch to maltose.

• Food softened, moistened, lubricated by mucus & made into a soft ball called a bolus.

• Bolus swallowed via pharynx

Oesophagus

• Muscular tube to stomach.

• Bolus spends 4-8 seconds here.

• Bolus pushes up the soft palate & stops food from getting behind the nose as it moves into the pharynx at the top of the oesophagus. (epiglottis stops food entering the wind pipe).

• Peristalsis - a wave like contraction of the circular ring muscles along the gut wall pushes the food down to the stomach.

Stomach

• J shaped

• 2 layers of muscle

  • outer muscular- mechanical digestion - contraction of the thick muscular walls

  • inner glandular - secretes gastric juices (enzymes) for chemical digestion (3L produced daily)

• Sphincters (rings of muscle) at each end:

  • cardiac sphincter - at the top of the stomach, prevents food from moving back into the oesophagus (ie regurgitation)

  • pyloric sphincter - at the base of the stomach that contracts to let digested food into the small intestine.

Stomach Cont.

• Gastric juices

  • acidic $(HCl)$ environment to kill bacteria and help

  • enzymes (proteases) breakdown protein

  • mucus protects lining.

• Length of stay depends on food type - simple sugars, medicines, alcohol water and ions pass through lining quickly (accounts for rapid effect of drugs and alcohol), a hamburger several hours.

• Chyme (a soupy liquid) leaves the stomach after approx 6 hrs.

• Alcohol and some drugs absorbed via the stomach lining

Small Intestine

• Approx 6-7m in length

• Chyme spends up to 10 hours here

• Consists of three parts

  • Duodenum (25cm, pH 7-8.5)

  • Jejunum (2.5m not clearly defined in mammals, similar to ileum in structure)

  • Ileum (3.5m)

Small Intestine - Duodenum

• Chyme (acidic) enters in a thin soupy consistency

• Final digestion of food by gastric juices (enzymes) secreted from nearby intestinal glands, the PANCREAS and LIVER (bile)

• Bicarbonate produced to neutralise stomach acid (pH 7-8.5)

Pancreas

• Chemical digestion of food

• Hormones regulate blood sugar

• Secretes pancreatic juice via the pancreatic duct to aid digestion

• Juice contains bicarbonate soda to neutralise stomach acid

• Juice also contains enzymes

  • trypsin (breaks down long chain polypeptides, erepsins small chain polypeptides)

  • amylases (carbohydrates)

  • lipases (fats to fatty acids and glycerol)

Liver and Gall Bladder

• Reddish brown organ with 4 lobes of unequal size and shape.

• Largest internal organ (1.44–1.66 kg)

• It is connected to two large blood vessels - hepatic artery & hepatic portal vein

• Processes all food nutrients & toxins

• Converts excess nutrients to glycogen & fat for storage

• Helps digestion by producing greenish coloured bile

• Gall Bladder – stores bile which contains bile salts to emulsify fats to increase the surface area for enzyme action (emulsify - similar to detergent action as breaks down the fats into small droplets).

Small Intestine: Jejunum & Illeum

• Absorption of most of digested food (90%) and water occurs here by specialised finger like projections (folds) called villi

• Glucose and amino acids absorbed and carried away by capillaries to the hepatic portal vein and to the LIVER for processing or storage

• Fatty acids and glycerol absorbed by lacteals (lymph vessels) of lymphatic system

• Indigestible food moves into the LARGE INTESTINE

Small Intestine: Jejunum & Illeum Cont.

• Most nutrients absorbed in jejunum as soluble molecules

  • Simple sugars, Amino acids, fatty acids and glycerol

• Ileum absorbs vitamin $B_{12}$, bile salts and any remaining nutrients not already absorbed

• Indigestible food moves into the LARGE INTESTINE

Small Intestine and Absorption

• Long and thin

• Rich supply of blood and lymph vessels

• villi (one villus) & micro-villi

  • tiny finger like projection

  • increase the surface area of the intestinal wall to absorb more quickly

• Capillaries absorb glucose and amino acids into blood

• Lacteals absorb and transport fatty acids and glycerol via lymphatic system

What happens to Digested food?

• Digested food nutrients are processed by the liver

  • Glucose (carbohydrate)

    • used for energy - cellular respiration

    • changed to glycogen and stored as fat

  • Amino acids (protein)

    • built up into new proteins for growth and repair

    • deaminated to urea (excreted in urine)

    • Converted to glycogen and stored (sometimes used for energy)

  • Fatty acids & Glycerol (Lipids)

    • used for energy

    • Stored

    • Insulation and used to keep some tissues & organs in place

Large Intestine and Egestion

• Undigested food can spend up to 24-36 hours here

• Last nutrients removed (egested)

• Faeces forms

• Made up of the

  • Colon

  • Rectum

  • Anus

Large Intestine - Colon

• Ascending, transverse and descending colon

• absorption of water and mineral salts from undigested material

• caecum and appendix are a blind alley in the colon with no real use in humans. In herbivores it contains bacteria to aid the breakdown of plant cellulose.

Large Intestine – Rectum and Anus

• Undigested material collected here

• mainly plant cellulose (fibre), bacteria, dead cells, mucus and water.

• solid wastes (faeces) removed via the anus (sphincters keep it in until ready to go!)

• Removal of digestive wastes is called defecation or egestion.

Flow chart of digestion

1. Food enters the MOUTH

   • Chewed (1 min)

   • Covered in Saliva

2. OESOPHAGUS (4-8 secs)

3. STOMACH (few mins up to 6 hrs)

   • Muscles churn

   • Acid Bath

4. TO SMALL INTESTINE (up to 10 hours)

   • Chemicals Released

5. TO LARGE INTESTINE (up to 24 hours)

   • Plant fibres (leaves, grains)

   • Bacteria, salts, mucus ("snot")

   • Dead cells, old red blood cells

   • Amino acids, fatty acids, sugars, water, vitamins, minerals

     • Through villi in wall of small intestine (5 million villi)

     • TINY FOOD PARTICLES MOVE INTO BLOOD TUBES IN VILLI

     • most of the water removed, some vitamins

     • TINY BLOOD TUBES MEET UP TO BECOME BIG BLOOD VESSEL.

     • LEADS TO LIVER

     • FROM LIVER, BLOOD GOES TO HEART, THEN PUMPED TO ALL CELLS THROUGH BLOOD TUBES

6. squeezed out of the body as faeces through the anus ("bottom")

When things go wrong

• Tooth decay

• Food allergies and intolerances – nuts, lactose, wheat – coeliac disease

• Indigestion, reflux

• Malabsorption of nutrients – fructose, gluten

• Gall stones

• Structural abnormalities - Meckle’s diverticulum, ulcers, cancers

• Functional disorders – Diabetes, Irritable bowel, Crohn’s disease

• Appendicitis

• Gastro – diarrhoea, vomiting

• Eating Disorders – Anorexia & Bulimia Plus many more

Some Fun Facts

• What causes our stomach to growl?

  • Stomach growling occurs when the stomach receives signals from your brain to begin digestion but the stomach is empty. Your brain might sense you're running low on energy (glucose) or even seeing or smelling something you want to eat can get things going. The motion of the stomach muscles begins, but the organ is hollow. The movement of the muscles mixing the acids of the stomach in the hollow space of the stomach produces vibrations we hear as growling, or rumbling, or gurgling.

• We eat about 500kg of food per year.

• 1. 7 liters of saliva is produced each day.

• Most of us pass somewhere between 200 and 2,000 ml of gas (farts or flatus) per day (average, about 600 ml).

Student Activities (Skills Workbook)

• 3.10 Mind Map of the human digestive system page 69 - use the PowerPoint or your textbook

• 3.2.4 Absorption and the human gut page 72-74 Nelson Biology 1

• 3.2a Concept Questions 1-6 page 107

• 3.2b Concept Questions 1-6 page 109

Practical Activities

• Corn Caper Activity

• Investigation 3.2 Investigating the action of pepsin page 103-104

• Virtual Rat Dissection (IPads) – Looking at the digestive system

• Add to your Glossary of terms