Human Digestion: Processes and Anatomy

• The digestive system includes organs with specific locations and functions.
• Digestion involves amylase, proteases, and lipases.

Digestion

• Digestion is the breakdown of large, insoluble food molecules into small, water-soluble molecules.
• This process uses both mechanical and chemical methods.

Mechanical Digestion

• Mechanical digestion is the physical breakdown of food using teeth.
• Mixing of food with gastric juices in the stomach is part of mechanical digestion.

Chemical Digestion

• Chemical digestion occurs throughout the Alimentary Canal.
• Different enzymes break down different types of food.

Processes in the Digestive System

• Ingestion is defined as taking food into the body.
• Digestion is breaking down large food molecules into smaller soluble molecules.
• Absorption involves movement of smaller molecules into the bloodstream across the small intestine wall.
• Egestion is waste food passing out of the body.

Parts of the Alimentary Canal

• Mouth
• Oesophagus
• Liver
• Gall Bladder
• Large Intestine
• Appendix
• Anus
• Stomach
• Pancreas
• Small Intestine
• Rectum

The Mouth

• The mouth grinds up food mechanically using teeth.
• Saliva mixes with food in the mouth.
• The tongue forms ground food into a bolus for easy swallowing.

Salivary Glands

• Salivary glands produce saliva.
• Saliva begins the process of breaking down starch and helps lubricate the food.

Oesophagus

• The oesophagus transports food from the mouth to the stomach.
• Muscle contractions accomplish this, known as peristalsis.

Stomach

• The stomach secretes gastric juices.
• Gastric juices mix with the food, and contain enzymes to help break down proteins.
• Hydrochloric acid is secreted to kill bacteria.

Liver

• The liver produces bile.
• Bile neutralizes the acidic chyme from the stomach.

Gall Bladder

• The gall bladder stores bile.
• The bile is produced in the liver.

Pancreas

• The pancreas produces different enzymes to further break down food.
• Protease breaks down proteins, lipase breaks down fats, and amylase breaks down carbohydrates.

Small Intestine

• Chyme from the stomach mixes with bile from the gall bladder in the small intestine.
• Enzymes from the pancreas also mix with chyme.
• Nutrients are absorbed into the bloodstream.

Large Intestine

• The large intestine transports undigested food to the rectum.
• Water is absorbed into the bloodstream.

Rectum

• The rectum forms undigested food remains into solid waste (faeces).
• It also stores the faeces.

Anus

• The anus releases solid waste.

Enzymes

• Enzymes are biological catalysts.
• Enzymes speed up chemical reactions in living cells.
• They are made of proteins.
• Digestive enzymes convert food into small soluble molecules.
• Small soluble molecules can be absorbed into bloodstream.

How Enzymes Work

• Enzymes contain an active site where chemical reactions occur.
• The substrate fits perfectly into the active site of the enzyme and binds to it, like a lock and key.
• The enzyme remains unchanged.
• Following the reaction, another substrate can be broken down.
• Enzymes are specialized, meaning certain enzymes only work on a specific molecule (substrate)

Optimum Conditions

• Each enzyme operates best under its own unique conditions.
• These conditions are based on pH and temperature.
• pH is the acidity or alkalinity of a substance.
• The pH scale is 1-14 with 1 being highly acidic and 14 being highly alkaline.
• pH of 7 is neutral, like water.
• Temperature is a measure of kinetic energy.
• Te scale uses 0-100, with 0 and 100 being the melting and boiling points of water.
• The average internal body temperature of a person is 37°C.

Effect of pH on Enzyme Activity

• If the pH is either too high or too low, the activity of the enzyme ceases.
• This is due to a change in the shape of the active site.
• When this happens, it is said that the enzyme is denatured.
• At the optimum pH, the enzyme has the perfect shape to optimize its activity.

Effect of Temperature on Enzyme Activity

• At low temperatures, the enzyme doesn’t have much kinetic energy, resulting in a lower likelihood of binding with the substrate.
• If the temperature gets too high, the enzyme will become denatured and no longer work.
• At the right temperature, the enzyme has more kinetic energy and therefore a higher likelihood of binding.

Digestive Enzymes

• Amylase's substrate is carbohydrates.
• Salivary glands & the pancreas produce amylase.
• Amylase breaks down carbohydrates in the mouth, stomach and small intestine.
• Amylase's product is glucose.
• Protease's substrate is protein.
• The stomach and pancreas produce protease.
• Protease breaks down protein in the stomach and small intestine.
• Protease's product is amino acids.
• Lipase's substrate is fats.
• The pancreas produces lipase.
• Lipase breaks down fats in the small intestine.
• Lipase's products are fatty acids and glycerol.

Food Tests

• There are a range of tests for specific food groups in a sample.
• There are tests for glucose, starch, protein, and fat.

Benedict’s Solution (Test for Glucose)

• The food sample is crushed with water and an equal amount of Benedict’s solution is added to it in a test tube.
• The test tube is then heated in a hot water bath until a colour changes.
• The solution changing to indicates the amount of glucose present in the sample.

Benedict's Test Results

• Blue indicates no reducing sugar
• Green ppt. indicates a Traceable ammount (0.5-1 g%)
• Yellow ppt. indicates a Low ammount (1-1.5 g%)
• Orange-red ppt. indicates a Moderate amount (1.5-2 g%)
• Brick-red ppt. indicates a High amount (>2 g%)

Iodine Solution (Test for Starch)

• Food is placed on a spotting tile.
• A drop of iodine is applied.
• If starch is present, the orange-brown iodine will turn blue-black.

Biuret Solution (Test for Protein)

• Food sample is crushed with water and added to a test tube with a small amount of Biuret solution.
• If protein is present, upon gently shaking the color changes from blue to purple.

Ethanol (Test for Fats)

• Food sample is crushed with ethanol and then filtered.
• The filtrate is poured into a test tube containing water.
• If fats are present, the water will turn cloudy upon shaking.

Blood

• Blood transports carbon dioxide, oxygen, nutrients, waste products and hormones.

Circulatory system

• Transport in mammals is in the circulatory system.
• The circulatory system consists of continuous tubes (blood vessels).
• Blood vessels carry blood around the body.
• The heart is connected to blood vessels.
• The heart forces blood through the blood vessels.
• Valves in the heart and veins ensure blood moves in one direction.
• Double circulation involves blood passing through the heart twice in one circuit.
• Double circulation allows blood to return to the heart after picking up oxygen from the lungs.
• The heart pumps this blood around the body at a higher pressure.

The Heart

• There are two pumps in one.
• The right and left sides are separated by the septum.
• The right side pumps deoxygenated (without oxygen) blood to the lungs to collect oxygen.
• The left side pumps oxygenated blood around the body.

Heart Structure

• Right Ventricle collects blood flowing from the right atrium.
• It sends blood to the lungs.
• Valve stops blood flowing backwards.
• Left Atrium - Collects blood from the lungs.
• Left Ventricle - pumps blood around the body.

Blood Vessels

• There are three types of blood vessels: artery, vein, capillary.
• They help transport blood around the body.
• All consist of a cell wall and a lumen (a hole, like in a straw).
• Each have unique features.

Arteries

• Arteries pump oxygenated blood from heart to body.
• Blood is under high pressure.
• Features include thick walls and a small lumen.

Veins

• Veins pump deoxygenated blood from body to heart.
• Blood is under lower pressure.
• Veins contain valves to stop blood flowing backwards.
• Veins have thin walls and a large lumen.

Capillaries

• Capillaries are in between veins and arteries.
• They exchange gasses and nutrients with body.
• Capillaries have walls that are one cell thick to increase rate of exchange.
• They have thin walls (one cell) and a tiny lumen.

Components of Blood

• Plasma makes up 55% of blood.
• White blood cells and platelets make up 4% of blood.
• Red blood cells make up 41% of the total.

Plasma

• Plasma is the liquid part of blood.
• Plasma is yellow in color.
• Plasma carries dissolved nutrients, gasses, proteins, and waste products.

Red Blood Cells

• Red blood cells are small, red discs.
• They contain haemoglobin which binds to oxygen.
• Haemoglobin carries oxygen around the body.

White Blood Cells

• These are larger and lighter coloured than red blood cells.
• Neutrophils defend against infections via phagocytosis (engulfing of pathogens).
• Eosinophils defend against parasitic infections.
• Basophils produce histamine during allergic reactions.
• Lymphocytes are specialized in detecting specific infections.
• Lymphocytes release antibodies to fight infections.
• Monocytes (Macrophages) clean up infections and debris via phagocytosis.

Platelets

• Platelets are very small cell fragments.
• Platelets help clot blood.
• They seal wounds by clumping together at the site of bleeding.

Transport in Plants

• Plants also need a way to transport nutrients.
• In mammals, this is the circulatory system.
• In plants, it involves xylem and phloem.
• These are similar to veins and are found throughout the plant.

Xylem and Phloem

• Xylem and Pholem are found in the roots, stems, and leaves of plants.
• Xylem transports water from roots to leaves via transpiration.
• Phloem transports nutrients.
• Photosynthesis occur in the leaves.
• Nutrients from the leave is transported to rest of plant via translocation.

Location of Xylem and Phloem

• Blue xylem and red pholem are the diagrams
• Xylem and Phloem also include green epidermis and brown root hair cells

Root Hair Cells

• Plants need a lot of water and minerals.
• Root hair cells are specially designed to increase water uptake.
• Root hair cells have a large surface area to absorb more water.