10 IB Biology

Digestive System

Responsible for converting what we eat and drink into substances our bodies need to function.

Alimentary Canal

Also known as the Gastrointestinal Tract (GI tract).

Gastrointestinal Tract Length

The gastrointestinal tract is 9m long and made up of 4 functional parts.

Ingestion

The digestive process begins here with food entering the gastrointestinal tract through the Oral Cavity.

Oral Cavity

Consists of the mouth, tongue, teeth, salivary glands, epiglottis, pharynx and esophagus.

Digestion

Food is passed from the oral cavity to the Stomach and Small Intestine where it is broken down into smaller more basic substances.

Mechanical Digestion

Complex substances are broken down into smaller more absorbable pieces without being chemically changed.

Chemical Digestion

Complex substances are chemically broken down into more absorbable pieces.

Absorption

Material from the 'broken down food' that can be used by the body is absorbed by the Small and Large Intestines.

Egestion

Undigestable material and waste must be removed from the body.

Rectum

The location where undigestable material is passed to and released through the Anus.

Mouth

Consists of several structures including the cheek, lips, vestibule, hard palate, and soft palate.

Teeth

The primary agent of mechanical digestion in the mouth.

Deciduous Teeth

Humans have 20 deciduous (milk) teeth which are replaced by 32 permanent (adult) teeth.

Regions of the Tooth

There are 3 general regions of each tooth: The Crown, The Neck, and The Root.

Crown

The top of the tooth.

Neck

The central area of the tooth that contains the gums and nerve endings.

Root

Area below the gums that contains the blood vessels and supporting structures.

Enamel

Covers the crown of the tooth and is the hardest substance in the body.

Pulp Cavity

A hollow tube that runs through the middle of the tooth that contains blood vessels and nerve cells.

Periodontium

Holds the roots in the jaw.

Cementum

Bone with a high concentration of connective tissue.

Gums

Tissue that surrounds and supports the teeth and associated tissues, also known as the gingiva.

Tonsils

Part of the immune system that acts as a filter for foreign material in the mouth.

Pharynx

The muscle group that coordinates swallowing and controls the intersection between the digestive and respiratory system.

Epiglottis

The flap of tissue that prevents food from entering the trachea.

Salivary Glands

There are 3 sets of salivary glands (sublingual, submandibular and parotid) that produce saliva.

Salivary Amylase

An enzyme in saliva that chemically breaks down starch into glucose.

Tongue

The primary organ of the oral cavity made up of two parts: The Root and The Body.

Deglutition

The process of swallowing, consisting of two stages: Oral Phase and Pharyngeal Phase.

Deglutition - Stage 2: Pharyngeal Phase

The pharynx contains nerves that directly connect to the central nervous system. The presence of the bolus stimulates these nerves. The vagus nerve is responsible for the three activities in this area.

Deglutition - Stage 3: Esophageal Phase

The esophagus is a muscular tube that contracts to move the bolus down towards the stomach. This peristalsis begins in the pharynx and continues in the esophagus.

Enzyme

An enzyme is a biological catalyst that speeds up chemical reactions without being consumed or altered.

Activation Energy

An enzyme will lower the activation energy (the energy needed for a reaction to occur).

Enzyme Function - The Active Site

The active site is the region of the enzyme where the reactants (substances that are going to react) bind and where the chemical reaction takes place.

Substrate

A reactant that binds to the active site of an enzyme is called a substrate.

Enzyme - Substrate Complex

The binding of the substrate to the active site forms the Enzyme - Substrate Complex.

Inhibitor

When enzyme activity is not needed an Inhibitor Molecule will bind to the enzyme's active site, blocking the substrate molecules from binding with the enzyme.

The Stomach

The stomach is a J-shaped organ of the abdominal cavity where digestion occurs.

Regions of the Stomach

The stomach is divided into 3 regions: The Fundus, The Body, and The Pylorus.

Bolus Duration in Stomach

The bolus spends 2-3 hours in the stomach.

Cardiac Sphincter

Entry into the stomach is controlled by a ring of muscle called the Cardiac Sphincter.

Mucosa

The stomach is lined with a mucous membrane called the Mucosa, composed of gastric glands.

Parietal Cells

Parietal Cells produce hydrochloric acid (HCl) that is used to chemically breakdown proteins.

Epithelial Cells

Epithelial Cells produce mucous that protects the stomach lining from the effects of HCl.

Chief Cells

Chief Cells produce the enzyme pepsinogen, which becomes active and is called Pepsin upon contact with HCl.

Pepsin

Pepsin speeds up the process of protein digestion.

Rennin

Rennin slows the movement of milk and separates it into whey (protein) and curds (carbohydrates).

Gastric Juice

The combination of Pepsin, Rennin, and HCl in the stomach is referred to as 'Gastric Juice'.

Rugae

The mucosa contains ridges known as Rugae.

Chyme

The liquid formed in the stomach after food is mixed and dragged over the ridges is called Chyme.

Stimuli for Gastric Juice Flow

Three mechanisms work to stimulate the flow of gastric juice: 1. The thought, sight, smell or taste of food. 2. Food touching the lining of the stomach. 3. The stretching of the stomach lining causes the secretion of the hormone gastrin.

Fundus

The top ¼ of the stomach that holds gases released during digestion.

Pylorus

The exit point of the stomach controlled by the Pyloric Sphincter, which regulates the flow of chyme to the duodenum.

Small intestine

The major organ of digestion and absorption, measuring 7m long and attached to the abdominal wall by the mesentery.

Duodenum

The first part of the small intestine and the major site of digestion in the body, where 90% of digestion occurs with the help of accessory organs.

Jejunum

The second part of the small intestine, the longest section, responsible for additional digestion and absorption.

Ileum

The final section of the small intestine, which absorbs remaining nutrients from the chyme.

Pancreatic Juice

Produced by the pancreas, it contains bicarbonate ions, trypsinogen, pancreatic amylase, and pancreatic lipase.

Bile

Produced by the liver and stored in the gall bladder, it mechanically breaks down large fat molecules through emulsification.

Intestinal Juice

Produced by the duodenum, it contains enzymes such as intestinal lipase, erepsin, and disaccharases.

Mucosa

The inner lining of the small intestine, arranged in ridges called villi to increase surface area for nutrient absorption.

Villi

Structures in the small intestine that aid in digestion and absorption, lined with cuboidal cells and epithelial cells.

Cuboidal Cells

Cells that line each villus and contain microvilli to further increase surface area for absorption.

Epithelial Cells

Cells that produce mucous to protect the walls of the intestine from digestive juices.

Krypts of Leiberkuhn

Digestive glands found at the base of the villi of the duodenum and jejunum that release intestinal juice.

Lacteal

A lymph vessel in the villi that absorbs fatty acids and glycerol.

Capillaries

Blood vessels that absorb monosaccharides, amino acids, vitamins, and minerals into the blood.

Peristalsis

The constant movement of the small intestine when food is present, which has four main functions: squeeze chyme, mix with enzymes, break down food, and speed up absorption.

Macronutrients

Nutrients needed in relatively large amounts by the human body.

Micronutrients

Nutrients required in amounts less than 0.05% of body mass, including vitamins and trace minerals.

Vitamins

Organic compounds required for growth and metabolism, assisting in the formation of hormones, blood cells, neurotransmitters, and nucleic acids.

Trace minerals

Minerals required in small amounts, including Fe, Cu, Zn, I, Se, Mn, Mo, Cr, Co, and B.

Vitamins

Organic compounds that are essential for normal growth and nutrition, required in small quantities in the diet.

Fat Soluble Vitamins

Vitamins that dissolve in fat and are mostly non polar, such as Vitamin A and D.

Water Soluble Vitamins

Vitamins that dissolve in water and are polar, such as Vitamin C.

Macronutrients

Nutrients that include carbohydrates, proteins, lipids, and some minerals such as Na, Mg, K, Ca, P, S, and Cl.

Malnutrition

A condition that occurs when people do not get a balanced supply of nutrients, leading to compromised health and increased mortality.

Micronutrient Deficiencies

Deficiencies involving essential vitamins and minerals, such as iodine, vitamin A, and iron.

Iodine

An essential nutrient for the production of the hormone thyroxine, found in shellfish, yogurt, strawberries, and other seafood.

Vitamin A

A vitamin used to maintain healthy skin and good eyesight, found in yellow and orange fruits and vegetables, spinach, and egg yolks.

Xerophthalmia

A condition caused by Vitamin A deficiency, characterized by dry eyes and night blindness.

Iron

An essential part of hemoglobin, found in red meats, leafy green vegetables, nuts, and seeds.

Anemia

A condition caused by iron deficiency, characterized by fatigue, brittle nails, and low immunity.

Vitamin B3 (Niacin)

A vitamin whose deficiency causes Pellagra, characterized by dermatitis, diarrhea, and dementia.

Vitamin B1 (Thiamin)

A vitamin whose deficiency causes Beriberi, characterized by weight loss, fatigue, and swelling.

Vitamin C (Ascorbic Acid)

A vitamin whose deficiency causes Scurvy, characterized by bleeding gums and lowered resistance to infection.

Vitamin D (Calciferol)

A vitamin whose deficiency causes Rickets, characterized by softened and deformed bones.

Selenium

A micronutrient whose deficiency causes Kashin-Beck disease, characterized by atrophy and degeneration of cartilage.

Marasmus

A condition resulting from protein deficiency in infants, causing failure to gain weight and emaciation.

Kwashiorkor

A condition found in young children whose diet is high in starch and low in protein.

Causes of Malnutrition

Factors such as lack of distribution of global resources, depletion of nutrients in soil and water, and lack of education.

Possible Solutions to Malnutrition

Strategies such as fortification of food staples with micronutrients and increased availability of nutritional supplements.

Large Intestine

The part of the digestive system where undigested materials pass from the small intestine, measuring about 1.5m long.

Cecum

The first part of the large intestine where chyme from the small intestine is passed through the Ileocaecal Valve.

Appendix

A vestigial organ that stores a small amount of cellulose broken down by intestinal bacteria.

Colon

The part of the large intestine divided into the Ascending, Transverse, Descending, and Sigmoid regions.

Chyme

The semi-fluid mass of partly digested food that moves from the stomach to the small intestine.

Large Intestine

The part of the digestive system where water is reabsorbed and feces are formed.

Colons

Regions of the large intestines that absorb water and Vitamins B and K produced by intestinal bacteria.