Human Digestive System: Oral Cavity & Salivary Glands

The Human Digestive Tract

• Food is broken down into smaller substances for easy absorption, a process called digestion.
• The digestive tract includes the pharynx, esophagus, small intestine, large intestine, and anus.

Oral Cavity

• The oral cavity is the entrance to the digestive system and the site of ingestion, also called the mouth.
• Teeth are responsible for mastication.
• Adults have 32 permanent teeth, while children have 20 or fewer.
• The common parts of a tooth are the crown (above the gums), neck (within the gums), and root (holds the tooth in place).
• Mechanical digestion physically breaks down food into smaller pieces through biting, chewing, or churning.
• Chemical digestion breaks down complex food molecules into simpler ones through enzymes, acids, and other substances.

Tongue

• Papillae are rough surfaces on the tongue where taste buds are found.

Salivary Glands

• Saliva moistens food to facilitate swallowing.
• Salivary amylase is the enzyme that digests starch into maltose.
• The 3 major pairs of salivary glands in mammals are: parotid, sublingual, and submandibular glands.

Pharynx

• The pharynx, commonly called the throat, is a muscular tube that serves as a passageway for food and air.
• The epiglottis is a flap of tissue located near the front end of the pharynx and behind the tongue.

Esophagus

• The esophagus conveys chewed food from the pharynx to the stomach.
• It is made up of involuntary muscles and is 25 cm long.
• Peristalsis is a wavelike muscular contraction that moves food through the digestive tract.

Stomach

• The stomach is a J-shaped, 20 cm long, expandable organ that receives food from the esophagus.
• It can accumulate 1 to 1.5L of food and becomes empty again about 3-4 hours after eating.
• The inner lining secretes gastric juices and contains hydrochloric acid which softens fibrous foods and kills microorganisms, with a pH between 1 and 2.
• Pepsin breaks down protein into simpler forms.

Small Intestine

• The small intestine is the longest part of the digestive tract, about 7m long and 2.5 cm wide.
• It is the site of absorption, where nutrients from food are diffused to different parts of the body.
• The sections of the small intestine are the duodenum, jejunum, and ileum.

Large Intestine

• The large intestine is shorter but wider than the small intestine, measuring 2cm long & 7cm wide.
• Undigested and unabsorbed food is moved here from the small intestine.
• The appendix is a vestigial organ attached to the large intestine.
• The rectum is an expandable storage chamber.
• The anus is the opening where solid wastes are eliminated.

Accessory Organs

• The liver is the longest gland in the human body.
• Its main function is to produce and secrete bile.
• Bile is an alkaline fluid with a pH of 7-8 that aids the breakdown of fat into tiny droplets.
• The pancreas is a gland found behind the stomach.
• It secretes substances that help break down fats, proteins, and carbohydrates.
• The pancreatic duct secretes pancreatic juices, bicarbonate ions, and enzymes like lipase and amylase.
• The gall bladder is a small pouch under the liver.
• It stores the bile produced by the liver.

Nutrients Essential to Life

• Nutrients are compounds in food that provide energy and essential components for metabolism, growth, and repair.
• Assimilation is the process in which nutrients are absorbed by each cell of the body in the form of energy.
• Assimilated nutrients include carbohydrates, proteins, lipids, vitamins, minerals, and water.

Carbohydrates

• Carbohydrates are used by the body to build and replace certain types of cells.
• They provide energy needed for daily activities.
• They are essential due to their ability to be broken down into glucose.
• Glucose is a form of simple carbohydrate and an immediate source of energy.

Proteins

• Proteins help the body build tissues.
• They are essential in growth and development.
• They help in transporting hemoglobin and other nutrients to and from the blood.
• Amino acids are the building blocks of proteins, necessary for growth and repair of worn-out tissues.

Lipids

• Unsaturated fats are healthier than saturated fats, except for trans fat.
• They are energy reserves of the body, giving as much energy as carbs and proteins.
• Trans fat, a form of unsaturated fat, is known to have negative effects.
• Saturated fats are solid at room temperature, and unsaturated fats are liquid at room temperature.

Water

• Water is vital to all the physiological and chemical processes that release energy in the cell.
• It helps regulate body temperature.

Vitamins

• Vitamins are essential because they speed up chemical reactions and regulate the release of energy in the body.
• Fat-soluble vitamins include A, E, D, and K.
• Water-soluble vitamins include B and C.

Minerals

• Minerals are inorganic substances that are essential for the proper growth and functioning of the cells.
• Hydrogenation is a process in food manufacturing in which unsaturated fats are turned into saturated fats to prolong shelf life.
• Macronutrients are needed in great quantities.
• Micronutrients are needed in minute quantities.

Care for the Digestive System

• Brush your teeth and visit your dentist regularly.
• Avoid overeating.
• Eat a lot of fibrous foods.
• Defecate regularly.
• Drink plenty of water.
• Chew your food slowly and relax when you eat.
• Don’t talk when your mouth is full.
• Consult your doctor if you have an eating disorder.

Importance of Exercise

• Exercise increases your energy level.
• It helps you sleep better.
• It helps maintain a healthy weight.
• It boosts confidence and self-esteem.
• It releases endorphins, which makes one happier.
• It is good for the heart as it improves blood circulation.

Diseases and Disorders

• Diarrhea is caused by the ingestion of contaminated food or water or irritation of the colon.
• Constipation is caused by a lack of dietary fiber and fluids.
• Appendicitis is the inflammation of the appendix due to infection.
• Gastric ulcers are soreness and inflammation of the stomach lining due to Helicobacter pylori.
• Beriberi results from low levels of vitamin B1.
• Gastroesophageal reflux disease occurs when acids from the stomach enter the esophagus.
• Marasmus is a deficiency of all macronutrients: carbs, fats, and proteins.
• Kwashiorkor is malnutrition that occurs from severe protein deficiency among infants.

Top Eating Disorders

• Anorexia nervosa involves severely restrictive calorie intake and an intense fear of gaining weight.
• Pica is eating things that are not considered food and don't provide nutritional value.
• Bulimia nervosa involves eating large amounts, then compensating by purging it out.
• Rumination disorder involves regurgitating the food that has been previously chewed and swallowed.
• Binge eating disorder is eating large amounts of food until uncomfortably full.
• Avoidant/restrictive food intake disorder is a lack of interest in eating or a distaste for smells, flavors, texture, or temp.

Cell Reproduction

• Heredity is the passing of traits from parents to offspring.
• Variation demonstrates differences among individuals.
• Genetics is the study of heredity and variation.
• It is how traits can be passed onto the next generation, and how variation arises.

The Cell Cycle

• The nucleus contains chromosomes.
• Parts of the nucleus include the nuclear membrane/envelope and nucleolus.
• Centrioles are involved in the movement of chromosomes during cell reproduction.
• Spindle fibers also play a role in chromosome movement.
• The cell cycle includes interphase and M-Phase.
• Interphase is the longest phase and a preparatory stage.
• M-Phase is mitosis/cell division.
• G1 (growth) involves an increase in the number of organelles (mitochondrion, ribosomes) and an increase in the size of the cell.
• S (DNA synthesis) is the duplication of deoxyribonucleic acid (DNA replication).
• G2 (growth and preparation for mitosis) involves cell growth and double-checking for errors.

Mitosis

• Mitosis is the production of 2 daughter cells from the parent cell.
• The daughter cells are identical to the parent cell.
• PMAT stands for Prophase, Metaphase, Anaphase, and Telophase.

Prophase

• DNA coils and thickens, forming the chromosome.
• The nucleolus disappears.
• The nuclear membrane disintegrates.
• Spindle fibers start to appear.

Metaphase

• Chromosomes align at the center of the cell.
• Spindle fibers are responsible for pulling the chromosomes to the center.

Anaphase

• Sister chromatids detach from each other.
• Spindle fibers shorten and pull the chromatids to the opposite poles/ends of the cell.
• Each sister chromatid is now considered one chromosome.

Telophase

• The nucleolus reappears.
• The nuclear membrane reappears.
• Spindle fibers disappear.
• Chromosomes uncoil.
• Cytokinesis is the division of the cytoplasm.

Meiosis

• The purpose is to produce gametes or sex cells (egg cell and sperm cell).
• Sex cells have a haploid number of chromosomes (Egg cell - 23 chr., Sperm cell - 23 chr.).
• The process involves two cell divisions.
• The product is 4 gametes (sex cells) with half the chromosome number of the parent cell.

Prophase 1

• The nuclear membrane and nucleolus disappear.
• Spindle fibers appear.
• Chromosomes coil/condense.
• Unique events: synapsis (pairing of homologous chromosomes) and crossing over (exchange of genetic information between homologous chromosomes).

Metaphase I

• Homologous chromosomes align at the center of the cell.

Anaphase 1

• Chromosomes of each homologous pair move toward the opposite poles.

Meiosis 1

• Telophase 1 and cytokinesis occur, where the nuclear membrane and nucleolus reappear.
• Spindle fibers disappear.
• Chromosomes uncoil.

Meiosis 11

• This is the same process as mitosis.
• The product is daughter cells with the haploid number of chromosomes.

Gametogenesis

• Spermatogenesis is when the spermatogonium matures into a primary spermatocyte.
• The spermatocyte undergoes Meiosis 1 and 11.
• The product is four spermatids.
• Spermatids mature into sperm cells.
• Oogenesis is when the oogonium matures into a primary oocyte.
• The oocyte undergoes Meiosis 1 and 11, producing one ovum or egg cell and 3 polar bodies.

Chromosomal Disorders

• Down Syndrome (Trisomy 21) occurs when chromosomes in a pair fail to separate from each other during Anaphase 11.
• The individual will have 47 chromosomes in his or her cells.
• Extra chromosome 21 will lead to an imbalance of genetic material in the cell.
• Cri du chat syndrome occurs when a part of chromosome 5 is lost.
• It results in a round, moonlike face, free cries, and mental delay.

Interactions in the Ecosystem: Energy Flow in the Ecosystem

Producers

• Producers transform energy from the sun into food.
• This process is called photosynthesis.
• Autotrophs: plants, algae, some bacteria.

Consumers

• Consumers depend on other organisms for their energy requirements.
• These are heterotrophs.

Decomposers

• Decomposers break down dead matter into simpler substances.
• They play an important role in nutrient cycling.

Energy Flow

• The energy flow is one way: Sun > Producers > Consumers.
• This is illustrated in a food chain or food web.
• The pyramid of energy shows the amount of energy in each group of organisms.
• As the trophic level increases, the available energy becomes less.
• The pyramid of biomass shows the total mass of all living organisms.
• The amount of biomass decreases as you go up a trophic level.

Ecological Pyramids

• These show the link between living organisms at different trophic levels across a food chain.
• Types include the Pyramid of numbers, and Pyramid of energy.
• Energy flows from the bottom to the top.
• Autotrophs transmit the highest amount of energy.
• Lower trophic level energy is larger than higher trophic level energy, and herbivores outnumber.
• The availability of energy or biomass decreases with each successive level of the pyramid.

The Nutrient Cycles

Hydrologic Cycle

• Also known as the water cycle.
• The driving force is the sun's energy.
• Processes involved: evaporation, condensation, precipitation.
• Roles of plants and animals: transpiration, respiration.

Carbon Cycle

• CO2 is released by plants and animals.
• CO2 is used by plants.
• O2 is released by plants.
• O2 is used by plants and animals.

Nitrogen Cycle

• Nitrogen Fixation (air to soil): Nitrogen gas from the air is turned into a form plants can use through bacteria or lightning.
• Ammonification (decay to ammonia): When plants and animals die, decomposers turn nitrogen into ammonia (NH₃) or ammonium (NH₄⁺).
• Nitrification (ammonia to nitrates): Bacteria change ammonia into nitrites (NO₂⁻), and then into nitrates (NO₃⁻), which plants absorb.
• Denitrification (back to the air): Bacteria convert extra nitrates back into nitrogen gas (N₂), which returns to the atmosphere.

Impact of Human Activities

• Water pollution decreases the quality of fresh water.
• Deforestation results in less evaporation, less precipitation, and increases CO2 concentration.
• The burning of fossil fuels increases Earth's temperature.
• It speeds up phase change and increases the concentration of gases.