A Close Look at How the Human Body Functions

The Digestive System

The Basics of Nutrition Heterotrophs (can NOT synthesize organic nutrients) Digestion involves: ingestion: taking in food digestion: breaking down the food into a form that can be transported across the cell membrane egestion: getting rid of undigested wastes

The Basics of Nutrition Nutrient: any substance that provides energy for growth and repair: Carbohydrates Proteins Lipids Vitamins Minerals Water

Food molecules must be converted into subunits that can pass easily through cell membranes

large molecules end products of digestion 1. Carbohydrates Monosaccharides (polysaccharides) 2. Proteins Amino acids (polypeptides) 3. Lipids Fatty acids and Glycerol

Structure of Digestive System Continuous tube extending from mouth to anus Accessory organs attached along the way (appendix, gall bladder, liver, pancreas)

Organs of Digestive System Mouth – “oral cavity” Pharynx – “throat” Esophagus Stomach Small intestine Large intestine – “colon”

The Mouth Ingestion occurs here Contains teeth, tongue, and salivary glands Both chemical and mechanical digestion occur here. Chemical: salivary amylase is an enzyme in saliva that breaks down ( Starch) carbohydrates. Mechanical: teeth grind food increasing surface area for enzyme action

saliva also lubricates the food by adding water and mucus

Mechanical or Chemical?

a. food we swallow is called a bolus

Pharynx Back of the throat Where openings to trachea and esophagus meet Epiglottis: flap of connective tissue that closes over the trachea when swallowing

Esophagus tube that connects the oral cavity with stomach peristalsis: muscular contractions that squeeze food towards the stomach

Muscular Contractions of the Digestive System Peristalsis Muscular Contractions of the Digestive System

Stomach muscular organ that mechanically digests food lined with cells that secrete - mucus to protect stomach lining - protease ( Pepsin ) to chemically digest protein - hydrochloric acid (HCl)

 HCl has several functions - lowers the pH in the stomach (pepsin works best at pH 2) - helps to kill microorganisms ingested in the food

The acidic chyme leaves the stomach and enters the small intestine

Absorption of nutrients into the bloodstream occurs here SMALL INTESTINE Absorption of nutrients into the bloodstream occurs here VILLI - finger-like projections lining the small intestines for increased surface area for…… DIFFUSION of nutrients to occur

Small Intestines: - length is approximately 9 feet: food remains here for a long time - villi: Increases the surface area to about 300 m2 (size of tennis court)

Most of the chemical digestion of food occurs in the SI by the time food passes through the duodenum – (first 25 cm of the SI)

The Villi

Digested end products are taken into the villi by active and passive transport

Accessory Organs Pancreas: - produces enzymes that break down carbohydrates,, lipids, proteins and releases them into the SI - produces sodium bicarbonate – neutralizes stomach acid - Also produces hormones that regulate blood sugar levels (Endocrine Hormones)

pancreatic juice contains: proteases - digest proteins lipases - digest lipids amylases - digest carbohydrates

Small, non-vital organ – storage of bile Bile – emulsifies fat Gall Bladder Small, non-vital organ – storage of bile Bile – emulsifies fat Tucked on underside of liver

Gallbladder The gallbladder releases bile into the SI

Bile is NOT an enzyme - its function is to break down fat globules by a emulsification

Emulsification: mechanical digestion of fats molecules dissolved into smaller droplets

The Liver Function: Largest internal organ – opposite stomach Produces bile (breaks down fats) Converts glucose to glycogen Produces urea (the main substance of urine) Filters harmful substances from the blood (such as alcohol) Responsible for producing cholesterol

Bile is produced in the liver then stored in the gallbladder

Bile is a mixture of 3 chemicals cholesterol - excess cholesterol removed from the blood by the liver

2. bilirubin - a yellow pigment formed from dead red blood cells

3. bile salts - to help break up the fat structure

Appendix Pouch located where small and large intestines meet A vestigial organ: Non-vital – we notice no side effects when it is removed Thought to house important bacteria needed for balance in body Could possibly play a role in immunity In evolutionary past – scientists believe that there were 180 vestigial structures – today there are virtually none!!!

LARGE INTESTINE All indigestible waste at this point – no nutritional value Known as the colon Regulates water concentration of fecal matter before EGESTION through the RECTUM and ANUS Function is to reabsorb most of the water that was not picked up by the SI Too much or too little water can be problematic…

A large colony of bacteria known as E. Coli lives in the LI They Help produce vitamin K - needed for blood clotting

Human Digestive System What Can Go Wrong?? Malfunctions of the Human Digestive System

Ulcers Erosion of the stomach lining by digestive enzymes or acid due to lack of protective mucus.

Constipation Large intestine is difficult to empty due to too much water being reabsorbed in the colon – waste hardens.

HEARTBURN Cardiac sphincter stretches and stomach acid splashes walls of esophagus. Burning and pressure in chest Caused by overeating, acidic foods, or caffeinated beverages

Not enough water is absorbed out of waste before egestion Diarrhea Not enough water is absorbed out of waste before egestion Usually caused by bacteria Results in watery feces Could cause SEVERE DEHYDRATION Picture?

Appendicitis Inflammation of the appendix Could be very dangerous if it explodes – infection will spread in bloodstream throughout body

Gallstones Accumulation of hardened cholesterol in the gall bladder

HEPATITIS AND CIRRHOSIS Hepatitis (inflammation of the liver) Type A , B, & C Cirrhosis Distorted or scarred liver as a result of chronic inflammation

Question #1 The principal function of the large intestine is to: Produce salivary amylase Produce bile Store bile Reabsorb water from feces

Question #2 Choking on food is most likely caused by an interference with the proper functioning of the Diaphragm Oral cavity Esophagus Epiglottis

Question # 3 What is the role of teeth in digestion? They break down food mechanically, increasing the surface area of the food for enzyme action. They break food down mechanically, stimulating enzyme synthesis in the food. They break down food chemically, aiding in the movement of food down the esophagus. They break down food chemically, mixing saliva with the food for easier digestion.

Question # 4 In the human body, hydrochloric acid is responsible for the low pH of the contents of the Lungs Kidneys Pancreas Stomach

Question # 5 In humans villi that absorb small, soluble nutrients into the bloodstream are found in the Large Intestine Small Intestine Esophagus Stomach

Question # 6 Bile is a secretion produced by the liver, which aids in the emulsification of Lipids Proteins Sugars Starches

Question #7 Feces is usually about 40% water and 60% solid matter. Reducing the water content to 20% would most likely result in Diarrhea Ulcers Gallstones Constipation

Question # 8 Which nutrient should provide the largest percentage of calories in a well-balanced diet? Proteins Saturated fats Water Carbohydrates