Do Now: Why do you think the food you eat must be broken down into subunits? Aim: The Digestive System and how does it help keep homeostasis in the body?

Why do we eat? Humans are heterotrophic organisms (can’t make their own food) We need to get energy (glucose) from eating other organisms We also need food to get raw materials (amino acids, fatty acids and nucleic bases) to help us grow and to repair.

What happens to the food that we eat? Because most foods contain molecules that are too big to pass through our cell’s membrane, food must be broken down into small molecules (subunits). This is done in two processes: Mechanical digestion Chemical digestion

Steak Mechanical Digestion Mechanical Digestion is the process of breaking large pieces of food into smaller pieces of that food. This creates more surface area for enzymes to act on. Steak Steak Steak Steak Steak Steak

Chemical Digestion Chemical Digestion is the process of breaking food molecules into it sub-units with the use of enzymes: Starches into simple sugars (glucose) Lipids into fatty acids Proteins into amino acids The sub-units are small enough to pass though a cell’s membrane

The Mouth Digestion begins at the mouth Teeth chop and grind large pieces of food into smaller pieces (mechanical digestion) Saliva from saliva glands contains the enzyme, amylase, which starts to breakdown starches (chemical digestion) in glucose

The Esophagus With the help of the tongue, the food is pushed to the back of the throat, where it enters a long tube called the esophagus. The esophagus connects the mouth to the stomach Food is squeezed down the esophagus by a wave of contracting muscles. This wave-like contraction is called peristalsis

The Stomach The stomach is a enlarged muscular tube, “pouch,” at the end of the esophagus. When the food enters the stomach, the stomach begins to contract, “churn.” This is mechanical digestion . The food is turned into chyme.

The Stomach (continued) While chyme present the stomach excretes the enzyme called Pepsin which begins to breaks down proteins. This is chemical digestion. The stomach also excretes gastric acids, which makes the stomach the lowest pH area in the body.

Where does the chyme go? The digested food (chyme) exits the stomach and enters a small tube called the duodenum. The duodenum is important because “accessory” organs connect into it.

What are accessory organs? Accessory organs are organs that are not directly part of the digestive track. Accessory organs secrete enzymes to further digest the food. Accessory organs include: The liver – aid in the digestion of lipids (bile) Gallbladder – a storage pouch for extra bile Pancreas – aid in the digestion of: proteins, carbohydrates and lipids

The Small Intestines The now digested food leaves the duodenum and enters a narrow but long tube called the small intestine. The small intestine is a narrow but very long tube (23ft). Its function is to absorb nutrients from the digested food and place it into the blood.

How does nutrients get absorbed? The small intestine have many mini structures which stick out called villi. These villi creates more surface area, allowing the small intestine to absorb more nutrients! Villi are one celled thick and surrounded by capillaries. Food diffuses from the small intestines into the caplillaries.

What happen after the digested food leaves the small intestine? Once the digested food passes through the small intestine it enters a large tube but short in length (5ft) called the large intestine. Digestion stops!!!!

The large intestine The digested food is basically nutrient-free. All the lipids, starches, sugars, and proteins have been absorbed It is now waste product, and the main job (function) of the large intestine is to remove water from the indigestible material that is left. Once this material passes through the large intestine it reaches the rectum and then the anus.

What happens when it reaches the anus?

How does the digestive system help the body maintain homeostasis? As you do work, your body needs glucose. Glucose, from digested foods, diffuses into capillaries surrounding the villi of the small intestines. The blood transport this glucose to body cells. The glucose is small enough to enter the cell. And with oxygen from the respiratory system, cells can carry out respiration.