Digestive System PDF

## Digestive System #### Parts and Functions: 1. **Ingestion**: Act of taking in food and drink into the body 2. **Digestion**: Chemical and mechanical 3. **Absorption**: Nutrient molecules absorbed from gut into bloodstream 4. **Elimination**: Ridding the body of undigested food waste Digestion...

## Digestive System #### Parts and Functions: 1. **Ingestion**: Act of taking in food and drink into the body 2. **Digestion**: Chemical and mechanical 3. **Absorption**: Nutrient molecules absorbed from gut into bloodstream 4. **Elimination**: Ridding the body of undigested food waste Digestion takes place within the **digestive tract**, which begins with the mouth and ends with the anus. **Digestion** can be either **mechanical** or **chemical**. * **Mechanical Digestion**: chewing of food, and churning and mixing of food in the stomach * **Chemical Digestion**: enzymes break macromolecules down into small organic molecules #### 1. The Mouth * **Chewing is Mechanical** * The mouth takes food into the body. * **Teeth**: composed of skeletal muscle and involved in chewing food * **Tongue**: involved in forming the **bolus** (a mass of food that is ready for swallowing) * **Roof of the mouth**: composed of a **hard palate** and a **soft palate**. Prevents ingested food from entering the nasal cavity. * **Tonsils**: contain lymphoid tissue that protect against infections * **Salivary Glands**: produce saliva to keep the mouth moist. Saliva contains an enzyme that digests starch #### 2. The Pharynx * The pharynx is a passageway that receives air from the nasal cavities and food from the mouth. * **Swallowing** (a reflex action) occurs in the pharynx. * The soft palate moves back to **close** off the nasopharynx * The trachea moves up under the **epiglottis** to cover the glottis (the opening to the larynx (voice box)). * During swallowing, food enters the esophagus because the air passages are **blocked**. #### 3. The Esophagus * The esophagus is a long muscular tube that moves food from the mouth to the stomach by **peristalsis**. * Ends in the **cardial sphincter** * **Peristalsis** (rhythmic muscular contractions) pushes food along the digestive tract. * Begins at the esophagus and ends at the anus #### 4. The Stomach * The stomach is an organ that receives food from the esophagus, mechanically and chemically digests food, and moves food into the small intestine. * The human stomach has thick walls with folds (called **rugae**) that allow it to expand and fill with food. * **Lining of the stomach**: has **gastric glands** that secrete gastric juice containing **juice** and **lipase enzymes** * Alcohol and other liquids are absorbed in the stomach, but most solid food is not. #### Functions 1. **Storage of a Meal** - most expanded structure along the alimentary canal 2. **Mechanical Digestion** of food - Stomach is very muscular, and it squeezes to churn and mix food to physically break it down * When food leaves the stomach, it is a thick, soupy liquid called **chyme**. * Chyme enters the small intestine by way of the **pyloric sphincter**. 3. **Chemical Digestion** of food - Adds **pepsin enzyme** to start chemically breaking proteins into small peptide chains. - HCI (acid) helps activate enzymes, but it also helps kill many of the bacteria that we ingest. 4. **Protection** against germs #### 5. The Small Intestine * The small intestine receives chyme from the stomach and completes the digestion of food. Macromolecule are broken down into nutrients, which are absorbed in the small intestine and passed into the blood. * The small intestine is composed of three parts: * **Duodenum**: upper part of the small intestine * **Jejunum**: middle part of the small intestine * **Ileum**: lower part of the small intestine. * **Villi**: fingerlike projections that contain **microvilli** * Increase the surface area of the villus for the absorption of nutrients * Each villus contains **blood capillaries** and a **small lymphatic capillary** called a **lacteal** * Nutrients are **absorbed** into the blood capillaries and the lacteals, which carry them to the body cells. #### 6. The Large Intestine * The large intestine absorbs water, salts, and some vitamins. It also stores indigestible material until it is eliminated as feces. * The large intestine includes: * **Cecum**: a small pouch that forms the first part of the large intestine * **Colon**: includes the ascending, transverse, descending, and sigmoid colon * **Rectum**: the last part of the large intestine; opens at the anus * **Anus**: rectum opening; site of defecation (expulsion of feces). * When feces are forced into the rectum by **peristalsis**, a **defecation reflex** occurs * Eliminating feces from the body is a way the digestive system maintains **homeostasis** * Feces are about three-quarters water and one-quarter solids. * Solids: **bacteria**, **fiber**, and other indigestible materials. * **Bacteria** break down some indigestible material, and produce some vitamins that our bodies can absorb #### Accessory Organs: **1. The Pancreas**: The pancreas is an organ that has both **endocrine** and **exocrine** functions. * **Exocrine**: cells produce **pancreatic juice** (NaHCO3 (baking soda)) and **glucagon**. * **Endocrine**: secretes **insulin** and **glucagon** (hormones that regulation blood glucose (sugar) levels) #### Hormones secreted: * **Insulin**: * Hormone secreted when blood glucose level is **high** * Stimulates the **uptake** of **glucose** by cells (liver, muscle, adipose tissue) to lower blood glucose * **Glucagon**: * Hormone secreted when blood glucose level is **low** * Stimulates the liver to break **glycogen down into glucose** to increase blood glucose * Stimulates **adipose tissue to break fat and small intestine** down to glycerol and fatty acids (to make glucose). * **Somatostatin**: * Also produced by cells in the **stomach** * Inhibits the release of **growth hormone** * Suppresses the release of **insulin** and **glucagon** * Decreases the absorption of nutrients **2. The Liver** * The liver is the largest gland in the body. The liver has many functions. * The liver contains about 100 000 **lobules** that serve as its structural and functional units. * Three structures are located between the lobules: * **Bile duct**: takes bile away from the liver * **Hepatic artery branch**: brings oxygen-rich blood to the liver * **Hepatic portal vein**: transports nutrients from the intestines #### Functions of the Liver: 1. Detoxifies blood by removing and metabolizing poisonous substances. 2. Stores **Iron (Fe2+)** and vitamins **A, D, E, K, and B12**. 3. Makes many plasma proteins, such as albumins and fibrinogen, from amino acids. 4. Stores glucose as **glycogen** after a meal, and breaks down glycogen to **glucose** to maintain the glucose concentration of blood between eating periods. 5. Produces **urea** after breaking down amino acids. 6. Removes **bilirubin**, a breakdown product of hemoglobin, from the blood and excretes it in **bile**, a liver product. 7. Help regulate blood cholesterol level, converting some to bile salts. 8. Produces **bile**. **3. The Gall Bladder:** * The gall bladder is a muscular sac attached to the surface of the liver. * Excess **bile** from the liver is stored in the **gall bladder** * **Bile** leaves the gall bladder and proceeds to the **duodenum** via the common bile duct #### Digestive Enzymes * Digestive enzymes help break down the major components of food: carbohydrates, proteins, and fats. #### Carbohydrates * The digestion of starch (a carbohydrate) begins in the mouth. 1. **Salivary amylase** (produced by the salivary glands) digests starch into **maltose** (a disaccharide) *does the same thing in different spots* 2. **Pancreatic amylase** (produced by the pancreas) digests starch into **maltose** 3. **Maltase** (produced by the small intestine) digests **maltose** in the small intestine to **glucose** (a monosaccharide). Glucose can be absorbed by the small intestine. * **Lactase** is an enzyme that digests lactose, a sugar found in milk. #### Protein * The digestion of proteins begins in the stomach. 1. **Pepsin** (an enzyme produced by gastric glands that acts on proteins to produce peptides). 2. **Trypsin** (produced by the pancreas) acts on proteins to product peptides. 3. **Peptidases** (produced in the small intestine) break down peptides into amino acids #### Fats * Fat digestion begins in the duodenum. 1. **Bile** (NOT AN ENZYME) breaks fat into smaller fat droplets so they are easier to digest (more surface area) → Liver produces bile, gallbladder stores bile. 2. **Lipase** (produced by the pancreas) acts in the small intestine and digests fat molecules in the fat droplets after they have been by bile salts. * Glycerol and fatty acids enter the cells of the villi, where they are rejoined and repackaged as **lipoprotein droplets** (chylomicrons) before entering the lacteals. #### Regulation of Digestive Enzymes Enzymes function best at an optimum temperature and pH that helps maintain the proper shape to fit their substrate: * Ideal temp is *37 degrees Celcius*. * Stomach pH is *1–3*. * Small intestine pH is *7.4–1.9*. | Enzyme | Produced By | Site of Action | Optimum pH | Digestion | | :--- | :--- | :--- | :--- | :--- | | Salivary Amylase | Salivary glands | Mouth | Neutral | Starch + H2O → maltose | | Pancreatic Amylase | Pancreas | Small intestine | Basic | starch + H2O → maltose | | Maltase | Small intestine | Small intestine | Basic | Maltose + H2O → glucose + glucose | | Pepsin | Gastric glands | Stomach | Acidic | Protein + H2O → peptides | | Trypsin | Pancreas | Small intestine | Basic | Protein + H2O → peptides | | Peptidases | Small intestine | Small intestine | Basic | Peptide + H2O → amino acids | | Nuclease | Pancreas | Small intestine | Basic | RNA and DNA + H2O → nucleotides | | Nucleosidases | Small intestine | Small intestine | Basic | Nucleotide + H2O → base + sugar + phosphate | | Lipase | Pancreas | Small intestine | Basic | Fat droplet + H2O → glycerol + fatty acids |