Lecture Outline - Chapter 4

4.1 The Digestive System (p. 80, Fig. 4.1)
	1.	The digestive system is a continuous tube from the mouth to the anus. It receives and decomposes food into molecules small enough for cells to absorb. It also absorbs nutrients and eliminates leftover materials.
	2.	Mouth Receives (p. 80)
		a.	The mouth receives food and prepares it for swallowing.
		b.	Taste buds on the tongue determine the taste of food.
		c.	Three pairs of salivary glands secrete saliva into the mouth when food is present. Saliva moistens and binds food.
		d.	Saliva also contains salivary amylase. 
		e.	Teeth Chew Food (p. 81, Fig. 4.2)
			i.	Teeth have various separate functions but collectively break up larger food particles for swallowing.
			ii.	Tooth decay is a result of bacterial action in the mouth. 
	3.	Pharynx Swallows (p. 82, Fig. 4.3)
		a.	The pharynx is a dual passageway at the back of the mouth for breathing and for swallowing food.
		b.	Swallowing involves a reflex that raises the soft palate and the larynx, which, in turn, shuts off the trachea. Food passes past the glottis into the esophagus. 
	4.	Esophagus Conducts (p. 82)
		a.	The esophagus is a muscular, collapsible tube that conveys food from the throat to the stomach via peristaltic contractions.
		b.	Neither digestion nor absorption occurs in the esophagus.
		c.	A constrictor controls the entrance of food into the esophagus, and a cardiac or gastroesophageal sphincter regulates the passage of food into the stomach.
	5.	Wall of the Digestive Tract Has Layers (p. 83, Fig. 4.4)
		a.	The lumen of the digestive tube is lined with mucosa that secretes protective mucus in the stomach and houses digestive glands.
		b.	The submucosa is a layer of loose connective tissue with blood vessels that nourish and removes wastes from other layers.
		c.	The muscularis is made up of two layers of smooth muscle and functions in peristalsis and mixing of food.
		d.	The serosa is the outermost layer, made up of serous membrane. 
	6.	Stomach Stores (p. 84, Fig. 4.5)
		a.	The stomach stores food and mixes it with gastric juice.
		b.	Gastric glands in the mucosa of the stomach make gastric juice. Pepsin breaks down proteins and requires the acidic environment that hydrochloric acid provides. Hydrochloric acid kills most bacteria present in food.
		c.	Only a limited amount of absorption occurs in the stomach.
		d.	After mixing with gastric juice, chyme leaves the stomach.
	7.	Small Intestine Absorbs (p. 85, Fig. 4.6)
		a.	The small intestine is the major site of nutrient absorption. Its lining is convoluted into villi, and microvilli increase the surface area.
		b.	The duodenum receives chyme from the stomach, digestive juices from the pancreas, and bile from the liver.
		c.	Nutrients are absorbed into the microvilli and passed to the bloodstream. Fats are reconstructed within the cells of the small intestine lining and passed to lacteals.
	8.	Digestive Secretions Are Regulated (p. 86, Fig.4.7)
		Hormones (gastrin, gastric inhibitory peptide, secretin, and cholecystokinin) control digestive secretions.
	9.	Large Intestine Eliminates (p. 86, Figs. 4.8 and 4.9)
		a.	The large intestine includes the cecum, colon, rectum, and anal canal.
		b.	The large intestine compacts and eliminates feces.
		c.	Polyps (p. 87) 
			Polyps are small growths arising from the epithelial lining of the colon. They can be benign or malignant.
		d.	Diarrhea and Constipation (p. 87)
			i.	Infection or nervous stimulation causes diarrhea. The effect is reduced reabsorption of water from feces, leading to watery, frequent movements.
			ii.	Constipation is caused by lack of water in the diet, too little fiber, or inhibition of the defecation reflex. 
4.2 Three Accessory Organs (p. 88)
	1.	Pancreas Produces Enzymes (p. 88)
		a.	The pancreas secretes pancreatic juice, a mix of digestive enzymes and sodium bicarbonate. 
		b.	Digestive enzymes include pancreatic amylase for starch digestion, trypsin for protein digestion, and lipase for fat digestion.
	2.	Liver Produces Bile (p. 88, Figs. 4.10 and 4.11)
		a.	The liver functions as a gatekeeper to the blood. 
		b.	The liver stores glycogen, which can be readily mobilized when blood glucose is low.
		c.	The liver produces bile, which emulsifies fats in the small intestine.
		d.	Serious Liver Disorders (p. 89)
			i.	Jaundice has several causes and results in a yellowish cast to the skin and eyes.
			ii.	Hepatitis is the inflammation of the liver.  
			iii.	Cirrhosis of the liver is the progressive replacement of active liver tissue by scar tissue due to chronic alcoholism.
	3.	Gallbladder Stores Bile (p. 89)
		The gallbladder is a muscular sac lying within the lobes of the liver that stores bile.
4.3 Digestive Enzymes (p. 90, Fig. 4.12, Table 4.2)
	1.	The digestive enzymes are hydrolytic enzymes that break down foods by adding water to them. Each has its own optimal pH.
		a.	Carbohydrate digestion begins with salivary amylase and continues in the small intestine with pancreatic amylase.
		b.	Protein digestion begins in the stomach with pepsin and is completed in the small intestine with pancreatic trypsin.
		c.	Fat digestion begins in the small intestine with pancreatic lipase after bile has emulsified fats.
		d.	Glucose, amino acids, fatty acids, and glycerol are absorbed in the small intestine and enter the circulatory system. Fats re-form in small intestine cells and enter lacteals as lipoproteins.
	2.	Best Conditions for Digestion (p. 91)
		Research indicates that the best conditions for digestion include the proper enzymes, optimal pH, and warmth.
4.4 Working Together (p. 93)
	The Working Together box on page 92 shows how the activities of the digestive system coordinate with those of other organ systems to maintain homeostasis.
4.5 Nutrition (p. 93, Fig. 4.13)
	1.	Nutrients can be divided into macronutrients and micronutrients.
	2.	Carbohydrates Are Quick Energy (p. 94, Fig. 4.14)
		a.	Carbohydrates supply the bulk of energy for the body and glucose for the brain. 
		b.	The bulk of the diet (58%) should be composed of unrefined complex carbohydrates that supply energy, micronutrients, and fiber.
	3.	Proteins Supply Building Blocks (p. 95, Table 4.4)
		a.	Proteins in the diet are used as structural building blocks.
		b.	Proteins should supply the essential amino acids.
		c.	Reliance on plant proteins is a healthier choice than consuming large quantities of red meat. 
			HEALTH FOCUS: Fat Is Everyone's Issue (p. 96, Table 4.4)
			i.	Saturated fats have been linked to cardiovascular disease and cancer.
			ii.	Polyunsaturated and monounsaturated fats have now both been found to reduce LDL (low density lipoprotein) cholesterol while maintaining HDL (high density lipoprotein) levels. 
			iii.	The diet should include no more than 30% of calories from fats.
	4.	Lipids Are Stored Energy (p. 98)
		a.	The body stores lipids in adipose tissue.
		b.	Cholesterol, also a lipid, is carried in the blood. LDL carries cholesterol from the liver, and HDL carries it back to the liver. The liver converts HDL to bile salts.
		c.	Saturated fats raise LDL cholesterol. 
	5.	Vitamins Help Metabolism (p. 98, Fig. 4.16, Tables 4.5 and 4.6)
		a.	Vitamins are essential organic molecules that often play roles as coenzymes in cellular metabolism.
		b.	Vitamin A is a precursor of a visual pigment that prevents night blindness.
		c.	Some Vitamins Are Antioxidants (p. 100)
			Vitamins C, E, and A are antioxidants that remove free radicals from cells and help maintain cell health.  
		d.	Vitamin D Makes Bones Strong (p. 100)
			A precursor in the skin produces vitamin D after UV exposure. Vitamin D leaves the skin, is modified in the kidneys, and is then activated to calcitriol in the liver, which promotes calcium absorption from the intestines.
	6.	Minerals Are Needed Too (p. 100, Table 4.7)
		a.	Minerals are inorganic substances from the soil. Examples include iron, calcium, phosphorus, sodium, and zinc.
			ECOLOGY FOCUS: Our Crops Deserve Better (p. 101)
			i.	Plants concentrate minerals and nutrients within their structures.
			ii.	The same environmental pollutants that affect human health affect plant health.
			iii.	Soil erosion is contributing to the loss of productivity of agricultural fields.
			iv.	If plants do not survive the environmental degradation caused by humans, neither will humans.
		b.	Calcium and Bone Disease (p. 102, Fig. 4.17)
		Calcium is a major component of bones and teeth. 
		c.	Too Much Sodium (p. 102, Table 4.8) 
		Too much sodium in the diet can lead to hypertension in some people. 
	7.	Analyzing Eating Disorders (p. 103) 
		a.	Obesity should be treated with a low-fat diet and exercise.
		b.	Bulimia is a binge-purge disorder. Bulimics are usually depressed and may suffer many side effects of the disorder.
		c.	Anorexia nervosa occurs most often in adolescent women who perceive themselves as fat when they are not. It may be a desire to suppress their sexuality.