Digestion, Nutrition, and Excretion

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Digestion, Nutrition,and Excretion

• Chapter 24

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Hips and Hunger

• Fat-storing cells
• adaptation for survival in lean times
• Once formed, adipose cells stay forever
• Dieting decreases fat in cells
• Hormones affect appetite
• Leptin decreases appetite
• Ghrelin increases appetite

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Hormones and Hunger

• Without leptin, mice keep eating

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Two Types of Systems

• Incomplete digestive system
• One-way, saclike digestive cavity
• Complete digestive system
• Tube with opening at each end

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5 Tasks of Digestive Systems

• 1. Mechanical processing
• - break up, mix, and move food material
• 2. Secretion
• - of enzymes into tube where digestion occurs
• 3. Digestion
• break down of food particles into smaller
  molecules
• 4. Absorption
• of nutrients and fluids
• 5. Elimination
• of wastes and residues

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Digestive Specialization

• Digestive system is often subdivided into
  functional regions
• Specialization reflects feeding behavior

crop
gizzard
cloaca
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Specialized Teeth

• Structure of teeth reflects feeding behavior
• Antelope brush teeth against dirt as they eat
  wear down crowns

ANTELOPE MOLAR
HUMAN MOLAR
crown
crown
root
root
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Antelope Stomach

• Multiple chambers allow rechewing and breakdown
  of cellulose

stomach chamber 1
stomach chamber 2
stomach chamber 3
stomach chamber 4
to small intestine
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Human Digestive System

• Complete system with many specialized accessory
  glands and organs
• About 10 meters long
• Lined with mucus-secreting epithelium
• Movement is one way, from mouth to anus

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Major Components Again with the Test Question

• Mouth (oral cavity)
• Pharynx (throat)
• Esophagus
• Gut
• Stomach
• Small intestine
• Large intestine
• Rectum
• Anus

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Accessory Organs

• Salivary glands
• Secrete saliva
• Liver
• Secretes bile
• Gallbladder
• Stores and concentrates bile
• Pancreas
• Secretes digestive enzymes

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Mechanical Processing

• Teeth break down food

molars (12)
premolars (8)
canines (4)
incisors (8)
lower jaw
upper jaw
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Saliva

• Produced by salivary glands at back of mouth and
  under tongue
• Saliva includes
• Salivary amylase (enzyme)
• Bicarbonate (buffer)
• Mucins (bind food into bolus)
• Water

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Swallowing

• Complex reflex
• Tongue forces food into pharynx
• Epiglottis and vocal cords close off trachea
  breathing temporarily ceases
• Food moves into esophagus, then through
  esophageal sphincter into stomach

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The Larynx (Respiratory System) and the Epiglottis
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Structure of Stomach

• J-shaped organ lies below the diaphragm
• Sphincters at both ends
• Outer serosa covers smooth muscle layers
• Inner layer of mucus secreting epithelium faces
  lumen (inside)

sphincters
serosa
muscle
mucosa
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Stomach Secretions

• Secreted into lumen (gastric fluid)
• Hydrochloric acid (HCl)
• Mucus (protective)
• Protein-digesting enzymes
• Stomach cells also secrete the hormone gastrin
  into the bloodstream
• As gastrin increases, HCL secretion does too

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Small Intestine

• Longest segment of digestive tract
• Receives chyme from stomach
• Receives secretions from liver, gallbladder, and
  pancreas
• Digests food into absorbable subunits

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Walls of Small Intestine

• Projections into the intestinal lumen increase
  the surface area available for absorption

one villus
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mucosa (inner lining)
Fig. 24-6a, p.407
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microvilli at the free surface of an absorptive
cell (brush border cell)
cytoplasm
mucus secretion
hormone secretion
lysozyme secretion
nutrient absorption
Fig. 24-6b2, p.407
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Nutrient Absorption

• Passage of molecules into internal environment
• Occurs mainly in small intestine
• Various methods of absorption
• Osmosis, transport proteins, diffusion

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Absorption Mechanisms
INTESTINAL LUMEN
monosaccharides
carbohydrates

• Monosaccharides amino acids are actively
  transported across plasma membrane of epithelial
  cells, then from cell into internal environment

amino acids
proteins
EPITHELIAL CELL
INTERNAL ENVIRONMENT
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Fat Absorption
bile salts
bile salts

micelles
fat globules (triglycerides)
fatty acids, monoglycerides
emulsification droplets
triglycerides proteins
EPITHELIAL CELL
chylomicrons
INTERNAL ENVIRONMENT
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Into the Blood

• Glucose and amino acids enter blood vessels
  directly
• Triglycerides enter lymph vessels, which
  eventually drain into blood vessels

Know the difference
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Controls Over Digestion

• Nervous system
• Secretion of acids and enzymes
• Smooth muscle contractions
• Endocrine system
• Appetite (leptin and grehlin)
• Digestion (gastrin, secretin, CCK)

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Large Intestine (Colon)

• Actively transports sodium ions out of lumen
  water follows
• Removing water from system is the primary job of
  the colon
• Concentrates and stores feces
• Resident bacteria produce vitamins
• Diseases
• Appendicitis
• Colon cancer

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Cecum and Appendix
ascending portion of large intestine
last portion of small intestine
appendix
cecum
Fig. 24-8, p.409
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Human Nutrition
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Carbohydrates

• Bodys main energy source
• glucose
• Complex carbohydrates
• starch, nutrients, fiber
• Refined sugars
• lack fiber, minerals, vitamins

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Lipids

• Energy reserves, cell membranes, insulation
• fats, phospholipids, sterols
• Essential fatty acids
• must be obtained from food
• Excess saturated and trans fats
• Heart disease, stroke, cancers

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Proteins

• 20 amino acids
• 9 Essential amino acids
• must be obtained from diet
• Complete proteins
• animal sources
• supply all essential amino acids
• Incomplete proteins
• all but one plant source
• must be combined

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Dietary Recommendations

• Whole foods help prevent chronic disease

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Vitamins and Minerals

• Vitamins
• Essential organic substances
• Minerals
• Essential inorganic substances

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Vitamins

• Fat-soluble
• Excess accumulates in tissue
• Vitamins A, D, E, K

• Water-soluble
• B vitamins
• Pantothenic acid
• Folate
• Biotin
• Vitamin C

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Table 24-2, p.412
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Major Minerals

• Calcium Magnesium
• Chloride Phosphorus
• Copper Potassium
• Fluorine Sodium
• Iodine Sulfur
• Iron Zinc

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Table 24-3, p.413
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Body-Mass Index

• An indicator of weight-related health risk
• BMI Weight (lbs) X 700
• -----------------------------
• Height (inches)2
• BMI greater than 25 indicates health risk

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Maintaining Weight

• Caloric input must equal caloric use
• Calories burned depends upon
• Activity level
• Age
• Height and build