Download Chapter 5 - Los Angeles City College

Chapter 5 (and a bit of Chp 4)
Biology 25: Human
Biology
Prof. Gonsalves
Los Angeles City College
Loosely Based on Mader’s Human Biology,7th
edition
Integumentary System
Components: Hair, skin, and nails.
Functions:
 Protects the body from:
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Infection: Barrier to microbes.
Mechanical injury
Excessive heat or cold: Thermoregulation
Water loss
Communication:
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Receives stimuli from environment
Gives out subtle signals (blushing, etc.).
Homeostatic Role:

Helps maintain constant body temperature.
1. Digestive System
Components: Mouth, salivary glands, throat,
esophagus, stomach, intestines, liver, gallbladder,
pancreas, rectum, and anus.
Functions:
Ingest and mechanically break down food.
 Digest food: Stomach and small intestine
mainly.
 Absorb nutrients and water.
 Eliminate waste.

Homeostatic Roles:
Supplies energy for life’s activities.
 Supplies building blocks for
macromolecules

Stages of Food Processing
1. Ingestion: The act of eating. Usually involves
placing food in mouth or oral cavity.
2. Digestion: Macromolecules in food (fats,
proteins, polysaccharides, etc.) are too large to
be absorbed by digestive system.
Must be broken down into small molecules
(amino acids, simple sugars, etc.) so they can be
absorbed and utilized by the body.
Involves two processes:
Mechanical: Chewing and churning.
Chemical: Enzymatic breakdown of food.
Stages of Food Processing
3. Absorption: Cells lining the digestive
cavity take up building blocks (simple
sugars, amino acids, etc.), which then
enter the bloodstream.
Circulatory system distributes nutrients
in blood to cells throughout the body.
4. Elimination: Undigested food materials
are discharged from body.
Stages of Food Processing
Parts of the Human Digestive System
Alimentary canal: Long tube like structure.
 Mouth
 Tongue
 Pharynx (throat)
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Rectum
 Anus
Digestive glands: Produce enzymes, bile, and other
substances important for digestion.
 Salivary glands
 Pancreas
 Liver and gallbladder
Human Digestive System
Mouth:

Ingest and mechanically break down food.

Digestion: Saliva lubricates and starts to digest
food.
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Starch is digested by salivary amylase
Other enzymes in saliva kill bacteria.
Part of the Human Digestive System
Pharynx (Throat):
Throat opens into both the trachea
(respiratory system) and esophagus
(digestive system).
 As food enters pharynx, swallowing reflex is
triggered:
 Esophageal sphincter relaxes
 Epiglottis blocks tracheal opening
 Food is directed towards esophagus
Esophagus:
 Muscular tube that conveys food to
stomach.
 Peristalsis: Wavelike involuntary muscle
contractions squeeze food through
alimentary canal (towards the stomach).

Swallowing Reflex and Esophageal Peristalsis
Smooth Muscle Peristalsis Moves Food
Along Alimentary Canal
Part of the Human Digestive System
Stomach:
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Located on left side of abdominal cavity, right below
diaphragm.
Stores food (can stretch to accommodate up to 2
liters of food and water), and breaks it down with
acids and enzymes.
Gastric juice is secreted by stomach. Contains
hydrochloric acid (HCl), enzymes (pepsin), and
mucus.
Protein digestion starts in stomach with pepsin.
Food is churned in stomach with gastric juice to form
chyme.
Food remains in stomach from 2 to 6 hours, after
which it is released into the small intestine.
Part of the Human Digestive System
Small Intestine:
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Huge surface area, about 300 square meters.
Most digestion and absorption occurs here.
Pancreas and liver empty digestive enzymes and bile into the small
intestine.
 Pancreatic amylase: Breaks down starch
 Trypsin and Chymotrypsin: Break down proteins
 Lipases: Break down fats
 Peptidases: Break down proteins
 Nucleases: Break down DNA and RNA
 Bile: Helps fat digestion by emulsifying fats.
Very large surface area for absorption due to:
 Large circular folds (villi)
 Tiny cell surface projections (microvilli).
Capillaries drain nutrients from small intestine and then sends them to
first to liver and then rest of body.
Small Intestine is Site Most Enzymatic
Digestion
Human Digestive System
Large Intestine (Colon):
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1.5 m long and 5 cm wide (diameter)
Most water absorption occurs here (up to 90%).
Undigested remainder of food is converted into feces.
Site of bacterial synthesis
 Vitamin K
 Folic acid
 Biotin
 Several B vitamins
Appendix: Small fingerlike projection. Involved in immunity.
Rectum:

Stores feces until ready to eliminate
Human Digestive System
Digestive Glands -- Liver:
 Structure
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Composed of 2 lobes made up of about 100,000 lobules
Functions
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Removes bilirubin, a hemoglobin breakdown waste product, from the
blood and incorporates it into bile.
Produces bile which is stored in gallbladder.
Bile is released into the small intestine after a meal.
Bile contains no enzymes, but helps solubilize fat particles.
Detoxifies blood by removing and metabolizing poisonous substances
Stores iron and fat-soluable vitamins A, D, E, K, and B12
Makes plasma proteins, such as albumins and fibrinogen, from amino
acids
Synthesizes and degrades glycogen to maintain homeostatic levels of
glucose
Produces urea after breaking down amino acids
Pancreas:
Produces several digestive enzymes
which are emptied into small
intestine.
 Enzymes digest starch (pancreatic
amylase), protein (trypsin), fats
(lipase), and nucleic acids (nucleases).

Pancreatic Juice

Contain H20 , HC03- and digestive enzymes.
Enzyme
Zymogen
Activator
Action
Trypsin
Trypsinogen
Enterokinase
Cleaves internal peptide bonds
Chymotrypsin
Chymotrypsinogen
Trypsin
Cleaves internal peptide bonds
Elastase
Proelastase
Trypsin
Cleaves internal peptide bonds
Carboxypeptidase
Procarboxypeptidase
Trypsin
Cleaves last amino acid from carboxylterminal end of polypeptide
Phospholipase
Prophospholipase
Trypsin
Cleaves fatty acids from phospholipids such
as lecithin
Lipase
None
None
Cleaves fatty acids from glycerol
Amylase
None
None
Digests starch to maltose and short chains
of glucose molecules
Cholesterolesterase
None
None
Releases cholesterol from its bonds with
other molecules
Ribonuclease
None
None
Cleaves RNA to form short chains
Deoxyribonuclease
None
None
Cleaves DNA to form short chains
Gallbladder
Liver produces about 1,000 ml of bile a
day with excess being stored in the
gallbladder.
 Gallbladder reabsorbs water making bile
thick and mucuslike.
 Gallstones may form due to precipitation
of cholesterol.

Vitamins and Minerals
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Small organic molecules that serve as coenzymes
in metabolic reactions or have highly specific
functions.
Must be obtained from the diet because the body
does not produce them, or does so in insufficient
amounts.
Certain vitamins function as antioxidants.
2 classes of vitamins:
 Fat-soluble
 Water-soluble
Vitamins
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Water-soluble vitamins:
 Serve as coenzymes in the metabolism of
carbohydrates, lipids, and proteins.
 May serve as antioxidants.
Fat-soluble vitamins:
 Serve as antioxidants.
 Bind to nuclear receptors.
 Involved in regulating fetal development.
 Regulate Ca++ balance.
Minerals
Needed as cofactors for specific enzymes
and other critical functions.
 Trace elements:
 Required in small amounts from 50 mg to
18 mg/day.

Free Radicals and Antioxidants
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Electrons are located in orbitals.
 Each orbital contains a maximum of 2
electrons.
Free radical:
 When an orbital has an unpaired electron.
 Highly reactive in the body.
 Oxidize other atoms or reduce other atoms.
Major free radicals called:
 Reactive oxygen or nitrogen species.
 Oxygen or nitrogen as unpaired electron.
Free Radicals and Antioxidants
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Functions of free radicals:
 Help to destroy bacteria.
 Produce vasodilation.
 NO, superoxide radical, and hydroxy radical.
Exert oxidative stress contributing to disease states.
Antioxidants:
 Protective mechanism against oxidative stress.
 Can react with free radicals by picking up unpaired
electrons.
 Glutathione, vitamin C, and vitamin E.
Obesity
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Obesity is often diagnosed by using using a body
mass index (BMI).
BMI = w
h2
 W = weight in kilograms
 H = height in meters
Obesity in childhood is due to an increase in both
the size and the # of adipocytes.
Obesity defined as BMI > 30.
Healthy weight as BMI between 19 – 25.