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The Digestive System. Features of the Generalized Vertebrate Gut. Oral Cavity - Origin. 1. Origin Heterostomes - most of the invertebrate phyla Mouth originates from the blastopore

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The Digestive System

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The digestive system

The Digestive System

Features of the generalized vertebrate gut

Features of the Generalized Vertebrate Gut

Oral cavity origin

Oral Cavity - Origin

1. Origin Heterostomes - most of the invertebrate phyla

Mouth originates from the blastopore

2. Deuterostomes - not formed early, but breaks through later in development; anus originates from the blastopore



1. Origin - dermal denticles

2. Structure

  • Enamel - hardest substance in the body,

    occurs above the gum line

  • Cementum - continuation of enamel

    below the gum line

  • Dentin-matrix

  • Pulp-living portion of tooth





Blood vessels

and nerves

Glands of the mouth

Glands of the mouth

  • Salivary glands secrete saliva

    • mucin - lubricant

    • salivary amylase - converts starch to glucose



1. Length-short in fish, longer in tetrapods to bypass lungs

2. Muscles

Upper end- striated

Lower 2/3 - smooth

3. Modifications of the esophagus - crop in birds for storing food



1. Occurrence

  • Present in invertebrates with complete digestive tract

  • Absent in most lower chordates, even fish

    2. Regions

Functions of the stomach

Functions of the stomach

  • Little absorbtion by stomach - water and alcohol

  • secretes

  • HCl - very acid pH

  • mucin - lubricant

  • pepsin - digests proteins to shorter peptides

  • gastrin - hormone which regulates HCl secretion

Specialized stomachs

Specialized stomachs

  • Muscular gizzard of ground birds

  • 4 chambers of grazing mammals - ruminants

    rumen is specialized for storing food to be chewed later

Small intestine

Small Intestine

  • Primary site of digestion

  • Digested food absorbed here - absorbtion

  • Enzymes

    • peptidases - peptides to amino acids

    • lactase - lactose (milk sugar) to simple sugars

    • maltase - maltose to glucose

    • sucrase - sucrose to simple sugars

Absorbtion in the small intestine

Absorbtion in the Small Intestine

Pancreas enzymes for digestion

Pancreas - enzymes for digestion

  • lipase - fats to triglycerides

  • trypsin - proteins to shorter peptides

  • nucleases - DNA & RNA

  • secretin - hormone which stimulates buffering of HCl



  • large sac at junction of small and large intestines

  • contains symbiotic bacteria that digest cellulose

  • our appendix is a rudimentary caecum



  • no digestion

  • reabsorbs H20 and ions

  • contains bacteria that synthesize Vitamin K

  • Fermentation of gases by bacteria



A. Development - outpocket of the gut - tube that remains is the common bile duct

B. Digestive function - produces bile that emulsifies fats

  • Bile is stored in the gall bladder for secretion into the small intestine

Other function of the liver

Other function of the liver

C. Other functions -

  • stores glycogen

  • stores fats - cholesterol

  • filters and stores toxic materials

  • destroys red blood cells

Circulation and the liver

Circulation and the Liver



A. Origin - outpocket of the gut

B. Functions

1. Exocrine - produces digestive enzymes

2. Endocrine - produces insulin that regulates blood glucose levels

The fate of food

The fate of food



  • Nutrient - specific substance that must be taken into the body in sufficient quantities to meet the body’s needs

    • Essential Nutrient - required preformed; body cannot make it or cannot make enough to meet needs

    • Nonessential nutrient - body can make IF raw materials are available

  • Body needs BOTH to function

Nutrient classes

Nutrient Classes

  • Water (H2O)

  • Carbohydrate (CHO)

  • Protein (Pro)

  • Lipid (Fat)

Amount of energy

Amount of energy??

  • calorie - energy needed to raise 1 gm of H2O 1 degree Centigrade

  • Kilocalorie (kcal) - 1000 calories; energy needed to raise 1 liter of H2O 1 deg. C

  • Direct Calorimetry - measuring the heat (energy)

  • Indirect Calorimetry - measuring the CO2 & O2 and “deriving” the energy

Energy from nutrients

Energy from Nutrients

Phytochemicals plant

Phytochemicals (plant)

  • Only few of 10,000’s studied

  • associated with

    • decrease CVD & cancer risk

    • decrease infections

    • increase immune function

  • examples - flavonoids; carotenoids (> 600); isoflavones; plant sterols

The digestive system

  • Best to get from food NOT supplements

  • ** soy; tomatoes, garlic, onions, legumes, green tea; cruciferous vegetables, red wine, grapes


Water micronutrients

Water & Micronutrients

  • Functions

  • Intake Sources

  • Losses

  • Dehydration

  • Balance

  • Maintaining Hydration

Water functions

Water Functions

  • Regulates body temperature

    • cools body temperature AND evens heat throughout body

  • Environment for cells & chemical reactions

  • Transport (blood)

    • blood pressure fxn of volume of H2O

  • secondary lubrication of joints

  • takes part in chemical reactions

Body water 45 liters

Body Water (45 liters)





Sources of water

Sources of Water

  • Fluids - 550 - 1500 ml

  • Foods - 700 - 1000 ml

  • Metabolic H2O - 200 - 300 ml

  • Total1450 - 2800 ml



  • Introduction to CHO

  • Terminology

    • Simple/sugars

    • Complex/Starch

  • Digestion

  • Metabolism Overview



  • First link in the food chain

  • Photosynthesis - plants store some of sun’s energy (0.1%) in chemical bonds of CHO

  • CO2 + H2O -----> CHO

  • ALL PLANT foods have CHO

  • Only significant animal sources of CHO are milk and some milk products

  • Energy source for man - 8% Eskimos; >70% some non-industrialized countries

Cho functions

CHO Functions

  • Energy - all cells use

  • Some cells (RBC, brain) can use only CHO until starvation sets in

  • Needed for effective burning of fat

  • Spares protein from use for energy

  • Fiber, alternative forms of CHO, provides a number of benefits

Cho terminology

CHO Terminology

  • Saccharide = building block

  • Simple CHO = “sugars”

    • (1-3 saccharides)

    • mono (1), di (2), tri (3)

  • Complex CHO = Starch or Amylose

    • (many saccharides) - poly

  • Complex CHO = Fiber

    • Different bonding than starches



  • Glucose (Glu) - most abundant CHO; part of table sugar; “blood” sugar

  • Fructose (Fru) - found in fruit & honey; part of table sugar

  • Galactose (Gal) - part of milk sugar; generally not found free in nature



  • Sucrose = Glu + Fru

    • Table sugar

  • Maltose = Glu + Glu

    • product of amylase digestion; beer; sprouts

  • Lactose = Glu + Gal

    • Milk sugar



  • multiple glucose (usually) units bound together

  • Starch/Amylose = many Glu

    • Storage form of energy in plants

  • Fiber - # different kinds; some are multiple Glu units but different chemical bonding from Amylose

    • examples - cellulose; pectin

The digestive system

  • Fiber (cont.) - often the structural CHO in plants


  • Glycogen = storage form of CHO in animals (many Glu units)

    • very highly branched to aid release

Major hormones of digestion

Major Hormones of Digestion

  • Insulin - made in pancreas; lowersblood glu; increasesallenergy stores

  • Glucagon- made in pancreas; raises blood glu; decreases adipose fat & liver glycogen stores

  • Epinephrine (adrenaline) - made in adrenal glands; raisesblood glu; decreases all energy stores

The digestive system

  • CHO Health Issues

    • Fiber

    • Abnormal CHO Metabolism

      • Lactose Intolerance

      • Hypoglycemia

      • Diabetes Mellitus

        • Type 1 diabetesResults from the body's failure to produce insulin, the hormone that "unlocks" the cells of the body, allowing glucose to enter and fuel them. It is estimated that 5-10% of Americans who are diagnosed with diabetes have type 1 diabetes.

        • Type 2 diabetesResults from insulin resistance (a condition in which the body fails to properly use insulin), combined with relative insulin deficiency. Most Americans who are diagnosed with diabetes have type 2 diabetes.

        • Gestational diabetesGestational diabetes affects about 4% of all pregnant women - about 135,000 cases in the United States each year.

        • Pre-diabetesPre-diabetes is a condition that occurs when a person's blood glucose levels are higher than normal but not high enough for a diagnosis of type 2 diabetes. There are 41 million Americans who have pre-diabetes, in addition to the 20.8 million with diabetes.

      • Syndrome X –

        • insulin resistance (the inability to properly deal with dietary carbohydrates and sugars), abnormal blood fats (such as elevated cholesterol and triglycerides), overweight, and high blood pressure.

Sources of sugar

Sources of Sugar

The digestive system

  • Take 12 oz H2O

  • add 10 tsp sugar

  • drink

  • ~ 160 empty calories, i.e.,

  • A soda



  • Structure

  • Digestion

  • Absorption

  • Roles in Body

    • Tissue maintenance & Growth

    • Regulation & Control

    • Energy

Distribution of body proteins

Distribution of Body Proteins

Protein structure

Protein Structure

  • Made up of carbon, oxygen, hydrogen & nitrogen (C, O, H, N)

  • Amino acids (aa) are building blocks

  • 9 essential

  • 11 nonessential (can be made from other aa or carbon skelton (“glucose”) if N available

  • AA differ by side chain (R group)

Regulation control functions

Regulation & Control Functions

  • Enzymes

  • Hormones (some)

  • Antibodies; immune system

  • Transport

  • Acid-base balance (buffers in blood)

  • Fluid & electrolyte balance

Protein sources us

Protein Sources (US)

Protein in foods

Protein in Foods



  • Classes

    • Triglycerides (TG)

    • Phospholipids (PL)

    • Sterols

  • Class Functions

  • Terminology

  • Digestion

  • Transport - Lipoproteins

Lipid classes

Lipid Classes

  • Triglycerides

    • made of 3 fatty acids (fa) & 1 glycerol

    • fa 4-22 Carbons long; mostly 16-20

    • 95% of dietary lipids (fats & oils)

  • Phospholipids

    • 1 fa replaced by a phosphate group

  • Sterols

    • complex ringed structures; noncaloric

    • ex. cholesterol & Vit D

Tg functions

TG Functions

  • Concentrated energy (diet and main storage form)

  • Provides essential fatty acids (linoleic; linolenic)

  • Carrier of Fat Soluble Vits (A,D,E,K)

  • Body Insulation & padding around organs

  • Cell membranes

  • Adds flavor & texture to foods

  • Contributes to satiety

Phospholipid functions

Phospholipid Functions

  • Cell membranes

  • Help transport other fats in blood

  • Precursor for some neural transmitters

    • Lecithin ----> Acetyl Choline

  • emulsifier in foods

Cholesterol functions

Cholesterol Functions

  • Cell membranes

  • Precursor for Vit D & some hormones (estrogen, testosterone)

  • Major component of bile


  • not an essential nutrient since man makes

Saturated fats

Saturated Fats

  • maximum # of Hydrogen atoms

  • usually solid at room temp.

  • mostly from animal sources

  • Exceptions - tropical oils (palm, coconut) are very saturated

  • raise blood cholesterol

Unsaturated fats

Unsaturated Fats

  • fewer H atoms; double bonds b/t Carbons

  • usually liquid at room temp.

  • mostly plant and fish sources

  • more chemically active (turn rancid faster)

  • lower blood cholesterol

  • Monounsaturated fat acid (MUFA) - 1 double bond (minus 2 H)

  • Polyunsaturated fat acid (PUFA) - 2 or more double bonds

The digestive system

  • Dietary fats (TG) really mix of saturated and unsaturated fats

  • Classified by predominate type

  • Fatty acids can differ by 1) degree of saturation or 2) length (# carbons) BUT NOT by calories (all 9 kcals/g)

Essential fatty acids

Essential Fatty Acids

  • Linoleic (Omega 6/n-6)- found mostly in plant oils

  • Linolenic – (n-3) found mostly in cold-water fish and some plant oils (canola oil, nuts, seeds)

  • Deficiency leads to poor growth, liver problems, dermatitis

  • O-6 to O-3 ratio MUCH higher than in Hunter Gatherers - inc risk # diseases or adverse outcomes (CVD, pregnancy, learning, bone health)



  • Transport lipids

  • mixture of protein and lipids

    • Pro & phospholipids are water soluble

  • packaged so water soluble cpds on outside and insoluble cpds on inside

    • like homogenized milk

  • LP have different forms, functions, & effects on CVD risk

Low density lp ldl

Low Density LP (LDL)

  • remnant of VLDL after most TG removed

  • very HIGH in Cholesterol

    • major component of total blood cholesterol

  • not always effectively cleared by liver so other tissues remove including artery walls

    • esp when cholesterol has been modified

  • risk of “high blood cholesterol” is from LDL, i.e., increases risk of CVD

High density lp hdl

High Density LP (HDL)

  • made by liver & intestine & then altered in blood

  • carries cholesterol from tissues (including arteries) & other LP to Liver

  • Reduces risk of CVD

  • Ratio of LDL/HDL may be better predictor of CVD risk than any single LP or total blood cholesterol level

Levels of lp cvd risk

Levels of LP & CVD Risk

  • HDL > 60mg/dl = Low risk

  • HDL < 35 mg/dl = High risk

  • LDL/HDL ratio < 4 = Low risk

  • men’s HDL run from high 30’s to high 40’s

  • women’s from low 50’s to low 60’s (estrogen effect)

Sources of fat

Sources of Fat

The digestive system

  • ~50% fat from animal sources

  • ~ 75% Saturated fat from animal sources

    • 6 foods foods provide 1/2 sat. fat

  • cheese; beef (esp ground), milk, baked goods, margarine, butter

  • Trend towards less animal & more plant fat

  • lower % of fat 42% (60’s) -> 36% (80’s) -> 34% now BUT

  • > amount of fat

Excretory system

Excretory System

  • Among vertebrates the #1 Apparatus in the Excretory System is the KIDNEY

  • Filters 2000L of blood/day

  • 3 Functions

    • Filtration – Blood Filter

    • Reabsorption – Selective – take back the good stuff – leave the waste

    • Secretion and Excretion– secretion of foreign molecules and waste across membranes of capillaries and kidney tubules – opposite of reabsorption

      Excretion of waste - Urine

Basic structure of kidney units

Basic Structure of Kidney Units

The mammalian kidney

The Mammalian Kidney

Route of waste

Route of waste

  • In the nephron tubule,

    • filtration occurs from glomeruli into Bowman's capsule The filtrate passes from Bowman's capsule through the PCT (proximal convoluted tubule), the loop of the nephron (loop of Henle), the DCT (distal convoluted tubule), before reaching a collecting duct.

    • Now, just dumping out the filtrate would be a waste (literally) and would not address issues of osmoregulation.

Functional unit of kidney nephron

Functional Unit of Kidney - Nephron

  • Glomerulus

  • Bowman’s capsule

  • Proximal convoluted tubule

  • Loop of Henle

  • Distal convoluted tubule

  • Collecting duct

  • 2 types – Juxtamedullary and cortical

Nephron filtration

Nephron - Filtration

  • Filter is non-selective except for size ( <70,000 MW; 7 nm in diameter).

  • Blood cells and proteins do not pass through the filter.

  • Fluid in Bowman's capsule much like plasma without the proteins.

The digestive system

  • Large amounts of water are necessary for filtration.

  • Most of this water is reabsorbed back into the circulation through the tubules - proximal & distal conv. tubules and Henle’s loop.



  • Need to reabsorb stuff (H20, ions, nutrients) or animal literally urinate itself to death

  • 180L of water leave the blood in filtrate

  • Water, selected ions, glucose, and other items must be reabsorbed

  • This reabsorption most typically involves the use of energy to reclaim sodium (and other items tagging along with it)

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