The Human Body a Nutrition Perspective

Chapter 3: The Human Body A Nutrition Perspective

Objectives

Upon completion of this chapter the student will be able to: • identify the function of the cellular components:• define tissue, organ, and organ system.• list some characteristics of the 12 organ systems and outline a role

for each related to nutrition.• understand the role of genetic background in the development of

nutrition-related diseases.• outline the overall processes of digestion and absorption, including

the roles played by the organs of the gastrointestinal tract and the related accessory organs.

• become familiar with some specific enzymes and hormones that act in digestion of the various nutrient groups.

• identify the major nutrition-related gastrointestinal health problems and typical approaches to treatment.

Human Physiology

• Trillions of cells.• Join together to form tissues. • Tissues combine to form organs.• Organs form systems (e.g., digestive).

– Common purpose.

• Body tissues are continually turned over.– Continual degradation/synthesis– Requires energy, adenosine triphosphate– Requires nutrients in healthful diet

The cell structure and function

• The basic structural and functional component of life.

• Many different types of cells with different roles.

• Subcellular specialization.– Organelles

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Cell (plasma) membrane

• Separates cell interior from exterior.• Double layered of lipid, CHO, and protein.

– Hydrophilic and hydrophobic ends.

• Controls passage of substances• Contains receptors for hormones and protein

markers – communication.• Glycoproteins and glycolipids .• Contains cholesterol.

Cell structure

Cytoplasm• Fluid material within the cell (excluding the nucleus).• Site of anaerobic metabolism.Mitochondria• Major site for aerobic energy production.• Present in all cells (except RBC).• Synthesis of other components, nonessential amino acids.Nucleus• Double membrane.• Contains genetic material DNA.• Directs protein synthesis and cell division.

Cell structure

Endoplasmic reticulum - communication network• Rough endoplasmic reticulum – contains ribosomes, protein synthesis• Smooth endoplasmic reticulum - fat synthesis, detoxification, calcium

storage.• The Golgi complex

– Protein export system.– Help forms other cell organelles.

• Lysosomes– Cell degradation system.– Sacs full of enzymes: suicide bags

• Peroxisomes– Detoxification.– Contain catalase.– Alcohol metabolism.

Organization of the body

• Groups of similar cells work together on a specialized task – tissue.

• Four primary tissue types

– Epithelial• lines the body surfaces, secrete, absorb and excrete.

– Connective• holds structure together, stores fat and produces RBC.

– Muscle• for movement

– Nervous• Brain, CNS - communication

These tissues organs organ systems.

Circulatory system

• Cardiovascular system– Heart and blood vessels– The heart is a muscular pump.– Blood leaves heart via arteries.– Exchange of nutrients occurs in

capillaries– Blood returns to the heart via the veins.

• Lymphatic system– Lymphatic vessels– Lymph tissues.

Cardiovascular system

• Blood– Plasma– Cells

• Pulmonary circuit

• Systemic circuit

Portal circulation in the gastrointestinal tract

• Absorbed water and nutrients portal circulation.

• Hepatic portal vein leads directly to the liver.

Lymphatic system

• One way network that moves lymph (clear fluid) which by muscular action.

• Similar to blood but contains no platelets or RBCs.

• Lymph empties into major veins.• Important role in the defense of the body against

pathogens.• Carries products of fat digestion and absorption.

Nervous System

• Regulatory system.– Detects sensations, controls

movement and controls intellectual and physiological functions.

– Carries out appropriate response.

• Sensory receptors.• Nerves.• Central Nervous System

– Brain and the spinal cord• Peripheral Nervous System

– Branches out to organs

A Neuron

• The structural and functional unit of the nervous system – NEURON.

• Elongated and highly branched.

• 100 billion neurons.• Respond to electrical and

chemical signals and conduct electrical impulses (changes Na and K permeability).

• Neurotransmitters carry signals across synapses or neuromuscular junction.

• Many nutrients are required for effective functioning of the nervous system.


Endocrine System • Secretes regulatory

substances (hormones)• Desire for homeostasis• Target cells with

receptor proteins• Message to the DNA

directly• Use of a second

messenger

Immune System

• Defense against infection.• Sensitive indicator of the body’s nutritional status

– Skin• Continuous barrier• A variety of nutrients contribute to skin health

– Intestinal cells• Produce immunoglobulins• A variety of nutrients contribute to good intestinal health.

– White blood cells.• Phagocytes• Cell mediated immunity.• Complement.• Interferons

Nonspecific Immunity

• Barriers• Mucous membrane• Mucus traps invaders• Acid in the stomach• Interferons

– stimulate the synthesis of antiviral proteins

• Swelling and fever

Specific Immunity

• Directed at specific molecules– Antibody-medicated immunity– Antigens and antibodies interaction – Immunoglobulins (B lymphocytes and antibodies).– Complement proteins.

• Constant resynthesis of WBCs requires nutrients:– Iron– Copper– Protein and vitamins

Digestive System

• Six separate organs.• Digestion and absorption into bloodstream.• Long tube from mouth to anus

– Epithelium lines the lumen– Submucosal layer– Muscularis

• Motility.• Secretion.• Excretes waste.• Nutrient production.

Autonomic control

The mouth

• Mastication reduces particle size.

• Tongue– Taste receptors – sweet, sour, salty, bitter.– Enzymes to help breakdown fatty acids

• Saliva– Enzymes to help breakdown simple sugars– Mucus to lubricate the food for easier swallowing– Lysozyme to kill bacteria

The swallowing process

• From the mouth food passes to the esophagus.

• Connects the pharynx to the stomach.


Esophagus

• Increase in muscle action – peristalsis.

• Forces food toward stomach.

The stomach

• Large storage tank.– Capacity of ~4 cups.– Holds food for 2-4 hours

• Lower esophageal sphincter and pyloric sphincter regulate input and outflow.

• Secretion of acid and enzymes aids digestion.• Also secretes intrinsic factor.• Result in the formation of chyme• Mucus layer prevents autodigestion

Production of stomach acid

Stimulated by • Gastrin• Stomach distention• Histamine• Thoughts of food (nerve input)• Food itselfPrevents autodigestion• Stop secretion when pH is ~2• Thick mucus layer

Stomach acid

• Destroys activity of protein

• Converts pepsinogen to pepsin

• Partially digests dietary protein

The small intestine

• Chyme from stomach enters the small intestine.• Total length = 10 feet

– Duodenum• ~10 inches in length• Primary site of digestion

– Jejunum• ~4 feet in length• Some digestion

– Ileum• ~5 feet in length• Little digestion

• The wall is folded• Villi projections are located on the folds• Absorptive cells (enterocytes) are located on the villi• Microvilli are located on the villi• Increases intestinal surface area 600 x • Peristalsis continues.

Intestinal mucosa

Absorptive cells constantly replaced -• Produced in crypts• Migration and maturation from the crypts to the tips of

the villi• Degradation of cells at the tips of the villi by digestive

enzymes• Newly formed cells constantly migrate to replace

dying ones (< 6 days)• High turnover causes the cells to deteriorate during

nutrient deficiency.• Materials from old cells can be reused.

The small intestine

• Absorption by– Passive diffusion– Active transport.– Pinocytosis– Phagocytosis

Movement Along the Intestine

• Peristalsis– A ring of contraction propelling material along

the GI tract

• Segmentation– A back-and-forth action that breaks apart food

• Mass movement– Peristaltic wave that contracts over a large

area of the large intestine to help eliminate waste

Site of absorption


The Large Intestine

• The contents of the small intestine enter the large intestine.• Only a small proportion of nutrients remain.• Physiological differences between the large and small intestine.• ~3 1/2 feet in length.• Cecum, ascending, transverse, descending and sigmoid.• Little digestion occurs – mucus production.• Absorption of water, some minerals, vitamins.• Bacterial population.• Formation of feces for elimination – some fluid remains.• Indigestible food stuff – dietary fiber, tough connective tissue.

Accessory organsPancreas, liver and gallbladder

• Do not participate directly in digestion.

• Ducts from pancreas and gallbladder enter small intestine

• Pancreas– Produces glucagon and insulin– Secretes bicarbonate and digestive

enzymes

• Liver– Nutrients are absorbed into the

portal vein and pass to the liver– Hepatic veins release nutrients to

the general circulation – Production and storage of bile– Enterohepatic circulation.– Detoxification

Urinary system

• Kidney• Ureter• Bladder• Urethra

The kidney

• Regulate the composition of blood and interstitial fluid

• Filtration of blood • Remove waste from the body and the formation

of urine• Controls blood volume and pressure• Maintains the pH of the blood: acid base

balance.• Produce active form of vitamin D.• Some gluconeogenic activity.

Storage capabilities

• The human body must maintain reserves of nutrients.

• These reserves can be utilized when nutrient needs are not met.

• Storage capacity varies between nutrients.• Fat stored in adipose tissue.• CHO stored in muscle and liver – short term.• Vitamins and minerals can be stored in the liver

What happens when the digestive processes go awry?

Ulcers

• Helicobacter pylori• Heavy use of aspirin• Excessive acid

production in the stomach• Symptoms

– Pain 2 hours after eating

• Treatment– Antibiotics– Antacid– Antisecretory drugs– Not milk!

• Perforation is a major concern

Heartburn

• Affects 50% adults in U.S.• Gastroesophageal reflux

disease• Gnawing pain in the upper

chest• Acid from the stomach to

the esophagus• Treatment

– Smaller meals– Less fatty meals– Stop smoking– Do not lie down after eating– Avoid offending foods

Constipation

• Slow movement of fecal matter• Increase fluid reabsorption; hardening of the

feces• Causes:

– Result from ignoring normal urge– Antacids, calcium and iron supplements

• Treatment– Plenty of dietary fiber and fluids – stimulate peristalsis– Laxatives

• Irritate SI muscle or draw water into the intestine

Hemorrhoids

• Piles

• Swollen veins of the rectum and anus

• Causes:– Added stress and pressure to the vessels

• Treatment– Check with physician– Warm compresses to reduce pain– Adequate fiber and fluid

Irritable Bowl Syndrome

• Harmless.• Cramps, gassiness and bloating.• Visible abdominal distension.• Increased stool frequency with onset of pain.• More common in women.• No cure• Eliminate specific foods• Low fat, more frequent meals.• High fiber foods.

The Human Body a Nutrition Perspective

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