The Digestive and Endocrine Systems

Following the Digestion of a Meal

Functions of the Digestive System

•Main function is to disassemble the food you eat into its component molecules s that it can be used as energy (ATP) by your body.

All of these organs work together to break down food into simpler

compounds that can be absorbed by the body.

•Steps of Digestion 1. System takes ingested food &

begins moving it through the digestive tract. As food moves it breaks down mechanically and chemically2. The system absorbs the digested food & distributes it to your cells3. It eliminates undigested materials from the body

The Mouth - The disassembly line STARTS at the

mouth• What happens when you chew?

– Your tongue moves food around & helps position it b/t your teeth

– Chewing is a form mechanical digestion = the physical process of breaking down food into smaller pieces. This prepares food for chemical digestion

– Chemical digestion = the process of changing food on a molecular level through the action of enzymes

• Chemical Digestion begins in Mouth

•Saliva in mouth contains digestive enzymes, called amylase, which breaks down starch into smaller molecules

•In the stomach, amylase continues to digest food for about 30 min.

Starch

• Swallowing Your Food

• Chewed food becomes a ball and is swallowed

• Swallowing forces food into throat and then to the esophagus = a muscular tube that connects the mouth to the stomach– Food moves through the esophagus by

peristalsis = a series of involuntary smooth muscle contraction along the walls of the digestive tract

Peristalsis

• The epiglottis = a flap of cartilage that closes over the opening to the respiratory tract as you swallow, keeping food out– After food passes, epiglottis opens again– If you talk or laugh as you swallow, food

may enter the upper portion of the respiratory tract

– Your response is to choke & cough, forcing food out of the respiratory tract

The StomachStomach = a muscular pouchlike enlargement of the digestive tract

• Muscle Churning– The walls of the stomach are composed

of 3 layers of involuntary muscles– When the muscles contract, they work

to physically breakdown food, creating smaller pieces

– The pieces mix with digestive juices produced by the stomach

• Chemical Digestion in the stomach

• The lining of the stomach contains millions of glands that secrete a mixture of chemicals called gastric juice

• Gastric juice contains pepsin & hydrochloric aced– Pepsin = an enzyme that begins

the chemical digestion of proteins in food

• The lining of the stomach secretes mucus that forms a protective layer b/t it and the acidic environment of the stomach

• Food remains in stomach for about 2-4 hrs

• When food leaves it is the consistency of tomato soup (YUMMY!)

The Small Intestine

- Small intestine = a muscular tube about 6 m long Called “small” because of how narrow it is (only 2.5 cm in diameter)- Digestion is COMPLETED here- First 25 cm of the small intestine called the duodenum

• Secretions of the Pancreas

•Pancreas = soft, flattened gland that secretes both digestive enzymes & hormones– The mixture of enzymes it

releases break down carbs, proteins, & fats

• Secretions of the Liver

• Liver = large, complex organ that produces bile• Bile = chemical substance that helps break

down fats– Made by the liver, but stored in the

gallbladder– From the gallbladder, bile passes into

duodenum– Bile causes further digestion by breaking large

drops of fat into smaller droplets– Gallstones form when bile in the gallbladder

becomes too concentrated due to high levels of cholesterol in you diet

LIVER

• Absorption of Food• Liquid food stays in the intestine for 3-5 hrs.

as it is moved through• As food moves it passes over thousands of

tiny fingerlike structures called villus = a single projection on the lining of small intestine that function in the absorption of food

• Now that food is in the form of small molecules, it can be absorbed directly into the cells of the villi (plural for villus)

• Food then diffuses into blood vessels of the villus & enter the bloodstream

* Villi are the link between the digestive system & the circulatory system

The Large Intestine

- All indigestible material from a meal then moves into the large intestine = a muscular tube that is also called the colon- Large intestine is only about 1.5 m long, but it is much wider that the small intestine ( about 6.5cm in diameter)

• Water Absorption•As indigestible mixture

passes through the large intestine, water and salts are absorbed by the intestinal walls, leaving behind a more solid material

•This way water in NOT wasted

•Bacteria in the large intestine make some B vitamins and Vitamin K, which are absorbed as needed by the body–These bacteria also stop

harmful bacteria from colonizing, reducing the risk of intestinal infections

• Elimination of Wastes

• After 18-24 hrs in the large intestine, the remaining indigestible material, now called feces, reaches the rectum

•Rectum = the last part of the digestive system

YOUR ENTIRE MEAL’S JOURNEY THOUGH THE DIGESTIVE TRACT HAS TAKEN BETWEEN 24-33

HOURS!

mouth

esophagus

stomachliver

gall bladder pancreas

small intestinelarge intestine

appendix rectum

anus

colon

•Ch. 35.2: Nutrition The Vital Nutrients

•- Six basic kinds of nutrients can be found:

–1. Carbohydrates»Main source of energy

–2. Fats»Used to store energy

–3. Proteins»Form part of muscles and many

cell structures, including the cell membrane

–4. Minerals»Serve as structural materials

–5. Vitamins»Needed for growth and metabolism

–6. Water»Facilitates chemical reactions, helps dissolve materials and helps maintain the body’s temperature

Ca

B12

CrMg

Vitamin CVitamin D

USDA USDA Food Guide PyramidFood Guide Pyramid

The Endocrine System

•Control of the Body –Internal control of the body is directed by 2 systems: •The Nervous System•The Endocrine System

–The Endocrine System is made up of a series of glands called endocrine glands •These glands release chemicals directly into the bloodstream

•The chemicals act as messengers, relaying information to other parts of the body

• Interaction of the Nervous & Endocrine Systems – The endocrine system and the nervous

system work together to maintain homeostasis within the body

– Hypothalamus = the portion of the brain that receives messages from other areas of the brain & internal organs•When a change in homeostasis is detected,

the hypothalamus stimulates the pituitary gland

•pituitary gland = the main gland of the endocrine system and is located in the skull just beneath the hypothalamus–The pituitary gland releases its own chemicals or stimulates other glands to release theirs

•Endocrine Control of the Body –Hormones = the chemicals secreted by endocrine glands•Hormones are chemicals released in one part of an organism that affects another part of the organism

•They convey information to other cells in your body, giving them instructions regarding your metabolism, growth, development, and behavior

•Hormones travel in the bloodstream and attach to specific binding sites of target cells

•These binding sites are called receptors

Lock and Key Analogy

Hormone = keyReceptor = lock

Like a key with a lock, hormones only fit certain receptors. Even a close fit won’t turn the lock.

•Example of Endocrine Control (hGH)– Human growth hormone (hGH) is a good

example of an endocrine system hormone– When your body is growing, blood

glucose levels are slightly lowered as the growing cells use up the sugar in your cells

– The low blood glucose level is detected by the hypothalamus, which stimulates the production & release of hGH from the pituitary gland into the bloodstream

– hGH binds to receptors on liver cells, stimulating liver cells to release glucose into the blood

– Your cells need this glucose in order to continue growing

LOW GLUCOSE detected by

hypothalamus(endocrine

system)

Pituitary gland

releases hGH

hGH stimulates

liver to release extra glucose

Homeostasis restored

glucose level is NORMAL

1. Hypothalamus tells pituitary to release hGH

2. hGH signals liver to release stored glucose

3. Higher glucose level signals hypothalamus that homeostasis is restored

•Negative Feedback Control–When homeostasis is disrupted the regulation of the endocrine system is controlled most often through one type of internal feedback mechanism called a negative feedback system

– In this system the hormones, or their effects, are fed back to inhibit the original signal (normal signal)

–Once homeostasis is reached, the signal is stopped & the hormone is no longer released

•Feedback Control of Hormones –The majority of endocrine glands operate under negative feedback systems

–Information regarding the hormone level or its effect on target cells is “fed back” to the hypothalamus or pituitary gland to regulate the production of the hormone

•Control of Blood Glucose Levels (sugar) – When you have just eaten & your blood

glucose levels are high, your pancreas releases the hormone insulin

– Insulin signals liver & muscle cells to take in glucose, thus lowering blood glucose level

– When blood glucose levels become too low, the pancreas releases the hormone glucagon

– Glucagon binds to liver cells, signaling the release of stored glucose

Glucose Feedback Loop

Blood Glucose Blood Glucose

HIGH LOW

Glucagon

release

secretesecrete

Insulin

pancreas

liver

Glucose

Target tissue

Glucose

stimulatesstimulatesstimulates

absorption

absorption

• Hormone Action2 Basic types of Hormones:

1. Steroid hormones = made from lipids (fats)• Diffuse freely into cells thru the

plasma membrane• Then travel to the cell nucleus

where thy activate the production of mRNA

• mRNA then produces the required proteins

Steroid Hormones

2. Amino Acid hormones = made from amino acids–Don’t diffuse easily through the plasma membrane

–Must bind to receptors in the plasma membrane of target cells to enter the cell

–Once inside they activate enzymes which will alter the behavior of other molecules in the cell

Amino Acid Hormones

•Adrenal Hormones and Stress –Adrenal glands play an important role in preparing your body for stressful situations.•Adrenal glands are located on top of the kidneys and consist of two parts–1. Outer Portion: secretes steroid hormones that help the body combat stresses by raising blood pressure»Ex: fright, temperature extremes, bleeding, infection, even test anxiety

– 2. Inner Portion: secretes two amino acid hormones•Epinephrine (sometimes called

“adrenaline”) & Nonepinephrine»These hormones increase heart rate,

blood pressure, & rate of respiration»They increase efficiency of muscle

contraction & increase blood sugar levels

* You may have experienced these symptoms if you have ever had to perform in front of a large audience and had an “adrenaline rush”

•Thyroid and Parathyroid Hormones – The Thyroid Gland:

– Located in the neck– Regulates metabolism, growth, and

development – Main metabolic & growth hormone of the

thyroid is thyroxine»Thyroxine affects the rate at which the

body uses energy and determines your food intake requirements

– Thryroid also secretes calcitonin»Calcitonin regulates calcium levels in the

blood by causing an increase in the release of calcium when necessary

–The Parathyroid Hormones •Parathyroid glands: are attached to the thyroid gland and are involved in mineral regulation–Ex: they regulate the absorption of calcium, phosphate, magnesium, etc.

* Hormones that are associated with the endocrine system are responsible for controlling many different functions in your body.

* Different hormones may play more important roles during some periods in your life than others.