Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 1 | 10

: Digestive System and Nutrition

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 2 | 10

Digestion The process of involves mechanical digestion of food to smaller pieces and

chemical digestion by specific enzymes.

It begins in the mouth and ends at then anus

Digestion functions to

The Mouth

enclose the mouth.

Its roof is formed by the hard (at front of mouth; has bones) and soft (at back

of mouth; no bones, just muscles) that separate it from the

nasal cavities. Soft palate ends in .

Three pairs of send

into the mouth. at the back sides protect against

infections.

The teeth 20 deciduous (baby) teeth are replaced by

32 adult teeth. Each tooth has

.

The crown has a layer of enamel, dentin,

and an inner pulp with nerves and blood vessels that extend into the root.

Fluoride treatments make tooth enamel stronger and reduce dental caries or

cavities. With aging, inflammation of the gums and

periodontal membrane are more serious.

The pharynx

The air passage and food passage cross in the . Swallowing is a reflex action.

The air passage is usually blocked off by the and , and the

moves under the to cover the opening to the windpipe.

Breathing and swallowing cannot occur at the same time.

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 3 | 10

The Esophagus This muscular tube conducts food through the and

begins in the ; this collapsed tube moves the bolus of food

downward after swallowing occurs. is a burning pain when acidic

stomach contents enter the esophagus.

The Wall of the Digestive Tract

The has four layers:

o (mucous membrane),

o (loose connective tissue),

o (smooth muscle),

o And (serous membrane).

The Stomach

The expands to store food (up

to 4L). Food in the stomach is churned, mixing

the food with gastric juices containing

hydrochloric acid and pepsin (for the digestion of protein to peptides).

In 2-6 hours, the soupy leaves

the stomach by way of

.

, open sores in the wall of the stomach are usually caused by a bacterial infection that prevents protective mucus from being produced.

The Intestine

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 4 | 10

The Small Intestine The averages about 6 meters

in length; it has a slightly basic pH. The first 25cm is the that receives

bile (emulsifies fat) from the as

well as pancreatic juice that contains pancreatic

lipase, trypsin for digestion of protein to

peptides, and lipase for digestion of fat to glycerol and fatty acids.

Pancreatic juice contains NaHCO3 that is basic

and neutralizes the acidic chyme. Enzymes that finish the process of digestion are

produced by the intestinal wall.

Wall of the small intestine have finger-like projections called where nutrient

molecules are absorbed into the cardiovascular and lymphatic system.

The small lymphatic capillary in a villus is called a .

Regulations of Digestive Secretions

Both the nervous system and hormones regulate .

In response to eating protein-rich foods, the is produced by the lower

part of the stomach and flows through the bloodstream to stimulate the stomach to

produce digestive juice.

The produces to inhibit gastric gland

secretion.

The and ) are produced by the duodenal wall

and stimulate the pancreas to secrete digestive juice and the gallbladder to release

The Large Intestine

The consists of the

The large intestine does not produce

digestive enzymes but does absorb water

salts, and some vitamins

The is an extension of the

cecum

Indigestible material is stored in the

until the anus allows defecation

in the feces break

down indigestible material and produce

some vitamins that we use

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 5 | 10

Water tests that show the presence of Escherichia coil indicate water is contaminated and

unsafe for swimming/drinking.

The digestive system - an animation

https://www.youtube.com/watch?v=P5lyQUtq1KQ&feature=kp

Polyps

are small growths arising from the epithelial lining that may be benign or

cancerous

Consuming fat may increase the risk of colon cancer, while consuming fiber may

decrease the risk of colon cancer

Diarrhea and Constipation

Causes of include infection of the lower tract and nervous stimulation, both

moving feces more rapidly than normal, but also causing dehydration if prolonged

Water and fiber in the diet can prevent where the feces become too dry

are enlarged and inflamed blood vessels at the anus.

Question

1. How do we ‘taste’? Answer: Sensory receptors called occur primarily on the tongue, and when these

are activated by the presence of food, nerve impulses travel by way of cranial nerves to the

brain.

2. What is ‘dental caries’, and how/why does it occur? Answer: Tooth decay, called , or cavities, occurs when bacteria within the mouth metabolize sugar and give off acids, which erode teeth. It is commonly caused by eating a substantial amount of sweets, not brushing and flossing of teeth regularly and so on.

3. Trace the path of the food from the mouth to the large intestine. Answer:

4. Why can’t we breathe and swallow at the same time? What happens when food ‘goes down the wrong way’? Answer: The air passage and food passage cross in the pharynx which takes food to the

. When we swallow, the soft palate closes off the , and the moves up under the to cover the glottis. The is the opening to the larynx

(voice box), and therefore the air passage. During swallowing, food normally enters the

esophagus because the air passages are blocked.

When food ‘goes down the wrong way’, which may be either into the nasal cavities or into the

trachea. If it is the latter, will most likely force the food up out of the trachea and into the pharynx again.

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 6 | 10

5. i) What is a sphincter and ii) why is there a sphincter at the opening of your stomach and esophagus? Answer: i) are muscles that encircle tubes and act as valves; the tubes close when

sphincters contract, and they open when sphincters relax. The entrance of the esophagus to the stomach is marked by a constriction that is often called a sphincter, although the muscle is not

as developed as it would be in a true sphincter. ii) Relaxation of the sphincter allows the bolus to pass into the stomach, while contraction

prevents the acidic contents of the stomach from backing up into the esophagus.

6. What do the 4 layers of the walls of the esophagus do? (Not what are they made; do not answer for muscularis)

A layer of epithelium supported by connective

tissue and smooth muscle lines the lumen (central cavity) and contains glandular epithelial cells that secrete digestive enzymes and goblet cells that secrete mucus.

A broad band of loose connective tissue that

contains blood vessels lies beneath the mucosa. Lymph nodules, including some called

Peyer’s patches, are in the submucosa. Like the tonsils, they help protect us from disease. Two layers of smooth muscle make up this

section. The inner, circular layer encircles the gut; the outer, longitudinal layer lies in the

same direction as the gut. (The stomach also has oblique muscles.) Most of the digestive tract has a serosa, a very

thin, outermost layer of squamous epithelium supported by connective tissue. The serosa

secretes a serous fluid that keeps the outer surface of the intestines moist so that the organs of the abdominal cavity slide against one another.

7. What is a hormone? Answer: A is a substance produced by one set of cells that affects a different set of

cells, the so-called target cells. Hormones are usually transported by the bloodstream.

8. What is the purpose of diarrhea? Answer: It is to purge substances which the body perceived as harmful by decreasing the time

they remain in the body. So, it's not an entirely useless condition. However, other conditions can also cause diarrhea, such as food sensitivity and gastrointestinal inflammation.

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 7 | 10

Common Duct

The of digestion send secretions

They are:

o

o

o

The Pancreas

The produces pancreatic juice, which contains digestive enzymes for carbohydrates

(i.e., salivary amylase), protein (i.e., trypsin), and fat (i.e., lipase) digestion.

The pancreas is also en that secretes insulin and glucagon to help regulate

blood glucose levels.

The Liver

The produces , which is stored in the gallbladder.

The liver receives blood from the small intestine by way of the .

The liver regenerates very rapidly, although it is possible to irreversibly harm it

The liver:

o

o

o

o

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 8 | 10

o

o

o

Liver Disorders

is a yellowish tint to eyes and skin that

indicates abnormal levels of bilirubin in the blood

is inflammation of the liver; different strains

of virus cause , etc.

o (Hep A: drinking sewage contaminated water;

Hep B: Unprotected sex, contaminated blood

transfusions)

is scar tissue that can form when the liver is

diseased or killed by alcohol concentrations

The Gallbladder

The , which is a sac attached to the

liver, stores bile until it is sent to the

duodenum. Water is reabsorbed in the

gallbladder making the bile thick;

Assists in fat digestions; bile emulsifies fat

are crystals of cholesterol;

gallstones may block the bile duct of the

gallbladder, in which case it must be removed.

None.

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 9 | 10

The Fundamentals Digestion and Enzymes in The Human Body https://www.youtube.com/watch?v=_5TaS0-VaDo

Enzymes in digestion https://www.youtube.com/watch?v=u_pDxx2s0Ck

Hydrolytic Enzymes

are present in digestive juices and introduce water at specific bonds

to break down food into sugars, amino acids, fatty acids, and glycerol

are absorbed into the blood capillaries of the villi

rejoin in the villi to produce lipoprotein droplets which enter

the lacteals speed specific reactions and functions best at a warm body

temperature an optimum pH For digestion to occur,

1) List 8 digestive enzymes, what each one breaks down and into what it converts the breakdown products. Answer: Refer to Table 14.3 on the top of this page.

Digestion takes place within a tube called the digestive tract, which begins with the mouth and ends with the anus. Digestion involves mechanical and chemical digestion. The Mouth

Biology 12 Chapter 14 – Digestive System and Nutrients Notes (Ve 2.10) P a g e 10 | 10

The mouth receives food and contains the sensory receptors that make eating food an enjoyable experience. Due to enzymes in saliva, chemical digestion begins in the mouth. The Teeth The teeth begin the process of mechanical digestion. The Pharynx The pharynx is a region that receives air from the nasal cavities and food from the mouth. Swallowing occurs in the pharynx. The epiglottis covers the opening to the larynx. The Esophagus The esophagus is a muscular tube that passes from the pharynx to the stomach.

Peristalsis pushes the food along the digestive tract. The Wall of the Digestive Tract The wall of the esophagus has four layers: mucosa, submucosa, muscularis, and serosa. The Stomach The stomach receives food from the esophagus, stores food, starts the digestion of proteins, and

moves food into the small intestine. The Small Intestine The wall of the small intestine contains fingerlike projections called villi that aid in the absorption of nutrients. Regulation of Digestive Secretions The secretion of digestive juices is promoted by the nervous system and by hormones. The Large Intestine

The large intestine absorbs water, salts, and some vitamins. It stores indigestible material until it is eliminated at the anus.

The pancreas, liver, and gallbladder are accessory digestive organs. The Pancreas

The pancreas is an endocrine gland that secretes insulin and glucagon to keep blood glucose levels within normal limits. For the purposes of digestion, it is an exocrine gland. It produces pancreatic juice, pancreatic amylase, trypsin, and lipase to aid in digestion.

The Liver The liver acts as the gatekeeper to the blood. It maintains the blood glucose level and produces bile. The Gallbladder The gallbladder stores bile.

The various digestive enzymes present in the digestive juices help break down carbohydrates, proteins, nucleic acids, and fats. The enzymes required for digestion work at particular pH optimum.