Nutrition

Process by which organisms obtain and utilize their food.

There are two parts to Nutrition:

1. Ingestion- process of taking food into the digestive system so that it may be hydrolized or digested.

2. Digestion- the breakdown of food (either chemically or mechanically) in order to

utilize nutrients

Types of Nutrients

• Micronutrients- vitamins, minerals, & water

• Macronutrients- proteins, lipids, carbohydrates, etc…

Human digestive system

GI (gastrointestinal) tract = alimentary canal

Ingestion

• Mouth– mechanical digestion

• teeth– breaking up food

– chemical digestion• saliva

– amylase

» enzyme digests starch

– mucin

» slippery protein (mucus)

» protects soft lining of digestive system

» lubricates food for easier swallowing

– buffers

» neutralizes acid to prevent tooth decay

– anti-bacterial chemicals

» kill bacteria that enter mouth with food

mouthbreak up fooddigest starchkill germsmoisten food

Mouth• Chemical and

mechanicaldigestion.

• Food is chewed (masticated) mechanically.

• A bolus (lump) is formed with saliva and the tongue.

TEETH

• The teeth, or dentes are accessory digestive organs located in sockets of the alveolar processes of the mandible and maxillae

• The alveolar processes are covered by the gingivae or gums, which extend slightly into each socket. The sockets are lined by the periodontal ligament or membrane which consists of dense fibrous connective tissue that anchors the teeth to the socket walls.

• A typical tooth has three major external regions: the crown, root, and neck.

• The crown is the visible portion above the level of the gums. Embedded in the socket are one to three roots.

• The neck is the constricted junction of the crown and root near the gum line.

• Internally, dentin forms the majority of the tooth. Dentin consists of a calcified connective tissue that gives the tooth its basic shape and rigidity. It is harder than bone because of its higher content of calcium salts (70% of dry weight).

• The dentin of the crown is covered by enamel, which consists primarily of calcium phosphate and calcium carbonate. Enamel is also harder than bone because of its even higher content of calcium salts (about 95% of dry weight).

• In fact, enamel is the hardest substance in the body. It serves to protect the tooth from the wear and tear of chewing. It also protects against acids.

• The dentin of a tooth encloses a space. The enlarged part of the space, the pulp cavity, lies within the crown and is filled with pulp, a connective tissue containing blood vessels, nerves, and lymphatic vessels.

• Narrow extensions of the pulp cavity, called root canals, run through the root of the tooth. Each root canal has an opening at its base, the apical foramen, through which blood vessels, lymphatic vessels, and nerves extend.

• The blood vessels bring nourishment, the lymphatic vessels offer protection, and the nerves provide sensation.

• Humans have two dentitions, or sets of teeth: deciduousand permanent.

• The first of these—the deciduous teeth also called primary teeth, milk teeth, or baby teeth—begin to erupt at about 6 months of age, and approximately two teeth appear each month thereafter, until all 20 are present

Swallowing (& not choking)

• Epiglottis– flap of cartilage

– closes trachea (windpipe) when swallowing

– food travels down esophagus

• Peristalsis– involuntary muscle contractions to move food along

Pharynx• The back of the

throat.

• Larynx- passage for air, closes when we swallow.

• Is approximately 15cm long.

Digestive Glands

• Groups of specialized secretory cells.

• Found in the lining of the alimentary canal or accessory organs.

esophagus

• The esophagus is the swallowing tube through which food passes on its way from the mouth to the stomach.

• The main function of this organ is to propel food down into the stomach. There is also a mechanism to prevent food from coming back up or "refluxing" from the stomach into the esophagus.

• The esophagus is a long, muscular tube that also has two muscles (or sphincters) at the top and bottom.

• All of these muscular areas must contract in an exact sequence for swallowing to proceed normally.

• series of involuntary wave-like muscle contractions which move food along the digestive tract

Peristalsis

STOMACH

• The human stomach is a muscular, elastic, pear-shaped bag, lying crosswise in the abdominal cavity beneath the diaphragm.

• The stomach is an expanded section of the digestive tube between the esophagus and small intestine.

• The right side of the stomach is called the greater curvature and the left the lesser curvature.

• The most distal and narrow section of the stomach is termed the pylorus - as food is liquefied in the stomach it passes through the pyloric canal into the small intestine.

• The stomach is divided into 3 regions

• Fundus

• Body

• Antrum

• When the stomach is inactive the pyloric sphincter is relaxed and open, and when the stomach contains food the sphincter is closed.

Walls of the stomach

• There are 3 layers of smooth muscle fibers

• An outer layer of longitudinal fibers

• Middle layer of circular fibers

• Inner layer of oblique fibers

• The arrangement allows for the churning motion as well as peristaltic movement.

Type of cells secretion notes

Surface Mucous Cells (or "Mucous Surface Cells")

secrete a mucus

Neck Mucous Cells (or "Mucous Neck Cells")

secrete a mucus whose acidity is more neutral than that secreted by the cells at the surface of the stomach lining.

The mucus secreted by the muscous neck cells has a more neutral pH than that secreted by the cells at the surface of the stomach lining.

Chief Cells secrete pepsinogen Pepsinogen is an inactive gastric enzyme which is converted to pepsin, a protein-digesting enzyme.

Parietal Cells secrete hydrochloric acid, and an intrinsic factor (involved in the absorption of vitamin B12).

Hydrochloric acid assists in the conversion of pepsinogen to pepsin.

Type of cells secretion Notes

Gastric Juice: The secretions of the surface mucous cells, neck mucous cells, chief cells, and parietal cells are known collectively as gastric juice. (Hence gastric juice includes mucous, pepsinogen, hydrochloric acid and intrinsic factor.)

G Cells - produce and secrete the hormone gastrin.

Gastrin :stimulates secretion of gastric juice, increases the contractions of the gastro-intestinal (GI) tract, and relaxes the pyloric sphincter.

Function of stomach

• After food is chewed and moistened in the mouth, it passes through the esophagus into the stomach.

• Food is mixed with stomach acid and enzymes to break the food down into smaller pieces. This combination of food and stomach "juices" is called chyme.

• The stomach also stores food temporarily, releasing chyme in small amounts into the small intestine, where it is further broken down into nutrients to be absorbed into the body

Stomach

• Functions– food storage

• can stretch to fit ~2L food

– disinfect food• HCl = pH 2

– kills bacteria

– chemical digestion• pepsin

– enzyme breaks down proteins

But the stomach is made out of protein!What stops the stomach from digesting itself?

mucus secreted by stomach cells protects stomach lining

stomachkills germs break up fooddigest proteinsstore food

sphincter

sphincter

mouthbreak up fooddigest starchkill germsmoisten food

Gastric Juices

• Secreted by the stomach.

• Acidic (pH 1.5-2.5) (HCl).

• Pepsin- an enzyme that breaks down large proteinsinto amino acids.

• Food is further broken down into a thin liquid called chyme.

Accessory Organs

• Pancreas

• Liver

• Gall Bladder

Pancreas

• An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine)

• ** Pancreatic juice digests all major nutrient types.

• Nearly all digestion occurs in the small intestine & all digestion is completed in the SI.

• Digestive enzymes

– digest proteins

• trypsin, chymotrypsin

– digest starch

• amylase

• Buffers

– neutralizes acid from stomach

• The pancreas a retroperitoneal gland that is about 12–15 cm (5–6 in.) long and 2.5 cm (1 in.) thick, lies posterior to the greater curvature of the stomach.

• The pancreas consists of a head, a body, and a tail and is usually connected to the duodenum by two ducts.

• Pancreatic juices are secreted by exocrine cells into small ducts that ultimately unite to form two larger ducts, the pancreatic Duct and the accessory duct

• The pancreatic duct (duct of Wirsung) is the larger of the two ducts.

• In most people, the pancreatic duct joins the common bile duct from the liver and gallbladder and enters the duodenum as a dilated common duct called the hepatopancreatic ampulla (ampulla of Vater).

Composition and Functions of Pancreatic Juice• Each day the pancreas produces 1200–1500 ml of

pancreatic juice, a clear, colourless liquid consisting mostly of water, some salts, sodium bicarbonate, and several enzymes.

• The sodium bicarbonate gives pancreatic juice a slightly alkaline pH (7.1–8.2) that buffers acidic gastric juice in chyme, stops the action of pepsin from the stomach, and creates the proper pH for the action of digestive enzymes in the small intestine.

• The enzymes in pancreatic juice include a starch digesting enzyme called pancreatic amylase

• several protein digesting enzymes called trypsin, chymotrypsin , carboxypeptidase and elastase the principal triglyceride-digesting enzyme in adults, called pancreatic lipase and nucleic acid – digesting enzymes called ribonuclease and deoxyribonuclease.

Liver

• Function– produces bile

• bile stored in gallbladder until needed

• breaks up fats– act like detergents to breakup fats

• The liver is the heaviest gland of the body, weighing about 1.4 kg (about 3 lb) in an average adult.

• The gallbladder is a pear-shaped sac that is located in a depression of the posterior surface of the liver. It is 7–10 cm (3–4 in.) long and typically hangs from the anterior inferior margin of the liver

• The liver is divided into two principal lobes—a large right lobe and a smaller left lobe by the falciform ligament.

• Histologically, the liver is composed of several components

• Hepatocytes

• Bile canaliculi

• Hepatic sinusoids

• Hepatic lobule

• Portal lobule

• Role and Composition of Bile• Each day, hepatocytes secrete 800–1000 ml of

bile, a yellow, brownish, or olive-green liquid. • It has a pH of 7.6–8.6 and consists mostly of

water, bile salts, cholesterol, a phospholipidcalled lecithin, bile pigments, and several ions

• The principal bile pigment is bilirubin. The phagocytosis of aged red blood cells liberates iron, globin, and bilirubin (derived from heme)

• The iron and globin are recycled; the bilirubin is secreted into the bile and is eventually broken down in the intestine.

• One of its breakdown products—stercobilin—gives feces their normal brown color

• Bile is partially an excretory product and partially a digestive secretion.

• Bile salts, which are sodium salts and potassium salts

• of bile acids (mostly chenodeoxycholic acid and cholic acid), play a role in emulsification, the breakdown of large lipid globules into a suspension of small lipid globules.

• The small lipid globules present a very large surface area that allows pancreatic lipase to more rapidly accomplish digestion of triglycerides.

• Bile salts also aid in the absorption of lipids following their digestion.

Functions of the Liver

• Carbohydrate metabolism

• Lipid metabolism

• Protein metabolism.

• Processing of drugs and hormones.

• Excretion of Bilirubin

• Synthesis of bile salts

• Storage

• Phagocytosis

• Activation of vitamin D.

Gall bladder

• Pouch structure located near the liver which concentrates and stores bile

• Bile duct – a long tube that carries BILE. The top half of the common bile duct is associated with the liver, while the bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine.

pancreasproduces enzymes to digest proteins & starch

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

liverproduces bile

- stored in gall bladderbreak up fats

Small Intestine• Most chemical digestion

takes place here.

• Simple sugars and proteinsare absorbed into the inner lining.

• Fatty acids and glycerol go to lymphatic system.

• Lined with villi, which increase surface area for absorption, one cell thick.

Small intestine

• The small intestine is continuous with the stomach at the pyloric sphincter and leads to the large intestine at the ileocaecal valve.

• In the small intestine the chemical digestion of the food is completed and most of the absorption of the nutrients takes place.

• The small intestine consists of 3 main section

• Duodenum

• Jejunum

• Ileum

• The duodenum is about 25cm long

• Secretions from the gall bladder and the pancreas are released into the duodenum through the common structure, the hepatopancreatic sphicter.

• The jejunum is the middle section of the small intestine and about 2 meters long.

• The ileum is about 3 meters long and controls the flow of materials to the 1st part of large intestine.

Intestinal juices

• About 1500ml of intestinal juice are secreted daily by the glands.

• Water, mucus, mineral salts

• The pH of the intestinal juices is usually between 7.8 and 8.0

Function of small intestine

• Onward movement of its contents by peristalsis

• Secretion of the intestinal juice, also inc by the parasympathetic stimulation.

• Completion of chemical digestion of carbohydrates, protein and fats in the enterocytes of the villi.

• Protection against infection by microbes that have survived the antimicrobial action of hcl.

• Secretion of the hormones cholecystokininand secretin.

• Absorption of nutrients.

Small intestine

• Function– chemical digestion

• major organ of digestion & absorption

– absorption through lining• over 6 meters!

• small intestine has huge surface area = 300m2 (~size

of tennis court)

• Structure– 3 sections

• duodenum = most digestion

• jejunum = absorption of nutrients & water

• ileum = absorption of nutrients & water

Duodenum

• 1st section of small intestines

– acid food from stomach

– mixes with digestive juices from:

pancreas

liver

gall bladder

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

pancreasproduces enzymes to digest proteins & starch

Absorption in the SI

• Much absorption is thought to occur directly through the wall without the need for special adaptations

• Almost 90% of our daily fluid intake is absorbed in the small intestine.

• Villi - increase the surface area of the small intestines, thus providing better absorption of materials

Absorption by Small Intestines• Absorption through villi & microvilli

– finger-like projections

– increase surface area for absorption

VILLI

Large intestine

• The large intestine is about 1.5 meters long, beginning at the caecum and terminating at the rectum and anal canal deep in the pelvis.

• Its lumen is about 6.5cm in diameter, larger than the small intestine.

• The colon is divided into

• Caecum

• Ascending colon

• Transverse colon

• Descending colon

• Sigmoid colon

• The caecum is the 1st part of the colon

• It is a dilated region which has a blind end inferiorly and is continuous with the asendingcolon superiorly.

• The ascending colon passes upwards from the caecum to the level of the liver where it curves to the left at the hepatic flexure.

• The transverse colon that extends across the abdominal cavity in the front of the duodenum and the stomach to the area of the spleen and curves downwards.

• The descending colon passes down the left side of the abdominal cavity then curves towards the midline.

• The sigmoid colon is a s shaped curve in the pelvis that continues downwards to become rectum.

• The rectum is about 13cm long it leads from the sigmoid colon and terminates in the anal canal.

• The anal canal is short about 3.8cm long in adults and leads from the rectum to the exterior.

function of large intestine, rectum, anal canal

• Absorption

• Microbial activity

• Mass movement

• defecation

Large intestines (colon)

• Function

– re-absorb water

• use ~9 liters of water every day in digestive juices

• > 90% of water reabsorbed

– not enough water absorbed

» diarrhea

– too much water absorbed

» constipation

• Solid materials pass through the large intestine.

• These are undigestiblesolids (fibers).

• Water is absorbed.

• Vitamins K and B are reabsorbed with the water.

• Rectum- solid wastes exit the body.

You’ve got company!

• Living in the large intestine is a community of helpful bacteria

– Escherichia coli (E. coli)

• produce vitamins– vitamin K; B vitamins

• generate gases– by-product of bacterial metabolism

– methane, hydrogen sulfide

AppendixVestigial organ

Rectum

• Last section of colon (large intestines)

– eliminate feces

• undigested materials

– extracellular waste

» mainly cellulose from plants

» roughage or fiber

–masses of bacteria

Digestive Homeostasis Disorders

• ULCERS – erosion of the surface of the alimentary canal generally associated with some kind of irritant

• CONSTIPATION – a condition in which the large intestine is emptied with difficulty.

• Too much water is reabsorbed

• and the solid waste hardens

Digestive Homeostasis Disorders

Digestive Homeostasis Disorders

• DIARRHEA – a gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine.

• This results in increased, multiple, watery feces.

• This condition may result in severe dehydration, especially in infants

Digestive Homeostasis Disorders

• APPENDICITIS – an inflammation of the appendix due to infection

• Common treatment is removal of the appendix via surgery

Digestive Homeostasis Disorders

• GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder

• Can either be “passed” (OUCH!!) or surgically removed

Digestive Homeostasis Disorders

• ANOREXIA NERVOSA - a psychological condition where an individual thinks they appear overweight and refuses to eat.

• Weighs 85% or less than what is developmentally expected for age and height

• Young girls do not begin to menstruate at the appropriate age.

Digestive Homeostasis Disorders

• HEART BURN – ACID from the stomach backs up into the esophagus.