CHAPTER 16: DIGESTIVE SYSTEM

16.1 FUNCTIONS OF THE DIGESTIVE SYSTEM

Digestive system - with the assistance of the

circulatory system, is a complex set of organs,

glands, and ducts that work together to

transform food into nutrients for cells.

The functions of the digestive system include

the following:

1. Ingestion is the consumption of solid or

liquid food, usually through the mouth.

2. Digestion is the breakdown of large organic

molecules into smaller molecules that can

be absorbed. Digestion occurs through

mechanical and chemical means.

3. Absorption is the movement of molecules

out of the digestive tract and into the blood

or lymphatic system. The epithelial cells

that line the lumen of the small intestine

absorb the small molecules of nutrients

(amino acids, monosaccharides, fatty acids,

vitamins, minerals, and water) that result

from the digestive process.

4. Elimination is the removal of undigested

material, such as fiber from food, plus other

waste products from the body as feces

16.2 ANATOMY AND HISTOLOGY OF THE DIGESTIVE

SYSTEM

Digestive system consists of the digestive tract,

or GI tract, plus specific associated organs.

The specific portions of the digestive tract

include:

(1) Oral cavity, (mouth)

(2) Pharynx (throat)

(3) Esophagus

(4) Stomach

(5) Small and large intestines

(6) Anus

The specific associated organs of the digestive

system are

(1) Salivary glands, which empty into the

oral cavity

(2) Liver

(3) Pancreas

The liver and pancreas empty into the small

intestine.

Stratified epithelium – Line the oral cavity and

the esophagus and protects them from the

abrasion of chewing and swallowing.

Columnar epithelium – Line the stomach and

intestine and is specialized for absorption of

nutrients and secretion of digestive fluids.

The digestive tract consists of four major tunics,

or layers: The four tunics are: (1) the mucosa,

(2) the submucosa, (3) the muscularis, and (4) a

serosa or an adventitia

1. Mucosa - innermost tunic consists of three

layers:

(1) Inner mucous epithelium

(2) Loose connective tissue called the

lamina propria

(3) Thin outer layer of smooth muscle,

the muscularis mucosae.

2. Submucosa - lies just outside the mucosa. It

is a thick layer of loose connective tissue

containing nerves, blood vessels, and small

glands. An extensive network of nerve cell

processes forms a plexus (network) within

the submucosa. Autonomic nerves

innervate this plexus.

3. Muscularis. In most parts of the digestive

tract it consists of an inner layer of circular

smooth muscle and an outer layer of

longitudinal smooth muscle.

Enteric nervous system - Together, the

nerve plexuses of the submucosa and

muscularis compose this nervous system,

which is a division of the autonomic

nervous system, and is extremely important

in controlling movement and secretion

within the tract.

4. Serosa/Adventitia - The fourth, or

outermost, layer of the digestive tract.

Serosa - consists of the peritoneum, which

is a smooth epithelial layer, and its

underlying connective tissue.

Adventitia - Regions of the digestive tract

not covered by peritoneum are covered by

this connective tissue layer, which is

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16.1 FUNCTIONS OF THE DIGESTIVE SYSTEM

 Digestive system - with the assistance of the circulatory system, is a complex set of organs, glands, and ducts that work together to transform food into nutrients for cells.  The functions of the digestive system include the following:

Ingestion is the consumption of solid or liquid food, usually through the mouth.
Digestion is the breakdown of large organic molecules into smaller molecules that can be absorbed. Digestion occurs through mechanical and chemical means.
Absorption is the movement of molecules out of the digestive tract and into the blood or lymphatic system. The epithelial cells that line the lumen of the small intestine absorb the small molecules of nutrients (amino acids, monosaccharides, fatty acids, vitamins, minerals, and water) that result from the digestive process.
Elimination is the removal of undigested material, such as fiber from food, plus other waste products from the body as feces 16.2 ANATOMY AND HISTOLOGY OF THE DIGESTIVE SYSTEM  Digestive system consists of the digestive tract, or GI tract, plus specific associated organs.  The specific portions of the digestive tract include: (1) Oral cavity, (mouth) (2) Pharynx (throat) (3) Esophagus (4) Stomach (5) Small and large intestines (6) Anus  The specific associated organs of the digestive system are (1) Salivary glands, which empty into the oral cavity (2) Liver (3) Pancreas  The liver and pancreas empty into the small intestine.  Stratified epithelium – Line the oral cavity and the esophagus and protects them from the abrasion of chewing and swallowing.  Columnar epithelium – Line the stomach and intestine and is specialized for absorption of nutrients and secretion of digestive fluids.  The digestive tract consists of four major tunics, or layers: The four tunics are: (1) the mucosa, (2) the submucosa, (3) the muscularis, and (4) a serosa or an adventitia
Mucosa - innermost tunic consists of three layers: (1) Inner mucous epithelium (2) Loose connective tissue called the lamina propria (3) Thin outer layer of smooth muscle, the muscularis mucosae.
Submucosa - lies just outside the mucosa. It is a thick layer of loose connective tissue containing nerves, blood vessels, and small glands. An extensive network of nerve cell processes forms a plexus (network) within the submucosa. Autonomic nerves innervate this plexus.
Muscularis. In most parts of the digestive tract it consists of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. Enteric nervous system - Together, the nerve plexuses of the submucosa and muscularis compose this nervous system, which is a division of the autonomic nervous system, and is extremely important in controlling movement and secretion within the tract.
Serosa/Adventitia - The fourth, or outermost, layer of the digestive tract. Serosa - consists of the peritoneum, which is a smooth epithelial layer, and its underlying connective tissue. Adventitia - Regions of the digestive tract not covered by peritoneum are covered by this connective tissue layer, which is

continuous with the surrounding connective tissue. Peritoneum  Serous membrane of the abdominal cavity and the abdominal organs  Visceral peritoneum - or serosa, the serous membrane that covers the organs  Parietal peritoneum - The serous membrane that lines the wall of the abdominal cavity  Mesenteries - held in place many of the organs of the abdominal cavity by connective tissue sheets.  “ Mesentery ” is a general term referring to the serous membranes attached to the abdominal organs  Mesentery proper - applied specifically to the mesentery associated with the small intestine  Lesser omentum - The mesentery connecting the lesser curvature of the stomach to the liver and diaphragm  Greater omentum - The mesentery connecting the greater curvature of the stomach to the transverse colon and posterior body wall  Retroperitoneal organs :

Duodenum
Pancreas
Ascending colon
Descending colon
Rectum
Kidneys
Adrenal glands
Urinary bladder 16.3 ORAL CAVITY, PHARYNX, AND ESOPHAGUS 16.7 LARGE INTESTINE  Anatomy of the Large Intestine The large intestine consists of (1) Cecum (2) Colon (3) Rectum (4) Anal canal Anatomy of the Large Intestine Cecum  The proximal end of the large intestine where it joins with the small intestine at the ileocecal junction.  Located in the right lower quadrant of the abdomen near the iliac fossa.  A sac that extends inferiorly about 6 cm past the ileocecal junction.  Appendix – is a tube attached to the cecum that is about 9 cm long.  Appendicitis - an inflammation of the appendix that usually occurs because of an obstruction - can also cause a slight fever, loss of appetite, constipation or diarrhea, nausea, and vomiting - If this bursts, the infection can spread throughout the peritoneal cavity, causing peritonitis with life-threatening results.  McBurney point – specific point particularly in the right lower quadrant where a sudden abdominal pain can be felt. Midway between the umbilicus and the right superior iliac spine of the coxal bone. Colon  Is about 1.5–1.8 m long and consists of four parts: (1) Ascending colon (2) Transverse colon (3) Descending colon (4) Sigmoid colon  Crypts - Numerous straight, tubular glands in the mucosal lining of the colon, which contain many mucus-producing goblet cells.  Teniae coli - The longitudinal smooth muscle layer of the colon does not completely envelop the intestinal wall but forms three bands called Rectum  A straight, muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal.  The muscular tunic is composed of smooth muscle and is relatively thick in this part of the

amounts of fructose (fruit sugar) and lactose (milk sugar).  Starches, cellulose, sucrose, and fructose - are carbohydrates derived from plants  Lactose – carbohydrate that is derived from animals.  Polysaccharides - are large carbohydrates, such as starches, cellulose, and glycogen that consist of many sugars linked by chemical bonds.  Starch

- Is an energy-storage molecule in plants - Is/ can be broken down by enzymes  Cellulose - forms the walls of plant cells - A polysaccharide that is not digested but is important for providing fiber in the diet.  Glycogen - is an energy-storage molecule in animals and is contained in muscle and in the liver.  Salivary amylase - begins the digestion of carbohydrates in the mouth.  Stomach (for carbs) – continues the digestion from the oral cavity until the food is well mixed with acid, which inactivates salivary amylase.  Pancreatic amylase - enters the duodenum and continues the digestion of carbohydrates on the small intestine, so that absorption can begin.  Salivary and pancreatic amylase – these amylases break down polysaccharides into the smaller disaccharides  Disaccharidases – a group of enzymes called break down the disaccharides into monosaccharides. Are bound to the microvilli of the intestinal epithelium.  Lactase – one disaccharidase, which breaks down lactose (milk sugar)  Cotransport - Absorption of the monosaccharides, glucose, and galactose occurs through this transport  Liver cells - convert different types of monosaccharides to glucose, which then leaves the liver via the blood to be distributed throughout the body.  Glucose - enters the cells by facilitated diffusion.  Insulin - With this the rate of glucose transport into most types of cells is can increase tenfold. - Without this, glucose enters most cells very slowly. Lipids  Lipid molecules - are insoluble or only slightly soluble in water  Lipids include triglycerides, phospholipids, steroids, and fat-soluble vitamins.  Triglycerides - or fats, are the most common type of lipid. They consist of three fatty acids bound to glycerol.  Saturated fats - Fatty acids that have only single bonds between carbons. - Are solid at room temperature - Found in meat, dairy products, eggs, nuts, and certain oils such as coconut oil and palm oil  Unsaturated fats - Fatty acids have double bonds between carbons - Are found in fish and most plant-based oils  Monounsaturated fats - have one double bond  Polyunsaturated fats - Are liquid at room temperature. - have more than one double bond between carbons in their fatty acids  Lipase - secreted by the pancreas, digests lipid molecules  Fatty acids and monoglycerides - The primary products of this lipid digestive process.  Emulsification – Is a key step in lipid digestion by which bile salts transform large lipid droplets into much smaller lipid droplets.  Once lipids are digested in the intestine, bile salts aggregate around the small droplets of digested lipids to form Micelles.  Once inside the intestinal epithelial cells, the fatty acids and monoglycerides are recombined to form triglycerides. These, and other lipids, are packaged inside a protein coat. The

packaged lipid-protein complexes, or lipoproteins, are called chylomicrons Proteins  Proteins - are chains of amino acids. They are found in most of the plant and animal products we eat.  Pepsin - is a protein-digesting enzyme secreted by the stomach. Breaks down large proteins into smaller, individual polypeptides it digests only about 10–20% of the total ingested protein.  In the small intestine, the enzymes trypsin, chymotrypsin, and carboxypeptidase continue protein digestion. These enzymes are synthesized by the pancreas in an inactive state. Once they are in the small intestine, these enzymes are activated.  Peptidases - further break down small peptides into tripeptides (three amino acids), dipeptides (two amino acids), or single amino acids in the small intestine. These are bound to the microvilli of the small intestine.  Many, but not all , amino acids are absorbed by cotransport with Na+ similar to glucose cotransport  Amino acids - are used as building blocks to form new proteins, but some may be metabolized, with a portion of the released energy used to produce ATP.  The body cannot store excess amino acids. Instead, they are partially broken down and used to synthesize glycogen or lipids, which can be stored.  The body can store only small amounts of glycogen , so most of the excess amino acids are converted to lipids. Water and Minerals  9 L – Amount of water enter the digestive tract each day.  2 L – Amount of water we ingest in food and drink  7 L – Amount of water from digestive secretions.  92% – Percentage of water that is absorbed in the small intestine  7% – Percentage of water that is absorbed in the large intestine  1% – Percentage of water that leaves the body in the feces.  Water can move in either direction by osmosis across the wall of the digestive tract. The direction of water movement is determined by osmotic gradients across the epithelium.  When the chyme is dilute , water moves out of the intestine into the blood.  If the chyme is concentrated , water moves out of the blood into the small intestine.  Sodium, potassium, calcium, magnesium, and phosphate ions are actively transported from the small intestine.  Vitamin D - is required for the transport of Ca2+.  Negatively charged Cl− moves passively through the wall of the duodenum and jejunum with the positively charged Na+, but Cl− is actively transported from the ileum

CHAPTER 16: DIGESTIVE SYSTEM, Lecture notes of Anatomy

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Download CHAPTER 16: DIGESTIVE SYSTEM and more Lecture notes Anatomy in PDF only on Docsity!

CHAPTER 16: DIGESTIVE SYSTEM

16.1 FUNCTIONS OF THE DIGESTIVE SYSTEM