Chapter 4: Human Digestion, Absorption, & Transport

Muscular layer of GI tract

-Circular muscles, surrounded by the Longitudinal muscles.

2 Major Components of the Digestive system

-GI tract -Accessory organs

Types of Sphincters

-Lower esophageal sphincter -Pyloric sphincter

Stomach Functions

-Produces and secretes HCI -Secretes chemical messengers that regulate digestion -Begins chemical digestion of protein

3 Sections of the Small Intestine

1. Duodenum (dig for worms) 2. Jejunum (J-shaped hook) 3. Ileum (I caught a fish)

How long does the GI tract approximately extend in a living person?

16 feet in length

How much can a healthy person produce of saliva?

4-6 cups a day

Gastric juice

A digestive fluid secreted by the stomach.

Epiglottis

A flap of tissue that seals off the windpipe and prevents food from entering. Bolus normally lands on it, making it cover the opening of the larynx.

Secretin

A hormone secreted by the small intestine (duodenum) in response to low pH (e.g., from stomach acid). It promotes the release of bicarbonate from the pancreas to act as a buffer.

Cholecystokinin (CCK)

A hormone secreted by the small intestine (duodenum) in response to the presence of fats. It promotes release of bile from the gallbladder and pancreatic juice from the pancreas,and reduces stomach motility.

Esophagus

A muscular tube that connects the mouth to the stomach. Primary function is to transfer a bolus into the stomach.

Mastication

A physical activity that prepares solid foods for swallowing and chemical digestion.

Enzyme

A protein that speeds up the rate of chemical reaction without being altered in the process.

Bile

A substance produced by the liver that breaks up fat particles, its main function.

Bolus

A term used to describe food after it has been chewed and mixed with saliva

Hepatic portal vein

A vein connecting the capillary bed of the intestines with the capillary bed of the liver. This allows amino acids and glucose absorbed from the intestines to be delivered first to the liver for processing before being transported throughout the circulatory system.

Pancreas

An organs in the abdominal cavity with two roles. The first is an exocrine role: to produce digestive enzymes and bicarbonate, which are delivered to the small intestine via the pancreatic duct. The second is an endocrine role: to secrete insulin and glucagon into the bloodstream to help regulate blood glucose levels.

Chemical digestion

Breakdown of large nutrient molecules in food into smaller components, primarily by the action of the stomach acid and various enzymes.

Digestive System

Breaks down food into smaller molecules. Absorbs these nutrients into the body. Works in concert with the other organ systems of the body. If it's not functioning properly, the entire body eventually shows signs and symptoms of disease.

How does the digestive tract break down food?

By physical and chemical processes.

Active transport

Energy-requiring process that moves material across a cell membrane against a concentration difference. Unique transport protein and energy. -glucose -amino acids

Salivary amylase

Enzyme in saliva that breaks down starch and initiates chemical digestion in the mouth.

Why are Intestinal sphincters essential?

For the purpose of normal digestion and absorption. Help control rates of digestion and absorption by keeping the contents in place.

Simple diffusion

Form of transport. Movement of a solute from an area of high concentration to an area of low concentration. Does not require the input of energy. -water soluble vitamins -lipds -some minerals

Salivary glands

Glands of the mouth that produce saliva, a digestive secretion

Lumen

Hollow space within the digestive tract through which food and fluids pass.

Path of residue through the large intestine

Ileocecal sphincter, cecum, ascending colon, transverse colon, descending colon, and sigmoid colon.

Mucosa

Innermost layer of the GI tract. Surrounds the lumen. Incldes cells that secrete mucus.

Peristalsis

Involuntary waves of muscle contraction that keep food moving along in one direction through the digestive system.

What saliva enzyme stays inactive until it reaches the stomach?

Lingual Lipase, begins fat digestion.

What is the result of Mastication?

Makes food easier to swallow and increases surface area, which enables enzymes to have greater access to nutrients.

Jejunum

Middle portion of the small intestine, most digestion and nutrient absorption occurs here and the duodenum. Main site of nutrient absorption.

Facilitated diffusion

Movement of specific molecules across cell membranes through protein channels, specific transport protein for a specific type of nutrient. Does not require energy. -simulated sugar fructose

Primary components of gastric juice

Mucus, hydrochloric acid (HCI), intrinsic factor, digestive enzymes.

Upper esophageal sphincter (UES)

Not a true sphincter, but rather a section of the pharynx that relaxes when a bolus is swallowed, allowing the mass of food to enter the esophagus.

Chyme

Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.

Mechanical digestion

Physical treatments that food undergoes while it is in the intestinal tract; e.g. being chewed into smaller pieces and mixed with secretions. Facilitates chemical digestion.

Digestion

Process of breaking down large food molecules into nutrients that the body can use.

Liver

Processes and stores many nutrients. Produces bile. Makes cholesterol.

Lower esophageal sphincter (LES)

Ring of muscles between the esophagus and the stomach. Also called cardiac sphincter. Normally is closed, preventing the back flow of acidic stomach contents into the esophagus.

Large intestine

The last section of the digestive system, where water is absorbed from food and the remaining material is eliminated from the body. Its mucosa has no villi. Has goblet cells.

Small intestine

The part of the digestive system in which most chemical digestion takes place. Diameter is only about 1", longest component of the GI tract. 3 sections

Pharynx

The throat; the section of the alimentary canal that connects the nasal cavity with the top of the esophagus.

Absorption

The uptake and removal of nutrients from the digestive tract, or GI tract. Enter the bloodstream or the lymph.

Sphincters

Thickened regions of circular muscle that function like valves to control the flow of contents at various points in the GI tract. Relax, the passageway opens and allows contents to flow. Contract, closes passageway and restrict flow at that point.

Villi

Tiny finger-shaped structures that cover the inner surface of the small intestine and provide a large surface area through which digested food is absorbed. Has an outer layer of absorptive cells called enterocytes.

True or False: Under normal circumstances, very little carbohydrate, protein, or fat escape digestion and absorption in the small intestine.

True

What is the thickest and strongest wall of the GI tract?

Wall of the stomach; it has a third type of muscle, diagonal (oblique) muscle. By relaxing and contracting, these muscles can mix substances that are within the lumen and control the movement (motility) of the material through the tract.

Saliva

Watery fluid, produced by the salivary glands in the mouth, that contains lubricants, enzymes, and other substances. Moistens and lubricates food.

When does heartburn occur?

When the LES fails to close properly.

Cecum

a pouch connected to the junction of the small and large intestines.

Lysozyme

an enzyme found in saliva and sweat and tears that destroys the cell walls of certain bacteria

Gallbladder

concentrates and stores bile until it is needed for fat digestion and absorption.

Duodenum

first part of small intestines, most digestion takes place, chemicals released from liver, gall bladder, and pancreas. Bicarbonate (an alkaline fluid) is secreted.

Functions of the stomach

food storage, mechanical digestion, chemical digestion, production of chyme, begins chemical digestion of protein

Probiotics

live microbes applied to or ingested into the body, intended to exert a beneficial effect

Accessory organs of the gastrointestinal system

liver, gallbladder, pancreas. Play major roles in digestion.

Pylorus

portion of the stomach that connects to the small intestine and through which chyme leaves the stomach.

Pyloric sphincter

ring of muscle that guards the opening between the stomach and the duodenum

Segmentation

ringlike muscular contractions followed by relaxations that are designed to help to mix the chyme in the small intestine.

Parietal cells

secrete HCL, intrinsic factor (B-12 absorption)

Mucous cells

secrete mucus

Chief cells

secrete pepsinogen

Goblet cells

secretes mucus in the large intestine; primary secretion.

Gastrin hormone

stimulates secretions of HCl,the motility of the stomach & small intestine, and signals the ileocecal sphincter betwen the small and large intestines to relax.

Prebiotics

substances in food that are poorly digested by humans. nutrients that encourage the growth of beneficial microbes in the intestine

5 primary taste sensations

sweet, sour, salty, bitter, umami

Accessory organs

teeth, tongue, salivary glands, liver, gallbladder, pancreas

Bioavailability

the extent to which the body can absorb and use a nutrient

Ileum

the last and longest portion of the small intestine. minimal absorption.

Ascending colon

the part of the large intestine that ascends from the cecum to the transverse colon.

Gastrointestinal tract (GI tract)

the passageway or tube that extends from the mouth to the anus and in which the process of digestion takes place

Ileocecal sphincter

the ring-like muscle that controls the flow from the ileum of the small intestine into the cecum of the large intestine