anatomy unit 6: digestive system

functions of digestive system

digestion and absorption

processes of digestion

Ingestion

Propulsion

Food breakdown- mechanical digestion

Food breakdown- chemical digestion

Absorption

Defecation

Mechanical Digestion

mixes and divides food for further degradation by enzymes.

Examples

Mixing of food in the mouth by the tongue

Churning of food in the stomach

Segmentation in the small intestine

includes peristalsis and segmentation

Chemical Digestion

a sequence of steps in which large food molecules are broken down into their building blocks by enzymes.

mouth, stomach, small intestine

where does mechanical digestion happen

starts in mouth and stomach, small intestine

where does chemical digestion happen

Peristalsis

adjacent segments contract and relax, pushing the food along the tract.

This can be found throughout the system, from the pharynx down to the anus.

Segmentation

single segments alternatively contract and relax. The food is moved forward and then back again. So, the food becomes mixed rather than just propelled along the tract.

Found only in the small intestine

alimentary canal

The Alimentary Canal (also known as the Gastrointestinal Tract) is a continuous, coiled, hollow, muscular tube that winds through the body from mouth to anus

The canal is open at both ends.

9 meters/30ft in in a cadaver

Mouth

Pharynx

Esophagus

Stomach

Small intestine

Large intestine

The Organs of the Alimentary Canal

lumen

The hole/tunnel that the food material moves through

mucosa, submucosa, muscularis externa, serosa

the four basic tissue layers that make up the walls of the alimentary canal organs from the esophagus to the large intestine

Mucosa

the innermost layer, a membrane that secretes mucus and lines the lumen, of the organ. Consists primarily of epithelium. (Simple columnar epithelial)

Submucosa

found just beneath the mucosa. It is a soft connective tissue layer containing blood vessels, nerve endings, lymph nodules, and lymphatic vessels.

Muscularis externa

is a muscle layer made up of smooth muscle cells.

The serosa is the outermost layer of the wall.

mouth/oral cavity

opening where food enters the body and undergoes the first process of digestion

Palate

the roof of the mouth

Hard is in the front

Soft is in the back

Uvula

a fleshy finger-like projection of the soft palate, which extends downward.

Oral cavity proper

area contained by the teeth

Lingual frenulum

a fold of mucous membrane, it secures the tongue to the floor of the mouth and limits its posterior movements.

Pharynx

From the mouth, food passes posteriorly into the oropharynx and laryngopharynx, both of which are common passageways for food, fluids, and air.

Oropharynx

posterior to the oral cavity

Laryngopharynx

continuous with the esophagus below.

Epiglottis

flap of elastic cartilage that covers the air passageway whenever food passes through the pharynx and into the esophagus.

esophagus (gullet)

runs from the pharynx through the diaphragm to the stomach.

Two sphincters

Upper esophageal sphincter- separates the pharynx from the esophagus

Cardioesophageal sphincter- separates the esophagus from the stomach (aka: gastroesophageal sphincter OR lower esophageal sphincter)

Upper esophageal sphincter

separates the pharynx from the esophagus

Cardioesophageal sphincter

separates the esophagus from the stomach (aka: gastroesophageal sphincter OR lower esophageal sphincter)

cardiac region, fundus, body, pylorus

regions of stomach

stomach

The stomach is a C-shaped organ on the left side of the abdominal cavity, nearly hidden by the liver and the diaphragm.

cardiac region

(named for its position near the heart) surrounds the cardioesophageal sphincter, where food enters the stomach from the esophagus.

Fundus

the expanded part of the stomach lateral to the cardiac region

Body

the midportion of the stomach

Pylorus

is the terminal part of the stomach

Greater curvature

the convex lateral surface of the stomach

Lesser curvature

the concave medial surface of the stomach

Rugae

wrinkles of mucosa tissue on the stomach wall. (Increases surface area)

Gastric Pits

found in the walls of the stomach, within the mucosa layer.

Gastric Glands

the interior of the gastric pits. Consists of Mucous neck cells, Parietal Cells, and Chief cells.

Mucous neck cells, Parietal Cells, and Chief cells.

cells of the gastric pits

Chief cells

located in the Gastric Glands, produce pepsinogen.

Parietal cells

secrete Hydrochloric Acid (HCl), which transforms the pepsinogen into pepsin.

Neck cells

produce a sticky alkaline mucus, which clings to the stomach mucosa and protects the stomach wall from being damaged by the acid and digested by the enzymes.

Pepsin

enzyme that digests protein within the stomach.

how is food moved from stomach to intestine

Peristaltic waves act primarily in the inferior portion of the stomach to mix and move chyme through the pyloric valve.

Small intestine

The small intestine is the body's major digestive organ. Here usable food is finally prepared for its journey into the cells of the body.

pyloric sphincter

entrance to the small intestine. Controls food movement into the small intestine and prevents the small intestine from being overwhelmed.

Ileocecal valve

end of the small intestine, leads into the large intestine

Duodenum

curves around the head of the pancreas, about 25cm long (10 inches).

Jejunum

extends from the duodenum to the ileum, about 2.5m long (8 feet).

Ileum

the terminal part of the small intestine, about 3.6m long (12 feet).

circular folds, villi, microvilli

structures that increase surface area of small intestine

Circular folds

also called plicae circulares, are deep folds of both mucosa and submucosa layers. (Increases surface area)

Villi

finger-like projections of the mucosa that give it a velvety appearance and feel, much like the soft texture of a towel. (Increases surface area)

Microvilli

are tiny projections of the plasma membrane of the mucosa cells that give the cell surface a fuzzy appearance, also called the brush border. (Increases surface area)

Each Villus has a rich capillary bed and a modified lymphatic capillary, called a lacteal.

The digested foodstuffs are absorbed through the mucosa cells into both the capillaries and the lacteal.

Lacteals are really good at absorbing fats/ lipids; and the capillaries absorb just about everything else.

brush border

Surface of a cell covered with microvilli. increases surface area of a cell for absorption

lacteals

modified lymphatic capillary that absorbs fat and lipids

capillaries

absorbs everything else in the small intestine

Liver

Triangular shaped.

The liver is the largest gland in the body.

Located under the diaphragm next to the stomach.

Functions:

To detox the blood.

Produce bile to help emulsify fats.

Gallbladder

Bulb shaped organ

Sits beneath the liver

Function:

Stores the bile that the Liver produces.

Problem: if it stores too much cholesterol with the bile, gallstones can form

Pancreas

A weird shaped organ, it kind of looks like an elf's ear.

It is tucked underneath the stomach and liver.

The Pancreas is a dual organ, meaning it works with both the digestive system and the endocrine system.

For the Digestive System: produces pancreatic juice (juice that neutralizes the stomach acid and provides a lot of pancreatic enzymes to break down foods.)

For the Endocrine System: helps regulate blood sugar levels

Pancreatic duct

- tube that drains enzymes and pancreatic juice out of the pancreas

Bile

(formed by the liver to emulsify fats) enters the duodenum through the bile duct.

The pancreatic juice, enzymes, and bile join in the hepatopancreatic ampulla, then travel together through the major duodenal papilla into the duodenum.

hepatopancreatic ampulla

where the bile duct and pancreatic duct meet

major duodenal papulla

a rounded projection in the duodenum where the main pancreatic duct and the common bile duct empty,

large intestine

extends from the ileocecal valve to the anus.

Functions: absorbs water and electrolytes from the remaining indigestible food matter, converts the liquid waste into solid feces, and stores it until it can be eliminated from the body through defecation

- two sphincter

ileocecal valve and anus

Two sphincters are found in the large intestine.

Anus

the exit of the intestine and the entire digestive system. Controlled by both smooth muscle and skeletal muscle.

cecum, appendix, colon, rectum, anal canal

parts of large intestine

Cecum

sac-like and is the first part of the large intestine.

Appendix

hangs from the cecum, a potential trouble spot because it is usually twisted and it is an ideal location for bacteria to accumulate.

Colon

divided into several distinct regions: ascending, transverse, descending, and sigmoid

Rectum

lies in the pelvis comes after the sigmoid colon.

Anal canal

end of the large intestine and end of the digestive system.

Ascending colon

travels up the right side of the abdominal cavity and makes a turn at the right colic

Transverse colon

travels across the abdominal cavity and makes a turn at the left colic

Descending colon

travels down the left side to enter the pelvis, where it becomes the S-shaped sigmoid colon.

Sigmoid colon

the end of the colon, lies within the pelvis

Haustra

Sac-like pouches that line the inner surface of the large intestine (colon). They are formed by the contraction of three longitudinal bands of muscle called teniae coli.

teniae coli

Smooth muscle in the wall of large intestine that pulls on the wall causing haustra

Salivary amylase and pancreatic amylase

Enzymes that break down carbohydrates.

Pepsin

Trypsin

Chymotrypsin

Carboxypeptidase

enzymes that break down protein

Bile salts

Pancreatic Lipase

Brush border enzymes

enzymes that break down fat/lipids

Pancreatic Nucleases

Brush border enzymes

enzymes with nucleic acids as nutrients

enzymes in small intestine

Pancreatic amylase

Trypsin

Chymotrypsin

Carboxypeptidase

Bile salts

Pancreatic Lipase

Brush border enzymes

Pancreatic Nucleases

Brush border enzymes

Gastroesophageal reflux disease (acid reflux)

-occurs when stomach acid frequently flows back into the esophagus.

Gallstones

Gallstones are hardened deposits of bile that can form in your gallbladder.

Celiac Disease

is an immune reaction to eating gluten, a protein found in wheat, barley and rye. Over time, this reaction damages your small intestine's lining and prevents absorption of some nutrients.

Crohn's Disease

is an inflammatory bowel disease (IBD). It causes inflammation of your digestive tract, which can lead to abdominal pain, severe diarrhea, fatigue, weight loss and malnutrition.

Hemorrhoids

-are swollen veins in your anus and lower rectum, similar to varicose veins.

Irritable bowel syndrome

a common disorder that affects the large intestine. Signs and symptoms include cramping, abdominal pain, bloating, gas, and diarrhea or constipation, or both.

Ulcerative colitis

is an inflammatory bowel disease (IBD) that causes long-lasting inflammation and ulcers (sores) in your digestive tract. Ulcerative colitis affects the innermost lining of your large intestine (colon) and rectum.

Pyloric stenosis

Pyloric muscles thicken and become abnormally large, blocking food from leaving the stomach.

vestibule and oral cavity proper

mouth regions

vestibule

the space between the lips and cheeks (externally) and the teeth and gums (internally).

bolus

a small rounded mass of chewed food at the moment of swallowing.

chyme

the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.