A&P2: The Digestive System

Stomach

- C-shaped organ - The interior stomach wall has rugae

Mumps

- Clinical Application for Salivary Glands - a viral inflammation of the salivary glands. It is no longer common but outbreaks still occur, usually in schools and colleges. - the danger for adolescent and adult males is that it may infect the testes, although sterility usually does not occur.

Digestive System Functions

- Ingestion - Propulsion - movement of food through the GI tract by peristalsis. - Digestion of two kinds: 1) Mechanical (physical) digestion - chewing (teeth), churning (stomach) 2) Chemical - digestion enzymes break down large molecules into smaller molecules - Absorption of nutrients - Elimination

Salivary amylase

- Site of action: mouth - substrate: starch - End product: maltose

Nucleases

- Site of action: small intestine - substrate: DNA + RNA - End product: nucleotides

Trypsin

- Site of action: small intestine - substrate: large polypeptides - End product: small polypeptides

Carboxypeptidase

- Site of action: small intestine - substrate: small polypeptides - End product: amino acids

Bile* (not an enzyme)

- Site of action: small intestine - substrate: unemulsified fats - End product: emulsified fats

Lipsae

- Site of action: small intestine - substrate: emulsified fats - End product: glycerol and fatty acids

Maltase

- Site of action: small intestine - substrate: maltose - End product: glucose

Nucleosidases + Phosphatases

- Site of action: small intestine - substrate: nucleotides - End product: phosphate group, pentose sugar, nitrogen base

Aminopeptidase

- Site of action: small intestine - substrate: small polypeptides - End product: amino acids

Sucrase

- Site of action: small intestine - substrate: sucrose - End product: glucose

Pepsin

- Site of action: stomach - substrate: proteins - End product: large polypeptides

Tongue

- a muscular organ with both: a.) intrinsic muscles (not attached to bone) b.) extrinsic muscles (attached to the hyoid bone or the soft palate) - has papillae of 3 kinds: 1) filiform 2) fungiform 3) circumvallate

Esophagus

- a muscular tube about 25 cm long that connects the throat with the stomach - meets the stomach at the cardiac sphincter

Gallbladder

- a storage organ for bile - a small sac located in a shallow depression of the liver

Alimentary canal (Gastrointestinal tract) organs

- a tube that passes through the body - the organs are: mouth, pharynx, esophagus, stomach, small intestine, large intestine.

Large intestine

- about 7.5 cm in diameter. - segments of the large intestine include: 1. Cecum - appendix is attached 2. Colon - makes up most of the length of the organ - Ascending - Transverse - Descending - Sigmoid 3. Rectum

Small intestine microanatomy

- adaptations to increase surface area for absorption: 1. plicae circulares - circular folds 2. villi - finger-like projections off of the circular folds 3. microvilli - microscopic projections off the villi

Inflammatory bowel disease

- an autoimmune disease - over reaction of the immune system to intestinal bacteria, resulting in inflammation

Pancreas

- an oblong-shaped organ that lies behind the stomach - its secretions drain via the pancreatic duct into the common bile duct, then into the duodenum

Tumors

- can occur in all parts of the GI tract - 30% of all cancer deaths involve GI tract cancers, especially colon cancer (which can have genetic and diet components)

Clinical Applications for Teeth

- cavities (dental caries) - gingivitis - periodontal disease - root canal therapy

Cirrhosis

- chronic inflammation of the liver - liver cells are replaced by fibrous or adipose connective tissue, thus suppressing liver functions

Pancreatic cancer

- clinical application for pancreas - develops and spreads faster than almost any other type of cancer, and is often asymptomatic in early stages - the fast metastasis, combined with the loss of crucial digestive function, often makes it quickly fatal

Permanent teeth

- come in between the ages of 6 and 14. - the third molars may take longer. - the dental formula is 2 - 1 - 2 - 3 (total of 32 teeth).

Deciduous teeth

- come in during the first 2 years. - are lost between 6 - 12 years. - the dental formula is 2 - 1 - 0 - 2 (total of 20 teeth).

Pharynx (throat)

- common passageway for food and air - has 3 regions 1. Nasopharynx - behind nasal cavity 2. Oropharynx - behind oral cavity 3. Laryngopharynx - behind larynx

Liver lobule

- consist of 6 sides which includes many hepatocytes arranged in plates around a central vein - blood flow is through very leaky capillaries called sinusoids, which allow the blood to be processed by the hepatocytes

Hepatocyte function

- glucose is stored as glycogen - fat soluble vitamins are stored (A,D,E,K) - minerals, such as iron and copper, are stored - poisons, such as alcohol and ammonia, are detoxified - bile is produced and secreted

Cirrhosis causes

- hepatitis B (a viral disease) - certain toxins (poisonous mushroom) - alcohol abuse

Diverticulosis

- outpockets develop in the wall of the colon due to a low fiber diet - diverticulitis is an inflammation of the diverticula

Bile

- partially an excretory product (bilirubin) - partially a digestive secretion (bile salt)

In children, the gastric pits produce:

- rennin - gastric lipsae these functions are mostly lost in adult

Salivary Glands

- secretes saliva - has 3 pairs 1.) parotid 2.) submandibular 3.) sublingual

Small intestine

- so-called because it has a smaller diameter (2.5 cm) than the large intestine, not because it is shorter. - most chemical digestion and absorption of nutrients occur here!!!!

Liver

- the largest organ in the abdominopelvic cavity - overlies the stomach in the right upper quadrant - consists of two large lobes (right and left) and two smaller lobes (caudate and quadrate)

Large intestine functions

- waste elimination (feces) - re-absorption of water and salts - a site for bacteria

Substances that are absorbed into the blood include:

- water - ethyl alcohol - some drugs, such as aspirin

Pancreas's 2 functions that are carried out by 2 different classes of cells?

1. Acinar cells are arranged in clusters called acini - the cells secrete digestive enzymes called pancreatic juice (has a pH of 8.9) 2. Islet cells are found in islets of langerhans. - the cells make the hormones insulin and glycogen that regulate blood glucose levels

2 major divisions of the digestive system

1. Alimentary canal (Gastrointestinal tract) organs 2. Accessory digestive organs

2 dentitions (sets of teeth)

1. deciduous teeth 2. permanent teeth

Gastric pits - 4 cell types

1. enteroendocrine cells 2. mucous neck cells 3. chief cells 4. parietal cells

4 different kinds of teeth in mammals

1. incisors - for biting 2. canines - in humans are incisor-like 3. premolars - for crushing and grinding 4. molars - for crushing and grinding

Small intestine - 3 segments

1.) duodenum 2.) jejunum 3.) ileum

Lysosome

Antibacterial digestive enzyme

Amylase

Begins starch digestion

What cell type is present in the sinusoids?

Kupffer's cells, which are macrophages that destroy bacteria and recycle red blood cells

Saliva

Mostly water but contains enzymes

Accessory digestive organs

These include: a) Organs that manipulate food (teeth, tongue) b) Other organs that lie outside the GI tract but secrete their products into it (salivary glands, pancreas, liver, gall bladder)

What does bacteria do as a living?

They make a living digesting cellulose, which in return they make vitamin K and some vitamin B

What are at each of the corners of the lobule?

a portal triad, which contains 3 vessels - bile duct - arteriole - venule

round ligaments

a remnant of the fetal umbilical vein

Crohn's disease

affects small intestine, especially the ileum

Ulcerative colitis

affects the large intestine

rennin

an enzyme that aids in the digestion of milk protein

gastric lipsae

an enzyme that helps digest milk fat

periodontal disease

bacteria infects the bone around the teeth

cavities (dental caries)

caused by bacteria that secrete acid that dissolves the enamel and dentin.

gingivitis

caused by bacteria; cause gum inflammation.

Submucosa

connective tissue that holds the overlying mucosa to the underlying muscle layer

In muscularis, how is muscle contractions controlled?

controlled by the autonomic nervous system and cause segmentation, churning, and peristalsis of food

venule

delivers nutrient rich blood to the liver

arteriole

delivers oxygen rich blood to the liver

cystic duct

draining the gallbladder

hepatic duct

draining the liver

pancreatic duct

draining the pancreas

Bile salts

emulsify fats

What are the two important ligaments on the liver?

falciform and round ligaments.

Filiform

file-like, small and sharp

common bile duct

hepatic, cystic, pancreatic ducts drain into this

Muscularis

in most of the GI tract, this consists of smooth muscle in two sheets: - an inner sheet of circular fibers - an outer sheet of longitudinal fibers

duodenum

initial segment; receives the secretions of the pancreas, liver, and gall bladder.

Rugae

internal stomach folds

Bilirubin

is a bile pigment formed from the breakdown of red blood cells

Vitamin K

is needed to make clotting proteins

What is the problem with aspirin?

it disassociates with the stomach cells, causing acid conditions that can injure the stomach lining, producing ulcers.

What does the pancreas secrete?

it secretes the entire array of digestive enzymes, capable of chemically digesting all four classes of organic macromolecules

Circumvallate

large and round, holds tastebuds

What is each liver lobe composed of?

liver lobules

Parietal cells

makes HCl (hydrochloride acid) - has a pH of 2!!

jejunum

middle segment

Fungiform

mushroom-like, small and round, holds tastebuds

Mouth

oral cavity

root canal therapy

removal of infected or damaged pulp tissue, the pulp cavity is filled with inert material and the tooth is capped

Enterendocrine cells

secrete hormones that affect other digestive system organs ex.) gastrin causes smooth muscle contractions in the small and large intestine

Mucous neck cells

secrete mucous

Chief cells

secrete pepsinger, a precursor to pepsin, that begins protein digestion

bile duct

secretes bile from the liver

falciform

separates the left and right lobes

ileum

terminal segment; empties into the large intestine at the ileocecal sphincter

What is the primary site for chemical digestion in the GI tract?

the duodenum

Third cell type found in pancreas?

the epithelial cells that line the ducts. these cells secrete bicarbonate ions that makes pancreatic juice alkaline

Mucosa

the inner layer is a mucous membrane that lines the entire tract

Serosa (peritoneum)

the outer layer is a serous membrane that secretes serous fluid

Why does the muscularis of the stomach differs from the rest of the GI tract?

there is an additional oblique layer that acts to increase the churning force for mechanical digestion

Teeth

these are skeletal system structures located in sockets of the mandible and maxillary bones. They consist of: a.) enamel - hardest substance in body b.) dentin - primary substance c.) an inner pulp cavity - blood vessels and nerves

Liver's digestive function

to produce bile, which emulsifies fat.

Stomach's functions

two main functions: 1) stores food, 2) mechanical digestion (some chemical digestion).