Anatomy Digestive - chap 25

8/7/2019 Anatomy Digestive - chap 25

http://slidepdf.com/reader/full/anatomy-digestive-chap-25 1/34

The Digestive SystemThe Digestive System

Chapter 25Chapter 25



Function of the Digestive System

To break down food into a ³usable´

(absorbable) form

To supply our cells with the nutrients they

need for energy, growth & repair



Organs of the Digestive System

Gastrointestinal tract (GIT) ± continuous

passageway which contains the food from the time

it enters the body, until it leaves; organs include:

mouth (oral cavity), pharynx, esophagus, stomach,small intestine, large intestine, rectum, anus

Accessory organs - participate in digestive

processes; organs include:

teeth, tongue, salivary glands, liver, gall bladder,

pancreas



Processes of Digestion

1. Ingestion

2. Movement along GIT

Voluntary ± e.g. swallowing

Involuntary ± e.g. peristalsis

3. Secretion ± release of water, enzymes, acids,

buffers, mucous, etc. into GIT for physical(mechanical) & chemical digestive processes



Processes of Digestion4. Digestion

Mechanical processing ± physical breakdown

of food; e.g. mastication, emulsification, mixing

waves, segmentation

Chemical digestion ± chemical breakdown of food; disassembling of organic molecules into

their component parts; requires enzymes

carbohydrates disaccharides monosaccharides

proteins amino acids

lipids fatty acids & monoglycerides



Processes of Digestion

5. Absorption ± movement of nutrients from GIT into

blood capillaries (monosaccharides, amino acids,

H2

O, vitamins, minerals) or lymphatic capillaries

(fatty acids)

6. Excretion (Defecation) ± removal of waste

products from GIT



Histology of the GIT

epithelium ± stratified squamous or simple

columnar

lamina propria ± loose CT

muscuaris mucosa ± smooth muscle

Mucosa

Submucosa

Loose CT with

BV¶s, nerves &

lymphatics

Muscularis externa

Skeletal muscle at beginning & end of GIT, smooth muscle (inner circular;

outer longitudinal layer) from lower

esophagus to rectum

Serosa (a.k.a.

viseral peritoneum)

4 layers of tissue surround the

lumen of the GIT



Peritoneum & Mesenteries

The abdominal cavity is lined with parietalperitoneum & many of the organs within are

covered with visceral peritoneum

Folds of peritoneum called ³mesenteries´ attachsome organs to others

greater omentum

lesser omentum mesentery proper

mesocolon



Mouth (oral cavity) Regions include the vestibule & oral cavity proper

Roof comprised of hard & soft palate; floor primarily comprised of tongue

Mucosa of stratified squamous epithelium

(non-keratinized)

Joins to the oropharynx at the fauces



Tongue ±

stratified sqamous epith. over skeletal muscle

intrinsic & extrinsic muscles

papillae

filiform

fungiform

circumvallate



taste buds



Parotid

gland

Submandibular

gland

Sublingual

gland

Salivary glands ±

secrete saliva ± made

of H2O, salts &

³salivary amylase´

Parotid duct

Submandibular duct



Teeth ± involved in ³mastication´

2 sets of teeth ± deciduous & permanent

4 types of teeth ± incisors, cuspids

(canines), bicuspids (premolars), molars



Parts of a tooth ±

crown ± dentin surrounded by

enamel, has hollowed pulp cavity

filled with CT pulp

neck ± at gingival border

root ± within mandible & maxilla,

has hollowed root canal with BVs

& nerves, root canal opens atapical foramen



Pharynx

nasopharynx

uvula

oropharynx

epiglottis

laryngopharynx

Common passageway for air & food

oropharynx & laryngopharynx lined withstratified squamous epithelium (nasopharynx

lined with PSCC)

uvula & epiglottis protect airway when

swallowing (³deglutition´)



Esophagus muscular tube running from pharynx, posterior to trachea, down thoracic

cavity, through ³esophageal hiatus´ of diaphragm, to lower esophageal (a.k.a.

cardiac) sphincter at junction of stomach

functions in ³deglutition´ through action of peristalsis

mucosa is stratified squamous epithelium

variations in muscularis externa ± begins as skeletal muscle at upper 1/3,mixed skeletal & smooth muscle in middle, smooth muscle by lower 1/3



Stomach - Gross Anatomy

Lower esophageal (car diac) sphincter

Pyloric sphincter



Stomach - Histology

Rugae ± folds of mucosa & submucosa to allow

for expansion of stomach

Mucosa of simple

columnar epithelium with

mucous cells

Gastric pit leading to

gastric glands



Stomach ± Histology (cont)

- Secrete mucus to protect

epithelial cells from enzymes

& acid

- Secrete HCl (for protein

digestion) & intrinsic factor

(for B12 absorption)

- Secrete pepsinogen which

gets converted to ³pepsin´

whenmixed with HCl; for

protein digestion

- Secrete gastrin to regulate

stomach emptying

Entero-





Small Intestine - Anatomy- connects stomach to large intestine; 15-20¶ long; 1´ diameter; held

together in abdominal cavity by ³mesentery proper´

- site for completion of chemical digestion & absorption of nutrients

- comprised of three regions:

Duodenum ± 10´ in length;

receives chyme from

stomach, secretions from liver, gallbladder & pancreas

Jejunum ± 8¶ long; most

digestion & absorption

occurs here

Ileum ± 12¶ long; connects to

cecum of large intestine at

iliocecal valve (sphincter )



Small IntestineModifications in mucosa & submucosa of intestinal wall designed to

increase functional surface area:

Plicae

cir culares

Plicae cir culares (circular folds) ±

large transverse ridges; most abundant in

jejunum

Villi ± small finger-like projections of

mucosal folds across surface of intestine



Small IntestineVilli

Villi lined with ³absorptive cells´ - mucosal epithelium of simple columnar

epithelium with microvilli ³brush border´

Submucosa of each villus contains a capillary network & a ³lacteal´

(lymphatic capillary) for absorption of nutrients

Intestinal crypts

containing

intestinal glands

Intestinal glands within intestinal crypts secrete ³intestinal juice´ ± provides

watery medium to keep enzymes & digestive products in solution for help withabsorption



Pancreas

Stomach

Head

Body

Tail

Retroperitoneal elongated

organ

Both endocrine (pancreaticislets of Langerhans ±

secretes insulin & glucagon)

& exocrine gland (pancreatic

acini ± secretes pancreatic

juice)

Pancreatic

duct

Duodenum



PancreasPancreatic juice ± mixture of enzymes & buffers (sodium

bicarbonate) secreted by acinar cells into pancreatic duct &released into duodenum

pancreatic amylase

Starch maltose

lipase

Lipids fatty acids + monoglycerol

proteases (trypsin, chymotrypsin, carboxypeptidase)

Proteins & polypeptides small peptides

tri & dipeptides nucleases ± digest RNA & DNA

sodium bicarbonate ± neutralizes acidic chyme

because enzymes in small intestine need an alkaline pH



Liver - Anatomy Largest organ within the body

Comprised of 4 lobes:

Large right & left lobes divided by falciform ligament;

small caudate (by IVC) & quadrate (by gall bladder ) lobes

falciform ligament continues at inferior margin as

ligamentum teres (round ligament) (remnant of umbilical

vein) Lobes of liver functionally divided into microscopic lobules



Liver - Histology Lobules comprised of rows of Hepatocytes arranged radially around a

central vein

Hepatocytes surround blood sinusoids (capillary structures) which are

partially lined with phagocytic Kupffer (aka stellate reticuloendothelial) cells

hepatocytes central vein sinusoids



Liver Hepatocytes produce bile, which gets secreted into bile

canaliculi of lobule

Bile canaliculi merge to form bile ducts which eventually

merge to create the right & left hepatic ducts



Liver & gall bladder

Right & left hepatic ducts unite to form common hepatic duct

which merges with cystic duct of gall bladder to form commonbile duct which joins with pancreatic duct & enters the

duodenum

Gall bladder ± hollow

muscular sac under right lobeof liver; stores &

concentrates bile; releases

bile through cystic duct

Bile released into duodenum

functions in emulsification of lipids,

absorption of fats (due to presence

of bile salts), & excretion of bilirubin

Left hepatic ductRight hepatic duct



Pancreatic & bile ducts

Stomach

Body

Tail

Head Pancreatic

duct

Accessory

pancreatic duct

Common bile duct



Liver - FunctionsThe liver has over 200 functions including (but not limited to):

Bile production & excretion

Metabolic regulation ±

storage of glycogen, fatty acids, fat-soluble vitamins &

minerals

interconversion of nutrients (³gluconeogenesis´)

detoxification & removal of drugs, toxins & hormones

hematological regulation ±

phagocytosis of worn-out RBCs, bacteria & other

pathogens

synthesis of plasma proteins



Blood Supply to Liver

In order for the liver to perform all of its functions, it receivesblood through 2 vessels:

Hepatic artery - delivers oxygenated blood into sinusoids of

liver

Hepatic Portal vein ± delivers de-oxygenated, nutrient-richblood from digestive organs to sinusoids of liver

Liver uses O2

& nutrients within blood of sinusoids & then blood

drains into central veins of lobule which merge to form the

hepatic veins, which drain into the IVC



Large Intestine- Begins at the ilium & ends at the anus; 5¶ long; 3´ in diameter

- main functions ± H2O reabsorption; absorption of some vitamins & minerals;

formation & temporary storage of fecal material

Rectum

ileumIleocecal sphincter

Cecum

Ver mifor m appendix

Ascending

colon

Transverse

colon

Descending

colon

Sigmoid colon

Anal canal

Rectum

Rectum

Internal anal

sphincter

External analsphincter

Anal canal

Anus

- no chemical (enzymatic) digestion

but some bacterial

- 3 regions: cecum, colon, rectum

Hepatic (rt.

Colic) flexure Splenic (lt. colic) flexure



Large IntestineModifications in muscularis externa & serosa ±

longitudinal muscle layer forms bands called ³taeniae coli´ which create puckersknown as ³haustra´

serosa forms ³epiploic appendages´

haustra

taeniae coli

epiploic appendages

THE END (literally!)

Documents

Anatomy Digestive - chap 25