student.ccbcmd.edu

TOPIC 8Digestive System

Chapter 18pp. 651-677

Biology 221Anatomy & Physiology II

E. Lathrop-Davis / E. Gorski / S. Kabrhel

Digestive System Functions• Provide nutrients in usable form• Remove unusable wastes

Digestive System Overview Two main groups of organs:• Alimentary canal (a.k.a. Gastrointestinal tract)

– tube through which food passes– responsible for digestion and absorption of food– mouth, pharynx, esophagus, stomach, small

intestines, large intestines• Accessory organs

– organs, glands and structures which aid digestion but not part of GI tract itself

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

Fig. 24.1, p. 888

Processes of Digestion• Ingestion – entrance of food and drink into mouth• Mechanical digestion – physical breakdown into smaller

pieces• Propulsion – movement through gut• Chemical digestion – breakage of molecules into smaller

compounds• Absorption – uptake of nutrients from lumen• Defecation – removal of indigestible material

Fig. 24.2, p. 889

Peritoneum• Serous membrane• parietal peritoneum – lines abdominal cavity

– organs posterior to the parietal peritoneum are retroperitoneal

• visceral peritoneum (serosa)– covers surfaces of most abdominal organs– Mesenteries – double layer of peritoneum

extending from body wall to digestive organs– intraperitoneal organs are those in mesentaries

• Peritoneal cavity – fluid-filled “space” between visceral and parietal peritoneum

• Peritonitis – inflammation of the peritoneumSee also Fig. 24.5, p. 891 Fig,. 24.30, p. 929

Splanchnic CirculationArteries serving the digestive organs:• Celiac Trunk – very short; gives rise to:

– hepatic artery – liver; gall bladder; stomach; duodenum

– left gastric artery – stomach; inferior esophagus– splenic artery – spleen; stomach; pancreas

• Superior Mesenteric Artery – small intestines; most of large intestine; pancreas

• Inferior Mesenteric Artery – large intestine

Fig. 20.22, p. 759

Fig. 20.22, p. 761

Hepatic Circulation: Hepatic portal system

• Veins draining digestive organs and carrying nutrient-rich blood to liver– gastric vein – drains stomach– superior mesenteric vein – drains small intestine– splenic vein – drains spleen

° inferior mesenteric vein – drains large intestine• Venous blood from hepatic portal system mixes with

arterial blood (hepatic artery) in liver

Fig. 20.27, p. 771

Hepatic Circulation: Hepatic Veins • drain venous blood from liver into inferior vena cava

Fig. 20.27, p. 771

Mucosa• Mucous membrane lining gut• Consists of:

– epithelium – lining – lamina propria – areolar connective tissue layer– muscularis mucosae – smooth muscle

http://www.usc.edu/hsc/dental/ghisto/gi/d_1.html












Mucosa: Epithelium• Type varies depending on location

– stratified squamous epithelium found in mouth, esophagus and anal canal

– simple columnar epithelium found in stomach and intestines

• Secretes mucus, digestive enzymes, hormones• Provides intact barrier to protect against entry of

bacteria

http://www.usc.edu/hsc/dental/ghisto/gi/c_2.html
























Mucosa: Lamina Propria• Layer of areolar connective tissue• Blood capillaries nourish epithelium, absorb and

transport digested nutrients• Lymphatic capillaries provide drainage for interstitial

fluid and transport fats to venous circulation













Mucosa: Muscularis Mucosae• Smooth muscle used for local movement and to hold

mucosa in folds (small intestine)

http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab19/EXAMPLES/Exileum.htm











Submucosa• Dense connective tissue superficial to mucosa• Highly vascularized• Many lymphatic vessels• Lymph nodules

– MALT = mucosa-associated lymphatic tissue– especially in small (Peyer’s Patches) and large

intestineshttp://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab19/EXAMPLES/Exileum.htm











Muscularis Externa (Muscularis)• Two layers in most organs (3 in stomach)

– circular layer– longitudinal layer

• Peristalsis moves material through gut• Segmentation helps mix material with digestive

enzymes in small intestine

Fig. 24.3, p. 890

Serosa• Visceral peritoneum – simple squamous epithelium

(mesothelium) with areolar CT• Adventitia – dense connective tissue covering without

epithelium; found around esophagus• Retroperitoneal organs have both a serosa (of parietal

peritoneum) and adventitia (on side abutting body wall)

Enteric Nervous SystemIntrinsic nerve plexuses:• Enteric neurons

– neurons able to act independently of central nervous system

– communicate with each other to control GI activity• Two main enteric plexuses:

– submucosal nerve plexus – regulates glands in submucosa and smooth muscle of muscularis mucosae

– myenteric nerve plexus – regulates activity of muscularis externa (with aide of submucosal nerve plexus)

Central Nervous System Control• Enteric nerve plexuses linked to CNS by visceral

afferent (sensory) fibers• Digestive system receives motor input from

sympathetic and parasympathetic divisions of autonomic nervous system– parasympathetic outflow generally increases

activity– sympathetic outflow generally decreases activity

Mouth (Oral Cavity)• Oral oriface is anterior opening• Mouth is continuous with oropharynx• Lips and cheeks keep food in oral cavity• Three layers of tissue:

– mucosa (stratified squamous epithelium)– submucosa– muscularis externa (skeletal muscle)

Mouth: Palate• Hard palate

– palatine process of maxilla– palatine bones

• Soft palate – muscle only– prevents food from entering nasopharynx during

swallowing– uvula (part that hangs down in middle)

Fig. 24.7, p. 895

Mouth: Arches

• Palatoglossal arch – anchors soft palate to tongue

• Palatopharyngeal arch anchors soft palate to wall of oropharynx

• Fauces – area between arches– palatine tonsils – located in fauces

Fig. 24.7, p. 895

Mouth: Tongue• Lingual tonsil – sits at base of tongue; protects against

invasion by bacteria• Taste buds

– contain receptors for taste– found in some papillae

Fig. 24.8, p. 896

Mouth: Tongue• Tongue forms bolus

– ball of food– makes food easier to swallow– keeps food between teeth

• Muscles – served by nerve XII– intrinsic muscles – within tongue (not attached to

bone); allow tongue to change shape for swallowing and speech

– extrinsic muscles – attach to bone or soft palate; alter tongue position (protrusion, retraction, side-to-side)

Fig. 24.7, p. 895

Salivary Glands• Produce saliva• Two groups of salivary glands

– intrinsic glands (buccal glands) – within oral cavity– extrinsic glands – 3 pairs (see A&P I Unit VI for

innervation)° parotid glands (connected to oral cavity by

parotid duct; mumps is a viral infection of the parotid glands)

° sublingual glands° submandibular glands

Fig. 24.9, p. 897

Saliva• Mucus cells produce mucus (less common)• Watery saliva produced by serous cells; composition:

– 97-99.5% water– slightly acidic (pH ~ 6.8)– electrolytes (ions such as Na+, K+, Cl-, PO4

=, HCO3-)

– metabolic wastes (urea, uric acid)– proteins

Salivary Proteins• Mucin – glycoprotein portion of mucus that lubricates

oral cavity)• Lysozyme – antibacterial• IgA – antibodies that prevent antigens from attaching

to mucus membrane• Defensins – secreted by neutrophils; act as local

antibiotic and chemotatic agent when mucosa is damaged

• Salivary amylase – hydrolyzes starch

Control of Salivation• Sympathetic division

– stimulates production of mucin-rich saliva, or– inhibits salivation altogether at high levels

Control of Salivation• Parasympathetic division of ANS stimulates activity

– chemoreceptors (excited most by acidic substances) and baroreceptors (excited by mechanical stimuli) send messages to salivatory nuclei in pons and medulla

– parasympathetic motor output results in salivation– psychological control – response to visual,

olfactory stimuli, even thoughts of food– salivary nuclei are stimulated by irritation to lower

GI tract• Parasympathetic nerves

– facial – to submandibular, sublingual– glossopharyngeal – to parotids

Teeth• Lie in alveoli of mandible and maxilla (see A&P I

axial skeleton lab)• Primary dentition = deciduous teeth (20 milk or baby

teeth)– roots are absorbed as permanent teeth grow in,

causes baby teeth to fall out

Fig. 24.10, p. 899

TeethPermanent dentition = adult teeth (32)• 8 Incisors (central and lateral)• 4 Canines (eyeteeth)• 8 Bicuspids = premolars• Molars

– 4 first molars– 4 second molars– 4 third molars

° wisdom teeth° may become impacted as grow in

Fig. 24.10, p. 899

Fig. 24.11, p. 900

Tooth Structure• Crown - covered by enamel (hardest substance in

body); underlain with dentin• Neck• Root

– cementum – calcified connective tissue covering dentin of root; attaches root to periodontal ligament which anchors tooth to alveolus

– no enamel (dentin is under cementum)– pulp cavity – houses blood vessels and nerves that

enter/leave via apical foramen in the root canal

Pharynx• Only oropharynx and laryngopharynx are involved in

digestion (nasopharynx is only respiratory)• Lined with nonkeratinized stratified squamous

epithelium• Mucus-producing glands in submucosa produce

mucus that lubricates food• Skeletal muscle responds to somatic reflexes to move

food quickly past laryngopharynx• No serosa or adventitia

Esophagus• Runs from laryngopharynx through mediastinum to

stomach• All 4 layers present in wall

– Mucosa – consists of stratified squamous epithelium

– Submucosa – mucus-secreting esophageal glands













Esophagus• Muscularis – changes type as goes down

– top 1/3 – skeletal muscle– middle 1/3 – mix– bottom 1/3 – smooth muscle

• Adventitia – dense connective tissue covering

























Structures Associated with the Esophagus

• Upper esophageal sphincter – controls movement of material from pharynx into esophagus

• Esophageal hiatus – opening in diaphragm that allows esophagus to pass from thoracic cavity into abdominal cavity

• Gastroesophageal (cardiac) sphincter– thickening of smooth muscle of inferior

esophagus– aided by diaphragm to close bottom of esophagus– helps prevent reflux of acidic gastric juice

Esophageal Disorders• heartburn – failure of lower esophageal sphincter to

close completely allowing acidic gastric juice into esophagus

• hiatus hernia – protrusion of the superior portion of stomach above diaphragm

• esophageal ulcer – erosion of wall due to chronic reflux of stomach acid

Digestive Processes in Mouth, Pharynx and Esophagus

• Ingestion• Mechanical Digestion

– mastication by teeth (with aid of tongue)– formation of bolus

• Chemical digestion by salivary amylase produced by salivary glands– breaks starch and glycogen into smaller fragments

(including maltose [disaccharide] if left long enough)

– continues activity until reaches acid stomach• Absorption – essentially none (except some drugs,

e.g., nitroglycerine)

Digestive Processes in Mouth, Pharynx and Esophagus

• Movement – deglutition (swallowing)– moves food from oral cavity to stomach– voluntary in oral cavity (buccal phase)– reflexive in pharynx– involuntary peristalsis where smooth muscle is found

Fig. 24.13, p.904

Stomach: Gross Anatomy• Cardiac region (cardia)• Fundus - temporary storage area• Body

– greater curvature– lesser curvature

• Pyloric region – distal portion– Pyloric sphincter – controls movement of chyme into

small intestine

Fig. 24.14, p. 905

http://medlib.med.utah.edu/WebPath/GIHTML/GI194.html






















Stomach Histology• Mucosa

– simple columnar epithelium– muscularis mucosae throws mucosa into folds called

rugae• Submucosa – connective tissue• Muscularis – 3 layers create mixing waves in addition

to peristalsis– longitudinal layer– circular layer– oblique layer

• Serosa - covers stomach

http://www.gutfeelings.com/STOMACH.HTMLFig. 24.14, p. 905

http://www.gutfeelings.com/STOMACH.HTML

Microscopic Anatomy• Surface composed mainly of goblet cells (secrete

mucus)• Gastric pits

– tight junctions between epithelial cells prevent acidic gastric juice from reaching underlying layers

– contain gastric glands which secrete gastric juice° mucus neck cells° parietal (oxyntic) cells° chief (zymogenic) cells° enteroendocrine cells


Fig. 24.15, p. 906












Gastric Pit Cells• Mucous neck cells secrete bicarbonate-rich mucus• Parietal (oxyntic) cells secrete:

– HCl (buffered by bicarbonate rich mucus)– intrinsic factor (essential to absorption of Vit. B12

by small intestine)• Chief (zymogenic) cells secrete:

– pepsinogen (inactive form of the protease pepsin for protein hydrolysis)

– minor amounts of lipases (lipid hydrolysis)

Gastric Pit Cells• Enteroendocrine cells – release hormones and

hormone-like products into the lamina propria where they are picked up by blood and carried to other digestive organs– gastrin – generally stimulatory– histamine – stimulates H+ secretion– somatostatin – generally inhibitory

Digestive Processes in Stomach• Mechanical digestion

– mixing waves help break food into smaller particles

• Chemical digestion – produces chyme (pH ~ 2)– acid (HCl) secreted by parietal cells breaks some

bonds and activates pepsinogen into pepsin– pepsin –

° produced as pepsinogen by chief cells ° hydrolyses proteins

– rennin – protease secreted in children that acts on milk proteins

Digestive Processes in Stomach• Movement

– mixing waves mix food with acid and enzymes– peristalsis moves material through stomach and

into small intestine• Absorption – limited to lipid soluble substances

– alcohol– aspirin– some other drugs

Regulation of Gastric SecretionControlled by nervous system and hormones• Hormonal control

– gastrin stimulates secretion– somatostatin, gastric inhibitory protein (GIP), and

cholecystokinin inhibit secretion• Neural control:

– autonomic control (CNS)° parasympathetic division

- Vagus (X) nerve° sympathetic division - thoracic spinal nerves

– local enteric nerve reflexes ° distension of stomach stimulates activity° distension of duodenum inhibits activity

See Fig. 24.16, p. 910

Fig. 24.16, p. 910

Stimulation of Gastric Secretion• Cephalic Phase (cerebral)

• Gastric Phase (stomach)

• Intestinal Phase (duodenum)

Fig. 24.16, p. 910

Inhibition of Gastric Secretion• Cephalic Phase (cerebral)

• Gastric Phase (stomach)

• Intestinal Phase (duodenum)

Gastric Disorders• Gastritis – inflammation of underlying layers of wall• Gastric ulcers – erosions of stomach wall

– Helicobacter infections associated with ~90% of all ulcers (uncertain as to whether it is causitive agent)

– non-infectious ulcers associated with persistent inflammation

Gastric Disorders (con’t)• Emesis = vomiting

– usually caused by ° extreme stretching of stomach or small intestine,

or ° presence of irritants in stomach (e.g., bacterial

toxins, excessive alcohol, spicy foods, certain drugs)

– emetic center in medulla initiates impulses to ° contract abdominal muscles (increases intra-

abdominal pressure)° relax cardiac sphincter° raise soft palate (closes off nasal passages)

– excessive vomiting results in dehydration and metabolic alkalosis (increased blood pH)

Small Intestine: Gross Structure• Diameter ~ 2.5 cm• Length ~ 2-4 m (8-13’) (in cadaver, 6-7 m [20-

21’] because muscle is not contracted)• Small intestine designed for secretion (especially

proximal end) and absorption – site of most chemical digestion– site of most absorption

• pH 7-8• Three areas:

– duodenum (25 cm)– jejunum– ileum

Fig. 24.21, p. 916

Small Intestine: Duodenum• Receives chyme from stomach• Hepatopancreatic ampulla

– union of common bile duct and pancreatic duct– opens via major duodenal papilla– hepatopancreatic sphincter (sphincter of Oddi)

controls entry of fluid from ampulla• Duodenal (Brunner’s) glands – secrete alkaline

mucus

Fig. 24.20, p. 915













Small Intestine: Jejunum & Ileum• Jejunum

– extends from duodenum to ileum• Ileum

– extends from jejunum to large intestine– ileocecal valve controls movement of material into

large intestine

























Small Intestine: Innervation• Parasympathetic impulses supplied by Vagus nerve

stimulates activity• Sympathetic impulses supplied by thoracic

splanchnic nerves inhibit activity• Enteric nerves act locally

Fig. 14.5, p. 519

Fig. 14.4, p. 517

Small Intestine: Blood Supply• Arteries:

– common hepatic artery serves duodenum– superior mesenteric artery serves most of small

intestine

• Veins:– superior mesenteric vein drains entire small

intestine

Fig. 20.22, p. 761

Fig. 20.27, p. 771

Small Intestine: Overview ofSpecial Anatomical Features

• Plicae circularis – circular folds

• Villi – fingerlike projections of intestinal wall

• Microvilli – projections of cell membranes

See Fig. 24.21, p. 916


http://remf.dartmouth.edu/images/humanMicrovilliTEM/source/1.html






















http://www.shu.edu/ha/imgs/00000/8000/700/8754.jpg


Fig. 24.21, p. 916

Small Intestine: Plicae Circularis • Circular folds• Deep, permanent folds of mucosa and submucosa• Force chyme to spiral through lumen

– mixes chyme with intestinal juice– slows movementWhy is this helpful?

http://www.udel.edu/Biology/Wags/histopage/colorpage/csi/csiipcv.gif

http://www.shu.edu/ha/anirefs/8751.htm














Small Intestine: Villi• Finger-like projections of mucosa (over 1 mm tall)• Each villus contains:

– blood capillary bed– lacteal– smooth muscle - allows villus to shorten

° increases contact between villus and “soup” in lumen

° “milks” lacteal

See also Fig. 24.22, p. 917;Fig. 24.21, p. 916

http://www.udel.edu/Biology/Wags/histopage/colorpage/csi/csiivgc.GIF

http://www.udel.edu/Biology/Wags/histopage/colorpage/csi/csivv.GIF



























Fig. 24.21, p. 916

Small Intestine: Microvilli• Extensions of cell membrane• Called brush border• Functions:

– secrete brush border enzymes– increase surface area for absorption

See also Fig. 24.22, p. 917











Small Intestine: Mucosa• Renewed every 3-6 days• Simple columnar epithelium

– goblet cells – secrete mucus– absorptive cells – absorb nutrients

° bound by tight junctions° microvilli

• Lamina propria– blood vessels– lacteals

• Intestinal crypts (crypts of Lieberkuhn) – between villi– most cells secrete intestinal juice– Paneth cells secrete lysozyme (antibacterial)

See Fig. 24.21, p. 916


http://www.udel.edu/Biology/Wags/histopage/colorpage/csi/csidmbg.GIF












Small Intestine: Submucosa• Peyer’s patches – lymphatic tissue for protection

against disease• Duodenal (Brunner’s) glands

– secrete alkaline mucus rich in bicarbonate to raise pH of chyme from <3 to >7

– only in duodenum


http://medicine.ucsd.edu/pathology/~som213/HistologyImageBank/chapter_4/slide_61_peyers/pages/a.4.61.1.1.htm
























Small Intestine: Muscularis & Serosa • Muscularis – two layers of smooth muscle create two

kinds of movement– peristalsis moves chyme through intestine– segmentation mixes chyme with intestinal juice

° moves between segments a few cm at a time° intrinsic control in longitudinal muscle

(intrinsic pacemaker cells)– intensity altered by nervous system and hormones

° parasympathetic impulses increase strength of contraction

° sympathetic impulses decrease it

Small Intestine: Muscularis & Serosa • Serosa (visceral peritoneum) – outer covering

– Mesenteries ° visceral peritoneum° attach small intestine to posterior body wall

– Intraperitoneal organs - surrounded and supported by mesenteries

Small Intestine: Digestive Processes• Mechanical digestion – bile salts secreted by liver

(stored in and released from gall bladder) emulsify fat globules (make them into smaller droplets) to increase surface area lipases have available to work on

• Chemical digestion – hydrolysis of macromolecules– lipid digestion– protein digestion– carbohydrate digestion– nucleic acid digestion

See Fig. 24.33, p. 933

Small Intestine: Lipid Digestion• Pancreatic lipase• Most common lipids are neutral fats (triglycerides)

– glycerol + 1 fatty acid = monoglyceride– glycerol + 2 fatty acids = diglyceride– glycerol + 3 fatty acids = triglyceride

• Triglycerides cleaved into glycerol and 3 fatty acids or monoglycerides and 2 fatty acids

Fig. 2.14, p. 48

Small Intestine: Protein Digestion• Pancreatic and intestinal proteases break proteins into

amino acids• Pancreatic proteases: trypsin, chymotrypsin and

carboxypolypeptidase– secreted as inactive precoursers (trypsinogen,

chymotrypsinogen, and procarboxypolypeptidase, respectively) to protect intestinal mucosa from being digested

– cleave large proteins into small peptides• Intestinal proteases

– include aminopeptidase, carboxypeptidase, dipeptidase

– cleave small peptides into amino acidsSee Fig. 2.17, p. 52

Small Intestine: Carbohydrate Digestion

• Starches – cleaved into short chains (oligosaccharides) and maltose (disaccharide) by pancreatic amylase secreted by pancreas

• Disaccharides hydrolyzed by intestinal (brush border) enzymes:– maltase – cleaves maltose– lactase – cleaves lactose– sucrase – cleaves sucrose

Fig. 2.13, p. 46

Small Intestine: Nucleic Acid Digestion

• Pancreatic nucleases – cleave nucleic acids into nucleotides

• Nucleosidases and phosphatases – cleave nucleotides into sugars, phosphates, bases

Fig. 2.22, p. 58

Small Intestine: Absorption of Carbohydrates

• Absorption moves nutrients from lumen into cells, thence into interstitial fluid to blood or lymph

• Carbohydrates – absorbed as monosaccharides by:– cotransport with Na+ (based on setting up Na+

gradient using active transport; glucose and galactose)

– facilitated transport (fructose)

Small Intestine: Absorption of Proteins and Nucleic Acids

• Proteins – absorbed as amino acids– cotransport with Na+ (based on setting up Na+

gradient using active transport)– proteins rarely taken up intact (absorbed peptides

may cause food allergies)• Nucleic acids – actively absorbed as components:

sugar (ribose/deoxyribose), phosphate, nitrogen bases

Small Intestine: Absorption of Lipids

• Lipids– combine with bile salts to form micelles– absorbed passively through lipid bilayer as glycerol

and fatty acids or monoglycerides – combine with proteins within cell to form

chylomicrons which are then released into interstitial fluid

° chylomicrons enter lymph through lacteals (lymphatic capillaries) in villi and are transported to subclavian veins

Small Intestine: Absorption of Vitamins

• Fat-soluble vitamins (DAKE) incorporated into micelles and absorbed in same manner as fats (passively through lipid bilayer)

• Water-soluble vitamins (C, B complex) mostly absorbed by diffusion– exception is B12, which must bind to intrinsic

factor produced in stomach to be actively absorbed in ileum (recognition of B12-intrinsic factor

complex by receptors in plasma membrane of cells triggers active receptor-mediated endocytosis)

Small Intestine: Absorption of Electrolytes

• Most actively absorbed throughout small intestine– absorption based on how much is in food– Na+/K+ pump plays role (Na+ into/ K+ out)– K+ passively absorbed based on gradient created by

pump• Iron (Fe) and calcium (Ca) only absorbed in

duodenum– depends on needs of body– iron actively transported into cells where it

becomes bound to ferritin– calcium absorption regulated by vitamin D which

serves as cofactor in Ca transport

Small Intestine: Movement• Peristalsis moves chyme through intestine• Segmentation mixes chyme with intestinal juice

Fig. 24.3, p. 890

Hormonal Control of Small Intestine Activity

Gastrin – secreted by stomach – stimulates contraction of intestinal smooth muscle– stimulates relaxation of ileocecal valve

Vasoactive intestinal peptide (VIP) – from duodenum; acts on duodenum– stimulates secretion of bicarbonate-rich intestinal

juiceSomatostatin – from stomach and duodenum

– inhibits blood flow and absorption from small intestine

Nervous System Control of Small Intestine Activity

• Sympathetic impulses decrease activity• Gastroileal reflex – initiated by increased activity in

stomach– long reflex involving brain and parasympathetic

innervation– parasympathetic impulses increase activity

Accessory Glands: Liver Gross Anatomy

• Largest gland in body, approximately 1.4 kg• Upper right hypochondriac and epigastric regions• 4 primary lobes: right, left, caudate, quadrate• Covered by serosa except for uppermost region just

under diaphragm

Fig. 24.1, p. 888See Fig. 24.23, p. 919http://telpath2.med.utah.edu/WebPath/LIVEHTML/LIVER002.html

http://telpath2.med.utah.edu/WebPath/LIVEHTML/LIVER002.html







Liver: Hepatic Ducts• Right hepatic duct – serves right lobe• Left hepatic duct – serves other lobes• Common hepatic duct

– formed from union of right and left hepatic ducts– joins with cystic duct of gall bladder to form

common bile duct, which joins with pancreatic duct to form hepato-pancreatic ampulla

Fig. 24.20, p. 915

See Fig. 24.23, p. 919

Liver: Ligaments• Falciform ligament

– piece of mesentery that separates right and left lobes

– suspends liver from diaphragm and anterior abdominal wall

• Round ligament (= ligamentum teres) – remnant of umbilical vein

• Ligamentum venosum – remnant of ductus venosus


http://storm.aecom.yu.edu/virtualDissector/New_online_dissector/Abdomen/Abdomen5-6/photos/STEP3/PAGES/ligamentum%20venosum_jpg.htm























Liver: Blood supply• Hepatic artery – arterial blood• Hepatic portal vein – receives nutrient-rich venous

blood from stomach, intestines, pancreas, spleen (see lab for vessels)

• Hepatic vein – drains venous blood into inferior vena cava

Fig. 20.27, p. 771

Liver: Microscopic Anatomy• Designed to filter and process nutrient-rich blood• Composed of lobules with portal triad at each corner

of hexagonal structure– branch of hepatic artery (HA)– branch of hepatic portal vein (HPV)– bile duct (BD)

Fig. 24.24, p. 921













Liver: Microscopic Anatomy (con’t)• Sinusoids – specialized capillaries in which venous

and arterial blood mix– hepatocytes (liver cells) just inside walls of

sinusoid perform functions of liver– Kupffer cells (macrophages) found along wall –

remove debris, bacteria, worn out RBCs

Fig. 24.24, p. 921

Liver: Microscopic Anatomy (con’t)• Central vein drains lobule

– join to form hepatic veins• Bile canaliculi = channels between hepatocytes

– join to form bile ducts– bile flow is counter to blood flow

Fig. 24.24, p. 921

http://www-edlib.med.utah.edu/WebPath/LIVEHTML/LIVER003.html

http://www-medlib.med.utah.edu/WebPath/LIVEHTML/LIVER003.html









Liver Functions• Process blood-borne nutrients• Store glucose (as glycogen) • Store fat-soluble vitamins• Store iron (Fe)• Detoxify poisons• Produce plasma proteins (see Topic 1)• Cleanse blood of debris, including bacteria and worn

out RBCs• Produce bile

Liver Functions: Bile• Consists of bile salts, bile pigments, cholesterol,

neutral fats, phospholipids, electrolytes in water• Aid digestion of fat

– emulsify (break up) fat globules into droplets– form micelles (ferry fats to mucosal wall)

• Conserved by enterohepatic circulation (some is reabsorbed by ileum and returned to liver via hepatic portal system)

• Main bile pigment is bilirubin– formed from breakdown of hemoglobin– metabolized by bacteria in large intestine (becomes

brown pigment)

Control of Bile Production• Stimulated by bile salts returning via hepatic portal

blood• Stimulated by secretin (hormone secreted by small

intestine in response to fats in chyme)

Fig. 24.25, p. 923

Liver Disorders/Disease• Hepatitis – inflammation of liver, often caused by

viral infection– transmitted enterically (HVA) or through blood

(HVB, HVC, HVD)– blood-borne viruses are linked to chronic hepatitis

and cirrhosis• Cirrhosis – chronic disease characterized by growth

of scar tissue• Jaundice – yellowing of skin due to build up of

bilirubin from liver disease or excessive destruction of RBCs (e.g., neonatal jaundice)

Accessory Glands: Gall Bladder• Lies in depression on ventral surface of liver• Thin-walled, muscular sac (holds about 50 ml)• Stores and concentrates bile• Releases bile via cystic duct• Histology

– mucosa – cells contain microvilli for reabsorption of water

– submucosa – dense CT – muscularis – contracts to expel bile– serosa – over ventral portion only













Control of Bile Release• Bile produced by liver backs up into gall bladder

when hepatopancreatic sphincter is closed• Gall bladder releases bile into cystic duct when

stimulated by cholecystokinin (secreted by duodenum) and/or parasympathetic impulses

• Release inhibited by somatostatin produced by stomach and duodenum

Fig. 24.25, p. 923

Disorders of the Gall Bladder• Gallstones (biliary calculi) – result from

crystallization of cholesterol due to excess of cholesterol or too little bile salts

• Obstructive jaundice – yellowish coloration of skin due to build up of bile pigments caused by blockage of bile ducts

Accessory Glands: Pancreas• Mostly retroperitoneal, head encircled by

duodenum, tail abuts spleen• Acinar cells (acini)

– secrete pancreatic juice rich in enzymes, which are stored in zymogen granules until release

– pancreatic juice excreted through pancreatic duct

• Islets of Langerhans – endocrine cells– secrete insulin, glucagon, somatostatin

See Fig. 24.20, p. 915













Composition of Pancreatic Juice• Watery, rich in bicarbonate (HCO3

-)– bicarbonate makes it alkaline and neutralizes

acidity of chyme• Digestive enzymes – see Small Intestine: Digestion

– proteases released as zymogens (inactive precursors)

° trypsin – released as trypsinogen (activated by enterokinase enzyme in brush border cells)

° carboxypeptidase & chymotrypsin – activated from precursors by trypsin

Pancreatic Enzymes (con’t)• Digestive enzymes

– amylase – hydrolyzes starch and glycogen (animal “starch”) into short carbohydrate chains and maltose

– lipases – hydrolyze neutral fats into fatty acids and glycerol (or mono- and diglycerides)

– nucleases – hydrolyze nucleic acids into nucleotides

– nucleosidases – hydrolyze nucleotides into ribose, nitrogen bases and phosphate

Control of Pancreatic Secretion• Secretin

– released from small intestine in response to acidic chyme entering duodenum

– stimulates acini to produce juice rich in bicarbonate

• Cholecystokinin – released from duodenum in response to fatty or

protein-rich chyme – stimulates acini to secrete juice rich in enzymes

• Vagus nerve – stimulates secretion during cephalic and gastric phases of digestion

Fig. 24.28, p. 925

Pancreas’ Endocrine Role: Insulin• Secreted when blood glucose increases• Lowers blood sugar by

– stimulating uptake by body cells (except liver, kidney and brain)

– stimulates glycogen formation in liver and skeletal muscle

– inhibits gluconeogenesis (conversion of fats and protein to glucose) in liver

– stimulates carbohydrate metabolism in most cells

Pancreas’ Endocrine Role: Glucagon• Secreted in response to low blood glucose• Increases blood sugar by:

– Promotes breakdown of glycogen by liver (glycogenolysis)

– Stimulates synthesis of glucose from lactic acid and noncarbohydrate sources (gluconeogenesis) by liver

– Stimulates release of glucose into blood by liver– Inhibits uptake and use of carbohydrates by

skeletal muscle

Disorders of the PancreasPancreatitis – inflammation of the pancreas• may be caused by excessive fat in blood• activation of enzymes within pancreas (pancreas

digests itself)

Large Intestine• Located primarily in abdominal cavity, distal end is in

pelvic cavity• Larger in diameter, but shorter (~1.5 m) than small

intestine• Modifications:

– teniae coli – reduction of longitudinal layer of muscularis

– haustra – pocket-like sacs formed by motor tone of teniae coli

– epiploic appendages – small, fat-filled pouches of visceral peritoneum

Fig. 24.29, p. 928

Large Intestine: Subdivisions• Cecum

– vermiform appendix• Colon

– ascending– transverse– descending– sigmoid

• Rectum

Fig. 24.29, p. 928

Large Intestine: Anal Canal• Arranged as anal columns (long folds of anal

mucosa)– composed of stratified squamous epithelium– anal sinuses secrete mucus when compressed by

feces• Sphincters control defecation

– internal anal sphincter – smooth muscle– external anal sphincter – skeletal muscle

Fig. 24.29, p. 928

Large Intestine: Histology• Mucosa – thicker than in small intestine

– crypts contain numerous goblet cells– simple columnar epi. with lots of goblet cells– stratified squamous in anal canal

• Submucosa – thinner than in small intestine– less lymphatic tissue

• Muscularis – longitudinal layer is modified as teniae coli

• Serosa – covers all but region in pelvic cavity

See Fig. 24.31, p. 930













Intestinal Flora• Resident bacteria dominated by Escherichia coli (E.

coli)• Ferment some indigestible carbohydrates

– results in mixture of irritating acids and gases• Synthesize B vitamins and vit. K

Digestion in Large Intestine

• No additional breakdown of molecules except by bacteria

• Reabsorption of water and electrolytes (very important to water and electrolyte balance)

• Absorption of vitamins produced by bacteria

Movements in Large Intestine

Formation of feces• Haustral churning

– slow process in which distention of hastrum stimulates contraction which moves food into next haustrum

– mixes food residue and aids water reabsorption • Mass peristalsis

– long, slow movements along length of large intestine force food toward rectum

– stimulated by gastrocolic reflexes based on stretching of stomach

Defecation

• Parasympathetic reflex relaxation of smooth muscle (internal) sphincter

• Voluntary relaxation of external sphincter (skeletal muscle)

Fig. 24.32, p. 931

Large Intestine: Disorders• Appendicitis – inflammation of the appendix, usually

caused by bacterial infection• Diarrhea

– watery stools due to shortened residence time– caused by irritants, bacterial or viral disease– loss of water and electrolytes can lead to

dehydration and electrolyte imbalances• Constipation

– hard stools due to increased time for water reabsorption

– can also lead to electrolyte and pH imbalances

Large Intestine: Disorders• Hemorrhoids – inflammation of the superficial anal

veins• Colitis – inflammation of the colon• Diverticulosis

– formation of small herniations in mucosa of large intestine

– common in elderly, especially those whose diets are low in bulk (fiber from fruits and vegetables provides bulk)

• Diverticulitis – inflammation of diverticula• Crohn’s disease – chronic inflammation; usually in

ileum or large intestine

student.ccbcmd.edu

Documents

Transcript of student.ccbcmd.edu