Digestive System Part Two - Linn-Bentoncf.linnbenton.edu/mathsci/bio/jacobsr/upload/Digestive System 2.pdf · Anatomy and Physiology of the Digestive System ... Blind pouch ... Anatomy

Part 2

Digestive System

Anatomy and Physiology of the Digestive System

Small intestine

Major organ of digestion and absorption

2–4 m long; from pyloric sphincter to ileocecal valve

Subdivisions

Duodenum

Jejunum

Ileum


Small intestine

Structural modifications

Villi

Intestinal glands

Mucosa

Submucosa

Figure 23.1

Mouth (oral cavity)

Tongue

Esophagus

Liver

Gallbladder

Anus

Duodenum Jejunum Ileum

Small

intestine

Parotid gland Sublingual gland Submandibular

gland

Salivary

glands

Pharynx

Stomach Pancreas (Spleen)

Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Vermiform appendix Anal canal

Large

intestine

Figure 23.22a

Vein carrying blood to

hepatic portal vessel

Muscle

layers Circular

folds

Villi

(a)

Lumen

Figure 23.22b

(b)

Absorptive cells

Lacteal

Intestinal crypt

Mucosa

associated

lymphoid tissue

Muscularis

mucosae Duodenal gland Submucosa

Enteroendocrine

cells Venule

Lymphatic vessel

Goblet cell

Blood

capillaries

Vilus

Microvilli

(brush border)

Figure 23.3b

(b)

Microvilli

Absorptive

cell


Chemical digestion in the small intestine

Food entering SI = partially digested

Intestinal juice

Water, mucous

Crypt cells produce lysozyme

Figure 23.22b

(b)

Absorptive cells

Lacteal

Intestinal crypt

Mucosa

associated

lymphoid tissue

Muscularis

mucosae Duodenal gland Submucosa

Enteroendocrine

cells Venule

Lymphatic vessel

Goblet cell

Blood

capillaries

Villus

Microvilli

(brush border)



Pancreatic juice

Enzymes

Amylase

o Carbohydates

Lipase

o Fats

Trypsinogen, chymotrypsinogen, carboxypeptidase

o Activated to digest protein

Sodium bicarbonate

Neutralize stomach acid

Figure 23.27

Stomach

Pancreas

Epithelial

cells

Trypsinogen

(inactive)

Chymotrypsinogen

(inactive)

Procarboxypeptidase

(inactive)

Trypsin

Chymotrypsin

Carboxypeptidase

Membrane-bound enteropeptidase



Bile

Emilsify lipids

Disaccharides and peptidases

Protective mucous secreted as well

Figure 23.21

Jejunum

Mucosa

with folds

Cystic duct

Duodenum Hepatopancreatic

ampulla and sphincter

Gallbladder

Right and left

hepatic ducts

of liver

Bile duct and sphincter

Main pancreatic duct

and sphincter

Pancreas

Tail of pancreas

Head of pancreas

Common hepatic duct

Major duodenal

papilla

Accessory pancreatic duct


Accessory digestive organs

Liver

Pancreas

Gallbladder



Liver

Largest internal surface area of any body organ

Blood supply

Hepatic artery

Hepatic-portal vein

Hepatic vein

Copyright © 2010 Pearson Education, Inc. Figure 19.29c

(c) The hepatic portal circulation.

Hepatic veins

Liver

Spleen

Gastric veins

Inferior vena cava

Inferior vena cava

(not part of hepatic

portal system)

Splenic vein

Right gastroepiploic

vein

Inferior

mesenteric vein

Superior

mesenteric vein

Large intestine

Hepatic portal

vein

Small intestine

Rectum

Copyright © 2010 Pearson Education, Inc. Figure 23.25c

(c)

Interlobular veins

(to hepatic vein) Central vein

Sinusoids

Portal triad

Plates of

hepatocytes

Portal vein

Fenestrated

lining (endothelial

cells) of sinusoids

Bile duct (receives

bile from bile

canaliculi)

Bile duct

Portal arteriole Portal venule Hepatic

macrophages

in sinusoid walls

Bile canaliculi



Liver

Microscopic compartments = lobules

Lined by hepatocytes = screen blood

o Store nutrients

o Manage toxins

Figure 23.24a

Sternum

Nipple

Liver

Right lobe

of liver

Gallbladder

(a)

Bare area

Falciform

ligament

Left lobe of liver

Round ligament

(ligamentum

teres)

Copyright © 2010 Pearson Education, Inc. Figure 23.25a, b

(a) (b) Lobule Central vein Connective

tissue septum



Liver

Hepatocyte functions

Process blood borne nutrients

Store fat-soluble vitamins

Perform detoxification

Produce ~900 ml bile per day

Glucose is stored as glycogen

Copyright © 2010 Pearson Education, Inc. Figure 23.21

Jejunum

Mucosa

with folds

Cystic duct



Gallbladder

Right and left

hepatic ducts

of liver



and sphincter

Pancreas

Tail of pancreas

Head of pancreas

Common hepatic duct

Major duodenal

papilla


Cystic, Hepatic and Bile ducts



Liver

Bile

Yellow-green, alkaline solution

Bile salts

o Cholesterol derivatives that function in fat emulsification and

absorption

Bilirubin

o Pigment formed from heme

Metabolized to form urobilinogen → stercobilin

Lack of bile = grayish stools with fatty streaks (Acholic feces)



Liver Other functions

Makes heparin and other plasma proteins

Stores vitamins, minerals and lipid soluble toxins

Stores nutrients

Catabolizes nitrogenous wastes



Liver

Gallbladder

Thin-walled muscular sac on the ventral surface of the liver

Stores and concentrates bile by absorbing its water and ions

Releases bile via the cystic duct

o Flows into the bile duct



Pancreas

Function

Delivers digestive fluids and NaHCO3 to duodenum via pancreatic duct

Tissue types

Endocrine

o Islets of Langerhans → insulin and glucagon

Exocrine

o Acinar tissue → pancreatic juice

Figure 23.1

Mouth (oral cavity)

Tongue

Esophagus

Liver

Gallbladder

Anus

Duodenum Jejunum Ileum

Small

intestine

Parotid gland Sublingual gland Submandibular

gland

Salivary

glands

Pharynx

Stomach Pancreas (Spleen)

Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Vermiform appendix Anal canal

Large

intestine



Pancreas

Secretion mediated by hormones

Secretin

o Released in response to acid

o Stimulates release of base

Cholecystokinin

o Released when protein and fat enter intestine

o Stimulates the release of bile and pancreatic juice

Figure 23.21

Jejunum

Mucosa

with folds

Cystic duct



Gallbladder

Right and left

hepatic ducts

of liver



and sphincter

Pancreas

Tail of pancreas

Head of pancreas

Common hepatic duct

Major duodenal

papilla


Figure 23.26a

Small

duct

Acinar cells

Basement

membrane

Zymogen

granules

Rough

endoplasmic

reticulum

(a)

Figure 23.28

Chyme entering duodenum causes release of cholecystokinin (CCK) and secretin from duodenal enteroendocrine cells.

CCK (red dots) and secretin (yellow dots) enter the bloodstream.

CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3

–-rich pancreatic juice.

Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly.

CCK (via bloodstream) causes gallbladder to contract and hepatopancreatic sphincter to relax; bile enters duodenum.

During cephalic and gastric phases, vagal nerve stimulation causes weak contractions of gallbladder.

Slide 1

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Large intestine

About 1.5 meters in length in a cadaver (SI about 6m long)

Functions

Vitamins, water, and electrolytes are reclaimed

Propulsion of feces toward the anus

Colon is not essential for life

Figure 23.29a

Left colic

(splenic) flexure

Transverse

mesocolon

Epiploic

appendages

Descending

colon

Teniae coli

Sigmoid

colon

Cut edge of

mesentery

External anal sphincter

Rectum

Anal canal

(a)

Right colic

(hepatic)

flexure Transverse

colon

Superior

mesenteric

artery Haustrum

Ascending

colon

IIeum

IIeocecal

valve

Vermiform appendix

Cecum


Regions

Cecum

Colon

Rectum

Anal canal


Regions

Cecum

Blind pouch

Appendix attaches to this area

Bacteria

Immune function


Regions

Colon

Ascending

Retroperitoneal

Transverse

Anchored via mesocolons (mesenteries)

Descending

Retroperitoneal

Sigmoid

Anchored via mesocolons (mesenteries)

Figure 23.30c

Transverse colon

Greater omentum

Descending colon

Jejunum

Mesentery

Transverse

mesocolon

Sigmoid

mesocolon

Sigmoid colon

Ileum

(c)

Figure 23.30d

(d)

Pancreas

Liver

Lesser omentum

Stomach

Duodenum

Transverse

mesocolon

Greater omentum

Mesentery

Jejunum

Visceral peritoneum

Urinary bladder

Transverse colon

Ileum

Parietal peritoneum

Rectum


Regions

Rectum

Rectal valves stop feces from being passed with gas

Anal canal

Last segment of the large intestine

Internal anal sphincter

Smooth muscle (involuntary)

Spinal reflex arcs

External anal sphincter

Skeletal muscle (voluntary)

Figure 23.29b

(b)

Rectal valve

Rectum

Anal canal

Levator ani

muscle

Anus

Anal sinuses

Anal columns

Internal anal

sphincter

External anal

sphincter

Hemorrhoidal

veins

Pectinate line


Defectation

Mass movements force feces into rectum

Distension initiates spinal defecation reflex

Parasympathetic signals Stimulate contraction of the sigmoid colon and rectum

Relax the internal anal sphincter

Conscious control allows relaxation of external anal sphincter

Valsalva’s maneuver

Figure 23.31

Impulses from

cerebral cortex

(conscious

control)

Voluntary motor

nerve to external

anal sphincter

External anal

sphincter

(skeletal muscle)

Internal anal sphincter

(smooth muscle)

Sensory

nerve fibers

Involuntary motor nerve

(parasympathetic division)

Stretch receptors in wall

Rectum

Sigmoid

colon

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Distension, or stretch, of the rectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons.

A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter.

If it is convenient to defecate, voluntary motor

neurons are inhibited, allowing the external anal

sphincter to relax so that feces may pass.

Questions?

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Digestive System Part Two - Linn-Bentoncf.linnbenton.edu/mathsci/bio/jacobsr/upload/Digestive System 2.pdf · Anatomy and Physiology of the Digestive System ... Blind pouch ... Anatomy