The GI system - Organs Note PDF

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05.GI SYSTEM: GROSS ANATOMY1. THE GI SYSTEM – AN OVERVIEWA. Generally, split into 2 components: i. The digestive system: long continuous tube from mouth to anus ii. Abdominal organs: e. liver, spleen, pancreas, gall bladder2. ABDOMINAL COMPARTMENTSA. 4 quadrants divided by: i. Transumilical line ii....

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05.02.2019

GI SYSTEM: GROSS ANATOMY 1. THE GI SYSTEM – AN OVERVIEW A. Generally, split into 2 components: i.

The digestive system: long continuous tube from mouth to anus

ii.

Abdominal organs: e.g. liver, spleen, pancreas, gall bladder

2. ABDOMINAL COMPARTMENTS A. 4 quadrants divided by: i.

Transumilical line

ii.

Median line

B.

9 regions divided by: i.

2 midclavicular lines

ii.

Subcostal line

iii.

Trans tubercular line

3. THE ORAL CAVITY – OPENING TO THE GI TRACT A. Formed by the cheeks (lateral), tongue (floor) and palate (roof) B. Hard palate = bone C. Soft palate = mucous membrane D. Uvula = muscle E. Palate covered in a mucous membrane

4. SALIVARY GLANDS A. Release saliva (99.5% water with solutes including salivary amylase B. Increased secretion in presence of food C. Main salivary glands:

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i.

Parotid gland: anterior-inferior to ears

ii.

Submandibular gland: floor of mouth

iii.

Sublingual gland: superior to submandibular glands

5. THE PHARYNX A. Funnel shaped tube from the posterior nasal opening down to cricoid cartilage B. Skeletal muscle lined with mucous membrane C. Divided into 3 parts: i.

Nasopharynx

ii.

Oropharynx

iii.

Laryngopharynx

6. OESOPHAGUS A. The oesophagus begins in the laryngopharynx at C6 and extends down to T11 B. Muscular tube – expands with food bolus C. 2 layers of muscle (outer longitudinal and inner circular) for peristalsis D. It is 20 – 40cm long and about 1 – 2cm in width E. Positioned in between the vertebrae posteriorly (T1-T4) and the trachea anteriorly.

7. OESOPHAGUS I Food which travels down the oesophagus enters the stomach by passing through the abdominal hiatus of the diaphragm then through the lower oesophageal sphincter at the level of approximately T10/T11 to enter into the stomach A. The oesophagus has 3 portions:

3

i.

Cervical: oropharynx to cricoid (C5/6)

ii.

Thoracic: thoracic aperture (T1) to oesophageal hiatus (T10)

iii.

Abdominal: oesophageal hiatus to stomach

8. OESOPHAGUS II To get started right away, just tap any placeholder text (such as this) and start typing. A. The oesophagus has 3 normal constrictions: i.

Upper oesophageal/cervical (C5/6) – due to cricoid cartilage

ii.

Middle oesophageal/thoracic (T4/5) – due to the arch of aorta

iii.

Lower oesophageal/abdominal (T10/11) – hiatus of the diaphragm

9. STOMACH I A. The stomach is a roughly bean-shaped, muscular sac which can be anatomically divided into different regions: i.

Fundus

ii.

Cardia

iii.

Body

iv.

Antrum

v.

Pylorus

vi.

Lesser curvature

vii.

Greater curvature

10.

STOMACH II The stomach has to be fit for purpose A. It has a well-developed muscular coat: 3 layers of muscle 4

i.

Outer longitudinal layer

ii.

Middle circular layer

iii.

Inner oblique layer

B. Series of internal folds to increase surface area to allow stomach to expand

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11.

THE INTESTINES A. Small intestine i.

Approximately 4m long

ii.

Split into 3 sections

iii.

Digestion and mainly absorption

B.

Large intestine i.

Terminal GI tract

ii.

Formation and expulsion of faeces

iii.

Larger diameter than small intestine

12.

DUEDENUM I A. The duodenum is C shaped and begins immediately after the pyloric sphincter. B. Shortest portion at approximately 25cm. C. The duodenum can be divided into 4 distinct parts: i.

Superior

ii.

Descending

iii.

Horizontal

iv.

Ascending

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DUODENUM II To get started right away, just tap any placeholder text (such as this) and start typing. A. The descending part of the duodenum has two openings for bile to enter:

B.

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i.

Major duodenal papilla – sphincter of Oddi

ii.

Minor duodenal papilla – direct route for accessory pancreatic duct

The duodenum also has internal circular folds – valves of Kerckring

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DUODENUM III A. Circular folds- Valves of Kerckring, also known as Plicae circulares (seen in duodenum and jejunum) B. Permanent – unlike the rugae in the stomach C. Slows the passage of food and increase surface area

15.

JEJUNUM The jejunum begins immediately after the duodenum: duodeno-jejunal flexure A. Approximately 2/5 length of small intestine B. It is characterised by plicae circulares.

16.

ILEUM The ileum forms the majority of the small intestine A. Approximately 3/5 the length of the small intestine B. It is characterised by Peyer’s patches – lymphoid nodules C. Importance of Peyer’s patch: GI tract is open to the external environment; these provide an immune response to pathogens.

17.

LARGE INTESTINE A. Large intestine (colon) is approx. 1.5m long and extends from ileum to the anus B. Colon split into 5 parts: i.

Caecum and ascending colon

ii.

Transverse colon

iii.

Descending colon

iv.

Sigmoid colon

v.

Rectum and anal canal

C. Right colic flexure – hepatic flexure D. Left colic flexure – splenic flexure

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18.

GENERAL CHARACTERISTICS A. Large internal diameter compared to the small intestine B. Omental appendices: fat accumulations that hang off the large intestine C. Teniae coli: 3 bands of longitudinal muscle D. Haustra: sacculations of colon due to the shorter teniae coli

19.

CAECUM AND APPENDIX A. Caecum – pouch at start of colon B. Intestinal matter passes ileum – caecum through ileocecal valve and prevents back flow C. Caecum continuous with ascending colon D. Posteromedial wall of caecum – vermiform appendix (blind ended pouch)

20.

COLON A. Caecum -> Ascending -> Transverse -> Descending colon -> Sigmoid colon B. Splenic flexure: higher and more posterior C. Hepatic flexure: lower due to the liver D. Main function is excretion of waste products

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21.

RECTUM AND ANAL CANAL A. Rectum: approximately 15cm long lying anterior to the sacrum B. Anal canal is the terminal 2 – 3cm of large intestine C. Anal column – longitudinal folds of mucous membrane containing vessels D. Anus – opening controlled by:

22.

i.

Internal anal sphincter (smooth muscle – involuntary)

ii.

External anal sphincter (skeletal muscle – voluntary)

LIVER AND GALLBLADDER OVERVIEW A. The liver is the largest visceral organ B. The liver lies in the right upper quadrant below the diaphragm C. Gallbladder sits in depression on the visceral surface D. Main function is production, storage, and release of bile E. Other functions include drug metabolism, production and storage of vitamins

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23.

LIVER: LOBES AND SURFACES A. 2 surfaces of the liver: diaphragmatic and visceral B. Divided into left and right lobes by the falciform ligament (liver to anterior abdominal wall) C. Caudate lobe: bound by groove for IVC and fissure for ligamentum venosum (remnant of ductus venosus) D. Quadrate lobe: bound by gallbladder and fissure for ligamentum teres / round ligament (remnant of left umbilical vein)

E. Caudate lobe: bound by groove for IVC and fissure for ligamentum venosum F. 10

Quadrate lobe: bound by gallbladder fossa and fissure for ligamentum teres

24.

GALLBLADDER A. Gallbladder lies on the visceral surface of liver in fossa between right and quadrate lobes B. Divided into regions: i.

Fundus

ii.

Body (infundibulum)

iii.

Neck

iv.

Cystic duct

C. Connected to liver through biliary tree D. Receives, concentrates and stores bile

25.

BILIARY TREE A. Right and left hepatic ducts  common hepatic duct B. Common hepatic duct + cystic duct  common bile duct C. Bile duct + pancreatic duct  ampulla of Vater (hepatopancreatic duct) D. Enters descending duodenum through major duodenal papilla (controlled by sphincter of Oddi)

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26.

PANCREAS A. Pancreas lies posterior to the stomach B. Extends from the duodenum to the spleen C. Endocrine (blood) and exocrine (ducts) functions D. Secretes pancreatic juices

27.

PANCREAS – GROSS FEATURES A. Divisions of the pancreas: i.

Head – nestled in C-shaped duodenum

ii.

Uncinate process – posterior to superior mesenteric vessels

iii.

Neck – anterior to vessels

iv.

Body

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v.

Tail – anterior to left kidney (contact with spleen)

B. Pancreatic duct runs through pancreas and joins with common bile duct in the lower head of pancreas

28.

SPLEEN A. The spleen is lymphatic tissue and lies in the left upper quadrant between ribs 9 and 11 B. Costal surface: diaphragm C. Visceral surface: stomach, left kidney and splenic flexure) D. Hilum: contains splenic vessels and lymphatics E. Functions: immune response, blood filtration and storage

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29.

KIDNEYS AND ADRENALS A. Lie on posterior abdominal wall B. Functionally part of urinary system C. Anterior surfaces relate to other abdominal organs D. Located approximately T12 --> L3 (right kidney slightly lower) E. Superior and inferior poles (adrenal glands at superior pole)

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