GI system Flashcards
Primary Function of the GI system
- Bring nutrients into the internal environment of the body so that they can be used
- Extracts the necessary nutrients, fluids & salts from the food & water we ingest & uses it for energy & growth, & replaces losses that occur in the excreta & across the body surfaces
- Food → digestion → absorption → waste
The movement of which regions of the GI system are not caused by the contraction of just smooth muscle?
- Mouth: skeletal muscle
- Oesophagus: skeletal and smooth muscle
- External anal sphincter: skeletal muscle
4 actions of the GI system
- Motility
- Secretion
- Digestion
- Absorption
Structures of the GI System
- Gut tube
- Accessory organs
1) Gut tube:
- Oesophagus
- Stomach
- Small intestine (Duodenum, jejunum & ileum)
- Large intestine (cecum, ascending colon, transverse colon, descending colon, sigmoid colon)
- Rectum
- Anal canal
2) Accessory organs
- Salivary glands
- Pancreas
- Liver & gallbladder
- Appendix
GI system: Motility
- Patterns
- Where
- Control
- Contributes to
- Perstalsis (along GI tract)
- Segmentation (mixing w/in GI tract)
- Sphincters for control
Contributes to digestion & absorption
2 Types of gastric cells
- What they produce
- Identifiable by?
- Chief cells
- produce pepsinogen
- Lots of RER - Parietal cells
- produce acid and intrinsic factor
- Lots of mitochondria
Types of digestion and main action
- Mechanical - motility
- Chemical - secretion of fluid & enzymes
Physiological process of the GI system - Absorption
- Where does it occur?
- What is it aided by?
Transport from the GI lumen into the body
Occurs in:
- Small intestine (nutrients, salt & water)
- Large intestine (salt & water)
Aided by
- Motility
- Secretion
The peritoneum - Parietal peritoneum & Visceral peritoneum:
All organs in the abdominal & upper pelvic cavity are covered in peritoneum: it’s moist & slippery
1) Parietal peritoneum
- Lines the abdominal & pelvic cavities (peritoneal cavity)
2) Visceral peritoneum: Covers the external surfaces of most abdominal organs (incl. intestinal tract)
The peritoneum - Mesentery
What defines the mesentery?
What type of epithelium?
What does it secrete?
What is it’s function?
3) Mesentery: double layer of peritoneal membrane; where they join back together after covering the organ
- The peritoneal membrane: a serous membrane
- Simple squamous epithelium w/ underlying thin layer of connective tissue
- epithelium: secretes serous fluid = moist, slippery
Function
- to give mobility to the viscera
- to prevent friction
- continual movement along the gut tube (the gut tube is long, cannot get tangled/blocked - supported by mesenteries);
- Forms a mesentery of the GI tract (provides rich blood supply)
Definitions of the GI system
- Parietal & visceral peritoneum
- Mesentery
- Omentum
- Retroperitoneum
Parietal & visceral peritoneum - Single layer of peritoneal membrane Mesentery - Double of peritoneal membrane - Epithelium outermost - From body wall to organ Omentum - Double layer of peritoneal membrane - Epithelium outermost - From organ to organ Retroperitoneum - Behind the peritoneum - Organs become retroperitoneal when they lose their mesentery/have peritoneum on their anterior side only
Functions (5) of Peritoneum
- What does it form?
- What does the mesenteries do?
- What does the Omentum & mesentery store?
- What does this prevent?
- It forms a complete or partial covering for abdominal organs
- It forms the smooth lining which enables the abdominal organs to move over each other w/out friction
- The mesenteries of the peritoneum hold the abdominal organs in position
- Omentum & mesentery serve as store house for fat
- the fats of peritoneum prevents infections being carried to abdominal organs
Arterial supply to abdominal viscera features
Branch off abdominal aorta 1) Celiac trunk 2) Superior mesentric (midgut) 3) Inferior mesentric (hindgut) Supply the following regions - Early in development; supplied by 3 branches of aorta: foregut (celiac trunk), midgut (superior m. artery), hindgut (inferior m. artery)
Arterial supply to abdominal viscera - Celiac trunk
Branches to the structures that are derived from the foregut - Common hepatic → liver → Duodenum → Pyloric stomach → pancreas - Left gastric → Lower oesophagus → Stomach → Liver - Splenic → Spleen → Stomach → Pancreas
Arterial supply to abdominal viscera - Superior mesentric
Branches to the structures that are derived from the midgut - Intestinal arteries → Ileum → Jejunum - Ileocolic artery → Ileum → Cecum → Appendix - Colic arteries → Ascending colon → Transverse colon
Arterial supply to abdominal viscera - Inferior mesentric
Branches to the structures that are derived from the hindgut - Left colic artery → Descending colon - Sigmoid arteries → Sigmoid colon - Superior rectal artery → Rectum → Anal canal
Hepatic portal vein features (2)
- A large number & wide distribution of veins feed into the hepatic portal vein ( inferior mes. vein → splenic vein → HPV & superior mes. vein → HPV)
- Drainage via the hepatic portal circulation is nutrient rich
Hepatic portal circulation features (3)
- Capillaries → veins → (capillaries → veins - w/in the liver) → inferior vena cava
- There is a second capillary bed covering the liver
- Blood from GI tract → Liver via HPV
Structure of GI tract (Oesophagus → anus)
Layers?
4 layers
- Mucosa (innermost)
- Submucosa
- Muscularis
- Adventitia (outermost)
What is mucosa composed of?
- Epithelium (mucous secreting)
- Lamina propria (LFCT)
- Muscularis mucosa ( thin layer smooth muscle)
What is Submucosa composed of?
- Smooth muscle
What is Adventitia composed of?
- Fibrous connective tissue
what are the additional internal structures of the GI tract
- Glands (in submucosa)
- Gland ducts (in mucosa)
- Lamina propria (lymph nodes)
What is the epithelial tissue - location
- Simple squamous: peritoneum/peritoneal membrane
- Simple cuboidal: lining ducts
- Simple columnar: lining small intestine
- Stratified squamous: lining oesophagus & anal canal (hardwearing protects against abrasion)
Glandular epithelium structure
What type of epithelium?
- single duct (gland)
- greater than or equal to 2 (gland)
- Unicellular (eg goblet cells small intestine)
- multicellular
- Apical mucous granules
- Basal nucleus
- Columnar
- Goblet shape
- Simple = single duct (gland)
- Compound = >/= 2 duct (gland)
Stratified squamous epithelium: Mouth → esophagus
- Function
- Muscle transition
- For protection from abrasion
- Muscle transition from skeletal (voluntary control) to smooth (involuntary control) in esophagus
Simple columnar epithelium:
- functions
- Layers in: SI, LI, stomach
- Basic tube modified to carry out regional specific functions (secretion, digestion, absorption)
- Smooth muscle: small & large intestine, 2 layers - inner & outer longitudinal: stomach 3 layers (additional oblique layer); large intestine (3 bands of longitudinal muscle)
Structure & function of stratified squamous epithelium: anal canal
- For protection from abrasion
- Internal & external anal sphincter muscles
Mouth features (3)
- Wear & tear; stratified squamous epithelium
- Mechanical digestion (food ingested, digested begins)
- Through fauces; into oropharynx, into oesophagus
Salivary Glands - Parotid salivary glands
- What does it secrete?
- Location?
- How much saliva does it secrete?
- Serous only
- Largest salivary glands; located anterior & inferior to the ear
- Secrete 25-30% of total saliva
Salivary Glands - Submandibular salivary glands
- What does it secrete?
- How much saliva does it secrete?
- Location?
- Mixed (serous & mucous)
- Produce majority of saliva (60-70%)
- Submandibular duct opens through a papilla in the floor of the mouth next to the lingual frenulum
Salivary Glands - Sublingual salivary glands (under tongue)
- What does it secrete?
- How much saliva does it secrete?
- Location?
- Mucous mainly
- Contribute 3-5% of total saliva
- Contain multiple, tiny sublingual ducts that open onto the inferior surface of the oral cavity
Salivary Glands Functions
- What does it produce & secrete?
- Why does it secrete this?
- What type of digestion occurs?
- What enzyme is involved?
- Produce & secrete saliva into the oral cavity
→ Moistens ingested materials to become a slick bolus
→ Moistens, cleanses & lubricates the structures of the oral cavity
→ Begins chemical digestion of carbohydrates w? amylase
→ Antibacterial action w/ lysosome
→ Dissolves food so taste receptors on tongue can be stimulated
Oesophagus: Mucosa layer
- Epithelium
- Protective stratified squamous
Oesophagus: Muscularis layer
- Function
- Muscle transition
- Move food bolus; transitions b/w skeletal & smooth muscle
Oesophagus: Mucous secreting glands
- Function
- Ducts to surface epithelium; protective
- Need mucous to coat the lining of the oesophagus
Oesophagus: Lamina propria composition
- LFCT
Stomach features (3)
- Where?
- Structure?
- What is the large, apron-like fold of visceral peritoneum?
- Posterior to liver, anterior to pancreas & spleen
- Omenta (greater & lesser)
- Greater omentum: large, apron-like fold of visceral peritoneum that hangs down from the stomach over the small intestines & doubles back up to the transverse colon
Stomach functions
1) Fat deposition
2) Immune contribution
3) Infection & wound isolation (it may also physically limit the spread of intraperitoneal infections)
Key anatomical regions of the stomach
- Superior → inferior
Fundus → cardia → body → pylorus
Stomach structural features important for function
Function? Structure? - What allows the stomach to become larger? - What muscle is used for motility? - What breaks down proteins?
Function
1) Storage
2) Mechanical digestion
3) Chemical digestion
Structure
1) Rugae ( unfold → allow stomach to become larger w/out stretching; mucosa & submucosa layer) & sphincters (controls secretion of material, holds food in stomach)
2) Oblique muscles (motility; smooth muscles)
3) Epithelial cells (break down proteins)
Mucosal layer: what forms Gastric pits & glands?
- Infolding of columnar epithelium
Mucosa of the stomach wall - Gastric glands
- What cells are there?
- What do these cells secrete?
- Mucous neck cell; secrete mucous (protection)
- Chief cell; secrete enzymes pepsinogen (digestive)
- Parietal cell; acid HCl & intrinsic factor (produce)
- Endocrine cell; secrete hormones
Chief cell (CC) features (3)
- Rough ER
- Granules - opical
- Secreted = inactive // lumen = active
Parietal cell (PC) (pumps ions)(H+) features (3)
- Lots of mitochondria (energy)
- Large SA
- Folded → microvilli
Endocrine cells features (3)
- What stimulates digestive function?
- How?
- What stimulates appetite?
Hormones secreted
- Gastrin → stimulates digestive function, acts on PC to increase HCl
- Ghrelin → Stimulates appetite
- Nervous control (neuro-transmitters, receptors)
Enteric Nervous System (ENT) features (2)
- What is b/w oblique & circular muscle layers?
- What happens when stomach is filled?
- Neuronal cell bodies & nerve fibres b/w oblique & circular muscle layers (of stomach) → myenteric plexus
- Receptors: stomach filled → mechanical digestion
Location & arrangement of Small intestine (SI)
- What is it framed by?
- What is it inferior to?
- What is it covered by?
- Framed by large intestine
- Lower section of abdominopelivic cavity (inferior to stomach & duodenum & transverse colon)
- Covered by greater omentum
SI:
- Sections and their specific function (if any)
1) Pyloric sphincter
- Controls the release of chyme from the stomach
- Thick, circular smooth muscle
2) Duodenum
- Protection from acid: mucous secreting cells in epithelium & alkaline mucous secreting cells in epithelium & alkaline mucous secreting glands in submucosa
- Neutralize pH: bicarbonate (also pancreas)
3) Jejunum
4) Ileum
SI wall: 4 layers (incl. specialisations)
Modifications to assist in digestion & absorption
- Mucosa - villi w/ microvilli
- Submucosa - plicae circulares
- Muscularis - 2 layers (circular & longitudinal)
- Adventitia
Plicae circulares
- Which layer(s)
- Specialisation to epithelium?
- Inner surface of SI: submucosa & overlying mucosa
- Each plicae circulare (fold) is covered by villi: increase SA for absorption; dont distend/stretch → permanent
Villi
- Covered w/?
- Covered w/ epitheelial columnar cells (enterocytes), which contain goblet cells → protection against abrasion
Microvilli features (3)
- What cells do they cover?
- Cover apical surface of the columnar cells on each villus
- Increase SA for absorption
- Glycocalyx = glycoprotein coat on microvillus → hold brush border enzymes for contact digestion
Segmentation & Muscularis layer features (5)
- What type of contractions?
- How do these contractions work?
- What is this movement for?
- What does segmentation do to chyme?
- What does peristalsis do to chyme?
- Segmentation = localised contractions of circular muscle of the muscularis layer of the alimentary canal
- These contractions isolate small sections of the intestine: moving their contents back & forth whilst continuously subdividing & mixing the contents
- Back & forth movement in lumen = mixes food w/ digestive juices & facilitates absorption
- Can slow progression of chyme, allowing time for digestion & absorption
- Peristalsis; movement along tube (cannot slow chyme)
2 Types of neural control and their function
- Submucosal plexus - regulation of secretion
- Myenteric plexus - regulation of motility
ENS vs. CNS
- Function
- Type of neural reflexes
- Enteric nervous system (ENS) → Primary neural system controlling GI function → Independent - short, local GI reflexes - Central nervous system → Modulates activity of ENS → Long neural reflexes
What do the endocrine cells of the GI tract secrete?
hormones
Accessory Organs:
- What are they
- What do they produce/release/store?
- Function of secretions?
- Liver
→ Produces bile salts, which emulsify lipids, aiding their digestion & absorption - Gallbladder
→ Stores, concentrates & releases bile in response to hormonal signals - Pancreas (exocrine)
→ Produces digestive enzymes & bicarbonate to help neutralize acidic chyme
Pancreatic duct
- Where does it lead to?
- What sphincter does it contain? Incl. its structure and function
- What duct is formed by the union of this duct and the common bile duct?
- Duodenum
- Sphincter of oddi (ring of smooth muscle): controls the release of digestive enzymes & bicarbonate from pancreas
- Hepatopancreatic duct (ampulla of vater duet)
What is the function of the endocrine hormones produced by the pancreas?
regulate blood sugar & pancreatic secretions
Large intestine:
- Diameter/length compared to SI
- Functions
- Wider in diameter but shorter in length than SI
Functions: - Stores faeces until defecation
- Absorbs water & ions
- compacts undigestible & wastes & solidifies them into faeces
LI attachment to abdominal wall
- What is the transverse colon attached to?
- What anchors the transverse colon and what is it anchored to?
- What is against the abdominal wall?
- Transverse colon attached to greater omentum
- Transverse mesocolon anchors the transverse colon to the back wall
- Ascending & descending colon are retroperia (against the abdominal wall)
Sections of the LI and the accessory organ attached
Cecum → Ascending colon → hepatic flexure → transverse colon → splenic flexure → descending colon → sigmoid colon → rectum → anal canal.
(+ appendix)
Distinguishing features (7) of LI
- What valve does it contain? b/w which sections?
- What type of folds?
- Specialsed structures (3)
- Sphincter(s)
- What covers its anterior surface?
- ileo-caecal valve (b/w ileum & cecum)
- Semilunar folds
- Haustra (sacs formed by contraction of Tania coli)
- Taeniae coli (outer longitudinal muscle is condensed into 3 tape-like strips)
- Epiploicae appendices (pouches for fat storage - adipose tissue)
- External anal & sphincter muscle
- visceral peritoneum
Wall of the LI structure
- What does it lack compared to SI?
- Layers and what they’re composed of (if relevant)
- LACKS plicae circulares & villi (of the SI)
- Layers (deep → superficial)
1) Mucosa
→ deep mucosal invaginations & numerous goblet cells
→ epithelium, lamina propria (FCT), muscularis mucosae
2) Submucosa
3) Muscularis
→ Inner: circular
→ Thin outer: longitudinal (taenia coli)
4) Adventitia
Mucosa transition LI –> anal canal
Transitions from simple columnar (containing goblet cells) to stratified epithelium at colorectal zone to anal zone.
Control of anal sphincters
1) Sensory nerve fibres (sigmoid colon)
2) Voluntary motor nerve to external anal sphincter
3) Involuntary motor nerve parasympathetic division (internal anal sphincter - month muscle)
Defecation: process/muscle responses
1) Rectum minimal stretch, minimal pressure: internal contracted, external relaxed
2) rectum becomes stretched: internal relaxed, external contracted
3) Conscious decision to defecate: internal & external relaxed; pressure from contraction of GI & abdominal muscles (rectum)
Function of LI
- What does it digest?
- What does it absorb?
- How does it propel faeces?
- How is faeces removed from body?
→ Digestion - Some remaining food residues are digested by enteric bacteria (which also produce vitamin K & some B vitamins)
→ Absorption - Absorbs most of the remaining water, electrolytes & vitamins produced by bacteria
→ Propulsion - Propels faeces toward rectum by haustal churning & mass movements
→ Defecation - Reflex triggered by rectal distension, eliminates faeces from body
What do the following vessels carry to/from the liver (via the portal triad):
- Hepatic artery
- Hepatic portal vein
- Bile (hepatic) duct
- Hepatic artery: oxygenated blood TO liver from aorta
- Hepatic portal vein: deoxygenated, nutrient-rich blood TO liver from digestive organs
- Bile duct: bile FROM liver to gallbladder
