Digestive System Flashcards
List the six digestive system processes?
Ingestion
Propulsion: Deglutition and peristalsis
Mechanical breakdown
Digestion: Enzymatic breakdown
Absorption Passage of nutrients through GIT
Defecation
What is the vascular supply to the oesophagus
Arterial supply
Branches from inf. thyroid aa
Oesophageal aa (aorta) Lt gastric a. (branch of celiac trunk); Lt inf. phrenic a. (aorta)
Venous Drainage
Inf. thyroid vv
Oesophageal vv azygous v.
Lt gastric v. portal v. (relevant in hepatic pathology)
Lymphatic Drainage
Paratracheal, inf. deep cervical, post. mediastinal nodes
Lt gastric nodes
What is the role of the oesophagus in propulsion
deglutition
-buccal phase
pharyngeal - oesophageal phase
Introduce the stomach
Location: between small intestine and oesophagus
Structure: shape of J letter, but varies
Function: blend food, gastric juice and intrinsic factor secretion
what are the regions of the stomach
Cardia: surrounds cardial orifice
Fundus: dilated superior region.
Body: region between fundus and pyloric antrum
Pyloric part
lesser curvature
greater curvature
lesser omentum
greater omentum
what is the neuromuscular supply to the stomach
Parasympathetic CNX VAgus
Sympathetic T6-T9 greater splanchnic N.
Visceral afferents
what is the neuro supply to the stomach
Parasympathetic CNX VAgus
Sympathetic T6-T9 greater splanchnic N.
Visceral afferents
What controls gastric emptying
Duodenal receptors sensitive to distension and low PH
What is the enteric nervous system?
Intrinsic Nerve supply to the GIT.
Submucosal N. plexus
Myenteric N. plexus
What is the difference between short and long digestive reflexes?
Short reflexes: mediated entirely by the ENS in response to stimuli in the GIT
Long reflexes: involve integration with the CNS and extrinsic autonomic nn
What are the principles of digestive regulation?
- A range of mechanical & chemical stimuli can provoke digestive activity
- Neurons & hormones control digestive activity
- Smooth mm & glands are the key effectors
Introduce the oesophagus
Location: between pharynx and stomach
Structure: 25cm long 2cm diameter. divided in three portions cervical Ts, abdominal
Function: passageway for food from mouth to stomach. propulsion
What are the locations of the 4 constriction points of the oesophagus?
Upper oesophageal sphincter
Where crossed by arch of aorta
Where crossed by the left main bronchus
Lower oesophageal sphincter
What are the other names for the oesophageal sphincter?
cardiac sphincter
gastroesophageal
What is the nerve supply to the oesophagus?
Upper ½ of cervical part
Recurrent laryngeal nn (branch of CNX)
Rest of oesophagus
Intrinsic nn: ENS
Extrinsic nn: Oesophageal plexus
Parasympathetic supply - CNX Vagus
Sympathetic supply via the cervical sympathetic ganglia, cardiopulmonary splanchnic nns, abdominopelvic splanchnic nns (greater and lesser)
Visceral afferents
How does food move in the oesophagus, during the Pharyngosephageal phase?
Food moves from pharynx into the oesophagus
blocking of trachea (epiglottis) & relaxation of UOS
Peristaltic waves propel food distally: adjacent segments of the oesophageal wall alternately contract and relax
Relaxation of LOS allows food to enter stomach
What is the vascular supply to the stomach ?
Lt gastric a. (directly off celiac trunk)
Rt gastric a. (from common hepatic a.)
Lt gastro-omental a. (from splenic a.)
Rt gastro-omental a. (from gastroduodenal a.)
4-5 Short gastric aa (from splenic a.)
what is the venous drainage to the stomach?
Veins run with the arteries
Rt & Lt gastric vv portal v.
Short gastric vv & Lt gastro-omental v. splenic v.
Rt gastro-omental v. SMV
SMV & splenic v. unite to form portal v.
What are the gastric gland cells of the stomach
Mucous neck cells
Parietal cells: acidity, vitamin B12
Chief cells
Produce pepsinogen & gastric lipase
Low pH required for conversion of pepsinogen to pepsin
Enteroendocrine cells
Gastrin (from G cells):
Histamine (secretion), serotonin (contractility)
What is the role of the stomach?
Mechanical breakdown & propulsion
Digestion
Pepsin begins digestion of proteins
Gastric lipase
Absorption
Some fat-soluble substances (alcohol, some drugs e.g. aspirin)
Additional functions:
- Food reservoir
- HCl contributes to immunity
- Intrinsic factor
What is gastric emptying?
Nervous (enterogastric reflex)
- Duodenal receptors are sensitive to distension and low pH
- Causes reflex inhibition of ENS & Vagus (reduced secretions & motility)
Duodenal hormones released in response to fatty, acidic chyme
- Cholecystokinin
- Gastric Inhibitory Peptide
- Secretin
Introduce the small intestine
Location: abdominal cavity from the stomach (pylorus) to the ileocaecal junction of the colon.
Structure: divided in three main parts Duodenum, Jejunum, Ileum
Function: Receives secretions from liver & pancreas
Mechanical & chemical digestion; absorption of nutrients
Transportation of undigested material to large intestine
Introduce the duodenum
D1: superior part (~5cm)
Direct continuation of pyloric region
D2: descending part (~7-10cm)
Runs between sup. & inf. duodenal flexures
D3: horizontal part (~6-8cm)
At the level of L3
D4: ascending part (~5cm)
Runs along Lt side of aorta
what is the nerve supply to the duodenum ?
Intrinsic nn: ENS
Extrinsic nn:
Parasympathetic: CNX Vagus
Sympathetic: Greater & lesser splanchnic nn (T5-9) via the celiac & sup. mesenteric plexuses
Visceral afferents
what is the vascular supply to the duodenum ?
Arterial supply
Gastroduodenal a. & sup. pancreaticoduodenal aa (common hepatic a., off celiac trunk)
Inf. pancreaticoduodenal aa (SMA)
Venous drainage
Duodenal vv follow aa, drain into the portal v.
Lymphatic drainage
Pancreaticoduodenal & sup. mesenteric nodes
What is the structure of the Jejunum and Ileum ?
6-7m long combined
What is the vascular supply to the Jejunum and Ileum?
Arterial supply
SMA provides 15 -18 branches (run between layers of the mesentery)
Venous drainage
SMV – unites with splenic v. to form portal v.
Lymphatic drainage
Sup. mesenteric nodes
What is the nerve supply to the Jejunum and Ileum?
trinsic nn: ENS
Extrinsic nn:
Parasympathetic: CNX Vagus
Sympathetic: Greater & Lesser splanchnic nn (T5-9) via the celiac & sup. mesenteric plexuses\
What are the cells of the vili and crypts?
Enterocytes
Absorptive cells endowed with microvilli
Crypt enterocytes secrete intestinal juice
Goblet cells
Produce alkaline mucous (relies on PGE2)
Enteroendocrine cells Secrete hormones (enterogastrones) e.g. CCK, secretin
Paneth cells
Release antimicrobial agents (lysozymes)
Stem cells
Renew the epithelium every 3-5 days
What is the role of the small intestine?
Mechanical breakdown & propulsion
Involved in segmentation and peristalsis
Digestion
Digestive enzymes delivered from pancreas
Brush border enzymes embedded in microvilli membranes
Bile produced by liver emulsifies fats & enhances digestion
Absorption
Breakdown products of CHO, protein, fat & nucleic acid digestion
Water, vitamins, electrolytes
Introduce the colon
Structure: 5 main regions Ascending, transverse, descending, sigmoid, colon and rectum
What is the Caecum?
Initial part of the colon
7.5cm length
blind intestinal pouch
RLQ - Rt inguinal region
What happens when the ileum enters the caecum
ileococecal orifice controls passageway to chyme superior and inferior ileocaecal folds are found.
What is the vermiform appendix?
pouch arising from the posteromedial aspect of the caecum 6-10cm length
What is the histology of the appendix?
lymphoid tissue Fucntion: immunity: produce and store lymphocytes reservoir for gut bacteria recolonises gut
What is the neurovascular supply to the appendix?
Caecum: ileocolic a. (terminal branch of SMA)
Appendix: appendicular a. (branch of the ileocolic artery)
Caecum & appendix: ileocolic v. SMV
Lymph: ileocolic nodes
Nerve:
Intrinsic nn: ENS
Extrinsic nn:
Parasympathetic: CNX Vagus
Sympathetic: abdominopelvic splanchnic nn (lower thoracic segments)
Visceral afferents from appendix: accompany sympathetics to T10 cord segment
Introduce the ascending colon
2nd part of the large intestine
location: RQ from caecum to liver. finishes at the Rt Colic flexure (hepatic Flexure
Introduce the Transverse colon
3th part of colon
Location : RT to Lt flexures
Lies at the level of the umbilicus
Vascular supply of the ascending colon
To ascending colon & hepatic flexure:
Branches from SMA
Ileocolic & Rt colic arteries
To ascending colon & hepatic flexure:
Veins w. same names as arteries
Drain to SMV
lymph:Epicolic & paracolic nodes ileocolic & Rt colic nodes superior mesenteric nodes
Vascular supply of the transverse colon
Mainly from middle colic a. (SMA)
Rt colic artery (SMA) & Lt colic artery (IMA)
venous: SMV
Lymph: middle colic nodes
Nerve supply of ascending and transverse colon
Intrinsic nn: ENS
Parasympathetic: CNX Vagus
Sympathetic: T10 - L2
Introduce the descending colon
Location: from colic flexure to iliac fossa, continuous to sigmoid colon
introduce Sigmoid colon
S shaped loop linking descending colon to rectum
Neurovascular supply descending and sigmoid colon
artery: Lt colic a. (IMA)
Superior sigmoid arteries (IMA
venous:IMV, which flows into the splenic vein and into the portal system
lymph:Epicolic & paracolic nodes
inf. mesenteric nodes
Nerve: Intrinsic nn: ENS
Parasympathetic: Pelvic splanchnic nn S2-S4
Sympathetic: lumbar part of the sympathetic trunk & superior hypogastric plexus
What are the macroscopic features of the colon ?
Tenia Coli
Haustra
Mental epiploic appendices
histology of the colon
Mucosa: simple columnar epithelium
crypts with goblet cells
Introduce the rectum
located between the sigmoid colon and anus.
What is the anorectal flexure?
where the rectum ends at coccus and turns sharply
What is the rectal ampulla
dilated aspect of distal rectum
What is puborectalis?
sling around inferior rectum. cause of incontinence
How does the peritoneum cover the rectum
Retroperitoneal
Superior 2/3: covered anteriorly & laterally by peritoneum
Middle 1/3: covered anteriorly
Inferior 1/3: no covering as this is subperitoneal
Females: peritoneum reflecting from the rectum to the posterior aspect of the vagina and uterus
Rectouterine pouch or the ‘Pouch of Douglas’
Males: peritoneum reflecting from rectum to post. Bladder
Rectovesicle pouch
Neurovascular supply to the rectum
Proximal rectum: superior rectal a. (IMA)
Mid. & inf. rectum: middle rectal a.
Anorectal junction: internal rectal a.
Superior rectal veins portal venous system
Middle & inferior rectal veins systemic system
Superior 1/2: pararectal nodes
inf. mesenteric & lumbar nodes
Inferior 1/2: internal iliac nodes
Intrinsic nn: ENS
Parasympathetic: Pelvic splanchnic nn S2-S4
Sympathetic: lumbar part of the sympathetic trunk & superior hypogastric plexus
what is the anal canal
its the terminal aspect of the large intestine.
What are the main structures of the anal canal?
Anal columns: longitudinal folds of mucosa
Anal sinuses: recesses between the columns that exude mucous when compressed by faeces
Two anal sphincters: external (under voluntary control) and internal (involuntary)
Pectinate line (L. ‘comb’) – marks the junction of the superior & inferior parts of the anal canal
Neurovascular supplies reflect embryological differences (superior – endoderm; inferior – ectoderm)
Neuromuscular supply to anal canal
Sup. to pectinate line: superior rectal a. (from IMA)
Inf. to pectinate line: inferior rectal a. (from internal iliac a.)
Middle rectal a. forms anastomoses
Sup. to pectinate line: internal rectal plexus sup. rectal v. IMV (portal system)
Inf. to pectinate line: internal rectal plexus inf. rectal v. (caval system)
External rectal plexus drains peri-anal region
Sup. to pectinate line: internal iliac nodes lumbar nodes
Inf. to pectinate line: superior inguinal nodes
Sup. to pectinate line: inf. hypogastric plexus
Parasympathetic: S2-S4
Sympathetic fibres
Visceral afferents: sensitive to stretch only
Inf. to pectinate line: somatic motor & sensory from pudendal nerve S2-S4
Sensitive to pain, touch & temperature
What is the histology of the anal canal?
Rectal mucosa: simple columnar epithelium
Anal mucosa: stratified squamous epithelium
What is the function of the large intestine?
Digestion: enteric bacteria
Absorption
Propulsion
Defecation
How does the colon move?
Haustral contractions 30min
Mass movements 3/4 times a day
Gastrocolic reflex
faecal components
How does the defecation system work?
Mass movement of faeces into rectum stimulate visceral afferents (distension)
Initiates a parasympathetic spinal reflex (S2-S4)
Contraction of rectum & relaxation of IAS
Message also reaches brain: allows for conscious decision on relaxation of the EAS
Constipation & diarrhoea will be explored next in Lecture 4B
