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Digestive System Flashcards

1
Q

List the six digestive system processes?

A

Ingestion

Propulsion: Deglutition and peristalsis

Mechanical breakdown

Digestion: Enzymatic breakdown

Absorption Passage of nutrients through GIT

Defecation

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2
Q

What is the vascular supply to the oesophagus

A

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

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3
Q

What is the role of the oesophagus in propulsion

A

deglutition
-buccal phase
pharyngeal - oesophageal phase

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4
Q

Introduce the stomach

A

Location: between small intestine and oesophagus

Structure: shape of J letter, but varies

Function: blend food, gastric juice and intrinsic factor secretion

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5
Q

what are the regions of the stomach

A

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

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6
Q

what is the neuromuscular supply to the stomach

A

Parasympathetic CNX VAgus

Sympathetic T6-T9 greater splanchnic N.

Visceral afferents

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7
Q

what is the neuro supply to the stomach

A

Parasympathetic CNX VAgus

Sympathetic T6-T9 greater splanchnic N.

Visceral afferents

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8
Q

What controls gastric emptying

A

Duodenal receptors sensitive to distension and low PH

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9
Q

What is the enteric nervous system?

A

Intrinsic Nerve supply to the GIT.

Submucosal N. plexus
Myenteric N. plexus

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10
Q

What is the difference between short and long digestive reflexes?

A

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

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11
Q

What are the principles of digestive regulation?

A
  1. A range of mechanical & chemical stimuli can provoke digestive activity
  2. Neurons & hormones control digestive activity
  3. Smooth mm & glands are the key effectors
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12
Q

Introduce the oesophagus

A

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

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13
Q

What are the locations of the 4 constriction points of the oesophagus?

A

Upper oesophageal sphincter

Where crossed by arch of aorta

Where crossed by the left main bronchus

Lower oesophageal sphincter

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14
Q

What are the other names for the oesophageal sphincter?

A

cardiac sphincter

gastroesophageal

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15
Q

What is the nerve supply to the oesophagus?

A

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

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16
Q

How does food move in the oesophagus, during the Pharyngosephageal phase?

A

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

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17
Q

What is the vascular supply to the stomach ?

A

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.)

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18
Q

what is the venous drainage to the stomach?

A

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.

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19
Q

What are the gastric gland cells of the stomach

A

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)

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20
Q

What is the role of the stomach?

A

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
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21
Q

What is gastric emptying?

A

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
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22
Q

Introduce the small intestine

A

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

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23
Q

Introduce the duodenum

A

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

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24
Q

what is the nerve supply to the duodenum ?

A

Intrinsic nn: ENS

Extrinsic nn:
Parasympathetic: CNX Vagus
Sympathetic: Greater & lesser splanchnic nn (T5-9) via the celiac & sup. mesenteric plexuses

Visceral afferents

25
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
26
What is the structure of the Jejunum and Ileum ?
6-7m long combined
27
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
28
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\
29
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
30
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
31
Introduce the colon
Structure: 5 main regions Ascending, transverse, descending, sigmoid, colon and rectum
32
What is the Caecum?
Initial part of the colon 7.5cm length blind intestinal pouch RLQ - Rt inguinal region
33
What happens when the ileum enters the caecum
ileococecal orifice controls passageway to chyme superior and inferior ileocaecal folds are found.
34
What is the vermiform appendix?
pouch arising from the posteromedial aspect of the caecum 6-10cm length
35
What is the histology of the appendix?
``` lymphoid tissue Fucntion: immunity: produce and store lymphocytes reservoir for gut bacteria recolonises gut ```
36
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
37
Introduce the ascending colon
2nd part of the large intestine location: RQ from caecum to liver. finishes at the Rt Colic flexure (hepatic Flexure
38
Introduce the Transverse colon
3th part of colon Location : RT to Lt flexures Lies at the level of the umbilicus
39
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
40
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
41
Nerve supply of ascending and transverse colon
Intrinsic nn: ENS Parasympathetic: CNX Vagus Sympathetic: T10 - L2
42
Introduce the descending colon
Location: from colic flexure to iliac fossa, continuous to sigmoid colon
43
introduce Sigmoid colon
S shaped loop linking descending colon to rectum
44
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
45
What are the macroscopic features of the colon ?
Tenia Coli Haustra Mental epiploic appendices
46
histology of the colon
Mucosa: simple columnar epithelium crypts with goblet cells
47
Introduce the rectum
located between the sigmoid colon and anus.
48
What is the anorectal flexure?
where the rectum ends at coccus and turns sharply
49
What is the rectal ampulla
dilated aspect of distal rectum
50
What is puborectalis?
sling around inferior rectum. cause of incontinence
51
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
52
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
53
what is the anal canal
its the terminal aspect of the large intestine.
54
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)
55
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
56
What is the histology of the anal canal?
Rectal mucosa: simple columnar epithelium | Anal mucosa: stratified squamous epithelium
57
What is the function of the large intestine?
Digestion: enteric bacteria Absorption Propulsion Defecation
58
How does the colon move?
Haustral contractions 30min Mass movements 3/4 times a day Gastrocolic reflex faecal components
59
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

SBO5 (16 decks)

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