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SBO5 > Digestive System > Flashcards

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
Q

what is the vascular supply to the duodenum ?

A

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
Q

What is the structure of the Jejunum and Ileum ?

A

6-7m long combined

27
Q

What is the vascular supply to the Jejunum and Ileum?

A

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
Q

What is the nerve supply to the Jejunum and Ileum?

A

trinsic nn: ENS

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

29
Q

What are the cells of the vili and crypts?

A

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
Q

What is the role of the small intestine?

A

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
Q

Introduce the colon

A

Structure: 5 main regions Ascending, transverse, descending, sigmoid, colon and rectum

32
Q

What is the Caecum?

A

Initial part of the colon
7.5cm length
blind intestinal pouch
RLQ - Rt inguinal region

33
Q

What happens when the ileum enters the caecum

A

ileococecal orifice controls passageway to chyme superior and inferior ileocaecal folds are found.

34
Q

What is the vermiform appendix?

A

pouch arising from the posteromedial aspect of the caecum 6-10cm length

35
Q

What is the histology of the appendix?

A 
lymphoid tissue 
Fucntion: 
immunity: produce and store lymphocytes 
reservoir for gut bacteria 
recolonises gut
36
Q

What is the neurovascular supply to the appendix?

A

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
Q

Introduce the ascending colon

A

2nd part of the large intestine

location: RQ from caecum to liver. finishes at the Rt Colic flexure (hepatic Flexure

38
Q

Introduce the Transverse colon

A

3th part of colon
Location : RT to Lt flexures
Lies at the level of the umbilicus

39
Q

Vascular supply of the ascending colon

A

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
Q

Vascular supply of the transverse colon

A

Mainly from middle colic a. (SMA)
Rt colic artery (SMA) & Lt colic artery (IMA)

venous: SMV

Lymph: middle colic nodes

41
Q

Nerve supply of ascending and transverse colon

A

Intrinsic nn: ENS
Parasympathetic: CNX Vagus
Sympathetic: T10 - L2

42
Q

Introduce the descending colon

A

Location: from colic flexure to iliac fossa, continuous to sigmoid colon

43
Q

introduce Sigmoid colon

A

S shaped loop linking descending colon to rectum

44
Q

Neurovascular supply descending and sigmoid colon

A

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
Q

What are the macroscopic features of the colon ?

A

Tenia Coli

Haustra

Mental epiploic appendices

46
Q

histology of the colon

A

Mucosa: simple columnar epithelium

crypts with goblet cells

47
Q

Introduce the rectum

A

located between the sigmoid colon and anus.

48
Q

What is the anorectal flexure?

A

where the rectum ends at coccus and turns sharply

49
Q

What is the rectal ampulla

A

dilated aspect of distal rectum

50
Q

What is puborectalis?

A

sling around inferior rectum. cause of incontinence

51
Q

How does the peritoneum cover the rectum

A

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
Q

Neurovascular supply to the rectum

A

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
Q

what is the anal canal

A

its the terminal aspect of the large intestine.

54
Q

What are the main structures of the anal canal?

A

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
Q

Neuromuscular supply to anal canal

A

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
Q

What is the histology of the anal canal?

A

Rectal mucosa: simple columnar epithelium

Anal mucosa: stratified squamous epithelium

57
Q

What is the function of the large intestine?

A

Digestion: enteric bacteria
Absorption
Propulsion
Defecation

58
Q

How does the colon move?

A

Haustral contractions 30min
Mass movements 3/4 times a day
Gastrocolic reflex
faecal components

59
Q

How does the defecation system work?

A

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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