mucosa of the small intestine contains:
- Brunner’s glands ( duodenal).
- Simple tubular glands or crypts: secretes
succus entericus. - Solitary lymph follicles in upper part &
aggregated follicles in ileum ( patches). - Enterochromaffin cells (secrete serotonin).
Succus entericus
Volume, pH, consists of:
- Volume: 2 L/day
& alkaline pH about 7.5 - It consists of: a. Enzymes (present in the cells).
b. Variable amount of mucin.
c. Alkaline secretion (mainly NaHco 3).
ENZYMES
Intestines
- Proteolytic enzymes
- Exopeptidases.- Present in mucosal cells. - Reach the lumen by the desquamated mucosal cells in
intestinal secretion.
- They are: 1. dipeptidases. 2. aminopeptidases. 3. carboxypeptidases.
- Exopeptidases.- Present in mucosal cells. - Reach the lumen by the desquamated mucosal cells in
- Intestinal amylase
- Non cellular debris secreted from simple tubular
glands in small amounts.
- Non cellular debris secreted from simple tubular
- Disaccharidases :Cellular debris enzymes which convert disaccharides
into monosaccharides:
A. Sucrase: splits sucrose into glucose & fructose.
B. Maltase: maltose into 2 glucose.
C. Lactase: lactose into glucose & galactose. - Intestinal lipase
- Convert neutral fats into fatty acids & glycerol.
- Nucleases
- act on nucleotides.
- Phospholipases
- Enterokinase (non cellular debris).
Mechanism of secretion
Intestine
- Local axon reflex or local stimuli
- This is the main mechanism.
- The presence of acid chyme in the intestine leads to
distension & irritation of the mucosa & stimulates
secretion either directly or by lockal axon reflex.
- This is the main mechanism.
- Vagal stimulation
- Stimulation of Brunner’s glands of the duodenum to
secrete mucus. - Hormonal
a- Enterocrinine.
b. Duocrinine.
c. Secretin, CCK, VIP, prostaglandins.
Movements of the small intestine
A- Rhythmic movements (segmentation contractions) - Myogenic.
- Functions:
1. Mix the intestinal contents with juices.
2. Helps the contact with villi.
3. Evacuate lymphatics & blood vessels in the wall
and this helps absorption.
B. Peristaltic movements:- Caused by local axon reflex.
- Functions:
1. Propulsion of intestinal contents towards the
colon.
2. Mix the contents with intestinal juice. 3. Help absorption.
C. Antiperistalsis
- occurs in duodenum & terminal ileum.
- Produced by local axon reflex.
D. Mass peristalsis
- Caused by the vagus.
- Evacuates the intestine for perception of food.
E. Movements of villi
1. side to side.
2. pumping movements.
- Hormonal by villikinin hormone (amino acids,
Hcl, bile)
Ileocaecal sphincter
- Usually contracted & resist pressure of 40-50 cm
water. - Relaxes only before a wave of peristalsis. - Not controlled by the vagus nerve.
Sympathetic produces its strong contraction.
Functions:
1. Prevent content of the cecum to return back into
the ileum.
2. Prevent rapid emptying of the ileum to give time
for absorption.
Movements of the large intestine
Are generally sluggish to allow for absorption &
storage.
Their frequency increases along the colon from 2/min
at ileocaecal valve to 6/min at the sigmoid colon.
1. Segmentation contractions: myogenic
- Mixing the content of the colon to help absorption.
- It occurs in the proximal colon.
2. Weak peristalsis: - It occurs in proximal colon. It is due to local axon reflex.
3. Weak antiperistalsis:
- It occurs in the in proximal colon. It helps complete absorption of water & electrolytes.
4. Mass peristalsis:(vagus n.)
- Simultaneous contraction of the smooth muscles
over large area of the colon. It drives the contents
of the colon into the rectum & this initiates
defecation reflex.
- It may occur 2ry to ingestion of meals (gastrocolic
reflex)
As the food leaves the stomach, the caecum
relaxes & this promotes the passage of food
from the ileum into the caecum.
Called
Gastroileal reflex
The 1st part of the test meal reaches the:
- Caecum in about ….. hours.
- Hepatic flexure in …… hours.
- Splenic flexure in ….. hours.
- Pelvic colon in …… hours.
The 1st part of the test meal reaches the: - Caecum in about 4 hours. - Hepatic flexure in 6 hours. - Splenic flexure in 9 hours. - Pelvic colon in 12 hours.
They first appears in feces after about ….. hours.
Most the residue is excreted within …… hours.
Total excretion occurs in more than …….
They first appears in feces after about 24 hours. Most the residue is excreted within 72 hours. Total excretion occurs in more than one week.
outward expulsion of faeces through anal canal.
Defecation
Defecation Is the function of the rectum & anal canal. - The anal canal is surrounded by 2 sphincters:
Is the function of the rectum & anal canal. - The anal canal is surrounded by 2 sphincters:
1. Internal anal sphincter (involuntary smooth ms.)
2. External anal sphincter (voluntary striated ms.)
Defecation Mechanism
Stimulus: rectal distension with feces.
- Spinal defecation reflex:Distension of the rectum produces;(30-40 mmHg):
1 . Strong wave of mass peristalsis.
2 . Reflex contraction of the rectum.
3 . Reflex relaxation of the internal anal sphincter.
4. Relaxation of external anal sphincter.
Afferent impulses are transmitted through the pelvic
nerve to the spinal defecation center ( LHCs of 2 nd, 3rd
& 4th spinal segments of the spinal cord).
Efferent impulses are carried through the pelvic nerve
to relay in a terminal ganglia from which postganglionic
cholinergic nerves that cause contraction of the
smooth muscles of the sigmoid colon and rectum with
relaxation of the internal anal sphincter.
Voluntary impulses are carried along the pudendal
nerve (arising from the AHCs of the 2 nd, 3rd & 4th
spinal segments of the spinal cord) to cause relaxation
of the external anal sphincter).
Voluntary control of defecation (conditioned)
From the second year of life.
Defecation is spinal reflex which can be inhibited voluntarily by impulses from cerebral cortex.
-Normally, rectal distension leads to sensation of
defecation desire by sensory impulses to cerebral
cortex.
The response will be determined according to:
1. If the conditions are unsuitable.
2. If the conditions are suitable.
