mouth to stomach Flashcards
what parts of the body are involved in digestive processing
Mouth
Stomach
Small intestine
Large intestine
Pancreas (revisited!)
Liver
bile
the pancreas is revisited Because it is also part of the endocrine system.
why do we need the digestive system
Provides food source for all cells of body
Can be considered as a huge disassembly line
Delivers these nutrients through circulatory system
You literally are what you eat!
what is catabolism and what does it do to the components
Breakdown of large complex food into small simple components
- Amino acids & monosaccharides are universal building blocks
Absorb these small components
Distribute them to cells & tissues
what are the 4 functions of the digestive system
Ingestion (take food in)
Digestion (breakdown large molecules into small ones)
Absorption (nutrients –> cells of digestive tract —> blood)
Defecation (eliminate undigested residue)
name the organs involved in the digestive tracts
Oral cavity
Pharynx
Oesophagus
Stomach
Small intestine
Large intestine
name the organs involved in the accessory organs of the digestive tract
Teeth
Tongue
Salivary glands
Liver
Gall bladder
Pancreas
what are the 3 steps to digestion
- Mechanical Processing - tearing & crushing with teeth - squashing & compaction by tongue
- swirling, mixing & churning of stomach & intestines - Chemical Breakdown - by digestive enzymes
- Secretion - release of water, acids, enzymes, buffers & salts by GI tract & glandular organs
GI = GastroIntestinal
dhow many layers are there in the GI tract
4
describe the layers of the GI tract
Same basic 4 layers in wall from lower oesophagus to anal canal
name the 4 layers of the digestive tracts and escribe
(lumen)
mucosa:
- epithelium (protective)
- lamina propria (small blood & lymph vessels, nerves)
- muscularis mucosa (sparse Smooth Muscle Cell layer)
SUBMUCOSA:
- (distensibility & elasticity; larger blood & lymph vessels; submucous plexus nerve network, termed “brain of gut”)
MUSCULARIS EXTERNA:
- (major SMC (smooth muscle cell) coat: circular to decrease diameter & longitudinal to propulse/mix; between is myenteric plexus nerve network)
SEROSA:
- (=serous membrane=lines body cavity, not open to external)
named MSMS for short
in different regions of the Gi tract there are what variations and describe
structural variations
Muscularis externa
- Stomach contains additional internal oblique muscle layer
- Upper oesophagus & sphincters of anus consist of skeletal muscle fibres
Serosa
- Continuous with mesentery, in most places
- Mesentery suspends digestive organs from inner wall of abdominal cavity
name the 3 main types of glands associated with the GI tract
Unicellular mucous glands in mucosa
Multicellular glands in mucosa & submucosa
Multicellular glands (accessory glands) outside GI
what is the mouth called
Oral or buccal cavity
name the functions of the mouth
Ingestion
Taste (& other sensory responses to food)
Mastication (chewing)
Chemical digestion (starch, in part)
Deglutition (swallowing)
Speech
Respiration
what is the mouth enclosed by
Cheeks
Lips
Palate
Tongue
the oral cavity is lines with what cells
stratifies squamous epithelium
what structure do the lips lead to
Oral orifice (lips)
lead to:
Fauces (throat)
what are the 2 different types of salivary glands
intrinsic
extrinsic
explain intrinsic salivary glands
Small, dispersed amid oral tissues:
Lingual (tongue)
Labial (inside lips)
Buccal (cheeks)
Small amounts saliva contain lingual lipase & lysozyme, moisten mouth & inhibit bacteria
explain extrinsic salivary glands
Larger, 3 pairs outside mucosa with ducts:
- Submandibular
- Parotid (swell with Mumps)
- Sublingual (floor)
which can produce:
Salivary or thinner
mucus fluid
(contains
amylas
& electrolytes)
what percentage of saliva is water
99.4%
what other than water is saliva made up of
0.6% includes assortment of :
- Electrolytes (Na+, Cl-, HCO3-)
- Buffers (pH ~7.0)
- Glycoproteins = mucins (lubrication)
- Antibodies (control bacteria)
- Enzymes: lysozyme =
antibacterial
amylase = polysacc.
—> disacc. - Waste products
salivary secretion is constantly stimulated by what
by parasympathetic nerve endings
how do parasympathetic nerve endings control salivary secretion
Trigger reflex
- Object in mouth
- Empty chew/smell/think
e.g., just thinking about pickled onions
describe the stomachs shape
Muscular J-shaped sac
what does the stomach do
Food storage organ
Mechanically breaks up food particles
Liquefies food
Begins chemical digestion of proteins & small amounts fat,
into, chyme (soupy mixture)
- (most digestion occurs once passed into small intestine)
name the regions the stomach is divided into
Cardiac (near heart)
Fundus
Body (main region)
Pyloric (near sphincter)
what happens to the stomach structure if its empty
mucosa forms folds = rugae
explain the cells lining the stomach
All portions of stomach lined by simple columnar epithelium, producing a carpet of protective mucus
describe the mucosa’s structure/cells
Mucosa full of shallow depressions = gastric pits
- Cells at base dividing to continuously replace old cells (3-7 days) by migrating up towards lumen (or down)
explain stomach glands in terms of location
At base of each gastric pit opens 2 or 3 tubular glands
how are stomach glands named and name some
named according to location in stomach:
- Cardiac glands
- Pyloric glands
- Gastric glands (in fundus & body)
how do glands in the stomach differ
differs in cellular composition & therefore what they secrete
In general:
Cardiac glands produce mucus Throughout which produces hormones.
Gastric glands produce acid and enzymes, which are gastric juice (2-3L/day including water)
explain gastric secretions of hydrochloric acid
Hydrochloric acid secreted by gastric parietal cells
HCl is not produced inside parietal cell
- would destroy it (pH can be as low as 0.8!)
Instead, H+ & Cl- transported independently by different mechanisms
explain the process of HCl secretion by parietal cells
Parietal cell takes CO2 from blood & combines it with water to make carbonic acid (H2CO3)
Carbonic acid breaks down into bicarbonate ion (HCO3-) & H+
H+ pumped into lumen of stomach in exchange for K+ by an H+-K+ ATPase
Bicarbonate ion returned to blood in exchange for Cl-
Cl- follows H+ into lumen, where they constitute HCl
what are the functions of stomach acid
Activates pepsin & lipase
Breaks up connective tissues & plant cell walls (liquefy & form chyme)
Converts ferric (Fe3+) ferrous (Fe2+) so can be absorbed & form Haemoglobin (Hb)
Destroys ingested bacteria etc.,
explain the intrinsic factor
Parietal cell glycoprotein essential for absorption of vitamin B12 by small intestine
Without it, cannot synthesize Haemoglobin
Leads to pernicious anaemia (fatal)
If gastrectomy this leads to requirement for regular Vit B12 (remove stomach) injection
- Vit B12 intramuscular injections only required every 3 months, as liver has large storage capacity for Vit B12 (cf. oral intrinsic factor (IF) or oral Vit B12; latter absorbed slowly in absence of IF). Anaemia not develop for several years due to liver storage.
what do chief cells do in terms of with producing pepsin
secrete the inactive enzyme (thus a zymogen) pepsinogen
what does HCL (from the parietal cells do to pepsinogen from chief cells
converts this inactive enzyme to the active enzyme pepsin
what does pepsin digest
protein
Once Pepsin is formed (from chief cells and HCL), it can activate what
activate its precursor, pepsinogen
- Pepsin can act as an autocatalyst, causing production of more of itself.
what other enzymes do chief cells secrete
In infants, chief cells also secrete:
- Gastric lipase –> digests butterfat of milk
-Rennin –> curdles milk by coagulating proteins
(Note: not the enzyme renin secreted by kidneys, which forms angiotensin to increase BP)
how many chemical messengers are there in digestion
20
what cells secrete hormones that are chemical messengers
Enteroendocrine cells
name and describe the chemical messenger hormones that Enteroendocrine cells secrete
Gastrin:
- stimulates gastrin gland ( HCl & enzymes) & intestinal motility
- relaxes ileocecal valve
Serotonin:
– stimulates gastric motility
Histamine:
– stimulates HCl secretion
Somatostatin:
- inhibits gastric secretion & motility, pancreas secretions, gallbladder contraction & bile secretion
- delays emptying of stomach
- reduces blood circulation & nutrient absorption in small intestine
what is gastritis
inflammation of gastric mucosa (due to alcohol, aspirin, stress, bacterial infection, strong acids/alkalines)
what is a peptic ulcer and hows it treated
erosion through lining
- Gastric
- Duodenal
Treat with antibiotics
or cimetidine
- H2 histamine receptor antagonist
to reduce acid production
what is peristalsis
Waves of muscular relaxations followed by waves of strong contractions that moves material through most of GI
why do we need Regulation of Gastric Function
To cope with full & empty stomach
regulation of gastric function is divided into how many stages and what does this depend on
Divided into 3 stages, depending on whether control from:
brain,
itself or
small intestine
name the 3 stages of regulation of gastric function
cephalic
gastric
intestinal
explain the cephalic stage of regulation of gastric function
function:
prepare stomach for food arrival
duration:
short (mins)
mechanisms:
Neural (CNS) eg. think/chew food
action:
increase vol of gastric juice
explain the gastric stage of regulation of gastric function
function:
enhance secretions; homogenise & acidify chyme; pepsin
duration:
long (3-4hrs)
mechanisms:
Neural (stomach distention) Hormonal Local
action:
increase acid, pepsinogen
explain the intestinal stage of regulation of gastric function
function:
Control rate of chyme entry to duodenum
duration:
long (hours)
mechanism:
Neural (contents enter duodenum), Hormonal secondary
action:
inhibit gastric motility phase
